AlllOO T^SSflO

_ NBS

Publications

NBSIR 82-2449

Technical Activities 1981

Office of Nondestructive

Evaluation

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Office of Nondestructive Evaluation

Washington, DC 20234

December 1 981

''"'Dared for f-QC*

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shington, DC 20234

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NBSIR 82-2449

ft (t TECHNICAL ACTIVITIES 1981

OFFICE OF NONDESTRUCTIVE

EVALUATION

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MAH 4 1982

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Harold Berger and Leonard Mordfin, Editors

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Office of Nondestructive Evaluation

Washington, DC 20234

December 1981

Prepared for U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
v;i

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Table of Contents

Page

Introduction 1

Technical Progress Reports

1. Acoustic Emission for NDE J. A. Simmons, R. B. Clough, and

R. Mehrabian 5

2. Electric Power Research Institute/National Bureau of Standards

Joint Program on Acoustic Emission D. Eitzen,

F. Breckenridge, N. Hsu, T. Proctor, R. Clough, and J. Simmons. . 7

3. NBS Conical Transducer: A Quantitative Acoustic Emission Sensor

T. M. Proctor 23

4. Electrochemical Noise U. Bertocci and J. Kruger 28

5. Characterization Kinetics Study of Amorphous Pd-Cu-Si by Ultrasonic Measurements M. Rosen and R. Mehrabian 29

6. Nondestructive Evaluation of Composites H. M. Ledbetter,

J. C. Moulder, and S. K. Datta 32

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

N. Carino 36

8. Monitoring of Segregation Processes in Metals by Electrical

Resistivity M. B. Kasen 38

9. Electrical Conductivity Standards A. J. McAlister 40

10. Eddy Current Standards and Instrumentation G. Free and

B. Field 42

11. Theoretical Modelling in Eddy Current NDE A. H. Kahn ... . 47

12. Leak Rate Reference Standards S. Ruthberg 50

13. Magnetic Measurements L. J. Swartzendruber 54

14. Optical Measurement of Surface Roughness E. Teague,

T. Vorburger, F. Scire, S. Baker, and C. Trahan 57

15. Optical Scattering for Nondestructive Evaluation A. Feldman

and G. S. White 62

i i i
16. Signatures for Holographic NDE C. M. Vest 66

17. Fluid Dynamics of Liquid Penetrant Flows J. M. McMichael . . 71

18. Use of Uranium-Doped Glasses for the Calibration of Apparatus

Employed in the Evaluation of Fluorescent Dye Penetrants

R. W. Burke and D. K. Hancock 72

19. Mechanical Properties Characterization for Quality Control and

NDE of Polymers D. L. Hunston and J. L. Rushford 74

20. Polymer Transducers S. Edelman and S. C. Roth 77

21. Doppler-Broadened Positron Annihilation Lineshape for Detection

of Defects in Materials R. C. Reno and L. J. Swartzendruber. 78

22. Scattering of Acoustic Waves R. D. Mountain 81

23. Ultrasonic Imaging/Instrumentation M. Linzer and

S. J. Norton 82

24. Ultrasonic Reference Block Standards and Measurements

G. V. Blessing 84

25. Laboratory Evaluation of Ultrasonics for Crack Detection in

Concrete L. I. Knab and J. R. Clifton 85

26. Reference Samples for Ultrasonic Residual Stress Measurement

N. Hsu, T. Proctor and G. Blessing 86

27. Nondestructive Evaluation of Nonuniformities in 2024 and 2219

Aluminum Alloy Plate--Relationship to Processing/NASA

L. K. Ives, L. J. Swartzendruber, W. J. Boettinger, M. Rosen,

S. D. Ridder, F. S. Biancaniel la, R. C. Reno, S. Fick,

D. B. Ballard, and R. Mehrabian gy

28. Safety Factors and Mathematical Modeling J. T. Fong .... 91

29. Visual Acuity Requirements for Nondestructive Testing

G. Yonemura 94

30. Wear Condition Monitoring A. W. Ruff 97

31. X-Radiography R. Placious, D. Polansky, C. Dick, and

J. Motz 100

32. Comparison of Non-Reactor Based Neutron Radiographic Facilities

W. L. Parker and D. A. Garrett 102

iv
33. X-Ray Residual Stress Mapping in Industrial Materials by Energy

Dispersive Diffractometry M. Kuriyama, W. Boettinger, and

C. Bechtoldt 105

Appendices

A. Conferences Sponsored IQg

B. Talks and Appearances by NDE Office Personnel 110

C. Awards and Recognition Ill

D. Publications 113

E. Technology Innovation Act 118

V

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, neutron or ultrasonic

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. The

commonly used methods are listed in Table I.

There are several reasons why NDE is important. Since the test object

is not destroyed, 100% inspection is possible and may be desirable in many

cases. Critical components involving safety considerations, such as primary components of an airplane, should all be tested. In this example,

one can recognize some of the growing interest in NDE because of product

liability problems. Liability considerations are encouraging many manu- facturers of consumer products to use NDE more effectively.

There are other incentives leading to increased use of NDE. If we can be assured that a component will contain defects such as inclusions,

cracks or voids only below a certain size, then the design can be tightened.

This can result in savings of material, energy and time. The impact is both

on conservation and productivity. Furthermore, there is a strong trade

incentive for manufacturers to produce quality products and components.

Competition at home and abroad is increasing. Many U.S. markets have fallen

not because of price but because of a perception of quality. Therefore,

NDE measurements in industry are, and will continue to be, on the increase

because of pressures from productivity, conservation, product liability and

competi ti on

.

Standards and calibration fill a very necessary role because ther is

a natural desire for accurate NDE measurements - and because customers

expect and often require traceable measurements. Traceability for many

NDE measurements is now available in the form of calibrations and Standard

Reference Materials (SRM's) from NBS. Traceable measurements include

calibration services for acoustic emission and ultrasonic transducers and

ultrasonic reference blocks. There are many NDE related SRM's available

including those for thickness and wear measurement, radiographic density and

newly announced SRM's, penetrant sensitivity plate (SRM 1850), and a silicon resistivity standard for eddy current testing (SRM 1523). Plans

include SRM's for eddy current conductivity measurements, for fluorescent

brightness and for radiographic sensitivity. Further information about

traceable measurements is available (see, "A Basic for Traceable NDE

Measurements" NBSIR 80-2109, December 1980).

1
The current status of the NBS program in NDE, including work toward

traceable measurements and improved procedures for NDE is described in

the technical reports that follow. Those desiring additional information

about the NDE activities at NBS are encouraged to contact the Office

of NDE. If your inquiry is about a specific technical report, inquiries

directly to the investigator/author are encouraged.

2
TABLE

I:

COMPARISON

OF

COMMON

NONDESTRUCTIVE

TESTING

METHODS

to • E to O CU T3 E . •I- C -r- to E O

to • 00 CO

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Visual

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scratches,

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Table I

(continued)

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•I- <u to to —1 Q- s o.
TECHNICAL PROGRESS REPORTS

1. Acoustic Emission for NDE

J. A. Simmons, R. B. Clough and R. Mehrabian

Metallurgy Division

Center for Materials Science

Acoustic emission (AE) testing shows promise for monitoring flaw growth

in structures and also for materials studies of rapid phase changes such as martensitic transitions and microcrack nucleation and growth.

At NBS a unique approach is being developed for acoustic emission

which has as its objective the reconstruction of the source in terms of its

stress drop tensor. This will make accessible quantitative observations on dynamic materials phenomena such as rapid solidification, martensitic phase

transitions, microcrack nucleation and devitrification of glasses.

Because of the tensor nature of the emission source, at least six

observation channels are necessary for source reconstruction via signal

inversion. With this in mind, a multichannel AE system has been constructed

and new experimental methods are being developed to permit us shortly to

perform a set of critical experiments which will establish the validity of

this approach.

Highlights of these activities include:

(1) Application of indentation acoustic emission, the new experimental

technique developed here, to A533B pressure vessel steel; through modification

of heat treatment and hydrogen charging, AE activity can be varied over the

widest possible limits, from virtually none to that of glass.

(2) Construction of the quantitative multichannel AE source characterization system.

(3) Experimental simulation of thermoelastic AE sources using a Nd-YAG laser.

(4) Exploratory AE studies of rapid solidification using directed

high energy sources.

The first two results are part of a continuing EPRI research program and are described on pages 11 and 12. The third was part of a guest worker program

with AERE Harwell in which Dr. Haydn Wadley took part. The last is part of a new program with DARPA that makes use of sophisticated new NDE techniques to study

rapid solidification as a dynamic process as well as to detect defects that may

be produced during solidification.

Experimental AE Source Simulation. A Nd-YAG laser is being used as a highly reproducible, thermoelastic, AE source for simulating defects such

as microcrack dipoles in a systematic set of studies. The reproducibility

of the source permits the use of a single channel for mapping the stress wave

fields generated by the thermoelastic source. These experimental results

will be compared with theoretical curves generated from computer codes that

were developed previously.

5
Rapid Solidification Studies. AE has great potential for the study of

dynamic materials events such as rapid solidification, where stress waves may

be generated by thermoelastic contractions, by phase change contractions, by

defects such as cracks produced during solidification, or by other solidification phenomena.

Virtually no information of this type has been obtained for rapid

solidification. Two approaches are being taken; the first is a wideband

technique for use with a pulsed laser, where solidification can be kept rapid

enough to capture the virgin stress waves before reflected waves distort the

signal. This technique would be useful for solidification events less than

about 100 ys in length. So far this approach has been limited to detection of

vaporization phenomena. The second technique is a low frequency, narrow

bandwidth method which is suited for solidification phenomena of duration of

the order of millisecond or more, such as are obtainable with a steadystate melt generated by an electron beam. For these conditions, exploratory

measurements have been made which show transducer ringing, a sign of acoustic

rather than electrical (noise) phenomena. Conditions are being established

to optimize the signal -to-noise ratio and to verify the phenomena. Verification can be accomplished, in part, by comparing signals generated in the solid

state by thermoelasticity with signals generated during solidification from

a steady-state melt following the termination of the beam current.

6
2. Electric Power Research Institute/National Bureau of Standards

Joint Program on Acoustic Emission

D. Eitzen, F. Breckenridge, N. Hsu and T. Proctor

Mechanical Production Metrology Division

Center for Manufacturing Engineering

and

R. Clough and J. Simmons

Metallurgy Division

Center for Materials Science

Acoustic emission (AE) techniques have great potential for determining

and monitoring structural integrity. Acoustic emission signals contain

potentially useful information about the location and intensity of defects

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

current signal reception methods do not preserve all of the available

information, and 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 in interpreting AE signals lies in the inherent comple:S:ity of

the generating mechanisms, the transient wave propagation details, and the

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

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 the first phase

of the program were summarized in (1) and included:

contributions to data interchangeability for laboratory and field

measurements through the development of a transducer calibration

service

contributions to the reliability of AE field data through the

development of calibrated sources

a better understanding of AE source behavior through theoretical

predictions of the behavior of AE sources

a better understanding of the limitations of conventional AE

methods through a critical analysis

a framework for understanding the AE process from source to

measured voltage

an analysis of the potential information in AE signals, an understanding of the modification to signals by wave propagation,

experimentally 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

demonstration of the feasibility of determining the^actual AE source function in glass and in steel from remote measurements

using time-domain deconvolution

development of a methodology for determining the significance of

defects from received AE signals

development of several additional very promising signal processing

techniques.

7
Some of these developments are being used in industrial applications

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

are consistent with the technical plan, additional information must be

developed before utility power plant operators can obtain all the information

from AE that is desired.

In this report we summarize our most recent work towards quantitative

acoustic emission measurements within the EPRI/NBS AE Program. The acoustic

emission work we describe here focuses on three areas:

calibration and sensor activities

characterization of AE sources materials effects

CALIBRATION AND SENSOR ACTIVITIES

In January 1980 we implemented a calibration service for acoustic

emission transducers using the surface-pulse method. Since then almost 200

calibrations have been performed, 68 for other laboratories, 40 for internal

quality control or improvements, 15 for other NBS units and about 70 for

the development of the NBS Conical Transducer. This calibration method makes

use of the theoretical solution for the normal displacement of a half-space

due to a point-force step-function. The surface-pulse calibration method

also relies on our ability to mechanically produce a point-force step-function

(we use the breaking glass capillary method (2-4)) and it relies on an accurate

measurement of actual surface displacement using a capacitive transducer (5).

Further Developments of the Surface-Pulse System

Repeatability of calibration has been a problem with certain types of

transducers. Although most transducers can be calibrated repeatably without

using any special or unusual mounting practices, there are some which

apparently require special measures to insure repeatability of the calibration.

The measures which we have developed are, in our experience, sufficient to

guarantee reproducible calibrations, although they are not always necessary.

The reason why some transducers require these measures, and others do not, is

not clear to us at this time. We suspect that porosity of the wear face may

cause air entrapment and resulting bubbles in the couplant layer.

Special measures used for troublesome transducers include:

the wear face of the transducer was optically ground and polished

to within approximately 3 fringes of being flat

any burrs on the steel block at the transducer mounting location were removed by hand lapping. The criterion here is that an optical flat should register no more than one half of fringe of

separation when held down by gravity

a clock oil was used as the couplant

great care was taken in the mounting of the transducer to

exclude dirt

a special hold-down device was used, which applied a downward

force (1 kg weight) to the center of the back of the transducer

8
The first of these measures requires modification of the transducer under

test, is expensive and time consuming, and in general, is not used. (If,

however, we determine that there is a problem with a certain type of transducer,

we may insist that the customer have the transducer ground and polished before

we will calibrate it.) Figure 1 shows three calibrations of a transducer with

re-mounting in between. The transducer frequency response curves in Fig. 1 also exhibit the aperture effect which results in nulls in sensitivity. The

locations of these nulls are reasonably predicted by the theory for a wave

train crossing a circular aperture. The phase response for this transducer

(not shown) has phase jumps at the null locations which are also predicted

theoretically.

Through-Pulse Calibration System

The technique of placing the standard transducer at a location symmetrical

to that of the unknown transducer cannot be used for the through-pulse

calibration method since the input source is located at the top surface of

the block and the unknown transducer is located directly below on the bottom

surface (epicenter). We may, however, compare the output waveform from the

unknown transducer against the theoretical waveform of the -thick plate,

epicenter solution.

Several through-pulse calibrations have been performed on the NBS Conical

Transducer and the results compared with those from surface-pulse calibrations

of the same transducer. For such a transducer, which has a small aperture, the

results should be comparable. One such comparison is shown in Fig. 2. Both

calibration curves are on the same absolute scale. It is apparent from the

figure that there is substantial agreement between the methods, but that the

absolute sensitivity indicated by the two calibrations differs by about 2 dB.

The source of the discrepancy is being investigated.

AE SOURCE CHARACTERIZATION

This part of the AE program is directed toward the deconvolution of the

AE source in order to determine its character, to improve system calibration,

and to improve defect location. The goal of source deconvolution is to remove

the effects of the propagating structure and the receiving transducer on the

evolved signal from the captured voltage-time waveform, thus revealing the source characteristics using causal analysis. We have shown (1) that for a plate

and a capacitive transducer we can determine the actual source function from the

received signal using the inverse transform function. In order to do source determination in more complex structures, we must experimentally determine the

transfer function and develop general inversion techniques. To carry this out

we must generate a repeatable known source which, along with the measured structural

response, can be used to determine the impulse response of any complex structure.

We also must develop a computational algorithm for inverting the impulse response

to obtain the operator which deconvolves the source waveform. This work also

provides a basis for system calibration and for minimizing flaw location

uncertainty.

Repetitive Short Duration Source

Comparisons have been made between electrical spark impact sources and

pulsed laser sources. The laser source is effective but the spark source has

advantages including portability, simplicity, and low cost. We have perfected

9
the charging, switching and triggering circuits so that a few-nanosecond highvoltage current pulse can be discharged with very low jitter between electrodes.

The resulting simulated AE waveforms in a structure are essentially identical

to one another.

The mode of the spark source is controlled by the configuration of the

electrodes. We have emphasized the configuration in which the plate (or

structure) is one electrode and a second electrode is just above the plate

surface. The stress wave thus generated in the structure can be modeled as evolving from local surface plasma heating, the same mechanism as when using

a pulsed laser source for radiation heating. Fig. 3 shows detected signals

due to sparking onto a 1.5-in. thick plate. Fig. 3a corresponds to the sensor located at the epicenter; Fig. 3b is for the sensor located on the same sur- face as the source and two thicknesses away from the source. From such experiments we conclude that: the source is extremely reproducible; the detected signals

agree well with theoretical predictions for a dipole source; the surface normal

motion has a well-defined negative pulse whose arrival is easily detected (a

fact that could be exploited for precise measurements of ultrasonic wave speed

measurements); the rise time for the stress wave is less than one-half microsecond; and, although the source generates EM signals, these can be easily

isolated in the time domain. In order to increase the signal -to-noise ratio

of such measurements, a computer program permits signal averaging of 100 repeated

source events in less than 10 seconds.

Signal Processing Techniques for Source Characterization

Signal processing subroutines, for the dedicated minicomputer-based AE

signal acquisition and processing system, will be used to deconvolve the AE source function from the received signal in "complex" structures. These

signal processing packages include:

a fast convolution program with one time series in core-memory

and one time series on disk

a direct, exact time-domain deconvolution program based on error-free

matrix inversion

a program, based on least-squares fit, for finding the coefficient

of the inverse filter by solving the Toeplitz normal equations

a program for power spectra estimation based upon the maximum

entropy method developed by J. P. Burg.

In order to evaluate various approximation techniques for the deconvolution

of the digitized signals in the time domain, the epicenter impulse response

function and its exact inverse are chosen for comparison (6). Figure 4 compares

exact deconvolution with an approximate least-squares deconvolution. Figure 4a

is the impulse response function (transfer function of the plate for the sensor at the eipcenter). Figure 4b is its exact inverse obtained by direct

matrix inversion, which we first reported in 1977. Figure 4d is the displacement

at the epicenter corresponding to a step function impact force. Figure 4c is the

convolution of the inverse function (Fig. 4b) and the step function displacement (Fig 4d). As expected. Fig. 4c is a step function. However, results

using a least-square approximate deconvolution are quite different. While the

approximate inverse function (Fig. 4e) is a reasonably "good" approximation

of the exact inverse function (Fig. 4b), the deconvolved step function displacement, Fig. 4f (the convolution of Fig. 4e and Fig. 4d), is far from

a step function. Further examination by convolving the impulse response and

10
the approximate inverse reveals that a error is present in the result which

accumulates for a step-function source. Clearly, the accuracy of the approximate

deconvolution is signal dependent. It is expected that if the source signal

is cyclic, then the deconvolved result will be much better than for the stepfunction source. Similar comparisons have been made for other types of sources

for the epicenter configuration.

MATERIALS EFFECTS AND CRACK CHARACTERIZATION IN STEEL PLATES

Substantial progress has been made on producing AE in A533B steel plates

and also on the longer term milestone of developing a multichannel source characterization facility for quantitative measurements of AE sources.

Reproducible AE in A533B Steel Plates

The generation of reproducible AE in A533B steel plate has been studied

using the indentation technique described previously (7). The as-received plate

is quite ductile and thus does not readily produce local stress concentrations

which could generate AE through rapid, localized load drops. A number of methods

for treating the plate to enhance its acoustic "emissivity" were examined. These

included indentation following fatigue, severe cold work, and surface modification with an electron beam. In addition, the electron beam and a Nd-YAG laser were used as sources on the material surface. Of the above, only two showed

promise: indentation following electron beam surface modification, and pulsed

laser excitation of the material.

