NAT'L

^

INST.^ OF

jH||0 jjllllll j AlllOb 034251

REFERENCE

Institute for Materials Science and Engineering

NONDESTRUCTIVE

EVALUATION

NBSIR 85-3187

U.S. Department of Commerce

National Bureau of Standards

-QC Technical Activities

100

.1)56 1985

85-3187

1985
Reconstruction of two simulated acoustic emission point sources in the presence of noise.

S. J. Norton and M. Linzer
I'TES RE5EASCH INECftMATIOfl CENTEB

Institute for Materials Science and Engineering

NONDESTRUCTIVE

EVALUATION

H. T. Yolken, Chief

L. Mordfin, Deputy

NBSIR 85-3187

Tf.S. Department of Commerce

National Bureau of Standards

Technical Activities

1985

Certain commercial equipment, instruments, or materials

are identified in this report in order to adequately

specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the

National Bureau of Standards, nor does it imply that the

materials or equipment identified is necessarily the best

available for the purpose.

11
iii
TECHNICAL ACTIVITIES

Table of Contents

Introduction 1

I. NDE STANDARDS

Measurement Methods, Calibration Procedures, and Standards

for Quantitative Eddy Current NDE 5 - J. C. Moulder, J. C. Gerlitz, B. A. Auld, and S. R. Jefferies

Eddy Current Coil Characterization 14

- T. E. Capobianco and F. R. Fickett

Standardization of Eddy Current Conductivity Measurements 23

- G. M. Free

Ultrasonic Absolute-Power Transfer Standards 24

- F. R. Breckenridge, S. E. Fick, and C. E. Tschiegg

Ultrasonic Artifact Calibration Methodology 25

• - G. V. Blessing and D. G. Eitzen

Document Standards for Ultrasonics and Acoustic Emission 28

- D. G. Eitzen and F. R. Breckenridge

Vector Transducer Calibration 29

- C. D. Turner, H. N. G. Wadley, and J. A. Simmons

Dynamic Displacement Transducers for Acoustic Emission 35

- T. M. Proctor, M. Greenspan, and D. G. Eitzen

Calibration Activities for AE Transducers 42

- F. R. Breckenridge and T. M. Proctor

Measuring Radiographic/Radiologic Sensitivity ^6 - R. C. Placious and D. Polansky

Self Test of Visual Acuity for Radiographers j

- R. C. Placious

Performance Assessment of Fluorescence Measurements 5' - K. L. Eckerle, J. J. Hsia, S. T. Chang, and K. D. Mielenz

Development of High Optical Density Standards

- J. J. Hsia, C. H. Popenoe, and L. E. Fink

Infrared Methods of Nondestructive Testing • - J. Cohen

iv
Standard Test Methods for Characterizing Performance of Thermal

Imaging Systems 56

- J. Cohen

Development of Leak Standards and Calibration Facilities at NBS 57

- C. D. Ehrlich and C. R. Tilford

Surface Methods for NDE 59

- L. J. Swart zendruber

Ferrographic Study of Wear Debris 62

- A. W. Ruff

NDE of Corrosion - Gun Barrels and Ammunition 63

- A. C. Fraker and A. W. Ruff

II. NDE METHODS FOR INTERNAL FLAW CHARACTERIZATION

Acoustic Emission Imaging ... 67

- S. J. Norton and M. Linzer

Experimental Green's Function and the Inverse Problem 71 - N. N. Hsu, T. M. Proctor, D. G. Eitzen, and A. Carasso

Ultrasonic Point Source: The NBS Conical Transducer as a Driver 76

- T. M. Proctor, N. N. Hsu, and S. E. Fick

Theoretical Studies of Acoustic Scattering 77

- R. D. Mountain

Design of an X-ray Camera Using a CCD Sensor 79

- R. Spal and M. Kuriyama

Long Thermal Wave Imaging Using Holographic Interferometry 82

- C. M. Vest

Pulse-Echo Method for Flaw Detection in Concrete 8M

- N. J. Carino, M. Sansalone , and N. N. Hsu

Transducer Design for Ultrasonic Testing of High Attenuation

Heterogenous Composite Materials 88

- N. N. Hsu, T. M. Proctor, N. J. Carino, and M. Sansalone

NDE of Distributed Damage in Metals 90

- R. J. Fields and H. M. Ledbetter

Creep Cavities in Copper: An Ultrasonic-Velocity and CompositeModeling Study 101

- H. M. Ledbetter and R. J. Fields

NDE Data Analysis, Reliability Modeling, and PC-Based Software

Research 103

- J. T. Fong, R. S. Cramer, D. F. Redmiles, M. R. Knapp-Cordes

and J. J. Filliben

v
III. NDE FOR INTERFACES AND COMPOSITES

Cure Monitoring of Composites Using Fluorescence Spectroscopy Ill

- B. M. Fanconi , F. W. Wang, and R. Lowry

Cure Monitoring in Epoxy Resins by Electrical Measurements 115

- F. I. Mopsik

Ultrasonic Characterization of Polymers 120

- S. I. Rokhlin, K. Lewis, and F. K. Graff

Sound Velocities and Elastic Constants of Reinforced Composites 122

- H. M. Ledbetter, M. W. Austin, and R. D. Kriz

Internal Strain (Residual Stress) in an SiC/Al Particle-Reinforced

Composite: An X-ray Diffraction Study 124

- H. M. Ledbetter and M. W. Austin

Effect of Interface Properties of Wave Propagation in. a Medium

With Inclusions 126

- S. K. Datta

Conductivity Profiling by Eddy-Current Measurements 128

- A. H. Kahn and K. R. Long

Ultrasonic Measurement of Surface Roughness 132

- G. V. Blessing and D. G. Eitzen

Optical Measurement of Surface Roughness 134

- T. V. Vorburger, D. E. Gilsinn, E. C. Teague, M. J. McLay,

F. E. Scire, and C. H. W. Giauque

Nondestructive Early Detection of Corrosion and Delamination Under

Protective Coatings Using Thermal Wave Microscopy 139

- T. Nguyen and M. E. McKnight

Thermal Wave Microscopy for Use in Near Surface Crack Depth and

Orientation Determination in Metallic Materials 1 5

- P. J. Blau and C. D. Olson

IV. NDE FOR PROCESS CONTROL

Nondestructive Evaluation of Distributed Damage in Ceramic Materials

Using Small Angle Neutron Scattering Techniques

- K. A. Hardman-Rhyne

The Phase Shift and Multiple Scattering in Small Angle Neutron

Scattering: A Theory for NDE of Ceramics • - N. F. Berk

Ultrasonic Measurements of Ceramics ' • - G. V. Blessing and M. P. Jones

vx
Thermal Waves . . .171

- G. White, L. Inglehart , M. Jones, A. Wilson and C. Nguyen

Nondestructive Evaluation - Green State Ceramics 177

- C. Robbins, W. Coblenz, and M. Jones

Ultrasonics in Metallurgy 1 81 - B. Droney, M. Linzer, J. Martinez, F. Mauer, S. Norton,

K. Sandstrom, C. Turner, and H. N. G. Wadley

Acoustic Emission as an NDE Technique for Characterizing

Martensitic Transformations 185

- Y. Berlinsky, H. N. G. Wadley, R. B. Clough, J. A. Simmons,

and M. Rosen

Dynamic Microindentation Evaluation of Materials 191 - R. S. Polvani

Use of a Commercial Hardness Testing Instrument as a Nondestructive Probe of Mechanical Properties 19^

- D. S. Lashmore and J. L. Mullen

Nondestructive Evaluation of Tool Wear and Chip Formation 199

- K. W. Yee, L. Evans, and D. Dornfeld

Ultrasonic Measurements on Thermal Insulation 205

- G. V. Blessing and D. R. Flynn

APPENDICES

A. NDE Seminars at NBS 207

B. Invited Talks by ONDE Staff .208

C. Publications .208

D. Awards 212

E. Principal Investigators 213

vii
INTRODUCTION

This report provides brief reviews of the technical activities in

nondestructive evaluation (NDE) that were carried out by or for the

National Bureau of Standards ( NBS) in fiscal year 1985 (October 1, 1984

through September 30, 1985). In addition to reports on work supported by

the Office of Nondestructive Evaluation (ONDE) , a number of reports are included on related NBS work not supported by ONDE. Collectively, these

technical activities constitute the Bureau's NDE Program, which is managed

programmatically and administered on a Bureau-wide basis by ONDE.

The most common application of NDE is the characterization of cracks,

voids, inclusions, and other kinds of flaws in materials, components,

assemblies, and structures. This usage of NDE is the basis of modern inservice inspection procedures as applied, for example, to aircraft,

bridges, pipelines, and pressure vessels. Recognizing that NDE measurements must be reproducible and that modern NDE must be quantitative, a principal mission of the NBS NDE Program has been to provide traceability

for NDE measurements to national measurement standards. To this end,

research must be carried out to achieve an adequate understanding of the

physical basis of the NDE measurement techniques and procedures that

require standardization. Furthermore, the results of the Bureau’s research

and development work on NDE measurements must be applied to several specific and meaningful problems in order to demonstrate the validity of the

results and to help disseminate them to the user communities. Thus it is

possible to think of the NDE Program as comprising three types of activities: research, standardization, and applications.

During the last several years quantitative NDE has been applied by

industry to the measurement of material properties and characteristics such

as residual stress, texture, and various other microstructural features.

Such applications have been receiving increased attention because of the

nationwide effort to raise the quality of manufactured products. Clearly,

the ability to monitor important material properties and characteristics

during a manufacturing process can often be used to guide or to control the

process and, thus, to help avoid the manufacture of subquality products or materials. In response to these developments, the Bureau's NDE Program has

for a number of years sponsored work on the application of NDE to the measurement of materials properties and characteristics and more recently has

placed major emphasis on such measurements in regard to on-line monitoring

and process control in manufacturing. The reviews in this annual report

are arranged in the following major areas as a useful way to focus upon and

to summarize the Program: (1) NDE Standards, (2) NDE Methods for Internal

Flaw Characterization, (3) NDE for Interfaces and Composites, and (4) NDE

for Process Control. Each of these sections is preceded by an introduction. The area of NDE standards, a cornerstone of the NBS NDE Program,

includes calibration techniques, measurement procedures, document standards, and artifact standards. The work in area (2) deals with improving

or developing new NDE methods for quantitative flaw evaluation and te

determine suitability and reliability for specific applications. 3 r dealing with the measurement of properties for process control appear

( 3 ) and (4), where the motivation is primarily to provide a researcn • for application to process control. Area (3) deals with interfaces
surfaces, near surfaces, and coatings) and composites. Research on interfaces and composites has been highlighted because of the substantial technical importance of these subjects to industry. In addition, this focus

was selected because of the difficulty that is usually encountered in utilizing NDE techniques in these applications. Area (4) deals, in general,

with bulk properties for materials process control. For example, ultrasonics in metallurgical processing and NDE for ceramic processing appear in area (4).

Reports such as this one have been issued on an annual basis since 1978

and are commonly referred to as the "NBS NDE Annual Reports.” A parallel

series of reports, also issued annually, presents bibliographies and

abstracts for the Bureau's technical reports and publications on NDE and

its supporting technologies. The purpose of both of these report series is

to serve as an introduction to the Bureau's NDE Program. Many readers will

want further details on specific aspects of the work or its outputs, and

such inquiries are welcomed and encouraged, both by the principal NDE investigators (whose names and affiliations precede each of the articles in

the report) and by ONDE. Either can be addressed in care of NBS,

Gaithersburg, Maryland 20899, or reached by telephone via (301) 921-1000.

Requests for further information and suggestions regarding the Program

always receive prompt and careful attention.

2
I. NDE STANDARDS

The first section of this annual report covers activities on NDE

standards and includes work on calibration techniques, artifact standards,

measurement methods, and document or written standards. The articles in

this section are arranged by technique and include, for example, reports on eddy currents, ultrasonics, acoustic emission, x-ray radiography, and optical, thermal, and magnetic techniques. Although many of the research ac- tivities described in the nineteen articles in this section will have a positive effect on NDE technology, the first two reports on eddy currents

are of particular interest and importance. This research has been very

productive and should lead to a substantial improvement in eddy current

techniques

3
4
MEASUREMENT METHODS, CALIBRATION PROCEDURES, AND STANDARDS

FOR QUANTITATIVE EDDY CURRENT NDE

J. C. Moulder and J. C. Gerlitz

Fracture and Deformation Division

Institute for Materials Science and Engineering

and

B. A. Auld and S. R. Jefferies

Edward L. Ginzton Laboratory

Stanford University

INTRODUCTION

The objectives of this research program are to develop measurement

methods, calibration procedures, and standards appropriate to quantitative

eddy current NDE. Experimental studies at NBS-Boulder are carried out in

close collaboration with theoretical studies at Stanford University, a cooperative effort that has continued for four years.

Past efforts have included the development of high-frequency, broadband

eddy current probes for inspection of high-resistivity aerospace alloys, ref.

1, 2; studies on methods for calibrating eddy current measurement systems,

ref. 3; development of a new measurement technique that uses a precision

impedance analyzer to measure changes in eddy current probe impedance caused

by surface flaws, ref. 3, 4; design and construction of an automated eddy

current scanner operating in the 30-60 MHz frequency range, ref. 4; and

detailed comparisons of experimental eddy current flaw signals with

predictions of the Stanford model for the interaction of a nonuniform

probe-field with surface flaws, ref. 5.

During the past year we have extended our studies comparing theory and

experiment in eddy current testing to more practical situations. The aim has

been to introduce new features into the theoretical model to reproduce more realistic situations and then test the modified theory against controlled

experiments. In particular, we extended theory and experiment to the case of

low.-conductivity materials and began more extensive studies of real fatigue

cracks, as opposed to artificial flaws.

A number of other studies were also undertaken this year. A new calibration method was devised and tested for uniform-field eddy current

probes. The influence of probe characteristics on eddy current flaw si -'nil was studied in cooperation with researchers in CEEE’s Electromagnetic

Technology Division. The use of electrical-discharge-machined (EDM) not :

5
for artifact standards in eddy current testing was considered from both

experimental and theoretical perspectives. Finally, a new method for

monitoring fatigue crack growth has been developed in the course of

preparing fatigue cracks for our own use.

NEW THEORETICAL AND EXPERIMENTAL STUDIES

Extension of Theory and Experiment to Low-Conductivity Materials

In the present probe-flaw interaction theory, the assumption is made in

calculating the magnetic field inside the flaw that the walls are perfectly

conducting. Finite conductivity is then introduced later, in evaluating

the electric field inside the flaw. The same method is used in analyzing

transmission lines and waveguides with high-, but finite-conductivity

walls.

In many practical situations, the conductivity of the workpiece is

relatively low and the predictions of the present theory are open to question. Theory indicates that the magnitude of the flaw signal, AZ, is

inversely proportional to specimen conductivity. Thus, flaw signals from

low-conductivity materials are expected to be larger than those from highconductivity materials for equal skin depths and similar flaws.

To match the assumptions of theory as closely as possible, our past

studies were limited to highly conducting materials such as aluminum. This

year, we extended the comparison of theory with controlled experiments to

flaws in a titanium alloy. Experimental flaw scans were obtained for both

EDM notches and fatigue cracks in Ti-6A1 -MV using air core and ferrite core

probes. Similar-size flaws in aluminum alloy were measured for comparison.

