A11103 Dfi77bfi

NATL INST OF STANDARDS & |ECH R.I.C

A1 11 03087768

Mechanical FaHures/Detection. dlaan^^^^^ QC100 .U57 N0.436, 1975 C.I NBS-PUb o is NBS SPECIAL PUBLICATION 436

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MFPG

Detection, Diagnosis, and Prognosis

JAN 1 4 1976

Proceedings of the 22nd Meeting of the ^ ' ^

Mechanical Failures Prevention Group,

held at Anaheim, California 92802

April 23-25, 1975

Edited by

T. R. Shives and W. A. Willard

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

The 22nd meeting of MFPG and these proceedings were sponsored by the

Office of Naval Research, Department of the Navy, Arlington, Va. 22217;

the National Aeronautics & Space Administration, Goddard Space Flight

Center, Greenbelt, Md. 20771 ; the Frankford Arsenal, U.S. Army,

Philadelphia, Pa. 19137; the Federal Aviation Administration, Department

of Transportation, Washington, D.C. 20591 ; and the Institute for Materials Research of the National Bureau of Standards, Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Rogers C. B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assisianf Secretary for Science and Technology

M,6NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

y\\ Issued December 1975
Library of Congress Cataloging in Publication Data

Mechanical Failures Prevention Group.

MFPG—Detection, Diagnosis, and Prognosis.

(NBS Special Publ ; 436) "Organized by the Detection, Diagnosis, and Prognosis Committee

of MFPG."

Supt. of Docs No.: C 13.10:346.

1. Metals—Fracture—Congresses. 2. Metals—Testing—Congresses.

I. Shives, T. R. II. Willard, William A. III. United States. Office of Naval Research. IV. Title. V. Series: United States. National Bureau of Standards. Special Publication ; 436. QC100.U57 No. 436 [TA460]

602'. Is 620.r6'3 75-619365

National Bureau of Standards Special Publication 436

Nat. Bur. Stand. (U.S.), Spec. Publ. 436, 366 pages (Dec. 1975) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. CI 3.10:436). Price $4.25 (Add 25 percent additional for other than U.S. mailing).
FOREWORD

The 22nd meeting of the Mechanical Failures Prevention Group was held

i\pril 23-25, 1975, at the Grand Hotel in Anaheim, California. The

program was organized by the Detection, Diagnosis, and Prognosis

committee of MFPG under the chairmanship of Mr. Raymond Misialek. The

DD^P committee, the session chairmen, and especially the speaJcers are

to be commended for the fine program.

The papers are presented in these Proceedings as submitted by the author

on camera ready copy, except for some minor editorial changes. In

addition to the papers, the Proceedings include the discussions of the

talks. The discussions were recorded at the meeting and have been

edited to improve readability.

Special appreciation is accorded the Endevco Corporation, and in particular to Robert M. IVhittier of Endevco, for hosting the meeting.

They were responsible for the excellent meeting arrangements.

Appreciation should be extended to Mr. T. R. Shives and Mr. W. A. Willard

of the NBS Metallurgy Division for their editing, organization, and

preparation of the Proceedings, to Mr. H. C. Burnett of the Metallurgy

Division for general coordination and registration, to Mr. P. Fleming

of the Metallurgy Division for handling financial matters, and to the

entire staffs of the Metallurgy Division and the Institute for Materials

Research for their assistance in many ways. Special thanks are accorded

Mrs. Marian L. Slusser of the Metallurgy Division for her diligent

efforts in transcribing the recorded discussions.

ELIO PASSAGLIA

Executive Secretary, MFPG

Chief, Metallurgy Division

National Bureau of Standards

III
TABLE OF CONTENTS

FOREWORD . -. . SESSION I: IECHNOLOGY/IECHNIQUES

1. Signal Analysis Techniques for Vibration Diagnostics.

Donald R . Houser "

2. A New Technology for Bearing Performance Monitoring.

Gerald J. Philips

5. Bearing Contact Resistance as a Diagnostic Aid.

Richard L. Smith

k. Nondestructive Tire Inspection. Manuel J. Lourenco

and Lloyd H. Emfery*

5. Measurement of Spectra in Internal Combustion Engine

Cylinders. Jere M. Marrs

Panel Discussion: Planning and Executing Experimental Verification

SESSION II: CASE HISTORIES

1. Sonic Analyzer - Case History. John L. Frarey

2. Oil Analysis in Perspective. Richard S. Miller

(Presented by Mike Hoobchaak)

5. Instrumentation for Predictive Maintenance Monitoring.

Ralph James*; Bill Reber, Bruce Baird^ and Wayne

Neal

Panel Discussion: Case Histories Applications

SESSION III: ON GOING PROGRAMS

1. Gas Turbine Engine Diagnostic Test Results Utilizing

a Thermodynamic Analysis Technique.

Robert L. Stenberg

2. Problem Areas Encountered in Establishing a Data Baseline and Evaluating the A-7E Inflight Engine Condition Monitoring System. Andrew J. Hess

3. Tri Service Oil Analysis Research and Development

Program. Peter B. Senholzl

IV
• k. Development of Inspection and Diagnostic Equipment

for Motor Vehicle Equipment for Motor Vehicle

Inspection. George L. Parker (presented by

Lloyd H. Emery)

5. On Vehicle Mobility Measurement and Recording

System. F. K. Chin* and R. Watts

6. VIDEC Ship Propulsion System Performance Monitor.

Richard P. Wallace and William L. McCarthy^

SESSION IV: COMING REQUIREMENTS

1. An Overview of Current Efforts to Detect and Prevent

Steel Wheel Failures. Gary L. Leadley

2. Diagnostics for Refrigerator Car Diesel Generating

Sets. Robert F. McKee

3. Using Acoustic Emission Technology to Predict

Structural Failure. Harold L. Dunegan

h. Applications of the Shock Pulse Technique to

Helicopter Diagnostics. John A. George*

Timothy C. Mayer, and Edward F. Covill

5. LST 1179 Diesel Diagnostic System Feasibility

Study. M. B. Peterson*, J. Frarey, D. Dominy,

H. Hegner, and H. C. Burnett

* Indicates speaker when a paper had more than one author.

LIST OF REGISTRANTS FOR THE 22nd MFPG MEETING

V
ABSTRACT

These Proceedings consist of a group of nineteen submitted papers

and discussions from the 22nd meeting of the Mechanical Failures

Prevention Group which was held at the Grand Hotel in Anaheim,

California on April 23-25, 1975. Failure detection, diagnosis and

prognosis represent the central theme of the Proceedings. Technology

and techniques, ongoing diagnostic programs, and coming requirements in

the field of DD&P are discussed. In addition, several case histories

are presented.

Key Words : Diagnostic case histories; diagnostic systems; failure

detection; failure diagnosis; failure prevention; failure prognosis

UNITS AND SYMBOLS

Customary United States units and symbols appear in many of the

papers in these Proceedings. The participants in the 22nd Meeting of

the Mechanical Failures Prevention Group have used the established units

and symbols commonly employed in their professional fields. However,

as an aid to the reader in increasing familiarity with and usage of the

metric system of units (SI), the following references are given:

NBS Special Publication, SP330, 1974 Edition, "The International System

of Units."

ISO International Standard 1000 (1973 Edition), "SI Units and Recommendations for Use of Their Multiples."

E380-72 ASTM Metric Practice Guide (American National Standard Z210.1).

Disclaimer:

Certain trade names and company products are identified in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the products are necessarily the best availalDle for the purpose.

VI
SESSION I

TECHNOLOGY

AND

TECHNIQUES

Chairman: R. Hohenberg

Mechanical Technology Inc

SIGNAL ANALYSIS TECHNIQUES FOR VIBRATION DIAGNOSTICS

Dr. Donald R. Houser, Associate Professor

Ohio State University, Columbus, Ohio 43 210

Vibration and sound measurements have been used for the detection of

faults in rotating machinery for many years. The classic picture of a mechanic listening to an engine bearing via a stethoscope or screwdriver

is a prime example of the basic technique. Because of the apparently

large amount of information contained in the vibration signal, investigators hav.e strived to use this signal to automatically determine the

condition of mechanical devices. Further still, the ability to isolate

specific faults on components in a mechanical system has also been

deemed highly desirable.

A schematic of a typical vibration diagnostic system is shown in

Figure 1. Here, forces from moving parts such as gears, bearings, or shafts excite their surrounding structures and cause structural vibration.

This vibration is then converted to a voltage via a vibration transducer,

most often an accelerometer in present day applications. The location of

the transducer may be very important since the structural dynamics

between the input forces and the transducer may greatly modify the signal.

I^Hien a single transducer is used to monitor several machine components,

the problem of the proper transducer location may become very complex.

The transducer signal is then conditioned and further analyzed via a mathematical processor. This processor, which may analyze the data

either statistically or deterministically in the time domain or transform

the data into the frequency domain, is used to generate discriminants (a

statistic or set of statistics) upon which a decision regarding the con- dition of a system or component within the system is based.

Figure 2 gives a much broader picture of many of the combinations of

transducers, signal conditioning, signal processing, and discriminants

available for vibration diagnostics. Many of the processing and con- ditioning techniques such as time summation, Fourier analysis, cepstrum, cross correlation, cross spectral density, and coherence function require

relatively complex data processors; whereas special purpose hardware is

much more feasible where simple discriminants are ascertained using band

pass filtering, peak detection, and rms meters.

By far the most common signal processing technique has been Fourier

analysis via either analog hardware or via the fast Fourier transform

algorithm on digital processors. The frequency domain presentation of

Fourier frequency spectra allows one to relate specific periodic occurrences in a machine member to specific frequencies in the data. Of the

time domain processing techniques, time summation and various relatively

simple time signal analyses such as crest factors and impact index have

been used. Time summation enhances data of a periodic nature and

5
eliminates the effects of random noise and periodic components which are

riot common to the summation period. However, a very accurate trigger

pulse is necessary to perform time summation successfully. Discriminants

are commonly selected through one of the following methods:

1. Pattern recognition

2. Mechanical model analysis

3. A combination of modeling and pattern recognition.

The pattern recognition methods of selecting discriminants and

their utilization in the detection of faulty components are usually

heavily statistics oriented. Often, very little physical insight is

used in the selection of discriminants by this method. Because of the

purely statistical means of data analysis, these techniques require

many samples of data for each failure mode which might be encountered.

Also, discriminants selected for one system component may not necessarily be the correct discriminant for a similar component located in

another device due to the different dynamic environment. Pattern

recognition techniques based on frequency spectra data have been used

for the detection of faulty gears and bearings by Butcher et al. [1]*

and Kukel et al. [2]

The second approach for the development of vibration diagnostic

discriminants is through the use of mechanical modeling to predict

changes which will occur in the vibration signal due to typical faults.

This approach is quite versatile and allows results for one specific

component, a gear for instance, to be applied to many different gear

situations. Most of the successful modeling techniques have been

applied to rolling element bearing faults, where the ball, cage, and race frequencies may be easily predicted [3]. Methods for predicting high

frequency resonances of bearing races have also been developed [4]

In Figure 3 the frequency spectrum from an analog simulation of a discrete bearing fault is shown. Each of the frequency peaks corresponds to a resonance in the system. The smaller peaks are spaced in

increments equal to the shaft rotational speed. The vibration frequency

spectrum of Figure 4 for an operating bearing having an outer race pit

shows the similarity between the model and the actual data. Figure 5

compares time traces for the model and the actual bearing.

Figures 5 and 6 show both model and running data for a gear having

a single pitch line pit. The model, which is discussed in reference [5],

provides both time domain and frequency domain responses for gears

running both with and without faults. Interesting results from the

figures are that the gear mesh frequency sidebands were found to be the

result of a torque oscillation in the system which was due to coupling

misalignment. The fault appears to give a very predominate periodicity

at multiples of the shaft frequency. A second less noticeable periodicity occurs at the first torsional natural frequency of the system.

"Numbers in brackets indicate references cited at the end of this

paper.

k
One possible means of developing a single discriminant for this type of

failure mode would be to obtain the cepstrum [6] of the spectra, since

the cepstrum Is very sensitive to periodicities In the frequency spectrum.

The third and perhaps most logical means of determining discriminants Is to combine modeling and pattern recognition, since statistical

confidence Is still required, even for discriminants determined from

physical models. However, this approach Is likely to reduce the total

amount of data necessary In developing the diagnostic technique.

Through the use of the above-mentioned approaches, many techniques

have been developed to detect failures In rotating components, with most

of the emphasis being placed on gears and bearings. Listed In Table 1 are techniques which have been attempted or utilized by other Investigators. Detailed discussions of these techniques may be found In

references [7] and [8]. Many of the techniques listed In Table 1 utilize discriminants and processing methods appearing In Figure 2.

Techniques of several different Investigators may often be included

under one technique class in the table. An example of this Is the

bearing high frequency "ring" technique which has been employed in

various forms by several investigators. The general narrowband technique

encompasses a large number of schemes V7hich utilize simple observations

of the frequency spectrum. Of the bearing techniques, the high frequency vibration techniques including the shock pulse method have been

investigated by many individuals and are presently being employed in

operating systems. At this time gear fault detection systems have not

shown as much promise as the bearing diagnostic schemes, primarily

because transducers can be located closer to the bearings, and bearing

mechanics are better defined.

In summary, this paper has presented an overview of the primary

methods of utilizing vibration data for diagnostic purposes including

signal processing and discriminant determination. A listing of many

of the diagnostic schemes which have been investigated or proposed has

also been presented.

References

1. Butcher, Robert R. , Russel Klrby, Jr., John Nakahihara, and T. C.

Watkins, UH-1 Test Bed Program Final Report , Northrop Corporation,

Electronics Division, USAAVSCOM Technical Report 72-19, U. S. Army

Aviation Systems Command, St. Louis, Missouri, September 1972.

2. Kukel, J., H. K. Zlebarth, J. D. Chang, J. E. Minnear , and J. L. Lau,

Turbine Engine Diagnostic Checkout System , Alresearch Manufacturing

Company, The Garrett Corporation, Technical Report AFAPL-TR-33,

Air Force Aero Propulsion Lab, Wright Patterson Air Force Base, Ohio,

June 1971.

5
3. Babkin, A. S., and J. J. Anderson, "Mechanical Signature Analysis of

Ball Bearings by Real Time Spectrum Analysis," J . Env . Scl

, Vol. 16,

No. 1, p. 9 (1973). .

4. Darlow, M. S., R. H. Badgley, and G. W. Hogg, Application of HighFrequency Resonance Techniques for Bearing Diagnostics in Helicopter

Gearboxes , USAAMRDL Technical Report 74-77, October 1974"^

5. Drosjack, M. J., D. R. Houser, and A. C. Tinney, Investigation of

Gear Dynamic Signal Analysis , USAAMRDL Technical Report, 1975.

6. Kemerait and Childers, "Signal Detection and Extraction by Cepstrum

Techniques," IEEE Transactions on Information Theory , Vol. IT-18

W06, pp. 745-759 (November 1972).

7. Houser, D. R. and M. J. Drosjack, Vibration Signal Analysis Techniques , The Ohio State University, USAAMRDL Technical Report No.

73-101, U. S. Army Aviation Materiel Research and Development Lab,

Fort Eustis, Virginia, December 1973.

8. Drosjack, M. J. and D. R. Houser, "An Analysis of Vibration

Diagnostics for Helicopter Power Trains," Proceedings 20th International Instrumentation Symposium , Instrumentation Society of

America, May 1974.

9. Dawson, W. H. , Refinement of Rej ect Criteria for UH-1 Sonic Analyzer , USAAVLABS Technical Report 69-89.

10. Hogg, G. W. , Evaluation of the Effectiveness of Using Sonic Data to

Diagnose the Mechanical Condition of Army Helicopter Power • Train

Components , USAAMRDL Technical Report 72-30, May 1972, AD 745-089.

11. Ziebarth, H. K. , J. D. Chang, and J. Kukel, Mechanical Component

Failure Prognosis Study , Garrett Airesearch Corporation, USAAMRDL

Technical Report 73-26, Eustis Directorate, U. S. Army Air Mobility

Research and Development Lab, Fort Eustis, Virginia, June 1973.

12. Smith, K. A., "Crest Factor Analysis for Rolling Element Bearings,"

MFPG Detection , Diagnosis , and Prognosis , Proceedings of the 18th

Meeting of the Mechanical Failures Prevention Group, September 1973,

NBSIR 75-252.

13. Sollecito, William E. , Binary Word Analysis, presented at Signature

Analysis and Diagnostics Conference, General Electric, June, 1968.

14. Kirschmann, A. E,, TF-34 Engine Vibration Analyzer , Final Report , General Electric Company, Contract 62269-70-C00315 , NASC,

Washington, D. C, June 19, 1971.

6
15. Thompson, R, A., B. Weichbrodt, Gear Diagnostics and Wear Detection , ASME Paper No. 69-VIBR-lO.

Frarey, J. L., "Development of Gear Failure Detection Methods,"

Office of Naval Research, December 31, 1970, AD-720 735.

17. Provenzano, James, John Games, A. Wyrostek, A. Ostheimer, and J.

Young, UH-IH AIDAPS Test Bed Program Final Technical Report,

Hamilton Standard Division of United Aircraft Corporation, USAAVSCOM

Technical Report 72-18, U. S. Army Aviation Systems Command, St.

Louis, Missouri, August 1972.

18. Howard, P. L., "Application of Shock Pulse Technology and Vibration

Analysis to Rolling Bearing Condition Monitoring," Proceedings of

20th International Instrumentation Symposium, Instrument Society of

America, May 1974.

7
Table 1. Sunimary of Diagnostic Techniques

Faulty Component

Detection

Discriminant

Conception

Technique

Name Bearing Gear Other Modsl

Pattern

Recognition Combination

Curtiss Wright

Sonic Analyzer [9]

/ / / /

'Noise-Corrected

i Spectrum Energy

|[10]

Correlation

Analysis [7]

/ / / /

'Composite

jExceedance [11] / /

SLikelihood

lAnalysis [2]

/ / / / / //

Impact Index

(Crest Factor)

[12]

/

Frequency of

Binary Word [13] / / /

/V

Gear Discriminant

[14]

' / /

Gear Wear Dis- i criminant [15,16] i / /

j

General Narrow j Band j / / / / / /

Test Bed (Hamil- i ton Std) [17] 1 / / /

Test Bed \ (Northrop) [1] | / / /

Bearing High \ Frequencies [4]

/ /

Shock Pulse [18] 1

1 / /

Optimum-Seeking

j Classifier [7] [ / / / / /

8
Time

ansducer 1

Structures

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15
Ik
FREQUENCY (kHz)

Figure 6. Frequency Spectra for Running Gears.

a) good gear

b) gear with pitch line pit on a single tooth

15
DISCUSSION

G. deLong, Naval Air Systems Command (Pacific) : I wonder whether your

bearing analysis has been used for quality control on new bearings?

D. R. Houser : I have not discussed quality control specifically with

bearing manufacturers in enough detail to really answer that question.

There may be some people here who can answer it.

P. L. Howard, SKF Industries : We at SKF use two basic kinds of tests to

check the quality of our bearings. One is three-band vibration, the

object of which is to give the customer as quiet a bearing as he is

paying for. The second is crest detection, described at earlier MFPG

meetings by Kemp Smith and me. In crest detection, the ratio of

vibration peaks to the RMS of the vibration is determined. The object

is to find assembly damage in the bearing. These techniques can be

equally well applied to incoming inspection, in fact, Du Pont in

Delaware is doing just that. They are examining incoming bearings using

both three-band vibration and crest detection. Another^ technique called

shock pulse was listed on one of Don Houser' s charts. That technique is

probably better suited for machine or assemble bearing checking than it

is for individual incoming bearing inspection because it picks out the

bearing source damage in the machine generated noise. So shock pulse

doesn't show as strongly as a bearing quality control tool as it does as

a machine diagnostic tool

0. E. Compton, Northrop Corporation, Aircraft Division : Have you

employed any analytical models on crossover loading effects in thrust

beari ngs?

D. R. Houser : I have not personally. Most of the bearing loading in

bearing models has been quite simple in nature as far as diagnostic type

appl ications are concerned.

D. B. Board, Boeing Vertol Company : I was interested in your model of

tooth damage because we have been doing some work in the high frequency

regime - a modulated carrier type analysis. On a test stand we damaged

a spurgear tooth and we did indeed see the exact type of one per

revolution trace that you showed when that tooth comes through the mesh

once each time. We got a very large signal change. But our experimental data disagree with your model since we could see nothing

changing in gear mesh at all.

D. R. Houser : I didn't say that the gear mesh changed significantly; in

fact, our model only shows that through the 3 db increase in amplitude

with the gear mesh.

D. B. Board : I thought you said there were side band changes.

16
D. R. Houser : The only time we got side band changes was when we put a torque oscillation in the system. There was a torque fluctuation, but

this was not due to the pit in the tooth.

D. B. Board : We did another test where there was a small crack in the

gear starting at the tooth and propagating through the web down to the

bolt hole where it is mounted. We again got very large one per

revolution signal changes. I believe that there was a torsional

stiffness change. We didn't see any change in the gear mesh.

D. R. Houser : The gear mesh frequency stiffness is so great relative to

the rest of the system that I would doubt very much if you affected the

overall stiffness changes in a once per revolution fashion enough to

produce the effect that we are talking about. We are talking about a fluctuation of 20 to 30/^ of mean torque.

W. R. McWhirter, Jr., Naval Ship Research and Development Center : Wh^re were you placing the sensor in your experimental analysis?

D. R. Houser : For our bearing work, we normally placed the sensor reasonably close to the bearing. On our rig, there were two ,shafts

driving a gear, and there were two sets of small bearings about a foot

apart. We tried moving the sensor to various positions on the rig.

W. R. McWhirter : To get an idea of the mechanical impedance?

D. R. Houser : To see how the signal travels. There was definitely a reduction in the high frequency oscillations as the sensor was moved

farther away from the bearing; however, we still did pick it up.

W. R. McWhirter : In one of the reports you did for Fort Eustis on the

gear trains for helicopters, didn't you place sensors on the bearing

housings or on the gear housings?

D. R. Houser : We didn't really place sensors there. Most of the data

analyzed for helicopter transmissions was obtained from AVSCOM. They

chose the transducer locations. In our gear work, we located

transducers as close as we could to the bearings. The gear box we used

was an offset gear box from a UH-1 main transmission. We did try

mounting transducers right on the flexible parts of the housing, but we definitely got a reduction in usable information.

E. DuBack, General Dynamics, Electric Boat : The bulk of your

presentation dealt with frequency domain results. What about other

domains?

D. R. Houser : For gears, we did only frequency domain work. We have

done some correlation work on some of our bearing rigs, but you just

don't get that much information relative to that from the frequency

domain.

17
A NEW TECHNOLOGY FOR BEARING PERFORMANCE MONITORING

G. J. Philips

Naval Ship Research and Development Center

Annapolis, Maryland 2140 2

Ball bearing rings are of relatively thin cross section.

These rings deform when the bearing is loaded. Under a pure

thrust load the rings expand equally at each ball position

as indicated in figure 1. As shown in figure 2, the contouring of these expansions are seen with the aid of holographic interferometry . In this case a 3h" diameter bearing is shown which has been loaded with 600 lb thrust. The

peak displacement was measured as 80 microinches. During

bearing operation, the ball complement rotates. This

causes the surface expansions to travel about the periphery

of the bearing rings. There is, then, a traveling wave of

sizable magnitude on the bearing rings.

A new approach towards monitoring bearing performance has

evolved since the first observation of these waves. An

important element of this new technology is the fiber optics

probe, shown in figure 3, which is used to monitor the

bearing ring displacements. This probe can be inserted

into a bearing housing perpendicular to the bearing outer

ring (see figure 4). The output of the probe, when displayed on an oscilloscope, generally produces a characteristic pattern very similar to a half-sine wave, figure

5. Since this wave is generated by the passage of balls

past the probe, it provides an exact measure of the ballpassage frequency. By additionally measuring the shaft

rotational frequency, and taking the speed ratio of shaft

revolutions to ball train revolutions, the measurement can

be converted to an operating contact angle. If the initial

geometries and clearances of the bearing are known, bearing

loads can be calculated. This capability to monitor the

speed ratio can be useful in several ways: checks for

improper machinery assemblies can be made since bearings

stuck or misaligned in their housings and fits which are too

tight are detectable; bearing performance during thermal

transients can be observed and thermal lockup prevented.

« 18
For example, figure 6 shows speed ratio measurements of

the "floating" bearing in a vertically mounted 75 hp motor

whose bearings were properly installed. After passing

through a brief thermal transient, the speed ratio settled

to a value very close to the calculated or design value

which was based on a 780 lb bearing thrust load. When the

same motor was assembled with bearings which were too tight

in their housings, the speed ratio varied as seen in figure

7, and did not settle close to the design value. Bearing

loads varied from 120 to 950 lb in this case as the motor

passed through the thermal transient following a startup.

The final load value corresponding to the equilibri-um speed

ratio was 250 lb as opposed to the desired design value

of 780 lb.

The fiber optics instrumentation system described above

can not only be used as a tool for correct bearing installation monitoring but also as ' a tool for the detection

of bearing faults. In this capacity, it is extremely

sensitive for it has been observed that bearing defects

can be positively identified from their inception with

this system. This is so because the probe is sensing bearing vibrations directly. Therefore, the signal is not

confounded by extraneous frequencies and resonances in

the machine structure. As explained earlier, a good bearing generates a smooth waveform. If a bearing has defects

they will first appear as discontinuities in that otherwise

smooth waveform. If a bearing has a flaw on its outer

race, discontinuities will be created as shown in figure

8a; i.e., one per wave as each ball impacts the flaw. An

inner race defect would produce the disruptions shown in

figure 8b; i.e., discontinuities on every wave but spaced

closer than the main wave. Figure 8c illustrates the

signal when a single ball has a defect; i.e., the discontinuities are centered about one wave only and the

spacing is equal to the ball spin frequency.

A case study of a bearing with a defect illustrates the

high sensitivity of the fiber optics system. Photographs,

figure 9, of bearing displacement waves indicated the

presence of a defect on one ball of a brand new bearing.

This defect was observed after 15 hours of operation in

an electric motor. After 381 hours, the bearing failed.

(Failure mode was extremely high audible and structure-borne

19
noise,) Concurrent vibration spectra recorded using an

accelerometer stud-mounted to the motor, figure 10, gave

no forewarning of the failure. Subsequent disassembly and

inspection confirmed predictions of the fiber optics probe.

A single ball, figure 11, was found which had a set of

ring shaped grooves cut into it. The figure shows a photograph of the intersection of a 100-microinch deep

groove with the wear track of that ball.

The accumulation of experience with this new application

of fiber optics is continuing.

20
21
Figure 3

Fiber Optics Probe

22
e. Control Box

a. Rolling Element Bearing

b. Bearing Support Structure

c. Non-Contact Fiber Optics Probe

d. Probe Holder

f. Oscilloscope

Figure 4

Probe Installation

Figure 5 Characteristic Displacement Wave

Form of a Good Ball Bearing

23
T -I 1 r 100 120 140 160 180 200

Time, Minutes

Figure 6

Speed Ratio: Loose Bearing-Housing Fit

2h
°F, Floating Bearing

,°F, Fixed Bearing

0 20 40 60 80 100 120 140 160 180

Time, Minutes

I I I Li.

200 220 240 260^24^

3.106

3.104

.2 ^-^^^

c2 3.100

•oI 3.098

3.096

3.094

3.092

3.090

Design ^

Value

0 20 40 60 80 100 120 140 160 180 200 220 240 260' 24 M8

Time, Minutes Hours

Figure 7

Speed Ratio:

Tight Bearing — Housing Fit

25
a. Outer Raceway Fault — One Discontinuity Per Wave

b. Inner Raceway Fault — Discontinuities on Every Wave, Spacing (x)

Uniform but Less Than Main Waveform (y).

c. Ball Defect — Discontinuities Clustered About

1 Wave Only and Spaced (z)

at Ball Spin Frequency

Figure 8

Bearing Fault Analysis

Figure 9

Bearing Wave Form

Showing Presence of

One Defective Ball
-.) is/w s-01 m 80V 27

DISCUSSION

J. L. Frarey, Shaker Research Corporation : You showed the vibration

spectra going into the high frequency region. Did you filter or demodulate any of the high frequencies as Dr. Houser mentioned?

G. J. Philips : No.

J. L. Frarey : I can see how you could get little spikes from bad balls

in ball bearings by looking at the outer race at one point, but how can you see outer race defects 180° away from the location of the probe?

G. J. Philips : That's one of the development areas that I want to look

at. Hopefully, the rigid body mocion of the ring itself will be

sufficient to enable us to pick up the signal. It may turn out we will

need more than one sensor.

D. N. Schuh, Beta Machinery Analysis, Limited : What are the amplitudes

of the motion that you are observing?

G. J. Philips : In one particular case that I mentioned earlier, 80 yin was the peak-to-valley displacement for that size bearing with 600 lbs.

load. Generally, the amplitudes are less than 100 yin. Some bearing

defects produced spikes corresponding to a displacement of 10 yin.

D. N. Schuh : And this occurs even though the bearing might be tight in

the housing?

G. J. Philips : Yes.

D. N. Schuh : Do you feel this is going to be a practical technique for

field type measurements? It seems that very high accuracy is required.

G. J. Philips : Yes, that is what we are shooting for. The big thing we

have going for us here is that the signal itself is so simple. We are planning this year to look at a large quantity of bearings to try to

develop some statistical confidence in what we are doing. As I mentioned we are going to be inspecting brand new bearings and looking

at failures that have been returned to us from the fleet. We will also

be looking at the assembly of electric motors. We are trying to' get as much experience with this technique as we can.

D. M. O'Dea, Exxon Research and Engineering Company : Why did you use fiber optics in preference to strain gauges to monitor the outer race?

G. J. Philips : We started this work about four or five years ago and I don't remember what governed my selection of the transducer. I'm not

saying this can be done only with fiber optics, but since I have been

using that transducer I found it very convenient. It is very easy to

work with. You need only a hole about one-eighth inch in diameter to

29
provide access to the bearing. A strain gauge must be wired to the

bearing, which is very awkward. Fiber optics is non-contact, it does

not interfere with the operation of the bearing.

R. M. Whittier, Endevco Corporation : Errors might be due to two things.

One would be the irechanical effects of the oil in the gap between the

outer race and the casing. The second would be the reflectivity of the

optic gauge on the race because of the presence of oil.

G. J. Philips : The displacement wave is a purely mechanical function.

It depends on the geometries involved and the applied load. The

reflectivity of the probe itself is affected by any kind of fluids

between the surfaces. I haven't done any correlation with exact

amplitudes. Right now, it's a go, no go type of gauge. Either the wave

form is smooth and has no spikes or it contains spikes.

C. E. Horten, Naval Ship Engineering Center : We are presently

monitoring some 50 pieces of rotating machinery at deployed sites with

^ real-time analyzer. We have been doing it for about five years and we

recommend bearing removal and replacement based on the sound cuts. We

send these bearings back to Annapolis for analysis. Very often the

acceptance tests that are run on bearings using an andarometer ^show the

bearings to be OK because a laboratory test stand is used. Are you

going to tie in your work on this new technique with the signatures of

bearings installed in the fleet?

G. J. Philips : When I checked the bearing that I showed with the ball

defect on our andarometer it ran smooth and quiet, like a noise-tested

bearing. When I mounted the probe on the andarometer head and looked at

the bearing vibration, I could again see spikes. The andarometer is a three-band vibration measuring instrument. It measures an RMS average

of vibration over a very broad frequency range. It's a rough quality

control instrument. This fiber optics probe goes beyond that. It

discriminates bearing faults whereas the andarometer can't. At

Annapolis this year, we will be looking at thousands of bearings from

current Navy stocks with this technique.

D. W. Long, Pacific Fruit Express Company : Have you done any work on cylindrical or tapered roller bearings and would you expect this

technique to be useful in the diagnosis of these bearings?

G. J. Philips : I haven't done much work myself with the roller bearings

because ball bearings are used to such a wide extent in the fleet, but

the theory of defects is the same for both roller bearings and ball

bearings; it is just a matter of the magnitudes. There is so much more contact area in a roller bearing that it might be possible to straddle a fault and not detect it.

30
BEARING CONTACT RESISTANCE AS A DIAGNOSTIC AID

Richard L. Smith

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, N.Y. 12019

The technique described below can be used to determine the relative

"health" of an operating bearing by measuring its contact . resistance.

The approach described is not presented as a "beat--all" bearing monitoring system but rather an alternative for certain bearing applications.

Use of the technique described, requires a small D,C. voltage (normally

less than 100 millivolts) to be placed across the bearing during the

time of fault detection. Most of the data shown on the figures below

are taken from an analysis of several freight car roller bearings used

in the railroad industry.

When two solid surfaces are put together, "asperity contact" occurs.

The degree of metallic interaction or asperity contact between bearing

components is determined by the lubricant film thickness within the

bearing. Lubricants used to minimize asperity contact in bearings

attempt to maximize this film through boundary or hydrodynamic means.

Variations in electrical resistivity as a result of asperity interaction

were for many years (1)'' observed with the oscilloscope. Photographs

similar to that shown in Figure 1 revealed the degree of asperity interaction within an operating bearing. A time varying contact signal can

be obtained from a rolling element bearing with the aid of the circuitry

and test arrangement shown in Figures 2 and 3.

Properly-lubricated bearings operate with a minimum of metal contact between rolling elements. Best designs operate with fluid films which are

at least four times the average component surface finish. Since most

lubricants are organic hydrocarbons, a high average resistance is maintained between the inner and outer race of a well-lubricated bearing.

Experience has shown that average bearing operating resistances may

range from one ohm in the case of the freight car bearing, to over a million ohms in a fully flooded instrument bearing.

Bearing average operating resistance is a function of operating film

thickness. Typical film thicknesses (2) calculated for a railcar

roller bearing are shown in Figure 4. This type of bearing has a surface roughness normally greater than four micro-inches. The analytical

film thickness shown assumes fully flooded oil lubricated conditions (3).

The railcar bearing operates on a grease film and is likely to have a

* Numbers in parentheses indicate references listed at the end of the

paper.

51
true operating film which is reduced (4) from the values shown. Freight

train bearings operate for most of their lives in the boundary lubricated regime as a result of their low average speed, which is reportedly 20

MPH (5) . Boundary lubrication implies a high percentage of asperity

contact.

Figure 5 is a qualitative functional display of contact resistance and

the nominal film thickness generated between the rolling elements of

a bearing.

Although functional dependence of resistance and films on unlubricated

solids with oxide layers is understood (6) for some metals; the dynamic

conditions of lubricated contacts present an extremely difficult analytical problem. Thus, prediction of the exact level of the mean re- sistance for a given operating bearing, to date, has not been attempted

to the author's knowledge.

An experimental display of how the "average" resistance changes when the

amount of oil in the bearing is altered and when the viscosity of the

lubricant is lowered is shown in Figure 6. The average here is based

electronically upon the percentage of time the contact resistance signal is below the selected center-scale-resistance. An effective bearing monitor would make use of this simple resistance level change.

Once a nominal operating range has been established, a level sensing

circuit could be used to automatically indicate when operation has gone

"bad".

Another experimental display of resistance level change is shown in

Figure 7. Displayed is the common variation in percent contact for a 202 size bearing while increasing load and keeping the speed fixed.

Three constant speeds of 280, 395, and 725 RPM are shown in the same

figure. As is well knovm, the average film thickness of a hydrodynamically lubricated bearing is relatively insensitive to load (inverse

1/11 power dependence). The average electrical contact resistance

in the same bearing, however, can change over several decade levels.

Asperity count rate level can also vary with improperly operating bearing components. Figure 8 shows a bearing with a cage which affected

the electrical contact rate during each rotational cycle. Bearing com- ponents which were forced into sliding as a result of the out-of-roundcage could be one explanation for the observed data.

A.C. as well as D.C. level changes in the asperity contact signal can

also be used to establish bearing "component health". A look at the

time varying asperity signal on the oscilloscope reveals what appears

at first glance to be a random signal filled with "white noise". The

real time spectral analyzer, however, reveals singular spikes in those

bearings which have inherent defects.

52
A comparison reference spectrum of a "new" bearing of the same size as four defective bearings whose spectra follow is shown in Figure 9. For

ease in comparing each of the following spectra shown, all electronic

controls of the spectrum and electronic contact analyzer, except one were held fixed during the experiment. The center scale resistance

(see Figure 2) was adjusted in order that the A.C. signal variation of

the asperity contacts were not suppressed by high or low level clipping.

Figures 10 through 13 display the spectra along with a photo of the inherent defect in each bearing used during the tests. The defects shown

were

1. Figure 10, a roller with a split seam line,

2. Figure 11, a bearing with surface corrosion,

3. Figure 12, a dented roller, and

4. Figure 13, a slightly spalled roller.

Sharp edged defects such as that displayed in Figure 10 result in many

harmonic "spikes" being present in the electrical contact spectra. An

extreme example of this is shown in Figure 14 from a ball bearing. Harmonics to 10,000 hertz at multiples of twice the ball passing frequency

are displayed. A ball with a "flat spot" causes this.

A comparison of two bearing diagnostic techniques is displayed in

Table I. A ranking of twelve bearings which had inherent defects is

shown. Some bearings screened by each technique were found to have

signals indiscernable from that of the "good" reference bearing. It

should be noted that each of the bearings had previously been found

"faulty" for at least one or more of nine reasons without electronic

means

Bearing "L" is found to be "good" with the high frequency diagnostics

scheme and ranks as third to the worst with the electrical contact

technique.

An opposite ranking for bearing "H" appears to hold. The point here is

that neither detection scheme appears to catch "all defects" and those

bearings found to be "good" comprised a mutually exclusive set from each

technique. It is reasonable that some critical bearing applications

could use the complementary aspects of electrical contact analysis.

REFERENCES

1. Furey, J.M. , "Metallic Contact and Friction Between Sliding Surfaces," ASLE Transactions 4, 1961.

2. Cameron, A,, Basic Lubrication Theory , Longman, London, 1971.

3. McGrew, J.M. , Gu, A,, Cheng, H.S., Murray, S.F., Elastohydro - dynam.ic Lubrication - Preliminary Design Manual , Technical Report

AFAPL-TR-70-27, Wright-Patterson Air Force Base, 1970.

35
4. Chlu, Y.P. , "An Analysis and Prediction of Lubricant Film Starvation in Rolling Contact Systems", ASLE Preprint Number 73AM-3B-4,

April 1973.

5. "Yearbook of Railroad Facts", AAR Publication, 1974.

6. Gupta, P.K, and Cook, N.H. , "Statistical Analysis of Mechanical

Interaction of Rough Surfaces", J. Lub. Tech., ASME Trans. Vol.

94F, 19-25, Jan. 1972.

3^+
HIGH

resistance'

i

BEARING

CONTACT

RESISTANCE

t

LOW

RESISTANCE

INFINITY

CENTER

SCALE

RESISTANCE

-0

TIME

Figure 1. Typical Bearing Contact Resistance Signal,

ASPERITY SIGNAL

BEARING

CONTACT

RESISTANCE

FIXED

RESISTOR

Hlilili- BATTERY

Figure 2. Electrical Contact Diagram.

r

ELECTRON IC

CONTACT

ANALYZER

o

0

SCOPE

REALTIME

SPECTRUfyi

ANALYZER

x-.y-T

PLOTTER

Figure 5- Typical Test Instrumentation Set-up.

55
ROLLING SPEED IN/SEC

Figure h. Cplculated Railcpr Roller Bearing Operating Film

Thicknesses.

10"^ 10° 10^ 10'*

FILM THICKNESS, Microinch

Figure 5. Contact Resistance and Nominal Operating Fluid

Film Thickness.

36
FILM THICKNESS, MIcroinch

301% OIL

TIME, 50S/INCH

Figiire 6. Percent Contact and Fluid Viscosity.

FIGURE 7 ASPERITY CONTACT LOAD/LEVEL SENSITIVITY

0 LOAD, LBS. 200

Figure 7- Asperity Contact Load/Level Sensitivity.

57
O

CAGE DEfECT SIGNAL

I PERIOD OF ^

CAGE REVOLUTION

TIME

Figure 8. Cage Defect Signal.

FREQUENCY, Hz 200

Figure 9- Reference Spectrum From New Bearing.

58
SPLIT SEAM LINE

BEARING "C

FREQUENCY, Hz

Figure 10. Split Seamed Roller with Spectrum.

200

CORROSION

FREQUENCY, Hz 200

Figure 11. Corroded Roller Bearing with Spectrum.

39
I

, FREQUENCY, Hz

Figure 1^. Spalled Roller Bearing with Spectrum.

1^0
u

TWICE BALL PASS

FREQUENCY

lUAJ

FREQUENCY Hz lOK

Figure ik . Spectrum of Faulty Ball Bearing,

HIGH FREQUENCY VIBRATION SCREENING TECHNIQUE

-BAD

GBIEAHKFD

F

G

H

D

K

E

I

J

CONTACT RESISTANCE SPECTRAL SCREENING TECHNIQUE

Figure 15 . Comparison of Tabulated Bearing Fault Results.
DISCUSSION

P. L. Howard, SKF Industries : How do you control the effect of

tunneling through the lubricant and what effect does dirt in the

lubricant have on your measurements? I noticed you were changing

resistance scales which changes the potential across the bearing quite

drastical ly.

R. L. Smith : I don't really control the tunneling. It occurs when the

lubricant film thins to one yin. When it occurs, the resistance must be

changed. I am not really controlling tunneling but I do use it. The

applied voltage, though, is small enough so that the percent contact is

not changed significantly, at least in the regions where I have been

looking. In other words, during an experiment the voltage can be

changed either by changing the center scale resistance or changing the

voltage in the system. If th,e applied voltage and applied current are limited, then there really isn't a change in percent contact until you

have reached a certain specific voltage. In one case I found the

voltage to be 0.86 volt applied across the bearing. Other people have

found it to be as high as 3 volts. Tunneling or discharge will occur

across the lubricant film when the film gets thin enough. When a particle goes through the contact zone, the film gets very thin and, of

course, there is a large change in resistance.

P. L. Howard : This is one reason people use capacitance variation.

R. L. Smith : Yes, my experience indicates that capacitance change can be used but it doesn't have that decade level change that resistance

offers. The percentage variation due to capacitance changes is always

masked by the large capacitance due to the geometry of the bearing

itself - the inner and outer races provide a large capacitance and the

small variations due to film thickness changes are a small percentage of

that large variation.

P. L. Howard : It becomes very valuable at low film level.

k2
NONDESTRUCTIVE TIR E INSPECTION

Manuel J. Lourenco and Lloyd H. Emery, National Highway Traffic

Safety Administration, Office of Vehicle Safety Research, Crash

Avoidance Research Division, Washington D. C. 20590

NHTSA in 1971 initiated a research effort in the area of nondestructive testing which would apply to inspection and test of motor vehicle

tires. This research task was assigned to the Transportation Systems

Center (TSC), Cambridge, Massachusetts which had previously been a research arm of NASA and was known as the Electronics Research Center.

The prime objective of this program was to determine the feasibility and

practicality of utilizing NDT techniques to inspect and predict dynamic

tire performance. The techniques that were investigated were:

X-Ray - (FIGURE 1)

Utilized by the industry in the tire development phase. It could

detect broken cords, ply overlap and belt doglegs.

Infrared Imagery - (FIGURE 2)

Not true NDT because the technique required some exercising,

although minor, of the tire to obtain its thermal profile.

Signal interpretation was very difficult.

Hoi ographic Imagery - (FIGURE 3)

Through double exposure holograms and the resulting fringe

patterns, anomaly (separation) detection was fairly precise.

Ultrasonics - (FIGURES 4a and hh)

Both the reflection and transmission techniques were investigated.

This technique proved to be the most cost-effective for new

and recycled tires respectively.

Resonance - (FIGURE 5)

This technique relies on exciting the tire to its resonant

frequency at the tread center and utilizing symmetrically placed

receiving transducers on the sidewalls to detect imbalances in

the output signals.

The latter NDT technique, because of its simplicity, ease of operation

and maintenance, direct application to mounted tires, short test time,

and low equipment cost was selected for motor vehicle inspection (MVI) use. The MVI of tires is the principal theme of this paper and the

following will outline the effort that has carried the system to the

prototype validation phase.
The first known active use of resonant vibration as a technique for

determining mounted tire integrity was published in Mr. James Weigl 's masters thesis (Ref. 1) in 1967 at M.I.T. The equipment used by Weigl

in his research and the laboratory system evaluated by Dr. D. Wilson

and S. Loebl also from M.I.T. did not validate the technique for

identifying defects or anomalies within tires. The Transportation

Systems Center in 1973, convinced that the resonance technique could,

with modifications, be utilized to sense and position abnormalities

within tires, undertook an in-house research effort to advance the

S. A. Loebl and D. G. Wilson system (Ref. 2). FIGURE 6 depicts a block

diagram of the M.I.T. developed system and its function and figure 7 is a photograph of the developed system.

The TSC developed system also utilized the vibrating resonance

properties of the tire but differs from the M.I.T system in that the

sensing technique for abnormalities is somewhat different. The system

difference can be seen in the TSC block diagram shown in figure 8 where

the vibration source is placed at the center of the tire tread area

and the receiver transducers are positioned in the same radial plane

equidistant from the source (Ref. 3). The TSC advanced prototype

(Ref. 4) system is shown in FIGURE 9 (Mechanical Design)and FIGURES 10

and M (Photographs).

To comprehend how the resonance technique senses anomalies or flaws in

the tire it will be necessary to understand and interpret the manner

in how a tire vibrates when excited sinusoidal ly.

The type of resonant mode pattern that is obtained in a tire is

dependent on the direction of the applied force and the position at

which it is applied. In the TSC developmental system the force

transducer was positioned at the center of the tread area. The

vibrating force transducer when in contact with the tire tread will

induce within the cross section a circumferential response (see FIGURE

12a) and simultaneously a tangential mode along the entire circumference (see FIGURE 12b). The combination of these two modes generates

a two dimensional mode pattern within the tire carcass. The resultant

mode patterns have been observed in tires by G. Potts (Ref. 5) through

time-average holography. Pictorial representation of resonant

vibration patterns from the Potts investigation are shown in FIGURES 15

and 14.

With an oscillating transducer applied to the tire tread center line,

the tire can be made to oscillate in a manner shown by the displacement envelope of the cross section indicated by the dotted lines in

FIGURE 15. The beads and the "X" marked points are the nodal points.

By placing receiver transducers in the same radial plane, at equal

distances from the source transducer (FIGURE 15), the vibrating

properties of the tire and the vibrating symmetry of the radial cross section can be measured. Rotating the tire about its axis and holding

1+1+
the oscillating and receiver transducers stationary, the vibrating

properties and radial symmetry for the entire tire carcass can be

measured. The oscillating transducer, through electronic control, will

maintain its resonance condition even if the properties of the vibrating

tire carcass change.

The tire defects of greatest interest to motor vehicle safety are those

which may lead to or result in the tire failure; these include cuts,

tread chunking, uneven wear, broken cords and separations. In all

cases, these defects will, in general, upset the symmetry of the tire

and therefore affect the resonant vibration properties of the tire.

The tire symmetry under inspection is that obtained in comparing the

two halves separated by a plane perpendicular to and through the

center of the tread area. The TSC system configuration for inducing

oscillations in the tire tread area and obtaining wave-forms off the

sidewalls will produce the comparative symmetry needed to determine

tire integrity. The system requires simultaneous circumference

readings of the two individual sensing transducers (designated A & B)

and the algebraic sum of the A + B readings to determine defect content

and placement. Full tire inspection is accomplished by rotating the

tire at a rate that will give a good signal to noise ratio.

Mechanical or electronic expertise will be required for maintenance or trouble shooting, but system operation can be accomplished by personnel

without prior technical training. In fact, the tire inspection process

is fairly effortless except for the selection of the applicable resonant

frequency at which to perform the inspection. The operator must be

indoctrinated in the basic understanding of the whys and how a tire carcass vibrates when excited sinusoidal ly. The selected resonance

frequency depends primarily on the tire size and construction. For

instance, FIGURES 16 and 17 holographical ly show that the second mode

of vibration is the most applicable for use with the TSC technique.

The resonant frequency for an H78-1 5 bias ply tire and for an HR78-15

radial ply tire turned out to be 168 Hz and 80 Hz respectively. The

lower mode would be less sensitive and the higher modes tend to

"break-up" and become unresolvable.

During laboratory evaluation the tires to be inspected were mounted on standard automotive wheels, inflated to normal operating pressure, and

placed on the tire tester hub. The exciting transducer input roller

was mechanically placed in contact with the tire at the center of the

tread. Using the exciter armature bias control, the input roller to

tire contact force was adjusted to approximately 3 pounds. The

receiver transducers were then positioned perpendicular to the tire

sidewall surface at equal distances from the input roller contact point.

The optimum position was determined to be between 70° and 90° from the

roller input point (See FIGURE 18). The receiver transducer to tire

surface contact force was readjusted to approximately 2 pounds.

^5
Having performed the mechanical requisites the electrical system is

then energized. The oscillator and the exciter amplifier are adjusted

to produce an energy level input that vn'll give desired signal outputs.

The oscilloscope presentation of the receiver transducer response is

then used to tune the exciter to the desired resonant tire mode and the

exciter is readjusted, if necessary, to the desired input energy level.

The operator now has the option of operating the system at a constant

frequency or using the automatic frequency tracking system.

The tire is rotated at about 1 rev/mi n. so as to minimize accel erometer

response from sidewall lettering or other tire surface anomalies, by means of the wheel shaft drive or the roller drum. The sensing

transducer signals are viewed visually in real-time with an oscilloscope and/or are recorded on an X-Y recorder (See FIGURE 19). When

using the X-Y recorder, a shaft encoder insures a point to point

correlation between the tire circumference position and the data

recording. Hard copy recordings (X-Y) were made of each transducer

response (A & B) and of the algebraic sum (A + B) of the two output

signals which is accomplished electronically.

System evaluation was based on numerous tests for which data recordings

similar to those of FIGURES 20, 21, and 22 were obtained and the tire was destructively analyzed to confirm the system's detection capability.

Excellent detection capability was obtained for the flaw types listed

in Table A.

The location of the tire flaws is determined by the signal amplitude

variance corresponding to a receiver transducer and its placement

along the developed circumference for the tire. A defect located in the

center of the tread area will be detected by both receivers but will

cancel out on the A + B trace. FIGURES 20, 21, and 22 are receiver

amplitude responses taken of tires containing known defects. The

system's response to the defects are obvious and are labeled as to

type, location and size on the recordings.

The resonance vibration technique is a valid process by which inservice automobile tires may be inspected quickly and inexpensively.

The tires can be inspected while mounted on the vehicle because the

weight of the automobile on the tire has no effect on system

performance. Based on the research and development effort conducted at

the Transportation Systems Center, NHTSA concluded that the technique

was valid and an automatic prototype system should be developed to

confirm its practicality and usefulness. To this end NHTSA awarded

Southwest Research Institute (SWRI) a contract (DOT-HS-5-01 066

"Passenger Vehicle Tire Inspection Equipment Development") which has

as its primary objective the design, construction and validation of a prototype system which will be less complex than the TSC system,

eventhough it will have a triple inspection function, and will

incorporate a go, no-go indicator to eliminate inspector subjectivity.

The three function system (FIGURE 23) will include the automatic

capability of simultaneously evaluating tire structural soundness,

hG
measuring tread depth and inflation pressure. The contractual effort

was 'initiated in January 1975, and the progress to date has not gone

beyond basic system layout as shown in FIGURES 24, 25, and 25 and

preparation of appropriate specifications. This research and

development effort is scheduled for completion in June 1977.

REFERENCES

1. Weigl, J., Investigation of an Advanced Vehicle Inspection System,

M.S. Thesis, M.E., M.I.T. Cambridge, Mass., 1967.

2. Loebl , S., and Wilson D., Fabrication and Evaluation of a Resonant

Nondestructive Tire-Testing System, DOT-TSC-NHTSA-73-4 , April 1973.

3. Lavery, A. L., Resonance Tire Inspection Unit, U.S. Patent

Application, Serial #325,292 Transportation Systems Center,

Cambridge, Mass., 1973.

4. H. Ceccon, A. L. Lavery, F. Coults, Nondestructive Tire Testing

Using Resonant Vibration Techniques - Report No. PM-T-16 of

April 1974.

5. Prototype Tire Testing Apparatus, Contract DOT-TSC-55-3 , Southwest

Research Institute, San Antonio, Texas.

6. Potts, G., Tire Vibration Studies - The State-of -the-Art

Akron Rubber Group Winter Meeting, January 1974.

7. J.E. Johnson, "Passenger Vehicle Tire Inspection Equipment

Development" (Briefing) February 19, 1975.

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50
51
52
55

POWER

SOURCE

I

X Y

RECORDER

FIGURE 6 - MIT Resonance System Block Diagram

55
56
SCHEME FOR MEASUREMENT

POWER

SOURCE

DETECTOR

MOTOR

VIBRATION

SOURCE

DETECTOR

MIXER

OSCILLOSCOPE

RECTIFIER

FIGURE 8 - TSC Resonance System Block Diagram

57
58
59
60
A) CIRCUMFERENTIAL

61
FIGURE 13 - RESONANT VIBRATION PATTERNS

62
63

140 Hz

FIGURE 16 - First, Second and Third Mode

Radial Vibration Resonances for

H78-15 Bias Ply Tire; 140, 168

and 278 Hz, Respectively

65
80 Hz

FIGURE 17 - First, Second, and Third Mode Radial

Vibration Resonances for HR78-15 Radial

• Ply Tire; 59, 80 and 96 Hz, Respectively

66
67

69
70
71
RIGHT TIRE

TRACK

MAX. TRACK

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MIN. TRACK

WIDTH

ENTRANCE

GUIDE

ROLLERS

PARALLEL

GUIDE ROLLERS

LEFT TIRE

TRACK

MAX. TIRE

WIDTH

pick-upZ.

HEADS

MOVABLE

DRIVE

ROLLERS FIXED

FIGUEE 23 - Automatic Centering System

72
75
REMOVABLE PEDESTAL FOR

DRIVE ON TESTS

FIGURE 25 - Laboratory Resonance Inspection Apparatus

7k _
75
DISCUSSION

J. M. Chudobiak, University of Saskatchewan : Why do you have to use resonance? That seems quite a drawback. I think that your method is

very much the same as Mr. Philips' procedure and you are just measuring

changes in symmetry.

L. H. Emery : The TSC results show that the resonance technique would

probably be the most practical from an MVI standpoint. At inspection

stations out in the states, tires come in dirty and wet - you want to

have low cost equipment and maintenance, you want it to be fairly

unsophisticated. The decision was made on the basis that resonance had

the least drawbacks.

J. M. Chudobiak : Can't you just drive at any frequency? You are tying

it down to specific frequencies which increases the sophistication.

