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REFERENCE

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Harold Berger and Leonard Mordfin, Editors

Office of Nondestructive Evaluation

National Measurement Laboratory

National Bureau of Standards

‘ IS. Department of Commerce

sshington, shine DC 20234

November 1980

Prepared for:Bureau of Standards

of Commerce

DC 20234

t i

NBSIR 80-2162

\

1 TECHNICAL ACTIVITIES 1980

OFFICE OF NONDESTRUCTIVE

EVALUATION

National Bureau of Standards

Library, £-01 Admin. Bldg.

FEB 2 7 1S81

OC/00

no.

(Qib

Harold Berger and Leonard Mordfin, Editors

Office of Nondestructive Evaluation

National Measurement Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

November 1980

Prepared for: National Bureau of Standards

Department of Commerce

Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technology, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TECHNICAL ACTIVITIES

Table of Contents

Page

Introduction 1

Technical Progress Reports

1. Absolute Acoustic Emission Sensor Calibration F. Breckenridge . . 6

2. Standard Transducer for the Acoustic Emission Calibration Service --

-- F. Breckenridge 10

3. Acoustic Emission Source Characterization--Laboratory Controlled

Experimental Study of the Physical Process of AE N. Hsu ... 12

4. Acoustic Emission Flaw Location N. Hsu 14

5. Improved Acoustic Emission Transducers T. Proctor 15

6. Acoustic Emission-Materials Characterization J. A. Simmons

and R. B. Clough 22

7. Electric Power Research Institute/National Bueau of Standards Joint

Acoustic Emission Program D. G. Eitzen 24

8. Polymer Sensors for NDE S. Edelman and S. C. Roth 26

9. Strength Development of Concrete J. R. Clifton 27

10. Application of NDE to Construction/Army J. R. Clifton and

L. Knab 29

11. NDE of Moisture in Roofing Systems/Air Force L. I. Knab and

R. G. Mathey 32

12. Eddy Current Imaging System B. Field 33

13. Eddy Current Conductivity G. Free 39

14. Theoretical Modeling in Eddy Current NDE A. Kahn 43

15. Eddy Current Standards L. H. Bennett, J. R. Cuthill and

L. J. Swartzendruber 44

16. Development/Application of Deep Penetration Eddy Current Techniques

J. B. Beal 45

17. Nondestructive Evaluation of Nonuniformities in 2219 Aluminum Alloy

Plate-Relationship to Processing/NASA L. J. Swartzendruber,

L. K. Ives, W. J. Boettinger, S. R. Coriell, D. B. Ballard,

D. E. Laughlin, R. B. Clough, F. S. Biancaniello, P. J. Blau,

J. W. Cahn, R. Mehrabian and G. Free 46

i
Page

18. Electrochemical Noise J. Kruger 54

19. Leak Rate Reference Standards S. Ruthberg 56

20. Magnetic Measurements L. Swartzendruber 60

21. Optical Nondestructive Evaluation G. S. White and A. Feldman . . 62

22. Quantitative Holographic NDE C. M. Vest and G. Birnbaum 66

23. Liquid Penetrant Test Blocks J. Young and F. Ogburn 67

24. Doppler-Broadened Positron Annihilation Lineshape for Detection of

Defects in Materials R. C. Reno and L. J. Swartzendruber ... 69

25. Standards for Ultrasonic NDE D. G. Eitzen 72

26. Ultrasonic Materials Characterization R. Mehrabian, S. Fick,

R. B. Clough and J. A. Simmons 74

27. Ultrasonic Imaging M. Linzer 75

28. Nondestructive Evaluation of Composites H. M. Ledbetter and

J. Moulder 76

29. Ultrasonic NDE Application Work D. Eitzen, G. Blessing,

D. Chwirut, D. MacDonald and C. Tschiegg 79

30. Reliability of Ultrasonic Weld Inspection/NRC D. G. Eitzen ... 80

31. X-Radiographic Standards and Applications R. C. Placious and

D. Polansky 82

32. Recommendation for Measuring Unsharpness in Radiography

D. Polansky and R. Placious 85

33. X-Ray Residual Stress Evaluation In The Interior of Industrial

Materials M. Kuriyama, W. J. Boettinger and C. J. Bechtoldt . 87

34. Accelerator-Based Radiography J. W. Behrens, R. A. Schrack and

C. D. Bowman 91

35. Measurement of the L/D Ratio for Neutron Radiography W. L. Parker

and D. A. Garrett 93

36. Wear Condition Monitoring A. W. Ruff 99

37. Safety Factors and Mathematical Modeling J. T. Fong 101

i i

Appendix 107
Introduction

Nondestructive evaluation (NDE) involves many measurement methods that

are used to examine materials or assemblies in such a way that the tested

object can be used after the test is finished. This is in contrast to destructive tests in which the tested object is destroyed in order to obtain

the required information, e.g., a tensile test in which the object is pulled

apart. NDE methods vary from straightforward visual inspection to sophisticated approaches in which three-dimensional images of the interior of

objects are reconstructed from x-ray, ultrasonic or neutron measurements.

These kinds of tests, involving optical, radiographic, magnetic, electrical,

ultrasonic and other similar phenomena, are chosen and used so as not to

impair the usefulness of the tested object. A comparison of the common methods for NDE is given in Table I.

The traditional reason for the use of NDE in industry has been to assure

safety. Therefore, NDE is particularly well used in critical industries

such as aerospace, nuclear and military. In recent years, a greater appreciation for the value of NDE in consumer industries has also become apparent.

In addition to providing improved safety, NDE, as part of an improved quality

assurance activity, offers potential for improved productivity, conservation

of both energy and materials and better quality products.

Despite the increasing use of NDE methods for practical purposes, there

are needs to improve NDE measurement methods and to relate measurements to

the actual performance of the material. The Office of Nondestructive Evaluation was established by the National Bureau of Standards to assist industry

and government agencies in improving the reliability of materials and structures; NBS is working to help industry develop methods for accurate and re- producible NDE measurements. This includes technical investigations, development

of standards (both measurement standards and procedural documents), characterization of instruments, and assessments of the meaning of NDE measurements in

relation to material performance. The main emphasis of the NBS program is on the needs for improved measurements, calibration standards and procedures for

many of the NDE methods commonly used in industry.

At the Bureau the NDE program is coordinated by the National Measurement

Laboratory. Strong interactions with industry, technical societies, and

government agencies have been established in order to solicit their advice

on needs and to aid in technology transfer for developed methods and standards.

An overview of the NBS technical program in NDE follows. More detailed

reports of recent progress in selected areas of the program are provided in

the next section of this report.

Work reported in the Technical Progress section includes several NDErelated programs not funded directly by the Office of NDE.

1
Table I

COMPARISON OF COMMON NONDESTRUCTIVE EVALUATION METHODS

Method Characteristics

Detected

Advantages Limitations Example

of Use

Ultrasonics

Changes in acoustic

impedance caused by

cracks, nonbonds, in- clusions, or interfaces:

Can penetrate thick

materials; excellent for crack detection; can

be automated.

Normally requires

coupling to material

either by contact to surface or immersion

in a fluid such as

water.

Adhesive as- semblies for bond integrity.

Radiography Changes in density

from voids, inclusions, material variations; placement of internal parts.

Can be used to inspect

wide range of materials and thicknesses;

versatile; film provides

record of inspection.

Radiation safety re- quires precautions; expensive; detection of cracks can be difficult.Pipeline welds

for penetration, inclu- sions, voids.

VisualOptical Surface characteristics such as finish, scratches, cracks, or

color; strain in trans- parent materials.

Often convenient; can

be automated.

Can be applied only to surfaces, through sur- face openings, or to transparent material.Paper, wood,

or metal for surface finish and uniformity. Eddy

Currents Changes in electrical conductivity caused by

material variations,

cracks, voids, or in- clusions.

Readily automated;

moderate cost. Limited to electrically

conducting materials;

limited penetration

depth.

Heat ex- changer tubes

for wall thin- ning and

cracks.

Liquid Penetrant Surface openings due

to cracks, porosity, seams, or folds.

Inexpensive, easy to use, readily portable,

sensitive to small sur- face flaws.

Flaw must be open to surface. Not useful on

porous materials.

Turbine

blades for sur- face cracks or

porosity.

Magnetic

Particles Leakage magnetic flux caused by surface or near-surface cracks,

voids, inclusions, material or geometry

changes.

Inexpensive, sensitive both to surface and

near-surface flaws.

Limited to ferromagnetic material; surface

preparation and postinspection demagnetization may be re- quired.

Railroad

wheels for cracks.

2
Acoustic-Ultrasonic Programs:

Work is in progress to develop and improve methods for calibration

of ultrasonic and acoustic emission transducers. Spectral characteristics,

beam profile, and total sound power measurements are being studied. Several

transducer calibration services, both in ultrasonics and acoustic emission,

are available.

NBS Researchers are investigating ultrasonic test blocks to improve

the measurement reproducibility of these metal calibration blocks. A calibration service for aluminum and steel ultrasonic reference blocks is available. Further directions for this effort include the development of

material -independent test blocks and the development of well-characterized

fatigue cracks that could serve as a calibration artifact for may NDE tests.

Electromagnetic Methods:

NBS Scientists are examining methods for the measurement of visual

acuity under typical NDE inspection conditions. This includes the effects

of subdued lighting common in radiographic reading rooms and of the dark

booth situations typically used in fluorescent penetrant and magnetic particle inspection. The program will characterize test methods used in NDE where

the human eye is an integral part of the system. Visual parameters critical

to the ability of people to detect and judge visual indications of defects

will be identified. These accomplishments will lead to recommendations for

improved visual acuity measurement methods.

Optical methods utilizing reflected and scattered light are being investigated for the characterization of surface defects and for the measurement

of surface roughness. A review of optical NDE methods is in preparation.

Consideration is being given to the need for standards in holographic NDE.

Facilities for dc and ac electrical conductivity measurements have been

completed. Procedures have been established for the measurement of conductivity over the range of 1-100 percent of the International Annealed Copper

Standard (IACS). Methods for the calibration of eddy-current test equipment

are under investigation. Conductivity standards for the range from 30 to 60%

IACS are available as an SRM.

The magnetics program is particularly concerned with improving measurements for magnetic particle testing. The work includes efforts to determine

the uniformity of magnetization within the inspected part, measurements of

magnetic leakage flux and determination of the leakage flux needed for

detection of subsurface defects.

3
Leakage Testing:

Reference standards for leakage rate are being developed to improve

leak rate measurements.

Penetrant Testing:

NBS scientists have developed a crack calibration plate for the evaluation

of penetrant sensitivity; this is now available as an SRM. The fluids and

particles used for penetrant testing are also of interest. Brightness measure- ments of fluorescent penetrants are planned, along with work on measurements of

key properties of the fluids.

Radiography:

Current programs involve work in both neutron and x- radiography. The

x-ray program includes investigations of standards for the measurement of

spatial resolution in radiographic systems, for the determination of response

of x-ray film and for the characterization of real-time fluoroscopic systems.

Developments in progress include work on improved x-ray screens and determination of scattered radiation content and its effect on radiographic detectors

and systems.

The neutron radiographic studies are made primarily at the NBS research

reactor and the 100 MeV linear accelerator. Work has also been carried out

with a 3 MeV Van de Graaff accelerator. A recommended practice for thermal

neutron radiography has been developed in collaboration with the American

Society for Testing and Materials. Standards for characterizing neutron beams

for radiography and gaging are under investigation. NBS scientists have investigated the use of three-dimensional thermal neutron radiography and have

shown the application of this inspection procedure to nuclear fuel subassemblies,

batteries, and art objects. Work has been done with resonance neutrons and

plans include radiographic studies with cold neutrons.

Thermal -Infrared:

A recently completed program resulted in the development of a method for

the nondestructive evaluation of batteries used in critical assemblies such

as cardiac pacemakers. A microcalorimeter capable of measurements in the 0.2

to 1000 microwatt range is used to measure heat generated in batteries and, in some cases, pacemakers under a variety of conditions. Heat generation by new and partially discharged batteries is measured under no-load conditions as a measure of self-discharge. The work has resulted in a nondestructive method

to determine power cell quality. Additional work on infrared NDE systems is

being considered.

4
Wear Debris Analysis:

Detection of worn metal in lubricants in mechanical machinery is now used in both military and civilian programs to determine the proper time for

engine, bearing, and transmission overhaul. This method is now being expanded

in a current NBS program, in which the wear debris particles in the lubricant

are detected, sized, and examined in order to determine where and by what

mechanism wear is occurring. X-ray microanalysis techniques have been developed

for particles in the micrometer range. The techniques offer increased sensitivity for engine condition monitoring compared to conventional SOAP methods.

5
Technical Progress Reports

1. Absolute Acoustic Emission Sensor Calibration

F. Breckenridge

Mechanical Production Metrology Division

National Engineering Laboratory

Acoustic emission (AE) techniques are widely used for inspection and

monitoring of high performance structures such as large pressure vessels (steam

boilers, nuclear reactors, etc.), piping, and aircraft and for control of manu- facturing processes. Central to all such work is the necessity to be able to

standardize and intercompare the equipment used and the results obtained. All

acoustic emission systems use transducers to convert the structure-borne sound waves to electrical signals. System characterization, therefore, depends on being able to characterize and understand the action of the transducers. The

need for a standard method of calibrating transducers has been stressed by the

ASNT, the ASTM, the ASME, and other technical organizations concerned with

using acoustic emission techniques. It is the fervent hope of many that the

calibration be in terms of absolute physical quantities such as open circuit

volts of output per meter of surface displacement as the transducer face. We

have made a major step in this direction by offering a calibration service for

AE transducers using an absolute surface-pulse method.

Results of any acoustic emission test, such as an event count or a ringdown count depend very much upon the sensitivities and frequency responses of

the transducers used. If the transducers of a source-locating array are of un- equal sensitivity or respond differently to a particular kind of wave motion,

then the results may be in error. By providing a standard basis on which transducers can be compared we have made it possible to compare results of one test

with those of another. It is now possible for a manufacturer or a user to set

up acceptance-rejection criteria for transducers so that repeatable results can be approached.

We have developed and implemented a calibration scheme, which we feel is

suitable for the purpose, and which yields the frequency response of a transducer to structure-borne waves at a surface of the type that are normally en- countered in acoustic emission work. Furthermore, the calibration is absolute

in the sense that the transducer output voltage response is measured for a given well-established, dynamic input displacement. This displacement is determined by two independent methods, both of which are absolute and which agree

with each other within a few percent. The calibration results can be given

either as a transducer impulse response, or as a frequency response to a con- stant displacement (or velocity or acceleration) input. In any case, the

units are output volts per meter (or meter per second or per meter per second

squared)

.

a American Society for Nondestructive Testing

b American Society for Testing and Materials

c American Society for Mechanical Engineers

6
The basic principles that make the calibration possible were described

by Breckenridge, Tschiegg, and Greenspan1 in 1975. These principles have

been applied by us in the calibration system we have constructed. A calibration system2 ’ 3 patterned after ours, but with some modifications, has been

built and is in use now by one major manufacturer of acoustic emission systems

and transducers. Another manufacturer is actively developing a system also

based on the research of this project.

We expect that most of the transducers submitted to us for calibration

will be used as secondary standards against which other transducers will be

calibrated. The techniques used to transfer the calibration to other transducers will, in most cases, be similar to that which we use in our primary

calibration. Furthermore, using the techniques that we have developed, it is

possible for any laboratory desiring calibrated transducers to design and

build a system which could calibrate transducers directly against measureable

physical quantities without reference to any secondary-standard transducer.

This calibration service (formally announced in SP 250 addendum dated

December 1979) has been received with considerable interest. Between January

and September 1980, 50 calibration events have been processed. Clients include

AET,^ B&K,

e Battel le, Dunnegan/Endevco, Rockwell as well as ASTM and the other

NBS units. While the now existing calibration service provides a basis for

traceability and some very important information, the service has a number of

caveats which we hope to eliminate. Provision of an epicenter calibration

capability will significantly enhance our ability to provide the required

information.

References

1. F. R. Breckenridge, C. E. Tschiegg, and M. Greenspan, "Acoustic Emission:

Some Applications of Lamb's Problem," J. Acoust. Soc. Am. 57\ 627-631

(1975).

2. Ching Feng and R. M. Whittier, "Acoustic Emission Transducer Calibration

Using Transient Surface Waves and Signal Analysis," paper presented at

the International Conference on Acoustic Emission, September 1979.

3. "Now Hear This," September 1979, Dunegan/Endevco, San Juan Capistrano,

CA.

Acoustic Emission Technology

e Brvel and Kjaer (Denmark)

7
2 . Standard Transducer for the Acoustic Emission Calibration Service

F. Breckenridge

Mechanical Production Metrology Division

National Engineering Laboratory

A critical part of the recently announced (Dec. 1979) calibration

capability for acoustic emission (AE) sensors is the standard transducer

against which a sensor under test is compared. A complete analysis of the

standard transducer has just been completed. 1

The standard transducer, shown in Figure 1, is a capacitive line sensitive device which makes an absolute measurement of the normal component of

dynamic surface displacement on a flat solid. It is used to measure the normal component of surface-wave motion, the direction of travel of the wave

being known. This is accomplished with a very high sensitivity and without

loading the surface which is measured.

The transducer consists mainly of a cylinder of brass supported above

the horizontal surface whose vertical motion is to be measured. The brass

cylinder, which is the charged electrode of the variable capacitor, has its

axis horizontal and is separated from the steel surface by an air gap of

about 4 ym. Thus the active area is a narrow strip approximating a line segment. The line segment is oriented so as to be tangent at its midpoint to

the advancing circular wavefronts from the point source used in the calibration. This is accomplished with the help of a small mirror attached parallel

to the transducer axis.

Calculation of the capacitance between a cylinder of finite length and a parallel plane, as well as calculation of the sensitivity of such a transducer,

is difficult. The problem is simple, however, for an infinite cylinder.

Accordingly, the transducer consists of three cylindrical parts, end to end,

with insulators in between, as shown in Fig. 2. The center part is the active

electrode and the two ends are electrical guards, which, when in use, are driven by a unity gain amplifier whose input is connected to the center part.

The center part may be considered as part of an infinitely long cylinder.

The transducer rests on very thin polycarbonate shims which determine the

air gap between the brass back plate and the flat surface. The supports are remote from the sensing portion and are compliant so that the measured surface

is practically not loaded at least over the range of 10 kHz to 1 MHz.

The sensitivity has been calculated starting with the known sensitivity

of an infinitely long cylinder parallel to a plane. Effects due to the motion

not all being in phase under the transducer have been analyzed. For example,

at 1 MHz this effect decreases the amplitude by about 0.71 dB and does not

shift the phase. Effects due to the line reception of a circular wave front

have also been analyzed and, for example, at 1 MHz this effect reduces the

amplitude by less than 1 percent and retards the phase by about 8 percent.

Transducer resonances have also been analyzed and measured and occur mostly

below 1 kHz.