A systematic study was performed on the effects, in A533B steel, of

temper embrittlement augmented by grain coarsening and hydrogen charging. It was found that this method worked quite well and that a combination of grain

coarsening at 1100°C, aging at 500°C up to 20 days, and hydrogen charging

produced a substantial increase in AE activity. Figure 5 shows the AE count rate

and load during indentation of A533B steel in the quenched and tempered condition,

i.e., prior to the temper at 500°C for embrittlement. The emission is rather

small. Figure 6 shows the AE rate after aging for 10 days at 500°C. This

shows an increase in count rate due to the aging, which is further enhanced

by hydrogen charging. For comparison purposes. Fig; 7 shows AE during indentation of hot-rolled 1020 steel and of glass, the latter being one of the

most active materials for producing AE. These results demonstrate that by

controlling the heat treatment and charging with hydrogen, the relatively

quiet as-received A533B can be converted to a material that emits at a rate

comparable to the most emissive materials. The temper-embrittled condition

is one which could occur, to some extent, in an A533B weld region in the

field.

Understanding of this phenomenon is further enhanced by a stress analysis

of the subsurface-deformed region of the indentation. There is a compressive

zone immediately under the indenter which produces a hemispherical region of

triaxial tension at one or more diameters away from the indentation. A typical

microcrack is shown in Fig. 8. Due to the shape of the tensile field, the

crack need not be directly under the indenter. In addition, there is a region

of enhanced hydrogen concentration near the surface which may be responsible

for microcracks in hydrogen-charged material generally being either surfaceconnected or shallow subsurface types. This leads to the occurrence of

cracks at the side, rather than under the indenter as was found previously

11
for tool steels that were not hydrogen charged. While the crack is on the

order of 200 micrometers in size, this is small relative to the shortest

wavelength examined (about 2400 micrometers) so that the crack will appear

to be a "point source". In addition, as shown in Fig. 9, many of the cracks were found to be associated with inclusions.

To summarize, a method has been found which is useful for producing AE in

A533B steel plates. Through controlling the heat treatment and through additional methods of modifying the material condition, the amount of AE can be

controlled while still keeping the material relevant to conditions in the

weld region. This method is now applicable for use on larger plates of A533B

steel, where signal reproducibility can be checked with the multichannel system.

Multichannel AE System for Plate Experiments

Another approach being taken in our AE research program is the development

of a multichannel AE signal acquisition and processing system to permit more

complete deconvolution of the AE stress drop source. An 02 tool steel plate

has been hardened by austenitizing and water quenching. Preliminary tests

using such a preparation show that multiple, reproducible AE signals can be

obtained during indentation. The indentation system is shown in Fig. 10.

It consists of a pneumatic loading indenter, a Faraday cage to minize rf

noise, and an XY translation table for positioning the plate specimen.

The multichannel system is diagrammed in Fig. 11. A set of six wide

band transducers (the new NBS Conical Transducer) has been fabricated and

there are at least six channels of preamplification, antialiasing filters, and

amplification up to 100 dB with a bandwidth in excess of 10 MHz, available

for the system. Computer codes for the dynamic plate response have been

extended to include all surface dipoles, and calculations have been made of

emission signals on a stainless steel plate which will be used for additional

tests on the wideband transducers. Computer codes for deconvolution, and

comprehensive driver programs for our high-speed interface, are being prepared

on our minicomputer system which, in turn, is being expanded to carry out

data processing.

REFERENCES

1. D. G. Eitzen, F. R. Breckenridge, R. B. Clough, E. R. Fuller, N. N. Hsu,

and J. A. Simmons. "Summary of Fundamental Developments for Quantitative

Acoustic Emission Measurements". EPRI Report NP-1877, June 1981.

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

Some Applications of Lamb's Problem". Journal of the Acoustical Society

of America 1975, pp. 626-631.

3. N. N. Hsu and F. R. Breckenridge. "Characterization and Calibration of

Acoustic Emission Sensors." Materials Evaluation 1981, pp. 60-68.

4. F. R. Breckenridge. A paper entitled "Transducer Calibration by Means of

the Seismic Surface Pulse." For submission to the Journal of Acoustic Emission.

12
5. F. R. Breckenridge. "Surface-Wave Displacement: Absolute Measurements

Using a Capacitive Transducer." Journal of the Acoustical Society of

America pp. 1177-1185.

6. N. N. Hsu and D. G. Eitzen. "The Inverse Problem of Acoustic Emission -- Explicit Determination of the AE Source Time-Function". Presented at

the AF/DARPA Review of Quantitative NDE, August 1981, Boulder, CO.

7. R. B. Clough and J. A. Simmons. "Reproducible Acoustic Emission

Signatures by Indentation in Steels". Materials Evaluation 1981,

pp. 1026-1031.

13
MPGNITUDE

(dB;

SPECTRUM MAGNITUDE: DIV; 328

Fig. 1

14
MRGNITUDE

(dB)

SPECTRUM MAGNITUDE: DIV: 239

15
VO

TIME

IN

MICROSECONDS
EPICENTER

DISPLACEMENT
A533B

BEFORE

TEMPER

EMBRITTLEMENT

18

1

min.
A533B

TEMPER

EMBRITTLED

10

DAYS

19

TIME
HOT-ROLLED

1020

STEEL

O)

o

o

O

o

20

1min.
Fig. 8

Fig. 9

21
Fig. IQ

SS»- HIGH SPEED CABLE

TO MINICOMPUTER

• SIGNAL DUMP AND REARM 'N < lOOms

• 100 dB DYNAMIC RANGE

Fig. 11

22
3. NBS Conical Transducer: A Quantitative Acoustic Emission Sensor

Thomas M. Proctor

Mechanical Production Metrology Division

Center for Manufacturing Engineering

Initial investigations with regard to new concepts in acoustic emission (AE)

transducers have taken place. The capacitance transducer used in the acoustic

emission calibration facility is an excellent transducer for standards work.

Its flat frequency response over a wide frequency range makes possible faithful

reproduction of the mechanical displacement. Such capacitive transducers are,

however, of low sensitivity. They are also difficult to use and require a highly polished surface on the mounting structure. Thus, there is a need for

a transducer that does not have these limitations and yet has good transient

response.

We have constructed such a transducer; it is a simple two-piece device

with a conical piezoelectric element of about 1.5 mm diameter and an extending

brass backing. The piezoelectric element has no wear plate and is small

enough so that it behaves nearly as a point receiver for AE signals. The

brass backing is a cylinder which is large in both dimensions compared to

the piezoelectric element. The simplicity of design, small size of the

element, and large size of the backing contribute to make it a very high

fidelity device with significant improvement over the normal commerciallyavailable piezoelectric transducers. Usually, commercial transducers have severe internal resonances which obscure the received mechanical signals

so badly that meaningful quantitative signal analysis is difficult. Certain

physical design parameters are the cause of these interfering resonances.

A comparison is demonstrated by Figures 12, 13, and 14. These figures

show the electrical signals from three transducers responding to mechanical

surface waves produced by a step force. Figure 12 is the output of the NBS

standard capacitance transducer. Figure 13 shows signals produced by a commercial ly-avail able AE transducer. This waveform shows the serious

problem caused by the transducer's internal resonances. The output should

be like that of the standard if it is to be optimally useful for signature

identification. Figure 14 is the signal from the piezoelectric transducer

constructed in this laboratory. This waveform demonstrates the feasibility

of designing better transducers for use in signature identification of

transient events.

Another comparison further demonstrates the quantitative potential

of the new NBS Conical Transducer. Referring to Figure 15, the upper curve

is the theoretical prediction of the normal displacement, at a particular

location, of a plate surface due to an AE source. The location for the

dynamic displacement is two plate thicknesses away from the source. The

assumed source is a point-force step-function. The theory is from Pao,

Gajewski and Ceranogla and was independently confirmed by Simmons, Hsu

and Willis. The lower trace is the digitized signal from the NBS Conical

Transducer which was mounted on a 25.4 mm thick plate, 50.8 mm away from a breaking-glass capillary source. The agreement is obviously very striking.

Continuing work on this new type of transducer will help to determine its

usefulness as a transfer or secondary standard and as a field device for

acoustic emission NDE.

23
24

TIME-
25

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200

IS

o

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26

TIME
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VOLTAGE

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20

60

100

140

transducer output : 4

27

Fig.

15
4. Electrochemical Noise

U. Bertocci and J. Kruger

Chemical Stability & Corrosion Division

Center for Materials Science

The noise measurement apparatus has been interfaced to a computer so that the calculations necessary to separate the deterministic response of

the electrode to the input signal from the random fluctuations, as developed

and described in a recently published paper*, can be done rapidly and

automatically, considerably increasing the productivity of the system.

Measurements are now being taken on specimens of nature similar to buried

cables to determine if the noise pattern depends significantly and reliably

on the corrosive environment.

Noise measurements on buried cables under field conditions have been taken

also. Although the instrumentation employed in the field is less sophisticated

than that used in the laboratory, limiting the observations to fluctuations

in the electrode potential, the use of a two-channel spectrum analyzer, with

capability to measure the cross-power spectrum, has enabled us to take some preliminary readings which seem to indicate that the noise signals observed

in the frequency range of a few hertz originate from specific portions of

the cable. Although these results are insufficient to show that noise

measurements can be successfully employed to detect localized corrosion

in the field, they do not preclude this possibility.

*U. Bertocci, J. Electrochem. Soc. 128, 520 (1981)
5. Characterization Kinetics Study of Amorphous Pd-Cu-Si by Ultrasonic

Measurements

M. Rosen* and R. Mehrabian

Metrology Division

Center for Materials Science

Metallic glasses exhibit interesting physical and mechanical properties.

A glass is generally not in a state of thermodynamic equilibrium and, therefore,

tends to structurally relax and ultimately crystallize into a more stable

structure when thermal conditions are appropriate. Changes in bulk density

and electronic structure associated with the crystallization process are rather insignificant. Nevertheless, appreciable, and in some instances

extraordinary , variations in several physical properties were observed.

Recently, there has been an increasing interest in the behavior of the elastic

properties of metallic glasses in relation with the glass transition and crystallization temperatures.

The objective of the present investigation was to study the crystallization

kinetics of Pdo. 775 Cgo. 06 Sio.i 65 ribbons (about 50 ym in thickness) by means of laser-generated and’ piezoelectrical ly detected, ultrasonic waves whereby

the extensional wave velocity and, consequently. Young's modulus can be

determined as a function of crystallization time. The amorphous-to-crystalline kinetics could thus be determined to a high degree of accuracy.

The inherent difficulty of measuring sound-wave velocities in thin

ribbons was overcome by developing a technique whereby a load was applied on the specimen by means of rapid deposition of energy from a single-pulse of a Q-switched Nd:YAG laser. A state of unbalanced compressive thermal stress is

produced. The stress gradient propagates along the ribbon in the form of an elastic wave. The piezoelectric crystal, at a distance from the spot where the

laser radiation was deposited, detects the local disturbance. Thus, the transit

time of the propagating wave could accurately be determined by means of a transient-pulse recorder. The complete waveforms, stored in a Perkin-Elmer

computer, have not yet been analyzed since they require definition of the

theoretical criteria with respect to specimen geometry, conversion of propagation modes and contribution of the detection sensor.

Results of the present investigation indicate that the transition from

the amorphous-to-crystall ine state in Pd-Cu-Si is time and temperature dependent (Fig. 16). The kinetics were determined at three isothermal -holding

temperatures. Therefrom, the activation energy for recrystallization was found to be 55 Kcal/mole. From the time dependence of the transformation

kinetics an insight was gained into the nucleation and growth mechanisms.

Corroborative metal lographic evidence was found to be in qualitative agreement with the ultrasonic data (Fig. 17) suggesting a linear growth law whereby

the crystallization front moves from the free surfaces toward the interior.

The present investigation has also revealed an initial increase of about

1 A% in the elastic modulus, out of 40% for the complete transition from the

amorphous to the crystalline state. It appears that this initial increase

can be related to a structural relaxation of the amorphous phase that may

precede the crystallization process.

*The Johns Hopkins University 29
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30
Fig. 17 Changes in microstructure as a function of time during

the amorphous-to-crystalline transition in Pd-Cu-Si at

390°C. View from the ribbon edge.

31
6 . Nondestructive Evaluation of Composites

H. M. Ledbetter, J. C= Moulder, and S. K. Datta^

Fracture and Deformation Division

Center for Materials Science

Detection of low damage levels in composites is a serious, unsolved

technological problem; appropriate, reliable nondestructive methods do not

exist. Internal friction, which is a gauge of energy dissipation within a material, should be sensitive to this type of damage, particularly at low

frequencies where the wavelength is comparable to specimen dimensions. In order to study the effects of small amounts of mechanical damage on the

Young's modulus and internal friction of composites, an existing forcedvibration apparatus was modified to permit operation as a freely vibrating

reed pendulum. Relative changes in Young's modulus were determined from

changes in the specimen's frequency of vibration; internal friction, Q"^, was determined by measuring the logarithmic decrement during the free decay

of oscillations.

A uniaxial graphite/epoxy composite (HMS/934) was chosen for study.

Three specimens 10 cm long and 2 cm wide were cut from a 0.85-mm thick panel

of graphite/epoxy with the fiber direction oriented parallel to the specimen

length. Young's modulus and internal friction were determined by several

measurements on each specimen before introducing any damage by mechanical

deformation.

Three types of deformation were used to introduce small amounts of damage

into the specimens: static tensile loading to approximately 90 percent of

the ultimate tensile strength (U.T.S.), tension- tension fatigue at a maximum

stress of 60 percent U.T.S. for 10^ cycles at 20 hertz, and thermal cycling

between room temperature and 77 K.

One result observed during the preliminary experiments was that the

specimens exhibited a linear dependence of internal friction on strain amplitude at the strain levels used (maximum surface strain <3 x 10"^). To remove

the influence of strain amplitude on the measured internal friction, data were

taken at several different strain levels and extrapolated to zero strain by a linear least-squares fit. Young's modulus, as indicated by the frequency of

free vibrations, did not depend on strain amplitude within the precision of

the measurements.

The derivative of internal friction with respect to strain, a, was observed

to change following mechanical deformation, often by an even larger percentage

than the zero-strain internal friction. This is illustrated in Fig. 18, which

shows the internal friction as a function of strain amplitude for a graphite/

epoxy specimen before and after tensile loading to 90 percent of the U.T.S.

As the figure shows, both the zero-strain internal friction and the slope of

the strain dependence increase by about 30 percent following mechanical

deformation. Young's modulus decreased following deformation by a much

smaller amount (-0.13 percent).

^Consultant to NBS, Department of Mechanical Engineering, University of

Colorado, Boulder, Colorado.

32
The deformed graphite/epoxy specimen was measured again 24 hours after

tensile loading and the changes induced by the deformation were found to

have "relaxed." Young's modulus increased to essentially the same value as before deformation. Internal friction decreased from 30 percent to only

11 percent larger than the value for the undeformed specimen. The strain

dependence of the internal friction increased over the 24-hour period from

30 to 60 percent greater than the undeformed specimen.

To further substantiate and elucidate these changes in Young's modulus

and internal friction with time following deformation, the specimen was loaded

to the same stress level and the modulus and internal friction were monitored

for several days following deformation. This procedure was repeated three

times. The results of one such experiment are shown in Fig. 19, where Young's

modulus and internal friction are plotted versus time. All of the results are summarized in Table II, which lists the relative values (referred to the

undeformed specimen) of Young's modulus, E, internal friction, Q"^ , and the

derivative of internal friction with respect to strain, a, in both the unrelaxed

and relaxed states following deformation. In the present context, "unrelaxed"

refers to measurements taken within 15 minutes of deformation while "relaxed"

refers to measurements made at least 95 hours after deformation.

The effect of subsequent mechanical deformation was to produce successively larger decreases in Young's modulus, followed by relaxation to a slightly

higher value. Internal friction increased by approximately the same amount

after each cycle of deformation, but the component of the increase remaining

after relaxation grew larger with successive cycles. The strain coefficient,

a, showed the largest effect, increasing by more than 200 percent after the

second cycle of deformation. The increase in a seemed to saturate after

three deformation cycles and the degree of relaxation following deformation

became insignificant after four.

The effect of thermal cycling on the Young's modulus and internal friction of graphite/epoxy was just the opposite of tensile loading: modulus

increased and internal friction decreased, as Table II indicates. Curiously,

the direction in which relaxation proceeded was the same as for tensile

loading: modulus increased slightly and the internal friction decreased with

time following deformation.

Contrary to expectation from the results on static tensile loading, fatigue

induced an increase in Young's modulus of about one percent and a 10 percent

decrease in internal friction. Once again, relaxation proceeded in the same direction as for other deformation modes: modulus increasing slightly and

internal friction decreasing somewhat more with time following deformation.

The conclusions that emerge from these preliminary studies are both en- couraging and sobering: encouraging in that dynamic elastic properties of

composites provide a useful tool for studying changes induced by mechanical

deformation; but sobering in the complexity of behavior that is revealed.

Further studies, both experimental and theoretical, are required to elucidate

this complex behavior.

33
Table

II.

Effects

of

mechanical

deformation

on

Young’s

modulus,

E,

internal

friction,

Q

,

and

the

derivative

of

internal

friction

with

respect

to

strain,

a,

for

a

uniaxial

graphite/epoxy

composite.

All

values

are

referred

to

measurements

made

on

the

same

specimen

prior

to

deformation.

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Fig. 18 Internal friction as a function of

strain amplitude for a graphiteexopy composite before and after

tensile loading to 90 percent of the

ultimate tensile strength.

Fig. 19 Internal friction and Young's modulus

of graphite/epoxy as a function of

time following tensile loading to

90 percent of the ultimate tensile

strength.

35
7. Application of NDE to Construction/Army

J. R. Clifton and N. Carino

Structures and Materials Division

Center for Building Technology

The use of NDE methods in quality acceptance of installed materials

in buildings has been investigated for the U.S. Army Construction Engineering

Research Laboratory. At present, when the military has a building con- structed, 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 acceptance testing

approach is based upon the use of NDE techniques.

NDE techniques applicable to quality acceptance inspection of commonly

used building materials were identified and assessed. Selection of NDE

methods were based on considerations of the important properties of the

materials which control their performance and durability. NDE techniques were assessed according to usefulness of information obtained, reliability

of the technique, level of expertise required to use the equipment and

to interpret the results, and cost effectiveness.

Building materials, components and systems covered in this study are listed in Table III. Their important design factors or properties are also

given. Selection of the materials, components and systems was largely based

on considerations of the level of their usage; frequency and severity of

problems caused by deficiencies in their quality, uniformity, or performance;

and the value of using NDE methods to inspect the material, component, or

system. For example, NDE inspection is not necessary to determine that a glass window is broken, while the location of reinforcing steel in concrete

is more readily accomplished by NDE inspection than by coring. Staff members

of the National Bureau of Standards, and of the U.S. Corps of Engineers

assisted in the selection process.

The results of the assessment of the NDE methods will be given in the

paper "Nondestructive Evaluation Methods for Quality Acceptance of Installed

Building Materials", which is being prepared for publication. The report

NBSIR 80-2163 "Nondestructive Evaluation Methods for Quality Acceptance of

Hardened Concrete in Structures", was published January 1981.