L. H. Emery : The second resonance mode seemed to give us the most

information in detecting these tire flaws.

J. M. Chudobiak : Did you try to drive it at various frequencies or did

you specifically select natural frequencies?

L. H. Emery : We tried to look at just the natural frequencies.

0. E. Compton, Northrop Corporation, Aircraft Division : What would rim

effects such as out-of-roundness, dents, etc., have on the side wall

when using a resonance type frequency?

L. H. Emery : I don't really know. I think we are going to see that

this year.

W. K. Mathison, Puget Sound Naval Shipyard : How do you determine the resonance for a particular tire? Do you use the same resonance frequency for a given type of tire or does it vary with the tire as it

is brought into the inspection station?

L. H. Emery : It varies.

W. K. Mathison : How do you determine it, then?

L. H. Emery : The operator goes through the procedure and looks for it.

W. K. Mathison : He doesn't take any holographs?

L. H. Emery : We just use signal analysis.

R. Lenich, Caterpillar Tractor Company : There have been problems with

tires because of varying stiffness due to the manner in which the plies were laid. Does this affect the weight pattern or influence your

readings?

76
L. H. Emery : We expect some problems with this. We hope that we will

be able to inspect for and find the major causes of tire failure.

E. DuBack, General Dynamics Electric Boat : In your test setup, you

mentioned a three-pound load due to the rollers. It seems that in

actual conditions you are going to have quite a bit more load when you

consider a car.

L. H. Emery : When the car is sitting on the two rollers, the load will

be set automatically so that the test head will come up between the two

rollers.

J. M. Chudobiak : Are you also trying to get tire pressures from these

vibrations?

L. H. Emery : No

77
MEASUREMENT OF SPECTRA IN INTERNAL COMBUSTION ENGINE CYLINDERS

Jere M. Marrs , Ph.D., Tektronix, Inc.

Beaverton, Oregon 97077

The emission of light from chemical reactions is a very general phenomenon. New molecules are being formed with excess electronic energy and

when that energy can be given off radiatively, the emissions can be observed. If one knows the exact molecular mechanism of the reaction, the

emissions during the reaction can in some cases be interpreted. Observation of such emissions can be of use in two separate and distinct ways:

1 ) interpreted spectra can lead to models of the reaction mechanism, if

not previously known, and identify the emitting species, and 2 ) empirical relationships can be determined from spectral observations as they

relate to known variations in the reacting mixture.

In internal combustion engines, a fuel is mixed with oxygen (from air),

compressed, and ignited. The very complex chemical reactions that then

take place are quite energetic, take place under high temperatures and ^ pressures, all of which ensure the vigorous emission of light. Spectral

measurements of light emitted during combustion processes in the past

have been of two types: measurement of temperature through optical

pyrometry, and observation of emission of light at single wavelengths.

Pyrometric measurements measure an equivalent temperature based upon a black body radiation law (Planckian radiator) . Measurements at single

wavelengths can be quite useful, but obtaining spectra using this technique would be quite difficult. It would be necessary to sample the

spectrum at a known time in the firing sequence of the engine at as many

wavelengths (in successive experiments) as is necessary to adequately

describe the spectrum. Unfortunately, the intensities vary considerably

from firing to firing making a statistical sampling necessary. Needless

to say, transient phenomena which could lead to or be the result of a failure would not be seen under such conditions.

It should then be considered: what sort of transient phenomena could be

observed and how could they be related to potential engine failures? To

illustrate a point, consider some hypothetical failure modes or abnormal

operations of internal-combustion engines and what spectral events might

occur. Consider four possible abnormal conditions: 1 ) oil burning, 2 ) rust or metal shavings in combustion chamber, 3 ) hostile ambient con- ditions such as salt mist, 4 ) abnormal fuel components. The effective

temperatures in a combustion plasma can be in the neighborhood of 4000 °f} or so. Under such conditions, any small metal fragments, dissolved elements, will be vaporized and atomized in exactly the same manner as in the

graphite furnace in an atomic absorption instrument. The atoms thus produced will become electronically excited and emit light at their

characteristic wavelengths modified some by the environment. It is then

78
possible to identify them. If condition 1 occurs, then all of the dissolved elements in oil are vaporized and excited. Suppose the oil

contained an additive with calcium in it. Then one might expect to see

the characteristic calcium emission line at 423nm. In condition 2 which

might be an engine that has not been used for a while or one in which

there is a catastrophic failure of some sort, the iron emission lines

would appear transiently upon starting the engine or at the onset of the

failure. Condition 3 might obtain if an engine is operating in a salty

mist created by salt-treated roads. One might then expect to see the

characteristic emission lines of sodium or calcium if any of the mist

penetrates the air filter and into the intake manifold. Similar observations are possible with fuel components in condition '4. The emission

spectra in the near infrared measured on a CFR (Cooperative Fuel Reseatch) engine appear to be molecular in origin. It is possible that the

addition of fuel components such as methanol, ethanol, or water could

change the appearance of that spectrum in a repeatable fashion. Thus, an empirical relationship between the particular fuel component and that

spectral observation could be made. Should the origin of the spectrum

ever be determined in terms of molecular processes during combustion, the

observed effect could be interpreted in terms of the molecular interaction with the fuel component studied. Considerable work is under way

to interpret these molecular-type spectra^ s ^ > and we feel that real-time

spectral observation will give new impetus to their study.

The instrument that was used to make spectral observations from internalcombustion engines is made by Tektronix, Inc. and is called a rapid-scan

spectrometer. Figure 1 shows a skeleton diagram of how the instrument

works

HORIZONTAL

DRIVE

TRIGGER SOURCES

Figure 1. Basic block diagram of the rapid-scanning spectrometer system.

79
The light to be measured enters the instrument slit and passes through a Czerny-Turner type polychromator in which the light is broken spatially

into its component colors or wavelengths. This spectrum is then imaged

on the target of a silicon-vidicon image tube. The target is an array of

microscopic photodiodes each of which detect light and store the signal

in the form of an electrical charge. An electron beam then scans the

thousands of photodiodes to read their charge, thereby measuring the

intensity of the total light that fell on them. lAThen the beam scans in

the wavelength direction, the intensity versus wavelength is read. The

signals thus obtained are sent to a cathode ray tube for display as intensity versus wavelength. Since all of the diodes can receive light

information all of the time, it is possible to record spectral events at

different wavelengths simultaneously. This detector capability is called

the multiplex advantage. If a transient event takes place very quickly

with respect to the scan time, its spectral distribution will still be

recorded. The polychromator and the vidicon detector are all housed in a single small box allowing measurement in some difficult locations.

Further, fiber optics can be used to pipe light from the source to the

instrument slit.

Spectral observations have been made using a CFR engine through the

courtesy of Professor John Mingle at Oregon State University, Department

of Mechanical Engineering. An insert was used in one of the many test

ports which contained a borosilicate window which allowed observation of

the visible light emitted during the combustion stroke. A fiber-optic

probe was affixed to this window cooled by forced air. The spectra obtained consisted of two very distinct types: sharp spectra and broad

structured spectra. By wavelength position, two of the transient sharp

lines were tentatively assigned as due to sodium (589nm) and potassium

(768nm) . This is reasonable since sodium and potassium occur due to dust

particles and dirt. The transient lines could be generated by striking

the intake manifold largely confirming this interpretation. Many of the

remaining spectral features appear to be characteristic of the combustion

process and appear to be molecular in nature. Some work has been done in

interpreting these spectra^ > > ^ , but with the capability of observing the

entire spectrum in real time, perturbation experiments may be possible to

confirm assignments or make new ones. Figures 2 and 3 are representative

of some of the spectra recorded. The sharp lines are most probably

atomic and the broader spectra are more likely to be molecular.

In looking toward future work, the observations could be made with more

efficient optical coupling to enhance the weak spectral features and to use window materials that will allow wider spectral observations. It

appears that spectral observations can add effectively to the measurement

arsenal for the diagnostics of failures in both internal and external

combustion engines.

80
t t 591 767

Figiire 2. Combustion spectriJin showing sharp lines due probably to sodiiom

and potassium. (wavelengths in nanometers)

f f t i f f

Figure 3. Combustion spectrum in the near infrared produced by the

combustion reaction. (wavelengths in nanometers)

81
1. Edwards, John B., "Combustion: Formation and Emission of Trace

Species", Ann Arbor Science Publishers Inc., Ann Arbor, Mich.,

240pp., 1974.

2. Ehigo, R. , Nishiwaki, N., and Hirata, M. , "A Study on the Radiation

of Luminous Flames", Proc . Eleventh Symp . (International) on Combus - tion , Berkeley, Cal. (Pittsburgh, Pa.: Combustion Institute, 1967)

p. 381.

3. Liebert, C.H. and Hibbard, R.R. "Spectral Emittance of Soot", NASA

TDN-5637 (February 1970).

4. Smith, D.S. and Starkman, E.S., "A Spectroscopic Study of the Hydroxyl Radical in an Internal Combustion Engine", Proc . Thirteen th

Symp . (International) on Combustion , Salt Lake City, Utah (Pittsburgh

Pa.: Combustion Institute, 1971) p. 403.

82
DISCUSSION

R. Lenich, Caterpillar Tractor Company : Do you foresee picking up dirt

or silicon in an engine because of an air intake or air cleaner system?

J. M. Marrs : I'm not sure about silicon, but certainly sodium and

potassium are picked up. If there is dirt in an engine, there is going

to be sodium in copious amounts and that is probably the most sensitive

probe for dirt.

H. 0. Northern, Detroit Diesel, Allison Division : Do compounds like

carbon monoxide and nitrogen compounds produce a recognizable signature?

J. M. Marrs : Carbon monoxide provides a recognizable signature in

absorption in the 2 to 14 micron infrared region. We are not operating

in that region. Our detector isn't sensitive in the infrared. However,

most carbon monoxide analyzers work by looking at the approximately 1900 wave number absorption spectrum of that species. There is a possibility

of measuring emission spectra of nitrogen ions and nitrogen oxides in

the combustion process, and this is one of the things we want to look at

in further research.

R. Hohenberg, Mechanical Technology, Inc. : Does the quartz fiber give

you limitations in the spectra that you observe?

J. M. Marrs : It doesn't limit us in the spectral region so much as it

does in the absolute level that we can see. There are losses in the

fiber optics at all wavelengths uniformly over the range of the

instrument. It would be best, of course, if you could use direct optics

rather than fiber optics. It would be very desirable to try to

determine the emissions from combustion reactions. The emissions are quite weak and would probably require a very efficient coupling into the

chamber. Fiber optics would probably lessen the possibility of seeing

the emissions.

C. R. Garbett, Shell Development Company : The width of the spectrum is

very limited with your instrument. Can you spread this out so that you

might be able to observe' various molecular species, the free radicals,

and things that would be of great interest to the people working on combustion? Could you in effect take a small range of the spectrum and

spread it out across the whole of your scale and look at it in detail?

J. M. Marrs : You can optically disperse the spectrum to a greater

degree. The videcon will have about 100 resolution elements across it

regardless of how much spectrum is displayed across it.

C. R. Garbett : Not 100,000?

83
J. M. Marrs : No, not 100,000, but lOO". If there are 4 nanometers

across the videcon, there will be 0.04 nanometer resolution. My feeling

is that under the conditions of combustion in which there are many

atmospheres of pressure, you have pressure broadened spectra. It is

virtually impossible to resolve such things as vibrational and

rotational lines because the molecules are under such pressure. They

are virtually continuous from the start with the exception of the single

atomic elements which are also pressure broadened. The molecular

spectrum would be broadened to the point where it couldn't be resolved

even if the instrument had the resolution.

0. E. Compton, Northrop Corporation, Aircraft Division : Does the

spectrum change quite radically as a function of the air/fuel flow

ratio; that is, the burning mixture itself?

J. M. Marrs : Where we have observed this near infrared spectrum, there

is no radical change in the spectrum as the mixture is changed. On the

CFR engine you can change these things while you are observing. There

was no radical change that I could observe other than a change of

overall intensity. When we went to a very rich mixture, the near infrared portion virtually disappeared, although the visible light could

still be seen. When we went to a very lean mixture, the same thing

occurred. But in the middle region and in the area that is considered

optimally tuned, the intensity seems to be at its maximum.

0. E. Compton : How about the oxides of nitrogen? Do they vary as a function of the combustion ratio itself?

J. M. Marrs : Yes, they do. The higher the temperature of the

combustion the greater will be the fraction of the oxides of nitrogen.

You can get that information without looking at the spectra but

ironically it turns out that when the engine is optimally tuned for

performance, the output of the oxides of nitrogen is maximized.

J. W. Forest, Ontario Hydro : What is the physical size of the 2500

square array?

J. M. Marrs : It's about an inch and a half round. The diodes are about

25 micrometers apart, so the electron beam actually addresses about 3

diodes at a time. As far as practicality is concerned, it is continuous

but if you look in the microscope you can see the individual diodes.

D. B. Board, Boeing Vertol Company : Do you plan to evaluate this

technique on a gas turbine engine?

J. M. Marrs : Well, that draws an interesting comparison between

internal and external combustion engines. The reactions that go on in

internal combustion engines are free radical reactions and many of the

spectra that are expected will probably be there. In external

combustion engines the reaction is largely an ionic one which might give

8i+ • , . -
rise to very different kinds of spectra. We haven't looked at a turbine

engine, but we plan to.

D. B. Board : Would this be a suitable device for measuring temperature?

J. M. Marrs : That is a possibility. I have done some very brief

reading about temperature measurement using sodium as an internal

standard, and it sounds possible.

D. B. Board : If burning is taking place in combustor liners or turbine

blades, can spectral lines be obtained from the burning elements as they

are ionized?

J. M. Marrs : If the metal gets into the plasma and is excited, I would

expect a characteristic emission. Spectral lines will be obtained if

the emission is intense enough and is within the spectral range of the

instrument.

D. B. Board : Have you to date encountered any problems in the

attenuation because the window gets blackened after a period of use?

J. M. Marrs : Yes, it does attenuate it as it runs. In the internal

combustion engine, we found that for some of the super fuels the window

doesn't get very dirty, but when you switch over to a pure iso-octane

mixture, the window blackens very quickly. So in an internal combustion

engine, it is a problem. We still see spectra; they are just

attenuated.

R. Hohenberg : I just wanted to say a gas turbine is an internal

combustion engine with continuous combustion rather than intermittant

combustion

J. M. Marrs : But if it indeed does have an ionic mechanism, there is a very distinct difference.

R. Hohenberg : That's right, but the question really is, is the ionic

mechanism associated with continuous versus intermittant combustion

rather than internal versus external combustion.

M. Dow, Eastern Airlines : Did you get some feel for how long this high

excited state would exist, for instance, in a jet engine?

J. M. Marrs : Molecules which fluoresce typically fluoresce within a few

nanoseconds after they are excited. In an engine, however, the plasma

lifetime is quite long compared to that. A sort of steady state of

emitters is generated even though each one will have an average lifetime

of a few nanoseconds. The results are the average of a large number of

excited molecules and not of a single decay.

85
M. Dow : I was thinking about the physical position along the length of

the engine. You want to look right at the hottest point, not ten feet

back, right?

J. M. Marrs : Yes, it would occur only in the combustion chamber and

would disappear long before it would ever exit.

86
PANEL DISCUSSION : Planning and Executing Experimental Verification

F^anel Moderator : R. Hohenberg, Mechanical Technology, Inc.

Panel Members : D. R. Houser, The Ohio State University

G. J. Philips, Naval Ship Research & Development Center

R. L. Smith, Shaker Research Corporation

L. H. Emery, National Highway Traffic Safety Admin.

J. M. Marrs, Tektronix, Inc.

R. Hohenberg : This panel discussion will revolve around a problem that we all face. We are looking for detection, diagnosis, and prognosis

technology, and a consistent stumbling block is the demonstration of

payoff. Well, that is kind of blunt and crass but really that's the

purpose of the technology, to pay benefits back for the doing of the

work. This payoff has to be demonstrated and it has to be demonstrated

by an experiment which is hopefully planned. I say hopefully because we

have seen so often that the statistical problem, the probabilistic

comparisons which are necessary, and the human element which is

introduced into these experiments tend to upset them. Most of the time

many of the experiments that have taken place to demonstrate the payoff

of DD&P have resulted in reports that invariably say: 1) the experiment

is a success - we have got to call it a success, otherwise why bother to

write it up; 2) unfortunately some very necessary data are not available

at the time of the conclusion of the experiment; and 3) let's do it over again. Well, I think it's worthwhile to discuss what we can do to

plan experiments so that when they are concluded and the reports are written, we don't have to do them over again.

R. L. Smith : DD&P experiments sometimes do lead to meaningful results.

The problem then is to convince management to implement your system and

sometimes they are not willing to put out the money. The dollar level

shown to them is not convincing enough, so you have to sell the

diagnostic system more than just telling them of the numbers.

R. Hohenberg : How do you design an experiment that overcomes an inherent problem such as avoiding failures in a population which is

usually very large? There is no sense going into diagnostics of

machinery unless there is some substantial population. You want to show

that if you didn't have the diagnostic equipment, more money would have

been put out "co maintain the machinery. And you somehow also have to

figure in the problems that are incurred due to the false alarms that

may be created. How does one set up the experiment? The laboratory

experiment is probably the easiest part in demonstrating that a particular mechanism has some benefit. It is more difficult to go to

the next step of boxing it up neatly and putting it into service. How

do you plan for that?

87
L. H. Emery : In any project that I have ever been associated with, you

always, without exception, would have done it slightly differently if

you could do it over again. It's probably impossible to anticipate all

of the problems that are going to occur and it's also very difficult to

get all the answers when you need them as you progress. It happens

quite frequently that you make some decisions along the way based on insufficient or unavailable information.

G. J. Philips : Rudy, if I understand what you are saying, an engineer

has to be a reactionary all during the course of his experiment. No

amount of super planning is ever going to make every experiment a total success. There are always going to be failures and unknown factors

cropping up during the test. These factors must be evaluated and they

may change the course of the experiment. You have to maintain a certain

flexibil i ty.

D. R. Houser : In the diagnostic avenues, a lot depends on the cost of

the test equipment. If you want to determine all the failures in a whole helicopter, the experiments are much more expensive than for

examining one bearing. And the statistics become qui te *different. A

statistic of one is not very valid. There are means of analyzing or building experiments statistically which can reduce the total number of

tests you have to conduct.

J. M. Marrs : Many times a diagnosis seems like the horse-out-of-thebarn type detection. The failure has taken place. In many cases during

failure analysis, you get information about the cause of failure and

will be able to change some procedure which will then eliminate these

failures. Therefore failures may be prevented rather than just

increasing the efficiency with which they may be detected.

R. Hohenberg : There is a school of thought that says that if you spend

all the effort that is now spent on failure avoidance and failure

detection in improving the basic design, you just won't have any

failures at all. And then there is the opposing school of thought which

says there is no way of avoiding all failures and that it becomes

desirable to make an effort to detect a defect at a time when the burden

of the failure is not yet fully realized. You can detect a failure in,

say a gear, while the gear is still functioning. A crack is there, but

the gear is performing its useful function before the catastrophic

failure has occurred and the damage causes loss of life or termination

of function of the whole machine.

A. J. Hess, Naval Air Test Center : We are using a diagnostic system

that the Navy has developed for its A7-E aircraft that is statistically

and cost effective. We have reached a point in the development of our system where we are about ready to implement it in a fleet

production-type program. We have gone through a very extensive,

sometimes careful, sometimes not too careful, data base expansion and

preproduction evaluation program. As we are developing the system we

try to collect the statistical data necessary to prove that the system
is cost effective in an actual fleet operational environment. We have

ten A7-E aircraft with this in-flight engine condition monitoring system

on board the Enterprise right now. It has been deployed since last

November and it had been operating in naval squadrons for about eight

months previous to last November. We have over 5,000 actual operational

hours in a fleet environment and we have big lists of finds that the

diagnostic system has discovered - engine discrepancies which normal

maintenance did not find. We have tracked these finds through

maintenance actions and verified a list that was valid and a list that

was invalid. Right now we are in the process of putting dollar figures

on where we saved in two different areas. One is a possible savings of

aircraft since this is a single engine airplane. The second is the area

of maintenance and logistics. You can put dollar figures on maintenance

man-hours saved at the line level and at the depot level. You can also

put dollar figures on secondary damage saved and on the logistics

problem. Hopefully, within two or three months we will have data

published to be used to verify that this system is cost effective. We

ran into problems in setting up the program, and some of the things we

learned are unique in the development of a condition monitoring system

which don't have to be rel earned for the next one when it goes into its

preproduction evaluation.

D. B. Board, Boeing Vertol Company : In the past year, one of the

mistakes that has been made in our programs was not determining before we started a test whether we were trying to demonstrate diagnosis or prognosis. Far too many reports come out with conclusions that make

implications about prognostic capability when the only real testing that

has been done that is valid statistically is diagnostic. We seem to say

the real measure of a diagnostic system is whether it detects defects.

When we find an indication of a defect, we never ask ourselves what its

meaning is. It is only meaningful if we know the probability of

obtaining a false indication from a part without a defect. Of even greater importance is determining the probability that the defect could

not be found. We always go around measuring the probability of finding

a defect of a known size. Very infrequently do we really plan the

experiment so that we get information that tells us how likely it is

that we would have indicated that something was wrong if it was not.

That is a statistical problem and it requires a lot of testing. You

can't afford to do a lot of testing on expensive machines, so you have

to find cheaper ways to do it. First of all you have to realize whether

you are doing diagnosis or prognosis. Then you have to design your

experiment so that it has enough of a statistical basis so that you are getting both of those reliability or accuracy probabi 1 i ties - not only

the probability of finding the defect when it's there, but the

probability of saying it's there when it is not.

89
p. L. Howard, SKF Industries : One major problem is going after a symptom that was thought to have caused a failure. In a diagnostic

approach, it is necessary to define what is being looked for. A very

nice diagnostic technique can be developed to look for a defect that

doesn't mean anything in the overall running of the system.

D. B. Board : I concur completely. That is one of the toughest nuts we

are eventually going to have to crack. Tied to the problem of what's

important to detect is the problem of what are the failure progression

rates. We can pretty much say what the consequences are going to be if

a gear breaks in half or a bearing starts to seize, but we really know

next to nothing about failure progression rates in all of the thousands

of different applications that machines run under.

R. Lenich, Caterpillar Tractor Company : I agree with Mr. Board. The

manufacturer talks about' diagnosis and the customer really isn't

interested in diagnosis unless he has to be. What he is interested in

is prognosis. You can only have prognosis if you have some kind of a deterioration rate. Things that break you can't prognose. The customer

knows it, he has detected it, the machine has stopped, and he really

isn't interested in spending money on diagnosis. He is interested in

having a machine that will run until some overhaul period. At that

point he doesn't mind seeing cracks or pits in gears and cracks in

weldments provided they haven't broken or damaged the machine. He

considers this a good prognosis because he can correct the problem at

that point. There must be a certain percentage of problems before

people will use diagnostic equipment. The customer really wants product

reliability and he expects the manufacturer to do the testing before it

is put on the market. What the customer is interested in is prognosis,

and he would rather have it on vehicle. It rings a bell and tells the

operator to stop the machine, and at no cost increase except maybe $3.00

for a transducer that will last 10,000 hours.

R. Hohenberg : I think you've pointed up something which is very

significant; that is, we are talking about two different things. One is

verifying that the condition of a new part is acceptable, which is an inspection procedure. The second is a prognostic procedure which

determines if a part has a reasonable amount of useful life left.

0. E. Compton, Northrop Corporation, Aircraft Division : One of the

weaknesses of our industry is that we too frequently do not issue the

proper software, or make an adequate study of the software, that goes

along with the testing device. The problem is - how well does the

software support the individual doing preventative maintenance?

U. Sela, Exxon Company, USA : I would like to talk as somebody that has

been involved with three phases: (1) sitting in a lab and looking at

phenomena which could be used to find out something, (2) having been

associated with- one who tried to develop a system such as signature

analysis, and (3) trying to use some of those systems or some of those

phenomena. The real question is: (a) what is going to fail, and (b) so 90
what? I tell them that I found all these wonderful things with my

wonderful technique. Those gears are seeing 10, 15, 20, 25 g's, the

side band ratio is such and such. The question is, can it run, for how

many months will it run? Who knows. Then they ask me what happens when

it breaks? What position will we be in? What will the damage be? How

long will it take to repair? What is still needed is to be able to

translate the signal into an actual stress so that we can make a calculation of what the safety factor of the part is and maybe later

determine when failure may occur. I feel frankly that with all that we

are learning I am no better off today than I was ten years ago.

J. A. George, Parks College of St. Louis University : I disagree with

the chairman's comment that we are interested in finding such things as spalls, pitting, corrosion, etc. The component may last many operating

hours with these defects. We are right back to what Mr. Sela said - when is it going to fail? In spite of a lot of the work that has been

done in many systems, we still don't know how to design a proper

experiment for prognosis. One method could be to run to failure.

That's kind of difficult if you put a bad gear or a bad bearing in a helicopter and tell the pilot to run this to failure. So you do it in a laboratory. Unfortunately, the mechanisms that we are interested in are more complicated than simple gears meshing together. There is a difference between laboratory experiments and those involved in an

actual operating condition. You have got to collect the data in a real

1 ife environment.

R. Hohenberg : John, I just want to defend myself a little. I did say

that it is desirable to detect spalls, but that is at the inspection

level when you are trying to make a part as good as it should be when

new. There is a different level of detection in the field when the

machine is already running, when you are trying to decide when to stop

it. There is a time when you want to detect minute defects and there is

a time when you want to detect precursors of catastrophic defects.

J. A. George : My point is, maybe the quality control is too rigorous.

Maybe we can stand some of these minor pittings and spalls and yet

fulfill some reasonable operational lifetime. Maybe we are trying to

make it too perfect.

H. U. Burri , RCA Corporation : What we have been talking about is

providing some sort of a magic black box which, when attached to some expensive piece of equipment, will act as a nurse and take the

temperature of the patient constantly. Who checks the nurse? I do know

that electronic equipment has a tendency to fail. There is a real

problem there to make sure that we do not get false alarms or missed

detections or fails just because the test equipment has failed.

91
R. Hohenberg : I think it's a very good thing that you brought that up

because it leads us directly to the human interface which does warrant a lot of attention. Any diagnostic equipment must operate to the

satisfaction of people, and these people are not scientists, they're not

engineers, they're not the owners of enterprises, they are mechanics.

To make them satisfied that the equipment is doing the job that it is

supposed to do, ideally you want three lights - a green light that says,

"Yes, this equipment is fine, leave it alone," a red light that says,

"No, stop the equipment, there is a malfunction impending," and a yellow

light that says, "The monitor is sick, the nurse is sick."

J. S. Bendat, Independent Consultant : I think there are many aspects to

this problem that are being raised simultaneously which is causing some confusion. If you are trying merely to monitor some simple component - bearing, gear, etc. - you're collecting data at one point and looking at

either its spectrum, or some other time history, by visual or some other

simple method determining whether a change has occurred. On the other

hand, if you are trying to analyze more complicated subsystems such as diesel engines, or motors in general, or if you want to analyze larger

systems such as automobiles and airplanes, etc., you need to look at the

problem from a much broader viewpoint as a multiple input-output type

analysis where there are many excitations occurring at many points

producing many responses at other points. In all of this work, there is

a requirement for practical experience in addition to any mathematical

modeling or statistical techniques. However, I would like to note that

there are many techniques available for analyzing periodic and random

data which are not being utilized as fully as they should. Any results

that are obtained should always be qualified to indicate that they are from a particular experiment and were collected under certain conditions

which are not likely to be duplicated. If anybody is to usefully

interpret these results, there should be some confidence bands inserted

stating that the results could be significantly different at some future

point in time. If either single point or multiple input-output type

analysis is conducted, you can get results which not only will be better

for diagnostic purposes, but which also will be a lot more useful for

prognosis. I would like to find out if anyone here has worked on some

of these larger problems where they are collecting a lot of data

simultaneously and trying to unravel all the various interactions and

effects that are taking place.

D. N. Fry, Oak Ridge National Laboratory : This is exactly the problem

that we are tackling right now in connection with detecting failures in

nuclear power plants. Our primary work is not necessarily with rotating

machinery, but with failures of structures connected with core components in the nuclear reactor itself. We are presently trying to

apply pattern recognition and signature analysis techniques to multiple

signal inputs. Part of the problem is to include in the total analysis

the error associated with each measurement, so that the algorithm that

makes the decision on whether the particular data you have just taken is

either normal or abnormal. This takes into account how much data

92
you already have and what the confidence is on the base line signature

that you presently have. We are probably not the first ones to do this.

I think it's in common use, but we really haven't heard much about it

here today.

J. W. Forest, Ontario Hydro : It seems that there is a conflict in the

goals which we are trying to establish. There is emphasis placed on diagnosing a defect and there is also emphasis placed on saying how long

.a component will function (prognosis). The conflict comes from not

being able to tell how long something will run until it fails. I have

some experience with a vibration monitoring system in a nuclear power

plant and on rotating equipment. One of our problems is of a statistical nature because no two failures are going to be the same even

if they are the same component. It's quite a task. I think the people

that are asking for the quick answer of prognosis are going to have to

wait a long time before it's resolved.

A. J. Hess : I'd like to comment on two of the points that were brought

up. First is the system/human operator interface. When we first

introduced the lECMS system to a fleet type environment, the pilots and

the maintenance operators didn't like it much. From a maintenance

standpoint, it was an additional engine subsystem which they had to

maintain and caused them to perform extra maintenance on the engine.

What they found out later was that by using the lECMS system they were better able to maintain their engines. The statistical data that we

generated showed that more maintenance was performed on lECMS equipped

engines than on engines not so equipped in about the same number of

manhours. From that you can deduce that the engines were perhaps better

maintained in the same amount of time. Initially the pilots did not

like this diagnostic system flying along and recording data and acting

as a tattletale on how they operate the engines. But as they used the

system, they experienced situations where the lECMS system verified

engine gripes and it enabled the pilot, the operator of the aircraft, to

interface better with the maintenance department to prove that he was right in situations where the maintenance department said he was wrong.

And conversely, we have had situations where the system verified a pilot

gripe as being wrong, but saved lots of unnecessary maintenance on that

engine. The initial interface between the human and the system becomes

a question of confidence level. The only way that you can build up this

confidence level is to let them have the system and use it in an operational environment. That's what we did and that's what we

experienced. The chairman made an interesting point when he mentioned

the three lights. We have three lights in the cockpit; one is to

indicate that the system is not operating and to ignore it, the other

two indicate that something is wrong with the engine. The other point

that was brought up that I would like to comment on is how to handle a multitude of inputs from different types of diagnostics. The lECMS

system does several different types of diagnostics such as vibration

analysis, gas path analysis, exceedance limits, and oil quality. The

95
only way you can realistically handle all those inputs is by some type

of computer software diagnostic logic routine. That's the way we tried

to do it. We expended our greatest effort in developing software

routines, not in developing the hardware.

P. L. Howard : In summary, the diagnostic manufacturers, as they have in

the past will now and probably forever, say that the success of their

system is based upon the detection of some fault. Not even the

diagnosis but the detection of some fault. The user will say the success of the system is in saving some catastrophic failure, and I think they will stay apart until the significance of the fault and its

relation to a catastrophic failure can be demonstrated.

9h
SESSION II

CASE

HISTORIES

Chairman: P. L. Howard

SKF Industries

SONIC ANALYZER - CASE HISTORY

John L, Frarey

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, N.Y. 12019

Introduction

The sonic analyzer was a diagnostic system aimed at detecting malfunctions in gas turbine engines and helicopter transmissions prior to

catastrophic failure. The program was active under several sponsors

during the 1960 's and early 1970' s. For a part of the time the overall

program was active, two parallel, competitive programs were conducted

by Curtiss -Wright and the General Electric Company. At the first MFPG

Meeting in April, 1967, both companies described their approach to

sonic analysis of gas turbine engines.

The purpose of this paper is to examine what can be learned from the

program experience, particularly in those areas that are common to today's diagnostic programs. In order to do this, the Curtiss-Wright

approach will be briefly described, its success analyzed and three

specific program areas that emerge as significant when the program is

reviewed with perfect 20-20 hindsight.

Sonic Analyzer Concept

Sonic analysis as employed is the same as today's vibration signature

analysis except that microphones were used rather than accelerometers

The discrete character of the frequency domain spectrum is analyzed

and characterized. Most discrete frequencies can be associated with

rotating components in the machine. Three types of signal character

changes were considered significant. They were changes in:

Amplitude

Harmonic Content

Modulation Character

The kind of changes that were looked for are illustrated in Figure 1 which compares the spectra of two hypothetical engines, one healthy

and the other side with the above three symptoms. The oil pump signal at approximately 1500 Hz illustrates the increase in amplitude

symptom. The appearance of the thrust harmonic of the fuel pump at

approximately 3000 Hz illustrates the harmonic control symptom and the

appearance of side bands on the compressor blade passing signal at approximately 1200 Hz illustrates the modulation symptom. This type of

analysis is still valid today and was considered quite advanced in the

early 1960's.

97
Figure 2 is a block diagram of the hardware built to implement the concept. It is a standard heterodyne analyzer with two exceptions, the

phase lock loop and the frequency ratio synthesizer. These two circuits

allowed the analysis of the signals as a ratio of engine speed and thus

independent of RPM. Again these two circuit developments as related to

vibration analysis were significant advances at the time. Figure 3 is a photo of the sonic analyzer as used in the field. The unit shown included a paper tape reader that allowed full automatic operation of the

analyzer, another advance. The unit was portable, however, it obviously

could benefit from today's integrated circuit technology. Also, today,

a laboratory receiver of the analyzer with superior characteristics can

be constructed from off the shelf instruments.

Over the period of its use, the analyzer was applied to the following

engines and helicopter transmissions.

Engines Helicopter Transmissions

J-65 UHl

J-57 CH46

J-79 , . CH47

J-52

JT-30

Jt-80

Results

Probably no two people associated with the program would agree on a rating of the success of the sonic analyzer. The safest thing that

could be said is that it would detect some of the defects claimed for

it on many of the engines and transmissions listed above. The purpose

of this paper is not to rate the success of the program but rather to

review what can be learned from it and applied to other diagnostic

programs. The following three characteristics of the sonic analyzer

program are common to every diagnostic program.

1. Laboratory Vs. Field Testing

2. Human Operation Skill and Bias

3. Assessing the Batting Average

These three characteristics are briefly discussed below and will be ex- panded upon in the presentation.

1. There probably is some optimum mix for a given program between lab

and field tests. The sonic analyzer program would have benefited by

more laboratory testing. For example, mechanical impedence tests to

determine signal transmission characteristics and coupling coefficients

to the air may have clearly identified the detection of some defects as impossible. Almost all diagnostic programs that have advanced too

quickly toward field condition have failed or had to return to more con- trolled conditions.

98
2. If an analyzer operator who has a very good understanding of the en- gine under test and the analyzer, consistently gets better results than

one who simply follows directions; then this is an indication that the

programmed limits alone are not sufficient.

3. Specific ground rules on how to grade the diagnostic system must be

implemented. Comparison with the parts replaced at overhaul is a very

unsatisfactory way of grading a diagnostic system. A significant proportion of the cost of any diagnostic system evaluation lies in this area.

99
LIN

1.0

0.8

Ob

0.4

O.Z

750 1000 1250 1560 1750 2000 2250 2500 27J0 30C0 3250 FREQUENCY Hz

SPECTROGRAM OF HYPOTHETICAL ENGINE OPERATING NORMALLY

LiN

1.0

0.8

0^

0.4

0.2

150 1000 1250 1500 1750 2CdO 2250 2500 2750 3C00 3250 FREQUENCY Mr

SPECTROGRAM OF HYPOTHETICAL ENGINE

OPERATING WITH FOUR MALFUNCTIONS

FIGURE 1

100
INDICATOR

o

HO

u

H

W

Q

+o

o

FREQUENCY PJ^TIO GENERATOR

BALA MODUI

CMW

PiBM

O

ACH. ICAT H

101
FIGURE 5

102
DISCUSSION

W. K. Mathison, Puget Sound Naval Shipyard : If you had the chance to

start again today with gas turbine engines, would you use the sonic

analysis again, or a vibration analysis, or something else?

J. L. Frarey : I would use anything I could lay my hands on that might

give me a hint as to what was going on inside the engine. The problem

with the sonic analyzer has been that very early in the game, we trapped

ourselves into exclusive use of the microphone because it was very easy

to use. It was very easy to put a microphone next to an engine compared

to screwing on an accelerometer or trying to bury something, or open a port, or this type of thing. Sonic analysis would work in some places.

I think that it should have been implemented all along with additional

accelerometers.

105
OIL ANALYSIS IN PERSPECTIVE

Richard S. Miller; Lt, USN

Arlington, Virginia 22217

Detection of component malfunction in lubrication and hydraulic systems, prognosis of the course and remaining system life and possible

diagnosis of the type(s) of failing component(s) have been the primary

objectives of most oil analysis activities. Several previous MFPG papers

and one entire meeting were aimed at describing the transfer of spectrometric oil analysis methodology in the 50 's from industrial internal com- bustion engines to rotating machinery, the success of this methodology,

and a description of non-spectrometric oil analysis techniques (1, 2,

3, 4). My objective is not to overview these papers but to review the

methodology of current oil analysis activities to indicate its weaknesses

with respect to future lubrication system design and reliability and to

indicate changes that appear to be desirable to provide meaningful "oil

analysis" services to future high performance equipments.

Oil Analysis Methodology

Present "oil analysis" methodology may be subdivided into three

parts. The first phase is sampling which assumes, sometimes mistakenly,

that the oil and the particulates in it are representative of those in

the system. The second part, composition determination, is accomplished

in a calibrated commercially available instrument; this wear metal con- centration data, along with available information such as operating

hours since the last sample, and oil change or addition data, is then

used by the "oil analyst" to infer that the rate of production of metal

in the system is increasing, decreasing, or remaining the same. The oil

analyst effectively makes periodically updated estimates of the wear

metal production rate based on this data. Ideal ly, concentration , con- centration change with time, and possibly oil consumption/addition data,

are inputted by the oil analyst into the equation in Figure 1 to obtain

the metal production rate. If the filter in the system is removing but

a small fraction of the particulates that are formed, (i.e. the filtration rate is small), the rate at which particulates are settling to

sumps and the rate at which dissolved metal is depositing on the system's

surfaces are low, then the "oil analyst" can make a fine prediction of

the wear metal production rate, its change with time, and a reliable

assessment of any change in machinery condition.

The original success of the analyst in predicting problems in diesel

and other systems engines which are generally equipped with coarse filters (40 + micron) therefore is understandable. However, others such as the hydraulic systems, which are installed in Naval aircraft and which

are equipped with relatively fine (5) micrometer filters, are not as responsive to conventional oil analysis methodology. As a consequence,

the spectrometers are not sensitive to the small concentrations of particles present in the system and the comparatively slow rate of change of

metal concentration with time, even when the system is wearing at abnormal rates. Unfortunately for the "oil analyst", this trend is continuing
because machine designers are beginning to recognize the benefits to be

obtained by specifying filters that remove a high fraction of particulates which can be deleterious to the life and reliability of the equipment. For example, the T-700 engine developed for the UTTAS helicopter

is to be equipped with 3 micron filters originally tested on the T-53

engine (5, 6).

Particle Size/Concentration and Machine Reliability/Life Relationships

Examination of the relationship between particle size, concentration

and machinery reliability and life is best begun by comparing particle

size and lubricant film thickness as a function of application for naval

equipments. I have chosen aircraft derivative bearings and gears, hydraulic system components and journal bearings typical of those supporting steam turbines as extremes. As may be seen in Figure 2, the film

thicknesses in these equipments range from 0 - 0.1 micrometers to 25

micrometers and installed filtration capability begins to compare favorably with film thickness only in the hydraulic and steam turbine journal

bearing application. Only in the case of the steam turbine journal application can sufficient particulate matter be expected to be in suspension

to be truly susceptible to spectrometric analysis and at the same time

not be deleterious to the mechanical system. These conservatively designed systems are inherently very reliable and are not a priority item

for oil analysis. The aircraft hydraulic system, because its sliding

components are very susceptible to deterioration by particulates and

therefore is much less reliable, is equipped with efficient filters and

renders spectrometric analysis almost ineffectual. Only in the case of

the aircraft bearings and gear systems is the lubrication system susceptible to spectrometric oil analysis because they are not now equipped

with efficient filters. The extent of the application of spectrometric

oil analysis will decrease as finer filters are installed in these systems to increase life. Preliminary evidence indicates bearing lives and

presumably the lives of these film gears can be increased many times by

using effective filtration techniques (7).

To illustrate the relationship between wear particle size, concentration detection limits, wear particle-surface interaction rate and sur- face damage, consider the following (Figure 3). A part per million of

iron as iron oxide particles with a one cubic micrometer volume in oil

results in a particle number density of approximately 400,000 particles

per cubic centimeter. A part per million represents 1 gram in approximately 275 gallons of lubricant or, in other more familiar volumetric

terms, 1 drop of vermouth in 16 gallons of gin (Figure 4). A part per

million of iron in oil is below the sensitivity of Navy emission spectrometers which actually are not sensitive to concentrations below 2 parts

per million (2000 parts per billion). In an el astohydrodynamic contact

of a ball bearing with a micrometer film operating a surface velocity of

1000 in/sec, the particle interaction rate with ball is approximately 1 per second. At a film thickness of 0.1 micrometer, the passage of a boulder 1 micrometer in size would occur on the average of every 10 seconds. Experimental evidence indicates these presently unfiltered parti

105
culates slowly but surely interact with the surface and initiate surface

fatigue cracks, a fraction of which propagate into the interior of the

bearing surface and thereby limit life. In addition, skidding damage to

future high DN aircraft turbine bearings during thrust reversals will

probably be aggravated by particulates.

Oil analysis using today's methodology and tomorrow's spectrometric

techniques, such as atomic fluorescence in well filtered systems will not

improve the situation appreciably because most of the wear debris will be

in the filter. However, the detection limits for iron of atomic fluores- cence spectrometers equipped with flame atomizers and pulsed hollow cathode lamps is 6 X 10"^ parts per million, which is a significant improvement over emission spectrometers in use today (8).

Oil Wetted Surface Condition Monitoring/Options for Future Lubrication

Systems

The application of filters efficient in the 0.1 to 1 micron range

in hydraulic and lubrication systems will require that current oil analysis methodology and instrumentation be abandoned or changed. An oil

analysis system using today's methodology and spectrometric instrumentation sensitive in the low parts per billion range will only rely on the presence of newly created wear metal particles, the small number of

statistically available particles that have previously oassed thrnuah the

filter, and changes in soluble metal compound content to detect abnormalities in the lubrication system. Abandonment of these oil sampling

and analysis procedures and introduction of inline detectors, although

presently unavailable, to detect the concentration of the available wear

debris or wear debris and dissolved metal and to provide time averaged

concentrations and approximate wear metal production rate data, is a second alternative. However, attempts to use light scattering, high

energy fluorescence, capacitive, and neutron activation detectors which

have been developed or proposed, or even inline Ferrographic devices for

these purposes, would be probably frustrated by the low wear metal con- centrations. As a third alternative, design into and installation of

centrifugal particle separation devices in hydraulic and lubrication

systems would provide wear debris for microscopic and spectrometric analysis, and would be desirable in some equipments. In other equipments,

where redesign is not practically or economically feasible, new types of

filters may provide the particle separation capability needed to improve

equipment performance and life, and provide wear particulates for diagnostic and prognostic analyses of machinery condition. High gradient

magnetic separators, which separate ferro or paramagnetic materials by

magnetic forces, may provide a measure of the desirable characteristics

listed in Figure 6 and are being evaluated for these applications.

To conclude, it is appropriate to mention the report of Alan Beerbower's study of mechanical failure prognosis through oil debris monitoring (5). Although the study was restricted to assessment of current

oil analysis methodology and suggestion for the improvement of oil analysis techniques for helicopter transmissions, his recommendations are

106
generally applicable. Beerbower finds that nearly 100% of transmission

failures could be detected rf spectrometric analysis is augmented by particle analysis of the larger particles which are collected by chip detectors or the presently installed filters. Mr. Senholzi will indicate

in a later paper how complementary techniques are being evaluated for

these purposes. Beerbower's report, in addition to providing the data

upon which to base his recommendations, provides a description of wear mechanisms, wear particle size distributions, and description of non- spectrometric oil analysis tools available today.

107
FIGURE 1

DEFINITION OF WEAR METAL PRODUCTION RATE

Y^ Y" + r PRODUCTION = ACCUMULATION REMOVAL

dc + cdm-. + r 'dt dt filter

r + r settling deposition

r r r PRODUCTION, ACCUMULATION, REMOVAL - RATES OF METAL PRODUCTION IN,

ACCUMULATION IN, AND REMOVAL FROM THE SYSTEM (GRAMS/SEC)

m-i - MASS OF LUBRICANT IN SYSTEM, (GRAMS)

c - CONCENTRATION OF WEAR METAL IN LUBRICANT (GRAMS METAL/GRAM OF

LUBRICANT)

r r r - RATES OF WEAR METAL REMOVAL BY FILTRAfilter, settling, deposition

TION, SETTLING AND DEPOSITION MECHANISMS (GRAMS/SEC)

108
FIGURE 2

MOVING SURFACE SEPARATIONS

FILM THICKNESS FILTER CAPABILITY

MICROMETERS MICROMETERS

GAS TURBINE BEARINGS, GEARS 0.1-1 10-40

HYDRAULIC COMPONENTS, AIRCRAFT 0.5-3 5

SHIP JOURNALS 25 25*

* ANTICIPATED

FIGURE 3

WEAR PARTICLE CONCENTRATIONS - 1 PPM IRON

1 GRAM IN 1,000,000 GRAMS FLUID

1 GRAM IN 275 GALLONS FLUID

500 BILLION PARTICLES IN 275 GALLONS

1.8 BILLION PARTICLES IN 1 GALLON

400,000 PARTICLES IN 1 CUBIC CENTIMETER

PARTICLES - 1 CUBIC MICROMETER OXIDE PARTICLES

109
FIGURE 4

i

, EMISSION SPECTROMETER SENSITIVITY

CONCENTRATION OF

IRON (PPM) READING (PPM) RANGE (PPM)

0 0 or 1 0-1

0.5 0 or 1 0-1

1 +1 . " 0-2

10 10 +2.2 8-12

100 100 +10.2 90-110

1 PPM = 1 DROP IN 16 GALLONS; 80 "FIFTHS"

1 CENT IN $10,000

1 INCH IN 16 MILES

1 MINUTE IN 2 YEARS

FIGURE 5

PARTICLE - SURFACE INTERACTION RATE

BASIS:

GAS TURBINE BALL BEARING CONTACT

25 METERS/SEC SURFACE VELOCITY

1 MICROMETER FILM THICKNESS

1 PPM IRON - 1 CUBIC MICROMETER OXIDE PARTICLES

RATE: 1 PARTICLE PER SECOND

110
FIGURE 6

IDEAL FILTER CHARACTERISTICS

0.1 - 1 .0 MICROMETER

HIGH DEBRIS CAPACITY

LOW PRESSURE DROP

PERMANENT FILTER ELEMENTS

WEAR PARTICLE RETRIEVAL FOR ANALYSES

NO EXTERNAL POWER

111
REFERENCES

1. Ward, J, M,, "Spectrometric Oil Analysis", Proc. of Mech. Failures

Working Group 2nd Meeting, pp, 15-21, 1967, AD 721359.

2. McGowan, J. A., "Diesel Engine Maintenance Control by Oil Analysis",

Proc. of Mech. Failures Working Group, 4th Meeting, pp. 10 - 12, 1968

AD 721359.

3. Rumbarger, J. H., "Rolling Element Bearing Life Margin Testing of

FIRL and Correlation of Spectrometric Oil Analysis Results with Life

Results", Proc. of Mech. Failures Working Group 5th Meeting, pp. 14 - 15, 1968, AD 721359.

4. Sawyer, W. T. , "Proc. of the 16th Meeting of the Mechanical Failures

Prevention Group", pp. 1-68, 1972, AD 738855.

5. Beerbower, A., "Mechanical Failure Prognosis Through Oil Debris Monitoring", Contract Final Report Number DAAJ02-73-C-0094, USAAMRDLTR-74-100.

6. Lynch, C. W. and Cooper, R. B., "The Development of a Three-Micron

Absolute Main Filter for the T-53 Main Engine", ASME Jour, of Lubr.

Tech. 93F, 430-436 (1971).

7. Dalai, H.; et.al., "Final Report on Progression of Surface Damage in

Rolling Contact Fatigue", ONR Contract N00014-73-C-0464, Feb. 74,

AD 780453.

8. V'inefordner, James D., "Atomic Fluorescence - Past, Present, Future",

Chem. Tech, 123-128, Feb. 1975.

112
DISCUSSION

L. Enochson, Time/Data Corporation : You indicated that the methods

would have to be abandoned with improved filters. Why can't you just

examine what's in the filter after you tear it down for inspection? .

iM. Hoobchaak : It should be examined periodically and not just at filter

teardown because then you have to go into the system and possibly

disturb the system itself.

R. Hohenberg, Mechanical Technology, Inc. : You referred to a report by

Beerbower. Could you give us more information on that?

M. Hoobchaak : The title of the report is "Mechanical Failure Prognosis

Through Oil Debris Monitoring." Beerbower has torn apart filters and

looked at the chips. He has also examined the debris in magnetic debris

collectors. He was able to detect almost all the failures which

occurred because large particles were found which were indicative of

very imminent failure in the transmissions.

P. L. Howard, SKF Industries : That paper points out one of the problems

that diagnostics people continually face. When a diagnostic system

indicates a problem, corrective action is usually taken. The corrective

action quite often reduces the effectiveness of the diagnostic system.

115
INSTRUMENTATION FOR PREDICTIVE MAINTENANCE MONITORING

Ralph James, Exxon Chemical Co. , Baytown, Texas 775Z0

BACKGROUND

Plant tests conducted by Exxon Chemical Company U.S.A. and The Boeing

Company in 1972 and 1973 at Baytown, Texas demonstrated the applicability

of onstream acoustic measurements to diagnose the condition of process

equipment. The basic high-frequency acoustic techniques for predictive

maintenance was reported at the 28th Annual ASME Petroleum Mechanical

Engineering Conference, September 17-20, 1973 at Los Angeles, California.^

In general, the mechanical "electrocardiagrams" studied during these

tests were shown to be effective for early detection of small defects in

bearings and gears, growing cracks in shafts and weld joints, loose

parts, and operating deficiencies such as pump cavitation. However, the

monitoring and interpretation of the data was manpower intensive and

could not be economically justified on a plant wide basis. Therefore,

to utilize this technology it would be necessary to automate most of

the data comparison; indicating service caused flaws and detrimental

changes in rotating machinery.

SYSTEM DESIGN PHILOSOPHY

(1) Ultimate Goal - Provide meaningful early indication of impending

i^ailure of critical process equipment so that: (a) corrective actions

can be taken, or (b) provide enough lead time so that the majority of re- quired maintenance can be performed during planned, scheduled shutdown,

or (c) for the case where there are no scheduled shutdowns, production

can be continued until the "final hour" with minimum probability of a catastrophic failure.

(2) Payout - Provide a minimum calculated benefit to cost ratio of 1.5

to 1. Estimated benefits were based on a statistical analysis of plant

failure data-assuming a cost differential credit for predictive maintenance planning, increased mechanical availability, material and labor

savings from a reduction in "wrecks" and manpower released from routine

vibration readings and associated checkouts.

(3) Rel iabi 1 i ty - (a) Design mean time between failures of monitoring

instrumentation to be significantly greater than that of the machine

being monitored -- say a minimum of 10 to 1. (b) All sensing elements

must be self-checking; i.e., loss of signal would alarm, etc. (c) All

primary sensing elements maintainable with equipment in operation.

(d) False alarms due to transients should be minimized.

1 See article in Oil and Gas Journal for December 17, 1973.

111+
(4) Safety - Monitoring system must me-et all required safety codes -- intrinsic safety preferred.

(5) F1 exi bi 1 i ty - Initial system to be primarily set up to read acoustic signals via accel erometer , but must be: (a) readily and economically expandable; (b) capable of monitoring existing machinery alarms

such as non-contact probes, temperature and delta temperature alarms,

and system or cycle efficiency calculations. However, in the initial

phases the emphasis was placed on the more nearly universal or fundamental monitoring sensors such as high frequency acoustic signature

analysis. Another promising on-line analytic technique to be pursued

is the use of the principle of X-ray fluorescence to detect impending

failure by detecting wear and/or degradation particles in liquid or gas

streams. These two monitoring techniques are the only ones we know of

that show promise of onstream detection of fatigue cracking of turbomachinery rotors and shafting.

(5) Alarm vs. Shutdown - Since the emphasis is on early detection of

impending failure the shutdown decision is retained by operating personnel. However, conventional minimum automatic shutdowns are locally

controlled on critical items such as low oil pressure, thrust bearing

temperature and high level in suction drums, etc. Also, a few machines

such as high-speed-air compressors have vibration shutdown switches.

PREDICTIVE MAINTENANCE MONITORING SYSTEM

Using the above stated criteria a plant system consisting of three minicomputer controlled surveillance systems was developed. The number of

sensing channels totaled about 800. Total plant area monitored was about 230 acres.

In order to obtain the specified benefit to cost ratio it was necessary

to make a number of trade-offs between cost and technical wants. For

example, we had to limit the computer controlled system to process

equipment considered essential to production. A portable acoustic

emissions analyzer was made a part of the plan to permit periodic monitoring of about an equal number of less critical machines. This analyzer

can be used for shop tests. Also, the number of sub-multiplexers had to

be optimized at the expense of additional sample time intervals. A final

example is that the co-ax cables within the unit limits were placed in

existing cable trays or strapped to existing piping instead of being

encased in conduit.

Exxon Chemical Company approved the installation of the proposed system

in August, 1973. By December, 1974 one of the three minicomputers was

in operation under engineering control (not yet released to operations).

The other two systems are scheduled for completion in mid 1975.

The first minicomputer covered four operating units and associated cooling tower and pump slabs. The sensor channels are divided as follows:

115
Crack detectors 63

Sleeve bearings 35

Gear interface 12

Gear interface plus

1 or 2 anti -friction

bearings 52

Anti -friction bearings 207

Total 369 Channels

Process equipment monitored includes pumps, motors, compressors, turbines,

extruders, gear boxes, turbochargers, and compressor header and lateral

piping. . .