8
Examining true errors (those for which corrections cannot be made)

results in an estimate of an uncertainty of about 3 percent. To test this

uncertainty, experimental results were compared to theory with an agreement

of 2 to 4 percent.

In summary, a capacitive, line-sensitive, displacement transducer has

been constructed for measuring the surface-wave displacement of a surface

without loading it. The transducer has a bandwidth of better than 10 kHz

to 1 MHz, and a displacement threshold of about 10“12 m rms. It has been

demonstrated that the output from the transducer can be calculated within

a few percent. The transducer is expected to be used in the calibration of

acoustic emission sensors.

References

1. F. R. Breckenridge and M. Greenspan, "Surface-Wave Displacement:

Absolute Measurements Using a Capacitive Transducer," to be published

in the Journal of the Acoustical Society of America.

9
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transducer. A and E are the electrical guards, C is the

active part of the transducer, B and D are insulators,

and F is the advancing wavefront.
3. Acoustic Emission Source Characterization— Laboratory Controlled

Experimental Study of the Physical Processes of AE

N. Hsu

Mechanical Production Metrology Division

National Engineering Laboratory

The ultimate goal of AE signal analysis is to determine the exact nature

of the AE source from detected signals so that the source mechanism can be

quantified and the reliability of AE technology can be assured. To achieve

such a goal, we studied the details of the physical processes of AE, from the

generation of the stress wave at the source to the detection of the electrical

voltage signals, through the combination of analysis, design, and conducting

of controlled experiments in our laboratory. The steps are:

1. Analyze the AE signal evolution process and break down the problem

into three separable parts.

2. Construct a laboratory experimental system with an analytical basis

such that the coupling between theoretical and experimental results

provides unambiguous and definitive interpretation.

3. Resolve the forward problem - make the signature of the detected AE

predictable.

4. Resolve the inverse problem - develop a signal analysis technique

to derive the AE source waveform explicitly from the remotelydetected AE signals.

Some relevant laboratory test results concerning the detected AE signals

and how they relate to the source waveforms have been reported and they are summarized below. While these findings showed the complexities of AE signals

and the difficulties of their analysis, these definitive findings did point

out the direction for future developments.

1. The detected AE signals have little resemblance to the original source waveforms.

2. Given a well-defined simulated source, the detected signals have

reproducible features which depend on (a) sensor characteristics,

(b) relative location between sensor and source, and (c) geometry

of the structure.

3. The initial part of the detected signal carries the essential information about the source when the sensor is close to the source. Furthermore the detected signal can be predicted by theory if the source waveform is known.

12
4. Under laboratory-controlled conditions the inverse problem, to

compute the source waveform explicitly from the detected signal,

can be solved.

Specific applications of sensor characterization, structure calibration,

and AE source quantification based upon the understanding of the physical

processes of AE are being developed. Source deconvolution techniques for

complex structures based upon experimentally determined impulse response

functions are also being developed.

13
4. Acoustic Emission Flaw Location

N. Hsu

Mechanical Production Metrology Division

National Engineering Laboratory

The detection of the differences in time of arrival of Acoustic Emission

(AE) from an active flaw to strategically placed sensors provides a unique

technique for determining the location of the active flaw. In this technique

the location of the AE source is computed by the triangulation method. The

technique has the advantage of being passive and is capable of monitoring a relatively large area in situ and in real time. Since 1979 we have initiated

a systematic study of the problems and possible solutions associated with AE

flaw location. The objectives of the study are to devise system calibration

techniques to ensure reproducibility and reliability and to define limitations

and optimization procedures through error analysis. Included in the study are the characterization of the various modules of a triangulation system and the

development of laboratory experiments and theory to analyze transient wave propagation in structures. The system characterization and the transient wave analysis are essentially an extension of the study of a well-characterized AE system

developed and reported previously.

Characterization of flaw location systems using triangulation involves

both instrumentation hardware and computer software. Methods are being developed for calibration of sensors, amplifiers, filters and switching pulsers, and

time coincidence counters. A time coincidence counter module has been designed

and constructed. The module is interfaced to a minicomputer through direct

memory access. Time of arrivals in modular units of 8 channels each can be

acquired and a self-test scheme is incorportated in the construction. Triangulation algorithms are classified into four groups: 1) over determined linearization; 2) direct computation based upon polar coordinates; 3) iteration schemes,

and; 4) sorting against pre-computed grids. These algorithms have been programmed

in FORTRAN. Detailed comparison of these programs with regard to their speed,

versatility, accuracy and limitation are being made.

14
5. Improved Acoustic Emission Transducers*

T. Proctor

Mechanical Production Metrology Division

National Engineering Laboratory

With the increased need for better signal interpretation in the Acoustic

Emission field, high quality mechanical to electrical signal reproduction is

of great importance to improvements in the acoustic emission NDE method of

determining and monitoring structural integrity. The importance of using transducers that are truly hi-fi cannot be overstated. Identification and characterization of AE events from signature information will only be possible through

the use of hi-fi transducers. Such useful schemes as deconvolution and coincidence techniques will only be put to full use for eliminating random and coherent

noise problems when hi-fi transducers are available. As a result, there exists

a need for a transducer which has very good response, and which is also conve- nient to use and which has good sensitivity. The capacitance transducer does

have very good frequency and phase response for vertical motion but it is delicate and somewhat difficult to use because of high surface finish requirements

and it has low sensitivity. We have been working on a series of improved piezoelectric transducers which have good frequency and phase response while being

much more convenient to use than the capacitance transducer and also having a much higher sensitivity.

Basically these improved piezoelectric transducers have been designed so

as to avoid any physical mechanism which would cause resonant conditions or coherent interference to occur in the frequency range of interest. This has

been accomplished by (1) reducing the reflection of the back wave in the transducer through the use of a matched backing (2) reducing the contact area of the

transducer such that its dimension is small compared to the smallest wavelength

of interest, (3) eliminating of extraneous parts of the transducer such as case,

connector, etc. in an effort to avoid coupled resonance conditions and (4)

eliminating the usual wear plate which often produced coherent interference in

the signal received.

A family of transducers which embody the four notions mentioned has been

constructed to establish feasibility. These transducers are primarily vertical

displacement sensors. Their performance is remarkably good. Over the band of

10. KHz to 1 MHz these transducers have a displacement spectra which is essentially

flat and is free- of any resonant conditions. The phase response is also very well

controlled. Figures 3 and 4 display the amplitude response and the phase response

as determined by the NBS acoustic emission transducer calibration procedure.

A third way of examining transducer response for faithful reproduction is

to compare the time waveform with the actual displacement- time history. Fig. 5

is the response of the standard capacitance transducer to a step force function.

It reproduces the surface vertical displacement due to this driving function

* Publication subject to patent disclosure.

15
almost perfectly. Figure 6 is the response of one improved piezoelectric

transducer. Fig. 7 is a typical response of a commercially available transducer to the same step force signal. When comparing this response with the

response of most of the commercially available transducers, it is apparent

that its response is much better while its sensitivity is comparable.

The surface and through-pulses produced by a step force are good signals

with which to test transducer responses and performance. This is primarily

because the wave solutions are known. Presently, we are working on throughpulse method for calibrating transducers. In particular, through-pulse com- parisions have been made using the improved piezoelectric transducer. The

results although not final, are very encouraging. Some of these results will

be available for reporting in a talk before the Acoustical Society in November.

In addition to the on-going research on transducers for vertical motion,

the same techniques will be applied to horizontal -motion sensors. We have every reason to believe that this will produce a good hi-fi, horizontal motion detector

for use in acoustic emission NDE.

16
MAGNITUDE

(dB)

SPECTRUM MAGNITUDE : DIV: 101
SPECTRUM PHASE: DIV: 101
TRANSDUCER

OUTPUT

VOLTAGE

180

-

14-0

-100

-60

-20

20

60

100

140

TRANSDUCER OUTPUT: STD: 101
TRANSDUCER OUTPUT: UNK : 101

6 . Acoustic Emission - Materials Characterization

J. A. Simmons and R. B. Clough

Metallurgy Division

National Measurement Laboratory

Acoustic emission (AE) relies on the detection of stress waves emitted

during the motion of flaws or from other microstructural changes in a highly

stressed region of a structure. This technique has been applied to aerospace,

petrochemical, bridge, and power plant structures to monitor structural integrity. It has also been used to detect faulty welds in production lines.

In addition, AE has been used for materials research studies on microstructure

related properties such as deformation mechanisms, phase transformations, and

fracture.

Highlights in the AE area in the Metallurgy Division during the past year

are:

1) Development of Indentation Techniques for the experimental production

of AE signals from material defects;

2) Experiment design for multichannel AE source characteri zation

3) Progress on acoustic emission theory and signal processing techniques.

1) Indentation techniques have been highly developed for use with ceramic

materials for studying crack growth under controlled loading. We have therefore begun to adapt the technique to use with metals as a new type of controllable

acoustic emission source. Besides the control possible on the growth of defects,

this method also ensures that the source location is fixed, an essential feature

for AE signal analysis and microstructure correlation. Such a technique provides,

under the proper conditions, a means of generating reproducible AE signals from

known types of sources, having predicable signatures. This allows one to actively

control AE and thus constitutes an advance in the technique from its present mode

of merely passive listening.

We have been developing the indentation method in metals and alloys so far

using three new types of methods: (a) indentation brittle fracture; (b) indentation fatigue; and (c) indentation stress corrosion cracking.

The brittle fracture method has been successful on steels which have been

hardened by heat treatment. It has been found that if the surface is hardened

to greater than 45±5 on the Rockwell C scale, indentation by a diamond pyramid

will produce subsurface penny-shaped median plane cracks generally less than a millimeter in size. By controlled loading it is possible to produce identical

repetitive signatures, typically on the order of 10 but sometimes over 100.

Comparison with SEM micrographs suggests that these signals are produced by

incremental crack growth along carbides and martensitic platelets. This idea

has been exploited in the design of a portable "acoustic embrittlement detector"

which can detect locally embrittled areas of structures such as in the heat

affected zones of welds or on critically stressed areas.

22
This technique has also been studied as a means of producing localized

fatigue cracks in 2024 and 7075 aluminum where, after sufficient load cycling,

reproducible signals are emitted. Comparison of AE signals and SEM micrographs

shows characteristic differences in signals in these alloys which are explainable in terms of the defect microstructure. Finally, fatigue cracks can be

generated and after removal of the indentor a drop of corrosive medium is

placed over the indentation. The residual stress is sufficient to generate

numerous stress corrosion signals which are also being studied in relation to

microstructure.

Interactive experiments with Dr. Wadley of AERE, Harwell, have also begun

using a plate indented with a bias stress to give further control on the defect

morphology. There are in fact a number of interesting experiments suggested

by this newly available research tool which cannot be summarized now but appear

quite fruitful.

2) A high speed interface has been designed and is being constructed for

monitoring up to 16 AE channels using 20 MHz transient A to D recorders with

variable timescale for synchronization, up to 100 dB dynamic range, and less

than 100 millisecond dead time to dump all channels. This interface will be

connected to our new Perkin-Elmer 3220 microcomputer and will be operated re- motely in the laboratory under computer control. Monitoring of experimental

parameters will also be under computer control. A loading machine capable of

producing bias stresses in large metal plates is oeing designed to permit creating defects under variable but controlled conditions. This instrumentation will

permit us to simultaneously monitor at several transducer sites AE from defect

sources produced on a plate by indentation or other directed energy loading.

Using the theory developed at NBS we will then be able to calculate the stress

drop history characterizing the source. Knowledge of the stress drop history

gives information on the defect orientation and geometry, the dynamics of the

emission process, and the local stress conditions. This information will be

used interactively with metallurgical examination and defect mechanism, modeling

to enhance our understanding of defect dynamics and to develop critical AE indicators to signal critical feature events.

3) The theory of acoustic emission from defect sources has been extended

to include inhomogeneities such as martensitic transformations and micro-cracks.

In addition, an extensive series of computations of waveforms to be expected in

steel and glass plates have been carried out. These calculations have graphically demonstrated the great directionality of acoustic emission signals as well as pointing to the potential of new signal processing techniques. The

plate code is currently under revision to allow more accurate Fourier transforms of the plate solutions to be computed, thus permitting more reliable

inversion methods. Finally, the theory of noise propagation has been carefully

studied using quadratic noise statistics and criteria have been developed for

optimal noise filtering to use in conjunction with deconvolution techniques.

23
7. Electric Power Research Institute/National Bureau of Standards

Joint Acoustic Emission Program

D. G. Eitzen

Mechanical Production Metrology Division

National Engineering Laboratory

The acoustic emission technique has great potential for determining and

monitoring structural integrity. Acoustic emission (AE) signals contain potentially useful information about the location and identity of defects and about

the criticality of the defects in a structure under load. However, current

signal processing techniques such as threshold counting, RMS recording, energy

measurement, peak detection, and spectral analysis often fail to extract the

remaining information unambiguously. The difficulty lies in the inherent com- plexity of the generating mechanism, the transient wave propagation details and

the physics of the sensor's mechanical-to-electrical conversion process.

The objective of the EPRI/NBS Joint Program on Acoustic Emission is to

develop certain of the information needed to form a basis for the AE monitoring

of nuclear reactor structures and to establish the feasibility of AE monitoring

in a simple structure. The achievements of this program include:

1. Contributions to data interchangeability for laboratory and field

measurements through the development of a transducer calibration

service.

2. Contributions to the reliability of AE field data through the

development of calibrated sources.

3. A better understanding of AE source behavior through theoretical

predictions of the behaviour of AE sources.

4. A better understanding of the limitations of conventional AE

methods through a critical analysis.

5. A framework for understanding the AE process from source to

measured voltage.

6. An analysis of the potential information in AE signals, an understanding of the modification to signals by wave propagation, ex- perimentally verified theoretical predictions of remote displacement

due to an AE source, and part of the basis for secondary sensor

calibrations, all through the theoretical solution for wave propagation in a plate.

7. Demonstration of the feasibility of determining the actual AE source function by making remote measurements based on having performed

this in glass and in steel using time domain deconvolution.

24
8. Development of a methodology for determining the significance of

received AE signals.

9. Development of several additional very promising signal processing

techniques.

Some of these developments are being used in industrial applications and

others are being used by other AE researchers. While these applications and

others are consistent with the technical plan, it appears that additional information must be developed before power producers can obtain all the information from AE that is desired. An extension of the agreement has been negotiated

and will result in further improvements in the transducer calibration capability,

in deconvolution of complex structures and in information about the significance

of AE sources.

25
8. Polymer Sensors for NDE

S. Edelman and S. C. Roth

Polymer Science and Standards Division

National Measurement Laboratory

Our recent work involved the use of polymer sensors to measure dynamic

elastic moduli and to detect wear in airplane control cables.

Making use of the sensitivity, low density, and flexibility of piezoelectric polymer strain gauges, we have worked out a non-resonant method for

measuring both the real and imaginary parts of both the dynamic Young's

modulus and the dynamic shear modulus of structural materials in the form of

long, thin rods. All four quantities can be obtained as continuous functions

of both frequency and static load. The frequency can be varied over a wide

range, and the static load can be varied from a large compressive value through zero to a large tensile value.

The method can be used to study the basic dynamic properties of materials.

It should be especially useful in studying composite materials and polymers,

materials whose dynamic properties are likely to vary with static load. In

the case of composite materials, variation of damping characteristics with

static load can be expected to be a sensitive test of the quality of the bonding between components. The method can be used to provide basic engineering

data needed for designing structures which are to be subjected to dynamic

stresses or for which particular levels of internal damping must be obtained.

Since all measurements are made on a single specimen under identical con- ditions (except for the type of excitation) any deductions about the internal

structure are free of the uncertainties introduced where measurements at different frequencies require different specimens and where measurements of the

different moduli require different apparatus. The method can be used for non- destructive evaluation of structural elements either for compliance with design specifications or for monitoring a change in properties during service.

A paper describing the method was presented at the April 1980 meeting of the

Acoustical Society of America. Support for a laboratory installation to apply

the method is being sought.

The study of airplane control cables is performed on an apparatus in

which the cable, under tension, is pulled around a small pulley by a cam which

converts the rotation of an electric motor to reciprocating motion. A polymer

sensor, attached to the cable near the pulley, detects the noise of the motion

of the strands as they deform on the pulley. The sensor can be removed from

the cable and reattached readily so that the same sensor can be used to compare

different cables or different conditions. An elaborate mechanical filter eliminates motor noise from the signal. A spectrum analyzer operates on the sensor

signal, and changes in the spectrum are monitored to detect the effects of

fatigue and wear.

26
9. Strength Development of Concrete

J. R. Clifton

Structures and Materials Division

Center for Building Technology

National Measurement Laboratory

The maturity concept is considered to be a promising NDE method for

estimating the compressive strength of inplace concrete at early ages. This

concept is based on the premise that the combined effects of curing time and

temperature can be mathematically related. Maturity (M) is defined by the

equation:

M = /(T-To) dt

where T is the temperature of concrete at time t, and To is the datum temperature. The datum temperature is the temperature at which the strength of immature concrete remains constant. Several relationships have been empirically

developed based on empirical considerations, e.g.,

c = A+B log M

I Where c is the compressive strength of concrete and A and B are regression

coefficients.

The development of mathematical models relating the development of strength

of concrete to maturity has been undertaken. In the first phase of this work,

a mathematical model developed at NBS for the hydration of tri calcium silicate

has been used to derive maturity relationships. Comparison of model output and

experimental data is shown in Fig. 8. The fit is believed to be reasonable

considering that concrete contains several cementitious constituents in addition

to tri calcium silicate and it also contains fine and coarse aggregates.

This work is contributing to the development of a more fundamental basis

for maturity-strength relationships which will ultimately facilitate the ac- ceptance of the maturity concept.

27
mfiuauis aAissajduioD pezLieuuoN

0,o

«

I

l

i

i

!

,

'

i

1

1

1

1

1

1

0

200

400

600

800

1000

1200

1400

Maturity

(°C-days)

Figure

8.

Normalized

compressive

strength

as

a

function

of

maturity.

Normalized

strength

is

ratio

of

strength

at

given

maturity

to

ultimate

strength.
10. Application of NDE to Construct!' on/Army

J. R. Clifton and L. Knab

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

The use of NDE methods in quality acceptance of buildings is being

studied for the U.S. Army Construction Engineering Research Laboratory. At

present, when the military has a building constructed, it depends largely on construction inspectors to determine if design specifications and acceptable

construction practices are being followed. However, often these inspectors

do not have the necessary skills and experience to be effective. Therefore,

the military is seeking alternative approaches. An approach being considered

is the incorporation of quality acceptance testing of the installed building

materials prior to acceptance of the completed building. This quality ac- ceptance testing approach is based upon the use of NDE techniques.