36
TABLE III. FACTORS CONSIDERED IN QUALITY ACCEPTANCE OF BUILDINGS

MATERIAL OR COMPONENT DESIGN FACTORS OR PROPERTIES

1

.

Concrete Strength, quality, density, reinforcing

steel, cracking.

2. Brick and Mortar Units Integrity, thickness, reinforcing steel,

presence of inner grout.

3. Wood and Lumber Integrity and general quality, density,

moisture content, adhesive bond for

laminated wood.

4. 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.

5. Roofing Systems Composition, moisture content,

permeability, slopes, self supporting.

6

.

Paints and Coatings Number of layers, film thickness,

integrity, adhesion, quality.

7. Soils Permeability, proper backfill.

8. Sealants Adhesion.

9. Thermal Insulation Thermal performance, location, moisture

contents.

10. Pipe and Drainage Systems Flow rate and pressure, no leaks,

presence of dielectric joints, no back

flow of water.

11. HVAC Proper flow rate.

12. Building Components Design factors or properties of walls

and ceilings, foundation and basement,

roof, building envelope and floor.

37
8. Monitoring of Segregation Processes in Metals by Electrical Resistivity

M. B. Kasen

Fracture and Deformation Division

Center for Materials Science

A nondestructive resistivity technique has been developed for quantitatively following the redistribution of solute during grain growth in

dilute copper and aluminum alloys. Unlike Auger and other techniques based

on analysis of fractured surfaces, the resistivity technique provides

information on the shift of solute from the interior of the grain boundaries

continuously during the segregation process.

The method involves careful monitoring of resistivity changes in the

10 ohm-cm range during systematic grain growth of recrystallized alloys

and a correlation of such changes with changing density of grain boundaries.

The influence of segregation on resistivity is determined from the separation

between experimentally observed curves relating resistivity to annealing

temperature (or grain size) and curves reflecting the predicted resistivity

change in the absence of segregation. The latter are calculated from

knowledge of the specific electron scattering probability of pure (unsegregated)

grain boundaries and from knowledge of the boundary density existing at

any point in the experiment. Electrical resistivity is sensitive to segregation levels because removing solute from solid solution removes it as an electron scattering source.

Although, theoretically, any resistivity method capable of detecting

changes in the 10’^^ ohm-cm range could be used, the experimental procedure

uses the eddy current decay method to assess changes in residual resistivity

at 4K. This permits rapid measurement of a series of specimens without the

need to attach electrical leads.

A typical result obtained during grain growth annealing of ultrapurity

aluminum containing 6 ppm atomic of iron impurity is illustrated in Figure 20

along with the calculated change in the amount of solute out of solid

solution, C^, during the segregation process. The perturbations observed

in the experimental curve (solid dots) provide useful information on the

details of the segregation process. For example, the first minimum in the curve is found to correspond to development of a segregate concentration

14 -2

of 2. 2-2. 6 X 10 impurity atoms cm of existing boundary, regardless of

the type or quantity of impurity. This is associated with attainment of a segregate level equal to full boundary saturation. Analysis of subsequent

resistivity perturbations is interpreted as a change in boundary structure

reflected in a change in boundary scattering probability.

This work is expected to significantly influence the theory of

segregation processes and theories of solute-controlled grain boundary migration

rates and to eventually impact on the understanding of the atomistics influencing brittle fracture and stress corrosion behavior.

38
x10"®r2cm

ANNEAL TEMPERATURE, °C

Fig. 20. Experimentally observed change in electrical resistivity,

and the resistivity change predicted fronuthe changing densiiy

of pure (unsegregated) grain boundaries , during stepisochronal grain growth annealing of ultrapurity aluminum doped

with 6 ppm at. Fe. 0$ is the concentration of solute removed from

solid solution by segregation. Zero on the ordinate scale represents the single crystal resistivity of the material. This resistivity is recovered after extended annealing at the terminal

temperature.

39
9, Electrical Conductivity Standards

A. J. McAlister

Metallurgy Division

Center for Materials Science

The eddy current method is widely used in both the ferrous and the

nonferrous metals industries for nondestructive detection of flaws such as cracks, inclusions, and variations in composition and microstructure in

metals and metal parts via local changes in electrical conductivity.

Primary conductivity standards are needed for reliable execution of this

work but, to date, this need has been supplied by industry itself. The

necessary range of conductivity for industrial testing is from 0.585 to

58.5

MSm~^ (1 to 100% lAC). NBS is currently acting to provide

A1 alloy standards in the mid-range of 17 to 35 MSm ^ (29 to 60% lACS).

One hundred sets of four aluminum samples covering this conductivity range

have been supplied to the Electrical Measurement and Standards Division

for final calibration.

The properties desired in a primary conductivity standard are longterm stability, durability, and low magnetic susceptibility. (In testing

of high susceptibility steels, normal practice has been to apply a saturating

magnetic field to reduce the differential permeability to a value near that

of vacuum). Hence, elemental metals and alloys of equilibrium phase com- position, upon which stable nonconducting surface layers can be formed, are desirable. The surface properties are important not only for durability

but for reproducible lift-off behavior as well.

The overall aim is the selection of metals and alloys suitable for

primary conductivity reference standards in the 5.85 to 14.6 and 35 to 58.5 MSm

conductivity ranges, and the preparation of specifications for their preparation and fabrication. Nine candidate materials which appear suitable on the basis of their reported physical properties and probable homogeneity and

phase and surface stabilities have been identified.

The following metals and alloys display conductivities within 1%

lACS of the stated values:

Material (w/o) Conductivity (% lACS)

OFHC Cu

1 .

5

Si + Cu

3.0 Si + Cu

1.3 Zn + Cu

2.4 Zn + Cu

21

.5

Zn, 2.5 A1 +Cu

7 A1 + Cu

101

85

72

23

17

12

7

Commercially pure Ti

8 A1 , 1 Mo, 1 V + Ti

3.5

40
For these materials we are investigating the likelihood of

attaining the desired metallurgical and surface properties.

Questions concerning these materials and their preparation -- quality of starting materials, conditions of melting and

solidification, heat and mechanical treatment, possible

adverse effects in cutting, machining, and surface preparation -- are being addressed by search of the literature, and inquiry of

industrial practitioners about their experience and methods,

and by specific research as necessary.

41
10. Eddy Current Standards and Instrumentation

George Free and Bruce Field

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

Efforts to make available to the general public electrical conductivity

Standard Reference Material (SRM) are nearing completion. Two primary standards

which will maintain the unit of resistivity have been calibrated, and initial

measurements have been made on some SRMs. Four electrical conductivity SRMs

will be available in the conductivity range 30%-60% International Annealed

Copper Standard (lACS).

The experiment determining the resistivity of the two primary standards

consists of two types of measurements, length and resistance. The resistivity

of a metal bar of rectangular cross-section is calculated using the relation

p = (R X A)/L. R is the resistance between two points on the bar, A is

the cross-sectional area of the bar and L the distance between the two points

at which the resistance is measured. Instead of measuring the resistance of

the total bar it was measured at a number of points on the bar. All of these

points were contained within a 0.12 m length. The relation R = R' + (a x L)

is established, in which R is the resistance measured at specific points, L is the position of the potential contact on the bar, R' and a are constants

determined by a least squares fit of the data. Since a = dR/dL the resistivity

is then p = a x A. This is the resistivity at a specific cross section of the

bar and not the resistivity over the length of the bar. This calculation

permits a more accurate determination of resistivity. Variations in p and in

the cross-sectional area which take place over the length of the bar are minimized by measuring a portion of the bar which has predetermined uniformity

of geometrical and electrical characteristics.

The cross section of the bar (nominal dimensions are 44.4 x 5.08 mm

was measured as follows: six measurements of the bar thickness and a measurement of the width were done at 25.4 mm intervals over the total

length of the bar. Approximately 200 thickness measurements and 35 width

measurements were made. This measurement scheme was repeated four times on each bar to gain some idea of the random error present in the dimensional

measurements. The systematic and random errors of the resistivity determinations are being evaluated.

The transfer of the unit of resistivity from the metal bars to the SRMs

is done using eddy current instrumentation. The eddy current instrument has

been undergoing various refinements to increase sensitivity and make the

instrument simpler to use. The present configuration is shown in Fig. 21

The sensitivity to changes in electrical conductivity is about 7 ppm. Several

problems were resolved during the past year. Lack of correlation was noticed

when measurements were made on a set of samples using coils of different

geometry. It was found that, although there is negligible coil heating due

to the low power levels used, the coil would change resistance value due to

42
heat transfer between the coil and the metal sample, i.e., the coil would

come to equilibrium at the temperature of the test sample. Temperature

coefficient corrections were determined for each coil and the temperature

of test samples is determined at the time of measurement.

The eddy current bridge measurements are made by varying the frequency

of the source voltage. It was found that any bridge unbalance, i.e., a difference of voltage between the two detector points, caused significant

error due to ground capacitance. Thus, the phase discrimination method of

eliminating lift-off errors had to be replaced. To make the bridge zero balancing for various amounts of coil lift-off, the coils have been calibrated

for changes due to lift-off and a computer algorithm has been written which

calculates the correction to frequency necessary to compensate for lift-off

and gives a true value of electrical conductivity. These calculations are based on the measured frequency and resistance when bridge balance is obtained.

In the FY 80 report a coil design. Fig. 22, using both driving and sensing

coils, was discussed. This coil was to be used both for comparison measurements

and for an absolute measurement of electrical conductivity. Numerous coils

using this arrangement have been made during the past year. The results of

tests on these coils show differences between measured values and theoretical

predictions of about \%. The driving coil was placed directly over the

sensing coil. In making the complete coil it was extremely difficult to make

surface (A) in the diagram flat. The outer surface of the sensing coils was either convex or concave due to the coil winding process. The difference

from the theoretical surface was enough to give the differences that were

measured. Due to this error and the precise nature of the planned experiments, it was decided to discontinue this approach to eddy current measurements.

The real-time eddy current flaw detection and characterization system

described in FY 80 has required the development of a suitable magnetic field

detector. Several types of devices have been investigated, including Hall

effect sensors, printed circuit coils and wire-wound coils. The major

requirements of any sensor used in the system are resolution of magnetic

fields at the microgauss level and "matched performance" between devices. Hall

effect devices were found unsuitable due to self-heating of the device, and

stray field pickup problems occurred with printed circuit coils. Thus,

recent work has involved building matched pairs of wire-wound coils.

The flaw detection system concept relies heavily on using sets (an array)

of matched magnetic field sensors. The dynamic range of the signal processing

instrumentation requires the sensor outputs to be matched within one percent.

We have been unable to produce wire-wound coils with matched responses under

the required operating conditions.

Traditional eddy current systems use self-excitation of the coil whereas

this system excites the pickup coil using an externally applied field. We

have been able to produce coils with nearly identical geometries that are well

matched when not in contact with an aluminum plate but produce anomalous

results when placed near the plate (i.e., the coils may produce signals of

equal magnitude but as much as 180° out of phase). The degree of mismatch is

43
a function of magnetic field orientation, frequency and thickness of the

aluminum plate. Fig. 23 shows the magnitude of the difference of two coils when

excited in an externally applied, horizontally oriented field separated from

any metal (air), and the difference when the coils are placed on an aluminum

plate and excited with either a horizontal or a vertical magnetic field.

Consultations have failed to provide any answers to why the coils are mismatched when placed on a metal plate. Until this problem can be resolved

we are not able to make any significant progress on the flaw detection and

characterization system.

Further investigation of coil geometries will have several objectives.

Of primary importance will be improvement in lift-off discrimination and

reduction of coil resistance change due to temperature variations. Finally,

several new approaches to the absolute measurement of electrical conductivity

using eddy currents will have initial testing to determine if further investigations are warranted.

Calibration of conductivity standards and of tensile specimens have been

done throughout the year to support the Metallurgy Division in its project

on the properties of various aluminum alloys. Conductivity measurements

were also made for Dr. C. V. Dodd of Oak Ridge National Laboratories. An

absolute determination of electrical conductivity using eddy currents is

being done at Oak Ridge and NBS examined the test pieces for uniformity of

electrical properties over front and back surfaces and measured the difference

in resistivity between the samples.

During FY 82 several projects are planned. Two more metal bars will

be measured by dc methods. The resistivity of these bars will be greater

than that of the present primary standards. Intercomparison of the bars

using eddy current methods will serve as a check on transfer techniques and

should decrease the total uncertainty of the dc measurement.

Work will be started on the manufacture of SRMs in the range 60-100%

I ACS. This will be part of the continuing effort to have SRMs available

throughout the commonly used conductivity range.

44
R. L

Fig. 21

i—iB

45
A0\

0 NiH 01 vkJ aiAotid

m

46

tOQH-^.

\KHL

/a

KHZ

iCO

KHZ

FRBqu£.Ncy
11. Theoretical Modelling in Eddy Current NDE

Arnold H. Kahn

Ceramics, Glass and Solid State Science Division

Center for Materials Science

Calculations have been performed of the eddy current density in the

vicinity of a crack in a plane slab of conducting material. This work

extends previous research performed here, and outside NBS, in covering the cases of arbitrary depth and angle of inclination of the crack with respect

to the slab. The calculations were performed by conversion of the eddy

current partial differential equation to a boundary integral equation for

which numerical methods could be applied. The results are in good agreement

with microwave experiments performed at Stanford University, and provide

insight into the effects contributing to eddy current signals.

The results of a typical computation are shown in Fig. 24, which

is for a perpendicular crack. The circles indicate the real part of the

calculated surface impedance and the triangles indicate the imaginary part.

The distance X is measured along the slab, and the distance Y along the

crack. In this particular case, the depth of the crack is four skin depths.

Calculations like this have been performed for a variety of depths and

angles of inclination. The technique has given a wide range of results

at low cost.

The total impedance change due to a crack is found by integrating

the curves of Fig. 24. The dependence of this change on crack depth is

shown in Fig. 25 for a perpendicular crack and in Fig. 26 for a crack

inclined at 45° to the surface.

47
IMPEORNCE,

REAL

RNO

IMRG.

PARTS

PLRNE SURFACE CRACK

Fig. 24. Normalized surface impedance as a function of position in the vicinity

of a perpendicular crack. The real

part is marked by circles and the

imaginary part by triangles. The

crack depth for this case is four

times the skin depth. The

normalization is such that the curves approach unity far from the

crack on the surface.

Normalized Impedance Change

vs.

0.0 1.0 2.0 3.0

Crack Depth (d/5)

Fig. 25. Normalized total impedance change as

a function of crack depth for a perpendicular crack. (6= skin

depth)

48
Normalized Impedance Change

vs.

0.0 1.0 2.0 3.0 4.0 5.0

Crack Depth (d/5

)

Fig. 26. Normalized total impedance change

for a crack inclined at 45® as a function of crack depth.

(5=skin depth).

49
12. Leak Rate Reference Standards

Stanley Ruthberg

Electron Devices Division

Center for Electronics and Electrical Engineering

The first phase of our effort toward improved reference standards was for the standard leak range of 1 to 1 x 10”^ atm. cm^/s. The second

phase was to extend the measurements range from 1 x 10”^ to 1 x lO”'^ atm.

cm^/s. We have obtained a capability to 1 x 10"® atm. cm3/s on an absolute

basis. _ A concept under consideration for extending our measurement range to

1x10^ atm. cm®/s is to employ a mixed gas passing through a larger leak,

as measured by the rate-of-rise method, and the calibration of a mass spectrometer by the gas components. Under continuum flow, all gas components

would be transported at the same rate so that the flow rate of any constituent

would simply be that fraction of the total flow equal_to its relative concentration. For example, a 1% He/N 2 _mixture in a 1 x 10"® atm. cm®/s leak size

capillary should produce a 1 x 10"^ atm. cm®/s partial leak rate of helium.

However, standard leak rates are determined with one atm pressure upstream

and zero pressure downstream, where no flow is completely continuum. Instead

the nature of the transport mechanism changes along the length of the channel

from laminar viscous flow at the entrance to combined slip flow and then free

molecular flow as the exit is approached; thus, fractionation of the gas

components can be expected. The effect of this fractionation on the accuracy

of the expected partial flow rate is a prime issue for this method.

Theoretical guidelines for anticipated behavior are appropriate to reduce

the amount of experimental effort that would be required otherwise. Unfortunately, the theory of gas flow through capillary tubes has only been treated

satisfactorily in two distinct and separated pressure regions: the low

pressure region of free molecular flow where the mean-free-path is large com- pared to the tube diameter; and the moderate pressure region of continuum

flow where the mean-free-path is much less than the diameter but where the

pressure is low enough to avoid turbulence. No solution has been obtained

from first principles for the complete pressure range that is required for

leak size measurement. In addition, both slip coefficient and the transmission probability of free molecular flow are significantly affected by wall

condition, which factor has not been formulated theoretically. We have used

two semiempirical formulations for analyses. One by Fryer(l), which modifies

the viscous flow with slip formulation as based on a phenomenological argument,

is appropriate for long tubes, does not account for wall condition, and is

in differential form. It predicts the nature of the transport pressure dependence. The second, by Lund and Berman(2), is a superposition of diffuse

and drift flows with modifying constants derived from a nonlinear least-square

fitting to experimental data, is applicable to any length-to-radius value,

and incorporates adjustable parameters to account for deviation from

theoretical transmission probability and slip coefficient.

Detailed calculations have been made. The total flow rate, the fractional contribution to flow rate of the several flow mechanisms, the pressure

profile along the capillary channel, and the pressure dependence of these

50
single gas species. A systematic examination of practically obtained

capillary dimensions indicates a severe constraint on choice. Figure 27

represents typical results for a series of capillary tube diameters and

Table IV lists the net values. The Fryer equation was first integrated

to obtain the total flow rate for one atm N 2 upstream and zero pressure

downstream, and then the differential form was used in an iteration procedure to derive the profile alonq_the tube lenath. Expected standard

leak rate (leak size) is 3.35 x 10”^ Pa.m^/s (~3 x lO’^atm • cm^/s) of

which 84.7% is laminar flow, 14.5% is slip flow, and 0 . 8% is molecular

flow. Increasing the diameter increases the percentage of laminar flow,

but then longer lengths are necessary to reduce flow rate. For example,

a 16ym diameter by 1-cm length produces a 4.92 x 10"^ Pa-m^/s flow rate

with 92.1% laminar, 7.7% slip, and 0.2% molecular flows; however, we would

need a capillary length of ~10 cm to reduce the flow rate to the 1 x lO"^

Pa-mVs value desired, which length cannot be drawn with any feasibility

For 16 ym diameter, the laminar flow profile is extended closer to the

exit as are the slip and molecular flows. Selection of long precision bore

capillaries require reduced upstream conditions with no consequent improvement.

In order to assess the amount of fractionation with mixed gas flow, we have to resort to guesswork, for mixed gas flows under these conditions have

apparently not been approached theoretically. To do this, we substituted

values for mixed gas viscosities into the Lund and Berman formulation,

selected midband values for slip coefficients, and chose appropriate values

for collision parameters. The determination of mixed gas viscosities is

usually not obtained from first principles because of the detailed collision

analysis required, and suitable approximations or empirical formulas must

be used. Experimental observations show that the net viscosity can be

altered significantly by small concentrations of a second gas and not in

readily predictable fashion for asymmetric molecules. We calculated the

viscosities from a Chapman-Enskog(3) formulation and approximated collision

cross sections with equivalent hard sphere diameters. Significant changes

in flow are predicted. Only when the tracer gas is held to small concentrations are the changes reasonable. For example, a 1% He/N 2 mix would in- crease the flow rate in the 8-ym diameter capillary by ~5% but decreases

the slip contribution by ~1%. Although the change in total flow rate could

be measured by rate-of-ri se, the amount of fractionation is not apparent

from these formulations.