INSTRUMENT DESCRIPTION

A. General

A single link through this system would consist of a high frequency

acoustic transducer, a preamplifier, and associated cabling and electronic processing circuitry for detecting those characteristics of the

acoustic signal which are representative of the incipient failure in

the device under consideration. The transducers, which use a PZT-5A

crystal, are mounted as close as possible to the machine part for which

incipient failure data is desired using an appropriate cement. The

particular type of cement is dependent on the application. For example,

we have had sensors cemented in place for over 1% years in a severe vibration and weather environment in the Baytown facility. Dental cement

was utilized and proved highly satisfactory in this application.

Short coaxial cables carry the signals from the transducers to preamplifiers located close to the transducers. Preamplifiers are required

because of the long cable runs from the instrumented machinery back to

a field sub-multiplexer or to the Control Room where the processing equipment is located and because of the high electrical noise activity common

in many petrochemical plants. Low voltage D.C. power to the preamplifiers comes from the same unit that it is feeding its high frequency data

to over the same coaxial cable. Thus a small coaxial cable, such as. RG 174/U (0.1 inch diameter), can be used.

The transducers, preamplifiers, and associated cabling are capable of

operating in Class I, Division II hazard areas, as defined by the

National Fire Protection Association (NFPA) Bulletin No. 493, without

any special provisions. For equipment operating in Class I, Division I hazard areas, barriers must be used in the cabling feeding the DC power

to the preamplifiers which makes the cabling and preamplifiers intrinsically safe. Thus, protective conduit does not have to be used in these

areas

116
B. Antifriction Bearings and Gears

Antifriction bearings and gears are monitored sequentially. A maximum

of two bearings and one gear, all in close proximity to each other, may

be monitored by the same transducer at the same time. The monitoring

sample time ranges from 10-seconds to 2-minutes, 40-seconds. The variable sample duration is computer controlled and depends on the statistical randomness of the acoustic signal. The sequential sampling is

sufficient for antifriction bearings and gears since even if the maximum

time of 2-minutes, 40-seconds were required for each bearing and gear

group, a minimum of 540 groups could be covered in one day. Since high

frequency acoustic data usually provide at least a week's warning

before catastrophic failure of an antifriction bearing or gear, this is

generally a sufficient sampling frequency.

The bearing and gear frequencies for all constant speed machine (± 1%

variation in RPM) bearings and gears being monitored are stored in the

computer, and used by the antifriction bearing and gear processor in

generating the spectral line data. For variable speed machines, tachometer inputs to the computer adjust these frequencies to their correct

values.

Figure 1 is a block diagram of a typical antifriction bearing and gear

system.

Tach

Cable

Runs

High

Freq

Preamps

\

/

QRemote

Location

1

Transducers '

Submux

1 Class 1 Div. 2 Area

Remote

Location

2 Submux

2

To Remote

Alarm Unit

A

Mai n Commu-|—Ib'r tator

ProcessTimi na HI

Printer

Control

Interface

Data MiniInter- computer

face

Figure 1 Anti-friction Bearing and Gear IFD System

117
Since the antifriction bearings and gears are sequentially sampled, they

can be sampled in the field by a set of sub-multiplexers since this will

reduce the cost of cable plus installation. Thus, instead of hundreds

'of cables, (as in Remote Location 1 in Figure 1), going from the preamplifiers to the Control Room, they terminate at a sub-multiplexer, and

only two cables are required from the sub-multiplexer back to the Control

Room.

The sub-multiplexers are all under the control of a main commutator which

is in turn under the control of the mini -computer thi^ough the control

interface. The sequence of events which allows the main commutator to

command a sub-multiplexer to switch from one transducer to the next is

as follows. Assume that we have just switched to a transducer monitoring

two antifriction bearings and a gear. After 10 seconds of monitoring,

the antifriction bearing and gear processor has generated nine outputs

which are representative of the following amplitude characteristics of

the high frequency signal from the transducer.

These nine outputs are compared by the computer with the nine values it

obtained the last time it looked at this bearing. If the values are the

same within some pre-set limits, (there are ten pre-set limits for each

variable), the computer commands the system to switch to the next transducer. If the values are different, they may be different for one of

three reasons.

1. A failing mechanism is occurring in the antifriction bearing

or gear.

2. The machines operating condition is changing, such as a changing load will cause the RMS Signal Level to change.

3. The ten second sampling time was not long enough to obtain a good statistical average for the random data being processed.

In order to eliminate item 3, the computer doubles the sample time, and

continues processing the data. Comparisons are again made at the end

of 20 seconds. The process continues up to a maximum of 160 seconds or

until all nine values are in agreement with the previously measured

values, after which the computer commands the system to switch to the

next transducer.

Any time a measurement from any of the processors does not agree with

its previous measurement within some pre-set limits, the change is

recorded on a digital printer along with a channel identification and

(a)

(b)

(c)

RMS Signal Level

Spike Energy

7 envelope detected spectral lines for

the three frequencies associated with

each bearing and the gear frequency.

118
the date and time of occurrence. Thus, only changes are recorded and the

requirement for maintenance personnel to look at reams of strip chart

recorded data to determine if any data changes are occurring is obviated.

The Printer prints 21 columns of information. This information is broken

into fields as shown below, along with an example of ANTIFRICTION AND

GEAR DATA.

21 15 14 13 10 9

DATE CODE f CHANNEL ID

SYSTEM

ID

EXAMPLE

DATA (9 DIGITS)

1 2 5 0 2 2 0 0 1 3 1 0 0 0 0 0 1 2 1 7

1 2 5 0 2 3 0 0 7 5 6

* 2

1 2 5 0 2 3 3 0 5 7 7 1 1

1 2 5 0 2 3 4 0 5 7 7 4 1

1 2 5 0 2 5 0 0 1 2 0 0 0 0 0 0 1 0 1 2

Column Assignments Are as Follows

Column 1 Column 2 Column 3,4,5

Column 6,7,8

Column 9

SPIKE ENERGY

RMS LEVEL

#1 BEARING -

#2 BEARING -

GEAR MESH -

OUTER RACE ^ SPECTRAL LINE

INNER RACE SPECTRAL LINE

ROLLING ELEMENT SPECTRAL LINE

OUTER RACE SPECTRAL LINE

INNER RACE SPECTRAL LINE

ROLLING ELEMENT SPECTRAL LINE

MESHING FREQUENCY SPECTRAL LINE

If only one bearing is being monitored, only zeros will appear in the

unused columns.

This technique for antifriction bearing monitoring is patented by The

Boeing Company.

C, Sleeve Bearings

Since sleeve bearings can fail very rapidly, and since it would be

possible to miss cracking in a sleeve bearing lining material if the

119
bearing was sequentially sampled, all sleeve bearings are continuously

monitored.

SLEEVE BEARING DATA (COLUMNS 1 & 5)

Only two columns are employed for sleeve bearing data (1 ^ 5).

Column 1 is a measure of SPIKE ENERGY

Column 5 is a measure of RMS LEVEL

Figure 2 is a block diagram of the sleeve bearing circuit. Computer

comparison with the previously measured data is done every ten seconds

High

Freqiiency

Preamos

Transducer

{>

Cabl e Runs

Cal

Processor Data

Interface

w

To

Minicomputer

figure 2 Sleeve Bearing Acoustic Monitor

21 15 14 13 10 9 6 5 4 2 1

DATE CODE SYSTEM CHANNEL ID

ID

EXAMPLE

BLANKS

RMS

1 2 5 0 2 2 0 0 1 3 1 0 0 0 0 0 1 2 1 7

1 2 5 0 2 3 0 0 7 5 6 2

1 2 5 0 2 3 3 0 5 7 7 1 1

1 2 5 0 2 3 4 0 5 7 7 4 1

1 2 5 0 2 5 0 0 1 2 0 0 0 0 0 0 1 0 1 2

BLANKS ,f„ wA

120
D. Crack Propagation

Again, since it would be possible to miss any crack propagation if the

suspected structures were sequentially sampled, all crack detectors are continuously monitored. Comparison with previous data is made every

10 seconds - any acoustic emission pulses from a propagating crack are counted.

CRACK DETECTOR DATA

21 15 14 13 10 9 2 1

DATE CODE SYSTEM

ID

CHANNEL ID

EXAMPLE

BLANKS

1 2 5 0 2 2 0 0 1 3 1 0 0 0 0 0 1 2 1 7

1 2 5 0 2 3 0 0 7 5 6 2

1 2 5 0 2 3 3 0 5 7 7 1 1

1 2 5 0 2 3 4 0 5 7 7 4 1

1 2 5 0 2 5 0 0 1 2 0 0 0 0 0 0 1 0 1 2

DATA

CRACK DETECTOR DATA (COLUMN 1)

A single column is used for crack detector data (Column 1)

measure of crack growth in pressure piping.

It is a

DATA CODING

The data in each column is independent of any other column and can have

a value from 0 to 9 . This is trend data and only indicates the magnitude of change from a previous data sample. Large changes will be

printed in RED and are indicative of serious problems with the unit

being monitored. It should be checked immediately and Mechanical

Technical Service notified to further analyze the problem. Small changes

are printed in BLACK and indicate less serious problems with a unit.

Figure 3 is a block diagram of an acoustic emission crack detector

system.

121
High

Frenuency

Preamps

Remote Location 3

I CI ass 1 Div. 1

Transducers

Cable

Runs

Barri er

Stri ns Processor

Interface

Cal i brat ion

and

Checkout

To

Minicomputer

Figure 3 Acoustic Emission Crack Detector System

122
DISCUSSION

J. L. Frarey, Shaker Research Corporation : Do you plan to incorporate

the low frequency vibration, the proximity probe outputs, and the

startup-shutdown critical speed analysis into the same minicomputer?

R. James : We do plan to incorporate all the failure detecting devices

in the same mini -computer.

B. C. Baird, Sr. : The system has a TI 960 computer in it. It's using

about 8K of memory right now. It's expandable to about 32K and the

racks are large enough to include a lot of equipment so that a lot of

processing can be done on the same mini-computer.

W. R. McWhirter, Jr., Naval Ship Research and Development Center : Can

you explain some of the problems you had with the mi ni -computer?

B. C. Baird, Sr. : IC's were the major problem. A lot of this was caused during our checkout phase by switching the computer off at night

and switching it on the next morning. I think we were thermally cycling

the computer and it was causing failure every fourteen days, or so.

W. R. McWhi rter , Jr. : Do you feel that this failure was peculiar to the

computer you used?

B. C. Baird, Sr. : It might have been because the computer components

are not thermally cycled before being shipped. Now we just leave the

computer on. Since it's been left on, it's been running for four or five months and the first failure has just occurred.

U. Sela, Exxon Company, USA : Are you looking at the acoustic emission

or are you using proximity probes as sensors for spectrum analysis?

B. C. Baird , Sr. : Several parameters from each bearing were measured,

but the proximity probes apparently just measure displacement. We

haven't done any spectrum analysis on the sleeve bearings. We just

measure an overall RMS signal and a spike distribution signal.

R. James : The proximity probes do measure displacement on each one of

the four rotors and these are the only vibration probes in the whole

plant that trigger automatic shutdowns. Due to the unreliability of the

proximity hardware, most of our proximity probes are only on alarm.

B. C. Baird, Sr. : We use high frequency (about 120 KHz) acoustic

emission for taking most of the data in the plant. We found this to be

a good frequency for defect detectabil i ty and for minimizing the

background noises and noise from other sources.

123
J

R. Lenich, Caterpillar Tractor Company : Have you had to do work

because of false alarms in the system?

B. C. Baird, Sr. : We haven't had any false alarms, as far as I know.

R. Lenich : What kind of experience have you had with the wiring of

connectors in the system?

B. C. Baird, Sr. : Wiring transducers and printouts is a problem. We

develop and build our own transducers very inexpensively. The wire we

use is RG174/U coaxial cable. There are about 600,000 feet of this

cable in the plant. The RG174 was selected because it costs 2 1/2

cents a foot. In certain vulnerable places, the cable is sometimes

inadvertently cut and has to be spliced. We are trying to protect the

cable in these places by putting casing and conduit around it.

0. E. Compton, Northrop Corporation, Aircraft Division : Have you

trended any of the data from the results you obtained to define planned

periodic maintenance intervals? Is the computer cost effective?

R. James : We don't feel like we have enough data yet to tell whether

it is cost effective. We are looking at at least a year's run in order

to get some information that would enable us to make a prediction.

C. R. Garbett, Shell Development Company : Do you have any experience

detecting flaws or incipient failures in pressure vessel equipment?

R. James : We have used this in the field to check for cracks in

compressor piping. We glued transducers to a pipe that we knew

contained cracks and discovered that we could find a running crack.

Because of this favorable experience, we have put 63 crack detectors on this particular system. We do not have them on reactors at the present

time, but the next step is to put them on some low temperature reactors

which are subject to brittle fracture.

J. W. Forest, Ontario Hydro : Could you give us some examples of

computer readouts? Do you take into account flow variations, process

changes, etc.?

B. C. Baird, Sr. : We do not consider those variables. We measure the

overall RMS signal level with a high frequency (120 KHz) acoustic

signal. We measure the signal level that exists above the 5 sigma

threshhold, which is a spike type signal. We do an envelope detection

of this signal and we look for the spectral lines that are associated

with the bearings in the machine. We have a little 21 line printer.

Included in the information on the printout is the date, time of the

day to the minute, and the transducer number. We have 10 quantized

levels for each variable. Initially we trend data for a good bearing

day run and quantize it in 6db increments. We are looking for gross

changes in this high frequency signal. Typically, from the inception

to the end, the signal will grow 100 to 1 . We have an alarm level set

12h
so that if some threshhold level is reached, we look at it. Built into

the system is the trend that is built up to this alarm level. The reason for this is to get trend data to more fully understand the

failure mechanism that is taking place. Hov; long can a man go before

he must shut down? Can he wait until a planned shutdown or should he

shut down right now? The only way we are going to determine this is

through a lot of operating experiences, a lot of failures, a lot of

collected data.

D. M. O'Dea, Exxon Research and Engineering Company : You have one process variable that you are measuring, that is machine speed. I am a little unclear as to why you are measuring it for variable speed

machines. Is it only because you measure the bearing frequencies as well as the acoustic energy?

B. C. Baird, -Sr. : Most machines vary only one percent. The band width

of ihe analyzer can be set wide enough to still give good sensitivity

and good defect detectibil i ty and still stay within that band width.

If the machine varies one percent or so you can still pick out that

spectral line. For a machine that varies over fifty percent because of

an operated change (one day it's operating at 100 RPMs, the next day at

200 RPMs), we set up a tachometer to measure that machine speed. This

information is fed into the computer which then calculates the actual

bearing frequencies of the spectral lines that it wants to look at. It

sets up the spectrum analyzer inside the system to look at just those

spectral lines associated with the ball pass frequencies. We feel this

is the earliest indication of a bearing defect. In all of our tests,

the earliest indication of any defect in that bearing, like a small

spall, starts with a spectral line starting to grow. The high

frequency envelope detects a spectral line perhaps months before the

bearing actually fails. ^ The second indication is an increase in

spikes. The third and final indication is that the RMS starts to grow.

Bearings of different manufacturers may have different frequencies due

to design. You may not be avjare of whose bearings are being monitored.

Therefore, you have to rely on spike information or RMS information.

There isn't as early a warning as we would like.

D. M. O'Dea : Are you saying that you may simplify the system in the

future if you find you really don't need to know the spectral line?

B. C. Baird, Sr. : You get the earliest warning from spectral lines.

On some curves that were shown there was an 8-day warning from pure

RMS. You introduce spikes and you get an earlier warning than that.

You introduce the spectral line and you get a still earlier warning.

P. L. Howard, SKF Industries : What is the logic for determining when

to change a bearing or gear?

125
R. James : Right now, we use either high frequency analysis or regular

RMS or, in some cases, a metric vibration meter. We will change a bearing if the meter reads 0.5 to 0.6 inch per second. That is the

limit on most of our process equipment. If it's up to 0.9 inch per

second, we shut down immediately.

P. L. Howard : How do you correlate between damage level and those

limits?

R. James : Those fires tell us.

'

C. Dean, Solar, International Harvester : You mentioned that you

monitor the anti -friction bearings periodically. At what intervals do

you monitor them?

B. C. Baird, Sr. : The computer is set up to look at a bearing for 10

seconds. It continuously moves from bearing to bearing every ten

seconds, so if there are 260 bearings, it will take 2600 seconds to

look at all of them. There is a statistical probabil ity that you will

obtain the correct data if you look at a bearing for 10 seconds. From

the first 10 second look, we set up our base line data and quantize the

base line measurements. If the second 10 second look agrees with the

first look, we go on to the next bearing. If it doesn't agree, we keep

on looking and quantizing and normalizing the data until we have looked

for up to 2 minutes- and 40 seconds, which we found is about as far as you have to go to get good statistical data. If there still is no agreement, we feel that the bearing condition has changed and this is

printed up. Typically for one unit with 370 points, you may get around

to the bearings every two or three hours. Sleeve bearings and cracks

are monitored continuously.

D. L. Dennis, Naval Weapons Center : How does management view funding

your effort at the present time and in the future?

R. James : Our management is extremely interested in predictive

maintenance. We consider the program that we are engaged in to be a 5-

year research and development program. We are in the second year now. The Baytown plant is the experimental guinea pig for the rest of the

circuit. We expect to know how good this approach is by the end of the

5-year program. We actually had two years of field tests before we got

into the computerized version. So we were able to convince our management, through problems they saw in the operation of the plant,

that predictive maintenance needed to be worked on.

D. R. Houser, The Ohio State University : Can you say anything about

your gear detection work?

126
/

R. James : This is one of the big values of acoustic emission testing.

Consider a one-to-one gear box on a rubber plant extruder. If we get a high signal, we don't know whether it is a gear, a shaft, or a bearing

unless we make a detailed analysis. We have been able to detect cracks

in shafting on this large one-to-one gear box as well as pick up

incipient bearing failures. We can actually tell by looking at the

acoustic signal whether the extruder is being operated correctly. It

is an operating guide.

127
PANEL DISCUSSION : Case Histories Applications

Panel Moderator : P. L. Howard, SKF Industries

Panel Members : D. B. Board, Boeing Vertol Company*

R. Eisenman, Endevco*

R. Hohenberg, Mechanical Technology, Inc.*

J. L. Frarey, Shaker Research Corporation

M. Hoobchaak, Naval Sea Systems Command

R. James, Exxon Chemical Company

*Panel members so identified delivered short presentations prior to the

panel discussion. These presentations are not included in the

Proceedings.

R. Eisenman : I think that any diagnostic program lends itself to

answering some very basic questions and I think there are three areas that should be considered. First, the user should determine what type

of problem he has - is he worried about gear contact problems, bearing

stability problems, plain old misalignment, flow problems. The second

point is to select a transducer that will provide the necessary

information for evaluation of the problems. The third logical point

would be to determine whether the user wants to develop his own inhouse

capabilities, or whether he just wants to monitor the signal for trend

diagnosis and call in somebody more specialized in diagnostics when he sees increasing trends.

P. L. Howard : Jack, would you like to lay out a nice hypothetical

program?

J. L. Frarey : I have to say the same thing I said earlier; that is, if

you want to rate a diagnostic system, the system has to tell you what

is wrong, what failure mode is involved, and the severity of the

problem. You have to tear the machine down as rapidly as possible and

immediately look at the component and determine whether the system told

the truth. We can't take a part out of an engine and let it sit around

for a month getting rusty and then try to make a decision as to what

the diagnostic system said. It's got to be done quickly, it's got to

identify the failure mode, and it's got to tell you the severity of the

problem, and I suspect anything other than that should be graded as a failure of the diagnostic system.

P. L. Howard : This points out one of the problems in trying to do

diagnostic work. There is an indication of a potential problem, but

you find that you are not the most important part of an evaluation

program. There are 17 other tests that have to be run and it won't be

possible to tear down the machine for three weeks. At that time, they

will tell you whether you were right. One other thing is that quite

often a diagnostic technique is preceded by a large marching band of

marketeers. Two points that marketeers always make, are (a) it's

128
simple, and (b) it can be evaluated by almost anyone who has a high

school education and no previous criminal record. The first job of the

diagnostician is to come through and say, "Well, yes that is almost

right, but we still have to take your machine apart." One of the most

intelligent approaches to finding out whether a diagnostic technique is

, going to pay off is the approach that Ralph James is taking. He has

already set aside a block of time. He is not bowing to what I am sure were initial marketing pressures to fully evaluate the system in two

weeks and write a final report in 48 hours thereafter. He is going to

take a long term look at it. What is the feeling of the panel on the

problem faced in diagnostic evaluation - that is, the diagnostician

would like to gather data forever so that his conclusion is firm and

final, the user quite often can't wait forever?

R. Hohenberg : The problems of the moment always seem to be the most

important ones and the most significant ones because they exact the

greatest limitations on our actions. However, they can be minimized

and we were all taught when we went to school that there was a way to

conduct an experiment. When an experiment is to be run, you must

define what it is you want to do, what the objective is, what

methodology is to be employed, how the physical laws that are understood and known will be invoked and played off against each other

to achieve the result, and also the kind of result that is to be

expected. Now that's simpleminded in the very complex situations that we have, but in many cases none of this is done. People rush into the

test area, they rush to slap the equipment on and they wait to see the

results. Then they wonder how it can be explained. The explanation in

the classical experiment is a selection of which of the anticipated

results were achieved rather than a searching of what really did happen

and I think that is one of the fundamental problems that we face today.

The experiment must be limited and focused on the population to which

you want it to apply.

P. L. Howard : Would any of the users like to comment on how you

overcome the impatience in your own management in order to give a diagnostic technique a fair evaluation.

R. James : Our present program is quite similar to what we had to go

through on gas engine diagnosis techniques. We had to convince

management that the maintenance costs on all of our gas engines were

too high. We had to ask for a period of time to prove that we could

bring the maintenance costs down. We did demonstrate that and got the

maintenance costs down in about a year and a half. It takes that long

to train the people and the people that use the equipment are the key

factors. We did prove it, and when we cut back on the monitoring work,

the maintenance costs went up. But it is a statistical type thing.

That's the only way you can prove it.

129
M. Hoobchaak : Our problem has been failures in hydraulic systems of

gun mounts. Down time has been 30 percent or higher in some cases. We are going to analyze the oil over a two year period. We are 8 months

into the program. We have been given the luxury of some time right

now.

P. L. Howard : I'm glad to hear that you really recognize that, with

the diagnostic manufacturers, time is a luxury. I would like Joe Kukel

to give us the benefit of his experience on AIDAPS and how he has tried

to overcome some of the diagnostic evaluation pitfalls that these

people have faced.

J. Kukel, Garrett Corporation : We are trying to follow the procedure

that Rudy Hohenberg mentioned. We are running experiments and

developing our technology level. I haven't come to the point of

application yet, that's the next step. You want to make sure the

technology level is firm.

P. L. Howard : Mr. Hess, would you like to tell us what pitfalls you

have encountered in the A7 program and how you have tried to avoid

pitfalls in determining whether the A7 diagnostics are successful and

how successful they are?

A. J. Hess, Naval Air Test Center : We had lots of pitfalls, of course,

and I. think there is a lot to be learned by some of the things that we

went through. As our evaluation program progressed, it seemed like our

basic definitions of what a valid and invalid diagnostic was, changed.

We had a Navy evaluation team on site gathering statistical data on maintenance lines, safety flight lines. It seems like they had one set

of definitions, program management people who were trying to market it

within the Navy had another set of definitions, all the contractors had

their own definitions. To really prove a system cost effective, you

have to develop the statistical data, and if you are using a bunch of

different definitions, the statistical data may not mean much. In any

diagnostic program, one of the first things that should be done is to

agree on a basic set of definitions.

We are trying to prove our system effective from the safety

applied standpoint. Since we are operating in a fleet environment, we

had a big problem with recordkeeping. The fleet had its own missions

to fly everyday - the pilots weren't very concerned about keeping

accurate records on our system, yet we needed their inputs. You have

the problem of a sophisticated condition monitoring system. During the

development phase the software is continually changing. It is a big

problem to document these changes so that you know at any point in time

exactly what software is being evaluated. We had to convince our program people that, while there were some major problems with the

system, software development was such that we were close to solving the

problems. To do that type of convincing, you really have to have a handle on the documentation of software.

150
Another major problem was deciding when the development effort

actually stops and the evaluation begins. Eventually you run out of

time and you have to stop the development - the evaluation starts then

and you ignore the statistical data that was generated during the

development effort and just pay attention to the evaluation.

P. L. Howard : Do you find that that is best done arbitrarily? Just

say, OK it's done?

A. J. Hess : You have to make an intelligent judgment.

D. M. O'Dea, Exxon Research and Engineering Company : I think all of us have fallen into pitfalls in setting up programs - starting out too

early in many cases or starting out with the wrong equipment. We all

have been called on to evaluate our equipment to see what we can do to

improve reliability and availability. We have to make these

evaluations and usually we have to decide just what is the basis for

determining whether a system is good or bad. Different techniques are applied. One famous technique is to pick something simple like

counting the number of pumps going into a shop before a program is

started. Then start the program and keep track of the number of pumps

going into the shop, and see how much of an improvement there is. That

has been very successful. One other approach has been to look at the

number of times there has been a failure and count how much down-time

has been spent on equipment in terms of days or lost product, then

start a program, see how many times you have either avoided down-time

or avoided the failure, or see how much faster you can come back on line with the new program. These are basically the evaluation tools we

use. What we find is that we have to stay simple. Ralph, you didn't

mention it, but I'm sure you are counting the fires.

R. James : Sure do.

P. L. Howard : One of the things diagnostic suppliers are continually

faced with is proving that there is a benefit from using the diagnostic

technique. It is usually in the form of a cost benefit. How do you go

about showing the cost effectiveness of a technique? I don't think

there is a diagnostic manufacturer here who wouldn't agree that

serendipity is one of the better ways of proving the cost effectiveness

of a system. Are there any other people who have planned cost

effectiveness tests for diagnostic equipment?

C. Dean, Solar, International Harvester : I can cite an example of how

it shouldn't be done. I entered into strictly a verbal agreement with

a manufacturer of diagnostic equipment to conduct some tests on some of our equipment. The first phase was going to cost our company say X number of dollars. The second phase, which was outlined at the time we began the program, was going to cost about lOX dollars which we were

prepared to spend at the time. However, at the end of the first phase, we really didn't get a report or any assurance that we had accomplished

what we had set out to do. I had no confidence that we could gain

131
anything from the second phase, so I terminated the program. I have

had many second thoughts since that time, because maybe I prematurely

shut off a program that was worthwhile to the company. However, I had

to make a judgment, and from the information that I had at that time, I just could not take the second step. My recommendation would be that

before a program is undertaken, the goals and pitfalls should be

clearly defined. The progress of the program should be thoroughly

reviewed from time to time to see if these goals are being met.

D. M. O'Dea : We have spent many hours and many thousands of dollars

trying to identify failures, and we have found two basic causes for

this loss of dollars. One of these is what could be considered infant

mortality, which is the failure of new machinery that's just been

installed. The other is the problems associated with a machine over

its lifetime - wear-out problems, or problems that come up as time goes

on. We have found that we can't separate the two causes completely.

We have been able to significantly reduce the infant mortality rate.

Lifetime problems on the whole are not that serious except where they

cause safety hazards or really influence production. Everything we

have started to do is based on a failure analysis. What we would like

to accomplish is to run our machines for the longest periods of time

without any internal inspections, without any overhauls. Before we

start a program, we have to identify what type of failure we are trying

to avoid. If there are existing engines that have been running, you

can look at the history of failure in those engines and then start a program of evaluation on the basis of that history. If there is a new product or a totally new design, what you have to do is a failure

analysis on the basis of the histories of components you are putting

into that new design before you really begin to set up a diagnostic

program.

R. James : I should have mentioned the importance of failure analysis.

Until we began to do a detailed failure analysis of every failure, we weren't making much headway. At that time everything was a maintenance

problem. But since we have been doing failure analysis, we have found

that maintenance is only one leg of a tripod. There are operator

problems and we have been able to correct many failures by training the

operators to operate the equipment properly. The third leg of the

tripod is design. Some of the failures are due to faulty design. We

try to indicate the basic cause of failure in our failure analyses.

A. Jaudet, Electricite de France : What Dennis O^Dea said is exactly the

kind of procedure we have followed in Electricite de France. We tried

to determine what kind of mechanical failures could occur in turbines.

From 10 years experience in running 250 megawatt machines, we have

established that most failures come from blade fractures or from high

pressure inlet valves. So we have established a way to diagnose such

152
failures. Now personnel that work on such power plants ask me not only

for diagnosis but for prognosis. They want to know because they have

only a certain period of time each year to do maintenance of their

turbines.

P. L. Howard : Would each panelist give us a short summary?

D. B. Board : First, before you start a program, you should clearly

establish what your objectives are - are you trying to diagnose or are you trying to prognose? Secondly, you should establish ahead of time

whether you are going to test the hypothesis, or if you are going to

demonstrate the feasibility of application for whatever you are going

to do. Thirdly, whatever you do, the person who plans the experiment

or the program and is responsible for carrying it out should not be the same person who evaluates the results and draws the conclusions. And

finally, I think it is most important that any program should involve

not just one perspective. For instance, in the aircraft diagnostics

field, you have got to have equal involvement of the airframe or engine

manufacturer, the diagnostic hardware manufacturer, and the using

organization. You absolutely must have those different perspectives or your program really isn't a program.

R. Eisenman : It is extremely important in any diagnostic program that

there be adequate feedback from the user. This is a very difficult

channel of communication, because often the problem that you have

diagnosed is discovered by a millwright on a graveyard shift and he never tells anybody about it. So again I can't overstate the

importance of feedback.

P. L. Howard : It is a two way street. If they want a good evaluation

in the user house, they have to do some work.

J. L. Frarey : I liked what Bob Eisenman said during his talk - that

you have got to combine diagnostic systems to get the total result. I happen to be an advocate of high frequency vibration. Frankly in our day-to-day troubleshooting in the petro-chemical and utility

industries, we probably make about 80 percent of our decisions based on low frequency data from proximity probes-low frequency vibrations.

R. Hohenberg : My goals are to find desirable applications for people

who have a significant problem where the failure mechanisms are understood. An approach can then be found with a simple methodology

which looks at the failure mechanism rather than at the traditional

operating parameters to, in a simple manner, define and prognosticate

the situation. And the approach I firmly believe in is at the sensing

end. It should be kept firmly in mind that the voltage coming out of a transducer is an observable which consists of useful signal and noise.

155
If you can find or develop a transducer that has a higher

signal-to-noise ratio, the extent of analysis that is made subsequently

is much reduced.

M. Hoobchaak : I agree with Rudy on keeping it simple. The simpler you

can make your system, the more likely it is that something will be done

if there is a failure.

R. James : That reminds me of our "KISS" program. It means "keep it

simple stupid," and we have had good results from trying to do that.

Our problem is that we don't start necessarily with the best equipment.

We start with initial cost considerations. I think we should look at

the long range cost of this equipment and look at the minor details

such as the bearings. If we did that, we wouldn't waste our time on things that should have been prevented in the design stage. Now in

order to do that you have got to take the system approach and have an early input from the maintenance engineer, from the design engineer,

the process engineer, who sometimes goes his merry way without any

consideration for the equipment.
SESSION III

ON GOING

PROGRAMS

Chairman: H. R. Hegner

General American

Transportation Corporation

GAS TURBINE ENGINE DIAGNOSTIC TEST RESULTS

UTILIZING A THERMODYNAMIC ANALYSIS TECHNIQUE

BY .

ROBERT L. STENBERG

'

U. S. Army Aviation System s Command, St. Louis, Missouri 63166

1.0 Introduction :

The US Army has a requirement to evaluate automatic Inspection

diagnostic and prognostic systems (AIDAPS) for use on future aircraft.

An effective engine health monitoring technique will be an important

part of the total aircraft diagnostic system. The T53 engine approach

currently being taken on the UH-IH prototype AIDAPS program is to collect

data on pertinent measurable parameters while the engine is operating

nominally and while known degraded parts have been Implanted. The above

two groups of data are then compared and differences noted for the proper

fault Isolation message. By Implanting known degraded parts, much more pertinent data can be generated and fault isolation software accomplished

during a given period of time. The purpose of this paper is to review

and analyze the results of the thermodynamic analysis on selected AVCOLycoming test cell data.

2.0 Thermodynamic Analysis Concept :

^

A flow chart showing the various steps in the thermodynamic process

is given in figure 1. Gas path logic is based on the principle that

parameter measurements are uniquely related to component physical condition (i.e. deterioration) since parameter and performance measurements

are uniquely related and performance measurements and physical deterioration are uniquely related.

Engine performance monitoring for the purpose of tracking engine

health normally consists of three basic steps: (1) establishment of

baseline performance, (2) comparison of current performance with baseline performance, and (3) Interpretation of performance deviations.

However, particular techniques can differ from one another in terms of

measured parameters, method of computation of performance indices and

method of interpretation of performance deviations.

In the AIDAPS approach variations in the performance indices are obtained by the influence coefficient method^. In implementation form,

engine-installed sensors measure certain gas path parameters (temperatures, pressures, etc). A test of the data is then made to determine

that it satisfies thermodynamic stability criteria.

Extensive background in the development of turbine engine controls

157
has demonstrated that the transient operation of an engine can significantly affect the diagnostic results. For instance, the occurrence

high steady-state temperature would be indicative of a potential engine

degradation but that same vibration which occurs during a transient

would only be indicative of the energy available to accelerate the engine.

A method of minimizing the effect of transient performance was needed.

The conditions that have been set up for steady-state involve basically

two requirements; sufficient high power and sufficiently steady engine

operation. Power is tested in terms of Nj^ , and a minimum N of 85% is

required. It turns out that in terms of the relative magnitudes of the

changes, sequence of occurrence, duration, and settling rates, SHP and

EGT are the best transient indications. The rate limits on these parameters are 0.2HP/sec and 0.2°F/sec, respectively 2, The rate-of-change

calculation and limits provide a settling typically between 10 seconds

and 30 seconds, depending on the magnitude of the transient.

During steady-state, uncorrected parameter data are suiraned in 10-

second segments. If steady-state criteria are met throughout a steadystate segment, the segment sums are added to interval sums. At the end

of a steady-state interval, the interval sums are averaged, producing

averaged values of the uncorrected parameters. If the steady-state intervals persist for more than 18 segments, the summing is terminated,

averages calculated, and steady-state criteria reset to ignore the rest

of that steady-state interval. Thus, a steady-state interval sample

consists of uncorrected parameters averaged over 10 to 180 observations.

Following calculation of the averages, corrected parameter

deviations from baseline are computed and these are compared to sensor

credibility limits and engine degradation limits. Exceedance of a limit

triggers an appropriate indication to signal the need (to maintenance)

for diagnostic processing. These operations are performed for each

steady-state interval data set.

Each steady-state interval data set (parameter averages) is stored.

The process of looking for steady-state, forming steady-state interval

data sets, testing the data set parameters, and storing the data sets

is continuous. The philosophy is to accept as much good data as possible, since it has been estimated that this will amount to only 5 to 20

steady-state interval data sets per flight. Present storage allocation

is such that at least 5 flights worth of data can be collected before

routine processing for refined health checks and prognosis will be

required.

Additionally, if no steady-state segments are encountered within a 10-minute period during engine operations, an unaveraged set of data

together with steady-state counter data are recorded to determine the cause of the lack of steady-state. Ground logic will isolate the cause

to either a particular instrumentation fault or to an engine instability.

158
Having satisfied the above mentioned steady-state conditions the

deviation of the measured parameters from that of the normal engine , condition are calculated. (In corrected form)

The primary measurable parameters are:

Tl Compressor Inlet Temperature

Pi Compressor Inlet Pressure

T3 Compressor Discharge Temperature

Compressor Discharge Pressure

Nl Gas Producer Spool Speed

N2 Power Turbine Spool Speed

Wf Fuel Flow

~

Q Torque Pressure

Exhaust Gas Temperature

A second calculation, using the engine thermodynamic relationship

is then used to determine performance changes of the engine from norma

by means of influence coefficients. The AIDAPS coefficients are based

on a differential equation model of the engine as shown in figure 2.

Model sets are stored for P3 = 70, 80, 90 and 100 psi.

In applying the model, a coefficient set is formed for the particular measured value of P-^ by interpolation between model sets. The

following independent parameters are then calculated:

T5 Turbine Inlet Temperature

W2 Airflow

Compressor Efficiency

Gas Producer Turbine Nozzle Area

Vg Gas Producer Turbine Efficiency

Power Turbine Efficiency

The above parameters have direct diagnostic meaning. T^ is a general health parameter, but also reflects on hot section condition

and degradation prone operation. W2 and Vc reflect compressor condition.

159
A5, and77pt reflect the conditions of the 1st stage turbine nozzle

area, gas producer turbine efficiency and power turbine efficiency, re- spectively. The tests on T5 and W2 will also consider VIGV operation.

A3 will be used as an indicator only with removal threshold significance

placed on the effect of A3 variations on T3 and "^g.

Limits on the performance changes as established from implant tests

using physically deteriorated parts (implants) or maladjustments are usee in a comparison manner to determine if the engine has exceeded acceptable limits. Prognosis is to be established by time-trending and projection to the removal limit. Current diagnostic limits are shown in

figure 3.

3.0 Results :

Major test results that will be discussed are compressor fouling

and erosion, fuel nozzle clogging and gas turbine temperature erosion ^^5. These problems are considered as major problems of the T53 engine.

COMPRESSOR FOULING TEST

The results of a compressor fouling test are shown in figure 4; the

compressor was progressively fouled by spraying oil-wood ash and oil

water into the compressor inlet. The top graph tracks the drop in

compressor efficiency and airflow (a three-point moving average was

used). The bottom bar graph shows the average of the computed performance parameter changes (model results). At that low point, AVCOLycoming test engineers believe that it was representative of the degree

of fouling that can be encountered in an operational environment.

Following the calibration runs, the engine was given a double cleaning

that appeared to restore its former performance level.

COMPRESSOR EROSION TEST

The results of an eroded compressor test are shown in figure 5.

This test was a combination compressor rotor (implant //AID 132) and com- pressor housing (implant //AID 133) .

All of the components were obtained from an engine which had been

returned to depot because of a surge condition. In the case of the

compressor rotor, erosion wears away the blade airfoil resulting in re- duced pumping efficiency. AID 132 has minimum erosion damage that is

within overhaullimits . AID 133 also has minimum, erosion damage that is

within overhaul limits. In the case of the axial compressor housing,

erosion wears away the vane airfoil (axial compressor stator vanes)

and increases tip clearance resulting in reduced pumping efficiency.

In the case of the impeller housing, erosion wears away material resulting in increased clearance between the housing and the impeller with a resulting loss in pumping efficiency.
The housing impeller clearance is considered critical because the

majority of compressor work is performed in the centrifugal stage. For

AID 133 the impeller housing shows severe wear at the entrance and exit.

In this test the drop in compressor efficiency tended toward larger

magnitudes with engine power level (the minimum change was about -2 percent; the maximum -3 percent (shown)). The results indicate that the

change in efficiency can be attributed almost entirely to the compressor

rotor, while the compressor housing erosion is responsible for about 1/2

of the change in pumping capacity.

FUEL NOZZLE TEST

Fuel nozzle clogging and erosion and consequent hot spots have been

identified as the only significant combustion section problems for the

T53 engine.

Figure 6 shows the results of successively clogging three nozzles;

No. 11; Nos. 11 and 10; and Nos . 11, 10, 9. All of these results were

clearly detectable.

The unshaded bars show the normal temperature distribution while the

shaded bars show the deviations for the test case. In each case the

temperature distribution rotates before reaching the thermocouples so that the minimum temperatures are detected by thermocouples 1 and 2 rather than 11 and 12. These results show that a clogged nozzle, or cold spot can definitely be identified by EGT spread measurement on the

T53 engine. However, it appears doubtful whether hot spots due to

eroded, high flow fuel nozzles can be identified. The problem is com- pounded by helicopter operation (power turbine rpm is held essentially

constant). The result is that exhaust gas in the tailpipe, has a varying degree of swirl dependent on power level. Since there is a certain

degree of natural temperature distribution in the exhaust gas, the swirl

causes a variation in the temperature profile measured by the EGT

thermocouples

BURNED 1ST STAGE GAS PRODUCER ROTOR TEST

Deterioration of the 1st stage gas producer rotor begins with a general deterioration of the 701 coating along the leading and trailing

edge of the blades. The rate of progression is slow until the combined

effects of the coating and sulfidatlon of the parent material progresses

at a rapid rate, resulting in material loss. The change in geometry of

the blades (e.g. increased tip clearances) results in decreased turbine

efficiency and an accompanying general increase in turbine inlet

temperature. The increased temperature level can be expected to increase

the degradation rate and initiate or promote the deterioration of other

turbine section components. The temperature increase also raises the

operating line of the compressor, thereby reducing surge margin.

1^1
Implant AID 153 is in the final stages of sulfidation. The vane contour shows loss of material due to erosion and burning. The vane tips

still have some of the original contour remaining. Both the leading and

trailing edge tips have been lost.

Analysis results are shown in figure 7. The implant has caused a severe loss in efficiency and a corresponding, essentially one to one,

increase in turbine inlet temperature. The decrease in airflow and in- crease in compressor efficiency are so-called cycle rebalancing effects;

that is, the increase in turbine inlet temperature has caused the operating point of the compressor to move towards decreased airflow and increased efficiency. While these latter changes are substantial, they are small in comparison to the change in turbine efficiency.

This implant is considered representative of degradation significant

ly above the threshold that AIDAPS is intended to detect.

4.0 Conclusions :

The last year of test cell work has conclusively shown that

thermodynamic analysis can pinpoint major gas turbine engine degradation

modes. Flight testing has also indicated that similar defects can be

detected by an on-board prototype system. Hov/ever, further areas of

work have been identified.

The variability of the measured gas-path parameters has to be kept

within an acceptable band (+ 1/2 percent). This has resulted in some instrumentation changes (new compressor inlet pressure (CIP) and torque sensor transducers, and a relocated compressor discharge pressure (CDP) sensor installation)

Two prognostic tests, temperature erosion (burning) and sand and

dust erosion were conducted in the test cell. These tests both demonstrat

ed the relatively slow rate of degradation, especially of the GP section.

Realizing that in practical day-to-day engine monitoring, sensor malfunctions can occur that do not go off the scale, a sensor malfunction and quality assessment of the diagnostic results must be fully

developed and tested.

The development of a bleed/leakage model to provide an auxiliary

capability for identifying increased bleed usage (associated with a malfunction of a bleed using device or significant external leakage flow

occuring prior to the turbine section. Use of the bleed model, however,

is complicated by its high sensitivity. If this problem can be solved

this model would supplement the basic model in the proper interpretation

of turbine section deterioration.

li+2
REFERENCES

1. UH-IH Automatic Inspection Diagnostic and Prognostic System (AIDAPS)

Test Bed Program, Hamilton Standard Division of United Aircraft

Corporation, USAAVSCOM Technical Report 72-18 August 1972

2. Second Interim Technical Report, AiResearch Manufacturing Company of

California, United States Army Aviation Systems Command, Contract

No. DAAJ01-73-C-0874(P3L) November 8, 1974.

3. Third Interim Technical Report, AiResearch Manufacturing Company of

California, United States Army Aviation Systems Command, Contract

No. DAAJ01-73-C-0874(P6C) April 1, 1975

li+5
MEASUREMENTS

i

SAMPLE DATA zn STABILIZED OPERATION

I YES

NO

COMPUTE CORRECTED VARIABLES

N, P3 T3 EGT Wf SHP

THERMODYNAMIC

MODEL COEFFICIENTS

BASELINES AVAILABLE NO

BASELINE FORMATION

YES

COMPUTE VARIATIONS OF CORRECTED

VARIABLES FROM THEIR BASELINES apI, atI.

VARIATIONS WITHIN CREDIBILITY LIMITS NO

SENSOR MALFUNCTION

DIAGNOSTICS

YES

MAINTENANCE ACTION MESSAGE

COMPUTE VARIATION OF COMPONENT PERFORMANCE COEFFICIENTS

A'»?c AW2 AT5 AA5 A'^g Vc W2 T5 A 5 Vq (

AA7 A^p, / AWl \

A7 Vp, / Wl /

YES VARIATIONS WITHIN LIMITS NO

DIAGNOSTIC ROUTINE

TREND ROUTINE MAINTENANCE ACTION MESSAGE

Figure 1.

Ikk
Ap, At^/^ Aw^/,, Ashp/shp Aegt/egt

^/P^ ^/T^ f/W^

.000 .ho8 -.129 .126 .886

^^2/^^ .000 .1^0 1.25^ -.2U2 -1.705

A'^c/^ .7^^ -2.278 .000 ^ .000 .000

-1.090 .576 1.290 -.196 -1.^77

^^8^ --936 1.900 .252 .175 -1.171

A^pt/^, + .000 -.128 -i.iUo .5535 .9^5

Example: AT AT A'J

^.^^ _2

5

= .408

5

- .129 -jjf

* .126 + .o36

^

Figure 2. Coefficient Matrix Set, N.^ model (P^= 80)

T5, Turbine inlet temp: + 5/0 W2 , Airflow (or comp pumping capacity): - 5^

17 c, Compressor efficiency: - 3'^ A5, Gas producer turbine nozzle area: + h'^o

"qg, Gas producer turbine eff.: - 5^"

T7pt, Power turbine eff.: - 5^

VIGV full open pt: 9^+ + 1.5fo N

Figure 3. Diagnostic Limits

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DISCUSSION

C. R. GarbeLt, Shell Development Company : What kind of meter did you

use to measure torque?

R. L. Stenberg : It was a torque pressure sensor. What we identified

was that the current torque pressure sensor that is on the UH-IH

aircraft may not have the repeatability we need for this system, so we

do have an alternate sensor on the aircraft. We are evaluating both sensors in paral lei . /

0. E, Compton, Northrop Corporation, Aircraft Division : What type of

correlation did you obtain between the air/ fuel flow ratio and the

measured temperature analysis?

R. L. Stenberg : We had a very close correlation between the air/fuel

results and the model results that we obtained.

0. E. Compton : Is that how you define the clogging of your nozzles? ;

R. L. Stenberg : Yes, "chat was one of the indications.

150
PROBLEM AREAS ENCOUNTERED IN ESTABLISHING A DATA BASELINE AND

EVALUATING THE A-7E INFLIGHT ENGINE CONDITION MONITORING SYSTEM

Andrew James Hess

Naval Air Test Center

Patuxent River, Maryland 20670

Various Engine Health Monitoring (EHM )systems have been formulated and

tested as operating prototypes with varying degrees of success. The true

worth of any such EHM system can only be determined after the prototype

system has been developed to the point where an expanded data baseline

can be employed and a significant number of pre-production systems can

be deployed in an operational environment.

The expanded data baseline is required to define the boundaries of the

distinctive variations or signatures of individual engines over the

general population of all engines to be monitored. That is, the expanded

data baseline is required to "fine tune" the software which was developed

and demonstrated with the prototype EHM system. A significant number of

pre-production EHM systems deployed in an operational environment is

required to generate the statistical data necessary to prove the costeffectiveness of the system. This statistical data is required not only

to demonstrate system effectiveness but to generate essential information

on the system reliability and maintainability.

SYSTEM DESCRIPTION

A system for engine health monitoring to detect actual and impending

engine and component malfunctions and to define necessary corrective

maintenance actions has been designated as lECMS (Inflight Engine Condition Monitoring System) by the U. S. Navy. The lECMS has been developed

for the TF41-A-2 engine installed in the A-7E aircraft. The engine manufacturer, Detroit Diesel Allison (DDA) Division of General Motors was assigned prime responsibility for system development and software generation while Teledyne was chosen to supply the system avionics.

The basic objectives of the lECMS were defined as:

-To detect actual and impending engine flight safety malfunctions.

-To define engine health status and Indicate corrective maintenance

actions.

To achieve these basic objectives, the following system design goals were

originally defined:

151
-To reduce engine caused aircraft losses by 50%.

-To achieve a minimum of 90% data recoverability

-To achieve a minimum level of 90% valid engine diagnostics.

-To handle current and anticipated engine problems.

The lECMS consists of four major elements as follows:

-Engine mounted sensors, transducers and subsidiary hardware for

measurement of 51 engine and airframe parameters.

-Aircraft mounted Engine Analyzer Unit (EAU) for data acquisition,

signal conditioning, data management (logic) and data output of the

engine and airframe parameters.

-Aircraft mounted Tape Magazine Unit (TMU) for mass storage of pertinent airborne data.

-Ground based Ground Station (GS) for complete analysis, presentation and storage of airborne collected data.

The lECMS sensor package consists of a total of twenty-one transducers

that have been installed on the engine for the measurement of temperatures, pressures and flows necessary for diagnosing engine operation.

Twenty-four additional sensors relating to switch positions, amperage,

voltage, etc. are monitored by way of modifications made to existing

engine components and/or wiring. Eleven sensors are extracted from airframe associated components. Appendix 1 gives a listing o f lEOls parameters .

The EAU continuously receives and monitors signals from engine and airframe parameters. These signals are conditioned, multiplexed and con- verted to digital format within a signal acquisition section of the EAU.

A data management section contains the airborne logic program in an addressable 8K core memory, advanced digital computer which receives

digital data inputs at a specified sampling rate. A special signal

conditioner is provided to convert certain unusual signals (vibration,

fuel flow, etc.) to a type that can be easily accommodated by conversion

circuits. Self test capability is incorporated via software programming

to continuously monitor memory and input/output functioning. Data is

outputted to the TMU as directed by the program logic flow. The EAU

measures 7.5" x 6.25" x 20.6" long and weighs 32 pounds. The front face

of the unit contains twenty engine limit exceedance status flag indicators, thumbwheels for entering documentary data, "self test" pushbutton

and lamp indicator and an electrical test/input connector for external

readout/entry functions.

The TMU is designed to store two parallel channels of digital information, with a data capacity of 2.8 x 10 bits on an endless loop magnetic

tape. A minimum of four flights can normally be stored on this 2.7

pound unit. If required a minimum of 44 minutes of continuous recording

can be accomplished before overlap occurs.

The GS accomplishes the final processing and evaluation of the airborne

152
data recorded on the TMU. The central processing facility of the GS is a Digital Equipment Corporation Model PDF 11/15 computer unit featuring 32K

of addressable core memory. All programs required for data analysis, presentation or storage are located on a 1.2 M word mass storage disc drive

unit. A reel type magnetic tape drive system is used for flight history,

data transfer and program update purposes. The additional elements that

make up the GS include a computer command console, line printer unit,

high speed reader /punch and tape interface unit.

The lECMS operational functions commence with the airborne EAU. The EAU

cotitinuously monitors all sensor parameters, determines the present mode

of operation (start, take-off, etc.) and decides on the need for recording data on the TMU. Recorded data is directed if any of the following

conditions exist:

-Start/Take-off.

-Engine exceedance. - -Engine transients.

-Engine power loss or fluctuation.

-Pre-defined conditional modes (ground idle, stable, flight idle,

end-of-f light)

After every flight, visual inspection of the Flag Display section determines if immediate analysis of the data is required. If no exceedance

flags were tripped and no pilot "gripes" registered, the engine is con- sidered in a "go" status for the next flight. After a series of no ex- ceedance flag flights, data is generally analyzed at the end of daily

operations

Whenever data analysis is required, the TMU is removed from the aircraft

and played back by the GS . Data analysis is performed within the GS by

a serial investigation of the airborne collected data. Logic flow is

determined by record mode identification and/or "reason for record"

indicators appropriately tasked by the EAU. Abnormal operation engine

problems or discrepancies found by the GS logic are documented by "hard

copy" message on the line printer. This engine health diagnostic message

will be accompanied by the assciciated corrective maintenance action re- quirements. Presently, 230 diagnostic messages are available in the

software program. Preceding data analysis, the GS is programmed to automatically search and output the engineering data relating to the diagnostic message to be used for further documentation and/or to aid the operator in verification of the message.

The following additional programs are available to the GS operator for

various types of data presentations:

-Flight profile.

-Engineering calculation trace.

-Detailed vibration program.

155
-Plot routine (9 parameters vs. time).

-Engineering data presentation.

BACKGROUND 5' .

Interest in an EHM system for the A-7 aircraft began in 1971 when an inflight oil quality indicator called the Environment One (EV-1) unit was

flight tested at the Naval Air Test Center (NATC) . The need for a more

comprehensive engine health monitoring system was recognized as the EV-1

unit showed potential as a useful indicator of inflight oil quality.

The EV-1 engine health monitoring program expanded in scope first becoming NADS (Naval Airborne Data System) and then lECMS. A combination

A-7 lECMS feasibility study and prototype "fly off" was accomplished at

NATC with 'two teams of manufacturers. Pratt and Whitney Aircraft and

Hamilton Standard developed a prototype lECMS for the A-7B aircraft

while DDA and Teledyne developed the A-7E prototype lECMS . Late in 1972,

the A-7E lECMS was chosen to continue development during a ten aircraft

baseline/pre-production evaluation in two operation squadrons based at

NAS Lemoore. This evaluation culminated with the lECMS equipped aircraft

deploying on the USS Enterprise in the fall of 1974.

To date the A-7E lECMS has demonstrated operational capability in both a shore and aircraft carrier based environment with approximately 5000

flight hours in over 3000 sorties. Evaluation reports indicate that the

lECMS hardware has demonstrated good reliability for a pre-production

system. The associated diagnostic software routines have been developed

to the point where they have demonstrated considerable potential as a maintenance tool which can automatically define actual and impending

engine discrepancies.

A significant number of lECMS diagnostic "finds" have been recorded and

validated. The majority of these have been engine maintenance action

indications but a few could be construed as safety-of-f light items.

lECMS hardware has passed all military specification bench testing. The

lECMS software has demonstrated the ability to recognize individual

engine vibration and performance baseline signatures. lECMS generated

flight history data has been used by the DDA engine Component Improvement

Program (CIP) for mission analysis investigations and to develop long

range trending capabilities.

THE EXPANDED DATA BASELINE

An expanded data baseline program is a necessary step in developing an EHM system from a single prototype system to a system capable of accu- rately diagnosing the health of any engine within the general population

of all engines. The main reason for conducting the expanded data baseline program is that every engine within the general engine population

is an individual and operates slightly different than the next engine.

Any single sample prototype development effort would, by necessity, tend
to "tailor" the EHM system to that single sample engine. An expanded

data baseline program is necessary to overcome this tendency to "tailor"

the system development to a singular sample engine and to develop an EHM

system which is useful for all engines in a general population.

The A-7E lECMS experienced this single sample "tailoring" tendency during

the initial prototype development. The need for an expanded sample data

baseline program was recognized and implemented with the 10 aircraft preproduction lECMS evaluation. Several of the unique problems involved

with establishing the expanded data base program will be presented in the

following discussion.