NDE techniques applicable to concrete quality acceptance were first

identified and assessed. The important properties and factors of concrete

which often need to be characterized and appropriate NDE methods are listed

in Table 2. These techniques were assessed based on consideration of use- fulness of information obtained, reliability, level of expertise required to

use the equipment and to interpret the results, and cost effectiveness. The

results of the assessments are given in the paper "Nondestructive Evaluation

Methods for Quality Acceptance of Hardened Concrete in Structures," NBS

Technical Note (in press).

The use of NDE for the inspections of other building materials and

building components is currently being addressed. The building materials

and components which are being covered in the current phase of the work are listed in Table 3.

Field demonstrations of selected NDE techniques are an important part of

this project. Purpose of these demonstrations is to convey to military personnel responsible for design and construction of military facilities, the

usefulness of NDE in quality control and quality acceptance programs.

29
TABLE 2. NDE METHODS FOR QUALITY ASSURANCE TESTING OF HARDENED CONCRETE

CONCRETE PROPERTIES RECOMMENDED TEST METHODS POSSIBLE TEST METHODS

Strength Windsor Probe

Schmidt Rebound Hammer

Cast-In-Place Pullouts

Maturity Concept

Cores

General Quality

and Uniformity

Windsor Probe

Schmidt Rebound Hammer

Ultrasonic Pulse

Gamma Radiography

Cores

Ultrasonic Pulse Echo

Microwaves

Thickness Covermeter

Microwaves (Radar)

Cores

Gamma Radiography

Ultrasonic Pulse

Air Content Cores Neutron Density Gage

Moduli of

elasticity

Dead Weight Loading

with Acoustic

Emission

Surface

Properties

Visual

Schmidt Rebound Hammer

Cores

Microwaves

Ultrasonic Pulse Echo

Density Gamma Radiography

Cores

Neutron Density Gage

Rebar Size and

Location

Covermeter

Gamma Radiography

Microwaves (Radar)

Ultrasonic Pulse Echo

Corrosion State of

Reinforcing Steel

Visual

Electrical Potential

Measurement

30
TABLE 3. FACTORS CONSIDERED IN QUALITY ACCEPTANCE OF BUILDINGS

MATERIAL OR COMPONENT DESIGN FACTORS OR PROPERTIES

1. BRICK AND MORTAR UNITS INTEGRITY, THICKNESS, REINFORCING STEEL,

PRESENCE OF INNER GROUT

2. WOOD AND LUMBER INTEGRITY AND GENERAL QUALITY, DENSITY,

MOISTURE CONTENT, ADHESIVE BOND FOR

LAMINATED WOOD

3. METALS

A. STRUCTURAL LOCATION, TYPE OF METAL, CRACKS,

CORROSION CONDITION, LOOSE CONNECTORS

B. WELDS WELD DEFECTS

C. PIPES AND TANKS WALL THICKNESS, LEAKS AND CONTINUITY,

CORROSION CONDITION

D. ELECTRICAL WIRING WIRE SIZE, TYPE OF METAL, CONDITION OF

ELECTRICAL INSULATION

4 . ROOFING SYSTEMS COMPOSITION, MOISTURE CONTENT, PERMEABILITY, SLOPES, SELF SUPPORTING

5. PAINTS AND COATINGS NUMBER OF LAYERS, FILM THICKNESS, INTEGRITY,

ADHESION, QUALITY

6. SOILS PERMEABILITY, PROPER BACKFILL

7 . SEALANTS ADHESION

8. PIPE AND DRAINAGE SYSTEMS FLOW RATE AND PRESSURE, NO LEAKS,

PRESENCE OF DIELECTRIC JOINTS, NO BACK

FLOW OF WATER

9. ELECTRICAL WIRING SYSTEMS CARRIES DESIGN LOAD, FUNCTIONS PROPERLY,

CIRCUIT BREAKERS OPERATE

10. HVAC PROPER FLOW RATE

1 1 BUILDING COMPONENTS DESIGN FACTORS OR PROPERTIES OF WALLS

AND CEILINGS, FOUNDATION AND BASEMENT,

ROOF, BUILDING ENVELOPE AND FLOOR.

JC/KLB

31
11. NDE of Moisture in Roofing Systems/Air Force

L. I. Knab and R. G. Mathey

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

The purpose of the NDE of moisture in roofing project, funded by the

Air Force was to investigate commercially available NDE methods for:

1. Their ability to quantitatively detect the minimum moisture

content, and

2. Their ability to quantitatively detect moisture beyond the

minimum amount.

During FY 78 and 79, a state-of-the-art report was prepared on the NDE

methods and a controlled laboratory study was conducted.

During FY80 a large amount of NDE data from the laboratory study was reduced and analyzed. The data represented three NDE methods (electrical

capacitance (three instruments), nuclear backscatter (two instruments), and

an infrared thermography instrument), two roof decks (concrete and steel),

two asphalt thicknesses, and five insulation types (fiberglass, perlite board,

fiberboard, polystyrene, and polyurethane) in one and two inch nominal thicknesses. The data, in the form of NDE response versus the moisture content of

roofing specimens, was computerized and analyzed. A technique was developed

for assessing the performance of the NDE methods on a quantitative basis.

An NBS Technical Note report on the state-of-the-art of NDE methods to

detect moisture in built-up roofing is currently in editorial and technical

review and will be published in 1980. A draft of the results of the laboratory

study has been completed and the paper, an NBS Building Science Series report,

will be submitted to editorial and technical review in October 1980.

32
12. Eddy Current Imaging System

B. Field

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

National Measurement Laboratory

The initial concept for a real-time eddy current flaw detection and

characterization system presented in last year's report has been proven

feasible this year. The system uses a relatively large-sized array of pickup coils surrounded by four separate exciting coils. This arrangement will

be used to determine the shape, location, size, and orientation of discountities in flat non-ferrous metal plates, and display this information in real

time on a video display. Presentation of the information is to be in a format

similar to a radiograph which should provide increased operator confidence in

the measurements.

The measurement configuration was described and a drawing of a prototype

probe system was included in the 1979 NDE Annual Report (NBSIR 80-2007). The

probe consists of a square array of pickup coils surrounded by four vertical

exciting coils that are energized in opposite pairs. The symmetry in two dimensions allows the system to be equally sensitive to discontinuities regardless of their orientation in the metal. We expect to energize one pair of

coils at a time with currents 180 degrees out-of-phase, thus creating a two

dimensional plane, perpendicular to the surface of the metal, where the com- ponent of magnetic field is zero in the direction parallel to the metal surface

(zero horizontal field). By varying the intensity of the current in the two

driving coils the plane of zero horizontal field may be moved across the surface

of the plate performing an electronic eddy current scanning of the plate. The

advantage of this method is the ability to accurately locate small defects with

a few relatively large area pickup coils.

To test the theory, the problem was reduced to a one dimensional experiment.

A slot type defect in an aluminum plate was mechanically scanned at several different field orientations using a single pickup coil. These data are plotted

in Fig. 9.

The output of the pickup coil (the voltage component in phase with the

driving coil voltage) is plotted in the vertical direction, and each of the

nine traces represent a different field orientation. The mechanical scanning

was used for convenience only and for this case is equivalent to a row of

closely spaced pickup coils. As can be seen from the figure, the magnitude

of the signal due to the defect changes with field orientation, and appears

to go to zero somewhere between trace 5 and 6. Thus if the relationship between the coil excitation currents and the field orientation (i.e., the position of the zero horizontal field plane) is known, the location of the defect

may be calculated based on measurements from sensors nearby, but not neces- sarily exactly at, the location of the defect. To do this the response pattern of the sensors must be known, and the sensors must be adequately sensitive

to respond to small defects. The latter attribute is a function of sensor geometry and the signal-to-noise ratio of the instrumentation.

33
Thus pickup sensors must be chosen with regard to the following

requi rements

.

1. High sensitivity to magnetic field perpendicular to the surface of

the plate. The horizontal component conveys no significant information in this configuration.

2. Spatial response of the sensor must be known, preferably uniform

sensitivity over the surface of the device.

3. The sensors must be matched in output response to permit sensitive

differential measurements to be made to improve the signal-to-noise

ratio. This also implies that a simple manufacturing technique is

needed for production of matched devices.

Candidates for sensors include printed-circuit type coils, wire-wound

coils, and Hall effect magnetic sensors.

Hall devices were investigated initially as they were known to be easily mass produced and have a uniform response to magnetic field over the surface

of the device. Although the devices exhibit low sensitivity to magnetic field

it was thought that this could be improved with sophisticated instrumentation.

Low sensitivity of Hall devices to magnetic fields not only requires more sensitivity in the measuring instrumentation but also increases the

problem of stray field pickup in the leads of the device. In general it is

not practical to use Hall devices at frequencies much above 500 Hz unless

special precautions are taken to reduce pickup to an absolute minimum. For our system extensive shielding is not possible and tightly twisting the leads

did not provide sufficient rejection of the stray field. To eliminate the

effect of stray field the Hall device was excited using ac (rather than dc as

is usual) and the device was then used as a non-linear mixer of the ac excitation and ac magnetic field. The output of the device was filtered and

synchronously detected to eliminate unwanted signals due to stray field

pickup and residual voltage. This procedure is explained by the short

derivation given below.

In an alternating magnetic field the Hall voltage can be expressed by:

where B is the magnetic field orthogonal to the device, K-j is the sensitivity

constant, R is the residual resistive component, and I is the Hall device

exciting current.

In addition there is pickup of stray field from the leads, thus

V

H

‘ K

1 #

+ RI + K

2

B

'

34
where B'

If

and

then

is the same frequency as B but of different magnitude and phase.

Bq

B = — sin w^t, I = I Q

sin w

2 t

B' = B

q

' sin(w^t + 0)

dB

ttt- = B^ cos w,t dt o 1

and

V

H = K

l Bo

I o^ cos w

i t )( sin w

2 ^) + RI

0

sin w

2 t + K

2 B o Sln ( w

-i t + 0)*

The product term can be expanded into an upper and lower sideband,

thus for w

2

> w-j

K

1 B I V

H

= —

[sin(w-| +w

2

)t + sin(w

2

- w-j)t] + RI sin w

2 t + K2 B

q sin (w-jt + 0).

If a high pass filter is used to eliminate all the frequency components

at w

2 and below, we are left with a signal at a frequency of w-j + w

2 that is

a function of only the magnetic field strength and the Hall exciting current

(which is known).

At this time we had only one frequency synthesizer available so a special

purpose single-frequency synthesizer was built to excite the Hall device and

provide a reference for a lock-in analyzer. As a result of measurements made

using this system two problems were identified. Unless the Hall device is

used with exciting currents substantially below the nominal magnitude, significant self-heating of the device occurs, which may locally alter the con- ductivity of the metal being measured. Also, large amounts of noise prevented

sensitive measurements from being made at the required microgauss level. Thus

it appears that Hall devices are not suitable for this application due to an insufficient signal-to-noise ratio, irrespective of the measuring instrumentation that is used.

A parallel investigation of the printed-circuit type coils shown in

Fig. 10 was also performed. This type of coil has the advantage of being

easily produced with close matching of the individual coils. The arrangement

shown in the figure consists of four coils electrically connected in a "star"

configuration for differential voltage measurements. Measurements of the coil

output voltages in a uniform magnetic field in air showed excellent matching

35
of coil properties. Placing the coils on a metal surface however produced

widely varying outputs among the simlar coils. These changes were found

to be due to the design of the coil which requires the connecting leads be

separated. This introduces a loop in the circuit that is sensitive to the

horizontally oriented field and which in this case contributes a significant

error to the coil signal. Different manufacturing techniques capable of

producing finer line-widths and thus coils with a greater number of turns, or the use of thinner backing materials will help reduce this problem.

Rather than go to complicated manufacturing techniques for a small number

of research devices, we decided to use carefully fabricated wire-wound coils

to simulate devices with a large number of turns. The coil dimensions were determined by Computer-Ai ded-Design (CAD) using several programs published by

C. V. Dodd1 for analyzing the defect sensitivity of reflect ion- type coils.

These new designs reduced the effect of stray field pickup by a factor of

more than 100. Careful manufacturing techniques yielded coils with outputs

that are matched to within 0.1% air. Unfortunately, the coils exhibit very

poor matching when placed in a uniform field on a metal surface. We speculate

that the problem may be due to small differences in interwinding capacitance

which cause changes in the resonant frequencies of the different coils. More

work in this area is planned.

We are satisfied with the design concept, however, further work is

required to develop a pickup sensor capable of meeting the requirements of

the proposed probe.

1 Dodd, C. V. , Cheng, D. C. , Simpson, W. A., Deeds, D. A., Smith J. H.,

Oak Ridge National Laboratory Report 0RNL-TM-4107, April 1973.

36
Fig. 9 Response of a pickup coil mechanically scanned over an aluminum

plate, containing a slot type defect, at different magnetic field

orientations.

;

I

'I

37
i

r n

A/

5

S

Fig. 10 Pattern of the printed-circuit pickup coil. The four coils are connected for differential voltage measurements.

38
13. Eddy Current Conductivity

G. Free

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

National Measurement Laboratory

The variable frequency eddy current bridge that had been developed1 is

extremely accurate but requires much time to balance the bridge on each test

specimen. Various modifications of the bridge were tried. The latest measurement scheme is now being tested for accuracy and precision. The bridge is

essentially a Maxwell bridge so that inductance and resistance of the test coil are known in terms of capacitance and resistance. The arms of the bridge which

usually contain a capacitor and resistor in parallel, a single resistor and the

Wien grounding network have been replaced by an operational amplifier network

(Fig. 11). This configuration has the advantage of requiring a single balance

of network components and places the input impedance of the voltage dividers in

a position where they have no effect on the bridge balance as frequency is

varied. Errors in measurement are due primarily to the leakage current. With

the use of a high performance operational amplifier and the proper choice of

resistance values this error should be quite small.

A second method of measuring electrical conductivity has also been developed

during the past year and may make it possible to measure conductivty with an accuracy in the ppm range. This new method is based on an entirely different

coil design. The theory related to the performance of this coil design is well

developed2

. The output voltage of a coil constructed as shown in Fig. 12 is a function of coil dimensions, frequency and conductivity of the test sample. By

making the length of the lower inner coil (lg) slightly greater than the length

of the upper inner coil (1 T

) a unique frequency for a given conductivity can be

found at which the output voltage is in-phase with the current driving the primary coil. A bridge shown in Fig. 13 is used to make the measurement. The equati

at balance is BR=V where V is the output voltage, R is the value of the resistor

and B is the setting of the inductive divider. The output voltage of the coil is

characterized in terms of a single resistor. The measurement can be made with

extreme accuracy and precision due to this dependence on only one standard.

Although other bridge components are necessary for the bridge balance their

values do not have to be known exactly.

A somewhat less accurate bridge is also being tested (Fig. 14). The

simplicity of the bridge and speed with which measurements can be made makes it one of great promise. Measurements are done quickly with only a single balance.

Further, when measurements are made at low frequencies, i.e., 1-10 kHz, the

bridge has only a slight sensitivity to lift-off in the 0.0 - 0.5 mm range.

Since many commercial coils which have been used in the NBS bridge were extremely non-linear, it was decided that experimental coils using computer

aided design3 should be constructed. The coils were designed to have maximum

sensitivity to conductivity change in the NBS bridge network. The agreement

between the theoretical calculations and actual coil performance was in the

1-5% range. It was found that coils could be made which are linear to about

0.4% over a measurement range of 10% IACS. A number of coils (6) were made for use in the eddy current program.

39
Fork is in progress to determine electrical conductivity in an absolute

manner using eddy currents. If successful this work would determine any difference that exists between the ac and dc determination of conductivity.

Theoretical studies and computer analysis are being used to determine the

accuracy that can be expected in the measurement. The major problem in designing an absolute experiment is that test coil dimensions must be known

with a high degree of accuracy and the coil must be geometrically uniform.

Both the construction and measurement of a coil to small tolerances is very

difficult. Thus, an experiment must be developed which is either independent

of the coil dimensions or must contain two measurements in which the dimensions

of the coil enter the coil equations in a different way. The approach being

considered uses a coil with an intermeshed secondary. The coil will have an inner diameter of approximately 2.5 cm so that the coil can be used on a flat

surface or with a metal rod inserted through the coil normal to the coil axis.

The driving voltage will have a triangular shaped waveform. With this type

of waveform the output voltage of the secondary will be a constant voltage ex- cept when the slope of the waveform changes sign. At this point an exponential

decay takes place which is a function of the conductivity of the test piece.

Several rough experiments indicated the feasibility of relating the decay rate

to the conductivity with sufficient accuracy.

References

1. Free, G. M. , "High Accuracy Conductivity Measurements in Non-ferrous

Metals," ASTM (STP) to be published in 1980.

2. Dodd, C. V. , Deeds, W. E. , Luquirre, J. W., "Integral Solutions to

Some Eddy Current Problems," International Journal of Nondestructive

Testing, Vol . 1, pp. 29-90, 1969.

3. Swartzendruber , Free, Mordfin, et al .

,

"Nondestructive Evaluation of

Nonuniformities in 2219 Aluminum Alloy Plate-Relationship to Processing,"

Technical Report for NASA, April 1980.

40
R L

COILS

Fig. 12

41
R L

VllK~

Fig. 13

Vlll

42
14. Theoretical Modeling in Eddy Current NDE

A. Kahn

Ceramics, Glass and Solid State Science Division

National Measurement Laboratory

We have examined methods for solving inversion problems by the analysis of

eddy current experimental data. If we limit the investigation to simple geometries,

such as a slab or a cylinder, it should be possible to use impedance measurement

as a function of frequency to construct a resistivity profile of the material by

examination. This inversion can be performed by a method of integral equations

(known as the Gelfand-Levi tan and Marchenko methods in quantum theory) and by

another method of direct Fourier analysis. Both methods are now being explored

for computational practicability.

In the problem of crack diagnosis by eddy current methods, there have been

reports of wide variability in the signals from real and artificially produced

crack or other defect specimens. Part of this variability may arise from the zone of plastic deformation in the vicinity of the crack. This plastic zone may

vary in dimensions and in material parameters, according to its method of production. Initial calculations show that expected resistivity variations in the

plastic zone have little effect on eddy current signals, but that possible variations in magnetic permeability, as in stainless steels, could produce a significant effect. A computational appraoch, based on the finite element method,

is being prepared for finding the eddy current distribution in the vicinity of a crack with allowance for the variation of material parameters in the plastic zone.

43
15. tuuy current Standards

L. H. Bennett, J. R. Cu thill and L. J. Swartzendruber

Metallurgy Division

Center for Materials Science

National Measurement Laboratory

The specifications for a set of aluminum conductivity standards were established. Four alloys were chosen to cover the conductivity range of 30

to 60 %IACS; 2024-T351 for a standard with nominal conductivity of 30 %IACS,

6061-T6 for a standard with nominal conductivity 40 %IACS, 2024-0 for a standard with a nominal conductivity of 50 %IACS, and 1100-F for a standard with

a nominal conductivity of 60 % IACS . These alloys are to be milled into coupons

44.5mn x 44.5mm x 9.5mm from a plate 12.7mm thick. The surface finish on both

sides is specified to be better than 1 urn RMS and each alloy is to be anodized

ir, a distinctive color. A set of 100 of each of these standards has been ordered

and received and turned over the the Electrical Measurements and Standards

Division for calibration. Work has been initiated on finding a suitable alloy

and specifications to cover conductivity standards in the range of 1 %IACS which

are required for use with titanium alloys, and to determine what standards would

be desirable for use with eddy current measurements on steel.