The results of one such comparison are shown in Figures 1 and 2, where

the magnitudes and phases of the flaw signals from similar-size, semicircular EDM notches in titanium and aluminum alloys are compared. These mea- surements were taken with a ferrite core probe operating at 550 kHz scanned

along the length of the flaw. The magnitude of the signal is larger for

the flaw in titanium, despite the fact that the skin depth is about six

times larger in the titanium specimen. This result confirms the

predictions of theory qualitatively.

To make quantitative comparisons of theory and experiment it is

necessary to know the intensity and spatial distribution of the probe’s

magnetic field. This information, used to compute the flaw signal, can be

calculated from existing theory for air core probes, ref. 6. (Analytical

expressions for the magnetic field of ferrite core probes are not yet

available, although numerical methods have been devised.) When the results

of similar flaw signal measurements made with air core probes were compared

to the predictions of the nonuniform-probe-field theory, we found

quantitative agreement, within the uncertainty of the experimental

measurements, ref. 7,8.

Another prediction of the theory is confirmed by the results shown in

Fig. 2. In this figure we observe that the phase of the flaw signal for the

6
aluminum specimen does not vary significantly as the probe is scanned along

the flaw's length, but the phase varies continuously for the titanium

specimen. As shown by theoretical calculations, this effect is related to

the ratio of flaw depth to skin depth, a/5. When a/5» 1, as is the case

for the aluminum specimen, the phase of AZ varies little with flaw depth.

But as a/6 approaches unity, as occurs for the titanium specimen, the

effect of varying flaw depth on the phase of AZ becomes as strong as the

effect on the magnitude of AZ.

Calibration Method for Uniform-Field Probes

Calibration methods for eddy current probes are vitally important for

obtaining quantitative results from measurements. Especially important are methods for determining a probe's magnetic field intensity, since this

quantity enters into every calculation of probe response. Relatively few

of the probes actually used for practical inspections are amenable to

calculation of the field strength; we therefore must turn to measurement.

A new calibration method for uniform-field eddy current probes was devised and tested this year in collaboration with Dr. E. Smith of United

Technologies Research Center. The method consists of measuring the

impedance change, AZ, induced in a probe by a cylindrical recess of known

volume in the surface of a specimen of known conductivity. These

quantities can be related to the value of H/I for the probe, the magnetic

field strength per unit current, according to the expression.

AZ i A

2 *

I a where a is conductivity, A is the surface area of the recess, d its depth,

and i = /-I

To test this calibration method, three cylindrical recesses 1.6 mm in

diameter with depth of 0.01 3» 0.127, and 1.27 mm were fabricated by electrical-discharge machining in a specimen of IN-100 (a nickel super alloy

whose nominal composition composition is 60£ Ni, 1555 Co, 10% Cr, 5.555 A1

4.755 Ti, 355 Mo, and 156 Va). The specimen was then sent to Dr. Smith at

UTRC to be tested with a new uniform field probe he developed. His mea- surements on these calibration recesses showed that, except for the deepest

recess, he could obtain consistent calibration factors that subsequently

enabled him to compare experimental flaw measurements to the predictions of

Auld's uniform-field theory, ref. 9. For the deepest recess, the depth far

exceeded the skin depth so that the field could no longer be considered

uniform.

Eddy Current Probe Characterizat ion

We have already mentioned the importance of characterizing the intensity

and spatial distribution of a probe's magnetic field for quantitative eddy

current NDE. This fact has influenced our strategy of using air core pr

in experimental studies, since magnetic fields can be calculated for

type of probe, permitting the results to be compared with theory. Th«- of Dodd and Deeds that is used in calculating probe fields, ref. 6,

widely accepted as accurate, has not been compared directly to measured f

7
before. This year we have made such a comparison for the first time in

collaboration with T. Capobianco and F. Fickett of the Electromagnetic

Technology Division.

The impetus for such a study is illustrated in Fig. 3, which compares

experimental measurements made using two nominally identical air core probes

with theoretical predictions for a rectangular EDM notch in 606 1 aluminum.

The figure shows that the two probes give results that differ by about 30

percent, the theoretical prediction falling between the two experimental

curves. No explanation for this discrepancy could be found in measurements of

the probes' electrical parameters such as inductance, impedance, or resonant

frequency. X-rays revealed no difference in the physical construction of the

probes.

The magnetic fields of these two eddy current probes were mapped using

techniques developed by Fickett and Capobianco. The results showed that

differences in the flaw signals produced by the probes for the same flaw could

be traced to a ten percent difference in their field strengths, ref. 10. The

measured field distributions were compared to the predictions of the Dodd and

Deeds theory, with reasonably good quantitative agreement being observed.

In another experiment, field mapping was performed for a probe with a ferrite core. The measured field profile was then used as an input for

calculating flaw signals using the nonuniform-probe field theory. Calculated

flaw signals were in good qualitative agreement with measured flaw profiles.

This is the first time that this has been attempted, and it is a very

important step in extending quantitative techniques to practical probe

designs.

EDM Notches as Artifact Standards for Eddy Current Testing

In many industrial NDE applications, eddy current test instruments are calibrated with artifact standards — artificial flaws especially fabricated

to approximate the size and shape of actual flaws that are expected to occur. Often these artificial flaws are made by electrical-discharge machining (EDM).

The EDM process produces a flaw with a relatively larger opening and smoother

walls than real fatigue cracks.

Despite the fact that the artificial flaws differ markedly from actual

flaws, many practitioners assert that EDM notches are ''conservative”

calibration standards, meaning that such calibration flaws produce a signal

that is smaller than the signal from a real crack of the same length and depth.

Yet theoretical and experimental results we have obtained this year show that

in general, the exact opposite is the case: EDM notches have larger flaw

signals than real fatigue cracks. This point is illustrated in Fig. 4, which

shows the magnitudes of flaw signals from two closely matched flaws in

Ti-6A1-4V, one an EDM notch and the other a fatigue crack.

However, it must be recalled that most eddy current instruments do not measure the absolute magnitude of the flaw signal, but rather, the magnitude

of the signal in quadrature to liftoff in order to discriminate against

8
liftoff. In this case, it might indeed be possible for the signal from an EDM

notch to be smaller than one from a fatigue crack, but clearly the matter

requires a careful, critical examination. We have performed such a study this

year in cooperation with Mr. Ward Rummel of Martin Marietta Denver Aerospace.

The results of our study suggest that a great deal of caution must be

exercised when using EDM notches to calibrate eddy current 'instruments. We

found that for aluminum alloys, the conventional belief was reasonable: the

quadrature signal from an EDM notch was smaller than the quadrature signal

from a similar size fatigue crack. However, for titanium alloys, this was no

longer true. The difference in these two cases stems from the fact that the

phase of the flaw signal depends upon the value of a/5, the ratio of flaw

depth to skin depth, whereas the phase of the liftoff signal depends on r/5,

the ratio of the mean radius of the probe coil to the skin depth. Therefore,

for any given probe there will always be some value of flaw depth below which

an EDM notch no longer gives a "conservative" calibration.

Eddy Current Monitoring of Fatigue Crack Growth

To provide well characterized fatigue cracks for our own studies, we developed methods for growing fatigue cracks in a predictable, reliable

fashion this year. We have shown that a reflection-type eddy current probe

can be used to monitor the growth of the crack, rather than the customary

crack mouth opening displacement (CMOD) gauge, which is less sensitive and

requires very large starter notches. The reflection probe used was demonstrated to have an output that is linear with flaw cross-sectional area. The length of the flaw can be determined by scanning the probe along its

length. Having the length and' area of the flaw permits determination of the

depth more reliably than can be done from CMOD measurements.

SUMMARY

This year we have extended comparisons of theory and experiment in eddy

current testing to low-conductivity specimens and fatigue cracks to more accurately model real test situations. In collaboration with our colleagues

in the Electromagnetic Technology Division, new studies were undertaken

showing that characterization of eddy current probes by magnetic field mapping

is a useful adjunct to experimental flaw measurements. The use of EDM notches

for eddy current calibration standards was investigated both experimentally

and theoretically, demonstrating that such standards must be used with caution.

In addition, a new calibration method for uniform field probes was developed

and a new method for monitoring fatigue crack growth was demonstrated.

Future studies will focus on comparing theory and experiment for

reflection probes, a much different type of eddy current probe than the

absolute probes we have studied to date. We also plan further studies on the

uniform-field calibration method to determine its accuracy and limitations.

9
REFERENCES

1. C. M. Fortunko and S. A. Padget, "High-Frequency, Broadband Eddy Current

Probes for Improved Flaw Characterization," in "Technical Activities 1982

Office of Nondestructive Evaluation," H. T. Yolken, editor, NBSIR 82-2617

(Dec. 1982).

2. C. M. Fortunko, J. C. Moulder, J. C. Gerlitz, A. C. Bennett, B. A. Auld,

and F. G. Muennemann, "High-Frequency, Broadband Eddy Current Probes for

Improved Flaw Characterization," in "Technical Activities 1983 Office of

Nondestructive Evaluation," L. Mordfin, editor, NBSIR 84-2815 (Dec.

1983).

3. J. C. Moulder, J. C. Gerlitz, B. A. Auld, M. Riaziat, S. Jefferies, and

G. McFetridge, "Calibration Methods for Eddy Current Measurement

Systems," Review of Progress in Quantitative Nondestructive Evaluation

4A, pp. 411-420 (Plenum, 1985).

4. J. C. Moulder, J. C. Gerlitz, B. A. Auld, M. Riaziat, S. Jefferies, and

G. McFetridge, "Eddy Current Characterization of Surface Flaws," in

"Technical Activities 1984 Office of Nondestructive Evaluation," L. Mordfin, editor, NBSIR 84-2944 (Nov. 1984).

5. B. A. Auld, G. McFetridge, M. Riaziat, and S. Jefferies, "Improved

Probe-Flaw Interaction Modeling, Inversion Processing, and Surface

Roughness Clutter ,Review of Progress in Quantitative Nondestructive

Evaluation 4A , pp. 623-634 (Plenum, 1985).

6. C. V. Dodd and W. E. Deeds, "Analytical Solutions to Eddy-Current

Probe-Coil Problems, "J. Appl. Phys. 39 , No. 6, pp. 2829-2838 (May 1968).

7. B. A. Auld and S. Jefferies, "Semi-Elliptical Surface Flaw EC Interaction

and Inversion: Theory," Review of Progress in Quantitative

Nondestructive Evaluation 5 , to be published.

8. J. C. Moulder, J. C. Gerlitz, B. A. Auld, and S. Jefferies,

"Semi-Elliptical Surface Flaw EC Interaction and Inversion: Experiment,"

Review of Progress in Quantitative Nondestructive Evaluation 5 , to be

published.

9. Eugene Smith, "Application of Uniform Field Eddy Current Technique to 3-D

EDM Notches and Fatigue Cracks," Review of Progress in Quantitative

Nondestructive Evaluation 5 , to be published.

10. T. E. Capobianco, F. R. Fickett, and J. C. Moulder, "Mapping Eddy Current

Probe Fields with a SQUID Magnetometer," Review of Progress in

Quantitative Nondestructive Evaluation 5, to be published.

10
MAGNITUDE

OF

AZ,

ohms

«tv

Figure 1. Magnitudes of the flaw signals obtained by scanning a ferrite core eddy current probe along the lengths of two semicircular artificial

flaws, one in Ti-6A1-4V apd one in 6061 Al. The flaw in the

titanium specimen was 3.15 mm long, 1.58 mm deep, and 0.43 mm wide.

The flaw in aluminum was 3.48 mm long, 1.74 mm deep, and 0.25 mm wide. The abscissa represents the position of the probe relative

to the flaw center, normalized by the mean probe radius.

Measurements were taken at 550 kHz.

11
MAGNITUDE

OF

AZ,

ohms

Figure 2. Phases of the flaw signals from the same two flaws in titanium and

aluminum alloys shown in Fig. 1

X/ Tjjvg

Figure 3 . Comparison of theoretically predicted eddy current flaw signal

(solid line) with experimental measurements made with nominally

identical air core probes. The flaw was a rectangular EDM notch in

6061 Al, 3.90 mm long, 1.17 mm deep, and 0.20 mm wide.

12
MAGNITUDE

OF

AZ,

ohms

Figure 4. Magnitudes of experimental flaw signals for a semicircular fatigue

crack and an EDM notch of similar size in Ti-6A1-4V. Measurements

were made with a ferrite core probe operating at 550 kHz.

13
EDDY CURRENT COIL CHARACTERIZATION

T. E. Capobianco and F. R. Fickett

Electromagnetic Technology Division

Center for Electronics and Electrical Engineering

INTRODUCTION

The major goal of this program is the investigation of experimental techniques for accurate characterization of eddy current test coils and determination of the effect of various coil defects or disturbances on the coil’s

electromagnetic signature. A unique feature of this characterization is that

it is made independent of the presence of a work piece. Such information is

necessary in two areas of eddy current NDE, the field evaluation of commercial

coils and the more esoteric problem of determining the interaction between an eddy current coil and a defect. In the first instance, we hope to develop a standard test method and, perhaps, a field-usable system for rapid prediction

of coil performance and, in the second, a technique for accurately mapping the near field of a coil. In this report we briefly describe our accomplishments

in both of these areas in FY 85 along with other interactions related to the

project. More technical details on the work can be obtained from the referenced publications.

ELECTRICAL PARAMETER CHARACTERIZATION

Last year's efforts were concerned with measuring variations in electrical

parameters in production run coils. We concluded that these variations were

not large enough to cause a probe to be unusable so we now have turned our attention to examining commercial probes which are known to be defective. We

obtained a collection of these defective eddy current probes from the Air

Force. We then measured the inductance, resistance and self-resonance of the

probes. As part of this evaluation we constructed a test circuit to run the

probes near their normal operating frequency and to allow measurement of

resonant frequency and impedance. This last test appears to be a promising

one for predicting coil sensitivity and is being evaluated further. The data

for the 5/16" bolt hole probes could indicate a connection between resonance

amplitude and defect sensitivity, but the sample population is too small and

the documentation is insufficient. The test circuit has been incorporated

into an automated system in anticipation of receiving more probes for evaluation. We are now trying to obtain more sample probes, both defective and

acceptable, for these measurements. Preliminary resonance measurements are tabulated in Table 1 and compared to the comments in the Air Force documentation received with the defective probe samples.

All of these probes are run close to resonance in service. It should be

pointed out that a rejected probe does not necessarily have poor sensitivity

to flaws. Defects in its physical construction can also be a cause for

rejection. The probes that we tested were all such that the coil can be seen. Other designs frequently encase the coil in a plastic rod and then non-optical

methods must be used to look for misalignment or other mechanical defects.

14
Table 1. Resonant frequency and amplitude measurements of defective probes

PROBE RESONANT

FREQ. (kHz)

IMPEDANCE AT

RES . (ohms)

A. F. DOCUMENTATION

5/16" bolt hole probes

6 135 194 "sensitivity very poor"

16 157 195 "unacceptable due to

insensitivity"

18 141 227 "too insensitive"

misc 90 338 "noisy" (no comments

about sensitivity)

3/16" bolt hole probes

20 93 393 "excellent

sensitivity"

52a 87 391 no documentation

52b 88 298 no documentation

52c 71 401 no documentation

52d 89 296 no documentation

One issue we have discussed with workers in the field but have not yet

addressed in our research is the claim of "polarity" problems with some ferrite core probes. Our speculation is that there may be a capacitive

coupling effect between the turns of the coil immediately adjacent to the

ferrite and the core itself. If the coupled lead is not connected to instrument ground, this undesirable coupling could be showing up as noise in the

output. The services have apparently a de facto instrument for day-to-day eddy

current work. It is not especially elaborate in design in light of modern

electronics, but it has proven to be dependable and is relatively inexpensive.