The major difficulty the A-7E lECMS effort experienced during the baseline program was that the problems involved with going from one to ten

aircraft were underestimated. Thus, the expanded data baseline program

was planned to be conducted concurrently with the actual pre-production

evaluation. This was an impracticable situation, where the pre-production evaluation could not actually begin until the data baseline effort

developed the lECMS to a satisfactory level of operation. Ideally, the

data baseline effort should be well along into providing a developed

system before the pre-production evaluation begins.

Another major problem experienced by the A-7E lECMS was that some new hardware was introduced into the data baseline systems without having

been first tried on the prototype system. Of particular trouble to the

lECMS was a change from velocity type to acceleration type vibration

sensors. This hardware switch caused large amounts of development time

lost because of the necessity to troubleshoot ten systems instead of just

a single prototype system. Thus, in the development of any EHM system,

hardware changes which are not first tested on the prototype system must

be very carefully planned.

Operating a large sample of development systems in a fleet type environment for an expanded data baseline causes difficulties. The fleet operators have operational commitments and specified missions to fulfill.

These operational missions are not always in keeping with the types of

missions necessary for an ideal data baseline program. The operational

missions always have priority and often, the data baseline program and

system development effort lose control over the aircraft. This makes

for a very long development phase as was the case experienced by the A-7E

lECMS program.

The process of going from a single prototype system to an expanded sample

data baseline program involves many inherent "shake down" problems.

These problems would be common to the development of any avionics system

but are especially bothersome in the case of an EHM system. This is be- cause of the initial difficulty in determining whether many unexpected

system problems were hardware or software generated.

There is again the problem of "tailoring" the EHM system to the prototype

155
situation. Operational pilots in a fleet environment, operated the aircraft and engines very differently than the test pilots who flew the p'rototype system. The limLts of these operational differences had to be defined at the beginning of the data baseline evaluation. This was the

first problem the A-7E lECMS experienced when initially introduced into

a fleet type environment.

The development or "fine tuning" of the EHM system software is the major

purpose of the expanded data baseline program. This in itself, is a major problem area of a continuing duration. Along with this major con- cern is the sheer logistics of continuously changing and updating the

software programs for a large number of aircraft. During software development, decisions have to be made as to which engines and aircraft

are most representative of the general population. Additionally, all

development efforts must be faithfully recorded for both evaluation and

documentation purposes. Similarly, the problem of documenting all software changes during this development phase is a large task.

The Pre-Production Evaluation

The whole process of justifying the effectiveness of an EHM system be- comes a statistical data gathering exercise. All diagnostic indications

have to be tracked, documented, and verified as either valid or invalid.

This becomes a very tedious but necessary bookkeeping task. Any safetyof-flight diagnostic "finds" have to be well substantiated and publicized

for these "finds" will give the greatest credence to the general acceptance of an EHM system. Maintenance man-hours saved is one of the hardest items to accurately document but must be carefully recorded. An

attempt should also be made to show savings in the overall engine logistics support effort and to define possible impacts on any engine development or component improvement program. A successfully implemented

EHM system should influence all of the above-mentioned areas.

A well planned and thoroughly executed pre-production evaluation can generate the statistical data necessary to prove the EHM system effective

in all areas of concern. The uncertainity of the conclusions about the

particular EHM system decreases as the accumulation of accurate statistical data on its performance increases. The A-7E pre-production lECMS

evaluation tried to generate the statistical data necessary to decrease

any inherent uncertainties and prove the lECMS effective in the operational environment.

In April 1973, the Naval Aviation Integrated Logistic Support Center

(NAILSC) was tasked to monitor and evaluate the application of the lECMS

for the maintenance of the A-7E aircraft. The NAILSC effort, in con- junction with the monitoring of the technical development of the lECMS

by the NATC, encompassed the pre-production evaluation.

While generating statistical data on the lECMS performance during the course of the evaluation, NAILSC was tasked to monitor and evaluate fleet

156 I
usage of these systems with particular attention to the following:

-Identification of those lECMS required maintenance actions which

would have resulted in safety-of-f light situations if not detected.

-The validity of maintenance actions indicated by lECMS

-The in-service reliability of lECMS

-The comparison of maintenance performed on lECMS equipped and nonlECMS equipped engines.

-Operation availability of lECMS equipped engines and aircraft.

-The logistics support requirements for lECMS and lECMS equipped

engines

In order to perform the pre-production evaluation, a detailed test plan was written. The test plan stipulated the precise requirements of all

activities and persons involved in the evaluation. This test plan had

to be agreed to and approved by all concerned persons involved with the

lECMS program before the evaluation could commence.

In spite of the meticulous preparation and planning, certain problem

areas emerged during the course of the A-7E pre-production lECMS evaluation. These problem areas seem to be unique to the evaluations of any

inflight EHM system. These unique problem areas are presented and com- mented upon in the subsequent discussion.

Probably the most difficult milestone to determine in any pre-production

evaluation is that point in time when the system development effort stops

and the actual evaluation begins. Statistical data, gathered during the

system development phase, could show poor system performance because of

major unsolved development problems. Unpredicted hardware and software

problems inherently occur during any system development effort and would

necessarily bias the results of a premature evaluation. The A-7E lECMS

program experienced exactly this phenomenon.

The pre-production evaluation took several "false starts" which were

"called back" because of yet unsolved hardware and software problems.

These hardware and software problems were causing too great a negative

bias on the statistical results to perform an accurate evaluation. This

problem is magnified by the fact that for a sophisticated EHM system,

the software development is an ever continuing effort.

A problem which must be faced at the commencement of the evaluation is

the definition of a valid diagnostic "find". This definition of a valid

"find" must be agreed to from the program onset by all persons concerned

with not only the evaluation but the whole program. The inherent tendency to change the basic definition of a valid diagnostic during the course of the evaluation could cause great inaccuracies in the statistical data. This confusion occurred during the A-7E lECMS program. The

situation developed where every evaluator plus the system manufacturer

and fleet operators seemed to have a different definition of a valid

157
diagnostic "find" by half way through" the evaluation. The same rule for

a single and continuous definition of the valid diagnostic "find" holds

true for the definition of an Invalid diagnostic.

As with the valid diagnostic "find", an exact definition of what is a safety-of-f light item should be stated from the beginning of the evaluation. Again, all persons involved should concur with this definition

and a working list of safety-of-f light items should be developed. This

problem also occurred with the A-7E lECMS evaluation. As engine discrepancies were discovered by the lECMS , there was great disagreement on which "finds" could be considered as safety-of-f light items.

The subject of safety-of-f light brings up the topic of operator confidence level. A pre-production EHM system will not and should not have

a total operator confidence level. As the system develops and proves

itself, the confidence level will increase. A major problem area develops when the EHM system has a cockpit warning indicator. The question

arises, should the pilot heed a system cockpit warning of a safety-offlight problem and abort an assigned mission or should the pilot consider

the warning just a false indication of a yet to be completely developed

system? This dilemma of operator confidence level is most prevalent to

a lesser degree when involving inflight indications but also is present

to a lesser degree when involving ground maintenance diagnostic indica- . tions. The A-7E lECMS evaluation addressed this problem of Operator

confidence level by following the doctrine of always believing the system

unless there are obvious contradictions to the system indications

present.

Validating diagnostic finds create another major problem area. Every

system diagnostic indication must be verified and validated by the performance of a resulting maintenance action. This becomes a significant

bookkeeping exercise for both the evaluation personnel and the operational maintenance department. Special records must be kept on every

engine discrepancy indicated by the system until the diagnostic is verified either valid or invalid. This problem becomes especially large

when the diagnosed engine component must be sent to a distant overhaul

facility for verification. A detailed documentation plan that addresses

diagnostic verification should be implemented well before the actual

evaluation begins.

The documentation problem also extends to the EHM system software development. The software programs will continually change as the EHM

system is developed. Updated documentation of the total system software programs should be supplied to the evaluating activity throughout

the evaluation. The current software documentation will greatly aid in

determining the total system integrity as development problems are addressed and solved.

The EHM system development effort and data baseline expansion program

158
must necessarily be conducted by the manufacturer's engineering personnel. This was the case with the A-7E lECMS program. The system manufacturer personnel also operated and maintained the lECMS during the

pre-production evaluation. This situation caused the A-7E lECMS preproduction evaluation to generate incomplete statistical data on system

maintainability and reliability as well as on required operator skill

level necessary to effectively use the system.

The evaluation should be conducted with user personnel operating and

maintaining the total EHM system so that a positive determination can be

made of system performance under actual operational conditions. After

the evaluation begins, the manufacturer personnel should be on site only

for diagnostic assistance or operator consultation. All contractor as- sistance must be documented so that additional personnel training can be initiated to eliminate deficient areas.

The user personnel involved in the evaluation should receive a thorough

training course on system software operation and hardware maintenance

well before the evaluation begins. To obtain the most accurate statistical data from the pre-production evaluation, the user personnel must

operate and maintain the total system. If this situation occurs a re- sponsive training plan can be developed and system maintainability and

reliability deficiencies can be defined early enough to allow corrections

to be made before the production EHM system is implemented.

CONCLUSION

It has been previously stated that the whole process of justifying the

effectiveness of an EHM system becomes a statistical data gathering

exercise. The A-7E lECMS experience has proven this true and shown that

the processes of setting up and conducting the required data baseline

and pre-production evaluation programs are far from easy. Much careful

planning and coordination must go into structuring these programs to

give the most informative and accurate results. Nevertheless, unexpected

problem areas will arise, causing the data baseline and pre-production

programs to be less than 100% effective. Some of these problem areas unique to the development and evaluation of an EHM system can be reduced

by the thoughtful observation of the mistakes made during previous programs as the A-7E lECMS experience.

159
lECMS MASTER PARAMETER LIST

ITEM NO. PARAMETER

1 HYDROMECHANICAL GOVERNOR PRESS.

2 HP PUMP INLET PRESSURE

3 HP PUMP OUTLET PRESSURE

4 LOW PRESSURE GOV. DELTA P

5 MAIN MANIFOLD FUEL PRESSURE

6 PILOT' MANIFOLD FUEL PRESSURE

7 , BY-PASS STATIC PRESSURE

8 BY-PASS TOTAL PRESSURE «r 9 HP COMPRESSOR OUT PRESSURE

10 OIL PRESSURE (DELTA P)

11 TURBINE OUT PRESSURE

12 LP COMPRESSOR INLET TEMPERATURE

13 HP COMPRESSOR OUT TEMPERATURE

14 TURBINE OUT TEMPERATURE

15 PMG L.H. SHORTING LOOP CURRENT

16 IGNITION EXCITER L.H. PRIMARY CUR

17 PMG A.C. VOLTS (L.H. COIL)

18 PMG R.H. SHORTING LOOP CURRENT

19 IGNITION EXCITER R.H. PRIMARY CUR

20 PMG A.C. VOLTS (R.H. COIL)

21 PMG D.C. VOLTS

22 AUTO RELIGHT ACTUATOR

23 COLD START SOL. VOLTS

24 . DOUBLE DATUM ARMED , 25 OVER DATUM RELAY

26 LPC SOLENOID CURRENT

27 LPC SOLENOID VOLTS

28 LP ROTOR SPEED

29 OIL SCATTER

30 OIL ATTENUATION

31 OIL FLOW

32 OIL MONITOR FAIL

33 FILTER (OIL) DELTA PRESSURE

34 INLET GUIDE VANE POSITION

35 POWER LEVER ANGLE

36 OIL TEMPERATURE

37 LP COOLING AIR ' 38 OUTSIDE AIR TEMPERATURE

39 TURBINE VIBRATION

40 COMPRESSOR VIBRATION

41 ACCESSORY VIBRATION

42 AIRCRAFT G. LOADING

,^ APPENDIX 1

l6o
ITEM NO. PARAMETER

43 IH SPARK RATE

44 R.H. SPARK RATE

45 HP ROTOR SPEED

46 FUEL FLOW

47 OIL LEVEL NORM

48 ' OIL LEVEL (1/2 FULL)

49 - - A/C IGNITION

50 ^ A/C MAIN/MANUAL FUEL CONTROL SW.

51 - A/C MANUAL FUEL VALVE POSITION

52 STARTER AIR

53 A/C WEAPON FIRING SWITCH

54 OIL COOLER DELTA P

55 LANDING GEAR SQUAT SWITCH

56 ALTITUDE

57 MACH NUMBER

58

59 HP PUMP FAILED

60 STALL DETECTOR

61 H.P. COMPRESSOR OUT PRESSURE

62 RUMBLE FILTER 1 63

64 TIME

65 FUEL TEMPERATURE

66' L.P. FUEL PUMP OUT PRESSURE

NOTE: Recently several of these parameters have been dropped due to

cost-effectiveness considerations

APPENDIX 1

l6l
DISCUSSION

0. E. Compton, Northrop Corporation, Aircraft Division : Did you

Identify the signature of a given engine on the test cell on the

ground?

A. J. Hess : The procedure followed when installing lECMS for the first

time is, in the process of normally trimming the engine, to establish a base line by stabilizing at 4 or 5 RPM points. The system

automatically records the engine data. This establishes the base line

signature information for each individual engine. The only time you

have to redo it is when you change airborne units or change something

within the gas path of the engine.

0. E. Compton : What if you were to place that engine in another

airplane?

A. J. Hess : If you place the engine in another airplane, you would

have to obtain another base line signature, but placing the engine in

another airplane requires another trim procedure anyhow, so you could

get that data with 20 minutes additional ground work.

0. E. Compton : So basically, the identification of a signature is an engine that is installed in the vehicle, and not on the test cell?

A. J. Hess : That's right.

0. E. Compton : What type of induction system variances, environmental

control variances, and shaft horsepower variances do you find among

different vehicles in trying to identify the specific signatures?

A. J. Hess : In a turbo-fan engine, you don't worry about shaft

horsepower. But, each engine does operate differently. We establish

nominal curves representing the general population of all the engines.

Then rejection tolerance bands or limits are established around each curve. The tolerance band has to be large enough to take into account

the variances within all engines in the general population, but it

can't be too large or engine discrepancies will be missed. A large

part of the data base expansion program is trying to find where to put

the tolerance bands.

J. S. Bendat, Independent Consultant : In regard to the vibration

analysis, did you do any narrow band analysis, any transfer function

analysis, or any of the more advanced analyses that would really define

what was going on?

162
A. J. Hess : Allison may have used these techniques, but they didn't . recommend them to be used in lECMS. Essentially, the vibration team

looks at these things: (1) the overall engine vibration level for each

of the three transducers, and (2) each of the 21 discrete one-third

octave frequency bands for a change either up or down above a certain

established "colerance limit. If either of these two things occur, we

get an exceedance flag. That tells you that there has been a change in

the vibration signature. This new signature is compared with

signatures for specific component failures. Those signatures were

generated from actual test cell failures that Allison experienced.

R. Hohenberg, Mechanical Technology, Inc. : What are the requirements

of transducers in order to achieve your goals?

A. J. Hess : The vendor, Allison, picked the transducers. We do have a requirement for very good accuracy. And we do have a requirement for

the transducers to live in a hostile environment, namely, the engine

bay where there are extreme changes in temperature and pressure. With

these requirements, the transducers are costly. The pressure

transducers are costing us about $1,000 a piece.

R. Lenich, Caterpillar Tractor Company : In what ways do the prototype

pilots differ from operational pilots in the way they handle airplanes

and which is more severe on the airplane?

A. J. Hess : The fleet pilot is much more severe. At Patuxent River

there are very experienced pilots who have been through the test

pilot's school. In developing the prototype system, these pilots fly

profiles to aid the contractor in developing the software. They

usually do what is asked of them. They are very smooth in the way they

handle the throttle and stick. In a fleet environment there are both

experienced and brand new pilots. Naturally, there are differences in

how they fly and in how they handle the engine. Also the missions they

fly are entirely different. Also the way the engine is handled differs

according to whether the pilot is flying lead or wing. The wing man moves around quite a bit more than the lead man. As fallout from the

lECMS program, we're learning very much about how that engine is

actually being operated. In the fleet envihonment, one of the things we are using that information for is to develop some type of low cycle

fatigue counter for certain critical engine problems.

T. Tauber, Tedeco : I have two questions: (1) did you attempt to

correlate your data with SOAP results and (2) what other oil analyses

techniques were considered and were evaluated and ultimately rejected?

A. J. Hess : This whole program started with the environment-one oil

quality transducer. We haven't had an airborne oil problem to date

(5,000 hours). We had a bearing failure on the lECMS equipped engine

that was run on a test cell at Allison. The environment-one unit

165
picked it up before the test cell vibration equipment picked it up.. The Navy is looking at new types of magnetic flux chip detectors.

Those could easily be integrated into an lECMS program. SOAP is a normal program in the Navy. We had false indications for the

environment-one unit early in the program. These were caused by the

unit failing. We did correlate them with SOAP.

M. Dow, Eastern Airlines : Can you give me some idea of how many man hours have gone into the program development so far?

A. J. Hess : I don't know how many man hours were involved, but the

development phase cost several million dollars. It took us the first

couple years to develop the hardware and it took us another year and a half or two years to develop the software. I don't think the

feasibility study has to ,be done again for the next system. Using

state-of-the-art-hardware, you could rely on our precedence and just go

into the development effort of software.

lA. Dow : Are there a large number of people engaged in this work?

A. J. Hess: Fifteen.

161+
TRT RKT^VTCK OTT, ANALYSTS

T^FISKAPHH ATJTl nKVET.OPN^NT PROCTAM

Peter B. Senholzi

Naval Air Engineering Center, Lakehurst, N. J. 08733

Oil analysis can be described as a preventive maintenance concept

utilized to predict impending mechanical failure through the examination

of used oil sam.ples . This concept, although varying in technique, has

been apolied for many decades. Initially, physical properties of oil

"were considered indicators of equipment wear. However, consistent

results were not obtained until examination emphasis shifted to the

analysis of oil carried wear particulates. The term oil analysis has

thus become synonymous with oil particulate analysis.

Spectrometric oil analysis has developed as the foremost analytical

technique utilized at the present time. This technique involves the

concentration measurement of various elements contained in a used oil

sample. Spectrometric analysis has demonstrated that the analysis of

wear metal particulate matter that accumulates in a closed cycle oil

wetted system can, with varying degrees of success, be used as a means

of gauging wear and thus predicting mechanical component failure. The

technical basis for the effectiveness variations exhibited by this technique, as well as related techniques, has not as yet been factually

defined

The optimal development process of an oil analysis technique can be

broken down into four distinct phases as shown in Figure I.

: DISPONENT

WEAR

MODES

PARTICULATE

CHARACTERISTIC

CORRELATION

ANALYSIS

TECHNIQUE

FIELD

APPLICATION

OIL PARTICUIATE ANALYSIS

Figure I

The first element in any such development program is the definition

and categorization of all pertinent mechanical system wear modes. This

categorization would list wear modes that contribute to lubricant particulate content. All oil wetted components would be considered in such

a study.

The second element of the development program would be to experimentally determine wear particulate characteristics and parameters and

relate these factors to the wear state of a component. This correlation

16^
effort would be instituted for each wear mode and serve to highlight

critical parameters. The monitoring of these critical parameters could

be directly related to the wear state of a component.

Based on the determination of critical particulate parameters, an analytical technique or combination of techniques can be developed. This

technique definition comprises the third element of the respective program.

The fourth and last element of this program would be the field

application of developed techniques. This application would serve to

provide effectiveness data as well as serve to dictate modifications if

required

Based on research performed under the Tri Service Oil Analysis

effort, the following determinations were formulated with respect to

past oil analysis technique development:

Numerous wear mode classification efforts have been performed.

Many analytical techniques have been developed.

Many techniques have been field tested.

An insignificant amount of effort has been performed correlating

wear modes with wear particulate characteristics and parameters.

These determinations reveal that a major element of the oil analysis technique development program has been neglected , Very little work

has been performed which serves to clarify which particle characteristics should be monitored. Analytical techniques developed to date are based on critical particulate characteristic assumptions and have been

applied by trial and error.

The Tri Service Oil Analysis Research and Development Program was conceived by the Naval Air Engineering Center (NAEC) to bridge the technological gap that now exists with respect to oil analysis techniques as described above. Its goal is to place oil analysis on a more secure

basis. Briefly the program can be summarized as follows:

Laboratory testing to determine the feasibility of predicting the wear state of oil wetted components through the

utilization of critical wear mode parameter monitoring.

In order to achieve this program goal, a three phase effort has

been instituted by NAEC. These phases consist of data base formulation,

laboratory study, and system application as depicted in Figure II.

166
DATA

BASE

LABORATORY

STUDY

SYSTEM

APPLICATION

OIL ANALYSIS PROGRAM

Figure II

Each program phase shall be discussed separately as follows:

(l) Data Base

The data "base phase of the program serves to provide information necessaiy to initiate meaningful laboratory testing as well as effectively evaluate test results. The initial thrust of this effort

was the derivation of wear mode matrices for each prime oil wetted

wearing component. Matrices were derived for ball bearings, roller

bearings, gears, and sliding contacts. These four components were determined to be prime components of oil wetted systems. Each matrix relates

component operational parameters to particular wear modes. Wear conditions encountered under laboratory test are cataloged through utilization of these matrices. Matrices are enclosed as Appendix I.

A secondary effort under the data base phase is the categorization of oil carried wear particle morphology. Under this effort, a number of distinctive particle types have been identified. The particle

types are as follows:

Rubbing Wear Particles

Rubbing wear particles are generated whenever two pieces of

metal rub together in the presence of a lubricant. It has been found

that they originate in a shear mixed layer which, in the case of steel,

is in the order of 1 ;jm thick and exhibits only short range crystalline

order. This layer, the significance of which has only recently been

appreciated, has unique properties different from those of the underlying metal. Most wear of rubbing metal surfaces is the result of flaking

off of pieces of the shear mixed layer as the result of a network of

cracks that gradually develop with repeated passes of the opposing surface. This type of wear is relatively benign and is fundamental to

boundary layer lubrication.

Oxide Particles

Some wearing systems show large quantities of the red oxide

of iron, hematite, Fe203. Such oxide particles are easily recognized

in the microscope using transmitted white light and are even more

striking using transmitted polarized light with crossed polars . They

are the result of rusting in the machine and generally indicate the

presence of moisture or moist conditions which permit the rusting to

16?
at the vearing surface, but is

insides of pines, and many

The oxides of other metals may be white, blue, green, or

ye I Low, depending on the metal.

Dark Metallo-Oxide Particles

Another category consists of dark metallo-oxide particles

"Which are thought to be principally FeqOij. (magnetite). These particles

are non-stoichiometric oxides and may be thought of as oxides with iron

dissolved in them. They are surprisingly more opaque than would be

expected from pure Fe^Oj^. These particles appear as black or very dark

chunk-like oarticles, similar to pieces of hard coal. It is postulated

that they are sufficiently hard to cause surface denting and subsequent

micro-cracking of the surfaces of rubbing elements in bearings.

A second type of dark chunk-like particle has been found

recently, usually accompanied by dark flat platelets witlf straight sides

They appear to be the wear product from carbon seals or separators. The

chunk-like particles do not have the sharp edges characteristic of magnetite; the fracture surfaces are concoidal, sim.ilar to that of glass.

Cutting Wear Particles

Cutting wear particles have the appearance of tiny lathe chips

or coils of fine wire. Such particles are the result of the failure of

the boundary layer lubrication and are usually associated with high sur- face contact forces. They may also be generated by the presence of

abrasives. An independent investigator has proposed that these abrasives can be synthesized on wearing surfaces.

Fatigue Chunks

Another type of particle is the fatigue chunk or grain. They

are composed of free metal, usually ferrous and show crystalline faces

containing considerable detail. They are approximately as long as they

are wide and are often several microns thick. Such particles are genera

ted by certain types of gear wear and are seen in other situations where

cracking perpendicular to the surface can develop.

Laminar Particles

Laminar particles are found in connection with gear and rolling bearing wear. They are exceedingly bright free metal particles most

frequently seen in connection with rolling bearing wear. The particles

are thin, typically 3/^ pi^ thick, and generally have holes in their surface. They appear to be the result of rolling out of the metal as could occur in the shear mixed layer on the ball bearing track or near the

occur. The rust is usually not generated

simply material flaked off of shafts, the

other places

168
pitch line of gears.

Spherical Particles (Free Metal Spheres)

Spherical particles are generated by the thousands in cases where micro-cracks are present in rolling bearings, such as ball bearings and roller bearings, lubricated by either oil or grease. They

range in size from less than 1 pm to more than 10 jam. The smaller sizes are much more numerous. Up to several million spheres can be g^-nerated

in the course of a bearing fatigue failure.

These spherical particles are not to be confused with pol}/rner

spheres or oxide spheres. The pol;;y7ner spheres are thought to be the

result of polymerization of oil around wear particles which serve as a nucleating catalyst.

Oxide spheres are produced in a variety of ways, but probably

the most common is fretting of steel surfaces. The non-free metal

spheres are easily distinguished from free metal spheres by virtue of

the reflectivity and opacity of the free metal. In bichromatic illumiination, free metal spheres appear red and the non-metallic or oxide

spheres appear green

Corrosive Wear Particles

Corrosive wear particles are those particles which have been

digested by the lubricant. They are distinguished from red and black

oxides of iron because they are generally colorless and much more transparent. They may be chlorides of the wearing material.

Non-ferrous Metallic Particles

These particles may belong to any of the first five classes.

Hybrid Particles

Hybrid particles are composed of non-ferrous material which

also contain some iron. They result from the wearing of some non- ferrous alloy, such as bronze, against steel.

Non-metallic Crystalline Particles

Non-metallic crystalline particles are common, the most

familiar example being sand. However, other oxides and carbides, such

as silicon carbide, are also frequently seen. The significance of such

particles depends on local conditions. The presence of sand, for ex- ample, can indicate an air filter failure or a bearing seal that is

leaking

169
Amorrihous Material

Amorphous material usually consists of deposits of material

"Which does not have a specific shape. The material is usually translucent but often contains thousands of metal particles. Various con- taminant polymers such as gasket material and plasticizers are the major

sources of this material.

The above two efforts constituted the bulk of the work performed under the data base program phase. Except for revisions, this

phase has been completed

(2) Laboratory Study

The laboratory study phase of the program, involves the bench

testing of nrime oil wetted components. The objective of this phase is

to monitor both the component surface wear condition and the respective

generated wear particle characteristics and parameters. Correlations

can then be drawn between surface wear progression and particle characteristic/parameter trends. Trend analysis will serve to identify

critical particle characteristics which reflect' the wear state of oil

wetted components

Under this phase, bench testing has been instituted for ball

bearings, roller bearings, gears and sliding contacts. These components have previously been identified as prime wear components in oil

wetted systems. Component test parameters reflect field operating con- ditions to the greatest extent possible. Examples of these parameters

are presented in Figure III. Each component is operated in an individual closed-loop lubrication system. Oil specimens are periodically

sampled from the lubricant system and subjected to a battery of particulate analysis techniques. These techniques include the following:

- Ferrographic Analysis

- Millipore Patch Analysis

SEM Microscopy

Optical Microscopy

Densitometer Analysis

Particulate Counts

- Acidity Measurements

Viscosity Measurements

Colorimeter Analysis

Spectrometric Analysis

TEM Microscopy .

-

The above techniques serve to classify wear particle, size,

size distribution, shape, color, density, and concentration among others

In addition to oil specimen sampling, the component wear sur*-

face is monitored at predetermined intervals during testing. Both

170
6309 Deep -Groove

Ball Bearing

LM1029U9/LM102910

Tapered-Roller

Bearing

1. Bore diameter (D, mm) ^5.2

2

Speed (N, rpm) 9,700 2,900

3. D X N X 10"^ oM 0.13

h. Lube MiL-L-23699 MIL-L-23699

5. Lube viscosity at 38/lOO°C 25/5.1 25/5.1

6. Radial Load (kN) 18.7 18.

7. Axial Load (kN) 0

8. Bearing Capacity (kN) 39.63 i+7.62

9. Theoretical Lio Life:

10^ TPvnT 1 ](" i nn 10^ stress cycles

10

50

10

130

10. Theoretical L50 Life:

10^ revolutions

10^ stress cycles

50

250

50

650

BEARING TEST PARAr-ffiTERS

Figure III

optical and scanning electron microscopy are utilized in this surface

monitoring effort.

Particulate analysis trend results are then compared and cor- related "with respective wear surface monitoring results. This correlation effort serves to identify critical particulate characteristics and/

or parameters

Component bench testing has been initiated for ball and roller

bearings, as well as sliding contact. Gear bench testing is imminent.

As a result of this early test stage, it would be premature at this time

to draw any conclusions from the above described correlation efforts.

Although correlation results have not been firmly established,

several significant findings have evolved from this laboratory study

171
program phase. The first area of findings involves oil sample storage.

In order to insure viable test results, representative oil specimens

must be taken from test systems. These samples when subjected to analy

tical techniques, after various storage periods, must remain representa

tive of the test system lubricant. Under the oil analysis program, a study was initiated to investigate the storage characteristics of oil

samples. The following findings, some still not fully explained, were

uncovered.

Different lubricants exhibit significantly different

abilities to retain particles in suspension.

The particle agglomeration characteristics of different

lubricants exhibit much variance.

- The longer an oil specimen is stored, the more difficult

it is to redisperse the contained particles.

Mild heating {"J2°C) followed by manual shaking has been

determined to be the most effective method to thoroughly

redisperse stored oil samples.

- Analysis of heated oil samples in contact with tygon

exhibits deposits of plastic gels. This plastic material

tends to coalesce near or around wear particles.

- Accelerated heat aging of oil samples in polypropylene

bottles results in the migration of components of the

plastic into the oil.

The most significant finding to result from this program has

been the full realization of what a truly clean lubrication system can mean in extending the life of operating components. Ultra clean lubrication systems, utilized in ball bearing bench testing, have consistently resulted in the extension of bearing operational life in excess

of ho times their calculated expected life. This life extension dramatically illustrates the major influence oil particulate contaminants

exert on the wear rate of a lubricated comnonent.

The above efforts and resulting initial findings constitute a brief overview of the work performed under the laboratory study program

phase. This phase is expected to be completed within the next six

months

(3) System Application

The third and final phase of the oil analysis program involve

the application of laboratory findings to field operating systems. The

objective of this phase is to verify laboratory component test results

and conclusions.

172
Under this phase various field control groups have been organized , Oil samples are collected from respective equipment that fall

within these groups. Each time a sampled piece of equipment experiences

.an oil wetted component replacement, the worn or broken part, as well as any pertinent reports, are collected. This process creates a repository

of failed parts and respective series of preceding oil samples. A

respository of this type serves as an excellent system application test

for laboratory developed results and conclusions. The application of

laboratory monitoring methodologies to repository oil sample failure

series will serve to verify the applied methodologies.

Control groups that have been organized under this phase con- sist of landbase, shipboard, and airborne equipment. Oil wetted systems

of the aircraft, UH-1 helicopter, m60 tank, and nuclear submarines

are presently being monitored . At the conclusion of the laboratory

study program phase, results will be verified by application to these

field control groups. This phase will be completed within the next

eighteen months.

The above described three phase program approach will serve to

bridge the technological gap that exists with respeict to oil analysis

technique development. Expected results to be derived from this program can be summarized as follows:

Definition of Wear Components.

- Identification of Critical Wear Modes.

- Feasibility of Identifying Critical Wear Mode Parameters.

Feasibility of Correlating Critical Wear Mode Parameter

Monitoring to VJear Component Failure.

Definition of Monitoring Criteria.

These results will serve to explain the variations in effectiveness

of existing oil analysis techniques as well as serve as a firm technical

basis for the development of a more sophisticated technique.

175
WEAR MODE MATRICES

APPEiroiX I

\

17^+
(16)

Cavitation

gouging

of

sui'faces

Below

atmos

pressures

will

cause

oil

bubble

collapse

and

impingement

System

should

be

designed

to

prevent

cavitation

conditions

(15)

Nicks,

Dents

and

Score

Marks

Abuse

and

mishandling

can

cause

damage

(11)

Fretting

Corrosion

Welding,

shearing

and

subsequent

oxidation

can

occur;

ex.

splines

May

allow

metal

-to-metal

contact

Can

contribute

to

fretting

corrosion

in

splines

(9)

Pitted,

Stained

Surfaces,

Corrosion Corrosive

agents

and

oxidized

products

can

attack

surfaces

Can

allow

corrosion

from

contaminants

including

water

Combustion

products

will

form

acids

which

attack

surfaces

Will

increase

chemical

activity

of

products

in

lubricant

and

from

combustion

(8)

Roughened

Mlcrodented

Surfaces, Abrasion,

Erosion

Metal

contamination

can

cause

abrasive

wear;

also

erosion

of

surfaces

from

flow

of

lubricant

Products

of

internal

combustion

such

as

carbon,

sulfides

will

damage

surfaces

(1)

Spalllng

ofa

Bearing

Surface, Fatigue

Can

cause

fatigue

damage

to

a

surface

subjected

to

repeated

loading

Material

may

have

inadequate

strength

to

resist

fatigue

cracking System

may

not

have

sufficient

strength

to

withstand

Shock

load

(15)

Smearing

and

Scuffing

in

the

Sliding

Direction,

Adhesion

Inadequate

film

strength

may

result

in

metal

-to

-metal

sliding

contact

May

prevent

localized

film

separation

May

prevent

adequate

film

strength

and

cause

oil

breakdown

Improper

surface

finish

may

prevent

film

separation

Surface

geometry

may

prevent

adequate

lube,

film

development

B)

Shock

load

D)

Vibration

F)

Deficient

lubrication

c)

Misalignment

H)

Incomplete

sealing

P)

Destructive

operating

environment

M)

High

environmental temperatures

I)

Manufacturing

and

material

deficiencies

J)

Incorrect

design

L)

Improper

175
(7)

Heavy

Cage

Wear

and

Breakage

Can

Impose

damaging

loads

on

cage

May

not

have

film

separation

on

land

riding

surface

Land

guided

cage

required

to

withstand

centrifugal

(6)

Pattern

of

Oblong

Scuff

and

Fret

Marks

on

Raceways

False

Brlnnelllng

May

occur

with

int.

clr.

and

poor

film

damping

(5)

Oblong

Dents

and

Flat

Spots

on

Rollers

and

Raceways

Brlnnelllng

Load

exceeds

static

capacity

May

cause

permanent

denting

Inadequate

capacity

tc

resist

brlnnelllng

(M

Heavy

Smear

Tracks

and

Discoloration

on

Raceways

and

Rollers

Can

cause

sliding

and

skewing

of

rollers

Insufficient

traction

can

cause

roller

skidding Boilers

may

not

slide

on

film

of

oil Increases

the

tendency

to

skid

with

light

load Too

much

Internal

play

can

contribute

to

skidding

(3)

Extensive

Glazing,

Frosting

Mlcrospalllng

of

Stressed

Surfaces

May

cause

a

break

through

of

a

thin

film Can

cause

film

breakdown

at

edges Can

cause

a

loss

of

film

strength

with

raetal-tomttal

contact

Poor

surface

finish

can

cause

surface

distrees

May

cause

lube

breakdown

with

loss

of

film

strength

(2)

Spalling

at

Roller

and

Raceway

Edge

of

Contact

Heavy

edge

loading

will

greatly

increase

contact

stresses

May

result

from

an

Inadequate

crown

on

rollers

and

raceways

(1)

Boiler

and

Raceway

Spalling

May

greatly

accelerate

fatigue

damage

Increase

in

stress

cycles

which

accelerates

fatiguing

of

surfaces

Soft

metal,

bad

grain

flow

and

size

can

increase

fatigue

likelihood

Insufficient

load

carrying

capacity

can

cause

fatigue

damage

A)

Heavy,

prolonged

load

,

B)

Shock

load

c)

Misalignment

D)

VlbratlOD

E)

Very

light

load

F)

Inadequate

or

poor

quality

lubricant

G)

Excessive

speed

H)

Incomplete

sealing 1}

Manufacturing

or

material

deficiencies J)

Incorrect

bearing

design

K)

Improper

mounting

L)

Improper

handling

M)

High

environmental temperatures

N)

Presence

of

electric currents

176
(15)

Nicks,

Deats

and

ecore

Marks

on

Bearings Abuse

and

rough

handling

may

result

in

damage

Crock

Formation

on

Rings

and

Rollers

Can

occur

with

thru-hardened

steels

Improper

heat

treat

can

cauae

cracking

Too

tight

a

fit 1

may

cause

ring

cracking

i

3 41

iilil A

loose

fit

may

cause

creep

and

fretting

corrosion

(10)

ITiermal

Growth,

Discoloration

and

Seizure

of

Bearing

Burnout

Inadequate

heat

removal

capability

Can

increase

heat

generation

Prevents adequate

heat

removal

from

bearing

(9)

Pits,

Stains

on

Raceways

and

Rollers,

Corrosion

Damage

may

be

caused

by

corrosive

agents

and

oxidized

products

in

oil Corrosive

agents

such

as

water

may

destroy

surfaces Electric

current

may

cause

extensive

pitting

of

(8)

Roughened,

Mlcrodented

Surraces

with

Increased

Ipternal

Play,

Abrasion

Metal

contamination

may

cause

abrasive

damage

to

surfaces

(IM

Excessive

'Papered

Roller

End

Wear

at

the

Cone

Rib

Can

cause

metal

to-raetal

sliding

contact

An

incorrectly

specified

fitup

to

control

end

play

or

preload

Incorrect

fitup

can

increase

roller

end

load

A)

Heavy,

prolonged

load B)

Shock

load

D)

Vibration

E)

Very

light

load

Inadequate

or

poor

quality

lubricant

G)

Excessive

speed

H)

Incomplete

sealing

I)

Manufacturing

or

material

deficiencies J)

Incorrect

bearing

design

K)

Improper

L)

Improper

handling jl2: N)

Presence

of

electric

177
19)

and Dn

Inward

ge

case

e

ue

to

1

a

case

soft

a

!|

case y

be

lent

Crushing

Distorti(

of

"the

Ci

May

dama,

if

sever

enough Damage

d

too

thin

and

too

core

Required

depth

ma

insuffic

(18)

Crack

Formation

on

Gear

Can

result

from

bad

heat

treatment

(17)

Fracture

of

Corner

Tip

of

Tooth

Can

cause

very

heavy

localized

bending

stress

Can

result

in

a

misaligned

gear

(16)

Fatigue

Fracture

of

Tooth

with

Focal

Ft.

and

Contour

Lines

May

exceed

bending

stress

limit

Bending

stress

may

be

insufficient

for

operating

conditions

(15)

Scoring

Lines

in

Direction

of

Sliding

Inadequate

film

strength

may

result

in

metalmetal

sliding

contact A

rough

surface

finish

may

result

in

lack

of

film

separation Inadequate

j

backlash

can

cause

gears

to

run

hot

May

result

in

lubricant

film

breakdown

(1)

Spelling

of

Tooth

Surface

Increased

contact

stress

promotes

fatigue

Can

increase

probability

of

fatigue

damage

Soft

metal,

bad

grain

flow

and

size

can

cause

spalllng

out

of

the

surfaces

Poor

gear

geometry

may

result

in

high

stress

levels

A)

Heavy,

prolonged

load B)

Shock

load

c)

Misalignment

F)

Deficient

lubrication

H)

Incomplete

sealing

I)

Manufacturing

and

material

deficiencies

J)

Incorrect

gear

design

L)

Improper

handling

K)

Improper

mounting

M)

High

environmental temperatures

178
(15)

Nicks,

Dents,

Score

Marks

Abuse

and

mishandling

may

cause

damage

(10)

Thermal

Growth

Discoloration

and

Softening

of

the

Gear

May

have

inadequate

heat

removal

capability

May

prevent

sufficient

heat

removal

(9)

Pits,

Stains

on

Tooth

Surface

Corrosion Corrosive

agents

and

oxidized

products

in

can

attack

surfaces

Corrosion

due

to

contaminants

such

as

water

can

destroy

surfaces

(8)

Roughened,

Microdented

Surface

with

Increased

Backlash Abrasion

Metal

contaminants

can

cause

abrasive

wear

of

teeth

(20)

Rolling,

Peening

with

Rippling

and

Ridging

Lines

on

the

Teeth

May

produce

plastic

flow

Possible

localized plastic

flow

A)

Heavy,

prolonged

load B)

Shock

load

c)

Misalignment

F)

Deficient

lubrication

H)

Incomplete

sealing

I)

Manufacturing

and

material

deficiencies

J)

Incorrect

gear

design

L)

Improper

handling

K)

Improper

mounting

M)

High

environmental temperatures

179
(7)

Heavy

Cage

Wear

and

Breakage

Can

impose

heavy

loads

on

cage

pockets

and

land

riding

surfaces

May

prevent

film

separation

of

land

riding

surfaces

Cage

must

be

balanced

and

land

guided

to

withstand

centrifugal

forces Cage

may

have

inadequate

strength

for

operating

conditions

(6)

Pattern

of

Oblong

Scuff

and

Fret

Marks

on

Raceways

False

Brinnelllng

May

cause

damage

when

there

is

a

lot

of

play

and

poor

film

damping

Mil

Iii!

Permanent

deformations

may

occur

if

load

exceeds

static

capacity

Can

cause

permanent

denting

Inadequate

static

load

capacity

Heavy

Smear

Tracks

and

Ulscoloration

on

Raceways

and

Balls

Insufficient

tractive

force

can

cause

ball

skidding

When

balls

skid

they

may

not

slide

on

a

film

of

oil Increases

the

tendency

to

skid

with

light

load

Too

much

Internal

play

can

contribute

to

skidding

Extensive

Glazing.

Frosting,

Mlcrospalllng

of

Stressed

Surfaces

A

heavy

load

may

cause

a

break

through

of

a

thin

film May

result

In

lack

of

film

separation

of

contacting

surfaces

A

rough

surface

finish

may

prevent

film

separation

of

the

surfaces

May

cause

lubricant breakdown

(2)

Peening

+

Spalllng

at

Race

Shoulder

Very

heavy

thrust

load

can

cause

ball

to

ride

over

shoulder

Wear

track

may

run

close

to

shoulder Shoulder

height

may

be

inadequate

for

load

conditions

(1)

Ball

+

Raceway

Spalllng

Heavy

load

can

increase

incidence

of

fatigue

damage May

impose

heavier

loads

Will

Increase

stress

cycles

which

accelerates

fatiguing

of

surfaces

Soft

metal,

bad

grain

flow

or

size

can

cause

spalllng

out

of

the

surfaces

Inadequate

load

carrying

capacity

can

increase

fatigue

damage

A)

Heavy,

prolonged

load

1 J C)

Misalignment

D)

Vibration

E)

Very

light

load

F)

Inadequate

lubrication

or

poor

quality

lubricant

G)

Excessive

speed

H)

Incomplete

eeallog

I)

Manufacturing

or

rrsterlal

inadequacies

J)

Incorrect

design

K)

Improper

mounting Improper

|

handling M N)

Presence

of

electric

currents

180
Score

Marks

on

Bearing

Abuse

and

rough

handling

may

result

in

damage

which

shortens

life

Crack

Formation

on

HlngB

and

BallB Can

cause

cracking

with

thruhardened

steels

Improper

heat

treat

can

cause

cracking

Too

tight

a

fit

may

cause

cracking

(11)

Bands

of

Rust,

Discoloration

+

Some

Glazing

on

Fitted

Surfaces

Fretting

Too

loose

a

fit

can

cause

creep

and

fretting

corrosion

(10)

Thermal

Growth,

Discoloration

and

:

Seizure

of

Bearing

Burnout ill

lit Can

greatly

Increase

heat

generation

Prevents adequate

heat

removal

from

bearing

Pits

and

Stains

on

Raceways

and

Balls

Corrosion

Can

result

in

corrosive

and

oxidized

products

attacking

surfaces

Corrosive

agents

such

as

water

can

destroy

surfaces Electric

current

may

cause

extensive

pitting

of

surface

(8)

Roughened,

Microdented

Surfaces

with

Increased

Internal

Play

Abrasion

Metal

contamination

may

cause

abrasive

damage

to

contacting

surfaces

A)

Heavy,

prolonged

load B)

Shock

load

c)

Misalignment

D)

Vlbrotlon

E)

Very

light

load

F)

Inadequate

lubrication

or

poor

quality

lubricant

G)

Excessive

speed

H)

Incomplete

sealing

I)

Manufacturing

or

material

inadeqxiacles

J)

Incorrect

design

K)

Improper

mounting

L)

Improper handling

M)

High

environmental temperatures

N)

Presence

of

electric currents

I8i
DISCUSSION

C. R. Garbeti, Shell Development Company : Did you carry out any studies

in relation to journal-type bearings? I should think that would be of

interest in nuclear submarines. It is certainly of interest to us in a lot of our industrial turbine compressor equipment.

P. B. Senholzi : All we consider right now are ball bearings and roller

bearings.

T. Tauber, Tedeco : In addition to oil samples, do you look at sediment

in the test rigs, transmissions, or gear boxes?

P. B. Senholzi : Our test rigs are built to have "no sediment." The oil

sumps were funnel shaped. The pump was located at the bottom of the

funnel. So supposedly, there was nowhere that particles could get

trapped. Even so, there were a lot of particles in the beginning but

they seemed to peter out and go somewhere. We do have all the oil that we saved from machines and that which was washed out from the sumps. We/

have two gallons of oil from each of 28 systems, and we are going to

look at what is left.

T. Tauber : Can you also describe your sampling technique?

P. B. Senholzi : The technique for the bearings utilized a syringetype sampler that was injected in the top of the funnel. We withdrew

oil samples just before it went into the pump.

T. Tauber : Was this after shutoff?

P. B. Senholzi : No, this is while the machine is on. It had a port in

the top of the cylinder.

T. Tauber : You mentioned the formation of gels due to the use of

plastics in the sampling bottles. What kinds of materials were subject

to that in addition to Tygon?

P. B. Senholzi : Polypropylene was the other one we tested, because that was what the bottles were made of, and a lot of the seals on the caps of

oil sampling bottles were made of the same polypropylene or Tygon.

T. Tauber : Basically it does not interfere with SOAP analysis. That is

probably why nobody has picked it up.

P. B. Senholzi : The particles agglomerate in this plastic gel and act

as one big particle and fall to the bottom. They wouldn't be picked up

in SOAP analysis if they were laying on the bottom of the bottle.

Because SOAP does not agitate the particles to any great extent, the

mixture is not homogeneous.

182
S. Pinel, Industrial Tectonics, Inc. : Would you describe the

filtration process for your test rig?

P. B. Senholzi : There was no filter.

S. Pinel : You mentioned that the low number of particles contributed

to the long life of your system. Could you expand on that a minute?

P. B. Senholzi : Well, before we ran any bearing we kept flushing the

system and making ferrograms of the flushing solution to see how many

particles were there. We didn't start until the system was thoroughly

clean. There weren't any particles in the system, above and beyond

those generated by the ball bearings themselves. Since there were

Teflon impellers in the pumps, anything the pump would generate we would be able to see as a Teflon particle as opposed to a metal

particle. There wasn't anything initially to dent the races, and this

is what contributed to the long life.

R. J. Salvinski, TRW Systems Group : There are some theories that

suggest that surface energy of the medium may have an effect on wear

particle size. Does wetability have any significance in your work?

P. B. Senholzi : We didn't consider that effect at all.

G. J. Philips, Naval Ship Research and Development Center : You

mentioned you put two defects on the inner race of the bearing. One

ended as a fatigue spall. What happened to the other?

P. B. Senholzi : We did this on 14 bearings and a good percentage of

the 14 spalled at one of the indents. The other defects ended with the

leading end normal and the lagging end extruded.

G. J. Philips : At what point did you dent the bearings? How long did

the bearings last with the dents in them?

P. B. Senholzi : They lasted about 200 million revolutions on the

average. We ran bearings without dents up to 250-300 million

revolutions without failure. We put dents in them and they failed

within a matter of maybe 30 million revolutions. Some of the new ones

that we put dents in lasted over 200 million revolutions, so it seems a new bearing is less vulnerable to a dent in the race than a bearing

that has already been run.

T. Tauber : Did you have a full design load on these bearings?

P. B. Senholzi : They were overloaded to the extent that we couldn't

get them to fail to begin with so we kept raising the load and the

RPMs. We got these 6309 bearings up to 9700 RPMs and we still couldn't

get them to fail even in a high speed condition. We had started them

at 2700 RPMs.

185
J. W. Forest, Ontario Hydro : It looks like your program has got a terrific byproduct - you keep the oil clean and go on forever.

P. B, Senholzi : If the oil is kept clean, one wear mode may be

eliminated, but you still have other wear modes that may cause the

bearing to fail

U. Sela, Exxon Company, USA : We find much reluctance to get the system

clean. Normally, operations people are happy having it 50 percent

•clean. Data to show that a clean system improves bearing life are very

important.

P. B. Senholzi : We are looking at a whole program initiated by that

result - the effect of the contaminants on the wear life of the

component.

0. E. Compton, Northrop Corporation, Aircraft Division : Did you vary

the temperature of the oil?

P. B. Senholzi : No, all constant temperature, constant load, constant

speed.

iQk
DEVELOPMENT OF INSPECTION AND DIAGNOSTIC EQUIPMENT FOR

MOTOR VEHICLE EQUIPMENT FOR MOTOR VEHICLE INSPECTION

George L. Parker

Head, Vehicles-in-Use Group

Crash Avoidance Eesearch Division

Office of Vehicle Safety Research

Research and Development

National Highway Traffic Safety Administration

Washington, D.C 20590

I. Program Overview and Philosophy

Motor Vehicle Inspection (MVI) , as practiced in 34 of our States and

territories, is primarily limited to those items which are easy to

Inspect and is a cursory examination of the most critical safety systems

and degradation modes. Inspection equipment used in most inspections

is not automated, is not necessarily suited for its intended use, and

does not reduce defects on vehicles-in-use to the desired degree. To

improve MVI, it is necessary to develop new equipment, which in addition

to addressing the most safety critical defects, is thorough, comprehensive, objective, and has a high throughput. Automated equipment must

include the essentials of control of the test sequence and automatic

comparison of inspection equipment output to inspection criteria.

While automated inspection equipment can overcome most of the problems

of existing inspection relative to items inspected and objectivity, most

states will rely on private garage/gas station/dealership inspections

for the foreseeable future. For this reason, there is a need to improve

this basically manual form of inspection. The first step in this

process is to recommend to the states only the most safety critical

defects as the basis for MVI programs. The second step is to develop

techniques, simple equipment and hand tools, and procedures to improve

manual inspection.

Regardless of whether it is automated equipment or manual techniques

and procedures, a deliberate development process must be followed. MVI

has been pursued in the U. S. since 1926 in a variety of ways with as many different objectives. Thus, a review of past accomplishments must

be made before proceeding to a solution. It is first necessary to

identify and justify any existing MVI deficiencies and current needs to

those, who through years of experience, have developed a reliance on existing techniques and equipment. This is not an easy task, but is

necessary to either justify further research and development or to

identify, evaluate, and verify the satisfactory existing approaches.

The last twenty-five years have resulted in a large and varied

generation of inspection equipment and techniques, and even a slight

change in the area could neither be accomplished in a short time nor be

185
accepted by the total following, regardless of the justification.

Therefore, all conclusions and recoininendat ions must be carefully

supported and verified.

Once the current climate has been evaluated, development of inspection

techniques and equipment may systematically proceed. Primary objectives

will relate to suitability, accuracy, objectivity, etc. This will

insure that the final product, if it can be developed, will not have the

deficiencies of existing techniques and procedures. New techniques and

equipment must be subjected to the rigorous evaluation that bore their

need. Although this is not the final proof or justification, it stands

as a major milestone to be satisfactorily completed. Perhaps the major

evaluation measurement will be the practicality of the techniques or equipment in an MVI environment. Then the evaluation results will not

only verify that a correctly identified problem is solved, but that the

solution is not an "overkill" .

Another constraint on the development of improved MVI techniques and

equipment is the consumer related aspect of motor vehicle safety and

MVI. The growth of engine diagnostic facilities has shown that con- sumers are interested in the performance condition of their vehicles.

On the other hand, they are unsatisfied with the attempts to repair them.

A goal of the program to develop MVI techniques and equipment is the

proper identification of specific safety-critical vehicle subsystem

degradation and vehicle repair needs in a rigorous manner that results

in consumer satisfaction. It is in their interest that the identification of vehicle repair needs not only be correctly identified, but

limited to only those subsystems or components specifically needing

repair, replacement, or adjustment.

A final goal of MVI technique and equipment development is the overall

streamlining and efficiency of the total MVI environment. Probably the

most important considerations are equipment integration, inspection

time, equipment cost, and operator skill level requirements. In the

long run, the overall effectiveness of new techniques and equipment

will have to be weighed against possible negative factors caused by the

development of new inspection techniques and equipment for specific

vehicle subsystems in separate development projects.

Research results in the areas of (1) the role of vehicle defects in

accident causation and (2) the relationship of vehicle defects and

degradation to vehicle performance degradation have determined the

following vehicle systems as being safety critical in the priority

listed

a) Braking systems

b) Tires ' c) Steering and suspension systems

Research to evaluate existing inspection techniques and equipment and to

develop new techniques and equipment have been conducted in each of the

three areas. Carrent and future research will also concentrate on these three systems.

186
II. Past and Current Research Activities

A. Automated Brake Inspection

The first effort to evaluate and develop inspection techniques and

equipment began in June 1972, with a research project whose primary

objective was to operationally demonstrate a cost-effective (in relation

to other systems) brake inspection system that is capable of detecting

and measuring safety critical defects and degradation of brake systems.

The work performed in this project consisted of the following:

1) determination of present brake inspection m.ethods,

2) development of a methodology for evaluating available brake

inspection equipment,

3) evaluation of available brake system inspection methods and

equipment

4) design and construction of single-station inspection systems,

and

5) physical verification of inspection system performance.

* The developed brake inspection procedures had to be able to determine

current brake system performance capabilities and to determine any

defects or degradation existing in a particular brake system that would

lead to near-future catastrophic failures or sub-level performance. The

primary measures of brake performance considered to be important are effectiveness and stability. Vehicle brake system design and performance characteristics that greatly influence the vehicle braking

performance are:

1) brake system gain,

2) brake system response,

3) brake force proportioning, front to rear,

4) brake force uniformity from side-to-side, and

5) friction material characteristics . The above discussion concerns primarily brake defects and degradation

leading to immediate changes in vehicle performance. Degradation

leading to eventual catastrophic failures cannot always be detected in

performance tests, therefore, inspection techniques complementary to

performance tests must be utilized. Brake components which are subject

to this type of degradation or deterioration are:

1) friction materials,

2) drum or rotors,

3) hydraulic system (leakage)

4) brake fluid (water contamination) , and

5) actuation system (pedal reserve).

Project results have included the following:

1) Current brake inspection, as conducted in various states, involves

the use of various combinations of three inspection techniques. These

techniques are visual inspection, low speed road stopping test (20 mph)

and low speed (5 mph) r.i.atform tester.