44
16. Development/Application of Deep Penetration Eddy Current Techniques

J. B. Beal (Research Associate - Martin Marietta Aerospace Corp.)

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

National Measurement Laboratory

Material characteristics, weight savings, life-cycle requirements, improved

welding methods and cost controls make it imperative that latest advances in

nondestructive evaluation (NDE) be explored and implemented for examination of

the welds on the External Propellant Tank of the Space Shuttle Program (900 meters

total). Objective of the eight month assignment to NBS was to evaluate eddy

current techniques to detect and characterize surface and internal flaws within

constant thickness and tapered welds of 2219-T87 aluminum alloy (3.65 to 5.59 mm

thickness range). Welded, tapered test panels were prepared with simulated

flaws (slots and holes) of various dimensions and orientations. These panels

(and other aluminum plates with simulated flaws) were evaluated, with available

off-the-shelf low frequency eddy current equipment, to determine flaw detection

capabilities at various depths. Frequency, probe diameter, scan speed, liftoff and sensitivity were evaluated to determine optimum factors for maximum

penetration.

An ongoing effort during this assignment has been document retrieval from

the NBS Library on multi frequency and pulsed deep penetration eddy current

techniques. Document review and discussion with investigators indicates that

pulsed deep penetration methods offer promise. Eventual application of eddy

current deep penetration techniques of flaw detection will substantially simplify

and reduce the current material and labor-intensive NDE method of radiography

and penetrants.

Results of equipment evaluations and recommendations for applications will

be published at the end of this year.

45
17. Nondestructive Evaluation of Nonuniformities in 2219 Aluminum Alloy

Plate - Relationship to Processing/NASA

L. J. Swartzendruber , L. K. Ives, W. J. Boettinger, S. R. Coriell,

D. B. Ballard, D. E. Laughlin, R. B. Clough, F. S. Biancaniel lo,

P. J. Blau, J. W. Cahn, and R. Mehrabian

Metallurgy Division

Center for Materials Science

National Measurement Laboratory

G. M. Free

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

National Measurement Laboratory

The work was initiated at the National Bureau of Standards at the request

of the National Aeronautics and Space Administration. It was motivated by

serious government and aerospace industry concerns on the possibility that

substrength aluminum alloys may have been used in aircraft and space vehicle

structures. These concerns originated from the discovery of "soft" spots in an anodized 2024-T851 aluminum alloy machined part in June 1979. The part was machined from a ^ 14 cm (5.5 inch) thick plate of the alloy produced at a particular manufacturing plant. It was postulated that the "soft" spots were

due to improper processing of the plate. Furthermore, it was established that

the same plant was producing a variety of other aluminum alloy plates including

the 2219 aluminum alloy which was the subject of this investigation.

The aim of this work was to develop specific relationships between processing variables used during ingot casting, working and heat treatment of the

alloy, and the resulting microstructures, properties and NDE responses. This

detailed blend of metallurgical examination of the alloy with its NDE response

is necessary not only to attack the specific problem at hand but also to gain a fundamental knowledge of the features of metallurgical microstructures which

cause changes in NDE parameters. We have focused primarily on eddy current

testing (conductivity) for the present but initial explorations into the use of

ultrasonic measurements (wave speed; attenuation) have also been conducted.

Work in this program is divided into five areas:

1. Studies on as-received plate of 2219 aluminum alloy - This is motivated

by the realization that the properties vary across plate thickness. These variations can have different effects on various NDE techniques.

2. Solidification-Segregation Studies - Part of the variation in

properties across finished alloy plate is caused by segregation of the alloy

components (Cu, Mn) during ingot casting.

3. Determination of time-temperature transformation diagrams (C-curves)

and the relationship between mechanical properties and conductivity - Samples

produced during various thermomechanical treatment have a wide range of mechanical properties (hardness, yield strength, tensile strength) and conductivity.

46
4. Electron microscopy studies done on the wide range of metallurgical

microstructures produced - Extremely fine scale (<100 A) particles are responsible for the strength of aluminum alloys and contribute to associated changes

in conductivity.

5. Predictions of heat flow conditions during malfunctions of the

commercial process, namely slow quenching from the sol utioni zing temperature;

and predictions using experimentally determined C-curves of the resultant

mechanical property degradations.

Conclusions reached in the study are listed below:

1 . As -received Plate

Moderate variations in composition, hardness, electrical conductivity and

mechanical properties were noted across the thickness of a 12.7 cm (5 inch)

thick 2219 aluminum alloy plate. Composition variations, which influence

measured conductivities, can be traced to the original ingot. The variations in hardness and tensile properties are mainly due to changes in

cooling rate across the plate during the quench and are probably influenced

by inhomogeneous mechanical deformation during processing.

2. Solidification Segregation Studies

Macrosegregation of copper in Direct Chill (DC) cast ingots of 2219 aluminum

alloy cannot be completely eliminated by chill face scalping and subsequent

thermomechanical treatment. Macrosegregation does remain in the finished

plate product. However, good scalping practice should limit copper content

to above the solid solubility limit with no deterioration in mechanical

properties.

Elements with equilibrium partition coefficients less than unity exhibit

macrosegregation similar to copper while those with coefficients greater

than unity are opposite to copper. The magnitude of deviations from the

nominal are related to the deviation of the coefficient from unity.

° The major phases present in cast 2219 aluminum alloy in this study have

been determined by electron microprobe analysis and electron diffraction.

They are a-aluminum solid solution, e-CuAU and Cu^FeAly. These phases

are also present in the heat treated finished plate product.

° Predictable macrosegregation has been obtained in laboratory ingots of

2219 aluminum alloy. Both positive and negative segregation similar to

DC cast ingots are observed and are caused by the flow of segregated interdendritic liquid (Fig. 15).

° Electrical conductivity determined by eddy current measurements of cast

2219 aluminum alloy is inversely related to copper content. This fact

complicates the relationship of conductivity to mechanical properties

used for nondestructive evaluation of the finished plate product. (Fig. 15)

47
Surface hardness and eddy current measurements may be very sensitive to

scalping depth in their ability to evaluate the condition of finished

alloy plate.

Hardness, yield strength and ultimate tensile strength of heat treated

2219 aluminum alloys decrease significantly when the average copper con- tent drops below approximately 5.5 wt%.

C-Curve Determination and Relationship between Mechanical Properties

and Conductivity

No significant difference in either strength or hardness was detected

between alloys stretched between 5 and 1 % permanent strain during the

thermomechanical processing of 2219 aluminum alloy.

The functional form developed by Cahn and used previously by Staley

for 7075-T6 and 6061-T6 aluminum alloy was found to give an adequate

representation of the C curves for 2219-T87* if the form was modified

to include a minimum value for each property in question. Some deficiency in this form at the highest and lowest temperatures was noted.

An efficient computer program was developed for using time-temperature

and property measurement data to establish C curve parameters.

For each heat treatment sequence, C curves were determined for hardness,

yield strength, tensile strength and electrical conductivity. These C curves can be used to determine the correlations between these properties.

C curves could not be developed for elongation, probably because this

property is more sensitive to grain size and other factors.

A small but significant difference was found between the C curves for

sequence A (direct transfer to salt bath) and sequence B (water quench and

reheat in salt bath) type quenches. For a given salt bath time and temperature, sequence B quenches resulted in a greater degradation of

mechanical properties.

The scatter in hardness and conductivity was found to be large. This

scatter can be expected to complicate NDE measurements and should be

properly taken into account when establishing NDE procedures and specifications (Figs. 16 and 17).

There is a great need for standardizing conductivity measurements in

order to bring about better inter-laboratory agreement.

2219 aluminum alloy is not as quench sensitive as some of the other high

strength aluminum alloys such as 7050.
4. Electron Microscopy Studies

The age-hardening response of 2219-T87* and T851 is determined principally by the formation of 0' precipitates with some contribution by 0

" precipitates.

An abnormal quench treatment which results in dwell times significant

with respect to the C curves leads to the heterogeneous nucleation and

rapid growth of 0 and 0 " precipitates.

0 The nucleation and growth behavior of the 0 and 0 ' precipitates formed

during an abnormal quench depend on the pre-existing microstructural

state of the material and on the thermal "path."

0 The large incoherent 0 and 0' precipitates formed during an abnormal

quench consume copper available from the matrix and thereby reduce the

concentration of 0' and 0 " precipitates that contribute to precipitation

hardening during subsequent aging.

0 The C curves are a measure of the concentration of large 0 and 0

' precipitates formed during the quench treatment.

5. Heat Flow Calculations - Property Predictions

Calculated plate properties, e.g., yield strength and hardness, decrease

monotonically with increasing distance from surface to centerline of a plate for fixed heat transfer conditions.

0 For symmetric cooling and sequence (a) C curves, the calculated minimum

yield strength (at the center of the plate) is 54.9, 53.7, and 51.8 ksi

for 2.54, 7.62 and 12.7 cm (.1 , 3, and 5 inch) thick plates, respectively.

For asymmetric cooling and sequence (A) C curves, the calculated minimum

yield strength (at the botton surface of the plate) is 54.4, 50.7 and

45.9 ksi for 2.54, 7.62 and 12.7 cm (1, 3, and 5 inch) thick plates,

respectively.

0 For plate thicknesses greater than 2.54 cm, sequence (b) C curves yield

lower properties values than sequence (A) C curves. For example, for

asymmetric cooling and sequence (B) C curves the calculated minimum yield

strength is 54.6, 48.0, and 41.5 ksi for 2.54, 7.62 and 12.7 cm (1, 3, and

5 inch) thick plates, respectively.

Interrupted (abnormal) cooling, in which the heat transfer coefficient at

the bottom surface changes from the same value as at the top surface to a zero value, can result in lower property values than found for asymmetric

cooling. For example, for a 12.7 cm (5 inch) thick plate and sequence (B)

C curves interrupted cooling yields a minimum yield strength of 39.0 ksi

compared with 41.5 ksi for asymmetric cooling.

49
Work in this program will continue in three general areas. A round robin

of conductivity measurements at various laboratories has been conducted on NBS

prepared 221 a aluminum alloys in various heat-treated conditions. This work

will lead to a set of aluminum alloy conductivity standards. Second, controlled

ultrasonic measurements are being planned for pure Al-Cu precipitation hardened

alloys. Thirdly, a program has been initiated to investigate the relationship

of processing to NDE response of 2024 aluminum alloy. This alloy appears to be more sensitive to heat-treating practice than 2219 aluminum alloy.

50
, %

COPPER

(

DISTANCE FROM BOTTOM CHILL, cm

Figure 15 Average copper content and electrical conductivity versus distance from

the bottom chill, in a unidirectionally solidified reduced cross section

laboratory ingot of 2219 aluminum alloy.

CONDUCTIVITY,

%

IACS

(-
HARDNESS

US

CONDUCTIUITV

-

2219-T87#

Oi

CO

X<IQ:QZIiJU)(A

Figure

16

Comparison

of

hardness

vs.

conductivity

data

with

the

correlations

predicted

by

the C

curves.

The

dashed

lines

are

the

scatter

band

95%

confidence

level)

obtained

from

a

least

squares

quadratic

fit

to

the

data.
ULTIMATE

TENSILE

STRENGTH

US

XIACS

-

2219-T87*

o>m

•r- -O

-C

fO </l M fO -—

<0 T3 r-

"O Oi

<u >

>>-= 01

-*—* I— r—

fO *a

a»

u

3

-ac

o

o

a*

• a +-> 00 C TO) 0> 4- > -O

i- -r- <_> 3 4- *r- U

(/> c

> 5

C

3

vs

in

CT» ti c" ^

01-0 -—- CJ C i.

O) T3 -O fa i- UJ c o

-*-> 4-> fa (_r

Crt LtO V)

O* "O l» +-> r- a <U irt •r- J_ 4-> ra CO Q. +-> O)

S= (Or0) 00 O ^ C W (O o 4- -r- 0) E

o +> x: o

<o +-» i- C r- 4—

O tv <11 00 i- J_ "O

t- (0 o

5- o c

OJ O oo -r- o. a» ra §

a» c 4-> -C •«“ -Q CJ +-5 o

T—I—I—I——I—I—I—I——I—|—|—I——l—I—I—

cu

cn


 o oo r- 0 9 0

<o in

a

i-3

i-ujz:(n*-H —iuj
18. Electrochemical Noise

J. Kruger

Chemical Stability and Corrosion Division

National Measurement Laboratory

Measurements on two electrochemical systems, copper in copper sulfate

and aluminum in boric acid/tetraborate buffer, have been carried out by re- cording the amplitude spectrum of the fluctuations in the current density.

For these measurements, a low-noise potentiostat developed and built at NBS was employed. In the case of copper, the current spectra are found to be

the deterministic response of the electrode to the noise voltage generated by

the potentiostat. The electrode characteristics for charge-transfer and for

diffusion could be obtained from the impedance plots derived from_the measure- ments when the level of the applied signal was of the order of 10" 7 V. In the case of aluminum, the deterministic response observed in the absence of pitting

gave way to random flucuations in the current in conditions leading to pitting.

It is shown that the onset of pit information can be detected from noise

measurements.

Random fluctuations in the passive current of electrodes under potentiostatic conditions have been measured also on a Fe-Cr-Ni alloy, both in the

amorphous and in the crystalline state, in sulfuric acid. The onset of pitting

can be detected by the large increase in current noise. The noise level is

different in the amorphous and crystalline Fe-Cr-Ni alloy, indicating that the

breakdown of the passive film differs in the two conditions.

The difference in behavior upon anodic polarization is shown in Fig. 18.

Spectra 1 and 2 were taken on the amorphous alloy. Even polarizing at 1.59 V,

where transpassive dissolution begins to occur and the dc current density in- creases more than 20 times the fluctuations are small. The crystalline alloy,

on the contrary, shows the characteristics of localized attack: an increase

in potential of 70 mV from 1.37 V to 1.44 V causes only a modest increase in

the dc current density, from 130 to 200 yA/cm2

, but has a spectacular effect

in the noise level as shown by spectra 3 and 4 of Fig. 18.

The remarkable difference in the noise spectra of the amorphous and

crystallized alloy clearly show that the latter has a much greater tendency

to localized attack, no doubt because of structural inhomogenity of the passive

film. Moreover, the noise measurements have revealed that the superior resistance to breakdown of the passive film in the amorphous alloy is not a result

of the static properties of this film because the overall current densities

observed did not differ greatly wehn comparing the crystallized and amorphous

alloys.

54
?

Current

Amplitude,

A/cm

Fig. 18 Current spectra for amorphous and crystalline jre 3? Nl 36^r

14

P 12

B 6

in 1 M H^SO^. Amorphous: 1) E=1.14 V; i d(_=1.5 * 10

4 A/an ; 2) E=1.59;

ij =3.5 • IQ"

3 A/cm2

. Crystalline: 3) E=1 .37 V; i

(j (.-1.3 • 10

4 A/cm2

;

4) E=1 .44 V; i dc

=2.0 • 10‘ 4 A/cm2 '

Reference: NHE. Averages over 256 spectra.
19. Leak Rate Reference Standards

S. Ruthberg

Electron Devices Division

Center for Electronics and Electrical Engineering

National Engineering Laboratory

Leak rate reference standards are used for the calibration of measurement

apparatus, for determining the sensitivity of a measurement procedure as applied

to a given system, and for providing precise flow-rates for control purposes.

Commercially supplied units range in value from approximately 10“ 2 atm*cm3 /s to

10

_9 atm*cm3 /s* with stated accuracies of 10 - 20%, although interlaboratory com- parison has shown a three sigma uncertainty of + 0.33 in the logarithm of

standard leak rate so that measured values differ by up to a factor of four. 1 Yet some standards for critical usage specify leak rate measurement uncertainty

of not greater than 20%, and leakage rates of <10_1 ° are now specified.

The objective of this project is to improve the uniformity and agreement

in leak rate measurements through more accurate reference standards. The first

phase of the effort is for the standard leak rate range of 1 to 1 x 10“ 5 atm*cm3 /s. Wi thin-laboratory precision is under evaluation for capillary leaks

as measured by pressure rate-of-rise (or fall) apparatus, and uncertainties are being analyzed.

The principle of the measurement procedure is embodied in Figure 19. A

leak specimen is inserted into a vacuum connector within the small chamber LC.

A gas pressure of one standard atmosphere ** is established in chamber I and

admitted into LC around the specimen. The resultant gas flow through the leak causes a pressure rise in chamber II which is initially at zero pressure. If

the upstream pressure (chamber I) remains constant and the downstream pressure

(chamber II) does not increase significantly from zero, the volume of chamber II and the rate-of-rise in pressure are a direct measure of the standard leak rate . A1 ternatively, the roles of the chambers can be reversed and a rate-of-fall in

pressure can be measured. The standard leak rate , then, is measured under very

specific conditions; however, if the mode of flow (laminar viscous, transition,

molecular) is determined and remains unchanged with pressure excursion, the

leak rate might be calculated by an integrated flow equation with pressure

points more widely spaced for greater measurements accuracy. This latter, though,

requires careful experimental investigation of the flow mechanism.

The actual gas handling system is depicted in Figure 20; standard symbols

are used to indicated the components. 2 Chamber II and connecting lines have

a volume of approximately 21 as measured by gas expansion techniques for an uncertainty of less than 0.2%; chamber I and lines have a volume of approximately

91 as measured to about the same uncertainty. The capacitance-diaphragm gauges

(CD) connected to the chambers are differential sensing types with sensitivities

of one part in 100,000. Reference arms are held at high vacuum. The low pres- sure instrument on chamber II is calibrated against a precision liquid nanometer3 and linear ionization gauge4 with pressure points generated within the system. 5 The high pressure instrument is calibrated against a reference barometer. A

second vacuum system is used to provide the reference vacuum for the capacitancediaphragm gauges and reference nanometers.

56
Capillary leaks in the range 10" 6 to 1 atm* cm3 /s have been fabricated in

glass, and entrance aperatures ranged from ^lym to ^25ym in diameter. Specimens

must be handled carefully to avoid contamination (dust, moisture).

Leak bodies have been measured repeatedly to determine measurements precision and leak stability. Dispersion within a measurement series has been

about 2 1/2%, while repeatability over a 1 year period has been within ^5%.

Capillary leaks for this range generally evidence laminar flow6

, and expected

uncertainty as provided by temperature and pressure variations is ^1%. Additional

imprecision is now due to operator manipulation and pressure readout procedures.

Flow analysis and stability measurements continue.

* 1 atm*cm3 /s = 0.1013 Pa*m3 /s.

i ** 1 std-atm. = 1.01325 x 105 Pa.