We have made numerous attempts to borrow one of these for our test program

with no success. We feel that certainly some of the problems causing the

rejection of large numbers of probes may have to do with interfacing to this

instrument. There is an indication from our interactions in recent months

that the services are tending to increase the sophistication of their NDE

techniques to a significant degree with the addition of computer controlled

systems. Many of the probe problems may be resolved by this change; or they

may become even more severe as the demands on the probes increase.

15
FIELD MAPPING STUDIES

Our work this year has been concentrated on producing very small inductive pickup coils and on making instrumentation improvements. The reduction

in the size of the search coils from that of our earlier work [1] has been

considerable and this is reflected in the turns-area product (nA) of the

co^ls. The search coil used in the work previously reported ^as an nA of 226 mm . The coils we are currently using have an nA of 0.823 mm . This is good news from the standpoint of scanning resolution, but it has required significant advances in our electronics because of much smaller signal levels.

In our efforts to develop the smallest possible hand-wound search coils

we encountered the problem that, as the coil size decreased, stray electromagnetic interference approached the expected signal size and, in some cases,

could completely obscure the signal. Our noise studies showed that two

factors were the largest contributors to this pickup. They were the presented

area between the leads and the presented area at soldered joints in the leads.

In order to minimize these problems two major improvements in coil design were

implemented: (1) the leads are wound with a very tight twist pitch; and (2) no joints are allowed between the leads and the coil. The leads from these

small coils are 25 cm twisted pairs of #44 copper wire with a twist pitch of

five turns per millimeter. The outside diameter of the coils is 0.43 mm and

the inside diameter is 0.20 mm.

Shielding studies were also made on the SQUID system in order to improve

the detection sensitivity. RF interference is a serious problem with these

devices under the best of conditions and, in our application where we are introducing the signal from room temperature, the problems are greatly magnified. Our work showed that by careful shielding of input leads to the dewar,

use of superconducting shields for the SQUID pickup transformer, and proper

adjustment of the input coupling to the SQUID itself, we could increase our sensitivity by more than an order of magnitude over that reported last year.

Measurements were made comparing the improved SQUID system to more

conventional electronics with our new small coils as input. We found that,

while the SQUID system offered some advantages in sensitivity, its limited

dynamic range and frequency response, coupled with the requirement of liquid

cryogens makes the system cumbersome and difficult to use. It is our (somewhat

surprising) conclusion that, with its present limitations the SQUID is probably

not the instrument of choice for measuring the relatively large ac magnetic

fields used in NDE at frequencies in the kilohertz range or greater. Simpler,

more conventional, methods are available. We should mention that SQUID

technology is still in its infancy and the electronics is being improved and

expanded in frequency range at a great rate. Unfortunately, delivery of the

newly purchased upgraded state-of-the-art electronics package for our system

has once again been delayed by a few months.

On the other hand, there are applications such as low frequency ac or dc

field detection with multi-axis gradiometer coils or detection at large

distances from the testpiece which would be difficult if not impossible to do

with any device except a SQUID. These areas are still unexplored territory in

NDE.

16
All of the data presented here were taken with a very sophisticated (and

expensive) lock-in amplifier system, although the SQUID-based system would

have served as well. With the lock-in system we have also had to make improvements over our original design including using differential inputs to the

amplifier and extensive shielding of the leads and all joints.

Two field mapping sensors were built. One is positioned to sense the

field parallel (tangential field) to the face of the eddy current probe and

the second measures the field perpendicular to the face (axial field)

Separate scans are required for each component. In each case the leads have

the same orientation with respect to the axis of the probe holder. This

allows us to scan two orthogonal components of the magnetic field of the eddy

current probes without changing the orientation of the search coil leads in

the eddy current probe field. As expected, this makes the lead pickup signal

nearly the same for the two coils. The positioner developed for these measurements is a stepping motor scanning system developed jointly with CMS. The

positioner itself allows us to radially scan a given eddy current coil at a any number of angles. The usual scan sequence is: first from the center of

the coil to beyond the outer radius; the . eddy current coil is then rotated

through 180 degrees and the radial scan repeated; a 90 degree rotation and scan is then followed by another 180 degree rotation and scan. When this is

done with both field sensors, a fairly comprehensive field profile is achieved.

Computer drive of the scanner and processing of the input data greatly reduces

the time involved.

Another device built in our laboratory is used to calibrate the pickup

coils. This is a relatively simple, but carefully constructed

, ^Helmholtz pa^r

with a coil radius of 2.9 cm and a field constant of 384 ± 4 m (4.83 0e*A ) which allows calibration of our pickup coils in uniform fields at the operating

frequencies.. The coils just mentioned have calibration constants near 6.4 x

10 yV*m*A (5.1 yV'Oe”; at 10 kHz.

In our latest series of measurements we mapped the fields produced by the

following four eddy current probes:

2 air core absolute probes;

1 ferrite core absolute probe;

1 differential or gradiometer probe

with ferrite core pickup coils.

The two air core absolute probes were nominally of the same construction, but

during use it was found that the response of the two probes varied by as much

as 30% when they were scanned over the same defects [2]. Field profiles of

the probes showed no significant differences in the spatial distribution of

the field, but the magnitude of the tangential field component varied by 10%

for the same level of probe excitation current. The tangential field profiles

are shown in Fig. 1. The variation of the axial component was 23%, but this

large effect is probably partially the result of liftoff differences of the sensor coil during the two scans. At present our positioning system lacks

precision in this dimension and the fields fall off very rapidly with increasing liftoff.

The tangential field data for the two air core probes were compared te

values calculated using the theory of Dodd and Deeds [3] with the results

17
shown in Fig. 2. The theoretical calculation was made for a liftoff of 0.7 mm

which is the built in liftoff of the coils of each eddy current probe (0.5 mm)

plus one sensor coil radius (0.2 mm). The figure shows good agreement in the

field distribution between theory (dashed) and experiment (solid) . The peak

values of the two experimental curves vary by 10% and the peak of the lower

experimental curve is within 20% of the calculated value. We consider the

agreement to be quite good given the uncertainties involved. We compared the

field distribution of the ferrite core probe to that of the two air core

probes. The average radius of the ferrite core coil is 1.9 mm. This is

slightly larger than the radius of the air core coils which is 1.6 mm. Fig. 3

is the plot of the normalized data. The sensor positional data (R) is normalized to the individual coil dimensions (R ave) and the radial field [H(r) in

A/mm] is given per unit of coil excitation current (A). The peak field

strength of the air core probes occurs at 1.41. The field concentrating

effect of the ferrite is evident in the larger magnitude and also the tighter

field pattern of the ferrite core probe. Its peak value occurs at 0.90.

The last probe in this group is a differential, or gradiometer, probe.

Its construction is shown in Fig. 4. It consists of an outer air core excitation coil and two inner ferrite core pickup coils which are connected in

series opposition. Field mapping results are shown in Fig. 5 for both tangential and axial field scans. On each graph, one scan is made across the face

of one of the ferrite core pickup coils and the other on a path between the

two. The pickup coils are open circuited for this measurement; power is to

the excitation coil only. Clearly, the field produced by the air core excitation coil is distorted by the ferrite cores of the pickup coils.

SUMMARY

It is clear from this work that field mapping of eddy current probes can detect differences in probes of supposedly identical construction. Field

profiles of ferrite core probes are difficult to calculate, but are necessary

information for quantitative flaw inversion work. Using our techniques, these

profiles can be measured directly. Better shielding methods have allowed us

to use search coils with areas that are several orders of magnitude smaller

than those we have used in earlier work. As a result, the resolution of our

scans is improved and field maps of eddy current probes are obtained with

relative ease. Greater detail on all of these topics is available in one of our recent papers [4].

COLLABORATIVE EFFORT WITH CMS

An informal joint effort was started this year with John Moulder of CMS

to investigate the application of our field mapping system and techniques to

the detection and sizing of actual flaws. For these experiments, we used the

differential or gradiometer eddy current probe described above (Fig. 4) to

measure several flaw specimens. Two well-received papers were presented at

conferences earlier this year as a result of this effort [5,6]. The differential probe was found to have an accurately linear response to flaw area

(length x depth) as shown in Fig. 6.

18
WIRE ROPE NDE

At the request of ONDE, Fred Fickett participated in a meeting at NBS

(Gaithersburg) in late September with J. Kharnak of the Bureau of Mines

regarding the use of magnetic techniques to detect incipient failure in the

wire rope used in mining operations. As a result of that meeting, a short

proposal outlining our thoughts on research needed in this area was prepared

and presented to the Bureau of Mines in October. In April, at the request of

OSHA and USBM, Tom Capobianco attended a meeting at the Department of Labor,

Mine Safety and Health Administration, Denver office on the NDE of wire rope.

The group, consisting of interested persons from both industry and government,

agreed to form a committee whose purpose would be to develop retirement

criteria for wire rope based on nondestructive test methods. Future meetings

are being planned, but our participation is uncertain since no funding is yet

forthcoming from USBM and magnetic testing is not the main thrust of our ONDE-sponsored research program.

REFERENCES

1. F. R. Fickett and T. E. Capobianco, "Magnetic Field Mapping With a SQUID

Device, "Review of Progress in Quantitative Nondestructive Evaluation

4:401 (Plenum, 1985).

2. J. C. Moulder, J. C Gerlitz, B. A. Auld, and S. Jeffries, "Semi-Elliptical

Surface Flaw EC Interaction and Inversion: Experiment," Review of

Progress in Quantitative Nondestructive Evaluation , Vol. 5, to be

published.

3. C. V. Dodd and W. E. Deeds, " Analytical Solutions to Eddy-Current Probe - Coil Problems," J. Appl. Phys. 39:2829 (1968).

4. T. E. Capobianco, F. R. Fickett and J. C. Moulder, "Mapping of Eddy

Current Probe Fields," Review of Progress in Quantitative Nondestructive

Evaluation , Vol. 5, (1986). To be published.

5. T. E. Capobianco, J. C. Moulder, and F. R. Fickett, "Flaw Detection with a Magnetic Field Gradiometer," Proceedings of the 15th Symposium on Nondestructive Evaluation . In press.

6. J. C. Moulder and T. E. Capobianco, "Detection and Sizing of Surface Flaws

with a SQUID-Based Eddy Current Probe," Review of Progress in Quantitative

Nondestructive Evaluation , Vol. 5, (1986). To be published.

19
H(r)/I

(mm

-1)

H(r)/I

(mm

-1)

aor

1.0 20 ao

POSITION (mm)

4.0

Figure 1. Reduced field parallel to the probe face for two

nominally identical probes.

Figure 2. Comparison of a theoretical calculation of the probe

fields with the experimental data of Fig. 1.

20
Figure 5a. Tangential field profile

of the differential probe.

Figure 5b. Axial field profile of the

differential probe.

Figure 6. Linear relationship of signal amplitude to

flaw area using the differential probe.

22
Figure 3. Comparison of field measurements of air core and

ferrite core probes.

Adjustable

Ferrite Slug

Excitation Coil

Figure 4. Cross-section of the differential probe.

21
STANDARDIZATION OF EDDY CURRENT CONDUCTIVITY MEASUREMENTS

George M. Free

Center for Basic Standards

National Measurement Laboratory

A program on eddy-current standards was initiated in the Office of

Nondestructive Evaluation. Since April 1, 1985, the Electricity Division,

Center for Basic Standards, has offered a new service in which electrical

conductivity reference standards for use in calibrating eddy current con- ductivity meters are measured at 20°C. Standards tested at the present

time are in the range from 15? IACS (International Annealed Copper Standard) to 100? IACS. The range will be extended down to 1? IACS by January

1986. Standards are measured at frequencies in the range between 10 kilohertz and 100 kilohertz, depending on their nominal IACS rating. Special

arrangements can be made for calibrating standards at user-specified frequencies for the calibration of fixed-frequency conductivity meters. The

standards are tested for uniformity of electrical conductivity over the

surface to be calibrated and conductivity reported is that measured at the

center of this surface. Standards to be tested must be non-magnetic and

have a specified geometry.

The 1984 Annual Book of ASTM included for the first time El 004-84,

Standard Test Method for Electromagnetic (Eddy Current) Measurements of

Electrical Conductivity. This recommended practice was developed by ASTM

Committee E-7 on Nondestructive Testing. The test method describes a procedure for measuring the electrical conductivity of nonmagnetic metals

using the electromagnetic (eddy current) method and commercially available

electrical conductivity instruments. Eddy-current measurements of electrical conductivity are widely used in industry for the sorting of metals with

respect to variables such as type of alloy, aging, heat treatment, corrosion, etc. This recommended practice should go a long way towards ensuring

that an individual worker makes such measurements in a reproducible manner

and that the results obtained by different workers are consistent.

23
ULTRASONIC ABSOLUTE-POWER TRANSFER STANDARDS

F.R. Breckenridge, S.E. Fick and C.E. Tschiegg

Mechanical Production Metrology Division

Center for Manufacturing Engineering

A transfer standard comprising a new^ type of transducer and suitablycustomized electronics has been developed to optimize the transfer of NBS

measurements of total radiated power in liquid media. With earlier transfer

standards, procedures necessary for the transfer of calibration constituted

sources of error comparable in magnitude to those of the underlying primary

measurement of ultrasonic power. The new transfer standard uses a transducer

with built-in rf metering circuitry; electronics embodied in the impedancematching unit provided with each transducer allow the field user to obtain a pre-determined level of ultrasonic power by making a single measurement of dc

voltage. Since the new procedure obviates the two absolute measurements of rf

voltage and two calculations required by earlier procedures, the significant

errors of the earlier procedures are precluded. The new transducer, unlike

its predecessors, is capable of high output at high-order harmonics, so that a single unit can be used to obtain more than a watt of ultrasonic power at

frequencies spanning 20 MHz in 1 MHz increments.

After the completion late in 1983 of two years of prototype testing,

fabrication of transfer standards slated for eventual distribution by the

Office of Standard Reference Materials (OSRM) was begun. Testing of the ten

calibration systems comprising the first "production run" began in April,

1984. Each system will be tested periodically until it is dispensed by OSRM.

As of March, 1985, data for the ten units indicates that errors in transferring NBS measurements of ultrasonic power to the field user should not exceed

0 . 5 %. The comparable component of error when other methods of transfer are used is typically ten times larger. Further analysis of the results of some

1000 measurements made on prototype and production transducers over a threeyear period has established that the previously-unknown long-term stability of

transducers using lithium niobate is indistinguishable from the well-known

high stability of quartz transducers.

SUMMARY

A new "universal" ultrasonic power transfer standard has been developed

and is available from NBS. The transducer and custom electronics eliminate

all of the difficult user’s problems previously identified with the transfer

of NBS measurements. The new device and transfer procedures also decrease the

uncertainty of the transfer by an order-of-magnitude to 0 . 5 %. Over 1000 tests

have established good stability for the device.

REFERENCE

1. S.E. Fick, F.R. Breckenridge, C.E. Tschiegg, and D.G. Eitzen, "An

Ultrasonic Absolute Power Transfer Standard," NBS J. Res. 89 , No. 2,

pp 209-212 (March-April 1984)

24
ULTRASONIC ARTIFACT CALIBRATION METHODOLOGY

G. V. Blessing and D. G. Eitzen

Mechanical Production Metrology Division

Center for Manufacturing Engineering

INTRODUCTION

The Ultrasonic Standards group of the National Bureau of Standards has an on-going responsibility for the improvement of ultrasonic reference block

calibration methodology. As part of this project, the Office of Standard

Reference Materials has supported an effort to improve block uniformity by

purchasing a special lot of aluminum bar material (nominally 2 inch diameter),

manufactured under specially controlled conditions which included a heat

treatment process to specifically enhance wave propagation performance.