187
2) Visual inspection is the only state-of-the-art technique for

detecting such items as worn friction materials, oversize drums, broken

or missing parts, etc. However, these inspections tend to be very

subjective.

3) The low speed road and platform tester stopping tests serve to

show that the inspected brake system has the ability to stop the vehicle

at low speeds and nothing more. These tests are manually controlled and

the results are visually observed. This type of test and inspection

control has inherent repeatability problems from test to test and from

operator to operator.

4) The brake analyzer and brake dynamometer are also used in brake

inspections. These machines use either electric motors or inertia

weights to supply energy to the test vehicle brakes through a set of

wheel rollers. All of these machines test either the front or rear axle set of brakes at a time, although one costly machine using inertia

weights has the ability to test all four vehicle brakes at one time.

5) Test data analysis indicated the d3mamic brake analyzer to be far

superior to the platform tester in capability, repeatability, and

sensitivity to vehicle brake performance levels. Also, higher energy

levels to the vehicle brakes and continuous performance readouts are available. Platform brake testers give only an instantaneous low-speed

readout of brake proportioning which is not usually repeatable. The

platform test cannot indicate brake system gain and possesses a high

brake force threshold.

6) The dynamic brake analyzer has proven itself capable of accuratelj

detecting outages in vehicle brake system performance with good repeatability.

A visual inspection of the brake system for component condition combined

with a dynamic brake test now appears to represent the most practical

approach to brake inspection where high throughput is desired.

The above results, when combined with the results of other research to

develop inspection items and criteria, resulted in the development of

a specification for a dynamic brake tester. The brake tester has been

built, evaluated, and will shortly be available for further, long-term

evaluation. The most significant features of the machine are:

a) low speed - high force capabilities,

b) automated input control, and

c) automated printout and defect decision making in the dynamic mode.

B. Shock Absorber Inspection

A research project was initiated in June 1973, whose objectives were:

1) Through analysis, an extensive literature review, and a shock

absorber survey, determine the important shock absorber parameters with

respect to safety and the range of these parameters in the passenger

vehicle shock absorber population.

188
2) Physically test each type of shock absorber test machine that is

available and determine its effectiveness with respect to the above

safety critical shock absorber parameters.

3) Recommend an approach and equipment for shock absorber inspection

that- includes the appropriate features of the evaluated equipment.

The contract has been completed with the basic finding that no existing

shock absorber inspection equipment is suitable for state MVI use. The

deficiencies range from inappropriate tests to lack of capacity. A

common deficiency is that vehicle performance with original equipment

shock absorbers must be known.

A recommendation for new equipment development was made which is based

on the fact that the primary shock absorber failure mode is loss of

fluid and that shock absorbers with low fluid levels result in aerated

fluid when exercised. The inspection philosophy then, would be to

design a machine which would exercise the wheel, spring, shock absorber,

and suspension system at various frequencies (or a frequency sweep) at

a fixed amplitude and would compare system damping at the start of the

test to later in the test. If the fluid level is low, it will aerate

and the damping will change. What is particularly desirable about this

approach is that no new-vehicle information is needed.

C. Tire Inspection

A research effort is currently underway to develop a means of inspecting

tires for inflation pressure, tread depth, and carcass integrity on an automated basis. The basis for the carcass integrity inspection is that carcass flaws (separations, chunking, delaminations , voids, etc.)

disrupt one of the symmetric modes of tire vibration. An exciter is

placed at the center of the tread with one pick-up on each sidewall.

The system is tuned to a symmetric resonance mode about 400 Hz and the

tire rotated and examined for defects by observations of the change in

resonance amplitude and frequency. This research is covered extensively

in the paper "Resonance Tire Inspection for Motor Vehicle Inspection"

given at this symposium and will not be covered further here.

B. Brake Component Inspection

In the previous section on brake dynamometer development it was stated

that a visual inspection of brake condition is required as a supplement

to the performance test of a brake dynamometer. However, a visual

inspection of brake condition is time consuming and inappropriate in a high throughput, automated inspection. Therefore, a research effort

was begun in June 1974, to develop a "static" brake inspection technique,

equipment, and procedures to perform an inspection of brake components

without wheel removal. The objectives of the project are:

1) Conduct a systematic state-of-the-art survey into existing static

brake inspection systems, proposed designs, inspection criteria.

189
techniques, and related literature.

2) Determine basic performance objectives of static brake inspection

systems, alternatives, evaluation criteria/weighting requirements, test

methodology for evaluation of alternatives, and preliminary analysis of

potential approaches.

3) Analyze and evaluate the more promising approaches and determine

the optimum static brake inspection system.

A) Construct and evaluate two prototype static brake inspection

systems based on related useable portions of the evaluated equipment

and/or new design requirements as needed, and develop the related

inspection criteria and techniques.

5) Demonstrate and verify both the operational capabilities of the

equipment and the validity of the inspection criteria and techniques to

detect arid assess the condition of automotive braking systems in the

static state.

This project is still in process but some results are available. It was hoped that a technique such as ultrasonics could be used to determine

brake lining thickness in drum brakes by placing a transducer on the

drum directed radially inward toward the lining. It was also hoped that

similar advanced techniques could be used for the inspection of other

brake components. It appears, however, that the most promising approach

is a modification of the braking system to facilitate the use of mirrors,

fiberoptics, etc., in viewing the components; and component modifications which indicate when wear limits are reached. An example of the

latter area would be a blind hole drilled in the friction surface of a brake disc that would be worn away when the disc wear limit is reached.

The only state-of-the-art technique which appears to have application

is the use of gas chromotography for detecting brake fluid leakage.

III. Future Research Activities

Since most state MVI programs will use low throughput private garages,

gas stations, and dealerships for the inspecting authority, it is

appropriate and essential that techniques, procedures, and equipment

for this type of program be developed. In some cases the equipment

developed for automated inspection can be simplified for such use.

During the second quarter of calendar year 1975, two research projects

will be initiated to respectively develop manual brake inspection

techniques and to determine the requirements and state-of-the-art of

on-board vehicle sensors. The latter effort is being conducted to

indicate to vehicle manufacturers our interests in this area. On-board

sensors are viewed as a complement to MVI in terms of both easing the

inspection task and providing real-time safety critical outage information to the driver.

The objectives of the manual brake inspection research are to systematically investigate, develop, and verify objective, manual inspection

criteria (replacement) techniques, procedures, and equipment aids to

190
replace 1) dynamic brake testing and 2) existing subjective brake

inspection procedures. Results from this project are expected by the

end of 1976.

The objectives of the on-board sensor research are to assess the stateof-the-art and potential areas of future development of on-board vehicle

sensors and to derive the applicability of on-board vehicle sensors to

brakes, steering, suspension, tire, lighting, and signaling systems.

Results from this project are expected in mid-1976.

In the near future (FY 1976-77) , research will focus on developing or improving manual inspection techniques for the remaining vehicle systems

requiring inspection. This effort will be keyed at increasing the

effectiveness of MVI when implemented by licensed private garages, gas

stations, and dealerships. A minimum amount of low-cost equipment aids

will be developed and combined with refined and objective inspection

criteria. This will improve test accuracy and acceptance at both the

inspector and consumer levels.

In the years FY 1977-80, research will focus on developing automated,

high throughput inspection equipment for passenger car steering and

suspension systems. Work on identifying or developing inspection

techniques for trucks, buses, and motorcycles v/ill begin in the same

time period. It is difficult at this time to envision the results of

this effort since an WJl program for these vehicles has not been

developed. One possible approach might be self inspection by fleets

combined with sampling or random inspection by state authorities.

IV. Diagnostic Equipment Development

A philosophy of the research to date is that diagnostic capabilities

are included in inspection techniques and equipment if their inclusion

does not significantly increase the time/cost of inspection. In other

words, the primary determination of these techniques are go-no go

decisions. Of course, many inspections are basically diagnostic in

nature, such as the inspection of brake components. However, performance

tests tend not to be diagnostic. For example, steering system lash

inspection is not diagnostic.

The 1974 amendments to Title III of the "Motor Vehicle Information and

Cost Savings Act," P.L. 92-513, require the Department of Transportation

to conduct demonstration projects that will aid in the development and

evaluation of advanced inspection, analysis, and diagnostic equipment.

An assessment of the capabilities of small repair garages is also included in the requirements. In order to satisfy the provisions of the

act, as amended, a research program should be conducted to develop the

advanced equipment. The primary reason for this is that existing

equipment is not compatible with the high throughput, mass diagnosis

intent of the demonstrations and the Act. Existing equipment is designed

191
for use by garages, dealerships, and diagnostic centers with low or, at

most, medium throughput. Medium throughput can only be obtained with a labor intensive operation which increases the cost of inspection and

diagnosis radically. As an example, using today's equipment for mass

inspection results in an estim.ated 82 percent of total costs for labor

and labor overhead and 7 percent of total costs for equipment.

It is also known that existing equipment is not objective, complete, nor

accurate. Certain types of equipm.ent provide a measurement means but

interpretation is left to the diagnostician. Other types of equipment

make inappropriate tests or tests limited in range. Furthermore, the

lack of automation means that vehicle specifications applicable to

specific tests must be listed in reference books or sheets and used

for each test or diagnosis.

Research is needed, therefore, to develop advanced inspection, analysis,

and diagnostics equipm.ent. This equipment must be thorough, accurate,

complete, objective, reliable, and allow for high throughput, non-labor

intensive vehicle inspection and diagnosis. In this way the spirit and

letter of P.L. 92-513 will be met, and the basis will exist for

effective demonstrations of an advanced approach to the diagnosis and

repair problem.

192
DISCUSSION

R. W. Adamson, California Polytechnic State University : We started out our meeting this morning in connection with determining the

effectiveness of any test program. Are studies being made to come up

with the data that would permit you to know where the problem areas are?

L. H. Emery : Yes, there are 10 to 15 extensive accident investigation

programs under way throughout the United States where trained accident

investigation teams try to determine the causes of accidents; i.e.,

whether they were due to a component failure, driver error, or environment. Also there have been extensive research programs to

determine the safety status of the nation's vehicles. The results of

these programs indicate that approximately 5 to 7 percent of the

accidents are either caused by or influenced by component degradation

and catastrophic failure.

J. K. O'Connor, Consumer Product Safety Commission : You said that the

shock absorber test was not going to depend on new vehicle performance,

but simply on a change of performance between the beginning of the test

and the end of the test. Then I thought you said that's predicated on partially filled shock absorbers and the oil aerated. Suppose you had

no shock absorbers and just had the mass damping of the system, then

would you get a change?

L. H. Emery : No. We conducted a research program to look at the major

modes of shock absorber degradation and to look at the existing shock

absorber inspection equipment, the majority of which is produced and

used in Europe. It was determined that 99 percent of the shock

absorber failures are due to loss of fluid. We discovered that the

technique used by one of the existing inspection machines in Europe is

able to detect a loss of fluid due to a change in dampening as the

shock absorber is exercised. The loss of fluid encourages a quick

aeration of the fluid and dampening is lost. We think that loss of

fluid in shock absorbers is the thing to look for in a shock absorber

inspection machine, and there is an existing technique. However, there

are no existing machines suitable for MVI use.

J. K. O'Connor : If you lost all the fluid you wouldn't get the change.

L. H. Emery : That's true but, it would be obvious that the car didn't

have any dampening.

0. E. Compton, Northrop Corporation, Aircraft Division : Is a loss of

fluid recognizable by a visual means - by looking at a shock absorber

itself - or do you need a piece of diagnostic equipment?

193
L. H. Emery : I don't know that it is always recognizable. In any

case, for a high through-put type of inspection it is desirable to

minimize the labor involved. I am not recommending my machine over a visual inspection. Our objective was to look at the problem and

develop some technology.

19k
ON VEHICLE MOBILITY MEASUREMENT & RECORDING SYSTEM

F. K. Chin R. Watts

MVCT-Mai ntenance

U. S. Army Tank Automotive Com.

Warren, Michigan 48090

General American Transportation Corp.

General American Research Div.

7449 N. Natchez Ave.

Niles, Illinois 60648

ABSTRACT

A prime long term goal of the U. S. Army is to field maintenance-oriented

diagnostic equipment which will improve the reliability and reduce the

cost associated with keeping vehicles operational. An important part of

making diagnostic equipment viable is the establishment of base-line

levels on a well operating vehicle so an adequate automatic judgement of

the operational status of a vehicle under test can be made. This paper

describes an on-going U. S. Army Tank Automotive Command, Maintenance/

Product Assurance Directorate program directed at establishing such levels

for the M35 (Figure 1). The program uses technology previously developed

for the Ml 51 vehicle. The current work involves instrumenting an M35A2,

2-1/2 Ton Truck with on-board transducers, signal processing, and tape

recording equipment, and running the vehicle 20,000 miles with various

"seeded" and "unseeded" components in both idle and running modes. The

data will be computer analyzed to establish "good" and "bad" levels for

diagnostic reference purposes. In addition to the actual measurements

made and the test program outline, the needs and objectives of the user--

the Maintenance Directorate of TACOM--will be discussed in terms of how

the current program relates to the general diagnostic goals of the Army.

INTRODUCTION

Modern maintenance procedures make use of sophisticated instrumentation

in order to analyze vehicle performance for indications of component

failure, imminent failure, or need for adjustment. Often this analysis

is conducted with the vehicle idling in a maintenance facility. Since

it is desirable to minimize repair time, analysis time requirements are minimized. The resulting situation is one of sometimes performing a brief, indoor idle test in order to assess the integrity of a heavy duty

vehicle designed for extended use in severe environment. In order to

define or refine appropriate maintenance analysis procedures and failure

indicating threshold levels, supportive operational base-line data is re- quired to correlate the brief idle test data with mobility data obtained

over a wide variety of operating situations representative of the vehicle's full design environment.

The mobility testing a vehicle undergoes during the preproduction and production phases of its life-cycle is used to validate the vehicle's

195
performance capability. It is important to know during this testing,

whether a particular vehicle was subject to under-testing, over-testing,

or the testing desired because the ability of a vehicle to pass its performance tests depends on how well the stresses generated during testing

correlate with the stresses estimated during the vehicle design phase.

The above types of information, if available, can help maintenance people

who are responsible for keeping vehicles operational, lual ity assurance

personnel responsible for vehicle test implementation, and engineering

personnel responsible for vehicle design. Ultimately quantized mobility

information from vehicle performance tests will help insure optimal ve- hicle cost, life, and service.

A system (MO/MARS) has been developed for a data gathering and reduction

system which -will allow efficient generation and analysis of data for the

above applications. This MO/MARS is centered around a small, rugged instrumentation and recording system mounted on-board the vehicle under

test (Figure 2). The system operates unattended for prolonged periods of

time in the vehicle operational environment. The data acquired is stored

on tape in the vehicle until it can be carried to an off-board playback

and reduction station. In order to reduce data storage requirements as well as data reduction time, data is not stored continuously. As an integral element of the on-board system, a data processor analyzes critical

data for deviations from normal conditions or changes of state. When a deviation or change occurs, a recording trigger is generated which causes

a complete scan or sample of each channel to be recorded in a digital format on magnetic tape. In the event that one of these triggers does not occur in five minutes, a trigger is generated so that "normal" perfor- mance is recorded. After tape completion, it is removed and taken to a data reduction center for detailed analysis and correlation on a commercial computer.

TECHNICAL DISCUSSION

The MO/MARS concept was implemented with a composite of off-the-shelf and

custom hardware constructed as a network of subsystems. Individual subsystems must operate under varying constraints depending on their function, their physical location, and their relationship to other subsystems.

One of the more varied requirements is that imposed by the local environment. Transducers are fully exposed to rain, mud, snow, and ice as provided by nature as well as vehicle dynamics (e.g., splashing and submersion). The remainder of the on-board equipment is protected from direct

effects by an environmental case shown in Figure 3 with the front cover

removed. Mild shock and vibration as well as temperature extremes must

still be accommodated. Off-board systems are housed in the usual temperature and humidity-controlled computer environment. Details of the transduction scheme and processing electronics are presented in the following

sections

196
Transducers

The various transducers used to monitor the parameters, listed in Table

1, are subjected to the most severe environment. In general, transducers

are exposed to local shock, water, electrical noise, temperature, and

solid impediments encountered on the test course. As a result, all transducers operate over wide temperature ranges with minimal error. Transducers mounted beneath the vehicle body are waterproof, while those above

the body are splashproof. In order to reduce the effects of electrical

noise, all outputs are high level (±1 V, typical) and low impedance

typical). Modest shock/vibration tolerance as well as physical ruggedness are included as well. The following subsections discuss individual

transducer groups.

Pressure Transduction

The Robinson-Halpern pressure transducers selected use LVDT's. They were

selected for their good record of transduction for TACOM and railroad locomotive pressure monitoring. They also have a military prescribed calculated failure rate of 0.34 failures per million hours. Their rugged

construction has been qualified to specifications MIL-S-901 for high impact shock and MIL-STD-167 for vibration. The housing meets weatherproof and water-proof Class IV NEMA standards and is designed for Class

I, Division 1, Group D explosion-proof service. Operating temperature

range is: -65°F to > +165°F. These pressure transducers have quoted

accuracy capability to 0.15%.

MO/MARS recordable accuracy is dependent on the pressure monitoring

points. For example, differential pressure across an oil filter is measured as close to the inlet and outlet ports of the filter as is practicable to eliminate the influence of pressure drops or turbulence in

associated components such as hoses. The selection of sensing points was based on these considerations as well as those of accessibility, ease of

calibration, and protection from damage. Specific locations of the various pressure monitoring points are given in Table 1.

All five transducers are mounted on a contoured plate, shown in Figure 4,

which in turn is mounted on the left engine compartment, side cover. In this location, the transducers are protected from physical damage and ex- treme temperature as well as being accessible for bleeding and calibration. Transducers are connected to pressure monitoring points by various

adapters, fittings, and hoses. The hoses used on the project have a working pressure rating of 500 psi , a temperature rating of 300°F and are compounded of oil and fuel resistant synthetic rubber. Wherever possible,

suitable commercial fittings are used. Specially designed fittings are

as simple as possible and made to interface commercial fittings.

Temperature Transduction

The selection of temperature monitoring points is of utmost importance.

197
Temperature sensors are located so they are always submerged or surrounded by fluid which is not stagnant, and monitor the fluid at a known, critical point. This can be illustrated by considering the measurement of

coolant and oil temperatures. Coolers are used in both circuits, and

maximum or minimum temperatures of the circulating fluid could be measured

and related to normal operating temperatures. However, an analysis of

the relationship between the measured variable and the overall system re- sults in the best choice of sensing points. The main purpose of the en- gine coolant is to maintain cylinder wall temperatures well below 500°F

to prevent overheating and breakdown of the piston-cylinder lubrication

film. The system sensitivity to overheating is greater at the inlet port.

For the oil circuit, the same reasoning applies. In addition, the temperature of the oil is critical. Below 200°F, a properly refined oil

will not oxidize excessively, but oxidation becomes appreciable above

250°F. Therefore, knowing the maximum oil temperature is of value, and

the sensor is located at the inlet to the cooler.

All temperature measurement was accomplished with a GARD-developed transducer. It is an operational amplifier-augmented resistive bridge with one active element. The active element is a platinum resistance bulb.

A precision reference voltage is derived from a temperature-compensated

zener diode. The circuit output is approximately ±1 V @ O.lfi for 0°F to

300°F. The circuit itself is also designed to operate over the full temperature range. Typically, outgut voltage error due to circuit temperature was found to be within 0.3 F over the range 0°F to 300°F. The circuit is constructed on a 1.0" x 1.2" printed circuit board and housed in

a cylindrical, stainless steel case. Typical of this transducer installation is that for transmission oil temperature shown in Figure 5.

Speed. Transduction, Clutch Slip, Odometer Transduction Consideration

The speed transduction design has evolved from a sequence of theoretical

considerations and on-board experimental tests. It was decided that

speed would be measured by counting gear teeth per unit time. Some of

the initial design considerations were tachometers, encoders, electronic

gear tooth counters, or electro-mechanical counters possibly driven by

adaptive gearing or pulley systems. Electronic gear tooth counters were

found to be satisfactory in the M151A2 MO/MARS. Gears on the truck were

found for indicating the respective speeds with minimal retrofitting.

On-board examinations of axle and gear structures corroborated by TACOMsupplied vehicle drawings showed that the electronic gear tooth counters

could be satisfactorily applied for all required speed transduction. Vehicle speed is monitored by counting teeth of the rear axle ring gear.

Engine rpm is measured by counting fly wheel ring gear teeth. Clutch

slippage is a measurement that compares shaft speed at the input of the

clutch to that at the clutch output. Since shaft speed at the clutch input is already derived by the engine rpm transducer, it is only necessary

to monitor clutch output speed for the comparative measurement. A

198
transmission gear was selected whose speed relative to the engine is invariant with transmission gear selection including neutral.

Experience with the M151A2 MO/MARS indicated that a time varying magnetic

flux density change (dB/dt) sensitive transducer works well with magnetically permeable material, such as steel, which is used for all gears monitored. Experience and specifications indicated that gapping and alignment problems would be minimal with this transducer.

An Electro, 5/8" diameter, digital magnetic transducer was selected for

speed transduction. The probe is modified mechanically to facilitate

mounting and adjustment, and a standard JT connector was added. Mounting

and adjustment is accomplished by screwing the transducer body into an appropriately tapped hole and securing it with a locking nut. For en- gine speed, a probe monitors gear teeth through a modified inspection

port on the flywheel housing (Figure 6). The transmission gear is monitored from an accessory plate on the side of the transmission housing.

The rear axle ring gear is monitored from a top inspection plate on the rear axle housing.

Battery Voltage Transduction

The magnitude of the battery voltage is indicative of the condition or well-being of the electrical system. Further, the condition or identification of electrical equipment or accessories may be determined from a monitor's indication of their effect on battery voltage.

The transduction accuracy or reliability could be affected by the choice

of sensing point. Transient or steady state currents from electrical

equipment, if allowed to flow through the measurement circuit, could

grossly affect the monitor's reliability. Thus, the transducer is electrically tied directly to the battery posts with twisted pair wires to

eliminate electromagnetic interference, thereby obtaining the most minimal path possible for interfering currents in the measurement circuit.

Battery voltage is monitored by a GARD-designed instrumentation type input circuit. Tests of the characteristics of the voltage have shown that

spikes due to inductive switching and ripple due to generator charging

will be present and must be contended with. A combination of low pass

filters and surge protectors protect monitoring electronics from transient destruction while accurately measuring battery voltage.

Time/Date Transduction

To facilitate a time correlation of data, a precision reference oscillator

is used to generate time of day and date information in digital accumulators. The accumulators are kept in the self-powered monitor, thus time

is kept continually beginning with time zero at the start of the test

program. The time accumulator is quite similar to an electronic wristwatch. Low power, CMOS family of digital logic is implemented in the

199
monitor. Time of day is recorded as elapsed time since midnight in hours,

minutes, and seconds. Date is recorded- in a Julian-like calendar form as day of year.

Elapsed time is also sensed for recorder triggers. That is, if 5 minutes, ±1/2 minute, has elapsed since a recorder trigger, the recorder

accumulates a data record.

Tape Status

MO/MARS is designed to be a self-initializing and sustaining system re- quiring minimal interaction from operator or test supervisor. However,

because of the finite data capacity of the magnetic tape and the desire

to accumulate all meaningful data, the tape supply will require periodic

refreshing . .

An aid for evaluating tape supply is the tape status indicator. The tape

status indicator signals the driver when the tape has reached a predetermined data capacity short of full. The capacity level for signalling

refresh is internally programmable from 75% to 90%, with a final value

best determined empirically.

Data Handling

All on-board data processing and recording is handled by a network of

processing elements shown in Figures 7, 8. The processor assembly is the

princip-al control operating the recorder and accessing the monitor as required. It contains analog signal processing, digital signal processing, monitor interfacing, and recorder control. The monitor is unique

in MO/MARS since it has a self-contained source of power, i.e., its

battery. In combination with low-power CMOS logic, extended operation

is possible independent of the vehicle electrical system. Thus, the monitor is capable of generating and/or storing long term data, typically

date, time-of-day, distance (odometer), and recorder tape supply status.

It also uses the vehicle accessory switch to sequence MO/MARS on when the

vehicle is running. The recorder is charged with recording data on magnetic tape which will eventually be removed from the vehicle for data

reduction. Analog data channels interface directly with the recorder

which contains a signal multiplexer and an analog-to-digital converter

both under program control. The recorder also contains a wide variety

of operational clocks ranging in frequency from 1 MHz to 0.028 MHz which

are brought out for use in the processor. A controller within the re- corder coordinates all functions (internal and external) including the

actual writing of magnetic tape and electro-mechanical control of the

tape transport. Also contained in the processor, is the clutch slippage

detection and analysis circuitry. It operates in a separate mode independently of the other subsystems, although it is integrated with existing logic where compatible. Clutch slippage requirements are so demanding that the processor incorporates electronic FIFO memory to buffer

data for recording and then record data in a unique, variable word-length

200
pattern

Trigger Detection

The triggering events which initiate recording are presented in Table 2.

Most triggers are derived by comparing a signal with some preset threshold level. The level is bounded by a hysteresis band to minimize re- peated triggering when the signal level is relatively stable and at

approximately the threshold value. Both analog and digital threshold

plus hysteresis circuits are used. Analog circuits are implemented on

the input/output (I/O) cards with integrated circuit comparators on analog voltage levels. Triggers derived in this manner include all differential pressures and temperature. Digital circuits are implemented with

integrated circuit digital comparators and digital levels extended via

DIP switches. Digital triggers are derived for speed, time, and clutch

slippage. Each circuit (analog and digital), results in a trigger signal which is sent to a trigger handler. The trigger handler alerts the

controller to initiate a recording cycle, then formats the trigger information for entry as data. The format includes identification of the

triggering event as well as the status of all triggers. Since wheel

speed can trigger multiple levels, the level -to-level transition re- sulting in a trigger is uniquely identified and recorded. Instantaneous

clutch slippage data is recorded in a separate, distinct mode of operation.

Time/Date Processing

Both of these data are derived from a low-power oscillator operated as part of the monitor from the monitor battery. The oscillator will be

counted down to 1 Hz with standard CMOS logic. The 1 Hz signal drives a "seconds" counter which presets at 59 seconds. The seconds counter reset

also drives a minutes counter which resets at 59 minutes driving an hours

counter limited to 23 hours. The hours reset drives the day or date

counter which is programmably reset at 365 or 366 days. A higher frequency can be injected at any stage for the purpose of initializing the

clocks under manual control

Tape Status and Odometer Storage

The total number of records recorded on a tape will be used as a measure

of tape available or tape used. Since it is anticipated that multiple

operational periods will be stored on a given tape, it is necessary to

keep track of tape status even when MO/MARS power is off. Since the monitor is always powered, it is appropriate to include some form of lowpower memory within the monitor for maintaining the total -records count

between MO/MARS operations. The odometer or distance record has similar

data maintenance requirements and is also stored in the monitor.

201
Wheel Speed/Engi'ne Speed

These speeds are measured by counting pulses in the pulse trains derived

from sensing teeth on appropriate gears. These pulse trains enter

through I/O modules which serve to filter noise, isolate the transducer

lines from the processor network, and shift the signal to TTL logic

levels. The logic level pulses are then counted for a programmable counting period. The number remaining in the counter at the end of a counting

period is proportional to the average speed over the counting period.

The number is recorded as a count and converted to engineering units during data reduction

Clutch Slippage

The method of measuring clutch slippage involves detecting relative displacement of the two sides of the clutch. A nonrotating tooth sensor is

mounted to sense the passing of teeth on each gear. Tooth counters are

connecte-d to each sensor. When the clutch is engaged and rotated, the

gears are synchronized and the two counters count exactly together.

When there is some form of partial disengagement present, the two gears

do not rotate precisely together. They are said to slip. As a matter of

convention, the transmission-side of the clutch is the reference. The

procedure for measuring slippage consists of counting a fixed number of

teeth on the transmission side and comparing the number of teeth counted

on the engine side in the same time interval to that fixed number. For

example, start both counters initially cleared at the same instant. When

the transmission-side counter reaches 100, read the engine-side counter.

If it too reads 100, there was no slip. If it reads 110, then the en- gine-side rotated 10 teeth more than the transmission side.

In studying clutch slippage, it seems desirable to detect not only the

presence or absence of slippage, but nature of the slippage. Is it a smooth phenomena uniformly distributed over several revolutions? Or is

it irregular, occurring in some non-uniform, perhaps discontinuous manner?

To answer these questions, the data required must project high magnitude

sensitivity, coupled with precise location. The only readily-varied parameter available is the number of teeth included in the reference. As

the reference increases in size, sensitivity increases, but locational

accuracy decreases. Decreasing the reference leads to better location,

but less sensitivity.

The method chosen was to simultaneously measure slip with several different references.

The actual numbers of teeth available for counting are not as easily

handled as those in the above discussion. The engine-side gear has 138

while the transmission side must be observed through a compound gear

which appears to have 16.57 teeth. However, four distinct levels of ref- erence equal approximately to 1/16 rev, 1 rev, 8 rev, and 64 rev are used.

Triggers are based on bands about the no-slip reference for each level.

202
Four similar circuits for each level are implemented. The interaction of

the four simultaneously operating circuits is quite complex and is not

presented within this report. The four-level network forms a string of

data which includes trigger level and trigger location with respect to

the previous trigger. At no slip intervals, engine vehicle speeds are recorded as well as all the other normally measured parameters.

This amounts to a large amount of data relative to the recording rate of

the recorder. Thus, it is necessary to use a buffer memory within the

processor to permit data compaction and data speed averaging. A variable

word length, self-identifying data stream is used to make the system com- patible with the recorder.

'Data Buffers

The data buffers are used to format data prior to entry into the recorder.

All of the required digital data is shifted into the buffer from the various processing elements. After data is assembled in an appropriate form

for recording, the recorder control is notified that the data is ready

for transfer to the recorder. Then the recorder control transmits appropriate strobes to load the data through the recorder onto magnetic tape.

Control

Each major group of elements has some control all under command of the

main processor control. The monitor has adequate control to accomplish

timing, clock up-dating, and vehicle status sensing. The recorder con- , trol sequences the tape transport on, sequences the signal multiplexer,

generates appropriate control characters and coordinates the writing of

digital and analog data on magnetic tape. The master controller within

the processor coordinates the monitor and recorder through their respective controls in order to respond to triggers and process data.

Power System

All power used in the on-board system is taken from the vehicle's 24 VDC

electrical system. Isolation from vehicle ground is achieved by converting the 24 VDC to standard 120 VAC which is easily transformer isolated.

This DC to AC conversion was accomplished with a Topaz Model 250-GW

static inverter. The AC voltage was used to power the recorder directly.

Various precision DC voltages for transducers and the processor were produced in the Power Module shown in Figure 3. All DC voltages were produced with commercially available power supplies.

Data Recorder

The recorder used is a Metrodata Model 620A shown in Figure 3. The unit

has been modified to record in both the digital and analog data input

modes on all of its twenty channels. In the normal data mode, eleven

channels from transducers are analog, and the remaining nine are direct

205
digital from digital type transducers. The digital channels are formatted

so that actually twenty-eight channels of unique data are available. The

recorder also records all channels in direct digital in the instantaneous

clutch slip and the compression balance modes. All recording is in a fourtrack binary coded decimal (BCD) format on 1/4 inch magnetic tape housed

in an endless loop cartridge. Analog signals in the range of ±1 volt are

fed to the recorder where they are internally analog to digital converted.

The unit was chosen for its ruggedness and performs well. Recording time

is dependent on the event oriented parameters measured. Nominally over fourteen thousand records are recordable which provides a capacity of

weeks without requiring a fresh tape supply.

Data Reduction

The data was reduced at GARD on the GA 1830 computer. A metrodata model

622 tape reader was interfaced to the 1830 through the computer's I/O

channel. It was controlled with an interrupt driver assembly language

subroutine. The data reduction program was implemented with the GA 1830

Fortran IV subset. Magnetic tape cartridges recorded with the on-board

system are read with the tape reader under computer control. As the raw data enters the computer for processing, it is stored on dtsk files for

analysis. All data from tape is thereby directly accessible with normal

Fortran mainline programs and subroutines. Raw data is converted to

engineering units through the calibration data entered initially as case

data. Conversion is done before processing to eliminate errors due to

transduction non-linearity. Converted data is stored on a disk file for

eventual use in tables. The maximum and minimum values of each parameter

are determined in a straightforward manner. The averages, standard deviations and the maximum/minimum values for each parameter are printed as

a lata summary as shown in Figures 9, 10, & 11. Idle and operating

summaries are illustrated. A listing in engineering units of all data

acquired comprises the data listing shown in Figure 12.

Summary and Conclusions

A total system comprised of hardware and software has been designed, developed, and installed on an M35A2 cargo truck. Hardware consists of on- board transduction elements and associated processing and recording systems. Software consists of all Fortran and assembler level routines re- quired to read and analyze the data that is recorded on magnetic tape.

All measurement points are calibrated by traceable standards from the

point of transduction through the recorder. A continuing calibration

program shall be implemented. Data is provided for hot and cold idle and

motive vehicle operation. Data is also provided for clutch slip, com- pression balance, and engine power measurements. The vehicle, with the

MO/MARS system installed, is presently undergoing road testing over highway, secondary and cross country terrain. All measured parameters shall

be uniquely observable over the entire length of the test.

20h
Acknowledgment

The results presented are based on work sponsored by the United States

Army Tank Automotive Command, Warren, Michigan. The authors wish to

acknowledge the contribution of Messrs. N. F. Muelleman of CARD and B. Emerson and D. L. Gamache of TACOM to the design and development of the

MO/MARS system.

Key Word Index

Mobile Vehicle Testing - Transduction

Recorder

Magnetic Tape

On-Board

205
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206
Table 2 - TRIGGERING EVENTS

Parameter

1) Differential Pressure

a) Oil filter

b) Fuel filter

c) Air filter

2) Temperatiore; coolant, engine

•3) Speed

a) Engine

b) Wheel ( four speed ranges with

transitions identified) range

limits

k) Time

5) Instantaneous Clutch Slippage

Triggering Condition

over 12 psid + 2 psid

over 15 psid + 2 psid

under 27 in H^O + l^<fo over 225°F + 5°F

over 2500 RPM + 100 RPM

0, 2, 15, 30, 50 MPH

over 5 minutes since

previous trigger

over E rad/T rad, E and T

programmable

207
208
FIGURE 2 MO /mass CABINET IN PLACE

AND REAR CO'JmS ATTACHED

209

- FRONT
MO/MARS

MOBILITY MEASUREMENT AND RECORUtNG SiSTE

MODEL 0074

PROCUCT ASSUB/SNCE - MAINTENANCE OISECTORATES USA TACOM CONTRACT OAAgO?-?4-C 014) GENSRAl AMERICAN RESEARCH DIVISION Gf MHAl AMERICAN TRANSPORTATION COnPOHATION

FIGURE 3 CON'IROL AND INDICATOR PAKEL

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FIGURE 8 NETWORK SUBSYSTEMS BLOCK DIAGRAM

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DISCUSSION

D. N. Fry, Oak Ridge National Laboratory : Are you going to use this

data for design purposes or for maintenance purposes?

F, K. Chin : We see it right now as being for both.

D. N. Fry : Are you going to have an active program of evaluating this

data and scheduling maintenance?

F. K. Chin : We are going to perform normal maintenance for 10,000 ^ miles, and then nothing - just drive the truck into the ground.

R. Lenich, Caterpillar Tractor Company : Is there an indicator for the

driver to stop the truck in case there is a malfunction or is this

strictly for data acquisition?

F. K. Chin : Basically, it is for data acquisition.

R. Lenich : If a truck component was not operating properly, the driver

would not know it at that point.

F. K. Chin: No, he wouldn't.

220
VIDEC SfflP PROPULSION SYSTEM PERFORMANCE MONITOR*

Richard P. Wallace

Raytheon Company, Portsmouth, Rhode Island 02871

V^lliam L. McCarthy

McCarthy Marine & Ocean Engineering Associates

Great Neck, New York 11023

INTRODUCTION

The Vibration Analysis and Deviation Concept (VIDEC) is an effort directed

and sponsored by the US Maritime Administration (MARAD) to develop an effective performance monitoring system for main and auxiliary marine machinery

plants. The project encompasses, within three phases, concept development,

performance specification, design and fabrication, installation, . operation

and evaluation. It spans nearly five years and involves six major participants

from the maritime community.

Historically, the Deviation Concept was conceived by J.K. Salisbury under

contract to the Bailey Meter Company for applications in heat cycle analysis in

large shoreside power generating plants-'-. The VIDEC Phase I contract was a program sponsored by the US Maritime Administration's Office of Commercial

Development (MARAD-OCD) and performed by a multidisciplined team at the

State University of New York Maritime College (SUNYMC) with the purpose of

applying this concept to the maritime industry. This work was performed during

1971 and 1972 and resulted in the formulation of a set of mathematical, thermodynamic and vibration processing expressions which were designed for a computer-based realtime shipboard monitoring system^. A set of performance

specifications was also developed during Phase I for such a computer-based

system.

The Phase n effort was initiated in early 1972 with separate contract awards

to Raytheon Company and Ingalls Shipbuilding Division of Litton Industries for

the respective tasks of system integration and shipboard installation aboard a *Original version of this paper presented at meeting of Society of Naval Architects

and Marine Engineers, New England Section, at Portsmouth, R. I. , 24 January 1975.

1 Dickinson, C. E. , "A Method for Propulsion Plant Performance Evaluation for

Marine Application," IEEE Transactions on Industry Applications , Volume

IA-10, No. 2, March/April 1974.

2 Gleicher, N. , Kramer, A. R. , Mathieson, J. , and Pergament, S. , " The

Deviation Concept: A Tool for Preventive Maintenance of Marine Power

Plants," Marine Technology , October 1972.

221
newly constructed American President Lines' (APL) vessel. MARAD was

assisted in technical liaison and coordination by the National Maritime Research

Center in Kings Point, NY (NMRC-KP). Consultation was provided by SUNYMC

during the transition from Phase I through the Phase II effort. The culmination

of Phase II was the computerized real-time machinery monitoring and display

system installed on board the SS PRESIDENT JOHNSON in January 1974.

Finally, the Phase III portion of the VIDEO project includes those constituents which are required to fully evaluate the effectiveness of a system of this

magnitude and potential. The major participants under MARAD direction include

Raytheon, NMRC and APL. The objectives of Phase III include technical and

economic feasibility analysis of the VIDEO system in a two-year operational

evaluation.

This paper discusses the Phase II and Phase in program evolution with

interim findings one year after ship delivery.

SYSTEM DESCRIPTION

The Deviation Concept is simply a method of performance analysis of the

propulsion plant whereby representative parameters are closely watched for

departure from a reference figure of merit (Baseline). Continued observation of

these variances should lead to certain deductions beneficial in effecting maintenance scheduling, efficiency regulation, manning improvements and increase in

overall ship availability. A properly chosen set of measurement parameters can

provide performance analysis to determine:

Machinery deterioration trends v The contribution of performance degradation of an individual machine to

the overall plant efficiency

Predicted time to failure estimates.

The VIDEO system contains the essential ingredients to put into practice

this Deviation Concept on board the American President Lines' containership

SS PRESIDENT JOHNSON. The key to successfully implementing this concept is

determining just what a "deviation" is. The characteristics of the marine steam

propulsion plant vary considerably depending on sea state and other operating

conditions. The resulting variations of these normal operating ranges and conditions are numerous and as many different modes of variation exist as there are parameters to be monitored. Therefore, a major requirement of the VIDEC

system was to provide the ability to ensure highly repeatable measurements with

comparison to precise reference operating conditions. In order to facilitate

control of such an intricate task, as well as to execute realtime thermodynamic

222
and vibration processing algorithms, VIDEC was developed as an automated

digital computer-based system.

This process of establishing the reference values for all monitored parameters and providing the means for normalizing this data for operating conditions

has been designated "Baseline Mode" . With a propulsion plant running at an optimum performance level (presumably during the maiden voyage) a complete

data set is acquired, processed and stored for several (five) operating load

points of shaft horsepower spanning approximately 80 percent SHP through 100

percent SHP where the heat cycle remains relatively constant. When the five

load points have been stored, further processing takes place to produce coefficients of an equation which represents abestfit curve for each parameter. It is to this curve that subsequent data will be referenced.

The system analysis is partitioned into two distinct categories: Vibration

Analysis and Thermal Analysis.

Vibration Anal3^sis —Vibration analysis consists of maintaining surveillance over 25 pieces of rotating machinery plus the line shaft bearing for deviations in

vibration levels measured by 104 fixed accelerometer sensors. Each vibration

"channel" is examined over a broad spectral range of frequencies with 1/3

octave resolution totalling 30 bands. In addition, combinations of these bands

are assembled together to form regions (four regions per channel). Regions are

tailored to the specific natural vibration forces of each channel; i. e. , RPM,

blade count, electrical frequency. Thus for each of the 104 channels, there are 30 bands plus four regions which are processed for amplitude deviation from a

reference containing over 3500 separate baseline curves. During the baseline

procedure several RMS samples are measured for each point and, based on a

statistical computation, the baseline level arrived at includes the sample

variance and allows for a 99 percent probability factor.

The 30 bands have assigned upper "alarm" limits which if exceeded actually

initiate an audible/visual alarm with a printed description of the deviation. The

four re^ons have assigned upper limits also but for another reason. The

regions, being representative of the specific machinery excitation forces, are maintained for trending purposes. The upper limits for the regions are used for a reference to wiiich a time to alarm prediction is computed based on a least

squares curve fit of a collection of past and current measurements. This information can facilitate maintenance scheduling by making maximum use of

machinery history.

Thermal Analysis—Thermal analysis involves a determination of performance deviation for the main and auxiliary machines within the steam cycle. The

performance measurement is based on a set of 73 calculations called "macro"

225
parameters which are indicators of the condition of 17 different components within the propulsion plant. These calculations are based on the measured "micro"

values of 99 discrete parameters and 22 on/off monitors including eight different

types of measurements:

1) Temperature ' 5) RPM

2) Pressure - 6) Valve position

3) Flow rate 7) Kilowatts

4) Torque 8) On/Off

The reference or baseline for the thermal analysis is established in a manner similar to vibration and at the same time. There are 99 "micro" and 73

"macro" baseline curves produced to which subsequent data are compared and

the deviation recorded. Alarm limits (upper and lower) are assigned to each

macro parameter and, if exceeded, cause an audible and visual alarm and

printed description of all measured and calculated values for the respective plant

component (Figure 1). All thermal values (micro and macro) are retained for

trending whereby the data history is presented in graphic form.

In addition to the micro and macro values processed in the Thermal Analysis

portion of the system, a set of 25 special computations called "Dollar Deviations" are made to estimate the respective penalty associated with a degradation

FEED PUMP 2

PARAMETER DEVIATION

***54 TURB STEAMRATE 28.5 20.18294

***55 PUMP EPF .502 .26077

***56 WATER HP 264. 74.07727

57 RPM 4472. 115.97852

90 MN FD PUMP FD WTR FLOW RATE2 LBS/HR 179386. 120906.90625

91 PORT MIM FD PUMP SUCTI DIM PRESS PSIG 53.6 7.33070

92 PORT MN FD PUMP SUCTION TEMP DEC F 296. 27.28949

93 PORT MN FD PUMP DISCHARGE PRESS PSIG 1132. 80.60327

94 PORT MN FD PUMP DISCHARGE TEMP DEG F 301. 28.26068

95 MN FD PUMP TURB STM FLOW RATE LBS/HR 15000. 14335.70703

96 PORT MN FD PUMP RPM RPM 4472. 1665.66602

Thermal alarm deviations are presented on the line printer with all associated parameter values and

deviations from baseline. For each report all macro and micro parameters for the affected machine

are presented.

Figure 1. Typical Thermal Deviation Report

22h
of efficiency. The calculation appraises the total additional fuel consumption

effect contributed by each machine and the "dollar" deviation refers to a unit

value per barrel of fuel oil.

Once the Baseline Mode has been completed, the VIDEC system functionsautomatically hy completely scanning all data once per hour in an Operate Mode,

logging and alarming any deviation which exceeds set alarm limits. At the end of

the day a complete report of all parameters is printed for hard copy history.

Prior to each Operate Mode, the system exercises a thorough equipment calibration and self-test routine reporting any errors along with a fault isolation code.

This code represents the result of a systematic troubleshooting analysis performed by the computer, and when used with the technical manual describes the

most logical problem area with identification of the failed module (s).

Several additional modes of operation are available to an operator via the

console control panel to retrieve data over and above that which is printed

regularly.

These operator modes Include the following:

1) Calibrate Mode 4) Baseline Mode

2) Demand Mode 5) Self-Test Mode

3) Standby Mode 6) In- Port Mode.

Calibrate Mode—provides a repetitive readout, via cathode ray tube (CRT)

display, of a selected thermal channel in engineering units for the purpose of span adjustment and calibration of sensor signal conditioners.

Demand Mode—allows the operator to select, via keyboard, 10 special

request operations from a CRT-displayed menu. These requests Include

the following:

• Vibration trend graphic display of a four-region history over the past

24 hours or past 30 days on a selected channel (Figure 2).

• Thermal trend graphic display of any micro or macro parameter

history over the past 24 hours or past 30 days (Figure 3).

• An up-to-date elapsed running time count (hours) for each of 22

pieces of machinery .

• Automatic initiation of an analog tape recording of 13 preselected

vibration channels for use in off-line narrowband analysis.

• Graphic vibration display, 1/3 octave, frequency vs amplitude spectrum for a selected channel (Figure 4).

225
CHANNEL I LINE SHAFT BRG NO.l (FWDEND)

DAY I REGION TIME TO ALARM

HOURS

NSC > 900.0

NSC > 900.0

NSC > 900.0

HOUR 0

331.1

The vibration trending function uses a graphic representation of time versus vibration vwitbin each of four

regions for a specified sensor address. The regions displayed are those bounds preselected for each particular channel and include the total signal summation of all bands (groups) within the defined bounds. The

deviation presented is a ratio of the measured data to the baseline data. A time-to-alarm estimate is printed

to the right of each region plot and is based on a linear least-squares curve fit.

The operator options available include:

1) Trend by hour for 24 hours

a) Previous day

b) Present day

2) Trend by day for up to the last 30 days.

Figure 2. Typical Vibration Trends Presentation

226
THERMAL MICROPARAMETERS

DAY I r 120

-96

-72

-48

-24

•-0

rl30

-104

-78

-52

-26

>20

-16

-12

-8

•-0 s

•-0

HOUR 0

\ I I I Ti I

\ r

I 34567890 23

1 - CONDENSER WATER INLET TEMP DEG F

2 1 CONDENSER WATER OUTLET TEMP DEC F

3 \ CONDENSER CONDENSER PRESSURE PSIA

4 ^ CONDENSER TEMP MAIN COND DEG F

Thermal trends of multiple microparameters are available on a graphic representation of time versus thermal

values for four channels simultaneously. Included in the display are the legends with engineering units with

respective measured values taken at the indicated times.

The operator options available include:

1) Trend by hour for 24 hours

a) Previous day

b) Present day

2) Trend by day for the last 30 days. ^

Figure 3. Typical Thermal Trends (Multiple Microparameter) Presentations

227
60

DB

50 -

40 -

CHANNEL 99

PREPROCESSED DATA

AFT STEER PUMP MTR FHD BRG

RHT HD

57 9

30 -

20 -

10 -

0 - BAND 2 3 4 5 6 7 90 I 2345678 2 9 0 I 2 3 4 5 6 7 8

3

9 0

CNTR B L 6 7 9 1 1 1 2 3 3 4 6 7 9 1 1 1 2 3 3 4 6 7 9 1112 3

FREQ B P 0 5 6 2 5 9 4 0 8 7 0 5 6 2 5 9 4 0 8 7 0 5 6 2 5 9 4 0

CPM XIO XlOO XIOOO XIOOOO

An on-line graphic plot of vibration level versus frequency for any selected vibration channel is available. The amplitude level axis (vertical) is scaled in dB reference 1 millivolt RMS. The frequency axis (horizontal)

is segmented in 1/3 octave bands with the exception of the first two. These two bands represent broadband

and low pass (1.25 to 9 Hz) respectively. The frequency axis is labeled in unit of cycles-per-minute for direct RPM correlation. The assigned regions are shown at the top of the graph in tick marks.

Figure 4. Typical Vibration Channel Preprocessor Presentation

228
• Graphic vibration display, broadband amplitude vs time over a 10-

minute period for a selected channel.

• A printout of past 30-day record for all daily averages at end of the

current day.

Also available via the Demand Mode is another menu which can be

accessed for the purpose of changing thermal and vibration constants

stored in the computer memory; e.g. , alarm limits, region allocation,

thermodynamic constants, etc.

Standby Mode—when initiated, places the VIDEC system in an idle condition whereby no processing takes place.

Baseline Mode—allows entry to stored data at any time to reestablish a new reference if major overhaul or replacement of a machine takes place.

Self-Test Mode—allows initiation of the system diagnostics at any time in

addition to that which automatically takes place once per hour.

In-Port Mode—extends vibration surveillance to include the period when

rotating machinery remains in operation while the propulsion plant is

either running below 80 percent SHP or secured.

The system configuration consists of 13 Signal Acquisition Stations, 203

sensors, an engineroom console, two signal processing cabinets, ASR-35 teletype, and an analog tape recorder (Figures 5, 6 and 7).

The purpose of the Acquisition Stations is to consolidate those sensor cables

within a local area and route them via a single (multiple pair) cable to the signal

processing units. No processing takes place in the stations with the exception of

signal conditioning needed to convert some sensor output signals to a form suitable for reliable transmission over long distances.

A complete list of system sensors is included in the appendix. All of the 104

vibration sensors are of the accelerometer type. The thermal sensors include

various types, each chosen for a specific application. A description of these sensors follows:

Temperature : All channels—platinum Resistance Temperature Detectors

(RTD)

Pressure : All channels—capacitance element

Flowmeters ; • Condensate, steam— A pressure (orifice/nozzle) • Fuel oil, saltwater—turbine • Distillate—variable area

229
250
1

Ti

Figure 6. VIDEC Console

251
Figure 7. VIDEC Analog and Digital Processors

252
RPM:

• Feed pump—Magnetic pulse pickup

• Main shaft—Torductor

Valve Position ; All channels—Linear Variable Differential Transformer

(LVDT)

Kilowatt : All channels—Hall effect transducer (current transformer pickup).

The Signal Processing Units contain all of the analog scanning and preprocessing hardware, system control hardware, computer, disc memory unit,

digital cassette recorder and power supplies. This portion of the system functions under complete software control via a Raytheon 707 digital computer and

every hardware processing function is dependent on a computer program instruction. All of these programs reside on the disc memory and are "called up" to core memory when needed. The disc also serves to retain all historical and

baseline data. A cassette unit provides a means to load new program changes

and also record historical data from the disc for permanent retention.

The Console, located in the engineroom, contains the following equipments:

High speed line printer for logging of daily reports, alarm descriptions

and 30 day reports

CRT display and keyboard for presentation of graphic trends, parameter

values, demand request menus and operator communications

Hard copier to reproduce CRT presentation

Time of day clock which acts to control the system time-dependent functions

Control panel to allow selection of system modes.

Other units include an ASR-35 teletype used for baseline operation only, and an analog tape recorder to make recordings of unfiltered vibration data for offline narrowband analysis.

SYSTEM IMPLEMENTATION • VIDEO implementation. Phase II, called for hardware and software design,

fabrication and installation of a fully integrated system applying the system equations and performance specifications developed during Phase I. The primary

objective of Phase H was to produce a system which would evaluate the VIDEO

concept using present day technology with minimum operator intervention.

255
The principal considerations included:

Instrumentation data integrity

Maximum use of proven, off-the-shelf hardware

Equipment reliability

Ease of accessibility and repair

Ease in operator-system interface

Flexibility of operation, expansion, etc.

Rapid installation at minimum costs

System simulation test

Training. :

During the initial system definition period several modifications were made

to the VIDEC sensor specifications involving deletions and reassignments of

sensors, for reasons of optimization. The final system sensor list wiiich was

implemented is shown in the appendix. Other modifications to the system specification were made throughout the project development to improve operator

interface and increase data collection. During these periods of redefinition which

affected all participating parties, the technical coordination of NMRC was substantial and quite beneficial.

A proper selection of sensor and transmission techniques is paramount in

achieving accurate, stable, and reliable measurement data over an extended time

period. To this end the following actions were taken:

Numerous sensor manufacturers were surveyed in order to acquire sensors of proven reliability

Susceptibility to EMi/RFI was minimized by using integral signal conditioners on each sensor wherever possible

For those sensors requiring non-integral electronics, the cable distance

between primary element and signal conditioner was minimized by use of

the local acquisition stations

An all-encompassing grounding and shielding design standard was developed for the entire system to suppress external signals generated by shipboard machinery

A special software-controlled treatment of sampled data was employed to

eliminate noise transients.

23h
The application of commercial off-the-shelf hardware was a major goal for

the VIDEC program. This presented no significant problems. Equipment tradeoff studies had shown that for each function required, there were several candidates which, with only minor ruggedization, could perform satisfactorily within

the shipboard environment specified. The fact that the processing equipment was

to be installed in an air-conditioned space allowed usage of the ASR-35 teletype,

analog tape recorder and commercial vibration analyzer directly with only shock

and vibration isolation added. Both the 707 computer and disc bulk storage unit,

crucial to the system operation, were chosen specifically because they were

designed for a harsh shipboard environment. The engineroom console required

considerable attention with respect to temperature, humidity, dirt, vibration,

etc. The commercial equipments (i.e., line printer, CRT terminal, realtime

clock and hard copier) were repackaged to withstand the vibration and shock; oil

and moisture seals were placed on exposed switches and indicators; air circulation was provided around all heat dissipating equipment; cooling air was provided

at the filter A)lower inlet from a ventilation duct; and quick access to all electronics was made via slide-mounted pull-out drawers with latching handles.

The system was designed to provide complete "hands-off" operation for

normal watchkeeping functions, the basis being that, to be consistent with the

Deviation Concept, only degradation from baseline should require attention.

However, when a deviation causes an alarm, and a closer look at data is necessary, a simple operator interface is provided using a concise conversational

mode. The subject of operator interface was of concern from the outset.

Because of the prototype nature of the VIDEC system, there are numerous display types, system variables, and data printouts intended primarily for system

performance analysis and not necessarily useful to the engineroom operator.

The conversational type operator interface via CRT terminal was chosen as the

best means to implement system flexibility and at the same time provide access

to operator demand modes. Through a displayed menu, the operator may choose

one of the graphic trend displays, a vibration signature, or alter system parameters; e.g. , alarm limits, sensor range, higher heating value for fuel oil, etc.