References

1. "Calibration of Helium Leak Detectors by Use of Secondary Standards,"

ASTM Designation F78-71 , 1979 Annual book of ASTM Standards, Part 43,

pp. 371-374.

2. Graphic Symbols in Vacuum Technology, Am. Vac. Soc. Standard 7.1 - 1966.

J. Vac. Sci. Tech. 4, 139-142 (1967).

3. Micrometer U-Tube Manometers for Medium-Vacuum Measurement, A. M. Thomas

and J. L. Cross, J. Vac. Sci. Tech 4, 1-5 (1967).

4. "The Measurement of Conductance to Free Molecular Flow by Substitution

Procedures," S. Ruthberg, J. Vac. Sci. Tech. *9, 1457-1469 (1972).

5. "Calibration to High Precision in the Medium Vacuum Range with Stable

Environments and Micromanometers," S. Ruthberg, J. Vac. Sci. Tech. 6_, 401-412 (1969).

6. "Flow Through Micro Openings," W. H. Hedley et al., Final Report. U.S.

Army Biological Center Contr. DA 18064-AMC-563(H) . January 1968.

Available from Defense Documentation Center, Alexandria, VA AD844907).

57
CJ>

GO

O 3 ca q_

Fig.

19

Basic

apparatus,

rate-ofrrise

leak

measurement.

I,

II-high

vacuum

chambers.

LC-leak

specimen

holder

chamber

with

vacuum

connect.

CD-capaci

tance-diaphragm

gauges.

RGA-residual

gas

analyzer.

One

standard

stmosphere

in

I,

pressure

rate-of-rise

in

II.
Ii II

I!

Fig.

20

Vacuum-gas

control

circuit.
20. Magnetic Measurements

L. Swartzendruber

Metallurgy Division

National Measurement Laboratory

One of the most extensively used techniques in magnetic NDE is the

magnetic particle method. The application of this method is currently guided

by empirical rules for the amount of magnetization required to achieve the

desired results. Also, there is no acceptable method for independently

testing magnetic inks. The first steps in placing magnetic particle inspection on a more quantitative and reporducible basis are an understanding of

how the leakage field from a defect is influenced by the defect geometry and

level of magnetization reached by the material, and a detailed description of

the influence of the leakage field on the formation of an indication by the

magnetic ink.

We have previously investigated the leakage fields from a steel ring with

artificial defects introduced by drilling a series of small holes at varying

depths below the sample surface. The ring geometry used was the same as specified

in MIL-E-6868E and in the new ASTM recommended practice for magnetic particle

inspection. It was found that all residual and active leakage fields could be

closely approximated using a linear dipole model provided that an apparent depth,

less than the actual depth of the defect below the surface, and an equivalent

dipole strength, greater than that predicted by the linear theory, were used.

One of the disadvantages of the ring geometry was that the magnetization level

actually achieved in the steel ring varied with the defect depth and could not

be monitored. It was also found that the artificial defects specified for the

ring were too close together in that the leakage field from one defect was distorted by its neighboring defects.

To overcome these difficulties a sample containing artifical defects with

the geometry shown in Figure 21 was constructed. Using the pickup coil shown,

the level of magnetization in the material can be monitored while the leakage

fields from the artifical defects are being measured. A Hall effect probe was used to measure the tangential and perpendicular components of the leakage field

at five different points on the hysterisis curve of the sample. These leakage

fields were least squares fitted to a linear dipole model. Typical data and

fits are illustrated in Figure 22. As for the case of the ring geometry, it was found that the residual and active leakage fields could be closely approximated using a linear dipole model with an apparent depth and an equivalent dipole strength. Both the equivalent depths and the equivalent dipole strengths

were roughly the same as those found for the tool steel ring. An interesting

feature of the results on the sample of Figure 21 is that the magnitude of the

leakage field increases almost linearly with the applied magnetic field even after the material is driven into saturation. Further studies are planned on other defect geometries including very narrow cracks and slots of various depths

in a sample similar to that of Figure 21. Using these results it should be

possible to devise more valid tests for the quality of magnetic inks and to

specify more precisely the level of magnetization required to detect defects

of a given geometry.

60
Fig. 21. Test yoke used for measuring leakage fields from

artificial defects. The entire yoke is 25 mm

wide. The ariticial defects are six holes drilled

as shown. The material is a low carbon steel. A

150 turn coil is used to magnetize the yoke and a 100 turn pickup coil is used to determine the

magnetization level reached inside the yoke.

TANGENTIAL LEAKAGE fields RAU data and model fit

13

12

11

le

9

8

712.0 12.2 12.4 12-6 12.3 13-0 13-2 13.4

HTSTANCE ALONG SAMPLE (CM) FIELD IN GAUSS

DIS

HI

ftEGCHT 3 MM ^PLIED

H ^

EL

N

Dm2;ER

0E

6RSTEDS

RAW DATA-X MODEL FIT- HOLE NUMBER 6

PERPENDICULAR LEAKAGE FIELDS RAU DATA AND MODEL FIT

Fig. 22. Leakage fields measured from the yoke shown in

Figure 1 compared with the field calculated from

a magnetic dipole model. (a) Tangential field

with an applied field of 24 oersteds. (b) Perpendicular field with an applied field of 24 oersteds.

The crosses are data points and the dashed line is

a least squares fit to a linear dipole model.
21. Optical Nondestructive Evaluation

G. S. White and A. Feldman

Cermanics, Glass and Solid State Science Division

National Measurement Laboratory

Optical scattering from defects is an area of importance in Nondestructive

Evaluation. It is the purpose of our research to determine whether quantitative

data, such as defect dimensions, is obtainable from optical scattering data. For

this purpose, we have been performing both measurements and model calculations of

radiation scattered from shallow grooves in metallic surfaces and have compared

theory with experiment.

In the experiments, chopped 10.6pm radiation from a 3 watt C0

2 laser was incident normal to a specimen containing a shallow rectangular groove. The

specimens were prepared by scribing of grooves into an aluminum coating that

had been evaporated onto glass optical flats. Two sets of specimens were used: one set of specimens was used as scribed; in the other set, the specimens were overcoated with an additional thin layer of aluminum. The groove dimensions in

both specimen sets were nominally 10, 20 and 50pm wide by 0.5pm deep. Figure 23

shows the measured profile of a 50pm uncoated groove.

The use of 10.6pm has several advantages: the effect on scattering of

surface microirregularities is minimized; the fabrication of well defined

grooves of dimensions comparable to the wavelength is facilitated; the far field

approximation in the model calculations can be used.

A schematic diagram of the measurement apparatus is shown in Figure 24.

Scattered radiation was measured by a pyroelectric detector that was swung about

the specimen in a plane that contained the incident beam and that was perpendicular to the groove in the specimen surface. Careful attention was paid to system

alignment because certain alignment errors were shown to cause severe distortion

of expected scattering patterns.

Model calculations of the expected scattering were performed on the basis

of Fraunhofer diffraction theory. The following assumptions were made: the

incident beam had a Gaussian intensity distribution; the beam width was significantly larger than the groove width; scattering was due to specular reflection from the specimen surface and the groove bottom but not from the groove

walls. The resultant scattering function obtained was the diffraction pattern

of a uniformly illuminated slit with the intensity uniformly modulated by a factor dependent on the depth of the groove. Figure 25 shows a comparison between experimentally determined scattering and an empirical fit to the data of

a single slit diffraction pattern. The points denote the measured scattering

intensity of a nominal 50pm wide uncoated groove as a function of scattering

angle. The solid curve is the diffraction pattern of a 52pm wide slit. Agreement appears to be quite good. Comparable results have been obtained with some of the other grooves; however, with certain grooves, large discrepancies were observed with are attributed to groove irregularities.

Further work is planned to compare scattering from deep groove with theory

and also to study the effect of polarization on the scattering function.

62
uirlos.

measured

by

diamond

stylus

profilimeter.
Specimen

Figure 24. Schematic diagram of scattering apparatus.
(simn Ajej^qjv) (Ausuejui) 6crj

Figure

25.

Logarithm

of

observed

scattering

(triangles)

from

uncoated

50ym

wide

specimen

superimposed

on

the

calculated

logarithm

of

n

(solid)

ideal

single

slit

diffraction

pattern

from

a

52jjm

wide

slit.
22. Quantitative Holographic NDE

C. M. Vest

University of Michigan

G. Birnbaum

Office of Nondestructive Evaluation

National Measurement Laboratory

Although holographic interferometry has been frequently applied to the

solution of problems in NDE, it has thus far been used as a qualitative method

of flaw detection. An experiment has been planned and is currently in progress

to make an initial assessment of the potential of optical holography for quantitative NDE. To this end, a pressurized cylinder with several end plates

containing different flat bottom holes has been designed. The deflection of

these end plates when the cylinder is pressurized has been computed by the

method of finite element analysis. Holographic interferograms will be taken

of the distorted end plates and compared with the theoretical predictions.

Further work may include the quantitative study of more complex geometries.

Should optical holography be used more quantitatively in the future, it is

felt that this experiment may help lay the development of appropriate standards.

66
23. Liquid Penetrant Test Blocks

J. Young and F. Ogburn

Ceramics, Glass and Solid State Science Division

National Measurement Laboratory

Liquid penetrants are frequently used to detect minute cracks in various

metals. There is a need for test blocks with cracks of known widths that would

be used to test the sensitivity of a liquid penetrant and the sensitivity of a penetrant test procedure.

A technique for fabricating a test block with isolated cracks has been

developed. In principle, a nickel panel is plated with a layer of copper the

thickness of which is the width of the desired crack. The copper is over plated

with a thick layer of nickel. A polished cross section of the composite will

reveal a thin copper line between two bands of nickel. When copper is etched

out, a "crack" is formed; see Figure 26.

During the past year many penetrant test blocks have been prepared with

crack widths of 0.2-2nm. Thirty of these have been sent to various individuals

and groups for evaluation. In general, responses were favorable; many responses

included suggestions for improvements. These suggestions were considered and

many were adopted. The modified penetrant sensitivity crack plate will soon ben available as an SRM.

/

67
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24. Doppler-Broadened Positron Annihilation Lineshape for Detection of

Defects in Materials

R. C. Reno and L. J. Swartzendruber

Metallurgy Division

National Measurement Laboratory

Positrons that annihilate in a metal produce gamma rays whose energy

distributions can be explained in terms of a Doppler shift caused by motion

of electrons. When defects are present in the metal, they attract and trap

positrons, and alter the Doppler shifts. A measurement of doppler-broadened

annihilation lineshapes thus gives information on the defect nature of materials.

Both the annihilation process and the method of detection leave the sample intact, so the technique is extremely useful for the nondestructive evaluation

of materials.

Doppler-broadened lineshape measurements are performed by placing a positron source in contact with the sample to be studied (see Fig. 27). Positrons

enter the sample, slow down to thermal energies, and then annihilate with electrons. Each annihilation produces two gamma rays with a total energy equal to

the rest mass energy of the positron-electron pair (1022 keV). The distribution

of energy between the two gamma rays depends upon the electronic and defect

structure of the sample, and is measured with a high resolution solid state

detector-multichannel analyzer system. A lineshape parameter, S, is defined

which is a measure of the inverse width of the distribution.

The addition of a small number of defects to a metal will cause a significant change in the lineshape parameter, and it is this sensitivity that is used

to observe changes in defect concentration and type. We have used this technique to study defects in cold 'worked titanium and, more recently, have begun

to study precipitation hardening in aluminum alloys. In the latter study, some results of which are shown in Figure 28, we observe significant changes in S

parameter as microprecipitates form during ageing.

69
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Figure

28.

S

Parameter

Data

for

a

2219

Aluminum

Alloy

at

Various

States

of

Ageing.
25. Standards for Ultrasonic NDE

D. G. Eitzen

Mechanical Production Metrology Division

National Engineering Laboratory

The detection and evaluation of defects using acoustic emission pulse/

echo ultrasonics relies heavily on comparative measurements. While these

techniques have great potential, they are sensitive to measurement system

characteristics and to the condition of the reference artifacts used. An

effort to improve the reliability and uncertainty of these techniques is

underway. Part of this effort has focused on the development of measurement

services for transducers and reference blocks. The measurement services now available along with improvements, extensions and applications are listed

below:

1. Ultrasonic Transducer Power Output Versus Frequency

Using a modified radiation pressure technique, the absolute total power

output of ultrasonic transducers is measured versus frequency over any part

of a range from about 1-20 MHz. The uncertainty is frequency dependent but is

nominally about +5 percent. In addition to its use in the calibration of

ultrasonic transducers for users, the system forms part of the basis for

traceability between the Food and Drug Administration and NBS ultrasonic power

standards. This is important for determining compliance of many ultrasonic

products to FDA promulgated regulations. Work has been done on improving the

vibration isolation of the radiation apparatus. Although the previous mounts

had a very good isolation factor (about 50) at the working frequency of the

apparatus, a new, inertial mounting system has been designed and constructed.

The additional isolation is useful at lower power levels and seems to offer

the best isolation factor of any table at the Bureau at the frequencies of

interest.

2. Ultrasonic Transducer and System Power Output by Calorimetry

Using a ultrasonic calorimetric comparator, the time-averaged total

absolute power output of a transducer or system is measured for any voltage

input waveform in the range of 1-15 MHz. The uncertainty is approximately +7

percent. The operating procedure for the device has been changed so that the

minimum sensitivity in now tens of microwatts, thus making many medical diagnostic and pulsed industrial systems accessible to measurement.

3. Ultrasonic Reference Block Calibration

Sets of ASTM flat-bottomed hole-type ultrasonic reference blocks are compared with an interim reference block and associated model using a wellcharacterized measurement system. The service provides a mechanism for com- paring sets of blocks through the NBS ultrasonic system. In addition to the

existing calibration service for aluminum reference blocks, a service for the

calibration of steel reference blocks has been established. Also, a more meaningful uncertainty statement has been developed based on a thorough statistical

analysis (with the help of the Statistical Engineering Division) of the

ultrasonic measurements of reference blocks.

72
4. By arrangement, carefully characterized ultrasonic source transducers

and aluminum reference blocks can be made available for loan. These can provide on-site calibration with the user's system. Using the accurately measured

ultrasonic source transducers, a user's power or frequency measurement system

can be calibrated in-situ. Four of these source transducers were used in an international intercomparison of ultrasonic power measurement methods piloted

by NBS. All data taking on the intercomparison has been completed. Measurements were made by seven laboratories in four countries. Analysis of this

data is underway. The loaner aluminum ultrasonic reference blocks which have

been carefully compared with the NBS interim reference standards, provide a means for users to compare their reference artifacts with those of NBS on their

own ultrasonic system. A set of these loaner blocks is currently being used

by Lockheed-Georgia to provide traceability between microprocessor controlled

electronic test block and the response of the NBS interim standard blocks.

Additional work on ultrasonic measurement systems is in process. Digital

measurements are being developed for the measurement of reference blocks. A' more basic, better defined instrumentation system for block measurements is also

being considered. Resumption of efforts to measure ultrasonic transducer fields

in a solid media is also planned.

73
26. Ultrasonic Materials Characterization

R. Mehrabian, S. Fick, R. B. Clough and J. A. Simmons

Metallurgy Division

National Measurement Laboratory

This is a new activity using ultrasonic techniques for nondestructively

measuring microstructural material parameters. Ultrasonics as commonly used

in pulse echo or imaging systems detects macroscopic discontinuities such as flaws or interfaces in material structures. However, the measurement of

ultrasonic attenuation and velocity changes of the study of the absorption

and transmission spectra of scattered ultrasonic waves provides a wealth of

detail on the mean microstructural properties of metallic materials. These

techniques have great potential for measuring texture, porosity, and multiphase distributions, as well as for studying the kinetics of phase transformations both by observing and inducing such transformations.

Work in cooperation with Prof. R. Green of Johns Hopkins University has

been initiated on ultrasonic characterization for "soft spots" in aluminum

alloys. Detailed description of the overall program in this area is given in

a separate section entitled, "Nondestructive Evaluation of Nonuniformities in

2219 Aluminum Alloy Plate - Relationship to Processing." The first priority

of the effort in this task is to develop a reliable alternate NDE method for

detection of these soft spots. Velocity, attenuation, and ultrasonic scattering techniques are being employed and their reliability assessed.

Currently, the relative merits of various developmental techniques for

measuring ultrasonic attenuation and velocity are being experimentally investigated. Since ultrasonic parameters are extremely sensitive to measure- ment techniques, considerable effort has been devoted to the optimization of

procedural and equipment design. Methodologies under investigation include

the use of test fixtures incorporating design features allowing transducer-tospecimen alignment independent of dimensional variations in the specimen. Test

fixtures employing long path and direct transducer-to-specimen contact in

liquid coupling media have been designed and constructed. Transducers capable

of high efficiency operation at the high frequencies necessary for adequate

sensitivity to precipitate development in a selected alloy have been designed

and fabricated. The use of conventional transducer designs at higher than

normal frequencies has also been investigated. Results obtained thus far indicate that further developmental effort is necessary and justified. Longer

term studies are contemplated of the kinetics of the aging process itself leading to better specifications for such alloys in the future.

74
27. Ultrasonic Imaging

M. Linzer

Signal Processing and Imaging Group

Center for Materials Science

National Measurement Laboratory

In the past year, emphasis was placed on various aspects of ultrasonic

imaging and computerized tomography. A theoretical and experimental analysis

of texture in ultrasonic imaging was carried out. Studies of cutting techniques for transducer arrays and tomographic image reconstruction from limited projections were completed. Exact solutions were obtained for the first

time for three-dimensional reflectivity imaging using broad bandwidth pulses.

Inversion formulas were derived for three transmit-receiver apertures--plane,

cylindrical and spherical. Substantial progress was made in developing perturbation and iterative correction schemes for velocity tomography. The

theoretical and computer simulation phase of this activity is expected to be

completed during the first half of the next fiscal year and experimental

demonstration of the techniques in the second half.

75
28. Nondestructive Evaluation of Composites

H. M. Ledbetter and J. C. Moulder

Fracture and Deformation Division

Center for Materials Science

National Measurement Laboratory

Elastic modulus and internal friction (damping) figure prominently in

engineering design; they also provide basic information on the structure of

a composite. Knowledge of the dynamic properties of composites allows the

designer to prevent undesirable resonance, flutter, buckling, or other

elastic instability. Despite their importance, few studies exist on the

frequency dependences of the elastic constants and internal friction of com- posites. Most studies have been performed at frequencies ranging from 50 kHz

to 10 MHz, owing to the ease of ultrasonic measurement techniques at these

frequencies. Yet, the frequency spectrum of applied load of most concern to

a designer ranges from dc to a few hundred hertz. Thus, there is considerable

interest in measuring the elastic moduli and internal friction of composites

at low frequencies (10~i to 102 Hz).

Another impetus to study low-frequency elastic properties of composites

arises from the possibility that such measurements may reveal low-level damage.