Ultrasonic tests are being made on this material lot to determine the degree

of (scattering and elasticity) homogeneity as a function of bar extrusion

position.

DISCUSSION

Five material specimens were chosen for detailed comparison studies:

four (three heat-treated and one non-heat-treated) from the special material

lot, and one from a (reference) lot of known good ultrasonic material. A set

of four shorter bars, varying in length from 1.25 to 6.00 inches,- was sectioned from each specimen to provide the needed amplitude and elasticity data

for wave propagation parallel to the bar axis. Using the pulse-echo

ultrasonic system prescribed in the ASTM El 27 document, metal-path-distance

amplitude relationships were obtained before and after drilling the on-axis

5/64 inch diameter flat-bottom-holes that act as ultrasonic echo gages.

Prior to hole drilling, distance-amplitude data for the bars taken from

the special materials lot did not show the expected monotonically decreasing

amplitude relationship with increasing bar length. As a result, detailed

ultrasonic scans across the bars were performed to elucidate the peculiar

behavior of the special lot material, of which the heat-treated samples showed

the most prominent effects. Figures 1 and 2 illustrate the difference,

respectively, between the reference and heat-treated materials. The anomolous

peak in the center of Fig. 2 is conjectured to be the result of material

inhomogenity due to a preferred crystallite orientation that inadvertently

resulted from the extrusion process. Elasticity measurements of the longitudinal wave velocity revealed a small (0.3 %) difference between the heattreated and the other materials. This was not considered significant.

Subsequent to hole drilling (making ultrasonic blocks) the peculiar

distance-amplitude relationships for the blocks fabricated from the spec! allot material (expectedly) persisted. As a result, preliminary analysis of

25
these data indicates this material lot is not suitable for the orginally

intended purpose of fabricating blocks with uniform ultrasonic properties to

also satisfy the requirements of ASTM El 27.

SUMMARY

ASTM requested that NBS become a source of "certif ied" raw stock which is

suitable for making flat-bottom-hole ultrasonic reference blocks to satisfy

ASTM El 27 Standard Practice. A large quantity of specially produced and heat

treated aluminum rod was obtained and evaluated. The ultrasonic response of

the raw stock was found to be anamolous and produces reference blocks with an inappropriately high reference signal.

Figure 1. Ultrasonic pulse-echo amplitude data of good (reference) solid

bar material six inches in length, scanning in the X-direction

and incrementing in the Y-direction. Wave propagation (at 5 MHz)

is parallel to the bar axis, with the relative amplitude proportional to the echo amplitude from the back surface (base) of the

bar.

26
Figure 2. Same as Figure 1, but of a heat-treated bar from the special

. material lot.

27
DOCUMENT STANDARDS FOR ULTRASONICS AND ACOUSTIC EMISSION

D.G. Eitzen and F.R. Breckenridge

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The goal of this project is to produce MIL-Standards and/or ASTM

Standard Practices covering basic areas of ultrasonics and acoustic emission.

This project has been supported by the Army Materials and Mechanics Research

Center, and, recently, partially supported by Navair.

One task is to develop "precise and consistent terminology for acoustic

emission test methods and procedures." Over 16 documents were used to develop

a data base for terms and definitions. About 37 terms were selected and

defined. These terms and definitions were successfully coordinated with the

three military services. As a result MIL-STD-1 945, "Glossary of Terms and

Definitions for Acoustic Emission Test Procedures" was published near the end

of 1984. ASTM Section E7.04.01 on AE Glossary is considering the terms for use in their glossary.

Another task is to "develop appropriate and precise terminology for

ultrasonic test methods and procedures using resources such as ASNT, ASTM,

ASME and military publications." In carrying out this task over 30 documents

were reviewed and a data base of terms and competing definitions were

organized. About 115 terms and definitions were proposed for a MIL-STD. This

draft MIL-STD is undergoing a second round of coordination among the three

military services. The terms and definitions are also being used as the basis

for a revised ASTM E500 Standard Definition of Terms Related to Ultrasonic

Testing. Some of these terms are now being balloted at the ASTM Society

level.

The task on MIL^Standards on acoustic emission transducer calibration is

also proceeding well. A draft MIL-document on the primary calibration of AE sensors has been delivered to the Army but alternative publication mediums are being discussed. This draft formed the basis of an ASTM Standard Method on

the Primary Calibration of AE Sensors. The ASTM document is currently being

balloted at the subcommittee level, having successfully passed an ASTM section

ballot. A standard on the secondary calibration of AE sensors is also being

developed. This document is envisioned as covering two or three alternative

techniques. A technical outline of one technique has been drafted and

distributed. A second technique may closely parallel the primary method.

Future plans call for the drafting of standards documents on secondary

calibration of AE sensors and on the use of Hsu (pencil) AE source simulator.

A MIL-document on characterization of ultrasonic transducers is also being

considered.

SUMMARY

One MIL-STD has been published and two draft MIL-STD's prepared on AE

ultrasonic methods. Two ASTM Standards based on this work are in the approval

process.

28
VECTOR TRANSDUCER CALIBRATION

Christian D. Turner, H. N. G. Wadley, and J. A. Simmons

Metallurgy Division

Institute for Materials Science and Engineering

For many acoustic emission applications it is necessary to determine

both the vertical and horizontal sensitivity of acoustic emission transducers. Indeed, partial knowledge of transducer sensitivity is not only

incomplete, but can be misleading. A theoretical formulation was presented

in last year’s report for deducing the complete sensitivity of a transducer

to displacement along all three coordinate axes. A simple formulation was also given which allows one to calibrate the relative horizontal to vertical sensitivity of an acoustic emission transducer assuming linear supraposition of response across the line of the transducer and a diameter of

approximately 15 mm or less. This year we report on the experimental

results for this simplified method.

In the configuration shown in Figure 1, the y 1 and y 2 axes lie on the

plane of a plate, while the y 3 axis (not shown) is vertical to the plate.

A horizontal force F is applied in y-, direction and produces both

horizontal and vertical responses in that direction, while producing only

horizontal responses along the transverse, y 2 , direction. For the

configuration shown, the motions of the transducer and the Green’s tensor

components are given in the rotated x.,

, x 2 coordinate system by:

= FG-|

i Cos 9 U

2

= FG22 Sin 9 U

3 = FG^-] Cos 9

where the Heaviside Green's tensor functions are shown in Figure 2 for a 100 mm distance on a 4140 steel plate of 3^.16 mm in thickness. We

recall that the first Green's tensor component refers to the direction of

response motion while the second component refers to the direction of

an applied force. We shall be concerned, however, only with the front end

or P & PP components of the signal, which are little affected by the

thickness of the plate (unless the plate becomes much thinner).

Even for transducers of finite size, the vertical displacements are of

opposite sign either side of 9 = 90°. Thus to a first approximation the

vertical stimulus presented even to a finite diameter transducer at that

position will be null. For a transducer which has purely vertical

response, we then expect the magnitude near the P wave arrival to behave

ascosine 9. A poled horizontal transducer with its pole at <f> = 0 will

display a similar cosine 9 dependence, while with the pole at 4> = 90°, the

dependence will behave as sin 9, although the magnitude will be less due to

the smaller value of G22 vis-a-vis Gi i .

29
A schematic drawing of the experimental apparatus is shown in Figure 3.

A 4140 steel disk 400 mm in diameter and 34.16 mm thick was used as the

test medium. The surface of this disk was machined down leaving a pin 1.75 mm in diameter and 3 mm high in the center of the disk. The surface was

then optically polished and mounted on a teflon ring in a rigid aluminum

block. The disk could be fully rotated through 360°. Both the disk and

the aluminum support block were marked so that the degree of rotation was known. The loading was accomplished by breaking a .5 mm lead horizontally

across the pin. The lead was suspended just above the surface to minimize

rotation moments.

Figure 4 shows the amplitude of the first wave arrival as detected by a capacitive transducer and plotted as a function of rotation angle. Since

the transfer function of this type of transducer is easily calculable, the

signal voltages were converted to absolute surface displacements in

picometers. The data agrees well with the dashed theoretical curves. The curve of first wave arrival versus 9 is shown in Figure 5 for an NBS type

conical transducer. Within the measurement accuracy of this experiment, no horizontal sensitivity can be seen. Given the signal to noise ratio of

this experiment, the vertical to horizontal sensitivity for this type of

transducer appear to be greater than 20:1.

Figure 6 and 7 show similar polar plots for a commercial shear

transducer with two different orientations <j>, and <J> 2

= <j>-| + 90°, where the

angle <j> was set to approximately agree with the poling direction of the

transducers. These plots show first wave arrival behavior offset by nearly

90°. The discrepancy in the signal strengths for each orientation can be

explained by noting that G-n

H>G22n . The cf> 2 plot indicates that this

transducer has little vertical sensitivity.

H

SUMMARY

We have demonstrated a simple method for estimating the vertical-tohorizontal sensitivity of an acoustic emission transducer. In order to

quantitatively predict the horizontal transfer function of an AE transducer

in more detail, a careful evaluation of the force function generated by the

horizontally breaking lead is required. This work is in progress. The

robust deconvolution methods we have implemented are relatively insensitive

to the particular form of this force function and should allow us to complete a quantitative determination of the transfer function.

REFERENCES

1. J. A. Simmons and H. N. G. Wadley, "Vector Transducer Calibration,"

Review of Progress in Quantitative Nondestructive Evaluation , Vol. 3B,

ed. by D. 0. Thompson and D. E. Chimenti, pp. 699-706, Plenum

Publishing Co., 1984.

30
Figure 1

yj

X,

\\\

Geometry and notation. All vectors drawn are in the plane of

the plate.

31
e

©

o©

co

oo

ui

uiuioon«Nlfl/uiui U! siueiuaoeidsia ISO

uilliqo i ibniN/ujuj ui s}ueui808|ds!0 330

o

«

</)3. C

0

uuujqoi. IBNW/LUUJ UI siuauiooeidsiQ UO

32

Figure

2.

Heaviside

green's

tensor

components

used

in

this

technique.

The

first

subscript

refers

to

the

direction

of

the

displacement

and

the

second

to

the

direction

of

the

force.
Vertical

Surface

Displacement

(pm)

16” Steel disc

Figure 3. Schematic diagram of the experimental arrangement.

—30r

• Experimental

Theoretical

-20

• \

—10

r\

\• \

45

\•

N\90

-Jr

•/

/ • to /

135 180 225 270/ 315 360

f

/

to —10

—20

\• \ • y

V

-30 LFigure 4. Magnitude of first wave arrival as a function of rotation ang.--,

0 for a capacitive transducer.

33
0

Figure 5. Polar plot of magnitude of first wave arrival versus 9 for an NBS

conical transducer. This plot

was independent of the angle <j>. Plus or minus signs indicate

direction of motion.

180

Figure 6. Polar plot of magnitude of first

wave arrival versus 9 for a shear

transducer with <p = <p-j oriented

along the poling direction. Plus

. or minus signs indicate direction

of motion.

o

Figure 7. Polar plot of magnitude of first wave arrival versus 9 for a shear

transducer with <j> = + 90 °. Plus of minus signs indicate

direction of motion.

34
DYNAMIC DISPLACEMENT TRANSDUCERS FOR ACOUSTIC EMISSION

T.M. Proctor, M. Greenspan, and D.G. Eitzen

Mechanical Production Metrology Division

Center for Manufacturing Engineering

INTRODUCTION

Transducers which measure dynamic surface displacement with high sen- sitivity and fidelity are being developed and modeled. Such transducers are needed as transfer standards for the secondary calibration of acoustic emission sensors, as a tool in developing signal processing techniques to

characterize acoustic emission sources, and as transducers for field

applications. Both the normal and tangential components of motion must be

measured to describe the dynamic displacement at a point on a surface. We

previously had developed the NBS conical transducer which measures the normal

component of displacement with a sensitivity of approximately 10 ^ meter.

This transducer is flat in frequency response from kilohertz to a few

megahertz within a few dB. Transducers based on this development are now available from at least four sources including the NBS Office of Standard

Reference Materials.

NORMAL DISPLACEMENT

A small level of effort was devoted to additional development of the NBS

conical transducer. A new backing design was developed which is much simpler

to construct than the polyhedral backing associated with the best model of the

transducer.

The new backing consists of a rectangular parallelepiped in which a machined cavity is filled with tin. This composite construction provides the

backing asymmetry needed to reduce back reflections and the tin improves

damping. Transducers produced with this backing are equal to the best

transducers using the complex, more difficult to machine polyhedral backing.

ANALYSIS

An ^nalysis of the operation of the NBS conical transducer is nearly

complete . The analysis is aimed at a better understanding of the device so that it can be optimized or at least tailored for specific applications.

The analysis computes the response of a transducer from the geometry anc material properties of the active element and the mechanical impedances looking into the mounting surface and into the backing block. The main problems

are

(a) construction of an equivalent circuit for a conical transducer,

(b) derivation of an expression for the terminating impedances,

35
(c) solution of the Pochhammer-Chree problem for a cone (of finite

length), and

(d) calculation of the finite-aperture effect.

The analysis resolves these problems; some approximations being

necessary. The analysis is compared with response curves^for conical

transducers calibrated on the NBS AE calibration facility . One such com- parison is shown in Figure 1 . The analysis predicts the general features of

the measured response well. It also quantifies the importance of the smaller

and larger diameters and mechanical impedances of the test surface and backing

material. The results also show a modification of the Pochhammer-Chree theory

would improve agreement. The roll-off at higher frequencies is, as yet,

unexplained.

TANGENTIAL DISPLACEMENT

The development of a high fidelity, sensitive transducer for measuring

dynamic tangential displacement continues. This problem is more difficult

than the development of normal displacement sensors. In the case of normal

displacement sensors, the poled direction is the same as the direction of

motion and stress and, since the electrodes of the piezoelectric element are

at the ends of this common axis, the element can be poled before or after

machining. Preserving this symmetry in a completed transducer is relatively

easy.

For tangential transducers, poling electrodes are placed so that the

element is poled parallel to the tangential motion. These electrodes are subsequently removed and measuring electrodes are placed perpendicular to the

poling electrodes. Then when shaping the element it is more difficult to

maintain appropriate symmetries and it is not possible to pole subsequent to

machining the element. These difficulties sometimes result in tangential

transducers with unwanted sensitivity to normal displacement. Newly developed

fabrication techniques have minimized this problem of cross sensitivity. The

response of the newest tangential transducer to normal displacement is more

than 20 dB below its tangential response over most of its 1 MHz bandwidth.

This newest transducer has quite good fidelity. Its time domain response to a point-force step-function input to the large calibration block is shown in

Figure 2 and compares well with the theoretically predicted waveform of tangential displacement shown in Figure 3. Figure 4 is the amplitude response

versus frequency obtained by comparing the FFT of the measured output with

that of the theoretical waveform.

SUMMARY

A new, easier to manufacture backing has been developed for the normal

displacement measuring NBS conical transducer. A thorough analysis of the

transducer shows good agreement with measured response and provides the tools

for optimizing transducer geometry for specific applications. The most recent

model of tangential transducer shows good fidelity, measuring waveforms that

compare well with theory.

36
REFERENCES

1. M. Greenspan, "The NBS Conical Transducer: Analysis, " to be submitted to

J. Acoust. Soc. Am.

2. F.R. Breckenr idge , "Acoustic Emission Transducer Calibration by Means of

the Seismic Surface Pulse," J. Acoust. Emission 1, No. 2, 87*-94; 1982.