System flexibility is inherent to the software-controlled nature of the VIDEC

which makes use of a powerful minicomputer software system.

A major concern associated with a system like VIDEC is how to thoroughly

test it before delivery. With the many modes, calculations, displays and parameter interrelations, the only practical method suitable was to develop a simulator

to provide a programmable representation of every system parameter. The

simulator hardware was developed and a test program prepared to test the system at the factory and again on board the ship as an installation checkout prior to

connecting actual sensors.

235
The simulator proved itself invaluable during factory test and also in the

training course which was held to familiarize the ship's engineering personnel

with the system. The training course included a mixture of theory, operation,

and hands-on working sessions. The attendees and lecturers included the ship's

Chief Engineer, First Assistant Engineer, Operations personnel and representatives from all of the participating agencies and firms.

INSTALLATION

As part of their contribution to the program, American President Lines

(APL) made the machinery plant of the SS PRESIDENT JOHNSON available for

integration with the VIDEO system. The vessel is the last of four PACESETTER

class container ships built for APL by Ingalls Shipbuilding Division of Litton

Industries, Pascagoula, Mississippi. She was delivered on 4 January 1974. She

is 680 feet long overall, displaces 22, 000 tons dwt, and has a maximum service

speed of 25 loiots. Her power plant consists of a cross -compounded single plane

steam turbine main engine and reduction gear set, two boilers and four stages of

feed heating. She is equipped with a GE Central Operating System (COS) for

propulsion control. The vessel is presently employed in APL's US East CoastWest Coast- Far East run. PROGRAM MANAGEMENT

In view of the great physical distances separating the parties involved in this

project and their varying operational philosophies, the coordination and management became a formidable task. The responsibility therefore was shared

between MARAD-OCD in Washington DC and the NMRC-KP. The CCD Program

Officer was responsible for the overall management of the project while NMRCKP was assigned certain technical review and coordination aspects. As the program moved into the fabrication and shipboard installation phase, the program

management function became critical and more demanding. The occurrence of

changes in design, delivery of critical items to the yard, and other last minute

events that seem to accompany a project of this nature became paramount as the

vessel neared completion. In many instances solutions were worked out with a verbal agreement. The cooperati_pn and involvement which was instilled in all

parties proved to be indispensable in achieving the system completion without any

major deviations in program schedule.

VESSEL DELIVERY SCHEDULES

The original schedule called for equipment delivery by January 1973 and

installation completion by June. Many long lead delivery items were involved

and procurement could not be initiated until ship piping design was completed and

256
these sensor specifications defined. However, the VIDEC installation contract

negotiations between MARAD and the shipbuilder were not complete until July

1972 and a specific hull was not defined until January 1973. The immediate

effects of these delays prevented the timely commencement of:

Specifying sensors for procurement

Development of interface specifications for shaft RPM and torque (supplied

via COS unit)

Defining sensor cable lengths for procurement

Defining cable lengths for cabinet interconnections

Finalization of software equations as affected by sensor specifications

Flowmeter orifice plate design and procurement.

A work-around schedule was implemented that minimized the effect of these

items on equipment delivery.

The system was designed for rapid installation so that equipment delivery

could take place at the last possible moment and not interfere with normal shipyard tasks. The installation plan called for: a) Early delivery of the acquisition

stations requiring shipyard wiring to terminals; b) connectorized cabinets with

the cables being made up in advance by the yard; and c) a parallel effort of sensor installation. System checkout was to consist of mounting of the cabinets,

plugging in the prefabricated cables, and repeating the simulator test previously run in the factory. In this manner the equipment checkout could proceed without

the need for all sensors to be installed or the steam plant to be fired up. All

went well with the exception that the simulation could not be accomplished. The

feverish activity in the engineroom prohibited the complete assembly of the console for an extended period of time. There were two 12 -hour shifts working due

to the tight delivery schedule. The CRT terminal and control panel turret, if

left assembled, would have been damaged. Also, the disc unit was damaged

during installation handling and the full program loading could not be implemented.

During the fabrication and installation phase, there were other activities of

interest taking place. To better define the signal levels anticipated and assist in

choosing exact placements for vibration sensors on typical machines, early in

the program a portable instrumentation package was taken on a sister ship, the

Farrell Lines' SS AUSTRAL ENVOY. The equipment included accelerometers,

the necessary amplifiers, and a tape recorder. Vibration data vere recorded

from several machines in various locations and the tape played back through the

in-house VIDEC system for analysis and verification.

257
All equipments underwent a 40-day (24 hour/day) burn-in period in order to minimize failures due to infant mortality. This burn-in applied to the entire

system including those electronic signal conditioners which were delivered to the

ship directly from the vendors. The VIDEC system was subject to US Coast

Guard and American Bureau of Shipping approval. Special Coast Guard approval

was extended for the use of a connectorized installation and unarmored low noise

vibration Triax cable.

The installation experience identified several considerations applicable to

future systems of this nature. The most severe conditions encountered by the

VIDEC system occurred during handling in the shipyard installation phase. It is

felt that shipboard simulation is the ideal method for installation checkout. Were

it not for the various difficulties described earlier, a very rapid and effective

system checkout would have been accomplished. The placement of the console in an open area on the main engineroom deck probably subjected it to more potential

damage than if it were an integral part of the engineroom console complement.

Temporary protection during this installation phase should be provided for all

equipment subject to physical damage. The disc unit, as an operational device,

running at its normal speed, is capable of withstanding large shock and vibration

conditions. However, during installation and handling it becomes more vulnerable as the sensitive pickup heads are resting on the disc platter. Special equipment such as this should be shipped separately from the main cabinets and

handled with special care. EARLY DESIGN CONSIDERATIONS AND RESTRICTIONS

It has been the general policy of MARAD-OCD during early negotiations with

ship operators, for the shipboard installation and operation of a prototype system, to ensure that a given system would in no way impact design, development,

construction, or operation of the vessel. Each system must incorporate the

ability to be quickly isolated from the particular subsystem being monitored or

controlled or must be designed so that its function is totally independent of actual

vessel operation. There was also an agreement with the ship owner which called

for equipment removal if the system proved unsatisfactory. It is within this

basic framework that Raytheon's application of Phase I results to the propulsion

plant of the SS PRESIDENT JOHNSON was undertaken. All of the VIDEO'S

instrumentation and therefore, all of its signal inputs were completely independent of existing sensors except for torque and RPM signals which were supplied

via COS.

These ground rules naturally created a situation where redundant instrumentation was required. VIDEC instrumentation duplicates and supplements the

COS sensor configuration for major engineroom machinery components. Other

258
aspects of VIDEC's design and installation were also impacted by these considerations. Orifice design and installation is a good example. Proper operation

of an orifice or flow nozzle for mass flow determination requires that sufficient

straight pipe be available both upstream and downstream. These lengths generally are based on the expected pressure drop across the orifice, steam line

pressure, pipe diameter, and other factors. Those familiar with marine power

plant design know that relatively long straight runs of high pressure steam piping are at best uncommon on ships due to space, expansion, and other considerations. Therefore, situations arose where the unavailability of straigjit pipe runs

and significant pressure drops across an orifice plate made flow measurement

unacceptable. Superheated steam flow rates from the port and starboard boilers

and steam flow to the main engine are examples. These signals are critical to the thermal analysis of the boilers and turbine set. By relocating certain flow

transmitters and making use of VIDEC's computer software flexibility to insert a mass flow summation to derive these critical values, the resulting elimination

of these orifice plates had little impact on the thermal analysis portion of the

system.

Another critical area for design consideration was cable length between

various system components. Integrity of signal transmission from sensors to

data processing components to display console was a major concern in determining maximum cable lengths. Excessive runs could cause signal degradation

and/or excessive noise pickup. Although certain system components were

located outside the engine spaces their location was limited due to cable length.

Generally, the course taken throughout system design and installation was one of

altering VIDEC to fit the ship rather than attempting to alter the ship to fit . VIDEC, with minimum effect on the resulting data.

Integration of a complex electronic system with a newly built vessel is

certain to impact the contractual guarantee of the ship's construction. VIDEC

was no exception. The 104 vibration sensors, for best results, should have been

attached directly to the various machinery by drilling and tapping holes in the

casings and attaching the accelerometers directly with cap screws. However,

this technique was found to be unacceptable as the drilling and tapping of

machinery casings constitute an alteration to the equipment and therefore, would

negate the warranty on these machines. The initial solution consisted of attaching drilled and tapped stainless steel mounting pads to the machinery with high

strength and high temperature epoxy. The vibration sensors were then secured

to these pads with cap screws. With the end of the six-month warranty period,

these sensors are now being attached directly to the machinery.

Inclusion of the VIDEC installation on board the new construction vessel

brought to view a unique situation. The VIDEC system, being an additional and

259
highly sensitive fault detection instrument, could significantly increase the number of initial machinery faults not normally detected within the ship's warranty

period. If utilized in this manner, the VIDEC system could affect warranty

liability. A settlement was reached in which the owner agreed not to use VIDEC

data for warranty purposes during the guarantee period.

SYSTEM OPERATION, VOYAGES 1-4 . , A series of management decisions made late in the vessel's construction

schedule affected the initial checkout and operation of VIDEC. In mid-December

1973 the ship owner requested delivery of the vessel as soon as practicable. In an effort to meet this request the shipbuilder assigned every available worker in

all trades to this vessel. In keeping with the ground rules discussed earlier for

the implementation of prototype shipboard hardware systems, virtually all work

on the VIDEC installation was stopped as all personnel working on VIDEC were

reassigned to other ship systems. VIDEC was not critical to vessel operation

and in no way could impact delivery schedules or schedule changes. Thus plans

for initial system lightoff, sensor checks, etc. , planned for s^a trials had to be

modified. When the ship departed Pascagoula on 5 January 1974, VIDEC

installation was partially completed with system startup, checkout, and calibration still remaining to be performed. ; Voyages 1 and 2 saw the completion of the system installation and initial

operation at sea. Items completed consisted of the sensor and signal conditioner

installation, pressure and differential pressure sensor taps into the piping, welding of various high pressure sensor flange adapters, and correction of installation faults. Fortunately, support personnel on board during this period, through

jury rigging and part swapping, were able to bring the system to an operational

status. Data processing, equipment installation hookup, and checkout went

smoothly except for two instances. As previously mentioned, the rotating disc

storage device was damaged during shipment or installation. When the data processing equipment sub-loop was energized, the disc would not function and had to be removed and shipped back to the manufacturer for repairs. By loading a temporary program into core memory, checkout of signal continuity from sensor

to CPU could continue until the disc was reinstalled. The second hardware fail- ure in the data processing sub-loop was the programmable gain amplifier located

before the 1/3 octave spectrum analyzer. This component was taken back to the

plant, repaired and reinstalled in a matter of a few days. Additionally, although

not a hardware failure, the late arrival of the cassette tape unit presented some

difficulty in system debugging. The flexibility that this device provides for

troubleshooting, system modification and data collection is invaluable.

2^+0
Prior to loading the data base or "Baseline", a thorough check of all 203

vibration and thermal channels was made. Calibration was performed on those sensors that required it. The majority of sensors had been factory calibrated

prior to delivery to the yard. Thermal sensor readings were cross-referenced

with local instrument and COS remote readings whenever possible as a check for

accuracy and repeatability. The following is a description of the actual procedure for baseline loading performed on 7-8 March 1974. It is typical of the

baselines loaded prior to and after this date.

The procedure for loading baseline is a simple one. However, complete

baseline involves a considerable amount of time. The three baselines loaded

during voyage 1 averaged 27 to 30 hours in length. An initial baseline is taken

for all sensors whether the components they monitor are on line or not. Data is

gathered at five operating points (100, 95, 90, 85 and 80 percent SHP). At the

end of the final run a curve fit is performed. During this curve fit, the redundant main and machinery components are transferred. At the end of the first curve fit, a baseline of the redundant equipment is performed as above. The

curve fit is repeated and at the end of this curve fit the system is ready for

normal operation. Each run, with all components included, required four hours

to complete. Of this time, vibration data gathering and processing took about 3

hours and 45 minutes. Thermal data processing required only 15 minutes.

Initially it was felt that one hour between runs was required to let the plant

stabilize at each new power level. This was especially important for thermal

data. However, this hour was not needed. Since vibration data was gathered

first, the plant had already run at a steady load for 3-3/4 hours. Ten hours

were cut from the time required for a full baseline by eliminating this one hour

warmup at each power level. Table 1 describes the baseline format followed for

the baseline taken on 7-8 March 1974.

From Table 1 it can be seen that a considerable amount of time must be

allotted for baseline operations. Although baseline could have been performed by

2 February 1974, vessel schedule and operational considerations took priority.

Loss of data due to main power frequency and voltage fluctuations caused by a turbogenerator governor malfunction in one instance and by VIDEO operator error in another instance made it necessary to acquire two additional baseline

runs. Although neither of these difficulties has recurred, an investigation into

the need for an uninterruptable power source (UPS) is underway and modifications

to the software have been implemented to prevent similar operator error.

OPERATION, VOYAGES 2-4

A major factor which affected both the vibration and thermal subsystem was

that, due to the energy shortage, the ship's operating speed was reduced to 20

2kl
Table 1. Baseline Loading Procedure 7-8 March 1974

All Channels

Run No.

SHP

(Meter)

1st STG Press.

(HP Turbine)

Start Complete

5 28, 500 370 psig 1510 (3/7) 1915

4 27, 100 350 psig 1920 2320

3 25,600 330 psig 2330 0435 (3/8)

2 24, 200 310 psig 0445 0830

1 22,800 290 psig 0840 1230

. Curve Fit 1 1230-1330

Redundant Component

Update

1 22, 800 290 psig 1335 142Q

2 24,200 310 psig 1425 1510

3 25,600 330 psig 1515 1600

4 27,100 360 psig 1700 1745

5 28, 500 370 psig 1755 1840

Curve Fit 2 1840-1940

knots which corresponds to approximately 75 percent SHP load. This meant that

the VIDEC system would seldom function in a normal operating mode (automatically cutting out below 80 percent SHP). Therefore, the system was placed

in In- Port mode, collecting vibration data only.

It was not until the second voyage (19 March to 9 June) that data of any con- sequence was obtained. A preliminary review of this first data set showed that

there were several questionable areas requiring investigation. The vibration

analysis data revealed a high number of false alarms and the thermxal data was

sparse.

Prior to voyage 3 the ship*s engineering officers were occupied with the

problems associated with new vessel adjustment. During this period there was

little confidence inspired due to the high false alarm rate and minimal thermal

2h2
data available for use. Following consultation, a decision was made to extend

the lower limit for the Operate mode to 70 percent SHP where it was felt that the

plant operating conditions would still be fairly stable.

Prior to voyage 4, both software and hardware modifications were incorporated. The 70 percent SHP mode change proved to be instrumental not only in

permitting collection of thermal data but also in drastically reducing vibration

false alarms. There was no baseline taken below 80 percent SHP due to data

storage limitations and it was decided to use the 80 percent load data as a refer- ence for all In- Port mode conditions. This proved to be erroneous for variable

speed machinery where the vibration signature changes with speed and contributed greatly to the false alarms observed. Efforts are under way at this time to

investigate the possible addition of a separate In- Port baseline reference below

70 percent SHP. During voyage number 4 (22 August to 1 November), the Chief

Engineer was able to become more involved with the system and contributed

valuable criticism defining potential benefits as well as system weak points.

During these first voyages, the VIDEC system has been supported with one

and two engineers full time. This effort has been necessary due to the many

problems involved with incomplete installation, debugging, improvements and

unavailability of ship's engineering force due to their involvement in new vessel

operation. There was a contractual arrangement with APL during this period

for MARAD and Raytheon to supply support until operating personnel were in a

position to assume responsibility for the system. VIDEC has reached a point in

its development where this full-time support should no longer be needed and the

intent at this time is to turn over operation to the ship's engineering officers

during voyage 6, scheduled to begin 5 February.

FINDINGS TO DATE

It is premature to report on overall system performance analysis. However, several findings have been identified at this point in the program. These

findings have been determined from the data collected, system reports, and

discussions with shipboard personnel.

The ability to make system revisions, modifications, etc. , has been facilitated through the inherent flexibility of this modular system being completely

software-controlled. The modifications incorporated would not have been

possible in a hard-wired system without major rework. The advantages for having

a software-controlled design for a first of a kind program are rather obvious.

However, other benefits of this flexibility have become apparent with the ease

with which operational changes may be made, such as sensor re scaling, demand

display requests, thermal parameter changes, rescheduling of events and the

addition of channels.

2.1+3
There is a definite impact on the data collected from the engineroom due to

shipboard operating conditions such as displacement, trim, sea state and shallow

water squat. These conditions affect both vibration and thermal measurements.

Frequent monitoring of such data has revealed periodic variances in vibration

levels and pressures related to the rolling of the ship and impact during heavy

seas.

Sensor relocations, rescaling and equation modifications became necessary

as a result of last-minute ship design changes and evaluation of the first data set. Owing to the flexibility within VIDEC, this trimming of the measurement system

to the ship was made possible.

System maintenance has not posed significant problems thus far and appears

to be well within the capability of the ship's engineering officers. This characteristic is very important and is facilitated by the automatic system self-test,

modular design, software-controlled hardware functions, hardware accessibility,

available diagnostics and realtime sensor display features such as calibrate mode

and vibration preprocessor display. *

The VIDEC system configuration is not the optimum from an operator's

standpoint. Much of the data displayed is intended for further analysis and does

not provide immediate answers as to what the machinery problems are. In order

to better serve as a performance monitoring system, improvements will have to

be made in this area to display more useful information for the machinery

problems which occur. The continuous operation of a computer-based monitoring system is proving

to be a highly practical concept with respect to reliability. The most sophisticated components of the system (i.e. , computer, disc, digital processing and

display equipment) have been the most reliable elements of the system. Figure 8

shows the distribution of system failures. To further qualify the chart, 20 percent of the failures were caused during the shipyard installation phase as a

result of miswires or handling, including the single disc failure. All of the

failures indicated under the "digital processing "/'clock and control" and "display

subsystem" were caused by loss of cooling air at the engineroom console. The

air duct installed for the purpose of directing outside air to the console blower

intake was inadvertently cut off.

Investigation into the cause of the failures which were experienced resulted

in several determinations.

Five of the sensor failures indicated constitute the same component, a

turbine flow meter magnetic pickup probe. Vendor analysis of the failed parts

revealed a discrepancy in the manufacturing process which was subsequently

corrected. . x

2kh
CO

LUD

O

z

10

9

8

7

6

5

4

3

2

1

0

a. SENSORS

b. SIG COND

c. ANALOG PROC

d. DIGITAL PROC

e. COMPUTER

f. DISK

g. PERIPHERALS

h. DISPLAY SUBSYSTEM

i. CLOCK & CONTROL

If: FAILURE OCCURRENCES SHADED REPRESENT INSTALLATION,

INFANT MORTALITY AND OPERATOR ERROR PROBLEMS.

Figure 8. VIDEC Failure Distribution

The turbine type flow meter used for measuring the mass flow rate of

circulating water outlet of the main condenser was found to be susceptible to being jammed with foreign matter. This type of sensor seems to be unsuitable

for the application.

Two of the signal conditioner failures which occurred were traced directly

to the operating temperature environment. The actual ambient temperature

experienced was greater than that expected. Once relocated, these units never

failed again.

VIDEC YEAR II The continuing effort with the VIDEC program for the next year is concentrated on evaluation with the objective being a qualitative determination of both

technical feasibility and economic value. The basis for this evaluation is an

objective analysis of data. The data includes system outputs, machinery logs,

deck logs, operations cost data (from the PRESIDENT JOHNSON as well as

sister ships) and evaluations by shipboard personnel. A common failing usually

associated with programs of this nature is that the large volumes of data

collected surpass the ability to analyze it. The VIDEC Phase III program was

designed to handle vast quantities of data. The entire set of system parameters
needed for evaluation is recorded on digital cassettes as part of the normal

VIDEC functions. Each cassette contains a complete set of data for two days of

operation. Machinery log information (repairs, preventive maintenance,

chemical water analysis, fuel oil characteristics, etc.) and deck log information

(sea state, draft, speed, etc. ) are recorded daily on prefermatted forms.

Retrieved once per voyage, the tapes and forms are merged in a chronological

format on computer tape reels via a sorting process. Hard copy reports and

printouts serve only as reference material if needed. Cost information including

operating, manning, repairs, etc. , will also be entered in a similar manner

where recall and analysis are accomplished under the control of a large data

processing system.

The evaluation process includes correlation of data to determine:

comparison of short term vs long term trends

validity of system failure prediction

effect of VIDEC-induced plant adjustments on overall fuel consumption

effect of ship operating conditions on plant efficiency

thermal/vibration deviation correlation

most cost effective plant performance indicators

accuracy of steam plant performance calculations

vibration failure modes for various machines.

The Phase III program is a well-coordinated effort under the direction of

MARAD with direct involvement by NMRC, Raytheon, and APL. In addition,

several notable specialists are assisting in the areas of thermodynamics,

machinery vibration, and economic analysis.

SYSTEM FUTURE

VIDEC is an integral part of MARAD-OCD's Unmanned Machinery Space

Development Program. It is a steppingstone in the development of an automated

closed loop monitoring and control system for engineroom applications suitable

for adaption to all types of vessels and power plants. At the end of FY '76 an optimum condition and performance monitoring system will be defined incorporating all of the desirable concepts in VIDEC. Once the optimum monitoring

system has been configured from the evaluation along with other inputs, development of a closed loop control system can be continued. Additionally, during this

period, data generated by VIDEC is made available to other related ongoing

MARAD-OCD R&D programs, such as the Integrated Ship System (ESS),

2k6
specifically as it applies to condition and performance monitoring areas. This is

done in accordance with MARAD's policy of cross-fertilization between related

R&D programs and to prevent duplication of effort. Finally, VIDEC will be

evaluated in a stand-alone aspect as a condition and performance monitoring

system from which a standard specification for such systems can be developed

for inclusion in specifications for future MAHAD-subsidized vessel construction.

Based on discussions with a number of ship operators to date, we believe

that there is a definite and increasing need aboard modern ships for a system

capable of reliable, automatic continuous monitoring of machinery status and

condition. The primary interest of these ship operators, at this time, is the

reduction of vessel downtime. The capability to detect imminent failures, to accurately diagnose the cause of machinery degradation and to predict future

deterioration and failures through trend analysis of monitored data will all contribute to reducing vessel downtime. Therefore, Raytheon is committed to the

design of software-oriented, modular monitoring systems employing the methods

and techniques utilized in the implementation of VIDEC.

By using digital microprocessor technology and modular architecture the

scope of such systems can be configured to the particular needs of the vessel's

machinery plant and the owner's budget, and readily modified or expanded as the

need arises. It is fully expected that the ultimate results of the VIDEC operational evaluation will demonstrate the usefulness of such monitoring and diagnostic systems.

CONCLUSIONS AND RECOMMENDATIONS

During the first year of operation, problems with the data processing and

display hardware were very minor. Sensor heat failures made up most

of the component failures.

The system software functioned very reliably; only minor changes were

required.

The operation and maintenance of this system is not beyond the capability

of responsible operating marine engineers.

From the experience to date, it would appear that the shipboard installation and operation of a high powered process control minicomputer and a

sophisticated software package are feasible.

From initial inspection of the vibration levels taken from the three baselines loaded during the first three months of operation, vibration appears

to be closely related to draft, displacement, sea state, and wind as well

as shaft horsepower. Other operating phenomena, such as squat that

2^7
occurs in shallow water passages, also appear to have an influence on

vibration levels.

Judicious equipment selection and location of key components in environmentally controlled spaces has significantly reduced casualties caused by

the harsh seagoing environment.

The 40-day burn-in period for all system data processing and display

components, a detailed system simulation to debug VIDEC software, and

the inclusion of a sophisticated self-test routine contributed greatly in

minimizing failures and problems encountered during operation.

Vibration failure detection is capable of detecting failures that occur from

actual physical changes within a component; e.g., when a balance weight

in a forced draft fan impeller flew off and when a feed pump packing

retainer ring backed out of its housing.

Improved system displays are required to present machinery diagnostic

data in a more suitable form for immediate operator evaluation.

BIBLIOGRAPHY

1) Lundgard, B. , "The Relationship Between Machinery Vibratipn Levels

and Machinery Deterioration and Failures, " Marine Technology , January

1973.

2) McCarthy, W. L. , "VIDEC, the First Six Months," NMRC-KP-132, July

1974.

3) VIDEC Training Course Manual, Raytheon Company, Submarine Signal

Division, Portsmouth, Rhode Island, September 1973.

APPENDIX

Vibration Sensor List

Thermal Micro and Macro List

Operator Demand Requests

Operator Parameter Update List

Adjustable Thermal Constants.

21+8

/
VIBRATION SENSOR LIST

LHAiN.Nh L

,\ UMrsh K

SENSOR

LOCATION

ohlNoi i iVi 1 1

1 • Line Shaft Brg No. 1 (FWD End) Radial

2 Line Shaft Brg No. 1 (AFT End) Radial

3 Line Shaft Brg No. 2 (Top End) Radial

4 Line Shaft Brg No. 2 (Side End) Radial

5 Line Shaft Brg No. 3 (Top End) Radial

6 Line Shaft Brg No . 3 (Side End) Radial

7 Port L.O. Serv Pump Radial

Motor Upper Brg

8 Port L.O. Serv Pump Radial

Motor Lower Brg

9 HP Turbine 1st Red Pin FWD Brg Radial

10 HP Turbine 1st Red Pin AFT Brg Radial

11 HP Turbine 1st Red Gear FWD Brg Radial

12 HP Turbine 1st Red Gear AFT Brg Radial

13 HP Turbine 2nd Red Pin AFT Brg Radial

14 LP Turbine 1st Red Pin FWD Brg Radial

15 LP Turbine 1st Red Pin AFT Brg Radial

16 LP Turbine 1st Red Gear FWD Brg Rad ia

17 LP Turbine 1st Red Gear AFT Brg Radial

18 LP Turbine 2nd Red Pin AFT Brg Radial

19 Line Shaft Thrust Brg Radial

20 HP Turbine FWD Brg Radial

21 HP Turbine AFT Brg Radial

22 LP Turbine FWD Brg Radial

23 LP Turbine Aft Brg Radial

24 Stbd L.O. Serv Pump Radial

Motor Upper Brg

25 Stbd L.O. Serv Pump Radial

Motor Lower Brg

26 Stbd L.O. Serv Pump Brgs Radial

27 Ma i n C ir c Pump Motor Upper Brg Radial

28 Ma in Circ Pump Motor Lower Brg Radial

29 Main Circ Pump Brg Upper Radial

30 Main Circ Pump Brg Lower Axial

31 STBD Cond Pump Motor Upper Brg Radial

32 STBD Cond Pump Motor Lower Brg Radial

33 STBD Cond Pump Brgs Radial

34 STBD Cond Pump Brgs Axial

3 5 Port Cond Pump Motor Upper Brg Radial

36 Port Cond Pump Motor Lower Brg Radial

37 Port Cond Pump Brgs Radial

38 Port Cond Pump Brgs Axia 1 39 SSTG Turbine FWD Brg Radial

40 SSTG Turbine AFT Brg Rad ia 1

2k9
VIBRATION SENSOR LIST (Cont)

CHANNEL SENSOR SENSITIVITY

NUMBER LOCATION

A 1 SS 1 b Pinion AFT Brg Radial

A 1 D D D . D . 5 S. W. Scrv Pump Radial

Mot 01 Upper Brg

A 1 SS 1 b Gear AFT Brg Radial

A A 4 4 SSTG AFT Brg : ., Radial

A C 4 b Engine FWD Brg

Engine AFT Brg

Radial

/I A 4 0

c D r\ Radia

/I 7 4 / C "D T"\ AFT Brg Radial

/I Q 4 o B . B . Q S. W. Serv Pump Radial

Motor Lower Brg

A Q 4 y B . B . ^ S. W. Serv Pump Brgs Radial

o U

o r> 1^ S 1 BD Main Feed Pump FRD Brg Radial

b i STBD Ma in Feed Pump AFT Brg Radial

b Z STBD Ma in Feed Pump Tlirust Brg Radia

b o B . B . 5 S. W. Feed Pump Brgs Ax i a 1 b 4 Port Ma in Feed Pump FWD Brg Radial

55 Port Ma in Feed Pump AFT Brg Radial

56 Port Ma in Feed Pump Thrust Brg Radial

57 Port Feed Pump Motor FWD Brg Radial

58 Port Feed Pump Motor AFT Brg Radial

59 Port Feed Pump FWD Brg Radial

60 Port Feed Pump AFT Brg Radial

61 STBD F. D . Blower Motor STBD Brg Radial

62 STBD F. D . Blower Motor Port Brg Radial

63 STBD F. D . Blower STBD Shaft Brg Radial

64 STBD F. D . Blower Port Shaft Brg Radial

65 Port F. D . Blower Motor Port Brg Radial

66 Port F. D . Blower Motor STBD Brg Radial

6 7 Port F. D . Blower Port Shaft Brg Radial

O 68 Port F. D . Blower STBD Shaft Brg Radial

69 STBD F. 0 . Serv Pump Rad ial

Mo tor Upper Brg

7 n QTR n F. 0 . Serv Pump Racl 1 al

Motor Lower Brg

71 STBD F. 0 . Serv Pump Brgs Radial

72 Port Atmos Drain Pump Brg Radial

73 Port F. 0 . Scrv Pump Radial

Mo tor Upper Brg

74 Port F. 0 . Serv Pump Radia

Motor Lower Brg

75 Port F. 0 . Serv Pump Brgs Radial

76 STBD Atmos Drain Pump Brg Radial

77 Port Cond Exli Vac Pump Radial

Motor STBD Brg

250
VIBRATION SENSOR LIST (Cont)

CHANNEL SENSOR •- SENSITIVITY

NUMBER LOCATION

78 Port Coiid Exli Vac Pump Radial

Motor Port Brg

79 Port Cond Exh Vac Pump STBD Brg Radial

80 Port Cond Exh Vac Pump Port Brg Radia

81 Salt Wa t p r Sptv Pniim Motor Radial 1 vex \x -X ex J.

82 Salt Water Scrv Pump Motor Radial

LowerBrg

83 Salt Water Serv Pump Brgs Upper Radial

84 Sal t Water Serv Pumn Rrps T ower Ax i a 1

8 5 STBD Air Comp Motor STBD Brg Radial

86 STBD Air Comp Motor Port Brg Radial

87 STBD Air Comp STBD Brg Radial

88 STBD Air Comp Port Brg Radial

89 Port L.O, Serv Pump Brgs Radia

90 Control Air Comp Motor FWD Brg Radial

91 Control Air Comp Motor AFT Brg Radial

92 Control Air Comp Brg Radial

93 FWD Steer Pump Motor FWD Brg Radial

94 FWD Steer Pump Motor AFT Brg Radial

95 FWD Steer Pump FWD Brg Radial

96 FWD Steer Pump AFT Brg Radial

97 AFT Steer Pump FWD Brg Radial

98 AFT J \ X X Steer 1 ' V-' W X Pumn X LA 1 I L LJ 1A.FT V X X Bre X^ 1 Cil Radial

99 AFT Steer Pump Motor FWD Brg Radial

100 AFT Steer Pump Motor AFT Brg Radial

101 STBD Cond Exli Vac Pump Radial

Motor STBD Brg

102 STBD Cond Exh Vac Pump Radial

Motor Port Brg

103 STBD Cond Exh Vac Pump STBD Brg Radial

104 STBD Cond Exli Vac Pump Port Brg Radial

251
THERMAL MICRO AND MACRO LIST

SEN- ADDSOR RESS MlCROPARAMIiTERS OP . MACROPARAMETERS

NO. NO.

-1 Condenser- -1 Condenser10 5 1 Temp Seawater 1 Condenser Sat Temp

106 2 Temp Circ Water Outlet 2 Temp Circ Wtr Outlet

107 3 Condenser Sat Temp 3 Condenser Film Coeff

108 4 Temp Main Condensate 4 Pet Ht Rej

10 9 5 Flowrate Circ Water

-2 11. P. Turbine- -2 H.P. Turbine110 6 Flowrate H.P. Turbine Inlet* 5 Cor 1st Stg Press

111 7 Flowrate H.P. Bid 6 H.P. Turb Eff

112 8 Flowr ate I . P . Bid

113 9 Temp H.P. Turb Inlet

114 1 0 Press H.P. Turb Inlet

115 11 Temp H.P. Bid

116 1 2 Press H.P. Bid

117 13 Temp I. P. Bid

118 14 Press I. P. Bid

119 15 Temp Crossover Bid

120 16 Press Crossover Bid

121 17 First Stg Press

- 3 L . P . Turbine - -3 L.P. Turbine12 2 18 Flowrate Crossover Bid 7 L.P. Turb Eff

12 3 1

Flowrate Drns L.P. Htr 8 Exhaust Loss

124 20 Press L.P. Bid

125 21 Temp L.P. Bid •

-4 H . P . 5L . P . Turbine

-4 H. P. 5L. P. Turbine12 6 2 2 Shaft Horsepower* 9 Pet Pwr in H.P. Turb

127 23 Line Sliaft RPM 1 0 Mech ^^ Ext Efficiency

128 24 Line Shaft Torque

- 5 H . P . q L . P . Heater - -5 ll.P.^L.P. Heater12 9 2 5 Sliell Press H.P. Htr 1

Pump 1 Flowrate

130 2 6 Temp Drns H.P. Clr 1 2 Pump 2 Flowrate

131 2 7 Temp Fd Wtr Outlet H.P. Htr 1 3 4tli Stg Coeff

132 28 Temp Fd Wtr Inlet I. P. Clr 14 Effectiveness

133 29 Press Fd Wtr Inlet I. P. Clr 15 Steam Flo/Feed Flo

134 30 Shell Press I. P. Htr 16 3rd Stg Coeff

13 5 31 Temp Fd Wtr Outlet I. P. Htr 1 7 Ef f ect iveness

13 6 3 2 1 emp Drns I . P . Clr 1

Steam Flo/Feed Flo

1 9 3rd Stg Inlet Temp

2 0 3rd Stg Outlet lemp

21 4th Stg Outlet Temp

-6 D.F.T. Heater- -6 D.F.T. Heater137 33 Temp Outlet DFT 2 2 Effectiveness

138 34 Temp Condensate Inlet DFT 23 Diff Saturation Temp

139 35 Temp Outlet Primary Sect DFT

140 36 Shell Press DFT

252
THERMAL MICRO AND MACRO LIST (Cont)

SENSOR

-N'O.

ADDRESS

XO.

MICROPAR.AMETERS OP. MACROPARi\METERS

-7 L.P. Heater- -7 L.P. Heater141 37 Temp Condensate Outlet L.P.ilt 24 Steam Flo/Cond Flo

142 38 Temp Condensate Inlet Drn Clr 25 Eff ec t i venes s 145 39 Sliell Press E.P. Heater

144 40 Flowrate Mn Condensate

-8 Boiler 1- -8 Boiler 1- 145 41 Temp Fd Wtr Inlet Stm Drm 26 Ef f iciency

146 42 Press Suphtd Stm 27 Feedwater Temp

147 43 Tot Temp Suplitd Stm 28 Slag Formation

148 44 Press Desuphtd Stm 30 Soot Formation

149 45 Temp Desuphtd Stm 31 Flowrate Difference

J. o u 4 i eiiip uab uuuiet mil dcLiik Tot Steam Flowrate

1S5 49 Pet Open Control Desuphtr

154 50 Flowrate Desuplitd Stm

155 51 Flowrate Suplitd Stm*

156 52 Flowrate Fuel Oil Burners

157 53 Temp Fuel Oil Burners

-9 Boiler 2- -9 Boiler 2- 159 55 Temp Fd Wtr Inlet Stm Drm 33 Ef f ic i ency

160 56 Press Suplitd Stm 34 Feedwater Temp

161 5 7 Tot Temp Suplitd Stm 35 Slag Formation

162 58 Press Desuphtd Stm 3 7 Soot Formation

163 59 Temp Desuplitd Stm 38 Flowrate Difference

164 60 icilip Vjdi vJU.LJ.cL 1^1 Jl JjclIlK X 0 Tot Steam Flowrate

167 63 Pet Open Control Desuphtr

168 64 Flowrate Desuphtd Stm

169 65 Flowrate Suphtd Stm*

1"(J 66 Flowrate Fuel Oil Burners

1

" i 6 7

'|"prnY-\ Pjipl Oil RllTnf^'TQ

-10 Regenerative Air Htr 1- -10 Regen Air lltr 1- 173 69 Temp Air Inlet Regen Htr 40 Ef f ectiveness

1"4 70 Temp Air Outlet Regen Htr

17 5 71 ICJIip Odo VJUL-LCL ixct^cJl IlLI

-11 Regenerative Air Htr 2- -11 Regen Air lltr 2- 176 72 Temp Air Inlet Regen Htr 43 E f f ec t i venes s 177 73 Temp Air Outlet Regen lltr 178 74 Temp Gas Outlet Regen lltr

-12 Feed Pump- -12 Feed Pump187 83 Flowrate Fd Pump* 50 Turb Steamrate

188 84 Press Fd Pump Suet 51 Pump Eff

189 85 Temp Fd Pump Suet 52 Water Hp

190 86 Press Fd Pump Discli 53 RPM

191 87 Temp Fd Pump Disch

192 88 Flowrate Stm Fd Pump*

195 89 RPM Fd Pump

253
THERMAL MICRO AND MACRO LIST (Cont)

SEN- ADDSOR RESS MICROPARAMETERS OP. MACROPARAMETERS

NO. WO.

-15 Feed. Pump- -13 Feed Pump194 90 Flowrate Fd Pump* 54 Turb Steamrate

19 5 91 Press Fd Pump Suet 55 Pump Eff

196 92 Temp Fd Pump Suet . ^ 56 Water Hp

197 93 Press Fd Pump Disch 57 RPM

198 94 Temp Fd Pump Disch

199 95 Flowrate Stm Fd Pump

200 96 RPM Fd Pump

-14 Turbo - Generator

-14 Turbo - Generator

201 97 Flowrate Steam Turbo-Gen 58 Turb Steamrate

202 98 Kilowatt Output Turbo-Gen. 59 Kw Load

-15 Distilling Plant- -15 Distilling Plant203 99 Flowrate Stm Distiller 60 Lb Stm/Lb Water

2 04 10 0 Temp Dist S.W. Utr Outlet 61 Temp Rise S.W. Htr

205 101 Temp Dist S.IV. Htr Inlet 62 S.W. Htr U 206 102 Temp S.W. Inlet Dist AE Condr

207 103 Shell Press Dist S.W. Htr

208 104 Flowrate Distillate

-16 Main Condensate Pump 1- -16 Main Cond. Pump 1-

10b Kilowatt Input Cond Pump 63 Water Hp

210 106 Flowrate Mi; Condensate* 64 Pump Eff

211 107 Disch Press Mn Cond Pump 65 Cond Flowrate

212 108 Suet Press Mn Cond Pump

213 109 Barometric Press*

-17 Main Condensate Pump 2- -17 Main Cond. Pump 2-

'1/1

1. i 4 i i U Kilowatt Input Cond Pump 66 IVater Hp

215 111 Flowrate Mn Condensate* 67 Pump Eff

216 112 Disch Press ^hl Cond Pump* 68 Cond Flowrate

217 115 Suet Press Mn Cond Pump*

218 114 Barometric Press*

-18 Miscellaneous- -18 Miscellaneous

226 122 Xstem Gld Stm Supply 72 Sliaft Horsepower

227 123 Xstm Mn Condr 73 Ov'l Sp Fuel Rate

228 124 Stm to Stack

251+
DEMAND REQUEST MENU

01 VIBRATION TRENDS

02 THERMAL TRENDS

03 ELAPSED TIME COUNTERS

04 TAPE RELOAD

05 PARAMETER UPDATE

06 NRT DATASTORAGE

07 BROADBAND POINT DISPLAY

08 PREPROCESSOR DISPLAY

09 RAW DATA

10 TRIP PRINT AT DAY END

11 ENTER OR EXIT INPORT MODE

TYPE NUMBER OF DESIRED SELECTION

PARAMETER UPDATE LIST

01 NO. OF BASELINE RUNS

02 NO. OF STANDARD DEVIATIONS

03 THERMAL RANGES FOR SCALING

04 NO. OF VIBR CHANNELS + SET ENDPTS

05 NO. OF BASELINE LOAD POINTS

06 NO. OF REGIONS

07 NO. OF BANDS/REGION + ID VECTORS

08 NO. OF GROUPS

09 NO. OF BANDS/GROUP + ID VECTORS

10 GROUP ALARM LEVELS

11 REGION TREND LIMITS

12 THERMAL LIMITS

13 DURATION OF MULTIDAY DISPLAY

14 MINIMUM TIME TO ALARM

15 NRT ID VECTOR

16 THERMAL CONSTANTS

17 NEW TRIP INITIALIZATION

18 MAXIMUM MACROPARAMETER DEVIATIONS

19 EXIT PARAMETER UPDATE

TYPE NUMBER OF DESIRED PARAMETER

255
ADJUSTABLE THERMAL CONSTANTS

1 AFLO Total flow area (condenser)

2 DV Design average velocity of circulating water in each tube (condenser)

3 DTO Design circulating water temperature out of condenser

4 DTI Design circulating water temperature into condenser

5 DDT (DTO-DTI)

6 RHOSW Used to calculate mass flowrate (condenser)

7 PSTD Reference throttle pressure (H. P. Turbine)

8 VSTD Reference throttle specific volume (H. P, Turbine)

9 SURFH Total heat transfer surface (High Pressure Heater)

10 SURFI Total heat transfer surface (Intermediate Pressure Heater)

11 ELNE Non-extraction exhaust loss (L. P. Turbine)

12 SHPNE Non-extraction shaft horsepower (L. P. Turbine)

13 SRNE Non-extraction exhaust loss (L. P. Turbine)

14 ZEGNE Non-extraction exhaust specific volume (L. P. Turbine)

15 HHVl Higher heating value of F;0. (Boiler 1)

16 HHV2 Higher heating value of F. O. (Boiler 2)

17 CPFOl Specific heat for I. 0. (Boiler 1)

18 CPF02 Specific heat for I. O. (Boiler 2) .

19 CI Constant for Feed Pumps

20 C2 Constant for Feed Pumps

21 PTEST RPM threshold (Feed Pumps)

22 AKTEST Kilowatt threshold (Condensate Pumps)

23 C Constant based on tube size and material (condenser)

24 FB Constant based on tube size and material (condenser)

25 SMC Total tube heat transfer area in main condenser

26 CPSW Specific heat of seawater (condenser)

27 DQ Design heat rejection (condenser)

28 SBTU BTU for dollar deviations

256
DISCUSSION

E, DuBack, General Dynamics, Electric Boat : Since you have very high

propulsion noise, how are you going to make your vibration readings

worthwhile?

W. L. McCarthy : This is one of the things that we are attempting to

tackle. As we pointed out, right now we don't have a lot of data, so although, according to the program managers, we are supposed to be in an evaluation phase, we just don't have enough data for evaluation. To the

operating people, it is a very obvious problem. With redundant

machinery, an off-line pump could be monitored for background noise to

establish a data base.

E. DuBack : Do you know how the threshholds were established?

W. L. McCarthy : The threshhold is three times the base line. This was established from our computer program. Perhaps we should have made use

of data that are available from other industry applications, but we wanted to try to get some hard facts on a shipboard application.

M. B. Peterson, Wear Sciences, Inc. : You mentioned as one of your

objectives reducing manpower in the engine room. Now that you have seen

the system, do you think you can reduce the manpower?

W. L. McCarthy : Obviously, I think that if you can prove the concept,

you can reduce manpower. Right now on the Johnson , during a normal

watch period, there are two men - a licensed engineer and an unlicensed

junior engineer. During maneuvering and other situations, more men

help. I think that you could eliminate the junior engineer. There are systems now in Europe where there isn't any watch on board during steady

state conditions. There is just the normal 8 to 5 workday. Again, this

is strictly a monitoring system. If we can prove reliability in a computer in terms of data gathering, etc., we could apply similar

techniques to control and automate the control portion.

257

SESSION IV

COMING

REQUIREMENTS

Chairman: B. K. Genetti

General Electric Company

AN OVERVIEW OF CURRENT EFFORTS TO DETECT

AND PREVENT STEEL WHEEL FAILURES

Gary L. Leadley

Association of American Railroads, Chicago, Illinois 6O616

INTRODUCTION

According to annual statistics compiled by the Office of Safety in the

Federal Railroad Administration^"'") there were a total of 324 reportable derailments* attributed to wheel defects or failure during 1973. While this number

represents only 4.4% of all such accidents during the year, it amounts to 18.4%

of equipment related derailments and continues the trend of increasing frequency that has been established in recent years. The impetous behind this

trend is primarily the parallel rise in both car loads and train speeds^^) which

have placed many critical components, particularly wheels, in a severe stress

environment. This situation will continue to be a driving force for railroads

and their suppliers to improve wheel designs and material properties. However,

until such efforts succeed in effectively eliminating wheel related accidents

there must be an energetic parallel program to investigate the use of nondestructive diagnostic techniques to identify defective components prior to a damaging failure.

This paper will review the nature of railroad wheels, including their

more detrimental defects and conditions, and then delve into several of the nondestructive detection and evaluation techniques currently being considered for

use in their assessment.

RAILROAD WHEELS

While all railroad wheels have a similar basic design (Figure 1) and

conform to certain dimensional requirements established by the Association of

American Railroads, there is actually a wide variety of cross sections in use

today. The exact contour of any given wheel is dictated by several factors;

such as the manufacturing process, the intended application and the desired

service life.

The first of these factors establishes a basic division in the character of

the wheel population. Presently, there are two basic methods used in making

*Those derailments which caused railroad property damage in excess of $750. 00.

261
wheels - forging and casting. According to procurement figures compiled by the

Association of American Railroads for the period 1970-1972 there were approximately twice as many cast wheels sold as forged (wrought) wheels. This sales

ratio is about the same today and has resulted in a population that is nearly

equally divided between the two types due to the more recent appearance of cast

wheels. '•

The second influencing factor is the intended application, that is, the

type and severity of service. As one would expect, higher car loads require the use of larger diameter wheels in order to maintain rail contact stresses at acceptable levels. Nominal diameters range from 28 in. to 42 in. (.71 m to 1.06 m) with corresponding recommended load limits of 21,600 lb. and

34,900 lb. (96,081 N and 155, 235 N). In addition to the load dictated design

requirements there are those associated with special types of service. Examples

of such special applications would be mass transit cars, industrial transfer cars and mine train locomotives.

A third factor that is considered in the design of a wheel is the desired

wear life. The vast majority of wheels ( 85%) in service are designed for a single tread life. This design is appropriately called a one-wear wheel.

Effective wheel life can be extended by making the rim sufficiently thick to allow

remachining of the tread to restore the original contour. Wheels with this capability are designated as either two-wear or multiple-wear depending on the rim

thickness. The Association of American Railroads' specifications for the one- wear, two-wear, and multiple-wear rims are minimums of 1.25, 2.0, and

2.5 in. (3.17, 5.08, and 6.35 cm), respectively. ':

Nondesign variables that can be adjusted to meet the various service

requirements wheels encounter are material properties. Properties such as hardness, yield strength, fatigue resistance, and thermal cracking sensitivity are controlled principally by material chemistry and heat treatment. Since many

properties are optimized by opposite adjustments of these factors it has been

necessary to establish five classes of wheels tailored to meet different service

requirements. The Association of American Railroads' chemical and hardness

specifications^^) for these classes are listed in Table I along with their intended

service.

There are two classes that receive no special heat treatment after fabrication - U and Ul. The three heat treated classes increase in carbon content,

hardness and severity of service with ascending alphabetical order. A, B, and

C. Heat treatment generally consists of quenching and tempering the wheel rim

only, leaving the plate and hub in a softer normalized condition. Entire wheel

quenching is permitted for wrought wheels, however, undesirable tensile stresses are introduced into the rim- by such processing. In comparison, rim quenching

262
produces compressive residual stresses there that impede the formation and

growth of cracks.

This basic review of railroad wheels illustrates the design and material

variables that tend to complicate the development of NDE systems capable of

inspecting all wheels with equal reliability and speed.

WHEEL DEFECTS

The types of wheel defects that are considered unacceptable for inter-

.change service are described and illustrated in the Association of American

Railroads' Wheel and Axle Manual (Sec. 3C) and the Association of American

Railroads' Interchange Rules (Rule 41). Since the detection of the more common

varieties of these defects should be the primary goal of any NDE system or combination of systems, it is appropriate to review typical examples.

One of the most common wheel defects is the fatigue breakdown of the

tread surface known as shelling. Figure 2 shows deep-etched cross and tread

sections of a rim from such a wheel. In this case the shelled band was 1.25 in.

(3.17 cm) wide and extended to a depth of 0.094 in (.239 cm). There are many

contributing factors to shell development including poor track conditions,

excessive loads and speeds, insufficient wheel hardness and undersized wheels

for the load. Such factors tend to increase the rail contract stresses above the

endurance strength of the material.

A mode of wheel failure that commonly results in the loss of rim and

flange sections is known as rim shattering. This type of defect usually initiates

at internal inclusions located under the high contact stress areas of the tread.

As shown in Figure 3, a fatigue plane, roughly parallel to the tread, extends out

from these sites (arrows), under continued cyclic loading, until the front and/or

the back rim face is penetrated to form a circumferential crack. At this point

the wheel becomes condemnable by the Association of American Railroads'

standards. Continued wheel operation usually causes cracking normal to the

fatigue plane along its periphery and the eventual loss of entire rim sections.

Another cause of wheel failure, that is particularly important from a frequency standpoint, is thermal cracking. The occurrence of these defects is

directly related to the fact that wheels function as brakedrums, as well as being

supporting members for the vehicle. Thermal cracks can initiate by fatigue as

the result of thermal cycling in repeated brakings or by a cleavage mechanism

where the tensile stresses developed in a few severe brakings are sufficient to cause a brittle crack to form. Once initiation occurs by either mechanism the

crack will extend under the continuing action of residual tensile stresses until

the critical crack size for brittle fracture is achieved. At that point unrestrained

crack growth will occur, which can result in explosive wheel fracture.

263
Examples of various thermally cracked wheels are shown in Figures 4-7.

The first specimen is characterized by numerous transverse cracks that

originated in the excessively heated outer tread and extended into the front rim.

Apparently stresses in this wheel did not build to a sufficient level to cause

brittle fracture. That condition was satisfied, however, in the wheel shown in

Figure 5. This 33 in. , wrought wheel developed a single thermal crack at the

front rim edge (arrow). Subsequent stressing resulted in the rapid propagation

of the crack through the rim and into the plate where it split to form two

circumferential cracks that encircled the hub causing the total separation of the

rim. Misalignment of the brake shoe over the rim edge was indicated by the

thermal crack location and local discoloration. Another example of misaligned

brakes causing excessive localized heat and resultant thermal cracks is seen in

Figure 6. In this case, shoe contact was at the upper portion of the flange and

the initial crack extended into the plate and almost 180° around the hub.

There is another railroad operation, not involving brake shoe application,

which may generate the necessary wheel heat to cause thermal cracking. Wheel

retarders, which physically rub against the back wheel rim, are used in

classification yards to control car speed during switching. In cases where the car is allowed to reach excessive speed, the retarder action might produce

detrimental heating on the back rim. Figure 7 shows a 33 in. cast wheel that

developed a thermal crack (arrow) in that location from heavy retarder use.

The next form of wheel failure to be considered is plate cracking.

Failures of this type commonly occur in either the back rim fillet (Figure 8) or

the front hub fillet (Figure 9), Crack development is associated with the high

radial tensile stresses that are generated in those fillet areas following prolonged

braking and under the action of heavy cyclic vertical and lateral wheel loads.

Initiation is usually by fatigue at surface defects such as imbedded mill scale,

machining tears or decarburization. Crack growth can proceed around the wheel

until arrest occurs, as in the two illustrations, or until the ends surface on the

tread and result in the loss of a rim section.

An important category of condemnable wheels not discussed so far are

those severely overheated in service from stuck or dragging brakes, but not

exhibiting thermal or plate cracks. Such wheels are potentially dangerous

because the high tensile stresses developed in the rim can lead to an instantaneous fracture in the presence of even small thermal cracks. At the present

time detection of this hazardous wheel condition depends on the interpretation of

visual evidence of overheating, such as charring of surface oil and the presence

of heat discoloration. Such evidence is unreliable at best considering that not

all wheels are oil covered and that discoloration is dependent on ambient conditions during heating, particularly humidity, and tends to disappear with further

weathering. . .

26k
In addition to those wheel conditions that are considered to be actual failures, there are many removal categories that deal with condemnable rim and

flange geometry changes caused by normal and abnormal wear. Excessive

flange wear causes particular concern because of its adverse effect on wheel

gage and truck stability through track switches. This concern is justified considering that 135 derailments^"^) in 1973 were caused by this type of wear

problem.

The preceding review of wheel defects is by no means complete, however,

those conditions that pose significant danger to the safe movement of freight and

passengers are included.

CURRENT WHEEL INSPECTION

Wheel inspection begins in the manufacturer's shop with procedures

defined in Association of American Railroads' specifications M107 and M208^'^)

for wrought and cast wheels, respectively. Both outline the same requirements

for ultrasonic inspection of rims and wet magnetic particle inspection of plate

surfaces for discontinuities , such as inclusions and voids. Adherence to these

specifications effectively sets a minimum quality limit for all new wheels entering service.

The techniques and frequency of in-service inspection are not specified

in the Association of American Railroads' rules, but are determined by the

experience of each performing railroad. All railroads rely principally on visual

inspection, with a modest use of magnetic particle or penetrant methods by some

in certain questionable cases. The frequency of inspection appears to be flexible

at best, depending heavily on the operating schedule of the vehicle and the repair

needs of other components. This lack of explicit inspection intervals, which is

almost inherent in the mobile nature of railroading, places an increased burden

on the inspection that does take place to find defects in their earliest stages.

Experience has shown that the vast majority of defective wheels are

detected visually before an accident can occur. Given this basic effectiveness,

visual inspection is characterized by several factors that tend to limit its

sensitivity and reliability. Primary among these is its inherent subjectivity.

Any system that relies solely on people for critical decisions is subject to the

inconsistencies generated by differences in individual motivation, skills, knowledge and health. Reliable wheel inspection depends heavily on such variables as inspector job satisfaction and visual acuity.

Another important factor to be considered is the variability of the inspection environment. Wheel inspection usually takes place in the yard where

variables such as the ambient temperature, humidity and sun light will change

throughout the year; influencing the comfort and, therefore, concentration of the

265
inspector. These variables are more controllable in the repair shop setting,

thus inspection decisions made there can be expected to be more consistent

throughout the year.