Detection of low damage levels in composites is a serious, unsolved technological problem. Appropriate, reliable nondestructive methods do not exist.

Previous studies in this laboratory failed to detect damage induced in graphiteepoxy by thermal cycling, mechanical fatigue, or tensile loading. These studies

used a Young's-modulus mechanical -deformation mode at kilohertz frequencies.

Low-frequency torsional -mode measurements should be especially sensitive to low

damage levels in polymeric-matrix composites. Since torsion induces nearly

zero strain along the torsion axis, the torsional modulus, T, of a uniaxial

composite depends principally on the properties transverse to the fibers; it

is less sensitive to the high -modulus fibers and more sensitive to the lowmodulus matrix.

An apparatus was designed and built for low-frequency (0.5 to 102 Hz),

forced-vibration determinations of torsional modulus, T, and the internal

friction, Q

-1

. The driving element consists essentially of a d'Arsonval

galvanometer. The displacement sensor is a laser optical-level with phasesensitive detection, capable of resolving strains of about 10~6

. One advantage of this type of apparatus is the number of alternative measurement

techniques that may be used. By choosing the specimen geometry so that any

mechanical resonances occur at frequencies far from the measuring frequency,

a forced-vibration mode of operation may be used. In this mode of operation,

the torsional modulus is determined from the ratio of applied force to observed

displacement; internal friction is determined from the phase shift observed

between the applied force and the resulting displacement. Alternatively, the

internal friction may be determined in the forced-vibration mode of operation

by displaying the applied force vs. displacement and integrating the area of

the resulting hysteresis curve. The forced-vibration mode of operation also

permits studying torsional modulus at a given frequency as a function of stress

level or the torsional modulus at a given stress level as a function of frequency.

76
Another mode of operation may be obtained by choosing the specimen geometry

to give a mechanical resonance at the freqeuncy of interest. In this forcedresonance mode of operation, the torsional modulus may be related to the

resonance frequency, while the internal friction is obtained from the halfwidth

of the resonance curve. Alternatively, internal friction may be measured in

this mode of operation by observing the free decay of oscillations when the

driving force is moved suddenly.

The apparatus has been used in both modes of operation to make preliminary

measurements on three materials: +45° boron-aluminum, glass-cloth/epoxy, and

uniaxial graphite-epoxy. Metallic specimens of known modulus were used to

calibrate the equipment. A representative resonance curve for a glass-cloth/

epoxy specimen is shown in Fig. 29. Experiments are underway to study the

possibility of detecting low damage levels induced by mechanical loading to

90% of the ultimate tensile strength.

77
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29. Ultrasonic NOE Application Work

D. Eitzen, G. Blessing, D. Chwirut, D. MacDonald and C. Tschiegg

Mechanical Production Metrology Division

National Engineering Laboratory

In addition to our core program on measurements research, we seek to

maintain a level of selected applications work. Part of the benefit of this

work is that it helps us maintain a fresh awareness of field measurements

problems and needs. A brief outline of some of these small projects follows:

DOT Pipeline Weld Project (Phase 1)

The purpose of the project was to evaluate the possibility of using some ultrasonic technique for determining the depth of a crack in the weld region

of gas pipeline. It was presumed that the flaw had been located and measured

laterally by radiography. For the size of pipes of interest and for a model

fracture criteria, flaws as small as 1 mm deep must be sized. The conclusions

were that tip diffraction time-delay techniques hold the most promise (or possibly spectroscopic techniques). Very good results were obtained on moderately

sized real and artificial defects. Real defects only 1 run deep will still be

a problem.

Well Characterized Fatigue Cracks for Ultrasonic and Eddy Current

For future studies the Air Force sought to obtain fatigue cracked aluminum

and titanium. It is important that tne profiles of the cracks be known with

good precision. Specimens were fatigued using several loading programs. Crack

profiles were measured nondestructively , using neutron radiography, ultrasonic

C-scan, ultrasonic crack-tip line-delay methods, crack opening displacement

(average length) and dye penetrant (surface length). The follow on work using

the specimens for ultrasonic and eddy current studies has not been formulated.

Titanium Weld Inspection by Ultrasonics

The Naval Research Lab has asked us to assist them in determining whether

it is possible to inspect titanium welds for gas contamination using ultrasonic

techniques. Specifically, the work involves measuring the weld region elasticity

of contaminated and non-contamtnated samples by ultrasonics to determine whether

the weld elasticity is a sensitive indicator of contamination. The results will

be analyzed and reported to NRL and recommendations for further work will be made.

Technical Support for Reactor Inspection Guide

A Regulatory guide has been proposed for the volumetric inspection of

nuclear reactor pressure vessel weldments. One of the tasks in this project is

to provide technical support on issues such as ultrasonic transducer beam spread

and scanning speed and evaluation of other positions taken with respect to the

Regulatory Guide. The other task involves the evaluation of the effect of

electronic distance amplitude correction (DAC) on the linearity of ultrasonic

flaw detectors of the type used for reactor inspection. If there is a significant effect, a method of measuring the linearity while using the electronic

DAC will be proposed.

79
30. Reliability of Ultrasonic Weld Inspection/NRC

D. G. Eitzen

Mechanical Production Metrology Division

National Engineering Laboratory

In 1965 the Pressure Vessel Research. Cojunuttee (PVRC) began an activity

which is intended to determine the capability of the ultrasonic inspection

method and of ultrasonic test procedures in evaluating thick section welds.

(Reference 1 gives a good summary of this activity.) Cooperating participants

prepared a variety of specimens with "intentional" flaws created by doping or modifying the welding process. Early in this activity some measurements were

made using the various techniques. After this, some prescriptional solutions

to some of the differences in procedures used by the different groups were

adopted. Subsequently, data were taken on specimens 201 and 251 J ; the results

for specimen 201 seem to have been the most published. The results of the

ultrasonic evaluation of specimen 201, in retrospect, were relatively good,

several teams apparently detecting seven to nine flaws out of ten. The flaws were small compared to ASME Section XI rejection criteria. After 201 and 251J

were inspected, the PVRC prepared a procedure compatible with ASME Boiler and

Pressure Vessel Code Section XI. This PVRC Section XI procedure was quite re- strictive or prescriptional. To determine if the further restrictions lead

to increased flaw evaluation reliability, trials were arranged using specimens

155, 202, and 203. An analysis comparing the data with the intended flaw locations produced very disappointing results.* A further analysis employing a two-point coincidence method which only makes use of test data (not intended

for actual flaw locations) was also performed2 with somewhat more encouraging

results.

The objective of this small study by the National Bureau of Standards for

the U.S. Nuclear Regulatory Commission is to examine the efficacy of further

analysis of the data on specimens 115, 202, and 203. More particularly, the

work was to gain an understanding of the procedures, the data taken on the

specimens and the subsequent statistical analysis, and to recommend whether it

would be profitable to do further analysis of the data prior to specimen

sectioning to determine actual flaw sizes and positions. If further analysis

is indicated, a plan for the analysis was to be prepared.

The conclusions of the study were that, in the main, additional analysis

of the data should await direct information about the specimen flaws, that

additional analysis of the data would generally be most appropriate after

metal! ographic sectioning of the specimens. This would permit standard

approaches to a statistic based on a comparison of measured versus known flaw

descriptions. In future analysis some attempt should be made to decompose the

analysis into probability of detection and probability of proper evaluation of

flaws. Also, the statistic used should be reevaluated; one is suggested that

averages in a more predictable and more meaningful way. Some additional recom- mendations are made regarding additional work of this type. The descriptions

of the full recommendation are contained in reference 3.

*It is emphasized that these results are preliminary, that radiographs indicate

actual locations of flaws different than intended and that the results are relevant only with respect to a specific restrictive procedure, if relevent at all.

80
References

1. Pressure Vessel Research Committee Round Robin, Ultrasonic Inspection

Results of Thick Section Weldments, A. Graber and 0. Hedden, to appear

as Welding Research Council Bulletin.

2. Analyses of the Ultrasonic Examination of PVRC Weld Specimens 155, 202,

and 203 by Standard and Two-point Coincidence Methods, R. Buchanan,

Interim Report to PVRC, August 1977.

3. Recommendations on Further Analysis of Data From PVRC Specimens 155,

202 and 203, D. G. Eitzen and C. Reeve, Report to the Office of Standards

Development, U,S. Nuclear Regulatory Commision.

81
31. X-Radiographic Standards and Applications

R. C. Placious and D. Polansky

Radiation Physics Division

Center for Radiation Research

National Measurement Laboratory

I. Radiographic Standards

1. Equivalent Penetrameter Sensitivity (EPS)

The measurement of the quantity "EPS" 1 has been applied to evaluating image

quality response of industrial radiographic film. 2 This method standard and

test device were described in some detail in the 1979 annual report of the

"Office of Nondestructive Evaluation". 3 At that time it had not yet passed

final review by ASTM. This review is now complete and the standard has been

formally accepted by ASTM. Coordination of the drafting of the document, the

fabrication of the test device and administration of round robin feasibility

tests were done by NBS with Office of NDE support.

Plans are now underway to make the test device available to users of the

standard through the NBS Office of Standard Reference Materials. At present

it appears that fabricating costs and expected demand do not make it attractive

enough for commercial production of the test device.

2. EPS at Megavolt Energies

The procedure discussed in (1) above applied to low energy x rays (200 kV).

The need has been expressed by many users for a similar system for high energy

x and y rays ( 60 Co to 10 MeV). In response to these requests NBS has assumed

the responsibility of designing the test system and coordinating the round robin

tests as was done for the low energy standard. This work is being done in

cooperation with ASTM Committee E7.01 on "Radiographic Practice."

Up to the present, two designs have been developed and tested. The image

quality indicators (IQI) used were fabricated and supplied by NBS to the participating laboratories together with a prescribed protocol for testing. These

IQI were patterned after the one developed for the 200 kV standard. The results

to date indicate that measuring EPS in this way at megavolt energies is feasible

but as yet we have not achieved the degree of sensitivity needed for small

changes in EPS in the region where it normally changes rapidly. A third design

has now been made which we hope will overcome this problem. If it succeeds in

separating small changes in EPS the next step would be to develop a document

within ASTM for its use and arrange for a full scale test of the system.

3. Unsharpness

Our present goal is to develop a method for measuring unsharpness which

is based on a realistic estimate of the sensitivity of the eye to small changes

in image contrast. For further details see the attached report, "Recommendation

for Measuring Unsharpness in Radiography." Because of this possible new approach

to evaluating unsharpness we have requested a delay in the final recommendation

of a measurement procedure.

82
4. Metal Screens

At this time we are developing a program for evaluating metal screens - particularly at high photon energies (megavolt region). Some of the ex- perimental work for this program can be done with help from those laboratories

cooperating with us in developing the EPS standard at high energies. Our goals

in this work are:

a. To evaluate the properties of metal screens - particularly as related to improved image quality.

b. To accumulate available data for metal screens on relative

speed or image quality either by measurement or literature search.

Relative to the primary goal (#1) image quality improvement can only be

achieved by reducing the total unsharpness in the radiographic image and by

minimizing x-ray scattering affects.

5. Film Processing Standards

Film Storage Standards

These are new areas of responsibility assigned to the film committee of

ASTM E7.01 in the recent reorganization of that subcommittee. This responsibility therefore now descends on NBS which is providing the leadership for the

film section. A task force has been launched with the request to provide an outline for drafting documents for these activities.

II. Radiographic Applications

1. Real Time Radiographic Inspection of Large Diameter (74 inch, 188 cm)

Motors (Outside Agency Sponsored, U.S. Navy)

D. Polansky is one of the principal consultants to the Navy for this

project. He is required to design and supervise qualification tests for both

the inspection procedures and the inspecting facilities. In work completed

this year, it was recommended that real-time inspection be implemented and that

it be regarded as the primary inspection for quality for the motor. This work

has high national priority.

2. Flaw Characterization by Radiography (Outside Agency Sponsored,

Dept, of Transportation)

This project was initiated as part of an effort to develop a more scientific

basis for flaw characterization in large pipeline welds. It began as a broadly

based effort in both material studies and NDE. The radiographic phase of this

work has been suspended at this time, per agreement with the sponsor. A final

progress report will be transmitted to the sponsor and other interested readers.

This report will address primarily the first objective of the work, that is,

recommendations on the radiographic information needed in order to evaluate a flaw for which a waiver request has been made.

83
References

1. For a definition of EPS see ASTM Standard E-142-77, "Standard Method for

Controlling Quality of Radiographic Testing," ASTM Book of Standards,

Part 11 , p. 273 (1979).

2. ASTM Standard E-746-80 (to be published).

3. "Annual Report 1979, Office of Nondestructive Evaluation," NBSIR 80-2007,

p. 43.

84
32. Recommendation for Measuring Unsharpness in Radiography

D. Polansky and R. Placious

Radiation Physics Division

Center for Radiation Research

National Measurement Laboratory

The total unsharpness in radiography is a function of geometrical, screen,

and motion unsharpness. Generally in industrial radiography, motion unsharpness equals zero and the screen unsharpness (when using metallic screens) is a fraction of the geometrical unsharpness. The result is that a straightforward

calculation of the geometrical unsharpness as published in the Annual Book of

ASTM Standards, Part 11, results in a number that has been representative of

the total unsharpness of the radiograph.

The recent increase in the use of real time radiography and fluorescent

screens in industrial radiography has required that the total unsharpness be

evaluated. The analytical expression of the total unsharpness

U

T

(u" +

g m

( 1 )

has been recently investigated by several authors with the opinion that the value

of n is most probably between 1.5 and 2.O. 1 In radiographic systems where the

unsharpness is individually measured or calculated, the value chosen for the ex- ponent obviously determines the total unsharpness value. At the present time we have no specific recommendation as to the specific value to be chosen for

the exponent ru

A schematic representation of the unsharpness in a radiographic system is

obtained when a densi tometric trace is made of the radiographic image of the

edge of a step object. The trace is the familiar S shaped curve. It is the

value of unsharpness determined from this curve that characterizes the system.

In general there is no standard way of measuring this unsharpness. Some

authors have used the X intercepts found by the line through the points

.16 ^ Dmax

“ D

min^ intersectl

* n 9 the horizontal lines of Dmax

and Dmin - 2

Harms and Zei linger in their work suggested several arbitrary definitions of

unsharpness for the practicing radiographer. Their suggestion was that if the

optical density variation near the asymptotes is of particular interest then

by choosing a convenient value for S(Xia) and S(.X2 a) to define Xi and X2

. One

can say that:

X2- X x S(X2 a) - S(Xia)

85
This suggestion seems to warrant further consideration. The effect of

unsharpness is to reduce image contrast and therefore the detection of small

low contrast anomalies. If the asymptotes of the S curve do not approach the

Dmav or Dm . value rapidly, the edge is said to be blurred. We therefore,

suggest measuring the Xa and/or X2 point at the asymptote as determined by an arbitrarily chosen aD of .04 from the maximum and/or minimum. The choice of

a aD of .04 to determine the X value offers two advantages: (a) this density

represents a brightness change of 9.6% and has a high order of reliability of

visual detection and (b) the microdensitometer has a capability of resolving

density differences of .02 so that reasonably accurate points can be measured

from the densitometer traces. What we propose is to use this value of X to indicate unsharpness or perhaps a resolution index. This value will be compared

with the value of unsharpness as determined by Klasens or an integration of the curve to ensure that the data are consistent with these methods. If such an approach is practical then the method will relate the unsharpness number to

resolution adax and may be termed a visibility index.

References

1. A. A. Harms and Z. Zeilinger, "A New Formulation of Total Unsharpness in

Radiography ," Phys. Med. Biol., 22^ (1977).

2. H. A. Klasens, Measurement and Calculation of Unsharpness Combinations

in X-Ray Photography, Philip Research Reports (1946).

86
33. X-Ray Residual Stress Evaluation In The Interior of Industrial Materials

M. Kuriyama, W. 0. Boettinger, and C. J. Bechtoldt

Metallurgy Division

Center for Materials Science

National Measurement Laboratory

R. C. Placious

Radiation Physics Division

Center for Radiation Physics

National Measurement Laboratory

Improved quality control of industrial materials and early detection of

flaws in these components require quantitative information concerning the stress

distribution near cracks and residual stress distributions after different types

of cold working and heat treating or under various conditions of load. These

demands naturally lead to the necessity of measuring residual strains in the

interior of materials. Among many nondestructive techniques for the measurement

of residual stresses, the x-ray diffraction technique, called Bragg diffractometry, excels in its accuracy. Yet this technique is incapable of detecting

stresses in the interior of bulk materials.

More than two years ago, we proposed1 an entirely different approach to the

x-ray evaluation of residual strains (or stresses) although it uses the principles of x-ray diffraction. This approach uses energy dispersive spectroscopy,

where an energy dispersive solid state detector is employed with a well -collimated

high energy beam of photons. Last year (NDE Annual Report 1979, p. 66), we

proved,2 using ordinary laboratory x-ray sources and thin materials, that the

desired resolution and detectability can be achieved for the determination of

residual stresses if this technique is employed simultaneously with the curve fitting technique. The objective of this year’s activity it to demonstrate

this capability using an industrial radiographic x-ray source with radiation

up to 200 kev and commercial steel and aluminum plates up to 1 cm (or a half

inch) and 3 cm (or one and half inch) thick, respectively. If the feasibility

of this technique is proved for use outside the laboratory, the mapping of a residual stress distribution inside an industrial material can be performed

with relative ease on site.

To achieve this methodology, the following three major principles are involved:

a. Well-defined diffraction energy peaks should be obtained at an energy

range of about 100 kev. These high energy photons can penetrate through relatively thick material, so that the diffraction peaks obtained by these high en- ergy photons guarantee to deliver the stress information within a bulk material.

b. These diffraction energy peaks should have a Gaussian profile so that the curve fitting technique can be used for the determination of the

centroid (or peak) positions, and

87
c. The measurement accuracy of lattice constants or their variations

(hence, residual stresses) should be increased by a factor of 100, compared

with the resolution limit of solid state detectors, by use of curve fitting.

The relationship between the improvement factor (that is, the accuracy of determined strains) and counting statistics should be investigated.

All of these principles have been confirmed with thin materials using low

energy photons. The use of high energy photons creates scattering problems and

background problems which directly affect the accuracy of our measurements. We

have succeeded in controlling these problems. The results are shown in the

following:

a. As shown in Figure 30, diffraction energy peaks are clearly separated

with significant intensities. This spectrum was obtained from a commercial

steel plate (AISI-C1015-SAE1015). 3/8 inch thick. In this case, the scattering

angle was set at 2e=5.7° with the incident divergence 3 mrad (0 . 1 7°=1 0 min.)

and the receiving divergence much less than 3 mrad, so that the diffraction

peaks can be obtained through the entire thicknesss of the sample at a given

point of the sample surface. The spatial size of the beam on the sample is

less than 1.5 x 1.5 mm2. The diffraction peaks are indexed as shown in Fig 30.