37
in

uir//

i aj 8P

38

Figure

1.

Amplitude

versus

frequency

for

a

conical

transducer

with

a

smaller

diameter

of

0.62

mm,

a

larger

diameter

of

1.74

mm

and

a

length

of

1.24

mm.

The

thick

line

is

from

the

analysis;

the

thin

line

is

measured

response.
HORIZONTAL

PIEZO.

585

a

in

h 1 H

a a a

a in

+-a

in

i a

a

i

a

a

in QO

csiNnao Nonvwora) indino aovnoA

39

Measured

waveform

using

the

newest

model

of

the

NBS

tangential

transducer.
a

a

.. a

cn

a

H 1 — 1 1 -j \. a

a a a a a

a a a a a

in a in a in

PJ PJ r—1 r—

C uid) INBHBDVldSra C331V inGHVO

40

Figure

3.

Theoretical

waveform

for

tangential

displacement.
HORIZONTAL

PIEZO.

585

a

m‘

a

-+- a

to a

(\i

ID

c\i

a

rvj

in

d

a

V*

OJa

3

•3

COc

OJU

c

<U00c

ca

COa

2

<U>

(U0)£

o

a.

COuu

u-o

OJ TO

>T

<Uu

00

Ciun/ A t 9-i 8P) A1 1 A 1 1 1 SN3S

41

FREQUENCY

(MHz)
CALIBRATION ACTIVITIES FOR AE TRANSDUCERS

F.R. Breckenridge and T.M. Proctor

Mechanical Production Metrology Division

Center for Manufacturing Engineering

INTRODUCTION

Based on recommendations by ASTM, ASME, and the AE Working Group a facility for the calibration of AE sensors was developed. This development

was partially supported by the Electric Power Research Institute and the

Office of Naval Research. The calibration subjects the device under test to a known dynamic displacement in order to determine its sensitivity as a function

of frequency.

^ The first method implemented makes use of the surface-pulse

configuration in which the mechanical input (a capillary-glass-break source

which produces point-force step function) and the device under test are located on the same surface of a large transfer block which approximates a halfspace. More recently, a through-pulse method has also been implemented; in

this configuration the mechanical input and the device under are centered on

the transfer block on opposite surfaces.

CALIBRATIONS AND TRANSDUCER DEVELOPMENT

Since the beginning of the calibration service for acoustic emission

transducers in January 1980, we have performed 633 calibrations, of which, 82 were performed in the past year. Many of these were on experimental

transducers constructed at NBS. For example, a number of calibrations have

been done as part of the development of transducers specifically designed to

measure the horizontal component of dynamic surface displacement with good

fidelity. Calibration of these horizontal-sensing transducers has been done

using the horizontal component of motion resulting from the glass-break source

and referenced to the calculated horizontal displacement. Results from

through-pulse calibration and surface-pulse calibration are combined to

evaluate the performance of horizontal sensing transducers.

The calibration facility has been improved by installation of a better

monitor for recording the glass-break force.

A batch of 20 NBS conical transducers is in the final stages of

production. They will be used by AE sensor manufacturers, research

laboratories, DoD, and testing services as a transfer standard for the secondary calibration of AE sensors. The transducers are being equipped with

buffer amplifiers to make them more immune to loading and stray capacitance

effects, thus increasing the accuracy of the calibration transfer. Other

features of the amplifier system include partial shielding of the hot

42
electrode of the transducer, gold contacts for reliability, and an equalizer

network to improve the flatness of the frequency response of the transfer

standards. Presently, the amplifiers have been constructed, but the

transducers need to be recalibrated with the buffer amplifiers in place on the

transducers.

Methods for the secondary calibration of AE sensors are being developed.

An outline of a possible secondary calibration system has been made. The

system would use a steel plate, 91 cm square and 3-3 cm thick. The source

would be an NBS conical transducer driven by a tone-burst generator, and the

calibration would be accomplished by comparing the unknown transducer against

a calibrated, NBS conical transducer, both transducers being placed on the

same side of the plate as the source transducer and equally distant from it.

A version of the NBS conical transducer having a scaled down active

element and conical backing was constructed. An amplifier with a small amount

of electrical equalization is used with this transducer to produce a somewhat

improved frequency response. Figure 1 shows the time waveform of this

transducer. This waveform is very close to the actual normal displacement.

Figure 2 shows its amplitude sensitivity versus frequency showing it to have

very good fidelity to above 2 MHz.

The calibration facility will continue to be used for the primary

calibration of transducers and for evaluation of transducer development.

Improvements aimed at assuring measurement process control will be developed

and implemented.

SUMMARY

The AE sensor calibration facility continues to be useful for primary

calibration and as a basic tool in transducer development.

REFERENCE

1. F.R. Breckenr idge , "Acoustic Emission Transducer Calibration by Means of

the Seismic Surface Pulse," J, Acoust. Emission 1, No. 2, pp 87—9 ^4 ( 1 982).

43
150

a

a

a

a)

a

oo

a

a

CD

a

LD

a

a

m

a

Pd

a

a

a a

a in

a a a

in a

a

n

<— o

<a -i- U -M

•r- «S C S- O -Q

•<- W) ns CO u

-o OJ

<u cu 4- to -a a> o -c E -M

l±j

ns sza >

-Q i-0) a ni

oj -t- > r—

•i- ns3

cOJ <D i.

CO (T3 (O U

E SJ- -t-> o o

4- ai

<D I— > a> ns2 -c

-M

0) -r- co 2

3 i~ G- <U

OJ 3

u -a • ra w ^ m— c o

S- IT3 o

3 i_ r—

OO +-> -Q

I

a>

s_3

CD B

3DV110A indj.no aBunnsNvai

44
DISPLACEMENT

RESPONSE

i S_

cuo

3D</>

A3

S_

rt3 O

O

u

on

U1> —o

>* u

4-> »— 1_ > 0)

-r— N

4~> •—

•r— *—

(/> ra e 3

oj

LT) a

CSJ

OJ

i-3

(wn/A i aa gP) A1IAI1ISN3S

45

FREQUENCY

(MHz)
MEASURING RADIOGRAPHIC/ RADIOLOGIC SENSITIVITY

Robert C. Placious and Daniel Polansky

Radiation Physics Division

Center for Radiation Research

Traditionally, the measurement of radiographic image quality depends on how well small holes at low constrast are imaged. Since an observer is part of

this system, this measurement requires that performance of the eye at different

contrast levels be included In the evaluation. Therefore, reference is often

made to the classical paper of Rose^ on fluctuations in the light signal

received by the eye and the later paper by Morgan and Sturm^ where this

principle was first applied to medical fluoroscopy. Not surprisingly, it was established that the smallest perceptible hole in the image was inversely

proportional to its contrast.

Ultimately, of course, fluctuations in the photon signal to the eye relate

back to fluctuations in the incident x-ray photons. For purposes of discussion,

however, it is sufficient here to refer to the signal received by the eye and

the fluctuations (noise) in that signal. Qualitatively, the relation between

contrast and detail detectability, (CDD), can be described as follows. As the

signal to noise ratio, (SNR), decreases, corresponding to reduced signal

photons, a point is reached where the image of a hole is undetectable

regardless of size. This, occurs as contrast or density difference is reduced.

On the other hand, as one goes to smaller detail (holes) a point is reached

where the detail detectability becomes poor due to resolution limits imposed by

the complete imaging system. The holes are not detected regardless of

contrast. This x-ray/eye system is illustrated in Figure 1. The radiographic

CDD curves are based on experimental data.3 The fluoroscopic curve is based on published curves given in McMaster.^ Superimposed on these curves are the

contrast/hole size ranges provided by the ASTM plaques which were designed to

measure equivalent image quality sensitivity.^ We conclude from this that while

the ASTM/NBS system for measuring EIQS sufficiently brackets the film range so that some holes are visible for a given film, the same device would not be

suitable for direct industrial fluoroscopy. If this type of device is to be

developed for electronic radiology we must obtain accurate CDD curves for such

systems

We have also superimposed on Figure 1 the proposed hole/plaque ranges we

are now testing for high energy radiography. This is done only for illustrating

that larger hole sizes are required for higher kilovoltages but that the thick- ness of the plaques, as a function of specimen thickness, are lower.

SUMMARY

We are, at present, in the process of developing a high energy EIQS system

based on the design now in use at 200kV. The last report indicated that changes

in design of the system-or a re-definition of the way in which we select the

numerical value of the EIQS for a given system-was needed. During this reporting period we have received, from outside laboratories assisting in this work.

46
many additional test results with the present design. Our analysis of this data

is continuing and we have made arrangements for some additional readings by

outside experts. However, based on what we now have, our preliminary conclusion

is that the design is suitable arid the manner in which the numerical value is

determined should be revised. This does not invalidate the proposed system of

measuring EIQS at high energies but it does differ from the method used on the

200kV. system. Since this proposed method makes the process of selecting the

value of the EIQS somewhat easier, it may eventually lead to a revision in the

low energy standard.

REFERENCES

1. A. Rose, J. Opt. Soc. Am., J38^ 196, (1948)

2. R.E. Sturm, and R.H. Morgan, Am. J. Roentgenol. 62. , 617 1949)

3. E.L. Criscuolo, Matls. Res. and Stds. 3_, 465 , (1963)

4. Nondestructive Testing Handbook, R. C. McMaster, Editor, _1_,19.29 ( 1959)

The Ronald Press, N.Y.

5. ASTM Standard E 746-83, Annual Book Of ASTM Standards 03.03, 651 (1984)

47
PERCENT

THICKNESS

SENSITIVITY

f-Ar^-100

Fiqure 1. Contrast-detail detectibi 1 i t.v curves for two film tynes and for

direct fluoroscoDv. Some ASTM imaqe qualities are also shown.

48
SELF TEST OF VISUAL ACUITY FOR RADIOGRAPHERS

Robert C. Placious

Radiation Physics Division

Center for Radiation Research

As a test for visual acuity for radiographers the detection of slit

images of varying width and contrast has been proposed by NBS.l The slit image

sizes as given in the reference are as follows:

Slit Width Minutes of Visual Angle

( eye/ film distance = 40 cm.)

.0089 cm. .0119 cm. .0178 cm.

0.75

1.0

1.5

For all widths the length of the slit is 1.24 cm. (0.5"). The contrast

range prescribed in the reference is as follows:

Contrast Film Density

Background slit

0.1 1.70 1.74

0.3 1.70 1.85

0.85 1.70 2.52

The third variable in this test is the edge gradient of the slit image.

One series contains a complete set of sharp edged slit images while the other

series contains blurred edge images.

At good contrast the normal eye should be able to detect a line having a visual angle of about 1.0 minute. Taking into account all of these conditions,

it is prescribed that a person with normal vision should achieve a seventy

(70%) percent or better passing grade on this test. The total number of slit

images is 72. If, for example, 4 more images containing no slits are included in

this test, the total is 76. Of this number, about 12 are judged to be quite

difficult to see. Therefore the person with acceptable vision should detect

about 64 images-easily achieving the desired passing grade.

We have estimated the signal to noise ratio (SNR) for three of Che above

cases. This estimate is:

SLIT WIDTH CONTRAST SNR

.0089cm. 0.1 21

.0119cm. 0.3 94

.0178cm. 0.85 533

This calculation is based on the x-ray photon signal only. It assumes an emulsion thickness of 6.25 (10“4

) cm. , an emulsion bulk density of ( 3 .82g/ cra-^

49
a monoenergetic photon energy of 100 keV. (attenuation coefficient = 0.966

cm2/gm)3 and the slope of the exposure/density curve = 0.48 Roentgens per unit

change of density.^ This SNR is for one source of noise only-the fluctuations

in the x-ray signal. Other sources of noise, such as x-ray scattering, will

reduce these values. The calculation is for a sharp edged slit only.

SUMMARY

We previously reported that a series of slit images had been produced by

radiographic means and sent to several DoD laboratories for testing. All of

those tested scored better than 90 percent. It was determined howevever that

the test was administered to skilled film readers and did not adhere to the

exact protocol specified for the test. We are in the process of modifying

some of the slit patterns according to some suggestions made by the testing

laboratories and to increase the difficulty of detecting some of the

patterns. When the entire series of slit images are completed another test

test will be made according to the protocol given in the reference.

REFERENCES

1. G.T. Yonemura, NBS Technical Note 1143 , U.S. Dept, of Commerce, June 1981

2. S.M. Seltzer, and M.J. Berger, Int. J. Radiat. Isot., 13 > 1189 (1982)

3. J.H. Hubbell , Int. J. Radiat. Isot., 33_ 1269 (1982)

4. Radiography in Modern Industry, Third Edition, Eastman Kodak Co.,

Rochester, N.Y., 14650

50
PERFORMANCE ASSESSMENT OF FLUORESCENCE MEASUREMENTS

K. L. Eckerle, J. J. Hsia, S. T. Chang, and K. D. Mielenz

Radiometric Physics Division

Center for Radiation Research

Fluorescent brightness, a visual quantity, is a property of fluorescent

penetrants that can be measured quantitatively. This project has as its goal

the performance assessment of fluorescent measurements made on fluorescent

penetrants. These penetrants are used to detect surface defects of materials

by non-destructive evaluations.

Work in the prior year was centered on a reference spectrof luorimeter designed at NBS (ref. 1,2,3). The objective of this work was to characterize

the spectrof luorimeter for wavelength scale, stray radiant energy, and linearity. The characterization has been completed.

Further work on the spectrofluorimeter has been aimed at measuring its

relative spectral response. This was done by two methods - using a NBS standard lamp, and a NBS standard detector. These were a vacuum tungsten strip

lamp and silicon photodiode, respectively. Preliminary technical emission

spectra for quinine sulfate dyhydrate have been obtained. Publication of some

of this work is anticipated.

Also, a commercial f luorimeter was purchased and modified to conform to

ASTM standards. Participation in an ASTM round-robin to evaluate three liquid

penetrants was accomplished in collaboration with L. J. Swartzendruber

Solutions of different concentrations were measured. In addition, thermal and

ultraviolet fading tests were performed.

Future work will be centered about the NBS reference spectrof luorimeter

and the search for a standard material. Also, we will continue to cooperate

with committees studying fluorescence and continue to monitor the literature

on this subject.

SUMMARY

In FY85, we have successfully obtained preliminary technical emission

spectra with the reference spectrof luorimeter, and have obtained data for the

ASTM round-robin using the commerical fluorimeter.

REFERENCES

1. K. D. Mielenz, "Photoluminescence Spectrometry", Optical Radiation

Measurements , Vol. 3 Measurement of Photoluminescence , pp. 17-19

(Academic Press, Inc., 1982).

2. E. D. Cehelnik, K. D. Mielenz, and R. A. Vdlapoldi, "Polarization E: :

51
on Fluorescence Measurements", J. Res. National Bureau of Standards 79 A

1 (1975).

3. K. D. Mielenz, E. D. Cehelnik, and R. L. McKenzie, "Elimination of Polarization Bias in Fluorescence Intensity Measurements", J. Chem. Phys. 64 , 370 (1976).

52
DEVELOPMENT OF HIGH OPTICAL DENSITY STANDARDS

J. J. Hsia, C. H. Popenoe, and L. E. Fink

Radiometric Physics Division

Center for Radiation Research

Optical density standards are required to calibrate radiographic films.

These films are used to detect internal and surface defects of materials by

NDE evaluation. The objectives of this project are to develop high optical

density standards (up to optical density of 5.8), and to base calibration of

master standards on the Inverse Fourth Apparatus (Ref. 1) through development

of hardware and software for the Inverse Fourth Apparatus and characterizations of the apparatus and high optical standards.