An alternate method which has been used to generate leak rates of less

than 1 X 10 ^ atm. cm^/s utilizes a porous column for which the pore diameter

is much less than the mean-free-path of the upstream pressure. However, it

may take repeated processing and periods of exposure of up to one year before the flow conductance stabilizes to ~1 percent. Replacement of the

porous plug with a fixed length of precision bore capillary and precise low

pressure generation upstream{4) to achieve pure molecular flow have been

analyzed similarly as above. Again, selection of capillary dimensions to

allow a measurable 10"^ Pa-m^/s (lO’^atm-cm^/s) leak rate at the upper

limit, while holding necessary pressures upstream, are constrained, but

prognosis is more positive than for mixed gas flow. A third method utilizes

a flow divider; this is susceptible to greater accuracy eventually but is more complex and requires extended apparatus.

51
References

1. G. M. Fryer, "A Theory of Gas Flow Through Capillary Tubes," Proc. Roy.

Soc. , A293 , 329-341 (1966).

2. L. M. Lund and A. S. Berman, "Flow and Self-Diffusion of Gases in

Capillaries, Part I and Part II". J.A.P. 2489-2495 and 2496-2508 (1966).

3. See E. H. Kennard, "Kinetic Theory of Gases", 1st ed., 4th impression

(McGraw-Hill, New York, 1938) p. 161.

4. S. Ruthberg, "Calibration to High Precision in the Medium Vacuum Range with

Stable Environments and Micromanometer" , J. Vac. Sci. Technical 401-412

(1969).

Table IV

Leak size and net fractional flow for small diameter capillaries,

1-cm length, nitrogen gas

diam leak rate laminar si ip molecular

(ym) (Pa*m3/s)* % % %

4 2.26 X 10"^ 71 27 2

8 3.35 X

10“6 84.7 14.5 0.8

16 4.92 X 10"3 92.1 7.74 0.24

*1 Pa-m 3/s = 9.872 atm-cm^/s

52
Figure 27. Pressure and flow profiles for nitrogen gas through a series of

capillary tubes of 4 ym, 8ym, and 16 ym diameter by 1 cm length. One atm

gas pressure is applied upstream and zero pressure is maintained downstream.

The fractions in percent of laminar, slip, and molecular flow are indicated

for any cross-sectional plane along the capillary length from the downstream

exit.

molecular flow; slip flow; laminar flow; pressure.

Fig. 27

53
13. Magnetic Measurements

L. J. Swartzendruber

Metallurgy Division

Center for Materials Science

Magnetic methods of nondestructive evaluation utilize the relationship

between material properties and static or slowly varying magnetic fields.

They find wide application both on the production line and in the field and,

where useable, provide a sensitive, rapid, and often relatively inexpensive

test method. Uses include measurement of important metallurgical properties,

detection of harmful defects, and measurement of coating thickness.

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 reproducible basis are in 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.

Previous investigations have led us to propose a detect! bi 1 ity criterion

for defects under magnetic particle inspection. Using this criterion, and a phenomenological description of the magnetic leakage field from cylindrical

defects, the detect! bi 1 ity of cylindrical defects as a function of defect

depth, defect size, and applied magnetic field can be predicted. In order

to apply this criterion, and to test its validity for more complicated

geometries, it is necessary to calculate leakage fields from more complicated

geometries. Computer modeling techniques to perform this function are being

developed.

Results have been obtained from a finite difference model using a square

grid and defects with a square cross section placed at various depths below

the sample surface. In the initial form of this model a linear isotropic

magnetic medium was assumed. After the model results were obtained they were least-squares fitted to the field expected from a magnetic dipole.

(The field from a cylindrical defect in a linear isotropic medium can be

calculated analytically and is a dipole field.) Figures 28 and 29 show the

fields perpendicular and parallel to the surface of the material, respectively.

It can be seen in these figures that the field from a square defect is almost

indistinguishable from a dipole field. Note that the field parallel to

the surface has a large bias field of 30 gauss. This added field is just the

applied field which was parallel to the surface. Using these results a quantitative comparison can be made with the field from a cylindrical defect.

The square defect gives a leakage field approximately ten percent higher than

that from an inscribed cylinder.

54
It is planned to continue these calculations for different geometries

such as rectangles and slots. In addition, the program is being modified

to cover the more realistic case on nonlinear media. For this case, a finite

element method will be employed in an attempt to reduce the expected larp

increase in computer time. The outcome of these calculations, along with

further experimental measurements, will be used to develop a critically

needed specification for the applied field necessary to detect defects of

a given size and geometry. The results will also be useful fora leakage

field measurement method which is a technique of growing use in the field

of nondestructive evaluation.

Fig. 28. Magnetic leakage field perpendicular to the sample surface

versus distance from the defect center (the field is antisymmetric about the origin; only the left half is shown). The

applied field is 30 gauss parallel to the sample surface and

the leakage field is assumed to be measured 0.3 cm above the

surface. The defect cross section is a square 0.2 cm below

the surface. The crosses are the calculated field and the

dashed line is a least squares fit to a dipole field.

55
F

IE

L

D

IN

G

U

s

s

Fig. 29. Magnetic leakage field parallel to the sample surface versus distance from the defect center (the field is symmetric about

the origin; only the left half is shown). The applied field

is 30 gauss parallel to the sample surface and the leakage

field is assumed to be measured 0.3 cm above the surface.

The defect cross section is a square 0.2 cm on a side with

the top 0.2 cm below the surface. The crosses are the calculated field and the dashed line is a least squares fit to

a dipole field.

56
14. Optical Measurement of Surface Roughness

E. Clayton Teague, Theodore Vorburger, Fredric Scire,.

Saul Baker, and Clare Trahan

Mechanical Production Metrology Division

Center for Manufacturing Engineering

There have been, over the last ten years, increasing efforts in the U.S.

and the rest of the world to use light scattering rather than the traditional

stylus instrument for nondestructive evaluation of the surface roughness of

manufactured parts. The roughness of these surfaces typically has irregularity

spacings of 10 to 1000 times that of visible light wavelengths, x, and irregularity heights of 0.25a to 10a. The theory of light scattering from

surfaces with such properties is not well understood. The quantitative measurement of surface roughness characteristics from light scattering measurements

in this regime is, therefore, not feasible with available information. To

meet this need for improved information about light scattering from manu- factured surfaces and to facilitate the anticipated transition from stylus

to light-scattering measurements we have begun both theoretical and experimental investigations of light-scattering techniques.

Toward the objective of establishing a solid basis for developing

recommended methods for optical measurement of surface roughness we have:

(1) Completed and published (1) the results of an extensive literature search

and analysis of the papers on experimental optical techniques for

measuring surface roughness. This paper (1) reviews state-of-the-art optical

techniques including specular reflectance, total integrated scatter, diffuseness, angular scattering distributions, speckle, el 1 ipsometry, and

interferometry. (2) Completed an evaluation and distillation of available

theoretical models that can be used to describe light scattering from rough

surfaces. Results of this work (2) appear in the September 1981 issue of

Annals of CIRP. (3) Designed a system for performing angular distribution

measurements of light scattered from a test surface. All major engineering

drawings and, with the exception of a fiber optic-detector array, all major

components of the system have been procured and are now being integrated

into a total system; completion and first operation of the system is planned

for December 1981. It is described more fully below. And (4) designed and

constructed a high-precision x-y stage for use in obtaining 3-D stylus

profilometry images for the microtopography of a specimen surface. Finally,

a general survey of optical nondestructive evaluation techniques was written

and will be published next year (3).

A schematic of the system being constructed for performing angular

distribution measurements is shown in Fig. 30. The system has been designed

to serve as a versatile research instrument which permits measurements of

the intensity of scattered light as a function of azimuth and elevation over

the full hemisphere above the test surface. In addition, the system was designed to serve as a prototype on-line measuring device which allows a rapid snapshot of the angular distribution of light scattered in the plane

of incidence. As shown in Fig. 30, the system consists of an array of 90

detectors interfaced through a 100-channel scanner/digital voltmeter to a Hewlett-Packard 9845T desktop computer. To facilitate the comparison of

light scattering and stylus measurements of surface roughness, the HP9845T

computer is interfaced with an RS-232 communication link to the computer, an

57
Interdata 7/32, which is being used to acquire, display and analyze the

3-D stylus profilometry measurements.

The goal of the combined stylus/light scattering measurements is to

measure a designated area of a test surface with light scattering, compute

from these measurements statistical characterizations of the surface

roughness, such as the 2-D power spectrum, relocate the identical area for

3-D stylus profilometry and compute the same statistical characterizations

from the stylus measurements. Comparison of characterizations from the

two methods should then enable us to build a solid empirical base for

developing better theoretical models for light scattering from manufactured

surfaces.

The optical and mechanical aspects of the detector array for lightscattering measurements are shown more completely in Fig. 31. Fiber

optics are placed on the yoke at angular intervals of two degrees with

each aperture subtending an angle of 1.2 degrees. For measurements in

the plane of incidence, defined by vectors along the incident light path

and the surface normal, the angles of incidence will also be confined to

multiples of two degrees because light must travel to the specimen along

paths between the fiber-optic connectors. When the yoke of the fiber

optics is rotated to permit measurements out of the plane of incidence, higher

resolution measurements can be performed if necessary. If measurements in

the plane of incidence at resolutions greater than two degrees are required

for specific tests, the laser light source can be manually repositioned to

permit measurements at intervals of less than 0.1 degree. The collected

light as a function of angle is then transmitted by the fiber-optic cables

to an array of photodiodes and amplifiers which, in turn, provide voltages

that are input to the 100-channel scanner. By allowing the placement of the

detectors in a compact isolated electrical unit, the fiber-optic approach

minimizes any potential problems with electrical noise which could be very

troublesome at the low levels expected for these measurements.

The x-y stage for obtaining 3-D stylus profilometry maps of surface microtopography moves the specimen in a rastered motion beneath a fixed stylus

location. As the specimen is moved beneath the stylus, the stylus' vertical

motion is used to produce an electrical signal. This signal is converted to a digital value at a 512 x 512 array of x-y positions. From this array of digital

values an image of the topography is generated in which the intensity at each

point is proportional to the surface height of the specimen at the corresponding

point. Three-D stylus profilometry images have proven to be very useful in

revealing features of the topography not easily detected with other methods,

including electron microscopy. The quantitative representation of topography

in these images is unique. Our present efforts in this area are to generalize

the algorithms we have developed for characterizing 2-D stylus profiles to enable

the computation of new characterizations applicable to 3-D topography. We are also carefully measuring the geometric errors present in the motion of the x-y

stage, i.e., pitch, roll yaw, and vibration.

58
References

1. T. V. Vorburger and E. C. Teague, "Optical Techniques for On-line

Measurement (5f Surface Topography," Precision Engineering 1981,

3, 61-83.

2. E. C. Teague, T. V. Vorburger, and D. Maystre, "Light Scattering

from Manufactured Surfaces," Annals of CIRP, Septanber 1981.

3. E. C. Teague, T. V. Vorburger, and G. Birnbaum, "Optical Nondestructive

Evaluation," to be published in Encyclopedia of Materials Science and

Engineering in 1982.

59
DETECTOR

ARRAY

ROTATION OP DETECTOR ARRAY

ROUGH

SURFACE

Fig. 30 Angular scattering system for measuring surface roughness

60
Rotating

Mirror

Varies

Angle

of

Incidence

61

Fig.

31.

Detector

array

for

laser

light

angular

scattering
15. Optical Scattering for Nondestructive Evaluation

A. Feldman and G. S. White

Ceramics, Glass and Solid State Science Division

Center for Materials Science

Using the apparatus developed last year for measuring the scatter as

a function of angle for 10.6 ym wavelength radiation incident upon surface

grooves, data were taken of scattering from shallow rectangular and deeper

V- and trapezoidal grooves.

The scalar model developed for the scattering from shallow (depth 'vO.OSa)

grooves accurately described the observed scattering and quantitatively

incorporated certain possible misalignments of the system.

Three deep V-shaped and three deep trapezoidal shaped grooves also were studied (Fig. 32) and scattering data were collected with the incident

electric field both parallel and perpendicular to the groove length. The

groove itself was normal to the scattering plane swept by the detector.

Differences in the scattering with polarization were observed. However, the

scattered fields maintained the same polarization as the incident field

with no measurable cross-over.

Scalar calculations used to fit scattering from the shallow grooves were completely inadequate for describing the scattering from these deeper grooves.

Daniel Maystre, a visiting French scientist from the CNRS, developed a vector

theory which could be used to calculate the scattering from any cylindrical cross section due to an incident electric field with E polarized parallel to

the cylinder axis.

With the help of Jay Marchiando and Ted Vorburger, in the Mechanical

Production Metrology Division, the cross sections of the grooves were measured

with a diamond profilometer and preliminary calculations were made for the

expected scatter.

Figure 33 is a composite of scattering data measured as a function of angle

for several locations along the narrow V-groove (crosses) and the calculated

scatter intensity (solid line). The calculations were made by measuring

the groove cross section at one position with a profilometer and calculating

the scatter from that profile. The agreement between the observed and the

calculated scatter intensities is excellent. Experimentally observed asymetries

are reproduced in the calculations at the correct angular positions and with

proper magnitudes.

The variability in the experimental data reflects the lack of uniformity of

the groove. This lack of uniformity also causes the asymmetries observed

in both the measured and the calculated scattering. The brass, during the

scribing process, flows into mounds on either side of the grooves. These

mounds are, in general, not symmetric and also change in height, width, and

shape along the length of the grooves. Another feature contributing to the

lack of symmetry in the observed scatter is that the grooves themselves are

not symmetric but have one side steeper than the other. All of these effects

are accounted for in the calculations.

62
Similar calculations have been made for the medium-sized V-groove and the

narrow and medium-width trapezoids with a 20-ym bottom. In these cases,

ideally shaped grooves were incorporated into the calculations because the

depths of these grooves were greater than the range of the profilometer.

Nevertheless, the calculated scattering presented the same qualitative

features, including number and approximate sizes and peaks, as those which

were observed experimentally. Quantitative features, such as angular

positions of the maxima and minima and observed asymmetries, are not yet

in agreement with experiment. However, it has been found that these features

vary significantly with relatively minor ('\^0.1 a) changes in groove shape.

Currently, work is progressing in fitting these data more quantitatively.

In the same vein, scattering from known positions on the narrow V-groove

samples is being compared with that predicted from profilometer measurements

at the same positions. Some work is also being done on the inverse problem,

using calculated phases and experimentally determined amplitudes in an attempt to reconstruct, mathematically, surface defects.

63
34 pm

90.7 pm

122pm

8.4pm

17 pm

43 pm

NARROW TRAPEZOID

a b c

S4 pm 21 pm 20pm

79 pm 27pm 21 pm

152 pm 77 pm 21pm

WIDE TRAPEZOID

a b c

89 pm 15|im 51pm

128 pm 57 [im 51pm

1 48 pm 69pm 51pm

-I c

1^

Fig. 32. and nominal dimensions of ideal deep V-grooves

64
(SlINO aUV) A1ISN31NI

65

SCATTERING

ANGLE

(DEGREES)

Fig.

33

Composite

of

experimental

and

theoretical

scattering

from

narrow

V-groove.

Solid

curve

was

calculated

from

one

profilometer

cross

section

measurement

of

the

groove.

The

points

are

experimental

data

obtained

from

three

different

positions

on

the

groove.
16. Signatures for Holograph NDE*

C. M. Vest

Dept, of Mechanical Engineering & Applied Mechanics

The University of Michigan

The primary objective of this research program is to experimentally

produce a series of "flaw signatures" of test objects with programmed flaws

by holographic interferometry and to compare them with predictions made by

the use of finite element analysis. The object under study has been an aluminum disk, outer radius R = 3.25 in. and thickness t = 0.25 in. The "flaws" are flat bottom holes of various radii, r, and depths, d, drilled from behind

at the center of the disk. This radial ly-synmetric configuration was chosen because the costs of computing deformation are greatly reduced by

the symmetry. In addition, the radially symmetric "flaw" is the "worst

case" experimentally because the flaw is placed at the region of the

lowest deformation gradient and because the flaw is concentric with the

basic fringe pattern.

A test rig was assembled in which dry nitrogen gas can be used to

pressurize the aluminum disks uniformly over their back surfaces. Each

disk can be bolted by eight bolts, equally spaced on a 3-in. radius, and

sealed by an 0 ring against the housing. Four disks were fabricated;

two had flaw diameters of 1-in; one had a depth of 1/8 in. and one had a depth of 3/16 in. Two other disks had flaw diameters of 0.5 in.; one had

a depth of 1/8 in. and one had a depth of 3/16 in. A steel ring was machined

for use as a clamping surface around the periphery of the test plates. Using

this clamping ring and a torque wrench to ensure uniform loading by the

eight bolts, we obtained interferograms of the test plates.

In order to compare experimental and finite element results some normalization is required because the finite element solutions assumed a 2.5 in. radius, corresponding to the centers of the bolts, while a 2.56 in.

radius, corresponding to the inner edge of the clamping ring, is more appropriate for the experimental results. It should be noted that the maximum

deflection of a plate with clamped edges is proportional to the fourth power

of the radius, so the results are strongly influenced by this choice.

i) Finite Element Results: Figure 34 is a plot of ^/^qcc versus R/R^

where w^^r is the maximum deformation of a plate with no flaw as predicted

by the finite element analysis, and R is the radius of the clamped edge. The

dimensions and material properties used to generate these results are:

E = 10^ psi, M = 0.333, t = 0.25 in., R^ = 2.5 in, P = 58.61 psi

ii) Experimental Results: Figure 35 is a plot of w/Wgy versus R/R^ for

four test disks. The measured normal displacement, w, is normalized with

respect to Wgy, the displacement of the center of the disk predicted by

plate theory. The displacement, w, is deduced from holograms.

The outer radius of the plate, R , was taken to be the inner radius

of the steel clamping ring. When Figures 34 and 35 are compared, significant differences are noted between the finite element predictions and

*Work performed under contract to the NBS Office of Nondestructive Evaluation.

66
the experimental results, particularly for the disk with the largest flaw.

Although the accuracy of the finite element solutions may be questioned to some extent, the most likely cause of the discrepancy is incomplete* realization of the "clamped" boundary conditions and subsequent improper normalization of the displacement. (Recall that w is proportional to Rq^.) This

interpretation is supported by Fig. 36 in which w/w^,-„n> where w°is the

measured displacement and wOEXP

Fig. ... ........ is the measured maximum displacement for the

test plate with the largest flaw, is compared with the corresponding values

determined by finite element analysis. These curves are in quite close

agreement. The results for flaw free plates are also shown in this figure.

This work was undertaken to determine if holographic NDE results can be

quantitative. The quantitative agreement between theory and experiment

which was obtained is encouraging, although the sensitivity of the results

to the exact loading configuration emerged. Future work will be concerned with

other flaw geometries and locations.