Note that the well-defined (211 ), (.220), and (310) appears in the energy range

between 90 kev and 150 kev in this transmission geometry. This result indicates

that the previously mentioned principle (a) is completely satisfied.

b. Figure 31 shows an example of the observed spectral profile, say (110),

which has been fitted by a Gaussian curve with a linear background. A perfect

Gaussian fitting demonstrated here certainly indicates a great promise in the

precision determination of centroid (or peak positions for each observed energy

peak. Hence, principle (b) has also been confirmed experimentally for high

energy photons.

c. We are now in the process of proving principle (c). And further

efforts are being made to increase the scattering angle without loss of re- sultant intensities in peaks, so that one can really determine stresses within

small volumes inside materials.

References

1. M. Kuriyama, W. J. Boettinger, and H. E. Burdette, ASNT National Fall

Conference, October 1979, Denver, CO, p. 49 (1978).

2. M. Kuriyama, W. J. Boettinger, and H. E. Burdette, Proceeding of

Symposium on Accuracy in Powder Diffraction, NBS Special Publ . 567,

p. 479 (1980).

88
3/8"

1015

STEEL.

1.5

Mfl

COLLIflATER

OOZSZHW

Figure

30.

A

Bragg

diffraction

energy

spectrum

obtained

from

a

commercial

AISI-C101

5-SAE1015

steel

plate

3/8

inch

thick.

The

scattering

angle

is

5.7°

ensuring

a

transmission

geometry

through

the

entire

thickness

of

the

sample.
110

PEAK,

1/2"

THICK

COLD

ROLLED

STEEL,

3.

84

DEG

2T

OODZhW

Figure

31.

An

example

of

the

observed

diffraction

profile,

(110),

from

a

steel

plate

1/2

inch

thick

fitted

with

a

Gaussian

curve

with

linear

background.
34. Accelerator-Based Radiography

J. W. Behrens, R. A. Schrack and C. D. Bowman

Nuclear Radiation Division

Center for Radiation Research

National Measurement Laboratory

Efforts continue for improvement of resonance neutron nondestructive

assay and for implementation of these methods using small accelerators suitable for an industrial environment. A two dimensional detector has been

developed and tested with 1 mm resolution. This detector was developed in

collaboration with the Oak Ridge National Laboratory. Taking into account

the greater surface area and greater detector thickness, an increase in performance compared to the 1-D detector of a factor 50 is achieved. This gain

may be taken in improved statistical accuracy or reduced source intensity.

The detector is shown in Figure 32 with its cover removed.

Design effort has begun on a new type of detector which promises to make

possible low energy neutron spectrometry without neutron time of flight. The

detector combines the properties of materials which capture neutrons with a probability inversely proportional to the neutron velocity with neutron interaction position sensitivity. The detector inherently has a high efficiency.

If successful, the large separation between source and detector for neutron

time-of-flight measurements would not be necessary. Neutron sources might

thereby be used with more than two orders of magnitude greater efficiency.

High accuracy resonance neutron radiography might then even be possible with

isotopic decay sources such as 252 Cf.

Resonance neutron radiography appears to have several useful applications

in nuclear safeguards, in reactor fuel burn-up measurements, and in assay for

water storage. It offers high selectivity also for many heavy metals including

precious metals. With further development, application to the more common fabrication metals appears likely.

91
Figure 32. Two dimensional position sensitive neutron detector

1

1
35 . Measurement of the L/D Ratio For Neutron Radiography

W. L. Parker and D. A. Garrett

Reactor Radiation Division

Center for Materials Science

National Measurement Laboratory

The last report of this work1 describes a method for determining the

L/D ratio for a neutron radiographic facility from microdensitometric measurements made of the shadow images of a series of small, identical, and parallel

linear obstacles placed at uniformly increasing distances from the image plane.

Also described were the test objects used--one borrowed from Aerotest Operations

and one built at the National Bureau of Standards.

(\ The report also defines the important parameters: L and h--the distances

of the source and obstacle from the image plane, respectively, and D = 2R and

d --the widths of the source and the obstacle, respectively.

The methods consists of approximating the microdensitometer tracings by

trapezoids and measuring the widths of the base (w^) and the top (w

c

) of the

trapezoid. When w^ and w

c are plotted vs. h, the resulting plots should be

approximately straight lines from whose slopes the value of L/D can be

determined.

Work this year has been largely concerned with the theoretical treatment

of the images to be expected when the source is circular instead of linear,

as was assumed in the earlier treatment.

1 . Theory

The detailed analysis will be published elsewhere and only the results are given here.

One of the most important derived parameters is the value of h for which

the umbra goes to zero, b; as was shown previously1 it is given by

b = Ld

o/D. (1)

For a parallel linear source and linear obstacle the shadow patterns will

be symnetrical trapezoids whose height will be constant as long as h < b with

w

d increasing and wc decreasing as h increases until the pattern becomes a triangle when h = b. For h > b, the pattern is again a trapezoid whose height

decreases, while w. and w. both increase as h increases. The area of the

trapezoid should remain c8nstant.

For the case of a circular source and linear obstacle when h < b the

pattern will have a constant central region and will approximate a trapezoid

with rounded corners. When h > b, there is no constant region, and the patterns

deviate more and more from a trapezoid as h increases.

93
Figures 33a and 33b are calculated shadow patterns from the same parameters

(L/D - 68.8, h = 0.25, 0.75, 1.25,..., 4.25 inches) for the linear source--

parallel linear obstacle and the circular source--! inear obstacle, respectively. Figure 33c is a reproduction of microdensitometer tracings from a radiograph

taken with the same parameters. The agreement of figures 33b and 33c is excellent although, if the two figures are superimposed, there are some slight

discrepancies.

The slopes of the plots for w

d

and w

c are found by fitting the data by

linear regression to equations of the form

w = aQ + a-jhO-h/L)" 1

. (2)

The slope values: a^, a-j c and a-| c+ are defined in the last report. 1 The

average slope is defined as follows:

a lav

= (2a ld

+ a lc-

+ a lc+) /4 (3)

The theoretical value of a, is MD/L, where M is the linear magnification of

the microdensitometer.

It follows then, that

(L/D)

exp

= M/a

lav Linear-linear (4)

where (L/D)exp represents the value of L/D obtained by this method.

The case of a circular source and linear obstacle is different. As is

evident from figure 33b, the patterns are approximately trapezoidal only for

quite small values of h. Furthermore, when h > b there is no region of con- stant illumination. It is assumed that the measurement line when h < b is

drawn through the "half-power point" with the slope of the shadow pattern at

that point, and that the intersections of this line with the top and bottom

of the trapezoid determine w. and w . When this is done, it is found that

a lav

= M (*/4)D/L and

a c

(L/D) = uM/ 4a-. Circular-Linear (5) va u I q y

When b < h < 2b, the plot of w

d va hO-h/L)

-1

is still very close to a straight line. It can be shown that a-j d

for this range will differ from that

for h < b by only a few percent. Since measurement errors are normally of this

order of magnitude, we use a value of a^ obtained for measurements for

0. < h < 2b. Values of w

c for h > b are not used and a^ av

= (a-j d + a lc _)/2.

94
It is apparent that the effect of going to a circular source, at least

when h < b, has been to replace D by ttD/ 4. In other words, the normalized

patterns for a circular source will approximate those for a linear source whose width is ( tt

/

4 ) D . This agrees very well with the experimental results.

The method described here which leads to equation (4) or (5) will be

called the NBS method of determining L/D.

The NU method developed by the Aerotest Operations group uses only w . Linear regression is used to find an expression such as equation (2) for c w

c = 0. The resulting value of h shall be called b

exp

. It is found that the

resulting values of L/D are

< L/D

>NU Wd

o Linear-Linear (6)

< L/D

>NU

' ” b

exp

/4d

o- Circular-Linear (7)

2. Experimental Results

The NBS method of determining L/D has now been used at the NBS 10 MW

Research Reactor and at three non-reactor-based facilities. The range of

L/D measured is from 12 to 170.

Figure 34 shows the results of measurements from twelve radiographs

taken at the NBS facility of the NBS test object described in the last re- port. 1 The size of the circles indicates the standard error. The straight

lines were obtained by linear regression to fit the equation

( L/D)

exp

= L o/D + L7D - (8)

L' is measured from the face (biological shield) of the reactor and L , the

distance of the source behind the reactor face is measured to be 32 inches.

The values of L and D resulting are within the standard error of what

o would be expected. Although a^ and a lc may differ by as much as twenty percent of their average, the NBS method appears to be correct for whatever

artifacts are producing the discrepancy.

Similar results have been obtained from the radiographs taken at the

non-reactor-based facilities, thereby increasing confidence in the validity

of the method.

The values of (L/D) derived from a set of radiographs taken with the

GX p same parameters as those for another set, but with a 0.070 inch lead sheet

between the test object and the cassette, agree with those derived from the

normal set to within the standard error with the fluctuations being random.

Accordingly it is felt that the results are not affected by capture gamma

rays from the obstacles or background gamma rays from the reactor.

95
The vaules of (L/D)^ obtained from equation (6) or (7) agree generally

to within 10 percent with the values of (L/D) obtained from equation (4) Ca |J or (5); but the internal consistency of the results from the NU methods does

not seem to be as good as that from the NBS method.

The NBS method is preferred to the NU method for two reasons: first, it uses more of the available data. In fact, for small values of L/D, the number

of measurements of w. used will be at least twice the number of measurements

of w used. Second, the NU method uses the value of d . which may not be

c o known to the desired accuracy, while the NBS method depends only on the fact

that all the obstacles have the same width.

References

1. W. L. Parker and D. A. Garrett, NBS Tech. Note No. 1117 (ed. F. J. Shorten)

1980.

96
Figure 33. Shadow patterns: (A) calculated for Linear-Linear

Case, (B) Calculated for Circular-Linear Case,

(C) Densitometer Tracings. See text for parameters.
*i

of

NBS

test

object.
36. Wear Condition Monitoring

A. W. Ruff

Metallurgy Division

Center for Materials Science

National Measurement Laboratory

This project involves the use of two techniques to nondestructive^

determine and monitor the wear condition in operating machinery. One technique recovers and characterizes lubricating fluids and the wear debris particles in the fluids. The other technique applies acoustic emission detection

methods to wearing components in order to monitor the development of fatigue

cracks associated with the wear contacts. The wear debris technique has been

used for several years in numerous programs in the DOD to monitor such systems

as turbine engine bearings, helicopter transmissions, and various pump systems.

The acoustic emission wear monitoring technique is new and at present is being

studied only under laboratory conditions.

Wear debris recovery and analysis is used in both military and civilian

systems for wear monitoring. Basically, the lubricating fluid is sampled periodically and the wear particles are removed by magnetic recovery methods, e.g.,

Ferrography, or by ul trafil tration. Chemical analysis of the oil is also done

routinely. It has been found in many studies that while chemical oil analysis

can detect small wear particles successfully, it is not a reliable method for

particles larger than a few micrometers in size. On the other hand, wear debris methods are particularly efficient at recovering particles greater than

1 ym in size. Thus, the two methods complement each other and are jointly used

in many condition monitoring systems. The more serious modes of wear frequently

involve the generation of relatively large wear debris particles, greater than

5 ym for example. Therefore, it Is important to capture and examine all the

larger wear particles in any wear monitoring program. Magnetic recovery methods

are proving to be quite satisfactory in this regard.

We are carrying out laboratory studies of the production of wear debris

particles under different conditions of load, speed, metallurgy and environment.

The particles are recovered using Ferrography and analyzed to relate the wear

mode and worn surface with the particle characteristics. Further improvements

in the system of identifying types of wear particles are needed and are being

worked on. We plan to apply quantitative microscope methods next year to this

problem. We are participating in an international activity on wear debris ana- lysis for system condition monitoring with the TTCP (Technical Cooperation Program, Action Group 7) group. Members represent Australia, England, New Zealand,

Canada and several DOD groups in the United States. This group has carried out

interlaboratory comparisons on wear debris collections and plans more activities

of this type. There is considerable interest in standardizing wear debris analysis. We have had preliminary discussions on the idea of providing samples of

reproducible reference wear particles and it seems feasible to do this. Work

next year in this project will apply more effort to this topic. In that connec- tion/ a conference at the University of Maryland in September will discuss particulate characterization methods and standards. We hope that some new, useful

99
concepts will emerge from this meeting. The NBS Office of Standard Reference

Materials is cooperating with our group on the characterization and possible

standardization of abrasive particles. We believe similar methods can be applied

to metal wear particles.

The second nondestructive method being developed in this project concerns acoustic emission monitoring of wear processes. We have assembled an instrumented system (with considerable consultation from NBS colleagues, Drs. Clough

and Hsu) for this purpose consisting of a broad band AE preamplifier and amplifier with gain adjustable from 60 db to 100 db. A conventional piezoelectric

transducer is used with the system. The amplified signals are fed to a video

tape recorder. We have characterized the frequency response of this system

over the band of interest (100 kHz to 1 MHz) and have studied the dynamic

range and transient response of the system and they seem acceptable. Our ex- perimental approach will be to tape record events during controlled wear ex- periments. Those tapes will then be replayed into the Metallurgy Division's AE

signal processing system including analog/digital conversion and computer processing so that significant events can be identified. The wear experiments will

be carried out on a computer-controlled block/ring wear system that has been

modified for locating the acoustic transducer on the block specimen in the epicenter position. The blocks will be fabricated and fatigued to contain a distribution of preexisting cracks. We plan to preload the specimens and carry out

wear on them so as to properly stress the cracks in the wear-affected volume of

the block. Growth of the cracks will then occur and be recorded by the system.

At the conclusion of the test, the specimen blocks will be sectioned and examined

metallographically to determine crack location, size, and other relevant details.

The wear experiments at first will emphasize the fatigue or delamination modes so that we have the best chance for success in detection. Specimen materials will

involve carbon and tool steels at first for which there is a good body of data on acoustic emission from cracks.

100
37. Safety Factors and Mathematical Modeling

J. T. Fong

Mathematical Analysis Division

Center for Applied Mathematics

Traditionally speaking, engineers adopt a numerical value known as safety

factor to convey their experience and .judgment in estimating the uncertainties

of a physical quantity such as loads, moduli, yield strengths, etc. Safety

factors also appear in design codes and operational guidelines for engineering

components and structures, and are usually arrived at by committee actions

based on knowledge of the best available experts in the field. The values

assigned by these experts reflect both their experience and their perception

of the prevailing quality of engineering work. The possibility of a crude verification of those values based on field performance data is seldom realized.

To shed some light on this extremely complex problem using the general

tools of mathematical modeling, a strategy was introduced during FY78 in re- sponse to the request by NBS Office of NDE. The technical work will be subdivided into three phases, each one lasting approximately 3 to 4 years depending

on the level of support:

Phase I - Development of a Mathematical Model with Special

Applications to the Utilization of NDE Data.

Phase II - Pilot Testing of the Proposed Model with Controlled

Experiments on NDE Measurement and Performance.

Phase III - Verification of an Updated Version of the Model with

Real-Time NDE Measurement and Field Performance Data.

During all three phases, it is essential that the project investigators keep

close contact with the appropriate technical communities in order to achieve

credible and relevant results. 1 A total of six tasks were designed to accomplish

the objectives of Phase I:

Task 1.1 Data Acquisition and Initial Screening

Task 1.2 Data Analysis and Sampling Theory

Task 1.3 Safety Factors and Fatigue Life Modeling

Task 1.4 Fatigue Life Modeling and NDE of Fatigue Damage

Task 1.5 NDE of Fatigue Damage and Safety Factors

Task 1.6 Conference Proceedings and Articles of General Interest

The first two tasks dealt with the processing of raw data before an interpretative model can be seriously developed. Tasks 1.3 through 1.5 were designed

to elevate the importance of NDE into the traditional concept of fatigue life

preditions. Finally, task 1.6 resulted from an active participation of project

investigators in technical conferences sponsored by ASTM, ASME, and ASNT. 2

101
During FY79, considerable progress was made in each of the six tasks with

visible output from Tasks 1.1, 1.3 and 1.6. The principal mathematical result

that was published under task 1.3 was a formula for the estimate of a safety

factor which took into account sample* size, allowable risk, and a modification

of the sample variance based on engineering judgment. 3

During FY80, four mathematical results were accomplished under tasks 1.1,

1.2, 1.3 and 1.5. A brief description of each is given below:

Task 1 .1 Mandel's Structure Index** Algorithm and Screening of NDE Data

Using the method of singular value decomposition (SVD) of a rectangular

array of data, Mandel 5 ’ 6 introduced a new analysis of variance model for a general class of data such that the eigenvalues of the analysis can be used

to define a structure number for a given array as an indication of its suitability for curve fitting. At Mandel's suggestion, a Monte Carlo study of the same array using random normal deviates to generate another structure number

is performed to calculate a structure index which can be used qualitatively

to assess the noise level of the given array. For example, if the structure

index (ratio of structure number of real array to that of random array) is

from 1 to 5, the real array is too noisy to yield any useful information. On

the other hand, if the structure index is 1,000 to one million, the array is

said to have a strong structure, and further analysis of data can proceed. A

documentation of this work is in progress and will be completed in FY81

Task 1 .2 Three- paramater Characterization of a Regression Line for

Comparing Experimental Data from Several Laboratories

A simple yet quantitative approach to assess interlaboratory fatigue crack

growth rate data is proposed. Seven sets of da/dN vs. AK data from six laboratories on nominally the same material and loading conditions in a cooperative

test program sponsored by the Society of Automotive Engineers are analyzed to

illustrate the approach. Each set of data is subjected to a standard firstorder linear regression analysis based on the method of least squares. Three

characteristics of the regress line, namely, the location of the "center" of

the data, the slope, and the vertical half-width of the confidence band (for some specified level of confidence), are used to define a composite measure of

the closeness of one regression line to another. A graphical representation

of the results of the six laboratories is given in Fig. 35. The work is being

published by ASTM in a forthcoming STP.

Task 1 .3 Four-Component Decomposition of Safety Factors for Fatigue

Life Design

In a paper delivered to a Critical Issue Symposium of ASME at San Francisco

in August 1980, it was proposed that four categories of uncertainties could be

identified and subsequently estimated in modeling the service life of a structure

or component. The four categories were:

a. Measurement Science and Statistics . This category includes measurement

errors and uncertainties on all aspects of testing and data gathering.

In particular, sampling errors are included in this category.
b. Materials Science and Modeling . This category includes variabilities

due to inherent material inhomogenieties as well as the uncertainties

associated with the empirical models of numerous mechanisms at the

microstructural level.

c. Scaling . This category includes all uncertainties due to scaling

effect in structural geometry and load spectra between real and

laboratory configurations.

d. Human Factors . It was emphasized at the conference that the 4-way

decomposition is necessarily of a vectoral nature, i.e., the safety

margins for the four components cannot in general be added to arrive

at an overall estimate on account of the interactive nature of the

four components. See Fig. 36.