Realignment of the optical system, refinement of the measurement procedure and modified software resolved the problem of the optical zero-offset

distance (Ref. 2). This distance is now a constant and is independent of the

optical density of the filter employed.

To conform to the new geometric condition by ISO 5/2-1985 (Ref. 3),

"Photography-Density Measurements - Part 2: Geometric Conditions for Transmission Density", an opal-diffuser collection system has been designed and

constructed. This system consists of an opal glass, a sample plate with

grooves for applying vacuum and pressure, and a specular-aluminum-hemispherical collector for diffuse light.

Measurements of photographic and x-ray step tablets using both opaldiffuser and integrating-sphere collection system have been performed. Preliminary data indicated that, below optical density one, measurements made

with the opal-diffuser gave lower optical densities than those made with the

integrating sphere. These differences are expected since the opal diffuser

introduces interreflections between the sample surface and the opal diffuser.

These differences are consistent with the measurements made by PTB, West

Germany.

SUMMARY

In FY85, we have resolved the problem of the optical zero—offset distance, designed and constructed the opal—diffuser—collecting system, and

intercompared the opal-diffuser and the integrating-sphere collection svstems.

REFERENCES

1. D. A. Swyt and J. G. LaRock, "Inverse—fourth apparatus for photometric

calibration". Rev. Sci. Instrum . 49^(8), pp. 1083-1089 (Aug. 1978).

2. C. H. Popenoe and J. J. Hsia, "Optical Density Determination with an Inverse-Fourth Instrument" in "Technical Activities 1984 Office of Non53
destructive Evaluation", Editor L. Mordfin, NBSIR 84-2944, pp. 92-101

(Nov. 1984)

3. International Standard, "Photography-Density Measurements - Part 2"

Geometric Conditions for Transmission Density", ISO 5/2, pp. 1-4,

International Organization for Standardization (1985).

54
INFRARED METHODS OF NONDESTRUCTIVE TESTING

Julius Cohen

Radiometric Physics Division

Center for Radiation Research

The purposes of this project are: (1) to develop expertise and maintain

an awareness of infrared methods of NDT, in particular thermography, as they are practiced in industry; (2) to evaluate the current and future needs

for standards and traceability for these methods; and (3) to assess the

Bureau’s role in this area.

Previous work on this project has generated (1) an NBS report ’’Elements

of Thermography for Nondestructive Testing" (ref. 1), (2) a current ASTM

activity of compiling a glossary for infrared thermography, and (3) an ONDE

sponsored project to develop standard test methods for characterizing

performance of thermal imaging systems.

(1) The NBS report presents an elementary review of thermal imaging

systems, with emphasis on the application of thermography to nondestructive

testing. Topics include heat radiation theory; thermal imaging systems;

performance characteristics; effects of emissivity, background temperature,

atmosphere, field of view; and examples of applications of thermography to

NDE. (2) The glossary cited above is based largely on this NBS report.

(3) Draft #1 of ASTM "Standard Test Method for Minimum Resolvable

Temperature Difference for Thermal Imaging" has been written; see J. Cohen,

"Standard Test Methods for Characterizing Performance of Thermal Imaging

Systems," elsewhere in this document.

REFERENCES

1. J. Cohen, "Elements of Thermography for Nondestructive Testing," NBS

Technical Note 1177 (May 1983).

55
STANDARD TEST METHODS FOR CHARACTERIZING PERFORMANCE OF THERMAL IMAGING

SYSTEMS

Julius Cohen

Radiometric Physics Division

Center for Radiation Research

The objectives of this new project are to develop standard test methods

for characterizing performance of thermal imaging systems for NDE purposes.

Specifically, the performance measures, minimum resolvable temperature

difference (MRTD), minimum detectable temperature difference (MDTD), and

noise equivalent temperature difference (NETD) are to be dealt with.

During FY 1985, the first draft of Standard Test Method for MRTD for

Thermal Imaging was completed and presented to ASTM Committee E7.10.04 for

deliberation. This method covers the determination of the MRTD capability

of the compound observer-thermal imaging system as a function of spatial

frequency. Included in the draft are terminology, summary of method, significance and use, apparatus, procedure, reporting requirements, and sample

calculations. The second draft is expected shortly to go to committee vote

For FY 1986, the plans are to complete the drafting of the standard for

MRTD and to draft an additional standard, MDTD for Thermal Imaging. *

This work is being carried out the the aid and cooperation of

Dr. R. Grot, CBT, who graciously permits us to use his thermographic

laboratory facilities*

56
DEVELOPMENT OF LEAK STANDARDS AND

CALIBRATION FACILITIES AT NBS

Charles D. Ehrlich and Charles R. Tilford

Temperature and Pressure Division

Center for Basic Standards

The need for improved leak measurement accuracy in a variety of

industries, and in some cases for legal traceability to a recognized

standards authority, prompted the development of leak standards at NBS. The

NBS Leak Standards Program began in FY84 with the objectives of developing

primary leak standards, characterizing transfer leaks, and providing a publicly accessible leak calibration service. ’FY85 has seen significant

progress towards these objectives.

An NBS primary leak standard has been developed, and measurements

performed on a sintered plug variable-rate leak have shown agreement with

measurements made at the Primary Standards Laboratory at Sandia National

Laboratories (SNL) of better than 555 over a range of leak rates spanning

three orders of magnitude (4 x 10“? to 4 x 10”^ moles/sec; 10 “^ to 10“^

std cc/sec) for three different gases; helium, argon and nitrogen. The SNL

primary standard is of a completely different type than the one at NBS, so that this initial agreement is very encouraging. Measurements made on a second leak of identical design but having a lower leak rate indicate that

the leak artifact has undergone some type of mechanical transformation

during the course of the year, and the artifact has been returned to SNL for

further testing and verification.

Besides the work that has been done characterizing these sintered plug

variable-rate leaks, characterization of helium diffusion leaks and sintered

silicon carbide leaks has also begun. Helium diffusion leaks of NBS design

that will allow variable supply pressures were constructed in FY85.

Experiments run during FY85 on a leak comparator device at NBS, designed to

provide a systematic study of commercial helium transfer leaks, show an exponential dependence of leakage rate with temperature, contrary to

conventional assumption and usage of these leaks.

Work toward providing a publicly accessible leak calibration service in

FY86 has proceeded predominantly along two lines, in addition to the work

already mentioned. First, documentation of the Primary Leak Standard has

begun, a prerequisite toward obtaining calibration status as the detailed

error analysis of the system is presented. Second, the NBS Primary Leak and

Vacuum Standards Laboratory has expanded in physical space, equipment, and

manpower. Floor space has essentially doubled; a dedicated leak rate

chamber has been constructed and put into service and a new bellows

flowmeter has been designed, constructed, and is ready for test.

57
As indicated, a substantial part of the FY85 work was done in

collaboration with Sandia Labs, who provided a major amount of the support

for this program. NBS involvement in the collaboration, besides the work

mentioned previously, included on site (at SNL) modification of the leak

comparator system to . incorporate a temperature control system developed at

NBS. Further collaboration will include joint presentation and publication

of results in an archival journal.

SUMMARY

FY85 has seen the development of an NBS primary leak standard that has

performed well against an established primary standard of different design

at SNL. Investigations of the temperature dependence of the most widely

used type of commercial leak indicate that conventional assumptions are incorrect. Work continues toward completing the documentation and

demonstrating the accuracy required f-or establishment of an NBS leak

calibration service in FY86.

58
SURFACE METHODS FOR NDE

L.J. Swartzendruber

Metallurgy Division

Institute for Materials Science and Engineering

This activity is involved with the development of procedures and

standards for surface methods of NDE. The methods of magnetic particle

testing, penetrant inspection, and Barkhausen noise analysis have been of

particular interest.

MAGNETIC PARTICLE INSPECTION

A number of the results obtained previously in the area of magnetic

particle testing have now been incorporated into a new military standard

on magnetic particle inspection, MIL-STD-1 949 , which supersedes the Air

Force document MIL-I-6868E, and the Army document MIL-M-11472 (actual

preparation of the document was funded by AMMRC). The new standard

includes a method for using Hall^effect probes or equivalent to determine

proper magnetization levels for effective inspection. This is possible

because we have shown, both theoretically and experimentally, that the

tangential value of the H field at the surface of the part being inspected

is the primary factor which determines the magnitude of the leakage field

from a defect of a given size. Previously it had been assumed that

optimum results would be obtained when the value of B/H was a maximum,

thus making the best value of applied field very difficult to measure and

strongly dependent on the material under test. Our results have shown

that, for the majority of materials, the optimum applied fields drive the

material well into the saturation region. In this case the material

properties are of secondary importance for determining the optimum applied

field. Correctly instrumented Hall probes can then be used to test for

proper magnetization when using either alternating or direct currents.

Another important factor in improving standards for magnetic particle

inspection is testing of magnetic inks and powders for proper physical

characteristics, including particle size, shape, and magnetic properties.

Current specifications, both in the existing ASTM document, and in the

Military Standard are inadequate in this regard. Future work will be

concerned with improving this area, primarily in cooperation with the ASTM

subcommittee.

DYE PENETRANT TESTING

In the area of dye penetrant testing we have participated in

designing and conducting a round-robin test of three proposed new ASTM dye

penetrant documents (this was done in cooperation with J.J. Hsia and

K.L. Eckerle of the Radiometric Physics Division, Center for Radiation

Research). The round-robin results for one of these draft documents w^r-.- considered encouraging enough to warrant submission for subcommittee

balloting. Results for the other two documents, one for measuring therm-.:

stability and the other for measuring ultraviolet radiation stability,

appeared unacceptable. Improvements of the techniques spelled out :r. these two documents and a new round-robin are in the planning stage.

59
work has pointed out the considerable importance for a strong effort at

NBS to provide a mechanism for the calibration of the ultraviolet

intensity meters used in NDE and for providing standards against which the

fluorescence of dye penetrants (and magnetic inks) may be compared.

BARKHAUSEN NOISE ANALYSIS

Because of the potential need for standards and specifications in the

field of Barkhausen noise NDE, an evaluation of this field, its

applications, and possible requirements for specifications and standards,

is being conducted. Although the field of Barkhausen noise is an old one,

serious efforts on NDE applications appear to have started around 1975

with the design of commercial apparatus by the Southwest Research

Institute in the United States, by the Technical Research Center in

Finland, and by a number of groups in the USSR. Barkhausen noise analysis

on metals using inductive sensors is basically a surface technique, being

most sensitive to material within approximately 0.3 mm of the surface. A number of studies have shown that Barkhausen noise from deeper regions in

a metal can be observed by sensing the acoustic emission which accompanies

a Barkhausen discontinuity. This has also been called "magnetomechanical

acoustic emission" and is due to the presence of magnetostriction.

Although this technique is generally less sensitive than the inductive

method, it can be expected to have a number of specialized applications.

Barkhausen noise analysis (BNA) has been shown to be correlated to

various material properties including grain size, hardness, internal

stress, and microstructure. It has also been suggested that BNA could be

used for flaw detection. Besides its evident application in quality

control of magnetic material such as silicon steel and ferrites, one of the

most interesting possibilities for BNA is in automated on-line testing in a steel mill, heat treating plant, or similar facility.

Several important principles can be enunciated concerning BNA.

First, since BNA utilizes a magnetic property of the material, its

characteristics will be sensitive to microstructure, internal stress,

etc., in a manner similar to other magnetic properties such as coercive

force and remanence. Measurement of magnetic properties is a well

established method for the NDE and quality control of steel and some other

materials. However, in many cases, the sample geometry prevents effective

measurement of such properties as the coercive force and, especially, its

variation from place to place on a large sample. In this situation BNA

can be used effectively. As with many magnetic properties, changes in the

Barkhausen noise spectrum result from a number of causes; if several

material properties change simultaneously, poor correlation with the

Barkhausen noise spectrum and the selected property may result. To carry

out BNA it is desirable to sweep repetitively through the hysteresis loop

of the material. Of primary interest is the frequency at which this is

accomplished. At all but the very lowest frequencies, noise comes in

"bursts" with sizes that vary with frequency. Thus, the power density

spectrum is a function of the fundamental frequency with which the

hysteresis loop is swept. It is generally necessary to keep this

frequency below 1000 Hz. Correspondingly, a crucial factor in effective

BNA is the design of the probes used to sweep the hysteresis loop, the

pickup coils used to sense the noise, and the method by which the noise

spectrum is analyzed and correlated to material properties.

60
There appear to be two important areas where NBS might make a contribution to the field of NDE using Barkhausen noise. One is in the area of coil characterization, and the other the provision of reference

materials with well characterized noise spectra which could be useful for

system comparison and calibration.

SUMMARY

In cooperation with the Watertown Materials and Mechanics Research

Center, a new standard for magnetic particle inspection has been issued.

In cooperation with ASTM, a Round Robin in support of a new dye penetrant

document was completed. An evaluation of Barkhausen noise NDE was undertaken and possible NBS input areas suggested.

61
FERROGRAPHIC STUDY OF WEAR DEBRIS

A. W. Ruff

Metallurgy Division

Institute for Materials Science and Engineering

This research has progressed to the point of identifying a primary limitation

of the accuracy in the technique of wear particle analysis called ferrography.

The technique extracts wear debris from lubricating fluids, or other liquids such

as hydraulic fluids, by passing samples through a magnetic field gradient in a specially designed instrument. The ferromagnetic particles are removed from the

fluid by the field and caused to deposit on a glass substrate so that they can be

subsequently analyzed. The method accomplishes a size separation during the

deposition step. The particles can then be microscopically studied in any of

several ways. A valid method for handling specimens from the as-received stage

as liquid samples to the final stage as particle deposits on the substrate has

been developed by a group of interested laboratories. These include the Air

Propulsion Lab at Wright Patterson Air Force Base, the Tri-Services Oil Analysis

Lab at Pensacola, Florida, the University of Missouri, the Michigan Technological

University, and NBS. A method was also proposed to measure the density of deposited

particles using optical densitometry. In a series of inter- laboratory comparisons,

it was found that the different laboratories disagreed on particle deposit density

by as much as 50%. The problem was identified to result from the lack of a method

to calibrate the optical densitometer at points other than the two end points,

0% transmission and 100% transmission. NBS has been working on a stepped density

plate to be used to calibrate the densitometers used at the laboratories. A prototype

plate has been used here with success. However, there has not yet been agreement

among the users on either the method to follow or the calibrating specimen to use. A related problem concerns the fact that some operate their densitometer in transmission and others in reflection; this choice determines the nature of the density

calibration specimen. Discussions have moved at a slow pace this year in part

because of changes of several key personnel at the other laboratories. Plans for

next year will continue to follow the path of seeking agreement on a density

calibration scheme at least among the principal laboratories.

SUMMARY

A method has been developed to calibrate the density measuring instrument used

in ferrographic analysis of wear debris particles. The method is being proposed

for widespread use among oil analysis laboratories.