The physical condition of the inspected wheel can also influence the

ability of visual examination to detect small defects. The presence of oil and

dirt on plate surfaces will hide all but the largest plate cracks. Similarly, hot

and cold working of the tread can obscure thermal cracks with flowed metal.

Recognition of the preceding factors affecting the reliability of visual

inspection lead to the development of an automatic system for objectively

evaluating the condition of wheels. The system, first marketed twenty-two

years ago by Wheel Checkers of Denver, Colorado, is designed for the detection

of broken flanges and loose wheels on vehicles that are on track and in motion.

The sensor system ('^) (Figure 10) consists of a series of 124 spring loaded

detector fingers oriented normal to a slightly offset section of rail. The

opposite rail section is fitted with a guard rail to keep passing vehicles tight

against it, establishing the necessary clearance between the inspected wheel and

the offset rail. The operation of the detector fingers is illustrated schematically

in Figure 11. The approach of a train triggers the application of a electric

potential between the detector fingers and the rail. A normal wheel of proper

gage will ride down the rail with the flange depressing the fingers sequentially by

contacting the insulated wear plates. Since the flange prevents the finger points

from touching the tread, the circuit remains open and no signal is generated.

Should one of the fingers contact the wheel where the flange is missing its point

would touch the tread and close the alarm circuit. When a wheel set that is out

of gage, due to wheel looseness, improper mounting or excessive flange wear,

passes over the detector finger contact is made with either the finger point or

the 1A03 spring depending on the direction of gage error. In either case, the

circuit is closed and an alarm signal is generated.

The baLio ffectiveness of the Wheel Checker system has been proven

over many years, however, being primarily mechanical in nature, it is

susceptible to failures allowed by insufficient maintenance. In addition, there

have been occasions when dragging train equipment has torn out the entire line

of detector fingers rendering the system useless.

DEVELOPMENT OF IMPROVED INSPECTION METHODS

In recent years there has been an accelerated effort, particularly by the

federal government through the Transportation Systems Center of the Department of Transportation, to stimulate development of improved methods of nondestructively evaluating the condition of in-service railroad wheels. Investigators are applying a variety of techniques to various aspects of wheel inspection including ultrasonics, Barkhausen noise analysis, acoustic signature

266
analysis and magnetic perturbation.

Before discussing the specifics of these techniques, it will be useful to consider the values obtained by Carter and Caton^^^ for the critical crack sizes

that can be associated with the various wheel classes under maximum probable

stress conditions. At the stress level of 55 ksi (Table 2) the critical length of corner thermal cracks is only 0.10 in. (.254 cm) in high carbon class C and U

wheels. Cracks into flat surfaces, such as the tread or back rim, can grow to 0.26 in. (.660 cm) in the same wheels before becoming critical. Plate cracks

that develop in the rim fillet of class C and U wheels become critical if their

length exceeds 0.16 in. (.406 cm). Finally, the presence of sharp bottom

surface defects, such as machining tears, in the rim fillet of a high carbon

wheel can initiate brittle fracture if its depth exceeds .028 in. (.071 cm).

While these critical crack values were calculated assuming the severest

probable stress condition, one that most wheels will never see, they do indicate

the level of crack sensitivity that any NDE system should approach to achieve

the highest reliability. The actual crack detection levels required by railroads

will depend on the cost and physical requirements for maximum detection.

Ultrasonics - The science of ultrasonics is being applied to the problem of

wheel evaluation in many forms. The first commercially viable system is the

Wheelfax system developed by Scanning Systems , Inc. ofDanbury, Connecticut. (^)

The search unit of this system fits into a special section of rail that is designed

to guide the outer tread of passing wheels over a fluid filled transducer boot.

Figures 12 and 13. Inside the boot are two oppositely directed transducers set

in a gimbaled support that allows them to maintain a constant entry angle to the

wheel tread. On contact with a wheel, couplent is sprayed on the boot and an ultrasound pulse is directed circumferentially around the tread as a surface

wave by one of the transducers. Initial and multiple order reflections are subsequently received by this transducer from any crack that has developed on the

rim faces, tread or flange. It is claimed that reliable detection of cracks 0.5 in.

(1.27 cm) long and 0.050 in. (.127 cm) deep can be achieved. After full

attenuation of this initial signal has occurred, in about five milliseconds, a second pulse is directed around the wheel in the opposite direction by the second

transducer. This dual pulse-echo technique enhances the chances of detecting

cracks that are inclined to the surface since they are anisotropic in their ability

to reflect sound. The use of dual transducers also allows the analysis of the

through transmitted signal for additional information on the wheels' condition.

Attenuation rate of this signal is indicative of the general wheel surface condition

and is believed related to the near surface stress level. This relationship to stress level could be used to detect uncracked, overheated wheels. The time

interval between multiple receptions of the through transmitted pulse is used to classify wheels by diameters and details of the pulse shape can reveal a high

flange condition.

267
The Wheelfax system has several operational advantages in addition to its

versatility. Primary among them is the ability of each search unit to inspect all

the wheels on one side of a train moving at up to 30 mph (48. 3 km/h). Reliable

inspection at this speed results in minimum interference with train operation and

maximum system utilization. Another operational advantage is the system's

totally automatic nature. The initiation and termination of testing, the data processing and recording, and the defect alarm system are all controlled electronically from a trackside control center.

A recent investigation by Becker at Battelle Northwest has confirmed

the feasibility of detecting wheel plate cracks by introducing ultrasound radially

into the tread. During the study two similar test procedures were considered;

one based on the generation of Lamb waves in the plate and the other on a more

conventional pulse- echo technique. -

Results of several tests conducted under optimum conditions for each

method indicate that the conventional pulse-echo technique is more suited to the

task of detecting plate cracks than is the Lamb wave method. One of the main

liabilities of the latter is its low signal to noise ratio. At the relatively low

frequencies required for generation of optimum Lamb waves (640 KHz) the

divergence angle of the sound beam is large compared to that found <at higher

frequencies in the more conventional pulse-echo method (1 MHz) . As a con- sequence, a portion of the energy fails to enter the plate and is reflected by the

adjacent rim surfaces. Such spurious reflections tend to reverberate in the rim,

yielding a multitude of false indications.

Another undesirable feature of the Lamb wave method is its inlierent

sensitivity to plate thickness variation. Since the allowable modes of wave propagation are governed by the frequency - plate thickness product (F x d) , it is

evident that the operating modes will change with thickness variations within a plate and with plates of different designs. The associated variability in propagation velocity negates the use of fixed time acceptance gates on the return

signal to isolate responses from the fillet areas for better resolution. This

problem is not found in the higher frequency pulse-echo technique because of its

constant propagation velocity across the wheel.

A third factor that limited the effectiveness of the Lamb wave method is

its relatively long near surface dead time that seriously restricted the detection

of rim fillet defects. The testing of one wheel at 640 KHz, with the transducer

driven by a 20 \\ sec. sine wave burst, resulted in a dead time of 30 sec. , which is equivalent to about 4.5 in. (11.4 cm) of steel.

Becker estimated that the minimum detectable flaw sizes for an automated, pulse-echo inspection system would be approximately 0.0225 in.

268
(.145 cm2) and 0.045 in. 2 (.290 cm2) for rim and hub fillet flaws, respectively.

Examples would be defects 0.09 in. (.23 cm) deep and .25 in, (.63 cm) long in

the rim fillet and 0. 125 in. (.32 cm) deep and 0. 36 in. (.91 cm) long in the hub

fillet.

One of the conceptual systems outlined by Becker for the automatic

inspection of wheel plates under moving cars involves a series of transducers

mounted in a special length of rail. Each transducer inspects a discrete radial

plane as the wheel passes over. An illustration of the proposed transducer

arrangement is shown in Figure 14. The transducers are held by a gimbaled

support structure encased in a fluid filled boot. The approaching wheel triggers

a couplent spray that keeps the outer boot surface wet. As the test wheel passes

along the series of probes a guard rail arrangement on the mate wheel controls

its lateral position while a spring loaded guide shoe positions the transducers

opposite the plate. The probability of defect detection will be directly proportional to the number of probes used to inspect a given wheel.

This system appears to offer a simple, nonmechanical, low maintenance

way of continuously inspecting wheels traveling at moderate speeds. These

advantages are countered, somewhat, by the reduced defect detection probability

that accompanies discrete radial inspection. In addition, the development of an adequate electronics system to operate the large number of transducers

required will be one of the primary implementation problems.

Another aspect of wheel inspection, where an ultrasonic technique is

being applied, is the detection of adverse stress conditions in the rim caused by

overheating. The principle behind this technique is that the state of stress in a metal influences the propagation velocity of ultrasound. Therefore, the precise

measurement of transit times through a known thickness of stressed material can give an indication of the average stress level. The key to obtaining reliable

results is the accurate assessment of the effect material variables, such as chemistry, preferred orientation and microstructure, have on the sound velocity

and the mitigation of these influences through adequate calibration.

Clotfelter and Risch^^^ have applied this ultrasonic stress measurement

technique to railroad wheels. The basic procedure was to measure the transit

time differential of simultaneously generated 2 MHz pulses through an un- stressed reference block and the stressed specimen. This was accomplished

using a dual trace oscilloscope to display the two signals and by expanding the

time base until individual pulse cycles could be seen. Since a difference in

transit time appears as a phase shift in the two signals, the delay - time

multiplier on the oscilloscope could be used to determine the differential by

making the pulses coincident.

269
The actual determination of stress in steel is complicated by its anisotropic nature with respect to sound propagation. Under compression shear waves

polarized parallel to the principal stress axis will travel faster than waves

polarized perpendicular to it. The difference between the transit time

differentials of the two wave orientations is, thus, a better measure of the aver- age stress than either orientation alone. As applied to the evaluation of wheel

rims, the parallel and perpendicular orientations correspond to the circumferential and radial directions, respectively.

The first step in utilizing this technique was the establishment of an acoustic stress constant for wheel material that relates ultrasonic velocity

changes to applied stress. This was accomplished by incrementally loading a block of j"im steel to simulate the circumferential compressive stresses found in

wheels and measuring the transit time differential of pulses traveling in this

block and an identical reference block. At each load level measurements were

taken with wave polarization both parallel and perpendicular to the principal

stress axis. The difference in transit time differentials of these two polarizations was used, in conjunction with the path length and the value of each load

level change, to establish an acoustic stress constant of 0. 405 nsec. /in. /ksi

(2.31 X 10 nsec./m/N/m ) for a typical wheel material.

Once the acoustic stress constant is determined the average stress across

a wheel rim can be calculated by measuring the difference in the radial and circumferential transit time differentials and by knowing the sound path length. In a similar manner, stress changes can be detected by making measurements

before and after the event of interest. The results of such an investigation by

Clotfelter and Risch^^) involving wheel braking tests are shown in Table 3.

These values reveal that a significant change has taken place in the sound propagation velocity as a result of wheel heating. This change is equivalent to an average compressive stress reduction of 13.9 ksi (9.6 x lo''' N/m^).

It has been demonstrated that accurate measurement of ultrasound propagation velocity in stressed wheels can be used to evaluate that stress condition.

However, the material variability found in wheels of different classes and manufacture would require the use of some independent technique to establish material

characteristics prior to any stress measurements. The technique also requires an accurate value for the sound path length, which may necessitate the actual

measurement of the rim width of each wheel tested.

Lodding Engineering Corp. of Auburn, Massachusetts,^^) is presently

marketing a device to measure ultrasound transit times to an accuracy of 0.

nanosecond.

Barkhausen Noise Analysis - Another technique recently applied to the task of

270
assessing the stress state of railroad wheels is that of Barkhausen noise

analysis.

The phenomenon which is the basis of this technique is the abrupt, discontinuous movement of microscopic magnetic domain boundaries that often occurs in ferromagnetic materials under the influence of an external magnetic

field. These nonuniform movements are reflected in the magnetization

hysteresis loop of the material as small, discontinuous increments in the curve known as Barkhausen jumps or noise, after their discoverer. It has been

established that the dynamics of domain boundary movement, and hence the level

of Barkhausen noise, is strongly influenced by the state of material stress. In the specific case of steel, noise intensity increases under the application of

tensile stress and decreases in a compressive stress environment.

An illustration of the basic elements needed for the excitation and

detection of the Barkhausen effect is shown in Figure 15. ^^^^ The excitation

field is developed by a variable electromagnet in contact with the specimen. An

induction coil between the magnet poles senses changes in specimen magnetization and translates this into a output voltage that is displayed on an oscilloscope. Cycling the external field polarity results in the output amplitude

achieving a maxima that is indicative of the material stress state. To develop

quantitative stress values from such information it is necessary to construct a calibration curve of stress versus Barkhausen noise intensity for the material

of interest. Figure 16(10) shows a curve of this type for a wheel steel. It is

evident that, in this case, maximum stress sensitivity occurs between -40 and

+50 ksi (-215 and +344 MPa) and that more extreme values would not be definable.

A Southwest Research Institute study(lO) recently established that the

Barkhausen phenomenon generated in railroad wheels is sufficiently stress

sensitive to be used as a stress indicator. However, there were significant

variations and soine inconsistencies in the data from wheel to wheel and at

similar locations on the same wheel. This situation was attributed to, in part,

the lack of a "magnetic feedback" system to detect variations in the effective

magnetic flux near the specimen surface due to local differences in magnetic

permeability. Such a system would sense the magnetic field and adjust the

electromagnet strength to maintain the predetermined magnetization cycle independent of material condition.

Another factor contributing to data variability in the Barkhausen

technique is the small volume of material from which the stress indication is

obtained. The near surface nature of the Barkhausen effect, when combined

with a coil pickup covering an area of only 0.01 in.^ (.064 cm^), causes the

technique to be more sensitive to short range stress gradients and shallow surface conditions than a conventional stress relaxation technique using strain gages.

271
Despite such characteristics, reasonable qualitative agreement was established

between the two methods. ('"^)

As a step toward utilizing the Barkhausen noise technique to classify

wheels according to the severity of overheating, the SwRI study tentatively

identified the area on the back rim surface nearest the tread as that most likely

to yield consistent linear results.

Acoustic Signature Analysis - One of the earliest methods of nondestructively

evaluating railroad wheels was to have car inspectors strike them with a hammer

and listen to the resulting sound. In this way it was possible to detect many

defective wheels because they rang differently than good wheels. A more

sophisticated version of this technique, known as acoustic signature analysis, is

being investigated by Finch, et al,^^"*-) at the University of Houston as a possible

basis for an automatic, in motion, wheel inspection system.

In the acoustic signature method a wheel is excited, by either natural or

artificial means, into vibrating and the radiant sound is analyzed for its

characteristic spectral content or signature. The introduction of discontinuities,

such as cracks, into the wheel will affect the modes of vibration and, consequently, the signature. Early results (11) have shown that artificial impact

excitation is the most suitable means of generating sound of sufficient intensity

and spectral content in the frequency range (1-5 KHz) found to be most sensitive

to wheel integrity. In addition, this form of excitation allows the use of damping

rate measurements as a supplemental indicator of wheel condition. It has been

also established that the best detection system is one using a trackside microphone, near the impactor, to pick up airborne radiation. The alternative

approach was to use a rail mounted accelerometer to monitor the impact induced

vibrations, however, rail resonances were found that conflicted with those of the

wheel, making this method undesirable.

An experimental impactor - microphone arrangement that was used in

initial field trials^"*-^) at the Union Pacific's Omaha East yard is shown in Figure

17. The impactor was designed to be wheel activated and adjustable in regards

to the impact point on the rim. During the trials tape recordings were made of

the sound emitted by a number of good and defective wheels under various

conditions of train operation and hammer impact location. The signature of each

wheel was processed by first converting it to a 1/3 octave band spectrum from

1-8 kHz. The spectrum was then normalized with regards to the overall

intensity level to negate differences in sound amplitude. The normalized

spectrum was compared to a- good wheel standard spectrum and the difference

found in each band was squared and summed. This summed value of deviation

from the good standard was then compared to a predetermined limit to establish

the presence of a defect. Additional defect confirmation could be obtained by

272
comparing the sound decay time with a standard or by comparing both spectra

and decay time of sound from two wheels on the same axle.

The initial field trials were successful in that the impactor survived

repeated wheel contact at various train speeds and was able to produce sounds

clearly distinguishable from the background noise. In addition, the spectrum

analysis program was able to call out all the defective wheels used, including one with a plate crack and three with only thermal cracks. Areas needing hardware improvements were also defined. The impactor design needs refinement

to insure that uniform excitation is imparted reliably to each passing wheel. It was also determined that the spectrum analyzer with a scanning time constant of

0.2 m sec was too slow to allow more than one spectrum reading on each wheel

at the train speeds used. A faster unit would average several spectra in the

allotted time, increasing the reproducibility of a given wheel evaluation.

Magnetic Perturbation - A unique method of detecting thermal cracks in moving

wheels was recently patented by Gieskieng of Wheel Checkers, Denver,

Colorado. ^^^^ The technique consists of moving a magnetic tapa, carrying an

alternating magnetic signal, across the magnetized tread of a wheel. In those areas where the wheel material is continuous little or no change will occur in the

tape signal, however, where a flaw or crack contacts the tape the external

magnetic flux at those discontinuities will effectively erase the signal. The detection of such perturbations in the tape signal will, thus, indicate the presence

of defects. A illustration of this phenomenon is shown in Figure 18.

A field installation of the Gieskieng system would involve a special

length of rail with the wheel magnetizing equipment at one end and the magnetic

tape arrangement at the other. The magnetization is accomplished using a long

narrow plate, wound as an electromagnet, attached parallel to one side of the

rail. As a wheel passes the plate the rim alone is transversely magnetized.

The detector portion of the system includes a continuous loop of magnetic steel

tape attached parallel to the rail so that the outer portion of the wheel tread will

contact it on passage. A schematic of the detector elements is shown in Figure

19. The tape, which rotates in a direction opposite to that of the wheel, is

erased of prior information by head 80 and an alternating magnetic carrier

signal of approximately 200 Hz is applied by head 81. After contact with the

wheel, the tape passes the pickup head (85) where any anomalies in the applied

signal will trigger a defect alarm. A contact switch located at point 86 is used

as an axle counter to correlate recorded defect indications with wheel position in

the train.

Modification of the basic tape loop location enables the Gieskieng system

to detect defects near the flange - tread fillet and on the top of the flange.

275
A prototype system has been constructed and tested with success in the

laboratory, however, there have been no field trials to establish its crack

sensitivity and mechanical durability in a railroad environment.

CONCLUSION

This paper has taken an overview of several detection and evaluation

techniques that have shown promise in the area of improved railroad wheel

inspection. The intent of these discussions was to stimulate interest in the

application of other techniques to the problem and the development of practical

methods of utilizing techniques already investigated.

When commercially viable NDE systems are developed for the railroad

wheel application, the nation as a whole will benefit from the improved transit

safety and the reduced railroad accident costs.

EXCLUSION

The Association of American Railroads does not necessarily endorse nor approve the equipment described herein. Statements made in this paper are not

to be used in any advertising or promotion implying Association of American

Railroads' approval.

REFERENCES

1. Accident Bulletin, No. 142, 1973 Edition, Office of Safety , Federal

Railroad Administration.

2. Yearbook of Railroad Facts, 1974 Edition, Association of American

Railroads.

3. Manual of Standard and Recommended Practices, Section A, M-107 and

M-208, Association of American Railroads.

4. Literature supplied by Wheel Checkers, Denver, Colorado plus private

communications.

5. C. S. Cater and R. G. Caton, "Fracture Resistance of Railroad Wheels",

September, 1974, Report No. FRA-ORD & D-75-12.

6. Literature supplied by Scanning Systems, Inc., Danbury, Connecticut,

plus private communications.

7. F. L. Becker, "Ultrasonic Detection of Plate Cracks in Railway Wheels"

DOT-FRA-726, via private communications with R. Steele, Transportation Systems Center, Department of Transportation, Cambridge,

Massachusetts. v

27!^ ' ' '

'

'
8. W. N. Clotfelter and E. R. Risch, "Ultrasonic Measurement of Stress in

Long Lengths of Welded Rail", NASA TMX-64863, July, 1974.

9. Literature supplied by Lodding Engineering Corp. , Auburn,

Massachusetts.

10. R. King, J. Barton, and W. Perry, "Stress Measurement in Railroad

Wheels via the Barkhausen Effect", DOT-TSC-713, December, 1974.

11. K. Nagy and R. D. Finch, "Feasibility of Flaw Detection in Railroad

Wheels Using Acoustic Signatures", DOT-FR-30002 , September, 1974.

12. K. Nagy, "Report on a Preliminary Yard Test of the Acoustic Signature

Method for Railroad Wheel Inspection", University of Houston,

unpublished report, 1974.

13. M. W. Gieskieng, "Method and Apparatus for the Detection of Cracks

and Flaws in Rail Wheels, Rails and the Like by Sliding a Prerecorded

Magnetic Medium Over the Test Piece", U. S. Patent 3,820, 016, June,

1974.

275
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FRONT BACK

FIGURE 1 TYPICAL RAILROAD FREIGHT CAR WHEEL

FIGURE 2

PORTION OF A SHELLED WHEEL AFTER DEEP ACID ETCH

277
FIGURE 3

A WHEEL WITH A SHATTERED RIM
FIGURE 6

THERMAL CRACK DEVELOPED ON THE FLANGE FROM

BRAKE SHOE CONTACT

279
i

FIGURE 7 WHEEL WITH THERMAL CRACK ON BACK RIM FACE

INDUCED BY RETARDER ACTION

FIGURE 8

PLATE CRACKING FOUND IN THE BACK RIM-PLATE FILLET
FIGURE 9

PLATE CRACK THAT DEVELOPED IN THE FRONT HUB- PLATE FILLET

FIGURE 10

FIELD INSTALLATION OF THE WHEEL CHECKERS BROKEN

FLANGE AND LOOSE WHEEL DETECTOR (REF. 4)

281
RAIL GAUGE 4' 9- 1/2"

GAUGE TO FINGER TIP A' 9"

NORMAL WHEELGAUGE POINT

,A03 SPRING

DETECTOR

FINGER

INSULATED

WEAR PLATE

NORMAL WHEEL

NORMAL GAUGE

NO DEFECT

CONTACT

IA03 SPRING

FLANGE HEIGHT DEFECT

1. BROKEN

(FOR 100^% DETECTABILITY

MUST BE BROKEN CONTINUOUSLY

FOR 3- 1/2" WITHIN I /2^' OF TREAD)

2. BUILT UP TREAD

3. FLANGE CAST LOW OR ECCENTRicj

CONTACT

A03 SPRING

CONTACT

A03 SPRING

DEFECT-DID NOT TRACK CORRECTLY

THROUGH DETECTOR

(MAY BE ON SIDE OPPOSITE DETECTION)

(WHEELS MUST BE TRAMMED)

1. LOOSE-MOVED IN OR OUT ON AXLE

2. MOUNTED OUT OF GAUGE

3. BENT AXLE

A. SHARP OR THIN FLANGE

5. SKEWED TRUCK

FIGURE 11

OPERATION OF THE WHEEL CHECKER WHEEL

INSPECTION SYSTEM (REF. 4) •

282
TABLE II

CRITICAL CRACK SIZES AT AN APPLIED STRESS

OF 55 Ksi (After Carter and Caton, Ref 5)

Class

THERMAL CRACKS

Corner Crack^ Surface Crack^

PLATE CRACKS

a h Surface Crack Surface Defect

A 0.25 0. 65 0.50 0.084

B 0.14 0. 36 0.25 0. 043

C 0.10 0.26 0.16 0.028

U 0.10 0.26 0.16 0. 028

^ Crack length in inches

^ Defect denth in inches

FIGURE 12

FIELD INSTALLATION OF THE WHEELFAX ULTRASONIC

WHEEL INSPECTION SYSTEM (REF. 6)

285
FIGURE 13

CLOSEUP OF WHEELFAX TRANSDUCER BOOT (B^F. 6)

FLUID FILLED

COUPLING BOOT — 6 I N . —

FIGURE 14

A CONCEPTUAL IN-RAIL TRANSDUCER ARRANGEMENT

FOR THE INSPECTION OF WHEEL PLATES (REF. 7)

28^
Wheel Position Time Beloro, nsee 'in

( nsec /in. ) Time After, n^^(;c/m ( nsec/in. )

1 ( 1 8. 00) 46b ( 11. 90)

2 536 ( 1:5. 60) 279 (7.10)

3 507 ( 1 2. 90) 276 (7.00)

4 4 92 ( 1 2. 50) 205 (5.20)

5 575 (14. 60) 330 (8.40)

6 575 ( 14. 60) 386 (9. 80)

7 Dl b

/ 1 '?Cl\

\ 1 O. £i\J ) 4 57 (11. 60)

8 614 (15. 60) 350 (8.90)

Average 565 (14.37) 344 (8. 73) TABLE III ULTRASOUND TRANSIT TIME CHANGES ASSOCIATED

WITH A BRAKING TEST (REF. 8)

Biasing Macrnet

Programmed

Power Supply

FIGURE 15

THE ESSENTIAL ELEMENTS OF A BARKHAUSEN NOISE

ANALYSIS SYSTEM FOR MEASURING STRESS (REF. 10)

285
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Apparent Residual Surface Stress, KSI FIGURE 16

BARKHAUSEN NOISE CALIBRATION CURVE FOR A WHEEL MATERIAL (REF. 10)

FIGURE 17

AN EXPERIMENTAL IMPACTOR- MICROPHONE ARRANGEMENT

USED IN ACOUSTIC SIGNATURE ANALYSIS WHEEL INSPECTION (REF. 12)

286

/
FIGURE 19

SCHEMATIC OF THE DETECTOR ELEMENTS IN

THE GIESKIENG SYSTEM (REF. 13)

287
DISCUSSION ,

H. E. Dunegan, Dunegan-Endevco Corporation : Has there been any

consideration about using acoustic emission for this problem?

G. L. Leadley : There are proposals for using acoustic emission.

288
DIAGNOSTICS FOR REFRIGERATOR CAR

DIESEL GENERATING SETS

Robert F. McKee

Pacific Fruit Express Company

San Francisco, California 94105

BACKGROUND: For over 100 years the ice bunker railroad refrigerator car was the standard transportation vehicle for

perishable foodstuffs between the fruit and vegetable growing areas in the south and west to the major population

centers in the east and middle west. The growth of the frozen food industry in the late 1930' s and during World War II,

however, led to the necessary development of refrigeration

systems capable of providing the 0°F holding temperature required by that industry, and which could not be obtained by

ice refrigeration.

The result was adaptation of commercial compressor - condensing refrigeration equipment to the railroad environment, and the early to middle 1950' s saw a fleet of frozen

food mechanically refrigerated cars grow into several thousand cars to serve the frozen food industry. Fresh perishable shippers also became interested in the advantages of

controlled temperatures as their shipping practices became

more sophisticated, so that by 1957 the last ice bunker refrigerator car was built in the United States and from then

through the 1960's the fleets of railroad refrigerator cars

were replaced by mechanical cars. In 1973, railroad icing

operations were terminated and all perishable movements are

now protected by mechanical refrigeration,

THE MECHANICAL CAR: There are now about 28,000 mechanical

refrigerator cars in the United States, of a general standard configuration as shown in Figure 1. The cars are generally configured with a 50 foot inside length and a machinery compartment at one end, which contains a diesel engine

driven generator set and the high temperature components of

the refrigeration system. The air circulation blower and

cooling coil are located within the insulated compartment at

the wall adjacent to the engine compartment.

The refrigeration system operates on 3 phase 60 Hertz

220 volt AC power supplied by the generator set, using standard commercial electrical controls and motors. Provisions

are made for connection to an outside source of power for

operation of the system within enclosed areas during loading

and unloading operations. On board fuel capacity is

289
provided for from 2 0 to 25 days continuous operation, and all

systems are designed with sufficient capacities of oil and

coolant to operate for this period without further servicing.

The systems are fully automatic. When the engine starter button is pushed and the engine starts, the control system

actuates the various ccxnponents to supply cooling or heating

as required to maintain thermostat settings from O^F to 70°F.

Heating is provided by electrical heating elements in the

cooling coil, which are also employed to defrost the coil

when the control system detects the need for defrost, which

is also fully automatic.

A multi-stage thermostat senses the car interior air

temperature returning to the cooling coil as shown in Figure

2. The thermostat provides stages of cooling by varying the

compressor capacity and/or diesel -generator speed to alternate the output to the actual refrigeration demand as the

thermostat setting is approached. At the thermostat setting

the refrigeration compressor stops and starts As required,

while the diesel engine runs constantly to provide power to

drive the air circulation system and the temperature and

electrical controls.

Should the temperature continue to fall the system

automatically switches to the heating mode, and continues to

maintain interior temperatures at any outside temperature

encountered. All controls are in the engine compartment,

visible and accessible through the side access door.

THE PROBLEM: The environment in which the railroad mechanical refrigerator car operates is inherently hostile to

operating machinery. In addition to ambient conditions which

can vary from -30°F to +150°F in the engine compartment, and

elevations of below sea level to over 8,000 feet, there are

the conditions imposed by movement over land and sea (by

railroad barges). These include coupling shocks to 20 g,

vibrations, dirt, dust, salt atmosphere and long periods of

unattended operation.

In the early stages of development of mechanical systems

the objective was to survive any given trip which might vary

from 5 to 15 days depending upon intermediate stops for loading and unloading. A process of survival of the fittest over

the early years developed tight specifications not only for

equipment operating characteristics to survive the environment, but eventually to individual designs of certain manufacturers which proved to be inherently superior.

This process applied to major components such as engines

290
and compressors, as well as to motors, valves, electrical

contractors, relays, wiring, and controls, gauges and indicators. As a result the industry has standardized the major

components and accessories, so the operating problems have

also become somewhat standardized. This is an industry-wide

problem, as mechanical refrigerator cars are interchanged

between owning railroads and others throughout the United

States, Canada and Mexico.

Experience has established that mean time between failures ranks as follows in ascending order:

Diesel Engine -Generator

Electrical System

Refrigeration System

Thermostatic Controls

Therefore, when the refrigerator car owners determined

to form a combined task force to determine means of improving dependability and reducing intransit failures the diesel

engine -generator was selected as the most applicable common

ground for a joint effort to develop diagnostic analysis systems. It was also the area of greatest standardization since

practically all diesel engines in current use are Detroit

Diesel Allison 2 cycle blower scavenged type in Model 2-71

and Model 3-53

Figure 3 shows a typical DDAD Model 2-71 generator set

of the most prevalent type in service. It operates at 1200

RR4 to produce 17-20 KW of 220 volt 3 phase 60 Hertz power,

with a dual range governor to operate at 800 RPM to provide

11-13 KW at 150 volts and 40 Hertz. (It is possible to

operate standard 60 Hertz equipment at 40 Hertz as long as

the voltage /frequency relationship remains constant, since

the impedance of inductive devices varies directly with the

frequency,

A SGLUIION: Upon the decision to concentrate on the dieselgenerator set, a contract for a feasibility study was let to

a firm who had previous experience not only with diagnostic

systems and their hardware, but who had also done studies

of the DDAD 2 cycle engine for military automotive applications .The engine generator was divided into sub-systems for

individual analysis consisting of:

Coolant

Lubrication

Fuel

291
Combust-ion

Mechanical

Electrical

Starting

Each sub-system was analyzed with a view toward selection of parameters for study, followed by sensing means for

collecting the necessary data for each system considering

the physical configuration.

Early in the study it was decided that sensing devices

must be applied at each engine test since the environment

was too severe for any practical service life of the necessary transducers. Therefore non-intrusive applications were

preferred, and rapidity of set-up prior to test was of high

priority. Sensing points selected were as shown in Figure

4.

Truth tables were developed based upon test of the

actual engine under all conceivable failure modes as previously experienced from analysis of available intransit pei^-

formance data from the various equipment owners. From these

were constructed the logical diagnostic sequences for each

sub-system, and for all sub-systems taken together.

The feasibility study indicated strong potential for a

diagnostic system which could provide advantages as follows:

1. In-car analysis of any or all sub-systems to ascertain

presence of incipient failure conditions prior to each

trip.

2. Status of sub-system at each subsequent inspection to

include trend analysis.

3. Provide data for improvement of components, servicing

practices and preventive maintenance procedures currently in effect.

4. Pre-overhaul analysis to enable more effective overhaul

procedures based on true needs of each sub-system.

5. Reduction of unneeded repairs.

6. Quality control improvement on engines tested after

overhaul

7. Receiving inspection of new engines to reduce infant

mortality during first few trips.

292
8. Develop information useful to the manufacturer for

product improvement

9. Provide data base for overall fleet analysis and actuarial projections.

10, Improve intransit performance by restriction of necessary maintenance and repairs to the repair shop,

STATUS: Upon completion of the feasibility study actual

hardware was acquired through request for proposals from

qualified suppliers having systems capability, with respect

to both the diesel engine generator and the diagnostic hardware and software. Again we were able to obtain service of

a firm already working with the manufacturer of the engine

in other applications

By applying our railroad experience and the approaches

suggested by the feasibility study, a diagnostic analyzer

design was developed to meet our needs as an exploratory

tool. This included the capability of revising programs and

procedures as actual usage and experience dictated for optimum results.

The design for the analyzer chosen is shown in the

block diagram in Figure 5. It enables storage of parametric

data for the particular engine under test, and is programmable for the different kinds of tests to be conducted. The

present equipment is being used with narrow band inputs, but

provisions are incorporated for wide band inputs which are

under consideration for the future with respect to signature

analysis for the mechanical and combustion systems.

The field test phase of the analyzer development is

just getting under way, and it has become obvious that the

most immediate problem is selection and application of transducers which lend themselves to use as part of a field tool

where they must be applied and removed, suffering the rigors

of the field mechanics' practices yet maintaining their

ability to supply useful data with a high degree of dependability and respectability. We are also finding that wiring

harnesses and connectors will require much development work

before they will be wholly acceptable.

Another side benefit from the field study of the analyzer has been its use as a tool to acquire and print out

transient information in further study of the operating

characteristics of each of the sub-systems. For example,

the behavior of the fuel system during changes in speed and

load is found to be somewhat different from what we were led

293
to expect from steady state data taken as individual readings

under differing levels of operation. This is enabling us to

revise procedures having to do with test of primary and

secondary fuel filters for preventive maintenance in a most

troublesome area v^ich is the greatest single cause of intransit engine shutdov/n,

THE FUTURE: As the diagnostic analyzer is developed for the

diesel engine -generator set it will also be considered for

application to the other components of the refrigerator car.

Next for consideration are certain troublesome areas in the

refrigeration system, to be followed by the electrical control system.

Another area for independent investigation is that of

the many bearings of all types on board the mechanical refrigerator car. There are at least a minimum of 50 bearings

in each car, of which many are in relatively inaccessible

locations for service, but which may be subject to successful signature analysis.

One peculiarity of the mechanical car environment is

the period of operation of the car when the various cooling

and heating systems are turned off. Experience indicates

much bearing degradation takes place during non-operating

time due to the shock and vibration from the car structure,

and from the temperature changes which occur within the system causing entrance of moisture vapor.

Much work remains to be done in the diagnosis, analysis

and prognosis of the various systems, and the state of the

art appears to offer much opportunity for application to the

railroad mechanical refrigerator car.

Another area for consideration is intransit monitoring

of the performance of the car during its unattended operation. As part of the attention being given to the diesel

engine, a correlative program is under way to develop an intransit monitor which will stay aboard the car and which

will indicate cause of engine shutdown. Such a device now

under development is shown in Figure 7.

It will indicate to an inspector investigating a dead

car the diesel sub -system which apparently led to shutdown,

since the time lapse between the cause of shutdown and the

first inspection capability upon arrival at a terminal may

be several hours and the symptoms long since gone. Many

engines will start and run normally during the short terminal

time within which to observe them, so a means must be
provided to signal the cause, such signal to remain available

from battery supplied power for as much as 24 hours to be

useful

Such a device becomes an on-board diagnostic tool for

intransit repairs, and data gathered from it will also be

available to the diagnostic system to point out areas requiring further attention on that particular engine.

A subsequent development now being considered is to provide a communication link between the car and wayside interrogators to enable all cars passing such points to report

their condition and cause of malfunctions which may be

present. This will permit repair forces to be waiting when

those cars requiring attention arrive, avoiding time lost

inspecting long trains to discover any such cars, when that

time could be used to effect repairs without delaying the

train

With the emphasis on use of rail transportation to handle the large volumes of perishable foodstuffs for an increasing population at the lowest cost in terras of precious

fuel, means of further improving the effectiveness of the

rail mode of transportation will be increasingly cost effective, enabling the state of the art in the industry to be

applied at an increased level of activity.

295
N

296
297

LIST OF SENSORS

SENSOR

NUMBER FUNCTION

AlA. Exhaust Manifold Surface Temperature (Cylinder

AlB Exhaust Manifold Surface Temperature (Cylinder

AlC Exhaust Manifold Surface Temperature (Cylinder

A2 Exhaust Manifold Riser Temperature

A5 Exhaust Manifold Pressure

Bl Engine Side Temperature (Air)

B2 Lower Radiator Temperature

B5 Upper Radiator Temperature

Bh Engine Block Coolant Temperature

B5 Radiator Pressure

B6 Block Coolant Pressure

CI Sump Oil Temperature

C2 Oil Cooler Return Temperature

03 Air Out Temperature

Ck Lube Pump Pressure

C5 Gallery Oil Pressure

Dl Fuel Pump Suction Pressure

D2 Fuel Pump Pressure

D5 Common Rail Pressure

D^i Fuel Line Suction

D5 Intake Manifold Pressure

D6 Air Box Pressure

Gl Crankcase Pressure

HI Cranking Current

llOH, llOL Alternator Frequency

23OH, 25OL Two-Speed Solenoid

SSV Starter Solenoid Voltage

BATTV Battery Voltage

STARTV Starter Voltage

Figure h. Model 7^+9 diesel diagnostic analyzer.

299
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301
- LOW OIL FHESSURE

LOW FUEL PRESSURE

LOW ENGINE SPEED -j

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Figure 7.

502
DISCUSSION

J. W. Forest, Ontario Hydro : What provisions, if any, are there for

isolating ihe systems from the shock and vibration of the railroad

environment?

R. F. McKee : For many years we didn't know what the environment really

consisted of. We knew that it was bad but we really didn't have any

good measurements. Our specifications call for a capability of 20 G's

longitudinal to the rail, 10 G's lateral to the rail, 5 G's vertically

as far as original manufacture is concerned. Through shake table and

impact experiments on equipment, we developed ways to either isolate

shock loads from the system or have a system capable of riding through

the spikes, by mounting equipment more solidly. In the beginning we

did a lot of isolating work. Now we are bolting things down pretty

solidly because we have found that we were getting secondary

relationships that were unmeasurable. Some things still have to be

isolated. The thermostat, for instance, has microswi tches in it which

are very sensitive and we still isolate that. We are getting insiduous

results on long-term service life of various components through the

vibration spectrum, and we are going to study this as our next phase.

K. R. Thomas, Deere and Company : Are you going to have a problem

getting mechanics to install all those transducers?

R. F. McKee : In our company we have a separate lab where the mechanics

come by and see what we are doing. They are always suspicious of us anyway so we think the best approach is to treat this as just one more sophisticated step in giving mechanics tools so that they are working

on the thing that needs to be worked on and not searching for the

problem.

505
USING ACOUSTIC EMISSION TECHNOLOGY

TO PREDICT STRUCTURAL FAILURE"

H. L. Dunegan

Dunegan/Endevco

San Juan Capistrano, California 92675

The problems associated with assuring structural Integrity of large

complicated structures, such as bridges and power plant pressure vessels,

have been the cause of much concern to the prime contractors manufacturing these structures, and to the licensing agencies and code writers

whose responsibility it is to assure public safety. This concern is

rightly justified since we are continually striving for greater efficiencies in the use of materials which call for higher strength-toweight ratios, higher operating temperatures and pressures, and economics

in manufacturing. Each of these factors requires that better inspection

techniques and more quantitative information be available for making a judgment of operating efficiency as well as safety.

One approach that has been taken to help solve some of the problems

is sponsored research in linear fracture mechanics and nondestructive

testing technology. Much progress has been made in both areas over the

last decade such that the combination of design based on linear fracture

mechanics coupled with a thorough NDT inspection is sufficient precaution

in most cases to prevent structural failures. Problems that can arise in

applying this technique come about by the inability, in some instances,

to accurately determine the stresses under operating environments and the

size and shape of the flaw. Both pieces of information are needed to determine the stress intensity factor at a flaw site, and therefore predict

structural failure.

The purpose of this report is to show how acoustic emission techniques can be used to estimate the stress intensity factor of a growing

crack, and therefore provide predictive ability for determining failure.

In acoustic emission, the energy input is in the form of strain

energy due to mechanical, thermal, or intrinsic stresses. Interaction

and redistribution of stresses within the vicinity of a defect on a local

level gives rise to the acoustic emission signal. This comes about due to

sudden irreversible phenomena (such as plastic deformation, cleavage, or phase transformation) which releases minute quantities of strain energy,

This paper is an excerpt from an article that appeared in METALS

ENGINEERING QUARTERLY February 1975

30h

/
part of which is emitted as an elastic wave - sometimes called a stress

wave

The step of displacement which generates this stress pulse can occur on the order of 10~ s. Thus, the stress pulse has very broad band frequency components. Most engineering structures are two-dimensional in

nature. Therefore, the stress pulse will normally be dispersive in

nature, taking on the characteristics of a guided wave. Since the acoustic emission transducer is normally attached to the surface of a structure, the primary modes of interest for detection are the shear and sur- face wave components of the stress pulse.

Both Lamb waves and Rayleigh waves can be detected at the surface.

With thin plates and detection frequencies between 0.1 and 1 MHz, Lamb

waves are the most important consideration, for thick-plates Rayleigh

waves become the more dominant. Both of these wave propagation modes

have the advantage that geometrical losses go as R""*", as opposed to R~^

for infinite medium waves where R is the distance of the wave packet from

the source. Thus, a piezoelectric transducer placed on the surface of a part subjected to stress will detect the stress pulses emanating from a localized deformation, even though it is physically removed from the source by some distance (tens of ft. in some cases). By measuring the

time of arrival of the stress pulse at several transducers located on a structure, one can accurately locate the source of the signal. (This is

analogous to locating the epicenter of an earthquake, which emits an

acoustic signal on an immense scale.)

FRACTURE CONSIDERATIONS

Most structural failures occur by the initiation and growth of a crack. The crack may already be present, or cracks may initiate due to

nonmetallic inclusions, hydrogen embrittlement , stress relief heat treatment, stress corrosion cracking, or fatigue at a stress concentration. In

other instances, a structure may simply fail due to accidental overload,

or become overloaded at working stresses due to thinning of material from

the working environment. Acoustic emission techniques appear to be more

suited to the first case where failures occur due to the growth of cracks

at gross stresses well within the design limits of the structure. A

failure of this type is usually caused by the slow growth of a crack to a critical size, such that catastrophic crack propagation occurs and the

structure fails.

A whole new methodology, called Linear Elastic Fracture Mechanics, has

developed over the past decade specifically directed toward determining

the stresses in the vicinity of cracks. These stresses are controlled by

a single parameter, K, known as the stress intensity factor. This

parameter depends on the body geometry, the shape, size and location of

the flaw, and the type of loading that is present. Since the acoustic

emission in a specimen containing a crack stressed below general yield is

305
dependent on the plastic strains in the vicinity of the crack tip, and

these strains in turn depend on the stress intensity factor, it was ex- pected, and found to be true,^ that the acoustic emission characteristics

should be closely related to the stress intensity factor for the cracks

present . ,

The importance of the relationship between acoustic emission and the

stress intensity should not be overlooked. Since the stress intensity

factor, K, is the controlling parameter for the stresses in the vicinity

of a crack, and the critical value of K (called K^,, or the fracture

toughness) is where failure will occur, failure of a structure can easily

be predicted if one can estimate, from acoustic emission monitoring of a structure, the value of K for the defects in the structure and the fracture toughness K^^ for the material is known. Therefore, one need not

know the 'flaw size, stress or any other parameter in order to make failure

prediction - it is the local stresses in the vicinity of the defect and

not the defect size or gross stresses alone that are important. From

this, one would expect a small defect in a highly stressed region or one containing tensile residual stresses to be a more important consideration

than a larger defect in a relatively lower stressed region, because the

stress intensity could be higher for the smaller defect (since it depends on both the flaw size and gross stresses)

Estimating Stress Intensity Factors

The fact that a defect is or is not present in a structure should not

be the most important consideration. It is the defect that will grow in

service that will lead to problems, and it is the detection of the growing

defect and the estimate of the stress intensity in the vicinity of the defect that will allow a technical judgment to be made for keeping a structure in service. The remainder of this report will show how acoustic

emission techniques can be used for estimating the stress intensity factor, K, near a growing crack for three types of service conditions: 1)

subcritical growth due to hydrogen embrittlement or stress corrosion;

2) subcritical growth due to fatigue; and, 3) subcritical growth due to

rising load tests that would be encountered for instance during proof

testing of pressure vessels.

FATIGUE CRACKING

Basically, two acoustic emission methods can be used to detect

fatigue crack growth. In one, the acoustic emission is recorded on a periodic basis from a structure that is loaded in a single cycle to a stress higher than the working stress (periodic overload). Second, the

structure can be continuously monitored during service.

306
Periodic Overload

This technique will work as well on subcritical growth due to hydrogen embrittlement or stress corrosion cracking, but has usually been used

in fatigue crack growth studies. The technique utilizes the "Kaiser"

effect, an irreversible nature of acoustic emission, in the following

way. Assume a structure containing a defect is initially proof loaded to

a value such that the stress intensity factor present at the proof load

is

Kp = Oio/a [1]

where

Kp = stress intensity at proof load

a = geometry function

Q = stress at proof load

a = initial crack size

The structure is subjected to its working environment for some period, and

is again loaded to the same maximum proof stress while monitoring acoustic

emission. It has been determined^ that the acoustic emission, N, as a function of the stress intensity, K, could be expressed as

N = AK^ [2]

If no crack growth has occurred during the working environment, Kp at the

proof stress will be identical to what it was during the initial proof

load. Because of irreversibility (that is, no new plastic deformation),

there will be no acoustic emission present during the second loading to

the proof load. On the other hand, if crack growth has occurred such that a in Eq . [1] is larger and the structure is loaded to the same maximum

stress, the stress intensity factor, Kp, will be greater due to the in- crease in the crack length. Therefore, new deformation will occur, and

acoustic emission will be present between the working stress and proof

stress. Thus, the presence of acoustic emission between the working

stress and proof stress during a periodic overload of a structure is a , qualitative measure that defect growth has occurred at the working stress

since the last proof test.

Recovery effects of materials especially under high temperature en- vironments may affect the irreversible nature of the acoustic emission

results. Palmer^ has conducted extensive experiments on pressure vessel

steels in the U.K., and reported that for temperatures encountered in

most power plant pressure vessels, recovery effects are minimal.

To get more quantitative results on a periodic overload test, one

needs to obtain fatigue crack growth data on the materials used in a

507
structure to be tested. Paris found that the fatigue crack growth rate

depended solely on the range of the stress intensity factor, K, encountered in a cyclic test.

da/dn = BAk'^ [3]

where

da/dn = crack growth per cycle

K = stress intensity factor

n = exponent ranging between 2 and 4

By conducting rising load tests on fracture toughness specimens while

recording acoustic emission, measuring fatigue crack growth rates as a function of K, and knowing an expression for the stress intensity factor, one can evaluate the constants in Eqs. [1], [2], and [3]. By simultaneous

solutions of these equations, one can obtain an expression for the acoustic emission counts observed during a periodic overload as a function of

the number of fatigue cycles at the working load. (See Refs. 6 and 7 for

more detailed analysis.) *

Fig. 1 shows what one experimentally observes while recording acoustic

emission during periodic overloads on a fracture specimen, and what one

can theoretically predict by combinations of EqS. [1], [2], and [3]. The

sharply increasing slope indicates impending failure, and a conservative

estimate of the number of cycles to failure could have been made on strictly theoretical considerations. Application of this technique to

welded pressure vessels can be found in Ref . 8.

Continuous Monitoring of Fatigue Crack Growth

Very little work was done until recently on the application of acoustic emission to monitor fatigue crack growth. One of the primary reasons

for this was the problem with background noise from grips, rubbing surfaces, etc. Nakamura, -'-^ one of the early researchers in this field, was able to overcome much of the interference with the background noise by

using spatial filtering techniques. Within the last two years, further

improvements in transducers and instrumentation techniques have allowed

crack growth measurements to be made in the presence of high background

noise. This has led to major breakthroughs in continuous monitoring of

fatigue crack growth, and a considerable amount of work is presently going

on in this area

Harris and Dunegan-'-'^ reported detecting fatigue crack growth rates of

10~^in./c and below on high strength aluminum alloy. It was also found

in this work that, if the acoustic emission counts per cycle were plotted

as a function of energy released by crack extension per cycle, data from

steel and aluminum were normalized for a given bandwidth and sensitivity.

It was also observed (Fig. 2) that a peak occurred in the data when

plotted in this manner. The peak was found to occur within the transition

308
region from plane strain to plane stress along the crack front,

phenomenon has important implications for possible quantitative

acoustic emission data for predicting fatigue lifetime.

This

use of

RISING LOAD TESTS

Large pressure vessels and many other types of structures are normally

tested to a proof stress higher than the working stresses prior to being

put into service. It was stated previously that the stress intensity

factor, K, controls the magnitude of the stresses at the crack tip.

Therefore, if one can measure the stress intensity factor during a proof

stress cycle using acoustic emission techniques, a judgment can be made

concerning the integrity of the structure. For example. Fig. 3 is a plot

of the acoustic emission from several specimens"'-^ containing different

crack lengths. We see that all the data is normalized when plotted as a function of the stress intensity factor.

20 Corle has extended this concept to improve the reliability of rocket

motor cases. He demonstrated the flaw detection improvement achieved by

the use of acoustic emission during proof testing of motor cases over the

reliability achieved by the proof test alone. From the acoustic emission

standpoint, the improvement was greater in air melted and welded structures than in unwelded,. vacuum melted structures.

Thus we see for small structures without a great deal of complexity

one can use acoustic emission to accurately evaluate integrity once the

material characteristics are established. For complex structures con- taining riveted joints and other types of mechanical fasteners, one must

locate the source of the acoustic emission signal to more accurately take

into account signals from several sources.

FLAW LOCATION

For some types of geometries (linear welds and tubes, for .example)

a one-dimensional location scheme is adequate. Bailey^ et al^\ used this

concept to good effect for locating fatigue cracks growing from rivet

fastener holes during fatigue testing of an aircraft structural section.

Fig. 4 shows the type of specimen and the acoustic emission display used

to locate the cracks. All cracks when first detected were under nuts,

bolt heads, or in faying surfaces - locations which are difficult to re- liably inspect by conventional nondestructive techniques. Bailey, et al,

also stated that the fatigue tests were only monitored 10 pet of the total

test time, and that 15 of the 18 potential cracks identified were con- firmed by visual means at 50 times magnification.

Thus we see that, under certain situations, economical and fairly

simple hardware can be used to identify that a crack is present, and the

extent of cracking, once located, can be checked by other methods. As

309
the size and complexity of a structure increases, many more channels of

instrumentation interfaced with a computer are normally required to properly locate and keep track of the acoustic emission signals.

Multi-Channel Computer Instrumentation

Previous sections of this report have shown how acoustic emission from

a defect can be used to estimate the stress intensity factor at the defect

site. In some instances on larger structures, more than one defect may

give rise to acoustic emission signals, and extraneous noise sources may

be present. Then one must be able to locate the source of the acoustic

emission as well as evaluate the signals from each source to judge the

degree of damage occurring.

A considerable amount of work has been done over the past few

years in the development and use of computer interfaced systems for flaw

location. Many different approaches have been used for handling and display of the data. The one common feature of all approaches is the measurement of time of arrival of an acoustic emission signal to a multiply

array of transducers located on a structure. From the time difference observed between individual sensors, computations can be made of the location of the defect.

Most of the work to date has been concentrated on accurate location of

the defect so that other methods (such as ultrasonic and X-ray techniques) can be utilized to evaluate the defect. More recent instrumentation designs have incorporated location, as well as a measure of the severity of

the defect, by determining the number of counts received from individual

locations.

Fig. 5 illustrates a portable 16-channel system, expandable to 32

channels, which incorporates a realtime CRT display of the location and

the number of counts received from each location. Fig. 6 shows four

transducers mounted on a plate with two symbols marked by black tape.

Ultrasonic pulses were coupled into the plate to simulate acoustic emission signals at the locations marked by the tape. Fig. 7 shows the CRT

presentation of the transducer locations and corresponding locations detected from the injected pulses. The distance between transducers in

this example was 16 in.

The accuracy with which one can locate a source of emission can vary

from 1 to 10 pet of the transducer spacing or greater, depending on the source of the signal, attenuation, and geometry effects and surface con- dition of the structure. The histogram shown by the eight small dots in

the lower left-hand corner of Fig. 7 represents eight different arrays of

four transducers each. In this example. Array No. 2 which is displayed

in the right portion of the CRT was used to accumulate data from the

plate. Approximately 400 signals were injected into the plate to provide

the readout as shown. A similar type of histogram can be displayed on

the CRT, which shows the number of ring-down counts from each array.

310
This gives a measure of the amount of deformation or crack growth occurring

at specific locations covered by each array.

The type of printout one can obtain from this system provides the

time difference information between transducers, the X-Y coordinates of

the source, the number of ring-down counts from the signal (which is a measure of the severity or the amount of crack growth) , and a parametric

input such as pressure, force, etc.

Thus we see that the ability to locate a source of acoustic emission,

coupled with the ability to evaluate individual signals from each location, allows us to treat the large complex structure as a composite of

many localized small scale components. We can apply the ability to estimate stress intensity factors at these local levels to determine structural integrity.

CONCLUSIONS

The combination of acoustic emission and linear fracture mechanics

can provide quantitative information regarding structural failure. This

report has shown that, for certain situations, acoustic emission techniques can be used to accurately estimate the stress intensity factor, K,

at a growing crack, and therefore provide predictive information regarding

structural failure. The importance of locating defects in large structures was also stressed, and a multiple-channel computer system was described for accomplishing this function. The ability to locate a growing

defect, coupled with the ability to quantify the growth rates with fixed sensors (no scanning required) places acoustic emission in the forefront

of new techniques for the prevention of structural failure.

311
REFERENCES

1. P.C. Paris and G. Sih: Fracture Toughness Testing and Its Applica- tions , ASTM Special Technical Publication No. 381, pp. 30-81.

2. G.R. Irwin: Structural Mechanics , pp. 567-91, Pergamon Press, Oxford,

1960.