Task 1 .5 Mandel's Approach of Variance Decomposition and an Estimate of

the Safety Factor for the Alaska Pipeline Girth Weld Defect Size

In a paper delivered at a Conference on the Mechanics of Nondestructive

Testing held at the VPI & State University, Blacksburg, VA, in September 1980, an algorithm for estimating the safety factor for defect sizes based on several

readings of the radiographs of those defects was given. The algorithm was based

on a 1977 paper authored by Mandel7 where a variance decomposition algorithm was introduced to analyze interlaboratory data. A numerical example for estimating

the safety factor of the length of a weld defect was presented using data from

the Alaska pipeline project. The documentation of this work is in progress and

will be completed in FY81

.

Future Directions

So far, we have accomplished

Task 1.1 Task 1.2

FY79 . FY80 yes yes

five mathematical results distributed as follows

Task 1.3 Task 1.4 Task 1 .5

yes

yes yes

The key result has appeared under Task 1.5 where a safety factor for defect

dimensioning can now be estimated. We consider this result the principal con- tribution of Phase I for this modeling project. FY81 will be spent mostly on documenting the results developed during FY80.

Where do we go from here? I believe it is not premature to discuss several

directions for the implementation of the Second and Third Phases of this project.

In particular, there are three logical extensions of Phase I in planning for

Phase II work:

103
Task 2.1 Computer-Aided NDE Data Screening and Analysis

This is a logical extension of tasks 1.1 and 1.2.

Task 2.2 NDE Measurement and Fatigue Mechanism Research

This is a logical extension of tasks 1.3 and 1.4.

Task 2.3 Human Factor Estimate for NDE Measurement

Again, this is a natural extension of task 1.5 using the variance

decomposition algorithm of Mandel to separate machine-induced uncertainty

from that due to human factors.

References

1. In May 1978, J. Fong accepted an invitation to serve ASTM as chairman of

its subcommittee E9.01 on fatigue research (130 members), and in Jan. 1979,

he became the chairman of the Materials and Fabrication Committee (over 100

members) of the ASME Pressure Vessel and Piping Division (4000 primary and

7000 secondary members).

2. Most of these conferences were co-sponsored by NBS in collaboration with

EPRI, DoT, NRC, PVRC, MPC, SwRI, and other prominent engineering-oriented

institutions.

3. See Fong, J. T., Nucl . Eng. & Design , 51 (1978) 45-54.

4. Private communication as a result of a lecture given by Dr. J. Mandel on Jan. 16, 1980 at a mathematical modeling colloquium sponsored by the Center

for Applied Mathematics, NBS.

5. Mandel, J. , "The Partitioning of Interaction in Analysis of Variance," J. Res., NBS, Vol . 73B, No. 4, pp. 309-328 (1969).

6. Mandel, J., "A New Analysis of Variance Model for Non-Additive Data,"

Technometrics , Vol. T3, No. 1, pp. 1-18 (1971).

7. Mandel, J., "The Analysis of Interlaboratory Test Data," ASTM Standardization

News , Vol. j5, No. 3, pp. 17-20 (1977).

104
!

. Fig. 35 Comparison of the Characteristics of Some Fatigue Crack Growth

Data from Six Laboratories with 95% Confidence Limits (Data
Number of cycles of repetitive service loads as a measure of the life of a structure

.36 A Schematic Fatigue Design Curve Indicating the Role of

Safety Factors and the Need for Its 4-Way Decomposition.

The four components are: (a) Measurement Uncertainties,

(b) Modeling Uncertainties, (c) Scaling Uncertainties,

(d) Human Factor Uncertainties.
Appendix

A. Publications, September 1979 to October 1980

1. "The Sounds of Failure, Developments in Acoustic Emission Research,"

M. Baum, Dimensions, May/June 1980.

2. "Resonance Neutron Radiography For Nondestructive Evaluation and Assay

Applications," J. W. Behrens, R. A. Schrack, A. D. Carlson and C. D. Bowman, NBS Special Tech. Publ. 594, pp. 436-439, National Bureau of

Standards (Sept. 1980).

3. "Recent Progress in Eddy Current Testing for Nuclear Applications,"

H. Berger, G. Birnbaum and G. Free, Proceedings of Symposium on New

Methods for NDE and Their Applications in the Nuclear Industry, Deutsche

Gesellschaft fur Zerstorungsfreie Prufung, Berlin (1979), pp. 99-106.

4. "Neutron Laminagraphy for Inspection of Nuclear Fuel Subassemblies,"

H. Berger, N. P. Lapinski and K. J. Reimann, Proceedings of Symposium

on New Methods for NDE and Their Applications in the Nuclear Industry,

Deutsche Gesellschaft fur Zerstorungsfreie Prufung, Berlin (1979),

pp. 275-282.

5. "National and International Standards for NDT: To Achieve Improved

Repeatability and Measures Related to Performance," H. Berger, Proceedings

of the Ninth World Conference on Non-Destructive Testing, Melbourne,

Australia, November 1979.

4. 6. "A Comparison of NDT Standards in the U.S. and U.S.S.R.," H. Berger,

V. A. Koukhar, and A. A. Maksimov, Proceedings of the Ninth World

Conference on Non-Destructive Testing, Melbourne, Australia, November 1979.

7. "Annual Report 1979, Office of Nondestructive Evaluation," H. Berger and

L. Mordfin, NBSIR 80-2007, National Bureau of Standards (1980).

8. "Nondestructive Testing in the 1980's," H. Berger, Metal Progress, 118 , No. 3, 33-37 (1980).

9. "Nondestructive Testing of Railroad Rail," H. Berger, Transportation

Research Record 744, pp. 22-26, National Academy of Sciences,

Washington, DC (1980).

10. "Three Dimensional Radiography," H. Berger and W. A. Ellingson,

Research Techniques in Nondestructive Testing, R. S. Sharpe, editor,

Academic Press, London, Vol. 4, 1-38 (1980).

11. "Ultrasonic Diffraction Technique for Characterization of Fatigue

Cracks," S. Golan, L. Adler, K. V. Cook, R, K. Nanstad and T. K. Bolland, Journal of Nondestructive Evaluation, Vol. 1, No. 1, 11-20

(March 1980).

107
12. "An Appraisal of Current and Future Needs in Ultrasonic NDE Standards,"

G. Birnbaum and D. G. Eitzen, a report to DARPA, NBSIR 79-1907 (Oct. 1979).

13. "Energy Dispersive XRF Composition Profiling Using Crystal Collimated

Incident Radiation," W. J. Boettinger, H. E. Burdette and M. Kuriyama,

Advances in X-ray Analysis, 23^ 209-217 (1980).

14. "A Simple Technique for Visualizing Transmitted or Reflected Sound Fields,"

D. J. Chwirut, Materials Evaluation 87, No. 13, pp. 29-32 (1979).

15. "Anisotropic Elastic Constants of a Fiber-Reinforced Boron-Aluminum

Composite," S. K. Datta, H. M. Ledbetter, Mechanics of Nondestructive

Testing, W. W. Stinchcomb, editor, pp. 215-230, Plenum Press, New York

(1980).

16. "Nondestructive Evaluation Program: Progress in 1979," D. G. Eitzen and

J. Quinn, EPRI NP-1234-SR, Special Report (December 1979).

17. "Ultrasonic Nondestructive Evaluation," D. G. Eitzen, PMTE Update 1_, No. 3 (December 1979).

18. "Critical Materials and Fabrication Issues for Pressure Vessels, Piping,

Pumps, and Valves," J,. T. Fong, R. C. Dobbyn and L. Mordfin, editors,

NBS Special Publication 588 (June 1980).

19. "Sizing of Cracks With Scattered Ultrasonic Waves," S. Golan, Ultrasonic

Materials Characterization, NBS SP-596, National Bureau of Standards (1980).

20. "Neutron Diffraction and Small-Angle Scattering as Nondestructive Probes

of the Microstructure of Materials," C. J. Glinka, H. J. Prask and C. S.

Choi, in Mechanics of Nondestructive Testing, W. W. Stinchcomb, editor,

pp. 143-164, Plenum Press, New York (1980).

21. "Elastic-Constant Variability in Stainless-Steel 304," H. M. Ledbetter,

N. V. Frederick and M. W. Austin, J. Appl . Phys. 51_, 305-309 (Jan. 1980).

22. "Orthotropic Elastic Stiffnesses of a Boron-Aluminum Composite,"

H. M. Ledbetter, J. Appl. Phys. 50, 8247-8248 (Dec. 1979)..

23. "Anomalous Low-Temperature Elastic-Constant Behavior in Fe-13Cr-19Mn,

H. M. Ledbetter, Metal! . Trans. 1 1

, 543-544 (Mar. 1980).

24. "Room-Temperature Elastic Constants and Low-Temperature Sound Velocities

for Six Nitrogen-Alloyed Austenitic Stainless Steels," H. M. Ledbetter,

Metal 1 . Trans. 11 A, 1067-1069 (June 1980).

25. "Correlation Between Superconducting-Transition Temperature and the

Cuachy Discrepancy in Body-Centered-Cubic Transition Metals, H. M.

Ledbetter, Phys. Lett. 77A , 359-361 (June 1980).

26. "X-ray Residual Stress Evaluation by an Energy Dispersive System,"

M. Kuriyama, W. J. Boettinger and H. E. Burdette, Proc. of Symposium

on Accuracy in Powder Diffraction, NBS Spec. Pub. 567, pp. 479-487 (1980).

108
27. "Evaluation of Ultrasound Echo Amplitude Measurements for Assessment

of Bond Integrity in Zirconium Alloy Samples," M. Linzer, J. G. Abbott

and S. I. Parks, Report to Westinghouse Atomic Power Laboratory,

West Mifflin, PA, DOE Contract No. EY-76-C- 11-0014 (1980).

28. "Program and Abstracts, Fifth International Symposium on Ultrasonic

Imaging and Tissue Characterization and Second International Symposium

on Ultrasonic Materials Characterization," M. Linzer and H. Berger,

editors. National Bureau of Standards, June 1980.

29. "NDE Publications: 1978," L. Mordfin, NBSIR 80-2080 (1980).

30. "Reliability of Nondestructive Evaluation," L. Mordfin, published in

NBS SP-588, Critical Materials and Fabrication Issues for Pressure

Vessels, Piping, Pumps, and Valves (June 1980).

31. "Further Development and Clinical Evaluation of the Expanding - Aperture Annular Array System," S. I. Parks, M. Linzer and T. H. Shawker,

Ultrasonic Imaging 1_, pp. 378-383 (1979).

32. "Positron Annihilation Study of Defects in Titanium," R. C. Reno, L. J. Swartzendruber and L. H. Bennett, NDT International, 224 (1979).

33. "Debris Analysis of Erosive and Abrasive Wear," A. W. Ruff, Proceedings of

the International Conference of Fundamentals of Tribology, MIT Press (1980).

34. "Studies of Microscopic Aspects of Wear Processes in Metals," A. W. Ruff

and P. J. Blau, NBS Report 80-2058 (1980).

35. "The Characterization and Calibration of Ultrasonic Transducers Used in

NDT and Materials Testing," W. Sachse and N. Hsu, Ultrasonic Materials

Characterization, NBS SP-596, National Bureau of Standards (1980).

36. "Ultrasonic Transducers for Materials Testing and Their Characterization,"

W. Sachse and N. Hsu, Physical Acoustics, Vol. 4 (1979).

37. "Amplitude Analysis of Pancreatic B-Scans: A Clinical Evaluation of

Cystic Fibrosis," T. A. Shawker, S. I. Parks, M. Linzer, B. Jones,

L. A. Lester, and V. A. Hubbard, Ultrasonic Imaging, 2 , pp. 55-66 (1980).

38. "Internal Friction and Sodium Transport in Beta Alumina," J. H. Simmons,

A. D. Franklin, K. F. Young, and M. Linzer, J. Amer. Ceram. Soc. 63,

pp. 78-83 (1980).

39. "Eddy Currents in a Conducting Cylinder with a Crack," R. D. Spal and

A. H. Kahn, J. Appl. Phys., 5jD, 6135 (1979).

40. "A Study of Deformantion and Fracture Processes in a Low-Alloy Steel

by Acoustic Emission of Transient Analysis," H. N. G. Wadley and C. B. Schruby, Acta Met., 27_, pp. 613-625 (1979).

41. "Inservice Data Reporting Standards for Engineering Reliability and Risk

Analysis," J. T. Fong, Nuclear Engineering and Design 60, pp. 159-161 (1980).

109
B. NDE Meetings at NBS

The NDE program has been active in sponsoring NDE meetings, both symposia

and workshops. The purposes behind this significant meeting activity include

(1 ) drawing attention of the the industrial community to NDE, (2) providing a good record of the state-of-the-art, (3) providing a forum for information ex- change, (.4) helping our NBS staff meet individuals active in NDE and learning

the status of current work in the field, and (5) providing a mechanism for NDE

people to discuss their NDE standard needs.

During this past year, NBS sponsored the Second International Symposium

on Ultrasonic Materials Characterization. The meeting, held in cooperation

with American Society for Nondestructive Testing (ASNT), was held at NBS on June 4 to 6, 1980. There was a one-day overlap of this NDE meeting with the

Fifth International Symposium on Ultrasonic Imaging and Tissue Characterization

(June 1 to 4, 1980) to encourage interactions between ultrasonic specialists

from the medical and industrial communities.

An NDE course was held at NBS on April 15 to 17, 1980. The course,

Fundamentals of Nondestructive Testing, was sponsored by the local sections

of the American Society for Metals and the ASNT.

C. NBS Seminars on NDE

A list of NBS-NDE Seminars held during the past year is given in Table 4 . Notices of the seminars are distributed broadly in the Washington area. Visitors are welcome and often attend.

110
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D. Awards

There were several recognitions of NBS-NDE people during the past year.

Awards include the following:

Industrial Research, IR-100 Award

NBS was recognized with an IR-100 Award for the second consecutive year

for an NDE-oriented development. This award recognized Dr. Nelson N. Hsu,

Mechanical Production Metrology Division, for his development of an acoustic

emission simulator.

The AE simulator is essentially a precision mechanical pencil with precision "lead", a holding fixture with a loading screw attached to a load cell

and a peak hold circuit with a digital force readout. To generate a simulated

AE event, the pencil lead is forced against a structure until the pencil lead

breaks. The breaking pencil lead generates a point force step function un- loading at the surface of the structure. Since the shape of the input load (a

step function) is known, a single number, the force step height, determines the

input. The load cell can be calibrated on an absolute basis so that the whole

simulator provides an absolute input for the calibration of AE systems and

subsystems

The Harry Diamond Award, IEEE

Martin Greenspan has been selected to receive the Institute of Electrical

and Electronics Engineers Harry Diamond Award for 1980. Greenspan, retired

from NBS in 1976 but still consults with the Center for Mechanical Engineering

and Process Technology. Greenspan was honored for many contributions in acoustics and elasticity over a long period of time. One of the areas in which

Greenspan's contributions were cited was NDE, particularly for the concepts

that led to the calibration methods for acoustic emission transducers.

112
E. Talks and Appearances by NDE Office Personnel

1. "Verification of Liquid Penetrant Examination Systems," L. Mordfin, ASME

Boiler & Pressure Vessel Subcommittee V, Subgroup on Surface Examination,

New York City, NY, October 31, 1979.

2. "National and International Standards for NDT: To Achieve Improved

Repeatability and Measures Related to Performance," H. Berger, Plenary

Lecture at the Ninth World Conference on NDT, Melbourne, Australia,

November 19, 1979.

3. "A Comparison of NDT Standards in the U.S. and the U.S.S.R. ," H. Berger

et al , paper presented at the Ninth World Conference on NDT, November 21,

1979.

4. "Nondestructive Testing of Railroad Rail," H. Berger 59th Annual Meeting

of the Transportation Research Board, Washington, DC, January 21, 1980.

5. "NDE Standards for Nuclear Power Systems: An NBS Perspective," L. Mordfin,

Third International Conference on Nondestructive Evaluation in the Nuclear

Industry, Salt Lake City, UT, February 12, 1980.

6. "Review of the NBS Program in NDE," H. Berger, Nondestructive Testing

Committee, American Iron and Steel Institute, Pittsburgh, PA,

February 13, 1980.

7. "NBS Program in Nondestructive Evalation," H. Berger, Physics Department

Seminar, Martin Marietta Laboratories, Baltimore, MD, March 17, 1980.

8. "Measurement of Residual Stresses: Problems and Opportunities,"

L. Mordfin, American Society for Metals Conference on Residual Stress

for Designers and Metallurgists, Chicago, IL, April 10, 1980.

9. "The NBS Program in NDE," H. Berger, Army Materials and Mechanics

Research Center, Boston, MA, April 29, 1980.

10. "What is NBS Doing in NDE?," H. Berger, Mohawk Valley Section ASNT,

Schenectady, NY, May 8, 1980.

11. "Introduction and Welcome, H. Berger, Second International Symposium on Ultrasonic Materials Characterization," NBS, Washington, DC, June 4, 1980.

12. "NDE Standards Program at the National Bureau of Standards," G. Birnbaum,

Pennsylvania North Central Section of the ASNT, Williamsport, PA,

June 10, 1980.

13. "Acoustic Emission Definition and Deformation Fracture of Metals,"

H. Wadley, Acoustic Emission Working Group of Materials Research

Council, DARPA, LaJolla, CA, June 18, 1980.

14. "Reliability of Nondestructive Evaluation," L. Mordfin, American Society

of Mechanical Engineers Symposium on Critical Materials and Fabrication

Issues, San Francisco, CA, August 14, 1980.

113
15. "Acoustic Emission Definition and Deformation Fracture of Metals,"

H. Wadley, IBM, Yorktown Heights, NY, August 20, 1980.

16. "The Role of Calibration in Nondestructive Evaluation," H. Berger,

National Conference of Standards Laboratories, NBS, September 22, 1980.

17. "Acoustic Emission Definition and Deformation Fracture of Metals,"

H. Wadley, Canadian Atomic Energy Authority, Chalk River, Ontario,

Canada, September 24, 1980.

114
U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. 3UBLICATI0N OR REPORT N J. NBSIR 80-2162

2.Gi /’L Accewlon No.

i_ ill

. mm,

&M'.A60Z/s.-/4y/w///. y.-y/A/.M: • . / .• •/. .

4. TITLE AND SUBTITLE

Technical Activities of the Office of Nondestructive

Eval uation

5. Publication Date

*. Performing Organization Code

7. AUTHOR! S) H. Berger and L. Mordfin

8. Performing Organ Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS lit. Prnject/Task/Work Onit No.

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

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15. SUPPLEMENTARY NOTES

j | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or teas factual summary of moat significant information . If document includes a significant bibliography or

literature survey, mention it here.)

A review of nondestructive evaluation programs at NBS, for FY1980 is

presented in this annual report.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Acoustic emission; eddy currents; imaging; leakage testing; magnetics; material

parameters; nondestructive evaluation; optics; penetrants; radiography; and

ul trasoni cs.

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