62
NDE OF CORROSION - GUN BARRELS AND AMMUNITION

A. C. Fraker and A. W. Ruff

Metallurgy Division

Institute for Materials Science and Engineering

The goal of this work is to prepare procedural documents for nondestructive evaluation of corrosion of gun barrels and ammunition. The project is supported by the U.S. Army Materials and Mechanics Research Center,

Watertown, Massachusetts. The progress of this past year consists of a further evaluation of the problem and the development of a draft outline

for preparing the document for the nondestructive evaluation of the corrosion of ammunition. The corrosion of gun barrels and that of ammunition

are considered separately due to the nature of the problems and the need

for simplification. Some time was spent visiting ammunition depots and

reading reports to get a better understanding of the problem. It is clear

that the development of the document for the nondestructive evaluation of

corrosion of ammunition would be cost effective and would have the added

benefit of providing a standard for increased quality assurance. Nondestructive evaluation of corrosion of ammunition is conducted using visual

methods and occasionally, x-radiography . Both of these methods are able to

detect corrosion after considerable damage has been done, but they cannot

detect the early, initial stages of corrosion. Descriptions of the types

of corrosion which occur with different materials and varying circumstances

will be helpful for the inspection of ammunition and for early detection of

corrosion. The types of corrosion which can be expected to occur with

ammunition have been identified, and the draft outline for the NDE document

is based on these forms of corrosion.

The types of deterioration which will be evaluated are (1) the condition of painted or coated surfaces, (2) pitting or localized corrosion,

(3) stress corrosion, and (4) hydrogen embrittlement. Reference documents

cited include military documents, ASTM specification, and NBS reports.

Written documentation will be provided to describe materials, exposure

conditions and evaluation results. Corrosion damage evaluation will be

made based on the materials, their use and one of the four relevant types

of corrosion. Expansion of this outline to a more detailed document is in

progress now. Test coupons could be packed with ammunition to assist with

NDE measurements of initial corrosion and to aid in the development of NDE

techniques for corrosion evaluation.

SUMMARY

The accomplishments of the project for 1985 include an assessment of

the procedures of ammunition inspection and ammunition storage and the

development of an outline for the nondestructive evaluation of corrosion

document

63
* 11 |Q| 1

v64
II. NDE METHODS FOR INTERNAL FLAW CHARACTERIZATION

The work in this section deals with improving or developing new NDE

techniques for quantitative flaw evaluation in order to determine suitability and reliability for specific applications. The first group of six

reports emphasizes research on measurement methods and the second group of

five reports focuses on NDE of specific materials such as concrete, steel

and copper. There are several notable advances reported in the section.

Two research reports deal with signal inversion for acoustic emission data

and another reports on standard methodology for NDE data analysis and

assessment of data reliability along with design of a prototype archival

computer data base.

65
66
ACOUSTIC EMISSION IMAGING

Stephen J. Norton and Melvin Linzer

Metallurgy Division

Institute for Materials Science and Engineering

In ultrasonics, numerous techniques exist for enhancing the

signal-to-noise ratio (SNR) of the ultrasonic signals at the receiver, such

as increasing the source power or signal averaging. In processing acoustic

emission signals, such signal enhancement methods are not possible, and

traditional source location techniques based on signal thresholding will fail

if the source signals are close to or below the receiver noise.

During the past year, we have continued an investigation into a new inverse-source technique for reconstructing images of random source

distributions which, to a considerable extent, overcomes the problem of

extracting source information when the receiver signal-to-noise ratio is low.

Signal enhancement is achieved by using an array of detecting transducers,

and by cross-correlating the emitted source signals recorded at all

transducer pairs. An image of the distribution of the source intensity is

then obtained by filtering the cross-correlated signals in an optimal fashion

and then appropriately summing the filtered signals in the image plane. The

filtering and summation operations are similar in principle to the well-known

f iltered-backprojection algorithm used in medical x-ray tomography.

Backprojection, here," refers to the process of adding the signals at each

point in the image plane to achieve constructive addition at points where

sources exist and cancellation at points where no sources exist. The result

is a reconstructed image of the source distribution. We have shown that the

point-spread-function of the image reconstruction algorithm can be

analytically derived for the case of random and spatially-incoherent sources.

Under the latter assumptions, the imaging approach is linear in source

intensity and is capable, in principle, of reconstructing quantitative images

of extended and complex source intensity distributions. The spatial

resolution in the source image is determined by the bandwidth of the emitted

radiation.

Under some conditions, acoustic emission signals generated by phase

transformations or microcracking may approximately satisfy the assumption of

spatial incoherence, and the above technique should be applicable in such

cases. Simulations have also indicated, however, that good results may be

possible even when the assumption of spatial-incoherence does not hold. This

opens the possibility of using the algorithm as a method of crack detection

and location.

Work this year has included a completion of the formal analysis, is

well as computer simulations of source reconstructions , in which a singl-.-

experimentally-recorded acoustic-emission waveform was used to simulate

multiple signals. As one example, we considered a simulated reconstruct:.:,

under conditions of significant receiver noise (SNR = 0.5). Figure 1 wc recorded acoustic-emission signal with no receiver noise, and figure

the same signal after adding broadband Gaussian noise to achieve a 0.5. Figure 3 shows a reconstruction of a two point source distribute:,

derived from 32 simulated received signals recorded by 32 hypothet: .

67
transducers with uncorrelated noise added to each signal to create a SNR = 0.5. Both sources are clearly discernible in the reconstruction, even though the individual signals are essentially invisible in the receiver noise

(figure 2)

This approach may have the potential to radically improve the

reliability of acoustic emission monitoring of crack growth in ductile steels

where signal amplitudes are often very low and background noise often

unavoidably high.

SUMMARY

In summary, we have this past year completed the theoretical development

of a new inverse—source reconstruction technique , and demonstrated the

resulting reconstruction algorithm by means of numerical simulations. Using

an experimentally-recorded acoustic—emission signal, the simulations have

shown, as predicted, that the algorithm is capable of reconstructing images

of sources whose emitted signals are buried in significant receiver noise.

REFERENCE

S. J. Norton and M. Linzer, Backprojection Reconstruction of Random Source

Distributions. J. Acoust. Soc. Amer. (to be submitted).

0.50

0.30

jjj 0. 10 Q

Q_^ - 0 . 10

-0.30

-0.50

•

MU. . nj Li IiaAvii MfAK *julA J\AJIAAAAn if Im* yyw nryYr'WAj

1

. —

0.0 16.0 32.0 48.0 64.0 80.0 96.0

TIME (MICROSEC)

Figure 1. Experimentally—recorded acoustic-emission signal created by

breaking a glass capillary on the surface of a steel plate.

68
AMPLITUDE

Figure 2. The acoustic-emission signal of figure 1 with broadband,

Gaussian noise added (SNR = 0.5).

69
Figure 3. Reconstruction of two point sources using 32 simulated noisy acousticemission signals. The algorithm assumed 32 hypothetical transducer

elements spaced around the circumference of a circle enclosing the source region. The 32 received signals were simulated by delaying the

acoustic-emission waveform of figure 1 and adding uncorrelated, broadband noise, yielding the 32 noise-contaminated signals (each of which

being similar in appearance to figure 2).

70
EXPERIMENTAL GREEN’S FUNCTION AND THE INVERSE PROBLEM

N.N. Hsu, T.M. Proctor and D.G. Eitzen

Mechanical Production Metrology Division

Center for Manufacturing Engineering

and

A. Carasso

Mathematical Analysis Division

Center for Applied Mathematics

INTRODUCTION

The detected Acoustic Emission (AE) signal contains the information about

the source, the sensor, and the structure, all mixed together through complicated convolutions. If the sensor transfer function is known and if the

details of how the waveform evolves in the structure are known then the

detected AE can be predicted by the source waveform and the source waveform

may be derived from the detected signal. To know the sensor transfer function, absolute calibration of the sensor is required. To know how the

waveform evolves in the structure, however, we have to solve the transient

wave propagation problem in detail. The present project is centered on developing techniques to solve the transient wave propagation problem in

arbitrary structures by the combination of controlled experiment and digital

signal .processing. In other words, we are formulating a procedure to determine experimentally the impulse response, represented by the Green's function,

of an arbitrary structure. Once the impulse response of the structure is

known, AE produced by different sources can be predicted and interpreted.

DISCUSSION

The Green's function is a complete representation for transient wave propagation in a structure due to a point force. For acoustic emission the

detected voltage signal, V(t), can be considered the convolution of three time

functions: F(x , t), the source waveform at location x ; GCxQ.x.t), the Green’s function for the structure and

a fixed configuration with detector at x and source at x ; T(t), the transfer function for the receiving transducer. 0

Letting denote the convolution integral,

V = T*G*F.

At least in principle, the Green's function of a complex structure can oe determined through this formulation if both the source and the transfer function of the sensor are known and if the deconvolution problem can be solved.

Recently we reformulated the problem and developed a new procedure

specifically designed for the experimental determination of Green's

71
1 2 functions ’ . The key to this reformulation is recognizing that the

source/sensor are subject to design. We assume that a simulated source is

generated by a transducer with transfer function T’ acted upon by a voltage

pulse V . Thus

F = T'*V

o and the received voltage becomes

Let

V - t*G*T'*V . o

L = T*T'*V . o

L represents those functions over which we have control through the design of

the sending and receiving transducers and the probing voltage waveform.- The

received voltage becomes

V = L*G.

In order to determine G we must solve this equation with measured V and "known

L" - a typical ill-posed deconvolution problem. The key question is: what

waveform for L will allow an optimum solution for G. We have found one probing waveform which allows us to solve for G systematically and with a good

estimate of the errors in G resulting from errors in the measured V. This

probing waveform is the inverse Gaussian function, K(a,t), given by

K(a,t) = -a

2

/4t

2Virt'

K may be considered a special approximation to a Dirac-delta function in which

the positive constant a controls the duration of the probe waveform. Taking L to be an inverse Gaussian function, the problem of determining G has been

changed over to one of solving a convolution integral with an inverse Gaussian

kernel, a problem for which some powerful tools have been ^ developed. These

include partial deconvolution and a strong error estimate .

We are now testing this deconvolution technique. The first tests were numerical simulations. The test signal was the calculated surface displacement which would occur if a point force inverse Gaussian waveform were imposed

on a plate. This test signal is then deconvolved to obtain an estimate of the

Green’s function which is compared with the exact Green's function. Figure 1 shows an example for a source and receiver on opposite sides of a plate and

two thicknesses apart. The top trace is the test signal (calculated

displacement), the middle trace is the estimate of the Green’s function obtained by deconvolution and the bottom trace is the exact Green's function.

Encouraged by these results we have begun to test the procedure

experimentally. From the definition of L given above, the practical importance of high-fidelity transducers becomes evident. For "perfect fidelity"

transducers, the transfer functions T and T' would be "unity". In

72
this case, our desire to probe with L=K only requires that the driving voltage

pulse V be an inverse Gaussian. Even though the NBS conical transducers are

very high fidelity, corrections are necessary to perform the deconvolution.

Experimentally, we have made use of two NBS conical transducers on a plate; one transducer is used as a source, the other as a receiver. A digital

to analog waveform generator is programmed with an inverse Gaussian function.

The low voltage waveform is amplified using an high power amplifier, developed

at NBS, which drives the source transducer. The resulting displacement-time

history is measured with the second conical transducer. Since T and T' are

not unity for the conical transducers, the transfer functions for the

transducers must be accounted for. (An alternative procedure would be to

modify V to account for T and T

f so that L is more nearly inverse Gaussian.)

T*T ’ is accounted for by independently determining the impulse response of the

transducer pair using the exact deconvolution available at epicenter . With

the transducers transfer function accounted for, the measured displacement is

subject to the general deconvolution procedure. An encouraging preliminary

result is shown in Figure 2. The curve represents the experimentally obtained

Green’s function for the sensor and source on opposite sides of a large plate

directly facing each other. The experimentally determined curve has the

details of the jumps and inflections which match extremely well the known

theoretically computed one.

Refinement of the technique such as further improvement of the

transducers and amplifiers are underway. However, to simplify the experimental procedure for data acquisition and processing still requires considerable

work.

SUMMARY

A procedure to determine experimentally the impulse response of an ar- bitrary structure is being developed. The concept involves two novel ideas:

(1 ) the theoretical formulation of a probing waveform which facilitates the

deconvolution process; (2) the design and construction of a system, a transducer pair together with high speed digital to analog conversion and

power amplifier, which introduces a pulse of specified waveform and detects

the propagated transient wave without loosing fidelity. Results are encouraging and further tests are in progress.

REFERENCE

1 . Alfred S. Carasso and Nelson N. Hsu, "Probe Waveforms and Deconvolution in

the Experimental Determination of Elastic Green's Functions," SIAM J

Appl. Math 45 , No. 3, PP 369^382 (June 1985).

2. D. Eitzen, N. Hsu, A. Carasso and T. Proctor, "Deconvolution by Design - An Approach to the Inverse Problem of Ultrasonic Testing," Review of

Progress in Quantitative NDE MA , pp 1 79~1 88 (1985).

3. N. Hsu and S. Hardy, "Experiments in Acoustic Emission Waveform Analysis

for Characterization of AE Sources, Sensors and Structures," Elasti? w. .••• and Non-Destructive Testing of Materials AMD-29, Y.H. Pao, ed., ACME, NY.

73
0 1 2 3 4 5

NORMALIZED TIME

Figure 1. Deconvolution of epicentral response; Heaviside time dependence.

74
DECONUOLUTION

OF

RESULT007.

USING

TRANSDUCTED

PULSE

ALDECON007.

Qw^CLJlyUJCUJZh

O LO ® LD

t • • • ru <S> o

<s»

in

i

o

h0.

• • • • • CX3 «-h <3> 


I Q*H(/)O.J<I<JUEur»-

75

TIME

PROGRAH

ULTRASONIC.

ALPHA*.

05.

3/28/85
ULTRASONIC POINT SOURCE: THE NBS CONICAL TRANSDUCER AS A DRIVER

T.M. Proctor, N.N. Hsu, and S.E. Fick

Mechanical Procduction Metrology Division

Center for Manufacturing Engineering

1 2

The NBS conical transducer ’ is an important tool for measuring dynamic,

normal surface displacements because of its sensitivity and high fidelity.

Reciprocity suggests that it may also be a useful tool for generating

prescribed point source ultrasonic waveforms. Conical transducers are being

evaluated for this application with very promising results to date. In addition to permitting the prescription of arbitrary waveforms, the approach

offers the advantages of repetitive signals over the Breckenridge (cappillary)

and Hsu (pencil) sources which are single, transient events. The repetitive

signals can be enhanced by signal averaging and more easily displayed upon

receipt.

Initial experiments have been performed with two conical transducers on a plate. The desired voltage time waveform is programed into a digital-toanalog converter. This output feeds an NBS developed high power amplifier

which drives one of the conical transducers with a voltage pulse of up to 850

volts. The second conical transducer is used as a calibrated receiver to

measure the resulting displacement. With the two transducers on epicenter,

the exact epicenter deconvolution developed by Hsu has been used to determine

the transfer function of the transducer pair.

It is expected that this approach will be used in the experimental determination of unknown Green’s functions. With further development conical

sources might also be useful in the primary calibration of AE transducers by

the surface pulse and through pulse methods; the latter method will require

signal averaging to obtain an acceptable signal to noise ratio.

SUMMARY

The NBS conical transducer is extremely useful as a high-fidelity

receiver. Preliminary tests indicate that is is also useful as a highfidelity point source driver and may become an important tool in AE as a simulator and in ultrasonics as a tailored transmitter.

REFERENCES

1 . T. M. Proctor, "NBS Conical Transducer: A Quantitative Acoustic Emission

Sensor,” Technical Activities 1981-Office of Nondestructive Evaluation, H.

Berger and L. Mordfin eds., NBSIR82-2449 , 23~27, (Dec. 1981).

2. T.M. Proctor, "Further Development of the NBS Conical Transducer."

Technical Activities 1982-Office of Nondestructive Evaluation, T. Yolken

ed., NBSIR82-261 7, 20-24, (Dec. 1982).