67
Fig. 34. Effect of flaws on normal deformation w (finite element computation).

68
Fig. 35. Effect of flaws on normal deformation w (holographic interferometry).

69
1.0

Fig. 36. Effect of flaws on normal deformation w (comparison of holographic interferometry and finite element results)

70
17. Fluid Dynamics of Liquid Penetrant Flows

J. M. McMichael

Fluid Engineering Division

Center for Chemical Engineering

Liquid penetrants are often used to detect small surface cracks in

various solid materials. A preliminary study* showed that once the penetrant

reaches a depth (z) which is large compared to a characteristic measure

of the crack width (R), penetration time (t) is governed by the RidealWashburn relation

t

~ a R COS 0 ,

where a is surface tension, y is viscosity, and e is the contact (wetting)

angle.

However, this result implies an infinite initial penetration velocity,

which is obviously incorrect. This singular behavior results from neglect

of fluid inertial effects during the initial flow development for small

times, and it may lead to significant underestimation of penetration time.

In addition, convective accelerations in the entry region of the crack will,

in principle, decrease the effective pressure gradient which drives the

flow, resulting in further underestimation of penetration time.

Initial studies were also limited to idealized geometries with uniform

crack dimensions. However, variations in crack width along the direction

of flow may also affect estimates of penetration time.

Current work is directed toward evaluating these two fluid dynamical

aspects of liquid penetrant flows. The problem is posed as an initial

value problem for time-dependent two-dimensional flow, and considers the

effect of the reservoir of penetrant initially applied to the surface of

the material. Asymptotic techniques are being applied to examine both

the initial flow development, and the effects of variable crack width.

A complete solution of the general problem requires numerical simulation

of the flow field with special attention to the interface boundary conditions

which involve a moving contact line with dynamic contact angles. Estimates

based on the asymptotic analyses underway should indicate the extent to which

such detailed numerical analysis is warranted.

An additional question currently being studied is whether the flow remains

two dimensional, or whether the advancing interface is susceptible to an instability resulting in the escape of trapped gases along some portion of

the crack length.

S. Deutsch, "A Preliminary Study of the Fluid Mechanics of Liquid

Penetrant Testing," Journal of Research, Vol . 84, No. 4, July-August

1979.

71
18. Use of Uranium-Doped Glasses for the Calibration of Apparatus Employed

in the Evaluation of Fluorescent Dye Penetrants

R. W. Burke and D. K. Hancock

Inorganic Analytical Research Division

Center for Analytical Chemistry

Fluorescent dye penetrant testing is used extensively for the nondestructive

detection of flaws in a wide variety of test objects. As currently practiced,

the procedures lack both reproducibility and reliability. Undoubtedly, at the

present state-of-the-art, many components with damaging flaws are now passed

while others are wrongfully rejected.

In order to provide a more valid basis for using fluorescent dye penetrant testing as a reliable screening device, work has been undertaken to

evaluate the use of uranium-doped glasses as comparative fluorescent standards.

Two forms of standards are currently in different stages of preparation and

evaluation. The first type consists of a single, rectangular piece of

Corning 3750 glass mounted in a metal heat sink. An engineering drawing of

this assembly is shown in Fig. 37. The main body of the metal block is

2024 aluminum that has been anodized flat black and the bottom plate is brass.

The slot milled in one half of the aluminum holder has been precision machined

to provide a close fit with the glass. Final positioning of the fluorescent

glass exactly flush with the top of the holder is accomplished under a microscope. It is subsequently held in place by filling the 1 mm void between the

bottom of the glass and the brass plate with a black adhesive. Ten of these

units have been built thus far and are now undergoing extensive homogeneity

and accelerated stability testing. Initial measurements obtained by

mapping the surface of these glasses in grid-fashion with a microspectrofluorimeter having a circular measuring aperture of 25 ym indicate

that the fluorescence does not vary more than two percent.

In addition to the ten heat sink units, two other units modified for

water thermostating have also been fabricated. These will be used to measure

accurately the temperature coefficient of the uranyl fluorescence in this

particular batch of glass. As soon as the above studies are successfully

completed, these assemblies will be sent out to the manufacturers and users of fluorescent dye penetrants for further evaluation and comment.

A second type of standard in the early stages of design and production

employs glass fibers having varying uranium concentrations and diameters in

order to obtain a graded series of fluorescent intensities and widths of

indication. Fibers having nominal uranium concentrations of 0.6 to 2.5

weight percent and diameters of 5 to 50 ym have been obtained.

Present plans call for making two variations of these fiber standards.

One will have a fixed uranium concentration and varying diameters that

approximate the widths of the indications commonly obtained in crack evaluation;

the other will consist of a series of fibers having a constant diameter and

a varying uranium concentration. Each type will be sandwiched between two

nonfluorescent quartz plates with a transparent cement whose refractive index

closely approximates the refractive index of the fiber. The diameter and

relative fluorescent intensity of each fiber in a series will be specified.

The final production, characterization, and testing of these fiber standards

will form the main thrust of our effort in FY 82.

72
50mm ^

2024 AL

Figure 37. Fluorescent uranium glass and heat sink assembly.

73
19. Mechanical Properties Characterization for Quality Control and

NDE of Polymers

Donald L. Hunston and James L. Rushford

Polymer Science and Standards Division

Center for Materials Science

Satisfactory performance of a polymeric material in a practical application

is often directly related to the proper matching of the mechanical properties

of the polymer to those required for the application over the range of temperatures

and time scales involved. As a result, the measurement of mechanical properties

can provide not only useful design data but also valuable quality control (QC)

and NDE information. The following paragraphs describe two of our efforts to

utilize this approach for QC and NDE; The first is an ongoing program performed

in cooperation with the Naval Research Laboratory and the second is a new effort

that is now being developed.

To obtain maximum benefit from mechanical property measurement, it is

important that the behavior be characterized over the widest possible ranges

of temperatures and time scales (or frequencies). In this regard a device (1) was constructed which combines dynamic mechanical testing and stress relaxation

experiments in a single instrument to provide data over an 8-decade time-scale

range at temperatures from -200°C to 400°C. This instrument, which measures

torsional shear behavior, includes on-line computerized data acquisition and

analysis. It is extremely versatile and has already been used to examine

f iber-reinforced composites, structural adhesives (2,3) high-temperature

plastics, elastomers, propellants, plastisols, and printing inks. To illustrate the use of this device three particular examples will be briefly discussed.

The problem of quality control for elastomeric materials is a difficult

one because many ingredients are used and a number of processing steps are involved. As part of the manufacturing procedure, it is customary to make

a number of small samples (ASTM plates) from each batch to serve as material

for QC test. Our test device has been adapted so that a small portion of an ASTM plate can be utilized to provide a detailed characterization of the

shear properties. For example. Fig. 38 shows a plot of the loss tangent

(the ratio of the loss modulus to the storage modulus) as a function of

temperature and frequency for a nitrile rubber. For this frequency range,

the data were obtained at lower frequencies using an ASTM plate and the

superposition technique was then verified and utilized to shift the results

to the desired range. With this information an improperly prepared batch can be detected easily and, since the mechanical properties are related to

molecular structure and morphology, it is possible in a number of cases to

determine what mistakes were made in the formulation.

The nondestructive nature of this measurement technique is particularly

helpful when the device is used to follow changes that occur in a material

during cure. Two examples of this type have been studied during the past year.

The Navy is interested in the properties of certain polyvinyl chloride plastisols

for their studies of the interactions between turbulent flow and complaint

surfaces. It was found, however, that the properties of this material change

as a function of time. Our studies were able to provide a characterization of

these properties and their time dependence (Fig. 39). A second example of this

type involves inks used by the Bureau of Engraving and Printing for printing

74
Fig. 38 The loss tangent for a nitrile

rubber is plotted against

temperature and frequency.

Log(w) (rad / sec)

Fig. 39 The dynamic shear modulus for a polyvinyl chloride plastisol is

plotted against frequency at^

various times after preparation:

ranging from one hour to 85 days.

75
currency. These inks cure during the printing process and good performance

can only be obtained when the flow properties change in the required ways at

the proper rates during cure. Studies are currently underway to characterize

the properties of the inks as a function of cure so that better quality control can be maintained.

In addition to the ongoing studies mentioned above, preparations are being made for work in another area. There are many applications such as adhesives, paints, and coatings that involve thin films. Although thin films are very difficult to study, ultrasonics often represents a useful tool

because the attenuation for shear waves can be large enough that the film

can be treated as if it were infinitely thick. The device (4) now being set up

utilizes a thin strip of aluminum or quartz in which a shear wave can be

propagated. When the strip is coated with a film, the wave in the strip

generates a shear wave in the coating. Although the wave in the coating

cannot be measured directly, it can be characterized by observing how the

wave in the strip is altered when the coating is applied. Moreover, if the

measurements are made as a function of time, a detailed picture can be obtained

for the application, wetting, spreading, consolidation, and hardening of the

film. Such information is ideal for optimizing the formulation of polymers

for film applications.

References

1. D. L. Hunston, W. D. Bascom, E. E. Wells, J. D. Fahey, and J. L. Bitner,

"Viscoelastic Characterization of Structural Adhesives via Forced

Oscillation Experiments," in Adhesion and Adsorption of Polymers,

Polymer Science and Technology Series, L. H. Lee, Ed., p. A 321

(Plenum Press, New York, 1980).

2. D. L. Hunston, W. Carter, and J. L. Rushford, "Linear Visco -- Elastic

Properties of Solid Polymers as Modeled by a Simple Epoxy," in

Developments in Adhesives - 2, A. J. Kinloch, Ed., pp. 125-172.

(Applied Science Publishers, Ltd., London, 1981).

3. 0, L. Bitner, J. L. Rushford, W. S. Rose, D. L. Hunston, and C. K. Riew,

"Viscoelastic Fracture of Structural Adhesives," J. of Adhesion, in

press.

4. D. L. Hunston, "Determination of the High Frequency Viscoelastic

Properties of Polymers Using Shear Mode Strip Delay Lines," J. Polym.

Sci., Pt. C, 35, 201 (1971).

76
20. Polymer Transducers

S. Edelman and S. C. Rpth

Polymer Science and Standards Division

Center for Materials Science

A method for nondestructive evaluation of the dynamic elastic properties

of some kinds of structural elements was worked out during previous years and

a paper on the subject was presented at the spring 1980 meeting of the Acoustical Society of America. t The measurement technique made use of the favorable properties of piezoelectric polymer strain gages to measure both axial

and shear motion on the same specimen.

During this reporting period, a set of the specialized piezoelectric

strain gages required by the method was fabricated. The gages were mounted

on a thin-walled PVC cylinder which simulated a structural element under load.

Several measurements were made at different frequencies. The real and

the imaginary parts of the dynamic Young's modulus were calculated. Reasonable agreement with published values of the real part was found. The results

of two sets of measurements at slightly different frequencies are given in

the table below. Each set consists of three nominally identical measurements.

Frequency a e El E 2 (m-1) (m-M (Pa) (Pa)

6915 3.19 27.33 3.37x109 7.97x10®

3.19 27.32 3.37x109 7.99x10®

3.19 27.33 3.37x109 7.99x10®

6836 2.82 27.36 3.32x109 6.91x10®

2.82 27.38 3.31x109 6.92x10®

2.83 27.38 3.29x109 7.45x10®

a and 3 are the attenuation and phase constants. which make up the propagation

constant Y =_a + 3 where Y is related to the wave amplitude £ by the

relation ^ = e'^ . El and E 2 are the real and imaginary parts of the Young

modulus, E

=^ Ei°+ i EzMeasurements are presently being made on a section of pipe while the

pipe is subjected to a changing tensile stress.

Measurement of Dynamic Elastic Moduli;

S. Edelman and N. Newman

77
21. Doppler-Broadened Positron Annihilation Lineshape for Detection of

Defects in Materials

R. C. Reno* and L. J. Swartzendruber

Metallurgy Division

Center for Materials Science

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. 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. This sensitivity is

used to observe changes in defect concentration and type. We have been

using this technique to study two phenomena: precipitation hardening in

aluminum alloys and crystallization of amorphous Pd-Cu-Si.

A commercial aluminum alloy (2219) was subjected to two different

thermomechanical heat treatments prior to age hardening. Positron S-parameters

were then measured as a function of aging time for each treatment (See Fig. 40).

Results indicate that positrons can distinguish between defects surrounding

the e" and e' precipitates formed in the two sets of samples.

Figure 41 shows S-parameter data for a Pd-Cu-Si alloy heat treated

at various temperatures in the amorphous and crystalline region. At the

onset of crystallization, the S-parameter first rises slightly and then

gradually decreases. Such behavior can be explained in terms of the generation of defects at grain boundaries during crystal 1 ization.

*University of Maryland, Baltimore.

78
5%

STRETCH

o

o

r- os

o

o

in

h- r- d313l^VdVd S

I

'S•H

fH

fOw

CO

irX

UJ2

I-CDZ

§

'gaw

o

6^ •H

fa

79
d313lNVdVd S

Fig.

41.

Positron

S-parameter

for

Pdyy

Cu0

Si

17

alloy

heat

treated"

at

various

teirperatures

.

Crystallization

begins

at

about

380®C.
22. Scattering of Acoustic Waves

R. D. Mountain

Thermophysics Division

Center for Chemical Physics

A theoretical study of the scattering of acoustic waves by inhomogeneities

in solids has lead to a new way of using scattering data to determine

the size and shape of the inhomogeneities. The essential features of

the method are embodied in this expression for the scattered power:

^ f

= E V [l -b-k^.. . .]

Here k is the wavevector of the acoustic radiation, E is a constant involving

material and geometrical factors, Cq is the volume of the scatterer and

b is an effective size parameter of the scatterer which depends on the

orientation of the scatterer relative to the scattering angle. Physically,

b is a special type of second moment of the scatterer. It is determined by

varying the frequency while holding the scattering angle fixed and then fitting

the results to this equation. Model calculations indicate that this expression

for dP/df2 is accurate as long as bk < 1. The shape of the scatterer can be

inferred by determining b for a variety of orientations of the sample being

studied. This procedure provides a "second-moment" solution of the inverse

scattering problem.

81
23. Ultrasonic Imaging/Instrumentation

Melvin Linzer and Stephen J. Norton

Signal Processing and Imaging Group

Center for Materials Science

A major breakthrough in ultrasonic imaging was achieved in 1981. The

first exact three-dimensional inverse-scattering solution incorporating

broadband illumination and based on variations in both compressibility and

density was reported by Norton and Linzer (1). The problem was formulated

and solved for three aperture geometries: plane, spherical, and cylindrical.

The solutions were obtained under the assumptions of the Born approximation

(i.e., weak scattering) and that only backscattering is measured.

An analysis and computer simulation of a new imaging system for acoustical

holography, based on an annular aperture, was also completed (2). Additional

work on image reconstruction was carried out in collaboration with T. Sato

at the Tokyo Institute of Technology. This included tomographic reconstructions

from limited projections using iterative revisions in image and transform

spaces (3,4) and a data selection approach for imaging through turbulent

media (5).

A theoretical development of perturbation techniques for correcting ultrasonic velocity images has also been carried out. This approach, which does

not require ray tracing, is based on a Taylor expansion of the line-integral over the refracted path about the straight line connecting transmitter and

receiver. The second term in this expansion is a correction representing

the difference in the time delay over the refracted path and the straight

path. This correction can then be used to modify the original line-integral

measurements, which in turn can be used to reconstruct an improved image

corrected for refraction errors. This approach gains little from iteration

and, because of its perturbation nature, may be assumed valid for velocity

fluctuations within about ±5 percent of the mean value, the range of velocity

variation in most materials. In fact, computer simulations suggest that

good results are possible for even larger variations.

Finally, an analysis of techniques for measuring ultrasonic parameters

of materials was made (6), and a manuscript on a sonic technique for detecting

interrupted cutting during automated machining was completed (7).

References

1. S. J. Norton and M. Linzer, "Ultrasonic Reflectivity Imaging in Three

Dimensions: Exact Solutions for Plane, Cylindrical, and Spherical

Apertures," ( Invited Paper), IEEE Trans. Biomed. Engineering BME-28 , 202-220 (1981).

2. S. J. Norton, "Acoustical Holography with an Annular Aperture, J.

Acoust. Soc. Amer. (submitted).

3. T. Sato, S. Norton, M. Linzer, 0. Ideda, and M. Hirama, "Tomographic

Image Reconstruction from Limited Projections Using Iterative

Revisions in Image and Transform Spaces," Appl . Optics 395-399 (1981 ).

82
4. T. Sato, K. Sasaki, Y. Nakamura, M. Linzer, and S. Norton,

"Tomographic Image Reconstruction from Limited Projections Using a Coherent Optical Feedback System," Appl. Optics (to be published).

5. T. Sato, M. Linzer, 0. Ikeda, and M. Hirama, "Array Imaging System

with Data Selection Processing," J. Acoust. Soc. Amer. 7^, September

1981.

6. M. Linzer and S. Norton, "Ultrasonic Tissue Characterization",

Ann. Rev. Biophysics and Bioengineering (submitted).

7. F. P. Higgins and M. Linzer, "A Sonic Technique for Detecting

Interrupted Cutting During Automated Machining," J. Eng. Ind.

(submitted)

.

83
24. Ultrasonic Reference Block Standards and Measurements

6. V. Blessing

Mechanical Production Metrology Division

Center for Manufacturing Engineering

Work has continued toward assessing the present limitations and potential

improvements of ultrasonic reference block calibration procedures. A

set of rogue aluminum blocks, previously observed to yield anomalously high

(600%) echo amplitude readings, has received further study, including dissection

and metallurgical examination. It has been determined that the high readings

were caused by radially inhomogeneous aluminum media, rather than improperly

drilled flat bottom holes. This was determined by visual inspection of a dissected hole, and amplitude scans of the block without the hole. Further

metallurgical studies are planned to determine the exact cause of the material

inhomogeneity.

84
25. Laboratory Evaluation of Ultrasonics for Crack Detection in Concrete

L. I. Knab and J. R. Clifton

Structures and Materials Division

Center for Building Technology

A laboratory study was performed to quantify the crack detection

capabilities of ultrasonic, through transmission, methods in concrete.

Pulse velocity and amplitude measurements were taken perpendicular to the

crack plane (in cracked concrete) and parallel to the crack plane (in

uncracked concrete). The path length was 152 mm. Parallel crack surfaces,

nominally 0.05 mm apart and having depths of 19, 38, and 57 nrn and lengths

of 152 mm, were fabricated in the specimens. Transducer frequencies of

150 and 54 kHz were used and specimens were tested at several ages.

Concrete with a 28 day compressive strength of about 36 MPa was used.

A "sensitivity" ratio was used to determine if the cracks could be

distinguished. The numerator of the "sensitivity" ratio was the difference

in velocity of amplitude values between the cracked and uncracked concrete

while the denominator represented the inherent batch- to-batch variability

of the velocity or amplitude values in uncracked concrete. With the 57

and 38 mm crack depths, almost all the "sensitivity" values for velocity

and amplitude were at least 1.0, indicating that these crack depths could

be distinguished under the test conditions. The velocity and amplitude

"sensitivity" values with the 19 mm crack depth were about 0.4 to 0.5,

indicating that the 19 mm crack depth could not be clearly distinguished.