3. M.L. Williams: Journal of Applied Mechanics , 1957, no. 24, pp. 109-14.

4. G.R. Irwin: Journal of Applied Mechanics , 1975, no. 24, pp. 361-64.

5. H.L. Dunegan, D.O. Harris, and C.A. Tatro: Engineering Fracture

Mechanics Journal , 1968, vol. 1, pp. 105-12.

6. H.L. Dunegan and D.O. Harris: Materials Evaluation , October 1970,

vol. -28, no. 10, pp. 221-27.

7. D.O. Harris, H.L. Dunegan, and A.S. Tetelman: Proceedings of the Air

Force Conference on Fatigue and Fracture of Aircraft Structures and

Materials , pp. 459-71, Air Force Flight Dynamics Laboratory Report

AFFDL TR70-184, 1970.

8. D.O. Harris and H.L. Dunegan: Testing for Prediction of Material

Performance in Structures and Components , pp. 158-170, ASTM Special

Technical Publication No. 515, American Society of Testing and

Materials, Philadelphia, Pa., 1972.

9., I.e. Palmer: Material Scientific Engineering , 1973, vol. II, p. 227.

10. Yoslo Nakamura: Materials Evaluation , 1971, vol. 29, pp. 8-12.

11. T.M. Morton, R.M. Harrington, and J.G. Bjeletlch: to be published in

Engineering Fracture Mechanics . 12. S. Smith and T.M. Morton, Experimental Mechanics , May 1973, vol. 13, no . 5

13. T.M. Morton, S. Smith, and R.M. Harrington: to be published in

Experimental Mechanics . 14. D.O. Harris and H.L. Dunegan: Experimental Mechanics , February 1974,

vol. 14, no. 2, pp. 71-81.

15. R.M. Wallace, M.C. Van Wanderham, and H.S. Pearson: "Investigation of

Fatigue Crack Propagation in Ti 6Al-2Sn-4Zr-6Mo and IN-100 Using

Acoustic Emission Techniques," Pratt and Whitney Aircraft, West Palm

Beach, presented at Autumn 1973 meeting of the American Society for

Nondestructive Testing, Chicago, Illinois, October 1973.

16. J.R. Mitchell, D.M. Egle and J.F. Appl, : Proceedings of the Oklahoma

Academy of Sciences , 1972, vol. 53, pp. 121-26.

17. A. Vary and J. Klima: "A Potential Means of Using Acoustic Emission

for Crack Detection under Cyclic Load Conditions," National Aeronautics

and Space Administration Technical Memorandum NASA TM X-68228, 1973.

18. D.O. Harris: "Effect of Gain and Frequency on Acoustic Emission

Observed from Growing Fatigue Cracks," Dunegan/Endevco Report DE-74-4.

19. H.L. Dunegan and D.O. Harris: Ultrasonics , 1969, vol. 7, no. 3.

20. R.R. Corle: "The Use of Acoustic Emission to Improve Motor Case Reliability," presented at AIAA/SAE 9th Propulsion Conference , Las Vegas,

Nevada, 1973, AIAA Reprint No. 73-1258.

512

/
21. CD. Bailey and W.M. Pless: "Acoustic Emission Used to Nondestructively Determine Crack Locations in Aircraft Structure Fatigue

Specimens," 9th Symposium on Nondestructive Testing , San Antonio,

Texas, April 1973.

22. ' A.T. Green: "Testing of Glass Hemispheres Using Aerojet General's

Stress Wave Analysis Technique," Report AD 825542, Aerojet General

Corporation, September 1967.

23. D.L. Parry and D.L. Robinson: USAEC Technical Report IN-1398, Reactor

Technology TID-4500, July 1970, pp. 97-99.

24. N.O. Cross: "Status of AE as a Nondestructive Testing Technique for

Pressure Vessels," Exxon Research & Engineering Company, 27th ASME

Petroleum Mechanical Engineering Conference, New Orleans, Louisiana,

September, 1972.

25. W.D. Jolly, T.J. Davis, and M.R. Compton: "Evaluation of the AE

System," EEI-TVA Rp79 Report No. 6, January 7, 1972 (NTIS No.PB207-

591) . 26. M.P. Kelly and R.L. Bell: "Detection and Location of Flaw Growth in

the EBOR Nuclear Reactor Vessel," Dunegan/Endevco Report No. 73-4,

February 1973.

27. P.H. Hutton: Nondestructive Testing , May 1969, pp. 111-14.

28. N.O. Cross, L.L. Loushin, and J.L. Thompson: Acoustic Emission , ASTMSTP-505, December 1971, pp. 270-296.

29. R. Gopal: EEI-TVA Rp79 Addendum Report, May 1973, pp. 49-88.

30. W.D. Jolly, E.R. Reinhart, and S.P. Ying: EEI-TVA Rp79 Addendum

Report, May 1973, pp. 120-123.

31. P.G. Bentley, E.J. Burton, A. Cowan, D.G. Dawson, and T. Ingham:

Proceedings of the ASME Second International Conference on Pressure

Vessel Technology, Part II , pp. 643-54, San Antonio, Texas, October

1973.

32. N. Cretien, P. Bernard, and B. Barrachin: Proceedings of ASME

Second International Conference on Pressure Vessel Technology , Part II , pp. 655-67, San Antonio, Texas, October 1973.

33. D. Birchon, R. Dukes, and J. Taylor: Proceedings of ASME Second

International Conference on Pressure Vessel Technology, Part II , pp. 669-84, San Antonio, Texas, October 1973.

315
ro

I O

10"' n

Fig. 1 - Experimental and theoretical results

of total counts observed during the

proof cycle versus the number of

fatigue cycles at the working stress

51^
315
Fig. 3 - Summation of acoustic emission as a function of stress intensity factor for

SEN fracture specimens of 7075-T6 Al

with different initial crack sizes

316
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517
Fig. s - Multiple

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Fig. 6 - Transducer placement on a metal plate

and symbols used for illustrating flaw

location by acoustic emission multiple

channel system

518

/
Fig. 7 - CRT presentation obtained by

injecting simulated acoustic

emission signals at location

shown by symbols in Fig. 6
DISCUSSION

J. W, Forest, Ontario Hydro : How do you go about establishing the

threshholds and how does that level affect the results?

H. E. Dunegan : You have to determine the signal level expected from a given increment and the background noise in a particular frequency

range. So it may involve using either changing sensitivities or changing frequencies depending on the conditions.

J. L. Frarey, Shaker Research Corporation : When a reactor is under

steady state loading, wouldn't the signal-to-noise ratio be a real

probl em?

H. E. Dunegan : We were pleasantly surprised. We have sensors on four

boiling water reactors now. We find that when the reactor comes up

under cold start-up, there is a lot of noise. Once temperature and

full operating load are reached, things quiet down drastically. So we were pleasantly surprised that under operating conditions the reactor

is actually quieter than it is when it is being started i4p,

J. L. Frarey : But also the crack isn't progressing as fast.

H. E. Dunegan : You may want to look at the ratio of activity from an area over the last 24 hours compared lo the activity over the last 30

days. Then you can construct a curve of the ratio of activity as a function of time. If there is a change in slope, that would be an indicator that there is something very active there. It's somewhat

difficult at this point to make quantitative measurements.

\

320
APPLICATIONS OF THE SHOCK PULSE

TECHNIQUE TO HELICOPTER DIAGNOSTICS

John A. George*, Timothy C. Mayert, and Edward F. Covillt

Parks College of St. Louis University, Cahokia, Illinois 62202

INTRODUCTION

An investigation has been carried out on the feasibility of

shock pulse techniques in the detection of failures in

helicopter power trains. A standard off-the-shelf SKF

Industries model MEPA-lOA was employed to construct shock

emission envelopes of shock rate versus shock level. Data

was collected from the hanger bearings of the tail rotor

drive shaft assembly, the 42° and 90° gear box assem.blies,

and the transmission and mast assemblies as installed on

operational UH-1 series helicopters of an Army Aviation

Reserve unit. Further data was obtained from helicopters

at Fort Rucker, Alabama with implanted bearings of known

condition. The correlation between the shock emission envelopes and the degree of degradation as revealed by teardown analysis will be described. This paper will summarize

the evaluation carried out to date

THE MEPA-lOA SYSTEM

Details of the SKF shock pulse meter (Figure 1) and its

operation has been described in an earlier MFPG proceedings^. Briefly, the technique employed is to construct a

shock emission envelope containing the rate of shock emission as well as the measurement of the amplitude of shock

developed by a particular bearing. When a bearing race, or

rolling element, contains a discrete fault, such as a pit

or spall, the contact between this fault and the rolling

elements will result in repetitive impacts of short duration. As a result of these impacts, a shock wave propagates through the structure. The shock pulse travels

through the bearing and causes a pulse displacement input

to an accelerometer . The equipment used in the MEPA-lOA

system includes a 38 kHz resonance response accelerometer.

The output of the accelerometer is passed through a high

gain amplifier tuned at the resonant frequency of the

*Professor, Aerospace Engineering

tResearch Associate

321
accelerometer . This amplifier acts as a very sharp band

pass filter. After the signal is suitably processed, the

output is displayed on a counter which provides the frequency of peaks above any desired peak amplitude. No other

processing is required for analysis.

A graph is made of the shock emissions (Figure 2) and from

this data a determination of condition is made. With the

accelerometer attached, an initial rate and value evaluation

is made. The rate found becomes the first point plotted on

the ordinate at a shock level of one. A threshold varying

dial, on the instrument housing, ranges from a level of one

to ten thousand on a logarithmic scale. As the threshold is

increased, successive rates are plotted until a curve

crosses the abscissa. This value at the intercept becomes

the highest potentiometer level at which at least one shock

pulse per second can be measured. Rate values are in pulses

per second and the shock level obtained is a function of the

accelerometer used. The curves are evaluated by their general curve form as well as the magnitude of rates and/or

levels obtained. Approximately three minutes is required to

obtain shock emission curve.

SKF Industries indicates in the operators manual of the

MEPA-lOA that all curve forms are a variation of three , general forms (Figure 2) : 1) one with high rates and relatively low levels--an apparent indication of foreign matter

in the lubricant of the bearing; 2) a curve shape of low

rates and relatively high shock levels--indicative of a bearing with insufficient lubricant or possible element damage; 3) a curve with both significantly high rates and levels, with the amount of "filling out" of the curve proportional to the extent of damage. However, in the helicopter

applications to date, the relationship between curve shape

and degradation was found to be more complex.

LABORATORY FINDINGS

A laboratory study was undertaken to provide experience and

to develop the methodology to be utilized on the actual

UH-1 aircraft. A bearing test rig was set up utilizing the

same type, make, and size as those employed as hanger bearings on the UH-1 series aircraft. The hanger bearing fixture was identical to that of an operational helicopter.

The major results:

1. The SKF-provided vice-grip to which the accelerometer

is attached proved unsatisfactory. Significant differences were found in readings dependent on placement and

522
security of the vice-grip attachment. A pressure clamp

has been fabricated which can be fitted to the lands of

the bolts which hold the bearing fixture in place. The

accelerometer , in turn, is attached to the pressure

clamp. Shock rates and levels are easily reproducible

'for a given bearing assembly. Figure 3 shows the

attachment on some assemblies investigated.

2. Differences between samples of new bearings and those

determined as unserviceable and rejected for aircraft

use could be seen (Figure 4)

3. The general shape of the shock emission curve varies

with type and extent of damage. Figure 5 shows artificially degraded bearings in comparison to data obtained from samples of new bearings. Although the

curves do not follow the SKF representation of Figure

2, the increase in level over the new bearing data is

evident

4. The rates and levels are speed dependent (Figure 6)

5. Although a damaged bearing could be discerned, it was

not possible to localize the damage as to inner or

outer race, rolling element, etc.

6. Laboratory readings of rate versus level differed

from those of the same bearing assembly installed on

a UH-IH helicopter. Thus, generalized damage assessment curves must be generated with the bearing in the

actual operating environment (Figure 7).

In addition to the hanger bearing tests, SKF Industries,

under subcontract to the College, investigated the ability

of the MEPA-lOA to detect gear-sourced shocks. The College

provided technical assistance and monitored the performance

of the task. Three UH-1 42° gearboxes with several different types of gear damage were subjected to shock pulse monitoring during runs at different loads and speeds. It was

detemined that the MEPA lOA can supply warnings as to the

onset of damage in a gearbox. If the damage originates in

the bearings, an indication directly correlated with damage

is received. If the damage originates in the gears, the

indication is obtained indirectly through the sensing of

particulate contaminant passing through the bearings

(Figure 8 )

525
UH-1 DATA

Hanger Bearings

Seventy-two hanger bearings as installed on UH-1 helicopters

were tested. The helicopters were made available on a noninterference basis by an Army Aviation unit stationed near

the College. All tests were at N2 = 6600 rpm. Selected

hanger bearings were removed for teardown analysis. These

include bearings with potentiometer levels from moderate to

high. The teardown analysis was performed either by Bell

Helicopter Company or by the College. Defects, if they existed, consisted primarily of pitting and corrosion varying

from slight to severe. Figure 9 shows the shock emission

curve of a bearing with marginal level of damage. Figure 10

illustrates the level of pitting and corrosion. Wherever a hanger bearing was removed for teardown analysis, readings

were taken on the new, or replacement, bearing. In each

case, a marked reduction in rates and levels was noted.

The extensive hanger bearing data has been summarized in a single damage-assessment shock emission curve (Figure 11)

Additional data was collected on hanger bearings installed

on helicopters in the AIDAPS program at Fort Rucker. These

hanger bearings were inspected and found acceptable prior to

their use in that program. In particular, the effect of engine rpm variation and anti-torque pedal (tail rotor) inputs

were investigated. Although shock emission curves varied

with rpm as previously noted, pedal deflection gave an insignificant increase in potentiometer level.

42° Gear Box

Readings were taken on forty-two 42° gearbox drive quills.

Nine gearboxes were removed for teardown analysis, either

due to high rates (rather than high levels) or due to excessive needle swing. Typical of the latter is given in

Figure 12 wherein the rate would not stabilize at a fixed

value but would vary between the limits shown. This swing

could be due to the multiple bearing and gear assemblies

present in the input and output quills. Teardown analysis

did indicate corrosion and pitting throughout the output

inner and outer ball, radial scratches in the output roller

bearing (Figure 13), as well as an output gear pattern too

high and too far toward the toe, and pits on the input ball

and roller bearings.

Further data was collected on the AIDAPS helicopters at

Fort Rucker, Alabama, from gearboxes of known condition.

32h
Each gearbox was completely disassembled, inspected, and

any necessary component replacement accomplished prior to

reassembly and use in the program. This data included that

from an implanted input quill duplex bearing with known

defects.

In one case, the outboard half of the duplex bearing had a single spall in the outer race, 0.14" x 0.14", with a definite depth; the inboard half had some corrosion-caused pitting with one pit in the ball's path. The increase in rate

and level when compared to a damage-free gearbox is evident

from Figure 14

A second case, a duplex ball bearing with a single shallow

spall approximately 0.08" x 0.08" in the outer race, gave

evidence of progressive damage while the test was in progress. The shape of the shock emission curve changed continually over a period of minutes in both rate and shock

level. Figure 15 shows two curves developed on a single

run. A change in slope takes place (A) , a sharp increase in

rate (B-C) , a continual change in slope (C-D) . Without

shutting down the engine, the second curve (E-F-G) was developed. After engine shutdown, an oil sample analysis revealed traces of metal, although not beyond that considered

acceptable. The dotted line is an extrapolation of the

initial slope and gives an indication of the shock level

stabilizing at a factor of ten higher. Two more runs were

made which essentially repeated curve E-F-G. Teardown

analysis showed that the original degradation had not

noticeably changed but the new spalls were found on the

outer race and on one ball bearing.

90^ Gearbox

Twelve 90° gearboxes were tested. Figure 16 is a scatter

diagram of shock emissions. Two assemblies indicate either

a higher rate or higher level than the average of those

tested. These are continuing to be monitored until replacement gearboxes are available. The curve labeled "damagefree" is taken from a gearbox of known condition installed

on an AIDAPS helicopter. Figure 17 shows the shock emission

envelope of a gearbox removed for teardown analysis. The

reason this particular one was chosen was because of the

continually changing curve shape during the test run. This

slope change could be indicative of progressive damage or

metal contaminants in the oil. Figure 18 shows the sharp

burred edge spall in the outer race and spalling in the

inner race of the small duplex bearing, as well as pitting

and corrosion in the outer race of the duplex bearing.

525
Mast Bearing and Transmission

Figure 19 is a scatter diagram of nine different mast

assemblies. The solid line, again, is from an AIDAPS helicopter. The assembly chosen for teardown was the one exhibiting the high rate and level . The outer race had

scratches one centimeter in length, scuffs, false brinnelling, heat discoloration and corrosion. Several balls had

scratches and nicks and the inner race ring also had

scratches (Figure 20) . After the new mast bearing was installed, the shock and

rate levels of the replacement bearing were markedly

reduced . v . , No transmission assemblies indicated any abnormal rates or

levels on readings taken from the input drive quill and

therefore, none were removed for teardown analysis.

Flight Tests

All the previous data was collected on ground runs. A

series of tests were conducted to compare ground runs,

hover-in-ground effect, low and high speed flight and

autorotation conditions. All data collected was from the

input drive quill of the transmission. This component was

selected because of ease of accelerometer mounting and lack

of necessity of any aircraft modifications. The various

flight conditions, and hence loadings, had negligible

effect on the shape of the shock emission envelope.

SUMMARY

The SKF MEPA-lOA has shown its effectiveness and reliability

as a bearing health analyzer in helicopter applications.

The shock pulse technique has proven its value as a quick

and accurate means to determine the general health of selected components on operational helicopters through the

means of the shock emission profile. When components were

tested and reviewed in comparison with others of the same

type, it becomes apparent that the shock pulse technique can

separate assemblies by degrees of degradation and damage.

However, it was not possible to localize the damage as to

the rolling elements, inner or outer race, gear teeth, etc.

All of the damage as revealed by teardown analysis was

correlatable to the data of the shock emission curves, that

is, moderate rates and/or levels indicated moderate degradation and high rates and/or levels indicated severe

degradation

526
Although an off-the-shelf piece of commercial equipment, the

MEPA-lOA did not have any malfunctions operating in field

conditions. Ambient temperatures ranged from -30OC to 40°C.

Accelerometers were exposed to exhaust gas temperatures in

excess of 200°C. Hov/ever, the present system of plotting

the shock emission data by hand and the necessary judgment

required to determine bearing health does not lend itself

for use by Army Aviation maintenance personnel . When a fully automated system is available, the shock pulse

technique will prove itself to be an effective tool in

reducing aircraft maintenance costs.

ACKNOWLEDGEMENTS

The study was performed under contract to the United States

Army Aviation Systems Command (USAAVSCOF^. Parks College

gratefully acknowledges the support and assistance of the

USAAVSCOM Flight Operations Division, Saint Louis, Missouri;

Hawthorn Aviation, Fort Rucker, Alabama; Bell Helicopter

Company, Fort Worth, Texas; United States Army Flight Test

Board, Fort Rucker, Alabama; and the 102d USARFFAC

Cahokia, Illinois.

REFERENCES

^P.L. Howard, "Shock Pulse Instrumentation", Proceedings of

the 14th Mechanical Failures Prevention Group Meeting, Los

Angeles, California, Jan. 1971; MFPG Technical Report 2,

Feb. 1971.

^T.C. Mayer, E.F. Covill, J. A. George, J.T. Harrington

"Applications of the Shock Pulse Technique to Helicopter

Diagnostics", USAAVSCOM Technical Report 75-18A,B, 1975.

527
528
529
rate

10° 10' lo' lO' 10*"

level

Figure Comparison of new and daraaged bearings

in a laboratory environment,

1000 -1

rate

Figure 5« Scatter diagrara of new bearings versus

artificially degraded bearings.

330
1000

1000 -

rato

100 -

10 -

10"

aircraft

laboratory

10' 10^

level

10- 10

Figure 7. Oomparison of hanger bearing shock emission

envelope from aircraft and laboratory,

551
luuO

rate

luo

10

l\.2 Groarbox Test

10

Basel ine

at lo,l\. hp,

jt^GO rpm

10' —TT10'

level

Daraaf^ed gears

at 13.25 hp,

^ 351-1-0 rprri

I 10 10"

Figure 8. Baseline versus damaged gears with particulate contaminant in the oil.

1000

rate

100

10 -

damaged bearing

level

Figure 9. Comparison of damaged and replacement

hanger bearing.

552

/
Figure 10. Damaged hanger bearing removed from

UH -IH helicopter.

553
rate

1000 -

100 -

10 -

10° 10*

I , 10"^

level

10*

Figure 11. UH -1 hanger bearing damage assessment

shock emission curve.

1000

rate

100 -

10 -

output quill

input quill

Figure 12, ;Shock pulse curve of 14.2 gearbox romoved

for teardown analysis. Lined areas indicate

variation in ouput readings.

33^
l\.2^ gearbox, output^ inner ball bearing with corrosion

damage on outer race.

i\.2^ gearbox, output, outer ball bearing with corrosion

and pitting damage on outor race.

Figure 13. Damage seen in I4.2 gearbox removed from

o])erational helicopter.

355
1000-1

icorate

10-

A with ST)all

baseline •

10 10' 10^

level

10 10

Figure OoMparison of baseline and degraded gearbox

implant®d with spalled duplex bearing.

1000 H

100

rate

10 -

Figure 13. Ii2 gearbox init^iantea with a spailcd duplex

bearing. iiividence of damage progressing.

536
1000 1

rate

level

Figure 17. Shock Ginission curve of 90** gearbox

removiid for teardown analysis.

537
small duplex bearing, outer race

ivith. burred edge

soall

small duplex bearing, inner race

with spalls

duplex bearing,

outer race with

pitting and

corrosion

Figure l8. Damage seen in 90° gearbox rtiirioved from

operational helicopter.

558

'

- r
1000 H

rate

dama-:-cd nast

replacement

damai-^e free

100

10 -

10 lu' 10'

level

Figure 19. Scatter diagram of mast assemblies.

539
false brinellinc' on

outer race of mast

bearing

pitting on outer

race of mast bearing

scoring on balls of

mast bearing

I

20, Damage as seen on raast. bearing removed

from operational helicopter,

5^0
criscussiON

R. Leni'ch, Caterpillar Tracior Company : Would the mechanic have

replaced all of the bearings that the shock pulse method indicated were

bad if the shock pulse method had not been used?

J. A. George : All of these were good operational bearings as far as the present inspection procedures indicate. But if these bearings were

sent to overhaul, there would be components replaced. In other words,

those that we said were good were indeed good, those that we said were moderate would be replaced because the bearing was out, and those that were severely damaged very definitely would be replaced.

J. L. Frarey, Shaker Research Corporation : Did you do enough work with

the speed dependence to determine if it is a linear or a square

relationship. In other words, do you think you could build this in as

a correction factor for a variable speed machine?

J. A. George : We did not look at it directly. Offhand, I would say

they are not directly linear.

J. L. Frarey : How far away from the bearing could you get. In other

words, could you do the 42 and the 90 in one central position if you

didn't care whether it was the input or the output?

J. A. George : If you are riding on the input side you could probably

detect eventual degradation on the output, but we have been riding as close to the bearing as we can. On the 90 there is only one place we

can go - we are detecting both input and output.

5^1
LST 1179 DIESEL DIAGNOSTIC SYSTEM FEASIBILITY STUDY

*M.B. Peterson

J . Frarey

D. Dominy

H. Hegner

H.C. Burnett

*Wear Sciences,, Inc. , Scotia, New York 12302

Introduction

The Mechanical Failures Prevention Group has been requested by Mr. Ray

Coulombe of the Engineering Branch of NAVSEC to undertake a study to

determine the advantages to be gained by the Navy in the development

and use of a propulsion condition monitoring system. In response to

this request a task force was formed by MFPG which is currently con- ducting such a study. This paper is a progress report on the results

to date.

Task Force

The task force shown in Table I was selected by the Executive Committee

of MFPG to conduct the study. The selection was based upon the individual's background to perform the functions as shown in Table II. In

addition, a committee of approximately 20 members of MFPG has been

selected to review the work of the task force so that the conclusions

can be said to represent the collected view of the MFPG.

Method of Operation

The advantages of a diagnostic system are quite well known to most

engineers who work in this field. However, one cannot assume that

these advantages will necessarily result in a real cost saving when

installed. In fact, one could imagine that with a reliable, trouble

free, well maintained engine there might be a cost penalty when one requires a better "read out" on its condition. For this reason the

task force proposed to compare the relative costs involved of ships'

maintenance with and without a diagnostic system. The 1179 class

LST was chosen by the Navy to use as an example.

To conduct this study, two areas of investigation were necessary.

First, one must propose a diagnostic system and then determine the

accumulated costs of development, manufacture, installation and

checkout. This requires a knowledge of the engine parameters and

malfunctioning components to be measured. These, of course, must

lend themselves to practical realities of shipboard conditions and

competence. Secondly, one must accumulate as accurately as possible
the total maintenance costs on the ship and the variety of malfunctions which make up these costs. The question of course to be

answered is which of these malfunctions and maintenance costs would

have been avoided if the proposed diagnostic system would have been

installed.

The work scope to accumulate the desired information is given in

Table 2. The task force is now in its fourth month of operation.

The purpose of this paper is to present the results on each of the

task items listed in Table 2 along with the conclusions to date.

Program

As a first step in the program, Mr. Dominy, who has had considerable

experience with this particular engine, made a list of all the engine

components and what in his experience generally go wrong with them.

He then proposed a list of measurements which would have to be taken

to diagnose malfunctions with these components. At this time the

practicality of the measurements was not given detailed consideration

The purpose of a diagnostic system is not only to diagnose component

malfunctions but also to determine if the engine parameters are within the prescribed limits. This was also included in the list of

measurements which are shown in Table 3.

The information provided by Mr. Dominy was supplemented by data from

the ship. First of all, a list of the measurements now taken on the

ship was made. These are the underlined quantities of Table 3.

It is immediately apparent that most of the measurements proposed are already taken on the ship in one way or another. Thus, we are not

really proposing anything new, only a better way of collecting and

presenting the information.

In reality, only three new types of measures are needed:

Contamination

Position

Vibration

As it turns out, these measurements are extremely important and will

diagnose the most troublesome malfunctions actually found on the LST

1179s. Of course, one could look at this from another point of

view. Maybe these are the most troublesome components because such

measurements are not now commonly taken.

This list of proposed measures was supplied to Mr. Hegner who is

determining their feasibility and practicality for shipboard use. His main concern is with means of measuring the new parameters and

the cylinder pressures. Many of the diesel inspectors rely quite

heavily on this quantity.
A considerable amount of time was also devoted to accumulating shipboard maintenance experience that is used in determining what propulsion system problems have been encountered in service and what

these problems have cost the Navy. Information on the most common problems were accumulated from the following sources:

(1) Interviews with shipboard personnel

(2) Diesel inspectors' reports

(3) Gibbs and Cocks Causality Report Review '

(4) Class maintenance problems

(5) 3M LST maintenance history

The 3M maintenance history was particularly valuable since it not

only allowed an independent problem review to be made but also

provided a means to determine the cost of each problem encountered.

For exanple, an injector change- out costs $7,250 plus 7 labor hours.

Based upon the 3M system the total repair costs per ship for the past

four years are shown in Table 4. This works out to an average of

1000 hours and $14,000 materials costs per year. These numbers,

although not excessive, seem rather high considering that these are brand new engines only 2 to 4 years old which are not used veiy often.

Furthermore, these are minimum costs since many of the material

charges may not appear, being charged to another account.

In the 3M system, charges are allocated by system categories.

Exanples are diesel engine, reduction gear, clutches and brakes,

exhaust, fuel oil, water, etc. Each system is then broken down by

equipment. Thus a complete review of the 3M system will yield the

high cost systems and the high cost malfunctions. These are listed

in Table 5. If the repair costs are to be reduced, the diagnostic

system must be able to detect these faults.

The repair costs are only one item of the total maintenance costs.

Others include the planned or scheduled maintenance costs, shipyard

costs, overhaul costs, engineering costs associated with shipboard

maintenance and personnel costs as represented by the type commander,

NAVSEC personnel, and NAVSEA. A review of these costs was also

made. Unfortunately, this information is only available for the last

two years; however, it does give a rough estimate of the level.

These data are given in Table 6.

Also shown in Table 6 is the hours devoted to engine watch apportioned

to sea and shore. This is representative of the fact that there are four men per engine room, three engine rooms, and three shifts of

eight hours each for a total of thirty- six men along with several

others. This is based upon the actual "underway" watch bill of a given ship.
The scheduled maintenance costs were acquired by collecting all the

maintenance cards for the propulsion system and adding up the total

number of hours in the 3-year cycle. This number is also low since

many of the maintenance cards say "as required". These hours were

not included.

The planning costs have not been estimated; however, these will

probably be small since only a few people are directly involved. Although a diagnostic system will greatly assist such people in planning

shipyard maintenance it will probably not reduce their costs.

The overhaul costs are somewhat uncertain since only two ships have

been overhauled to date. However, we may use the figure of $70,000

per engine once every five years as a representative figure. This

amounts to approximately $100,000 per year.

Evaluation

It is now necessary to ascertain what reduction in these costs would

result if a diagnostic system was available. Sufficient information

is now on hand to make a reasonable estimate; however, this will

depend upon the diagnostic system. Thus, final conclusions are not

as yet available. Some conclusions, however, can be made.

First, it is obvious that if substantial savings are to be made, they

will have to come from "watch", scheduled maintenance, shipyard or overhaul costs. So the following questions may be asked:

(1) Can the use of the proposed diagnostic system substantially reduce the "watch" man hours?

(2) Can the use of the proposed diagnostic system eliminate

a substantial number of scheduled maintenance items?

(3) Can early diagnosis of failures reduce the need for dry

docking or reduce repair costs?

(4) Might it be possible to postpone overhaul with the

proposed diagnostic system?

Of these questions the first appears to be the greatest source of

saving. The diagnostic system is intended to do exactly the same time as "watch". During "watch" the enginemen perform the following

type tasks:

Watch engine

Take readings

Run subsystems (purifier)

Oil analysis samples

Change filters

Set controls

3^^
It can be seen that no repair or scheduled maintenance is performed.

If it is only possible to reduce those hours by 1/2 and using the

direct labor rate of $3/hour, a saving of $87,000/ship or $1,740,000

for the LSTs will result. A diagnostic system almost seems justified

on this basis alone.

It should also be noted that the total man hours add up to 13 man

hours/hour. The only way this can be accomplished is to have 39 men

on board. These, of course, are not available and the scheduled

maintenance must be neglected. Thus, the diagnostic system would

release men for more productive activities.

The advantages of a diagnostic system are not limited only to the

above cost savings. Other more intangible benefits relate to the

advantages of greater awareness of the ship's condition.

These are as follows:

(1) Type Commanders (LST maintenance) have been involved

with the "day to day" ship repairs. With the re- organization recently completed the type Commanders will

only be involved in shipyard work. This will require

the ship's force to assume greater responsibility for

the planning and execution of repair work.

(2) In the past, repairs (RAV s/TAV s) were accomplished

when needed. A new system is now being instituted in

which ship repairs will be accumulated and accomplished

during a prescribed period of time (once per year) .

• With this system, greater planning will be necessary.

(3) Lead times on parts required for repair are becoming ex- cessively long (for example, gears require 18 to 24

months for LST)

(4) The maintenance cycle has been increased from three years

to five years.

(5) Engineers required to understand engine problems and to

prepare ship alterations rarely have sufficient information as to the background of the problem. In addition,

it often is difficult to determine if a solution has been

obtained.

The task force has tried to remain objective in its study and has

also considered the disadvantages of introducing a diagnostic system.

These are listed as follows:

(1) Cost -

(2) Over reliance
As far as the costs are concerned it is not only the diagnostic

system which must be considered but the costs to make it fully

'operational.

The second disadvantage is that the ships force may become too re- liant on the system. That is, no maintenance will be performed and

little attention paid to the propulsion system unless the lights

flash. The ship must be capable of operating as an independent unit

and close identification with the engine and its performance is

encouraged. To answer this criticism, experience ivith other

diagnostic systems is being ascertained.

Diagnostic Systems Initial Consideration

Figure 1 is the initial simplified block diagram of a possible

diagnostic system for the propulsion system of a LST 1179 class vessel.

The system employs one minicomputer along with peripheral input/output

devices. This portion of the system would be located in a central or convenient location on the ship. Each engine room is considered an independent entity and each is instrumented with the required transducers, signal conditioning equipment, multiplexing and data transmitting equipment. It is presently proposed that this portion of the

system contain an A/D converter so that all data transmission is

accomplished digitally.

Several modes of system operation are to be considered. Certain

modes- -for exanple, alarm indication- -take priority over others. A

time- sharing software package is envisioned that will allow different

operation modes to proceed seemingly simultaneously.

The requirements on the system are as follows:

(1) Continuously cycle through propulsion system measurements

and compare each measurement against engine limits. In the

event an out -of -limit condition exists, an alarm will be

sounded and backup details typed out on the typewriter.

(2) All parameters measured in 1 above associated with the

alarm will be continuously stored on the magnetic disc or tape for analysis after shutdown.

(3) Once a day at preselected propulsion system power settings,

data will be converted to engineering units and compared

with the last previous stored data at this power setting.

The data will be stored if different. If not different,

the data will be discarded. Since the ship will not go

through all preselected power settings each day, different

amounts of data will be recorded, depending on operations.

5^7
(4) Data trends will be analyzed and degrading components

identified. Once the degraded component has been identified, appropriate maintenance action will be typed out

on the typewriter.

(5) Periodically, the system will provide the engineering

officer a status report including data tabulations and

plots.

(6) Periodically while in port, system provisions will allow

the copying of data for transmittal to the class

maintenance officer.

(7) Periodically, data will be inputted to the system such as SOAP readings. These data will be stored and trended

along with measured data.

(8) The system will allow the engineering officer to use the

system as a preprogrammed or easily programmed microcomputer or programmable calculator.

The above system description is being used as a basis of review with

system manufacturers to obtain initial hardware/software costs,

lliese costs will be evaluated against the benefits derived from

system installation.
Table I

Task Force

M. Peterson

H. C. Burnett

D. Dominy

J . Frarey

H. Hegner

National Bureau of Standards

Mechanical Technology, Inc.

Shaker Research Corp,

General American Corp.

Wear Sciences, Inc.

Table II

Work Scope

Diagnostic Feasibility Program

Drive System Parameters

Common Malfunctions

Maintenance Experience

Sensor Measurem.ents

Diagnostic System Design

System Effectiveness

Report and Review

3U9
Table III

Propulsion System Measures

Ambient Pressure

Ambient Temp

RPM

Exhaust Temp

Firing Pressure

Cylinder Pressure

Torsional Vibration

FO Pump Pressure

FO HeaderT

FQ Rack Position

Fuel Analysis

Shaft Run Out

Coupling Displacement

Pedestal Temp

Clutch Temp

GOV Load Position

Propeller Pitch

GOV HO Pressure

Manifold Temp

Manifold Pressure

Turbo Exhaust T" Turbo Vibration

Turbo LO Pressure

Exhaust Smoke Meter

Water in T

Water Out T

LO Pump P

LO Header P

LO Level

LO Oil Analysis

GB Bearing Temp

GB LO Pressur*e

~

GB LO Temp

GB Bearing Position

Gland Temp

Contamination

550
Table IV

LST 1179 Ship Repair Costs

3M System

I^n Hours

bnip Commissioned Repair Material Costs

ll/y 9/69 52,913

lloU 4109 T M A 1 A 39,414

1181 8/70 O P 7 "7 2533 63, 682

118Z iz/oy 3936 51 , /zl

llo3 0/ /U 6919 /9 , 139

1184 3450 154, 236

118b 0/ /U 714Q 106, 26

118o 4167 r £Z All 56 , 417

1 1 R7 1 r\/ir\ -LU/ / u

18/11 Ql 81

1188 2/71 2994 56,772

1189 4/71 5217 108,642

1190 6/71 4601 48,402

1191 7/71 3252 45,364

1192 9/71 1625 35,687

1193 11/71 1668 34,047

1194 1/72 2847 24,766

1195 3/72 2189 44,788

1196 5/72 1715 10,252

1197 5/72 1791 12,596

1198 9/72 5467 18,042

551
Table V

LST 1179

Common Malfunctions

Operational Limits

Head, Valves

Injectors, Pumps, etc.

Salt Water Pumps

Turbocharger

Air Start Motor

Governor

Pistons

Fluid Contamination

Clutch and Brake

CPP Pumps

Gland Seals

Accessory Drive Gears

Fuel Oil Pump

CPP Gears

Linear Corrosion

Exhaust Leaks

Gear LO Pumps

552

- /
Table VI

Costs Per Year Per Ship

Man Hours Materials

Watch Sea 42,000

Shore 16,430

Repair 1,000 $ 14,000

Scheduled Maintenance 50,448 —

Shipyard 32 , 380

Overhaul --- 100,000

Engineering 5 4,000

Planning Ty Com — —

NAVSEA

353
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35^
DISCUSSION

R. A. Coulombe, U.S. Naval Ship Engineering Center : The second phase

of this work will be a pilot program on a selected ship and the

progress report indicates to me that this is going to be justified.

355
MECHANICAL FAILURES PREVENTION GROUP

22nd MEETING

Detection, Diagnosis and Prp-gnosis

List of Registrants

Robert W. Adamson

Cal . Polytechnic State University

M, E. Department

San Luis Obispo, California 93407

H. C. Burnett

National Bureau of Standards

Metallurgy Division

Washington, DC 20234

Leslie H. Adkins

TMDE Product Management Office

USAMMC, Attn: AMXMD-TR

Lexington, Kentucky 40503

Roger D. Baggenstoss

TRW Systems Group

1 Spruce Park, M2-2175

Redondo Beach, California 90277

Bruce C. Baird, Sr.

Boeing

P. 0. Box 58747

Houston, Texas 77058

R. H. Barber

Solar, Div. of International

Harvester Company

2200 Pacific Highway

P. 0. Box 80966

San Diego, California 92138

Dr. J. S. Bendat

Independent Consultant

833 Moraga Drive

Los Angeles, California 90049

David B. Board

Boeing Vertol Company

716 Peachtree Road

Claymont, Delaware 19703

J. E. Borhaug

Pretech, Inc.

3305 Vincent Road

Pleasant Hill, California 94523

Hans U. Burri

RCA Corporation, Non-Electronic

Test Engineering

M. S. 8-3

Box 588

Burlington, Massachusetts 01803

Colby E. Buzzell

General Electric Company

50 Fordham Road

Wilmington, Massachusetts 01887

Bruce E. Carver

Pacific Fruit Express Company

116 New Montgomery Street, Rm. 529

San Francisco, California 94105

F. K. Chin

General American Research Div./GATX

7449 N. Natchez Avenue

Niles, Illinois 60648

Dr. J. M. Chudobiak

University of Sasketchewan

Sasketoon, Saskatchewan

S7N OWO Canada

Henry A. Cole, Jr.

Randomdec Computers

84 Alvarado Avenue

Los Altos, California 94022

Kenneth Collinge

Avco Lycoming

550 Main Street

Stratford, Connecticut 06497

356
0. E. Compton

ORGN 3423/32

Northrop Corp., Aircraft Division

3901 W. Broadway

Hawthorne, California 90250

D. Costabile

Gfficer-In-Charge (Code 862)

FMSAEG/NWS, Seal Beach

Attn: GIDEP Operations Center

SETE/ Library

Corona, California 91720

Raymond A. Coulombe

U. S. Navy Department

1430 Ruatan Street

Adelphi, Maryland 20783

Edward F. Covill

Parks College of St. Louis Univ.

Cahokia, Illinois 62206

Frank Crapotta

Officer-In-Charge (Code 862)

FMSAEG/NWS, Seal Beach

Attn: GIDEP Operations Center

SETE/Project

Corona, California 91720

V. F. Cremonese

Hughes Helicopters

Centinella & Teale

Culver City, California 90230

C. L. Dean

Solar, Div. of International

Harvester Company

2200 Pacific Highway

P. 0. Box 80966

San Diego, California 92138

George E. deLong

Naval Air Systems Command

Representative Pacific, N.A.S.NI

San Diego, California 92135

Dwight L. Dennis

U. S. Navy (Naval Weapons Center)

531 Q Nimitz

China Lake, California 93555

Don D' Intino

Naval Air Engineering Center

Lakehurst, New Jersey 08733

D. Dominy

Mechanical Technology, Inc.

Latham, New York 12110

Max Dow

Eastern Airlines

Miami, Florida 33159

Earl DuBack

General Dynamics, Electric Boat

Eastern Point Road

Groton, Connecticut 06340

^ B. E. Duff

' Fruit Growers Express & Western

Fruit Express Company

16 Roth Street

Alexandria, Virginia 22314

Harold Dunegan

Endevco Corporation

Rancho Viejo Road

San Juan Capistrano, Calif. 92675

John H. Dunmore

Technical Marketing

Turbo Research, Inc.

1440 Phoenixville Pike

West Chester, Pennsylvania 19380

John Dziuba

Eastern Airlines

MIA International Airport

Miami, Florida 33159

Bob Eisenmann

Endevco

5625 FM 1960 West-Suite 513

Houston, Texas 77068

L. H. Emery

Department of Transportation

National Highway Traffic Safety

Administration

Washington, DC 20590

557
Loren Enochson

Time/Data Corporation

1050 E. Meadow Circle

Palo Alto, California 94303

Howard E. Fineman

RCA Corporation, Non-Electronic

Test Engineering

M. S. 8-3

Box 588

Burlington, Massachusetts 01803

Paul Fleming

National Bureau of Standards

Metallurgy Division

Washington, DC 20234

R. E. Ford

Pratt & Whitney Aircraft

P. 0. Box 2691

West Palm Beach, Florida 33402

Jerry W. Forest

Ontario Hydro

800 Kipling Avenue

Toronto, Ontario

M8Z 5S4 Canada

J. L. Frarey

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, New York 12019

Dwayne N. Fry

Oak Ridge National Laboratory

P. 0. Box X, Bldg. 3500

Oak Ridge, Tennessee 37830

Charles R. Garbett

Shell Development Company

P. 0. Box 481

Houston, Texas 77001

B. K. Genetti

General Electric

175 Curtner Avenue

San Jose, California 95125

John A. George

Parks College of St. Louis Univ.

Cahokia, Illinois 62202

Louis Greco

U. S. Navy

Naval Air Engineering Center

Lakehurst, New Jersey 08733

George B. Grim

Caterpillar Tractor Company

Technical Center, Bldg. A,

Research Department

Peoria, Illinois 61629

A. Halfacre United Aircraft of Canada

P. 0. Box 10

Longueui 1 , Quebec

Canada

R. L. Hamm

Experimental Project Engineer

Mechanical Technology, Inc.

Latham, New York 12110

Tom Harrington

The Franklin Institute Research

Laboratory

20th & Parkway

Philadelphia, Pennsylvania 19103

Henry R. Hegner

General American Transportation

Corporation

Research Division

7449 North Natchez Avenue

Niles, Illinois 60648

Charles L. Heizman

Time/Data Corporation

1050 E. Meadow Circle

Palo Alto, California 94303

Andrew J. Hess

Naval Air Test Center

Patuxent River, Maryland 20670

558
James L. Higgins

Endevco

30700 Rancho Viejo

San Juan Capistrano, Calif. 92672

G. William Hogg

U. S. Army Air Mobility Research &

Development Laboratory

Ft. Eustis, Virginia 23604

R. Hohenberg

Mechanical Technology, Inc.

968 Albany Shaker Road

Latham, New York 12110

Mike Hoobchaak

Naval Sea Systems Command

6312 Alamo Street

Springfield, Virginia 22150

Chris E. Horten

Naval Ship Engineering Center

(Sec. 6107C6)

Center Bldg., Prince Georges Center

Hyattsville, Maryland 20782

J. R. Houghton

Tennessee State University

1808 Ashwood Avenue

Nashville, Tennessee 37212

Dr. Donald R. Houser

Ohio State University

206 West 18th Avenue

Columbus, Ohio 43210

Paul L. Howard

SKF Industries, Inc.

1100 First Avenue

King of Prussia, Pennsylvania

19380

Ralph James

Exxon Chemical Company

Baytown, Texas 77520

Marvin Jasper

Teledyne Controls

200 N. Aviation Boulevard

El Segundo, California 90245

Andre Jaudet

Electricite de France - Service Map

17 Avenue du General de Gaulle

92 Clamart, France

James D. Johnson

PRD Electronics

6801 Jericho Turnpike

Syosset, New York 11791 .

Frank C. Jones

HTL K West

9371 Kramer Avenue

Westminster, California 92683

William J. Kelly

Hughes Helicopters

Centinela Avenue at Teale Street

Culver City, California 90230

H. M. Kiefer

Shell Oil Company

P. 0. Box 3105

1100 Milam Building

Houston, Texas 77058

Jerry Koons, Mechanic

Federated Department Stores

Hangar 28, 422 Wilmer Avenue

Lunken Airport

Cincinnati, Ohio 45226

Joseph Kukel

Garrett Corporation

30605 Rue Langlois

Rancho Palos Verdes, California

90274

R. S. Kulp

Pratt & Whitney Aircraft

P. 0. Box 2691

West Palm Beach, Florida 33402

Robert W. Lancaster

Bradford Computers and Systems,

Inc.

Rockville, Maryland 20850

359
G. L. Leadley

Research Metallurgist

Association of American Railroads

3140 S. Federal Street

Chicago, Illinois 60616 >

R. Lemch

Caterpillar Tractor Company

100 N. E. Adams Street

Peoria, Illinois 61734

Frederick- F. Ling

Mechanics Division

Rensselaer Polytechnic Institute

Troy, New York 12181

D. W. Long

Pacific Fruit Express Company

116 New Montgomery Street

San Francisco, California 94105

M. Lourenco

National Highway Traffic Safety

Administration

Department of Transportation

Washington, DC 20590

Dominick P, Lubrano

U. S. Army, Commander,

Eustis Directorate

SAVDL-EU-MOR

Ft. Eustis, Virginia 23604

Jaroslaw B. Luciw

Baird Atomic, Inc.

125 Middlesex TPK

Bedford, Massachusetts 01730

Dr. J. Marrs

Tektronix, Incorporated

P. 0. Box 500

Beaverton, Oregon 97077

Marvin P. Marsh

Vibration Instruments Company

1614 Orangethorpe Way

Anaheim, California 92801

William K. Mathison

Puget Sound Naval Shipyard

Route 1 , Box 396

Port Orchard, Washington 98366

T. C, Mayer

Parks College

Cahokia, Illinois 62206

Wil 1 iam L. McCarthy

M.M.O.E.S.

731 Middleneck Road

Great Neck, New York 11023

R. F. McKee

Pacific Fruit Express Company

116 New Montgomery Street

San Francisco, California 94105

Harry McNeill

Nuclear Regulatory Commission

Washington, DC 20555

William R. McWhirter, Jr.

Naval Ship Research and Development

Center

Code 2762, 3B, Fluid Systems Branch

Annapolis, Maryland 21402

L. D. Meyer

General Electric Company

P. 0. Box 43

Building 37, Room 680

Schenectady, New York 12301

Richard S. Miller

Office of Naval Research

Arlington, Virginia 22217

John Miner

Pratt & Whitney Aircraft

400 Main Street

E. Hartford, Connecticut 06108

Ray Misialek

NAVSEC, Philadelphia Division

Philadelphia, Pennsylvania 19112

360
Douglas J, Murray

Pacific Fruit Express Company

116 New Montgomery Street

San Francisco, California 94105

Prof. Douglas Muster

University of Houston

Department of Mechanical

Engineering

Houston, Texas 77004

Allen Naipo

Teledyne Controls

200 N. Aviation Boulevard

El Segundo, California 90245

W. Neal

Boeing Company

P. 0. Box 58747

Houston, Texas 77058

H. 0. Northern, Dept. 5876 S6

Detroit Diesel Allison Div., GMC

P. 0. Box 894

Indianapolis, Indiana 46206

John K. O'Connor

Consumer Product Safety Commission

Office of Product Defe-ct

Identification

5401 Westbard Avenue, Room 200

Washington, DC 20207

Dennis M. O'Dea

Exxon Research & Engineering Co.

P. 0. Box 101

Florham Park, New Jersey 07932

Charles C. Olsefsky

Hughes Helicopters

Culver City, California 90230

David H. Page

CP Rail

Room 1000, Windsor Station

Montreal, Quebec

Canada

G. L. Parker

National High Traffic Safety

Administration

Office of Vehicle Safety Research

Washington, DC 20590

E. Passaglia

National Bureau of Standards

Chief, Metallurgy Division

Washington, DC 20234

Marshall B. Peterson

Wear Sciences, Inc.

32 Sutherland Drive

Scotia, New York 12302

Gerald J. Philips

Naval Ship Research and Development

Center

Annapolis, Maryland 21402

Glen A. Phillips

RORCC Mechanics Subcommittee,

Santa Fe Railway Company

Motive Power Building

Crane and Branner Streets

Topeka, Kansas 66616

Stan Pinel

Industrial Tectonics, Inc.

18301 Santa Fe

Compton, California 90221

James F. Primm, II Atchison, Topeka & Santa Fe

Rai Iway

1001 E. Crane Street

Topeka, Kansas 66616

W. P. Quinn

McDonnell Douglas Aircraft Co.

3855 Lakewood Boulevard

41-55, Department Cl-270

Flight & Laboratory Department

Long Beach, California 90846

Wi n iam Reber

Exxon Chemical Company, Inc.

Baytown, Texas 77520

561
Alfred C. Renz

PRD Electronics, Inc.

1200 Prospect Avenue

Westbury, New York 11590

Stanton W. Ross

Fluor Engineers & Const.

3320 East La Palma

Anaheim, California 92806

Richard J. Salvinski 01/1261

TRW Systems Group

One Space Park

Redondo Beach, California 90277

Maurice V. Scherb

Consultant

Box 1055

Beverly Hills, ^California 90213

F. H. Schlereth

Electronics Laboratory

General Electric Company

Syracuse, New York 13201

Donald B. Schneider

Vibro-Meter Corporation

22109 South Vermo?ft Avenue

Torrance, California 90502

David N. Schuh

Beta Machinery Analysis, Ltd.

R. R. 4

Calgary, Alberta

T2M 4L4 Canada

Uri Sela

Exxon Company, U.S.A.

3400 East 2nd Street

Benicia, California 94510

P. B. Senholzi

Department of the Navy

Naval Air Engineering Center

Ground Support Equipment Dept.

Lakehurst, New Jersey 08733

T. R. Shives

National Bureau of Standards

Metallurgy Division

Washington, DC 20234

Norman L. Shute

Analysts, Inc.

P. 0. Box 2206

Rolling Hills, California 90274

Herbert B. Singer

Charles S. Draper Laboratory

68 Albany Street

Cambridge, Massachusetts 02139

Henry G. Smith

Consultant for Hughes Helicopter^

201 S. Francisca #1

Redondo Beach, California 90277

K. A. Smith

General Electric Company

P. 0. Box 43

Building 37, Room 680

Schenectady, New York 12301

R. L. Smith

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, New York 12019

Cdr. M. E. Southgate

British Defence Staff Washington

British Embassy

3100 Massachusetts Avenue, NW

Washington, DC 20008

Robert Stenberg

U. S. Army, AVSCOM

12th & Spruce Street

St. Louis, Missouri 63166

James W. Strosnider

Vibro-Meter Corporation

22109 South Vermont Avenue

Torrance, California 90502

562
T. Suzuki

Nippon Steel, U.S.A., Inc.

611 W. 6th Street, Suite 1320

Los Angeles, California 90017

William H. Tait

Dom. Foundries

P. 0. Box 460

Hamilton, Ontario

Canada

Paul M. Tanimoto

FAA-Western

15000 Aviation Boulevard

Hawthorne, California 90250

Dr. Thomas Tauber

Tedeco

24 E. Glenolden Avenue

Glenolden, Pennsylvania 19050

Kenneth R. Thomas

Deere & Company Technical Center

3300 River Drive

Moline, Illinois 61265

R. P. Wallace

Raytheon Company

P. 0. Box 360

Portsmouth, Rhode Island 02871

Robert J. Watts

USA Tank Automotive Command

Attn: AMSTA-MVC

Warren, Michigan 48090

Lyle Wells

Vibration Instruments Company

1614 Orangethorpe Way

Anaheim, California 92801

Dr. R. L. Wesson

U. S. Geological Survey

Menlo Park, California 94025

Robert M. Whittier

Endevco

Rancho Viejo Road

San Juan Capistrano, Calif. 92675

M. Wildman

Ampex Corporation

401 Broadway

Redwood City, California 94063

Robert E. Wilson

Sacramento City College

Aeronautics Department

3835 Freeport Boulevard

Sacramento, California 95822

Dan Woodward

Time/Data Corporation

1050 E. Meadow Circle

Palo Alto, California 94303

James Wright

Hughes Aircraft Company

Building 117, Stop 5 P. 0. Box 90515

Los Angeles, California 90009

D. E. Wulfhorst

Cummins Engine Company

1000 5th Street

Columbus, Indiana 47201

363

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actions help you estimate your potential for saving energy—and reducing costs. And EPIC contains much more—financial analysis procedures to evaluate projects, sources of information on energy conservation, engineering

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UERGT CDMSERVATION
U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SH E FT

1. PUBLICATION OR REPORT NO. 2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Detection, Diagnosis and Prognosis--Proceedings of the

22nd Meeting of the Mechanical Failures Prevention Group

5. Publication Date December 1975

6. Performing Organization Code

i.mxmm editors . T. Robert Shives and William A. Willard

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

nAIIUnALDUrvCAUUrolAiNUAKUj

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City. State, ZIP)

Office of Naval Research, Dept. of the Navy, Arlington, VA 222

NASA, Goddard Space Flight Center, Greenbelt, MD 20771

Frankford Arsenal, U.S. Army, Philadelphia, PA 19137

FAA, Dept. of Transportation, Washington, D. C. 20591

13. Type of Report & Period

1^.-, Covered

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15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card. Number: 75- 619365

16. ABSTRACT (A 200-word or less [actual summary of most si^ilicant information. If document includes a significant

bibliography or literature survey, mention it here.)

These Proceedings consist of a group of nineteen submitted papers and discussions

from the 22nd meeting of the Mechanical Failures Prevention Group which was held

at the Grand Hotel in Anaheim, California on April 23-25, 1975. Failure detection,

diagnosis, and prognosis represent the central theme of the Proceedings.

Technology and techniques, ongoing diagnostic programs, and coming requirements

in the field of DD&P are discussed. In addition, several case histories are presented.

17. KEY WORDS (six to twelve entries; alphabetical order; capital! ze only the first letter of the first key word unless a proper name; separated by semicolons

)

Diagnostic case histories; diagnostic systems; failure detection; failure

diagnosis; failure prevention; failure prognosis

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