85
26- Reference Samples for Ultrasonic Residual Stress Measurement

N. Hsu, T. Proctor, and G. Blessing

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The advantages of using an ultrasonic technique to measure applied or

residual stresses in solids are quite appealing. It is nondestructive, it can measure the average bulk stress as well as stresses in the surface layer,

and it can resolve biaxial stress states. Furthermore, techniques and

instruments are now reasonably well developed and readily available. However,

actual field applications of these techniques are still extremely limited.

The difficulties with ultrasonic residual stress measurements have

been: inability to determine the initial or zero-stress state, and the

presence of texture or texture gradients in most structural metals. In

field applications using ultrasonic measurements to determine residual

stress, the user usually has a material with both unknown distribution of

stress and inhomogenous distributions of crystal grain orientations. With

only ultrasonic measurements on the unknown stressed state, the user has

to rely on assumed values for reference ultrasonic parameters in order to

estimate the residual stress. This procedure causes a large uncertainty

which, in turn, leads to questions of the credibility of the ultrasonic

technique.

We have initiated the design of a reference sample for ultrasonic

residual stress measurement. Our goal is to manufacture a test sample which

can be easily reproduced from any structural material of interest and

which has a known distribution of stress as well as a zero-stress state.

The reference sample is first to be used to establish the reproducibility,

the sensitivity, and the resolution of the velocity measurements and then

to establish their correlation with other pertinent parameters.

The construction of the sample, a disk, consists of a cylinder

shrink-fitted inside a ring and machined flat after fitting. According

to the design, the disk has regions in which a zero-stress state or known stress state can be deduced. The sample can be used for both

longitudinal and shear wave verification and calibration. Initial experimental results are encouraging. Further improvements and detailed

measurements are still in progress.

86
27. Nondestructive Evaluation of Nonuniformities in 2024 and 2219 Aluminum Alloy

Plate - Relationship to Processing/NASA

L. K. Ives, L. J. Swartzendruber, W. J. Boettinger, M. Rosen, S. D. Ridder,

F. S. Biancaniello, R. C. Reno, S. Pick, D. B. Ballard and R. Mehrabian

Metallurgy Division

Center for Materials Science

This task was initiated at the National Bureau of Standards at the request

of the National Aeronautics and Space Administration shortly after the announcement

in August 1979 by the Reynolds Metal Company that about 31 million pounds of

aluminum were suspected of containing "soft" spots due to a possible malfunction

in the water cooling system at one manufacturing plant. Some of these "soft"

spots were reported to be as much as 45 percent below the strength specifications

used for the purchase of the aluminum by aircraft manufacturers and suppliers.

The initial concern of this task was the 2219-T87 aluminum alloy used

extensively on the space shuttle. The results of our investigations on this

alloy were used by the sponsoring agency to ensure that the testing necessary

to prove structural integrity had been accomplished prior to launch. The results

also had the fortunate effect of expediting the space shuttle launch by

eliminating a large amount of unnecessary testing.

The major portion of the work on 2219 has been concluded (1) and attention

is now being focused on 2024, an alloy which is more widely used in the

construction of commercial aircraft. Because our results established that

better nondestructive evaluation techniques are needed for quickly judging the

strength of an aluminum plate throughout its thickness rather than simply on the surface as given by hardness and electrical conductivity, on-going

investigations of the feasibility of using an ultrasonic technique as an alternative are being carried out on both the 2219 and 2024 alloys.

As with the studies on 2219, the goal of this task is to develop specific

relationships between processing variables used during ingot casting, mechanical

working, and heat treatment of the 2024 aluminum alloy, and the resulting microstructures, mechanical 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. Work in this program is divided into five areas:

1) Studies on as-received plate of 2024 aluminum alloy. This is

motivated by the realization that the properties vary through the

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.

87
3) Determination of time-temperature transformation diagrams (C-curves)

and the relationship between mechanical properties and conductivity. Samples

produced during various thermomechanical treatments have a wide range of mechanical

properties (hardness, yield strength, tensile strength) and conductivity.

4) Electron microscopy studies done on the wide range of metallurgical

microstructures produced. Extremely fine ('^^0.01 ym) particles are responsible for

the strength of structural aluminum alloys and contribute to associated changes

in electrical conductivity.

5) Predictions of heat flow conditions during malfunctions of the

commercial process, namely slow quenching from the solution heat treatment

temperature; and predictions using experimentally determined C-curves of the

resultant mechanical property degradations and changes in NDE response.

In the ultrasonic studies, continuous monitoring of the sound velocity,

ultrasonic attenuation, and hardness during the progress of the aging process

in 2219 was corroborated with an examination of the specimens by transmission

electron microscopy. The experimental data were interpreted within the framework of established theories of diffusional processes and models of precipitation

hardeni ng.

The highlights of this investigation were the following:

1. Demonstration of the operational feasibility of an ultrasonic

NDE method for monitoring the precipitation process in aluminum

alloys in real-time, over a wide temperature interval. Figure 42

shows the variation of the sound velocity (elastic modulus) during

the aging process. The minima represent the maximum rate of

formation of specific precipitates. Figure 43 shows the changes in

the sound wave attenuation (absorption of energy) while the samples

undergo the precipitation hardening. The peaks are related to the

formation of the particles as well as to the loss of coherency

(denoted by 3) of the precipitates with the aluminum matrix.

2. Determination of the mechanism and the kinetics of precipitation

by simultaneous measurements of changes in sound-wave velocity

and attenuation.

3. Calculation of the activation energies and other characteristic

parameters related to the formation and growth of precipitates.

4. Elucidation of the relationship between the nature of the precipitates and their specific contribution to strength and hardness

of the alloy. In this context the occurrence of attenuation peaks

at aging times when hardness peaks are developed, indicating the

loss of coherency of the precipitates with the matrix, is noteworthy in Fig. 43. In addition, the effect of prior plastic

deformation on the aging process was considered.

88
CHANGE

IN

SOUND

WAVE

VELOCITY

(m

sec"

The development of ultrasonic NDE experimental techniques and their use

in obtaining the data in this investigation have required research of both

a practical and a basic nature. The extension of techniques for ultrasonic

NDE to industrial applications requiring on-line, real-time, monitoring

during thermomechanical treatment necessitates further development efforts.

Improved control of material properties important to the end user offers

additional motivation for further study of basic phenomena, e.g., kinetics

and mechanism of the aging process in single crystal specimens in order to

determine the specific contribution of precipitates located on the

prominent crystal planes, and the effects of applied uniaxial and hydrostatic stresses during the precipitation process.

The investigation of 2024 will be completed during Fiscal Year 1982

when a final report on this alloy will be issued. The large amount of data

and the techniques developed are expected to be of value for improving both

the nondestructive evaluation of the finished product and the processing of

material

.

Reference

1. "NBS: Nondestructive Evaluation of Nonuniformities in 2219 Aluminum

Alloy Plate - Relationship to processing", NBSIR 80-2069, December 1980.

Fig. 42 Change in ultrasonic sound wave velocity as a function

of aging time at three different temperatures in 2219

aluminum alloy.

89
ATTENUATION

CHANGE

(dB)

AGING TIME (hrs)

Fig. 43 Change in ultrasonic sound wave attenuation as a function

of aging time at three different temperatures in 2219

aluminum alloy.

90
28. Safety Factors and Mathematical Modeling

J. T. Fong

Mathematical Analysis Division

Center for Applied Mathematics

Engineering decision-making is characterized by two information-gathering

processes

:

(a) Mathematical modeling of the performance of a component or system

using a combination of theoretical results and experimental data.

(b) Application of so-called "engineering judgment" to cover uncertainties due to a lack of information on all aspects of an engineering

problem.

The first process is, in general, quantitative, while the second is qualitative

by tradition and necessity except that at some point along the decision-making

process, a numerical quantity known as a safety factor is usually employed.

For engineering decisions involving public safety or the protection of the

environment, the traditional process of choosing a safety factor by committee

or peer review is vulnerable to the charge that the judgment factor has no rational basis. The issue arose in the summer of 1976 when the National Bureau

of Standards was asked by the U.S. Department of Transportation to assess the

integrity of about 600 welds of the Trans-Alaska Oil Pipeline which were

known to contain defects larger than allowable under the federal regulations.

The technical results of the 1976 NBS study consisted of two distinct

parts:

(a) Fracture mechanics analysis for the generation of allowable defect

size curves was found acceptable as a basis for a regulatory decision.

(b) Defect size estimates from field radiographs with insufficient

control on process parameters were found unreliable to contribute

to a technical assessment.

An attempt to introduce a safety factor on the defect sizes was rejected because

there was no framework to introduce engineering judgment either by a committee

of experts or by a theoretical model. The lack of a positive technical result

on defect dimensioning contributed, as believed by this author, to the final

ruling of the regulator that all defective welds except three under Koyukuk

River had to be repaired to assure the structural integrity of the pipeline.

Aside from the economical and political aspects of the regulatory decision,

the 1976 NBS study revealed a serious technical deficiency in the application

of NDE data. With all the training, application, and experience behind the NDE

industry, why should three reputable inspection or auditing teams disagree on their defect size estimates by factors ranging from 1 to 7? If human factors

were critical in the outcome of an NDE calU why didn't the NDE industry initiate

a research and development program to characterize this source of uncertainty?

If NDE was intended to be a critical element in engineering and regulatory

decision making, why was the subject seldom included as a required course in an engineering curriculum?

91
To answer these questions, this project was initiated in FY78 with some preliminary results reported in the 1980 Annual NDE Report. The following

is a summary of new results developed in FY81 and documented in a manuscript

entitled "Safety Factor on Defect Sizes: A Combined Statistical and Engineering Approach".

It is well known in the statistics literature that confidence interval

estimates for the true mean of a certain measured quantity of a population

can be made from knowledge of (a) the sample size, (b) the sample mean, and

(c) either the sample variance or an estimate of the true variance based on previous measurements. Based on the notation used in an NBS publication

( Experimental Statistics , by M. G. Natrella, NBS Handbook 91, 1963), the

one-sided upper bound XA for a 100 (l-a)% confidence interval for the true mean of a population is^given by either of the following two formulas:

s t (if the sample variance is used). (1)

/n

a

z (-jf the true variance is used). (2)

/n

_ 2

In equations (1) and (2), X denotes the sample mean, n, the sample size, s , the sample variance, a^, the estimated true variance, t, the tabulated value

of a t-distribution for 100(1 -a)% confidence and n-1 degrees of freedom, and

z, the tabulated value of a z-distribution for 100(l-a)% confidence and n-1

degrees of freedom.

Based on a method first introduced by Mandel ("Analysis of Interlaboratory

Test Data," ASTM Standardization News , Vol . 5, No. 3, p. 17, 1977), multi-team

inspection data on a defect dimension of n welds are analyzed as if m replicas

of measurements were made on each weld. Here m is the number of teams inspecting the welds. The variance decomposition formula used by Mandel (1977) can

be used here to provide an estimate of the reproducibility from one defect

to another (within-the-weld population) and the repeatability from one team to another (between-team) of the inspection process. Computational

formulas are omitted here for brevity except that the decomposition formula

with the appropriate change of notation can be exhibited to show the

simplicity of the approach:

“(X)

“ °U) im) ’

X' = X +

X' = X +

where denotes the variance of the mean, the between-team variance

which conceivably can include variabilities due to both the measurement process

and human factors, and the within-the-weld-population variance which

should indicate variabilities due to the welding process and the associated

human factors. Naturally, for a given set of NDE data, we can only estimate

those variances by computing ^^jy ^^rn)’ ^^n)’ however, not obligated to use those computed values if our experience on related applications

92
indicates that the true variances may be much higher. What we are proposing,

therefore, is a combination of statistical analysis and engineering judgment

in arriving at a formula for a safety factor for defect sizes:

where S. F. denotes a safety factor based on a set of data on n welds by m

inspecting teams, and X/

^ is the grand sample mean obtained by first calculating the mean of m repTi cates and then computing the mean of averages

from the n welds. Engineering judgment is introduced through the use of

^^(m) *^^(n)’

Additional formulas are used to guide the selection of those

variances based on estimated defect sizes. It is worth noting that the

terms in the first curved brackets on the right of equation (4) give an upper bound estimate of the true mean of the population, whereas the terms

in the second curved brackets bring together an engineer's total knowledge

on the variability of the measurement and welding processes including those

due to human factors.

Clearly, the computed safety factor would vary according to the level of

confidence one prescribes for the problem at hand. To illustrate this point,

numerical results based on length of elongated slag data of ten welds (#81135,

81180, 81293, 81397, 81401, 81411, 81420, 81424, 81451, and 81474) of the

Trans-Alaska Oil Pipeline, as documented in the 1976 NBS study report, indicate

that for three levels of confidence such as 99%, 95%, and 90%, the corresponding

safety factors decrease from 2.71 (for 99%), through 2.19 (95%), to 1.92 (90%).

This approach describes a framework for constructing a safety factor for

defect sizes based on a multi -team inspection or auditing of welds in a critical structure. This framework combines rigorous statistical techniques with

engineering judgment, and is particularly valuable for dealing with measurement

processes where the human factor is a significant contributor to the process

variability. This work was presented at an ASME-ASNT joint symposium on

NDE: Reliability and Human Factors, Oct. 12-13, 1981, Atlanta, 6a.

(nxm) (4)

93
29. Visual Acuity Requirements for Nondestructive Testing

G. Yonemura

Environmental Design Research Division

Center for Building Technology

National Engineering Laboratory

Quantitative measures describing the physical correlates of what the

eye is expected to detect should be the basis for designing the visual acuity

test targets for nondestructive testing. In radiographic inspections, dimensional descriptions of the defect measured on the material have limited value.

The inspector is asked to look at the radiograph, consequently the physical

measure of interest for visual acuity testing is the defect as displayed on the film, regardless of how much it may differ from the actual defect.

Based on microdensi trometric scans of sample radiographs and supporting

data from the literature, the recommended parameters are summarized in

Table V. The optotype should be a thin line darker than the background. The

background luminance of the test target is kept constant at 85 + 5 nit(25 +1.5

ftL). Three contrast levels are recommended. The line widths recommended are

0.75, 1.0 and 1.5 minute of arc. The length of the lines are kept constant at

107 minute of arc. These angular measures are based on a viewing distance of

40 cm (16 in). Two levels of line sharpness are recommended--one with a sharp

edge that will be similar to most optotypes used in visual acuity testing, and one with a blurred edge conforming to real-world radiographs.

Samples of the reference test targets are presented in Fig. 44. The

testees are asked to give the orientation of the line. These targets may be

used for periodic tests by the employer or for more frequent self testing

by the inspector himself.

Background materials and supporting literature are discussed in NBS

Tech Note 1143, Visual Acuity Testing of Radiographic Inspectors in Nondestructive Inspection. This document will serve as a core from which a consensus document will be developed for the military after discussions with

the health departments and radiographic nondestructive installations in the

mil itary.

94
Table V. Visual Acuity Test Parameters

Variable

Number of

Conditions Conditions

Figure-Ground 1 Dark on light

Background Luminance (nit/ftL) 1 85 % 5/25 % 1.5

Contrast 3 0.1, 0.3, 0.85

Line Width (minutes) 3 0.75, 1.0, 1.5

Line Length (minutes) 1 107

Viewing Distance (cm/in) 1 40/16

Blur 2 Sharp, blurred

Line Orientation 4 Perpendicular/hori zontal

oblique right/left

Light Source (viewer) 1 Incandescent, fluorescent

Total (combinations) 72

95
FRONT BACK

Vertical

Contrast 0.85

Sharp

i

0.5”

T

C/> 0.85 V

1 1 bo

CJ1

1 s

=

Rotated 90^

> 0.85 H

Horizontal

Contrast 0.85

Sharp — T

1.2”

±

Q8'0 —

S

CO

T 00 0.1 L

Oblique/Left

Contrast QJ.

Blurred \

12”

1 /

_L B

Rotated SO""

Oblique/R.ight

Contrast OJ

B.lurred

-* 0.1 R

\

B flO

Figure 44. Exanples of acuity tests showing line orientation and

dimensions

.

96
30. Wear Condition Monitoring

A. W. Ruff

Metallurgy Division

Center for Materials Science

This project is concerned with the problem of monitoring the condition

of operating mechanical equipment, particularly its wear. In many

cases involving rotating machinery, e.g., turbines, pumps, and motors, wear

is the principal life-limiting process of degredation. A number of different

methods are used to condition-monitor such systems. These include thermal

measurements, vibration measurements, dimensional measurements and lubricant

analysis. This project is addressing measurement and standard needs involving

two particular techniques: (1) wear debris recovery and analysis, and

(2) acoustic emission detection and analysis. Progress has been made this

year in both areas and is described below.

Many operating mechanical systems that are subject to wear failures are serviced by built-in lubrication systems. Techniques exist to determine the

condition of the lubricant using chemical analysis methods that will indicate

lubricant failure. However, it is frequently found that chemical analysis does

not give a sufficiently early warning of failure. A more direct approach

involves recovering the wear debris particles themselves from the lubricant

fluid. Analysis of the wear particle size, type, and amount can provide both

early and detailed information on the wear process involved, and the rate at

which wear is taking place. For example, in a rotating bearing system, it is

normal to observe the moderate generation of mid-sized wear particles initially

as the system begins to operate from the newly manufactured condition. After

this a low generation rate of small particles is found throughout the usual

operating life. Finally, a high generation rate of large particles is noted

that corresponds to the onset of rapid wear at the end of useful life. Wear

debris analysis methods can determine all of these stages and in many cases

can provide early indication of the onset of final high wear and failure.

Chemical analysis methods cannot provide this degree of information.

This project has been concerned with a magnetic method of recovery and

analysis of wear debris particles from lubricating oil. This method, termed

ferrography, can remove virtually all metal or metallic oxide particles from

the oil and precipitate the particles according to size on a glass substrate.

This "ferrogram" is very convenient for further microscopic study and

quantitative measurement of the wear particles. The density of particles can

be measured optically and can be proportional to the amount (or rate) of wear

in the system. This project has contributed significantly in past years

to the techniques of ferrography, in particular, to the analysis of wear

particle type and size, and their relation to worn surface damage. In the

past year, the project has emphasized standards needs in ferrography. A

group of six laboratories in the U.S. (including NBS) have been conducting

interlaboratory test comparisons (round-robins) for two years, and considerable

progress has now been made. The last measurement cycle involved three samples

of wear debris in oil: one produced at NBS by two methods of wear in a way that we expect is reproducible, and two obtained from field operating

97
systems. Both oil samples and pre-prepared ferrograms were circulated among

the 6 laboratories. Typical precision of measurement was about 5% coefficient

of variation (cv) on wear particle density at any location on the ferrogram.

However, the additional interlaboratory cv was about 40%. The problem was traced to the optical density measuring equipment used. It was clear that each

lab's instrument was operating differently and that proper standardization of

that step should reduce the disagreement considerably. The method for

preparing the ferrogram (recovering the debris particles and depositing them

according to size) was found reproducible and satisfactory. This particular

method is now being sent through an SAE committee on standards for official

U.S. approval. After over 5 years of development, largely through Navy

sponsored work, that standard should greatly improve the wear debris analysis

capability of any properly trained and equipped laboratory.

The remaining problem of interlaboratory error is best handled by the

development of standard reference materials. Two different materials are

needed. One will serve as a "standard" ferrogram; this will provide the

instrument operator with a means of calibrating his locating system, aperature

system, and general microscope operation. The second will provide 4 or 5

levels for calibrating particle density from 0 to 100%. Together, these

reference materials should enable reproducible measurement of wear particle

density to about 10% to 15%, thus putting the entire method on a firm

quantitative basis. These two developments should be complete in the next

year.

The second effort in this project is concerned with applying techniques

of acoustic emission detection to the wear problem. This approach could be

valuable in applications where sudden vjear failure of a critical component,

e.g., a gas turbine shaft bearing, cannot be tolerated. Sudden failure in

rolling bearings usually results from subsurface crack nucleation and slow

crack growth, over lengthy periods of operation. One crack will eventually

reach the surface, releasing a large wear fragment (spalling). The bearing

surface is then badly damaged and the process accelerates until total bearing

failure occurs. It would be extremely valuable to have techniques to detect

the development of spalling failure early enough to avoid the catastrophic

stage. Since the growth of the subsurface crack occurs incrementally and

slowly, acoustic emission monitoring of crack growth, involving bursts of

energy release, appears feasible. A laboratory wear test system has been

instrumented to carry out simple experiments to attempt such detection and

identification. The system involves a block-on-ring test geometry with the

block specimen undergoing cyclic wear and steady sliding wear. The sliding

wear background consists of random noise events associated with surface friction

and oxide rubbing processes. The cyclic wear component is intended to

lead to slow growth of preexisting cracks beneath the wear surface.

^ The

detection system consists of an adjustable 60-110 db low noise amplifier,

high frequency and low frequency filtering, a conventional AE transducer^

detector, and a modified video tape recorder. Wear experiments are carried

out during which continual recording of the detected acoustic signals takes

place. The recorded signals can be monitored on an oscilloscope and a stop

action feature permits inspection of any portion of the recorded waveforms.

98
The problems being attacked first include the choice of test material,

and the characteristics of the repetitive machine noise and the sliding wear background noise. Several different steel blocks have been explored,

including tool steels and plain carbon steels. It was found difficult to

pre-establish proper crack growth conditions in those steels. Current

efforts are on temper embrittled steels where the crack growth characteristics

of repetitive machine noise have been identified in several cases; however,

the background surface rubbing noise may prove more of an interference to

crack growth detection. Our plan calls for the use of AE signature detection

methods being developed by R. Clough and J. Simmons, using a digital signal

processing approach. We plan to play back the VTR signals into their processing system and identify the crack-specific information. Some results using

this particular approach should be obtained next year.

99
31. X-Radiography

R. Placious, D. Polansky, C. Dick, and J. Motz

Radiation Physics Division

Center for Radiation Research

This report describes the NDE activities of the NBS X-Ray Physics Group

pertaining to industrial radiography. The general goal of this program is to

provide assistance to groups involved in industrial radiographic inspection

by developing and making available improved standards, procedures, measurements, and imaging systems. This program is described by the following projects

in industrial radiography, which include the names of the principal investigators.

1. Standard Method for Measuring the Image Quality Response of

Industrial Radiographic Film (R. C. Placious and D. Polansky).

This standard method required the development of a test object

which is now available from the NBS SRM Office. This standard method was developed for low-energy (200-kV) use, and it will appear in the next printing

of the ASTM Book of Standards.

2. High-Energy Image Quality Measurements (D. Polansky and R. Placious)

The completion of the low-energy standard method mentioned above

generated interest in producing a standard which would perform essentially

the same function at high photon energies (cobalt-60 and industrial Linacs

up to 15 MeV). The NBS X-Ray Physics Group has undertaken the responsibil i ty

of designing and fabricating the high-energy test object, and then of arranging

for round robin tests among various industrial laboratories, and of coordinating

all the resulting test data. At the present time, the equivalent penetrameter

sensitivity is the basis for developing the high-energy standard method.

Present results indicate that the latest test object design can be successfully

used as a standard to distinguish between films in a specified radiographic

system. In order to obtain statistical data, the radiographs are being

evaluated at various reader stations throughout the country.

3. Radiographic Film Storage and Processing (R. C. Placious)

Another activity within ASTM which has been assumed by NBS is the

responsibility for developing appropriate standards for radiographic film

storage and processing. A draft for film processing has been developed and

is being reviewed by appropriate experts. Another draft will be developed for

film storage. Both drafts will eventually be ASTM standards and will supplant

the material now included in ASTM standard E-94-77.

4. Unsharpness Measurements (D. Polansky)

There were two approaches to possible methods of measuring unsharpness

that were investigated. First, the optical density variations at the extremities

of a density edge trace were measured. These measurements were not reproducible

since the automatic scanning densitometer was too sensitive to local density

100
variations. Further investigation is required in order to determine whether this

first approach is viable. In the second approach, the visibility limit of the

edges of a stepped slit was investigated. Using conventional radiographic

techniques it was determined that the visibility limit of film types AA and T were equal. Therefore, this second approach was not satisfactory because one could not differentiate between two industrial films that are considered to

produce radiography of different quality.

At the present time unsharpness measurements are made with the "CERL"

indicators developed at the Central Electronics Research Laboratory. A detailed

evaluation of the CERL indicator for this purpose will be made at NBS in the near future.

5. Radiographic Reference Standards for Pipeline Weld Flays (Welding

Research Council) (R. C. Placious)

The goal of this work is to produce a reference standard or standards

for assessing, under field conditions, the volume content or projected area of

three dimensional flaws in welds. Such reference devices would reduce considerably

the error in the reader's estimate of the flaw content. These estimates are presently based primarily on the reader's judgment and not on direct measurement.

Preliminary designs may take the form of overlays or radiographs of known flaw

content.

6. Applications of Fluorescent Screens to Industrial Radiography (C. Dick)

Real time imaging systems now under development for on-line inspection

require the use of an x-ray fluorescent screen to convert the x-ray fluence to a wavelength suitable for the electro-optical imaging devices being employed. In

this program, a method is developed to experimentally evaluate the image information

transfer properties of x-ray fluorescent screens for real time radiography.

Measurements have been made of the absolute x-ray detection efficiency and of

the number of optical photons emitted from the screen as a function of the

incident x-ray energy. Data have been obtained which show the number of light

photons emitted per absorbed x-ray for a calcium tungstate and a rare earth

oxysulfide screen as a function of the incident x-ray energy from 20 to 70 keV,

and which give the values of the x-ray detection efficiency and the detective

quantum efficiency for the above screens. These measurements are being

extended to approximately 500 keV and will thus encompass the range used in

industrial NDE. In addition, preliminary experiments are underway to

determine the energy conversion mechanism of metallic and fluoro-metallic

screens which are used at these higher energies.

tOl
32. Comparison of Non-Reactor Based Neutron Radiographic Facilities

W. L. Parker and D. A. Garrett

Reactor Radiation Division

Center for Materials Science

The objective of these investigations was to obtain a comparison of the

characteristics of three major thermal neutron radiographic facilities which

did not utilize a nuclear reactor as a source of neutrons. In the evaluation

of each facility, the radiographic results were quantified as closely as possible

utilizing results obtained with the National Bureau of Standards Research

Reactor (NBSR) as benchmarks.

The three facilities evaluated were:

a) The subcritical assembly at the Mound Research Laboratories, Miamisburg,

Ohio.

b) The 2.5 MeV Van de Graaff accelerator facility at the Pantex Plant

of the Silas Mason Hanger, Silas Mason Co. in Amarillo, Texas.

c) The Crockroft-Walton accelerator-based system at the Advanced

Technology Center of the Vought Corporation, Dallas, Texas.

In all cases, the primary neutrons possessed energies greater than

thermal energies, i.e., greater than 0.025 eV. It was necessary to thermalize

the primary neutrons by the process of inelastic scattering in a moderator

such as light water, graphite, or other low atomic number scattering medium.

For each neutron source, measurements were made of the L/D ratio at

varying distances from the aperture, and the size and position of the effective

aperture were determined. The ratio of the film darkening due to gamma ray

beam contamination to that due to the thermal neutron flux was used as a meaningful

measure of the n /x\-r ratio. The flux and cadmium ratio were not measured during

Y I the evaluation, but are given as reported from previous measurements.

252

The subcritical assembly consists of a multiplied Cf spontaneous

fission neutron source and produces a total primary fission neutron yield

of approximately 5.8 x lO^^n-sec”^.

252

The neutron yield from the Cf source is multiplied by a factor of 28

o-jc

in a U subcritical assembly having a k effective of 0.990. Primary neutron

moderation is achieved with light water. Assembly multiplication is controlled

by cadmium poison rods.

The 2.5 MeV Van de Graaff accelerator is employed to accelerate a deuteron beam onto a beryllium target. Neutrons having peaks at well defined

energies are produced in the energy range between 2 MeV and 5 MeV. The

primary neutron yield is based on the ^Be(^H,n)^^B reaction and is controllable

by varying both the accelerating potential and H beam current striking the

Be target. The target is placed at the center of a spherical steel tank and

neutron moderation achieved by inelastic scattering interactions with the H component of light water.

102
The Vought facility is based on neutron production utilizing a Cockroft-Wal ton accelerator. Deuterons are accelerated to 185 keV and

allowed to strike a tritium target. Primary neutrons having a well defined

3 2 4

energy peak at 14 MeV are produced, based on the H( H,n) He reaction. The

Cockroft-Wal ton accelerator is a commercial ly-avail able sealed-tube unit and

1

1

-1

produces a total primary neutron yield of 2 x 10 n-sec . The target is

placed at the center of a three-foot diameter spherical tank. Neutron moderation is achieved by inelastic scattering interactions with the hydrogen and

carbon components contained in the moderator medium.

The comparative data obtained as a result of this evaluation program

are given in Table VI. In all cases, the system characteristics were

determined with facility parameters that are employed under normal production

operating conditions.

During the course of these investigations, every effort was made to

keep the data-gathering process as uniform as possible for each system.

The conclusions are based on the system data gathered, past system performance

history, and hands-on experience. These conclusions are;

Subcritical Assembly

° May be left unattended during operation

° Low maintenance costs

° Capable of high resolution performance

° Large, heavy, costly

O 252

Cf spontaneous fission neutron source constantly decays with a half-life of 2.3 years

° Fixed installation

° Downtime less than 10 percent

Van de Graaff Accelerator

° Does not require a primary neutron source which constantly decays

° Shielding requirements less stringent than those required for the

subcritical assembly

° Downtime less than 10 percent

° Fixed installation

° Present units require constant operation attendance

° Intermediate cost

Cockroft-Wal ton Accelerator

° Transportable

° Low cost

° High reliability with negligible maintenance costs

° Beam rotation through 180°

° Present systems require operator attendance during operation

° Low neutron production rate

° High operating cost due to tube replacement at end of warranty period

° Negligible downtime and maintenance costs

103
Table

VI.

Non-Reactor

Based

System

Characteristics

Using

the

NBSR

asa

Benchmark

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104
33. X-Ray Residual Stress Mapping in Industrial Materials by Energy Dispersive

Diffractometry

M. Kuriyama, W. Boettinger and C. Bechtoldt

Metallurgy Division

Center for Materials Science

This project is part of the Metallurgy Division's participation in the

NBS NDE program. The objective is to develop a nondestructive method of

mapping the distribution of residual stresses within industrial materials of

considerable thickness. This has been carried out in collaboration with

Robert Placious, Radiation Physics Division, Center for Radiation Research.

Improved quality control of industrial materials requires quantitative

information concerning the stress distribution near cracks under load and

residual stress distributions after different types of cold work and heat

treatment. This information enhances our understanding of the crack formation

and subsequent propagation inside materials, and leads to a way to produce

better materials in industry. For monitoring the structural integrity of,

for example, weld zones, quantitative information is required for the strain

distribution near the weld zone including the heat-affected zone as well

as the fusion zone. The most accurate current method for the determination

of residual stresses uses x-ray Bragg diffractometry from the surface of

materials (1). Although the accuracy is far beyond any other techniques,

this technique is unfortunately incapable of detecting stresses in the

interior of bulk materials (>lmm).

Several years ago, we proposed (2) an entirely different approach to the

x-ray evaluation of residual strains (or stresses) although it also uses the

principles of x-ray diffraction. This approach uses energy dispersive spectroscopy, where an energy dispersive solid state detector is employed with a wel 1 -col 1 imated beam of high-energy photons. In energy dispersive spectroscopy, one is concerned with energy spectral profiles and peak positions at

different energy values, instead of Bragg angles which play a key role in

Bragg diffractometry. These Bragg energy peak positions represent the lattice

constants in a local volume, and hence local strains. We proved, 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 a curve fitting technique (3).

This year we demonstrated a similar capability using an industrial (250 kV)

radiographic x-ray source for commercial steel plates up to 3cm (or more than

one inch) thick. The distribution of stress can be mapped across the plates

with a wel 1 -col 1 imated incident beam and a well-defined detector opening.

In this method, well-defined diffraction energy peaks should be obtained

at energies of 100 keV or more, so that penetration of a thick material is

possible and can determine the stress within the bulk material. These peaks

should have a Gaussian profile so that the curve-fitting technique can be used

for the determination 6f the centroid (or peak) positions with the accuracy

increased by a factor of 100 over the resolution limit of solid state detectors.

All of these principles were confirmed previously (3) with thi n material s using

105
low-energy photons. This year's objective is to confirm these points using

high-energy photons with thick materials. Figure 45 shows the variation of

strains (and, in turn, stresses) across a weld zone measured by this proposed

technique in one of the Alaskan pipe lines (4,5). The material is 14.6 mm

thick and has a minimum welded zone 6 mm wide centered at position 0. The

statistical error (a-value) in this measurement is less than 1 x 10"^ in strain

and 3000 psi in stress. This indicates the detectability of stress. Reproducibility was also confirmed. In this example the counting times were

only moderate. With longer counting times or an increased photon flux, the

counting statistics can be improved. Using laboratory x-ray sources up to

40 kV, strains of 5x10"^ (300 psi) can be easily detected with reliable reproducibility and good counting statistics. Thus, the present demonstration of

the expanded capability to higher energy has shown a potentially powerful

scientific tool to study and characterize flaws and microstructure with great

accuracy; for example, weld zones can be studied across the zones through

the depth.

References

1. J. B. Cohen, H. Dolle, and M. E. James, "Stress Analysis from Powder

Diffraction Patterns," Proceedings of a Symposium on Accuracy in Powder

Diffraction, NBS Special Publ . 567, p. 453 (1980).

2. M. Kuriyama, W. J. Boettinger, and H. E. Burdette, ASNT National Fall

Conference, October, Denver, CO, p. 49 (1978).

3. M. Kuriyama, W. J. Boettinger, and H. E. Burdette, "X-Ray Residual Stress

Evaluation by an Energy Dispersive System," Proceedings of a Symposium

on Accuracy in Powder Diffraction, NBS Special Publ. 567, p. 479 (1980).

4. M. Kuriyama, "Procedure for Stress Measurement using Energy Dispersive

Di ffractometry and High Energy Incident Photons," Symposium on Nondestructive

Measurement of Wheel/Axle Residual Stress, DOT Publication (in press).

5. C. J. Bechtoldt, R. C. Placious, W. J. Boettinger and M. Kuriyama,

"X-Ray Residual Stress Mapping in Industrial Materials by Energy

Dispersive Di ffractometry," to be published in "Advances in X-ray

Analysis," Vol . 25; 30th Annual Denver X-Ray Conference, Denver, CO (1981).

106
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107

Residual

stress

distribution

across

a

welded

zone

in

an

Alaskan

pipe

line

steel

14.6

mn

thick.

This

mapping

is

obtained

ata

scattering

angle

5*

in

the

transmission

geometry

using

(211)

diffraction.

Positive

values

of

stress

represent

compression.
APPENDICES

Conferences Sponsored

1. 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 industrial community to

NDE, (2) providing a good record of the state-of-the-art, (3) providing

a forum for information exchange, (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 standards needs. In the past year the Office of NDE played

a strong role in the following meetings:

Symposium on- Ultrasonic Measurements of Stress, April 9, 1981.

Sixth International Symposium on Ultrasonic Imaging and

Tissue Characterization, May 31-June 3, 1981.

Briefing Workshop on Rapid Solidification Technology,

July 1-2, 1981.

Second International Conference on Durability of Building

Materials, September 14-16, 1981.

2. NBS Seminars on NDE

A list of NBS-NDE Seminars held during the past year is given in Table VII.

Notices of the seminars are distributed broadly in the Washington area. Visitors are welcome and often attend.

This year several of the NDE seminars were transmitted to the Boulder

Laboratory via a conference telephone line and the simultaneous use of visuals in Boulder.

108
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109
B. Talks by NDE Office Personnel

1. "Some New Developments in Radiography," H. Berger, Old Dominion ASNT

Section, Richmond, VA, October 28, 1980.

2. "NDE at NBS," Regional Workshop on Research in NDE, H. Berger, University

of Houston, Houston, TX, November 10, 1980.

3. "Toward the Nondestructive Characterization of Damage in Composite Materials,"

L. Mordfin, ASTM Symposium on Damage in Composite Materials: Mechanisms,

Accumulation, Tolerance and Characterization, Bal Harbour, FL, November 13, 1980.

4. "Nondestructive Measurement of Resuidual Stress: A Status Report," L. Mordfin,

Fifth Workshop on Government Supported R&D in NDE, Washington, D.C.,

December 1, 1980.

5. "Materials Testing Equipment and Technology for the 1980's". L. Mordfin,

DOC Technical Sales Seminars, Budapest, Hungary; Bucharest, Romania;

Prague, Czechoslovakia, January 20-28, 1981.

6. "The National Bureau of Standards Program on Nondestructive Evaluation,"

H. Berger, Nondestructive Testing Management Association, Las Vegas, NV,

February 4, 1981

.

7. "Development of Improved Standards for Leakage Rate Measurements," L. Mordfin,

ASME Boiler and Pressure Vessel Committee Subgroup on General Requirements,

New York City, NY, March 3, 1981.

8. "Measurement of Residual Stresses: Problems and Opportunities," L. Mordfin,

WESTEC '81 Conference, Los Angeles, CA, March 25, 1981.

9. "Standards for Residual Stress Measurement," L. Mordfin, ASTM Symposium on Residual Stress Effects in Fatigue, Phoenix, AZ, May 11, 1981.

10. "Introduction to Residual Stress Measurement," L. Mordfin, Symposium on Nondestructive Measurement of Wheel/Axle Residual Stress, Cambridge, MA,

June 16, 1 981

.

11. "Priority Issue No. 1 - Reliability of Nondestructive Evaluation," L. Mordfin,

ASME Pressure Vessels and Piping Conference, Denver, CO, June 23, 1981.

12. "New Developments in Radiography", H. Berger, Philadelphia Section ASNT,

Philadelphia, PA, September 3, 1981.

no
C. Awards and Recognition

Industrial Research, IR-1Q0 Award

For the third consecutive year an NDE-oriented development was recognized

with an IR-100 award. Mr. Thomas M. Proctor of the Mechanical Production

Metrology Division received the award for an improved acoustic emission

transducer.

The improved acoustic emission transducer accurately measures small

surface displacements due to acoustic emission events by converting the

surface motion to a voltage signal. The improvements produce a transducer

that has a very flat response over its working range (50 KHz to 1 MHz) and

sensitivity approaching that of a conventional piezoelectrc transducer.

Department of Commerce Medals

The Silver Medal of the Department of Commerce was awarded to E. Clayton

Teague of the Mechanical Production Metrology Division for technical

accomplishments and leadership in measurement of surface texture. Dr. Teague

leads the NDE program's activity on optical measurement of surface roughness.

Department of Commerce Bronze Medals were awarded to Donald G. Eitzen

of the Mechanical Production Metrology Division for his outstanding leadership in the development and execution of the NBS program in ultrasonic

standards, and to Lewis K. Ives of the Metallurgy Division for his

outstanding contributions to research in the wear of metals and microstructural analysis.

Professional Society Awards

The Illuminating Engineering Society of North America presented its

Special Presidential Award to Gary Yonemura of the Environmental

Design Research Division in recognition and appreciation for his

valued research and contributions. Dr. Yonemura is the NDE program's

principal investigator for efforts to establish meaningful measures

of visual acuity for inspection personnel.

George G. Harman of the Semiconductor Devices and Circuits Division

received the Internaional Society for Hybrid Microelectronics'

highest technical award for his pioneering efforts in the field of

wire-bonding process characterization which significantly reduced

field failures resulting from wire-bond problems. Mr. Harman is

the author of NBS Special Publication 400-59, "Semiconductor Measurement

Technology: Nondestructive Tests Used to Insure the Integrity of

Semiconductor Devices, with Emphasis on Acoustic Emission Techniques,"

September 1979.

Ill
NBS Scientist Named International NDE

Conference Chairman

It has been announced that Roger Clough will be the general chairman for

the Fifth International Conference on Nondestructive Evaluation in the

Nuclear Industry, to be held in San Diego in May, 1982. Clough, a metallurgist in the Metallurgy Division, has been active in NDE and materials

research at NBS, most recently with the quantitative acoustic emission method

being developed jointly by NBS and the Harwell Atomic Energy Research

Establishment.

112
D. Publications

1. "Eddy-Current Characterization of Materials and Structures,"

G. Birnbaum, G. Free, Eds., Proceedings of Symposium held at NBS

in September 1979, ASTM STP 722 (1981).

2. "Eddy Current Nondestructive Testing," NBS Special Publication 589,

G. M. Free, Ed., Workshop on Eddy Current NOT held at NBS in

November 1 977 (1 981 )

.

3. "Nondestructive Testing In The 80' s," H. Berger, Canadian Society

for Nondestructive Testing, 2 , No. 7, pp. 1418 (April 1981).

4. "Dimensioning Flaws in Pipeline Girth Welds by Radiographic Methods,"

R. C. Placious, D. A. Garrett, M. B. Kasen, H. Berger, Materials

Evaluation, No. 8, pp. 755-759 (July 1981).

5. "A Basis for Traceable NDE Measurements," D. G. Eitzen, H. Berger,

G. Birnbaum, NBSIR 802172 (December 1980).

6. "Technical Activities of the Office of Nondestructive Evaluation,"

H. Berger and L. Mordfin, Eds., NBSIR-80-2162 (Nov. 1980).

7. "Enhanced Reliability and Reproducibil i ty of Measurements of

Machinery Vibrations," L. Mordfin, B. Payne, S. Edelman, Proc.

Sixth Machinery Dynamics Seminar, Toronto, Canada, Sept. 1980,

pp. 4-0 - 4-22.

8. "Reliability of Nondestructive Evaluation," L. Mordfin, Critical

Issues in Materials and Mechanical Engineering, ASME, pp. 133-147

(1981).

9. "Measurement of Residual Stresses: Problems and Opportunities,"

L. Mordfin, Residual Stress for Designers and Metallurgists, ASM,

pp. 189-210 (1981).

10. "NDE Standards for Nuclear Power Systems: An NBS Perspective,"

L. Mordfin, H. Berger, Nondestructive Evaluation in the Nuclear

Industry - 1980, ASM, pp. 303-318 (1981).

11. "Criteria for Recommending Lighting Levels," G. T. Yonemura,

NBSIR 81-2231 (March 1981).

12. "Correlation of Source Microstructure and Acoustic Emission Signals

Using Indentation Fatigue and Stress Corrosion Cracking in Aluminum

Alloys," R. B. Clough, J. C. Chang, J. P. Travis, Scripta Metallurgica

(April 1981).

13. "Cryogenic Properties of Filamentary-Reinforced Composites: An

Update," M. B. Kasen, Cryogenic Journal, pp. 323-340 (June 1981).

14. "Interim Report on the Significance of Blunt Flaws in Pipeline

Girth Welds," M. B. Kasen, R. P. Mikesell, Proc. International

Conference on Pipelines and Energy Piping, Calgary, Alberta,

Canada, Oct. 1980, pp. 329-336 (1980).

113
15. "Effect of Blunt Flaws Studied in Pipeline Girth Welds,"

M. B. Kasen, R. P. Mikesell, Oil and Gas Journal, Vol . 79,

No. 13, March 30, 1981, pp. 155-158.

16. "Relationship Between Process Variables, Microstructures and

NDE of a Precipitation Hardened Aluminum Alloy," L. J. Swartzendruber,

W. J. Boettinger, L. K. Ives, S. R. Coriell, R. Mehrabian, Proc.

of NDE: Microstructures and Reliability Prediction, Pittsburgh,

PA., October 1980 (1981).

17. "Semiconductor Technology Program Progress Briefs," W. M. Bullis,

Ed., NBSIR 81-2230 (March 1981).

18. "Anisotrophic Elastic Constants of A Fi ber-Reinforced Boron-Aluminum

Composite," S. K. Datta, H. M. Ledbetter, Mechanics of Nondestructive

Testing, Proceedings of the Conference on Mechanics of Nondestructive

Testing, VPI, Blacksburg, VA, Sept. 1980, pp. 215-230.

19. "Piezoelectric Polymer Probe for Ultrasonic Applications," A. S. Dereggi, S. C. Roth, J. M. Kenney, S. Edelman, G. R. Harris, J. of

Acoustical Society of America, 69, 3, pp. 853-859 (March 1981).

20. "Ultrasonic Materials Characterization, " H. Berger, M. Linzer, Eds.,

NBS Special Publication 596, Proceedings of the First International

Symposium on Ultrasonic Materials Characterization, June 1978

(Nov. 1980).

21. "Laboratory Evaluation of Nondestructive Methods to Measure Moisture

in Built-up Roofing Systems," L. Knab, R. Mathey, D. Jenkins, NBS

Building Science Series 131 (Jan. 1981).

22. Nondestructive Evaluation Methods for Quality Acceptance of Hardened

Concrete in Structures," J. R. Clifton, E. D. Anderson, NBSIR

80-2163 (January 1981).

23. "Nondestructive Examination of A Defective Silver Braze Using

Resonance-Neutron Radiography," J. W. Behrens, R. A. Schrack and

C. D. Bowman, Nuclear Technology, Vol. 51, No. 1, pp. 78-82

(Nov. 1980).

24. "Piezoelectric and Pyroelectric Applications of Plastics,"

M. G. Broadhurst, S. Edelman, G. T. Davis, Organic Coatings and

Plastics Chemistry, ACS 179th National Meeting, Houston, TX,

March 1980, pp. 241-245 (1980).

25. "An Ultrasonic Investigation of Precipitation Hardening Phenomena

in 2219 Aluminum Alloy," M. Rosen, S. Fick and E. Horowitz,

Johns Hopkins U. Center for Materials Research, Semi-Annual Report

Sept. 1980 - March 1981 (March 1981).

26. "Summary of Fundamental Developments for Quantitative Acoustic

Emission Measurements," D. G. Eitzen, F. R. Breckenridge,

R. B. Clough, E. R. Fuller, N. N. Hsu, J. A. Simmons, Interim

Report - EPRI NP-1.877 (June 1981).

114
27. "1980 Annual Report: Technical Contributions to the Development

of Incipient Fault Detection/Location Instrumentation," W. E. Anderson, J. D. Ramboz, NBSIR 81-2235 (March 1981).

28. "Auto: A Real Time Diffractometer Control System," R. L. Snyder,

C. R. Hubbard, N. C. Panagiotopoulos, NBSIR 81-2229 (February 1981).

29. "Nuclear Safeguard Interrogation of Waste Containers with Resonant

Neutrons," Y. Cheng, D. A. Garrett, NDT for Energy Progress, ASNT

National Fall Conference, Houston, TX, pp. 97-99 (October 1980).

30. "The Use of X-Ray and Neutron Radiography to Evaluate Lithium/Iodine

Pacemaker Batteries," D. A. Garrett, R. C. Stinebring, NDT for

Energy Progress, ASNT National Fall Conference, Houston, TX,

pp. 215-219 (October 1980).

31. "Holographic NDE: Status and Future," C. M. Vest, NBS-GCR-81-318

(May 1981).

32. "Feasibility of Crack Growth Characterization in a Plate Geometry,"

H. Wadley, United Kingdom Atomic Energy Authority Harwell for NBS

(October 1980).

33. "Ultrasonic Reflectivity Imaging in Three Dimensions: Exact Inverse

Scattering Solutions for Plane, Cylindrical, and Spherical Apertures,"

S. J. Norton, M. Linzer, IEEE Transactions on Biomedical Engineering,

Vol. BME-28, No. 2, pp. 202-220 (February 1981).

34. "Optical Interferometric Visualization and Computerized Reconstruction of Ultrasonic Fields," F. P. Higgins, S. J. Norton,

M. Linzer, J. Acoust. Soc. Am., 68, 4, pp. 1169-1176 (October 1980).

35. "Characterization and Calibration of Acoustic Emission Sensors,"

N. Hsu, F. Breckenridge, Materials Evaluation, Vol. 39, No. 1,

pp. 60-68 (January 1981).

36. "AE Signal Analysis - Laboratory Experiments Examining the Physical

Processes of Acoustic Emission," N. Hsu, D. G. Eitzen, Proceedings

of the Fifth Acoustic Emission Symposium, Tokyo, Japan, pp. 67-78

(1980).

37. "Acoustic Emission Signatures and Source Microstructure Using

Indentation Fatigue and Stress Corrosion Cracking in Aluminum

Alloys," R. B. Clough, J. C. Chang, J. P. Travis, Scripta Metallurgica, Vol. 15, pp. 417-422 (1981).

38. "B-Scan Echo-Amplitude Measurement in Patients with Diffuse

Infiltrative Liver Disease," T. H. Shawker, B. Moran, M. Linzer,

S. I. Parks, S. P. James, F. W. Stromeyer, J. A. Barranger,

J. Clin. Ultrasound, 9, pp. 293-301, (Aug. 1981).

39. "Tomographic Image Reconstruction from Limited Projections Using

Iterative Revisions in Image and Transform Spaces," T. Sato,

S. J. Norton, M. Linzer, 0. Ideda, M. Hirama, Applied Optics,

Vol. 20, No. 3, (February 1981).

115
40. "Nondestructive Evaluation of Non-Uniformities in Aluminum Alloy

Plate," G. M. Free, L. K. Ives, R. Mehrabian, L. J. Swartzendruber,

ASNT Summaries, pp. 39-43, (1980).

41. "High Accuracy Conductivity Measurements in Nonferrous Metals,"

G. Free, in Eddy-Current Characterization of Materials and Structures,

ASTM STP 722, pp. 121-129 (1981).

42. "Dynamic elastic modulus and internal friction in G-IOCR and G-llCR

fiberglass-cloth-epoxy composites," H. M. Ledbetter,

Cryogenics 637-640 (1980).

43. "Temperature dependence of the Young's modulus and internal friction

of G-IOCR and G-llCR epoxy resins," H. M. Ledbetter and G. Maerz,

Cryogenics 655-658, (1980).

44. "Sound velocities and elastic constants of steels 304, 310, and

316, "H. M. Ledbetter, Metal Sci. Xi, 595-596, (1980).

45. "Young's modulus of a copper-stabilized niobium-titanium superconductive wire," H. M. Ledbetter, J. C. Moulder, and M. W. Austin,

Wire 3X (Jan. /Feb.), 27-29 (1981).

46. "Stainless steel elastic constants at low temperatures,"

H. M. Ledbetter, J. Appl . Phys. 1587-1589 (1981 ).

47. "A Boundary Integral Equation Method for Calculating the Eddy-Current

Distribution in a Long Cylindrical Bar with a Crack," A. H. Kahn and

R. Spal in Eddy Current Characterization of Materials and Structures,

ASTM Tech. Pub. 722, G. Birnbaum and G. Free, Eds., (1981), pp. 298.

48. "Viscoelastic Characterization of Structural Adhesives via Forced

Oscillation Experiments," D. L. Hunston, W. D. Bascom, E. E. Wells,

J. D. Fahey, and J. L. Bitner, in Adhesion and Adsorption of Polymers,

Polymer Science and Technology Series, L. H. Lee, Ed., p. A 321

(Plenum Press, New York, 1980).

49. "Linear Viscoelastic Properties of Solid Polymers as Modeled by a Simple Epoxy," D. L. Hunston, W. Carter, and J. L. Rushford, in

Developments in Adhesives - 2, A. J. Kinloch, Ed. (Applied Science

Publishers, Ltd., London, 1981, pp. 125-172).

50. "Viscoelastic Fracture of Structural Adhesives," J. L. Bitner,

J. L. Rushford, W. S. Rose, D. L. Hunston, and C. K. Riew, J; of

Adhesion, in press.

51. "Optical Techniques for On-line Measurement of Surface Topography,"

T. V. Vorburger, and E. C. Teague , Precision Engineering 3 , 61-83,

(1981).

52. "Light Scattering from Manufactured Surfaces," E. C. Teague, T. V.

Vorburger, and D. Maystre, Annals of CIRP, September 1981.

116
53. "A Basis for Traceable NDE Measurements Part 1," Eitzen, Berger, and

Birnbaum, Materials Evaluation, No. 9, p. 797-798, (Aug., 1981).

54. "Moisture detection in Roofing by Nondestructive Means--A State-of-theArt Survey," David R. Jenkins, Robert G. Mathey, and Lawrence I. Knab,

NBS Tech Note 1146, July 1981.

55. "Laboratory Evaluation of Nondestructive Methods to Measure Moisture in

Built-Up Roofing Systems," NBS Building Science Series 131.

56. "A-E Signal Analysi s--Laboratory Experiments Examining the Physical Process

of Acoustic Emission," N. N. Hsu and D. G. Eitzen, Proceedings of the

Fifth International Acoustic Emission Symposium, Tokyo, November 1980.

57. "Characterization and Calibration of Acoustic Emission Sensors," N. N. Hsu

and F. R. Breckenridge, Materials Evaluation, 39, No. 1, pp. 60-68.

(Jan. 1981).

58. "Surface-Wave Displacement: Absolute Measurements Using a Capacitive

Transducer," Franklin R. Breckenridge and Martin Greenspan, J. Acoust,

Soc. Am. No. 4, pp. 1177-1185, April 1981.

59. "NBS: Nondestructive Evaluation of Nonuniformities in 2219 Aluminum Alloy

Plate - Relationship to Processing," L. Swartzendruber, W. Boettinger,

L. Ives, S. Coriell, D. Ballard, D. Laughlin, R. Clough, F. Biancaniello,

P. Blau, J. Cahn. R. Mehrabian, G. Free, H. Berger, and L. Mordfin,

NBSIR 80-2069, December 1980.

60. "Neutron Diffraction and Small -Angle Scattering of Nondestructive Probes

of the Microstructure of Materials," D. J. Glinka, H. J. Prask and

C. S. Choi, Mechanics of Nondestructive Testing, Proceedings of the

Conference on Mechanics of Nondestructive Testing, VPI, Blacksburg, VA,

Sept. 1980, pp. 143-164.

117
u M.
Appendix'

E

FEDERAL LABORATORY

TECHNOLOGY APPLICATION ASSESSMENT

National Measurement Laboratory

National Bureau of Standards

NBS CONICAL TRANSDUCER

A new acoustic emission (AE) transducer, the NBS Conical Transducer,

is under development. It is already changing research and applications

approaches in AE because it faithfully measures dynamic displacement, whereas

commercially available sensors only detect a disturbance but do not faithfully

measure it.

The NBS Conical Transducer follows dynamic normal displacements nearly

as well as the standard capacitive transducer used in the NBS calibration

service for AE transducers. However, the new device is more rugged than the

capacitive transducer and is one to two orders of magnitude more sensitive -- about as sensitive as commercial AE transducers.

STAGE OF DEVELOPMENT

The usefulness of the device has been demonstrated experimentally.

Further research of a theoretical nature is planned to optimize the development.

APPLICATIONS

The NBS Conical Transducer is applicable to inservice monitoring of AE

on a broad variety of structural components.

PATENT STATUS

NBS has been granted an IR-lOO award for this development. No patent

action is contemplated at this time.

PUBLICATIONS

T. Proctor, "Improved Piezoelectric Transducer for Acoustic Emission

Signal Reception", Abstract KK-4, J. Acoust. Soc. Am. 68, Suppl. 1 (Fall 1980).

118
FEDERAL LABORATORY

TECHNOLOGY APPLICATION ASSESSMENT

National Bureau of Standards

National Measurement Laboratory

PENETRANT TEST BLOCK

The NBS Office of Standard Reference Materials has announced the availability

of Standard Reference Material (SRM) 1850, a penetrant test block containing

uniform "cracks” of known width for checking the sensitivity and performance

of surface-defect detecting materials and devices, mainly liquid dye penetrants

and dye penetrant systems. The test blocks were developed by the Corrosion

and Electrodeposition Group of the NBS Center for Materials Science in an

effort supported by the NBS Office of Nondestructive Evaluation.

Four cracks approximately 0.2, 0.5, 1 and 2 um wide are formed in a 1/2 x 2 cm section of an electrodeposited copper-nickel laminate mounted in an epoxy resin

disk about 5 cm in diameter and 1 cm thick. The depth of each crack is several

times its width—beyond the critical depth for showing dye penetrants. Each

crack is measured at the center of the blocks with an accuracy of 50% or 0.1 um

whichever is greater. The test block may be used indefinitely as it is easily

cleaned and corrosion resistant.

PATENT STATUS

No patent action will be taken.

PUBLICATIONS

H. Berger, and L. Mordfin, Eds., "Technical Activities 1980, Office of

Nondestructive Evaluation", NBSIR 80-2162, pp. 67-68 (Nov. 1980).

ADDITIONAL INFORMATION

SRM 1850 may be purchased from the Office of Standard Reference Materials,

Room B311, Chemistry Building, National Bureau of Standards, Washington, D.C. 2023A,

for $108. Telephone (301) 921-2045, FTS 921-2045. Further details are furnished

with the SRM.

119
NBS-U4A (REV. 2-80

U.S. DEPT. OF COMM. 1. PUBLICATION OR ! 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

January 1982

SHEET (See instructions) NBSIR 82-2449

4. TITLE AND SUBTITLE

Technical Activities 1981, Office of Nondestructive Evaluation

5. AUTHOR(S)

H. Berger and L. Mo rdfin , editors

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State. ZIP)

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This is the fourth in a series of annual reports describing the technical

activities of the nondestructive evaluation program at the National Bureau of

Standards.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Acoustic emission; eddy currents; imaging; leakage testing; magnetics; material

parameters; nondestructive evaluation; optics; penetrants; radiography; and

ultrasonics.

13. AVAILABILITY

Unlimited

I I For Official Distribution. Do Not Release to NTIS

[Jl Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

[X] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

124

15. Price

$ 12.00

120 USCOMM-DC 6043-P80

f4