76
THEORETICAL STUDIES OF ACOUSTIC SCATTERING

Raymond D. Mountain

Thermophysics Division

For the last few years, this work has been concerned with the

development of moment relations for acoustic scattering data. These studies

have lead to some new insights into the relationship between transient (time

domain) and steady-state (frequency domain) measurements and thereby into

how measurements made in these two domains are related. This was accomplished within the framework of the Born approximation by first

expressing the steady-state scattering by an isolated scatterer in terms of

a set of volume moments of the scatterer. Next, we examined the time domain

scattering by the same scatterer and recognized that moments in time of the

amplitude of the scattered signal involved the same volume moments of the

scatterer

This analysis leads to the effective size, a, of the scatterer being

given as

a

2

= 10\»

2

R

4 /R

2

where v is the sound speed in the material and R and R^ are the second and

fourth time domain moments of the amplitude of tne scattered signal provided

that the time origin is the instant the incident wave passes through the

center of the scatterer . [1

We have used measurements made by G. Blessing to assess the utility of

this relationship. We find that its domain of applicability lies in a region which is difficult to realize experimentally. There exist in the

literature, other schemes which employ the Born .approximation to obtain size

and shape information. [2] However, these procedures involve additional

approximations and assumptions^] which we have not included in our rigorous

application of the Born approximation to moment relations.

We anticipate that this type of analysis will be useful in other areas

of interest to the NDE community, such as thermal wave studies, by

clarifying the connections between steady-state and transient measurements

and through the development of specific procedures for analyzing

measurements.

REFERENCES

1 . R.D. Mountain and G. Birnbaum, "Scattering of sound waves by

inhomogenieties: Time domain analysis", Nondestructive Testing

Communications 1, pp 219-225 (1984).

2. D.K. Hsu, J.H. Rose and D.O. Thompson, "Reconstruction of inclusions

solids using ultrasonic Born inversion", J. Appl. Phys 55, pp 162-1*:

(1984).

' ~

77
3. G.J. Gruber, G.J. Hendrix and T. A. Mueller, "Exploratory Development for

a High Reliability Flaw Characterization Module", Technical Report No.

AFWAL-TR-84-41 72, Materials Laboratory, Air Force Wright Aeronautical

Laboratories, Air Force Systems Command, Wright-Patterson Air Force

Base, Ohio 45433, March 1985.

78
DESIGN OF AN X-RAY CAMERA USING A CCD SENSOR.

Richard Spal and Masao Kuriyama

Metallurgy Division

Institute for Materials Science and Engineering

This report describes the design of an x-ray camera using a commercial

CCD (charge coupled device) area sensor for direct detection of x-rays with

energies of about 10 kev. X-ray cameras may be classified as direct or indirect detection devices. A direct detection camera detects the electric

charge produced when x-rays strike a photoconductor, while an indirect

detection camera detects the visible light rays produced when x-rays strike a phosphor. The latter detection scheme is called indirect since the visible

light rays must still strike a photoconductor to produce an electric charge.

This scheme has the disadvantages that the spatial resolution is controlled

by the phosphor thickness, and the sensitivity is controlled by the

efficiency of converting x-rays to visible light rays (typically about 10

percent). While the sensitivity can be improved by inserting an image

intensifier after the phosphor, this further degrades the spatial resolution.

In comparison, current direct detection cameras based on the x-ray vidicon

tube have superior spatial resolution but inferior sensitivity. A direct

detection camera based on a CCD area sensor should have spatial resolution

comparable to the x-ray vidicon, but much better sensitivity. The resolution

is controlled by the CCD photosite size, which is currently as small as 15

by 15 microns for one commercial area sensor. The sensitivity is controlled

mainly by the photosite dark current. Since the sensor is small, it is

practical to cool it to reduce the dark current enough to detect single

x-rays. These advantages of spatial resolution, sensitivity, and size

promise to make the device useful for NDE radiography and synchrotron

radiation topography.

The CCD image sensor has a rectangular array of square pixels with 490 rows and 328 columns. The pixel dimension, and the center to center distance

between pixels, is 24.4 urn. Half of the rows are used for image integration,

and the rest for image storage. The integration period may vary from 1/60

sec to about 10 minutes. At the end of the integration period, the charge

accumulated in the image integration region is rapidly transferred to the

image storage region. During the next integration period, rows of charge in

the storage region are shifted through the storage region into a serial

register, and charge packets in the serial register are shifted through the

serial register to an output amplifier. The output contains a signal

component, a clock component, and a dark current component. The output is

processed to remove the clock and dark current components, and is converted

to a video signal. A commercial frame grabber stores the video signal, and

drives a TV during the integration period. Below is a detailed description

of the timing and signal processing circuitry.

A block diagram of the timing circuitry is shown in figure 1 . A system

clock, running at 14 MHz, drives a TV sync generator, the parallel image and

storage area clocks, and the serial register clock. The TV sync generator

provides horizontal reset (HRST ) , vertical reset (VRST), and composite sync

( CSYNC ) signals. The parallel image area clock (* pI) provides a , MHz pui3e

79
train of 245 pulses to transfer rows of charge through the image region to

the storage region. It is activated by VRST , and inhibited by an integration

signal (INTGRT) which controls the integration period. Similarly, the

parallel storage area clock ( 4>ps ) provides a 1 MHz pulse train of 245 pulses,

activated by VRST and synchronized with <j> pi to transfer charge through the

storage region. In addition, <j>pg provides a single pulse, activated by HRST,

to transfer a row of charge from the storage region to the serial register.

Both 4>pj and <j>pg control drivers which must drive a CCD load of 10,000 pF

between its high and low voltage levels in 200 nsec. The serial register

clock ( <j> s ) provides a 7 MHz signal to transfer charge from the serial

register to the output amplifier. It is inhibited by HRST, and controls a driver which must drive a CCD load of 100 pF between its high and low voltage

levels in 20 nsec. The high and low voltage levels for the parallel image

and storage regions, and the serial register, should be adjusted in the range

of -2 to 6 volts for the high level, and -20 to -12 volts for the low level,

in order to maximize the charge transfer efficiency.

A block diagram of the signal processing circuitry is shown in Figure 2.

The CCD output is amplified and sampled by a fast sample and hold amplifier

gated by <j> s

. The first six pixels of each row, which are not exposed to

radiation, are sampled again by another sample and hold amplifier, to

determine the clock and dark current components of the CCD output. The

outputs of the two sample and hold amplifiers are subtracted in a differential amplifier to get the signal component of the CCD output. The

signal is converted to a video signal, captured by a frame grabber, displayed

on a TV, and recorded by a tape recorder.

SUMMARY

In summary, we have described the design of an x-ray camera which should

have- a spatial resolution of about 25 microns and sufficient sensitivity to

detect single x-rays. These specifications represent a significant

improvement over currently available x-ray cameras. Construction of the camera is in progress, and comprehensive testing is planned.

80
system

clock

CCO

Figure 1 Timing Block Diagram

Figure 2 Signal Processing Block Diagram

81
LONG THERMAL WAVE IMAGING USING HOLOGRAPHIC INTERFEROMETRY

Charles M. Vest

Department of Mechanical Engineering and Applied Mechanics

The University of Michigan

INTRODUCTION

Prior to this year our work has emphasized the use of holographic

interferometry as a nondestructive evaluation technique. Emphasis has been

on evaluative review of the state-of-the-art of this technique, quantitative

aspects of holographic NDE, simultaneous measurement of tilt and

displacement, and flaw detection by moire analysis of interf erograms

including digitally-processed moire patterns. During the present year we initiated investigation of visualization of thermal waves by holographic

interferometry

INVESTIGATION AND RESULTS

A thermal wave is the oscillating and diffusing temperature distribution

induced in a material by an oscillating heat input at its boundary. Thermal

waves induced by modulated laser beams have been used to image thickness and

thermal diffusivity variations in thin objects. Frequencies typically are of

the order of 10-100 Hz and specimen thicknesses are typically of the order of

millimeters. Images are formed by scanning the object's surface and

measuring the temperature amplitude or phase at each point.

In holographic NDE, steady or pulsed heat inputs have been used by

several investigators as loading techniques. Holographic interferometry is

then used to detect the response of the object's surface to this input and

fringe anomalies indicate the presence of flaws.

Our work this year combines the fields of thermal wave imaging and

holographic NDE. We have used very low frequency heat inputs (1 Hz or less)

to stimulate long wavelength thermal waves in thin aluminum plates. We

explored several holographic techniques to visualize the response of surface

deformation to these waves. The best results were obtained by stroboscopic

holographic interferometry. Fig. 1 is a schematic diagram of the system.

Comparison of fringe patterns with those predicted by thermoelasticity

clearly indicate that we have succeeded in detecting the oscillating part of

the thermoelastic response. This technique therefore enables one to

visualize the propagation of long thermal waves in the medium.

82
In the future we hope to use this technique to learn about the

interaction of thermal waves with flaws, and to explore the possible uses of

this technique for nondestructive evaluation. If successful, this would lead

to a whole-field, analog NDE method. That is, by its very nature, the

thermal response is obtained by parallel processing, as opposed to the point

by point scanning used in normal photothermal imaging.

A paper in which this work is reported will be presented at the 1985

annual meeting of the Optical Society of America.

SUMMARY

The propagation of long thermal waves in thin aluminum plates has been

observed by stroboscopic holographic interferometry. Experimental results

are in good agreement with thermoelastic predictions.

Mirror

Fig. 1 System for visualization of thermal waves by holographic

interferometry

83
PULSE-ECHO METHOD FOR FLAW DETECTION IN CONCRETE

Nicholas J. Carino and Mary Sansalone

Structures Division

Center for Building Technology

Nelson N. Hsu

Mechanical Production Metrology Division

Center for Manufacturing Engineering

A cooperative effort between the Structures Division of CBT and the

Mechanical Production Metrology Division of CME is focusing on the development

of a pulse-echo technique for locating internal defects in concrete

structures. The project aims to fill a major need related to the evaluation

of existing structures - a necessary first step in repair and rehabilitation

of structures. The pulse-echo method can fill this need if a fundamental

understanding of wave propoagation in bounded, heterogeneous solids containing

internal flaws can be achieved.

Past research has concentrated on developing a reliable point source

- point receiver, pulse-echo system. Since a satisfactory transducer for

sending pulses into concrete does not exist, an alternate technique was adopted which utilizes a short duration mechanical impact as a point source

of spherical waves. The receiver is a broadband, conical, displacement

transducer developed at NBS for acoustic emission measurements. Experiments

and theoretical analyses have demonstrated that the impact technique can

be used to accurately locate planar defects in concrete [1,2].

FY85 research has focused on 1) the development of a fieldworthy system

which utilizes a spring-loaded, impactor with a spherical steel tip and a broadband, displacement transducer which is coupled to rough concrete surfaces

using a thin lead sheet; 2) signal processing for simple and reliable flaw

detection; and 3) experimental and analytical studies of defects within

reinforced concrete structures.

Our first approach to signal processing is frequency spectrum analysis.

Using the Fast Fourier Transform technique, the frequency content of both

theoretical plate responses and experimental echo patterns obtained from

concrete plate specimens has been studied as a function of the contact time

of the initial elastic impact, the spacing between impact source and receiver,

and the location of the reflecting interface. Characteristics of the

frequency spectrum can be used to determine the contact time of the impact

and the depth of the reflecting interface. For example, the maximum amplitude

in the frequency spectrum is related to the depth of the reflector. In a time domain trace, such as that shown in Figure la which was obtained from

a 0.5 m thick plate specimen, the depth of the reflector must be determined

by identifying the arrival time of the first compression wave echo in the

trace. The problem is that in the time domain, echo arrivals can be very

difficult to identify accurately in bounded structures. However, the maximum

84
amplitude in the corresponding frequency spectrum, which is shown in Figure

lb, allows easy and accurate determination of the depth of the reflector.

For comparison. Figure lc shows the frequency spectrum obtained from the

time domain trace of a theoretical infinite plate response calculated for

the same contact time and spacing between source and receiver as in the

experimental trace.

Currently, we are carrying out experimental studies to deteminine the

feasibility of detecting defects (cracks, voids, and honeycombing) within

reinforced concrete structures. This experimental work is to be performed

in conjunction with two- and three-dimensional finite element studies which

will simulate wave propagation in bounded solids containing flaws. Results

from a preliminary two-dimensional axisymmetric finite element analysis of

a plate subjected to elastic impact are shown in Figure 2. The deformed

meshes in this figure represent the displaced shape of the plate at 50 us

and 125 us after initial impact. Studies such as these will provide an understanding of the interaction between stress waves and defects within

bounded solids.

It is anticipated that the experimental and analytical studies of bounded

reinforced concrete specimens containing defects will lead to field testing

of the proposed pulse-echo system and eventually lay the groundwork for the

development of a standard methodology for pulse-echo evaluation of concrete

structures

SUMMARY

The significant accomplishments of FY85 to date include progress toward

the development of a fieldworthy pulse-echo system for concrete and the use

of frequency spectrum analysis for simple and accurate flaw identification

and depth determination. We anticipate that the remainder of the year will

see the development of a methodology for interpreting signals obtained from

reinforced concrete structures containing flaws.

REFERENCES

1. N. J. Carino, "Laboratory Study of Flaw Detection in Concrete by the

Pulse—Echo Method," Proc. Int. Conf. on In Situ/NDT Testing of Concrete,

Oct., 1984, Ottawa, Canada.

2. N. J. Carino, M. Sansalone, and N. N. Hsu, "A Point Source — Point

Receiver, Pulse-Echo Technique for Flaw Detection in Concrete," Accepted

for publication, April 1985, Journal of the American Concrete

Institute.

85
TIME DOMAIN TRACE

FREQUENCY SPECTRUM

-t— 1—' • i “

1— *~ —

i O 2 4 • MOWM4I rrrn ntcoucNcr (« « h/cp)

Figure 1. a) time domain trace obtained near the edge of a 0.5 m thick

concrete plate specimen; b) frequency spectrum of trace in la;

and c) frequency spectrum of a theoretical plate response which

was calculated for the same contact time and source-receiver

spacing as the trace in la.

86
Figure 2. Deformed finite element mesh of a plate subject to an elastic

impact at its center, a) deformed shape 50 us after impact; and

b) deformed shape 125 us after impact.

87
TRANSDUCER DESIGN FOR ULTRASONIC TESTING OF HIGH ATTENUATION HETEROGENOUS

COMPOSITE MATERIALS

N.N . Hsu and T.M. Proctor

Mechanical Production Metrology Division

Center for Manufacturing Engineering

and

N. J. Carino and M. Sansalone

Structures Division

Center for Building Technology

Techniques to evaluate high attenuation, heterogeneous materials such as concrete, polymeric composites, and porous ceramics are needed. Ultrasonic

techniques for measuring velocity, moduli, or thickness changes, and echo

detection could provide in-process control during fabrication as well as flaw

detection information. Because such materials are heterogeneous, they are highly dispersive and absorbing. Traditional ultrasonic techniques are difficult to implement on such materials. Even for simple thickness or velocity

measurements, through transmission techniques and the use of massive low

frequency transducers are necessary to compensate for the high attenuation

loss in such media. These techniques have poor sensitivity and resolution,

and are awkward to use.

Based upon our previous laboratory test results, which are summarized in

last year's report, we have taken a novel approach to the measurement problems

commonly encountered in testing high attenuation heterogenous material. The

basic concept consists of:

(1) use of a point impact source and piezoelectric wide band detection;

(2) use of digital recording and digital signal processing;

(3) use of computed theoretical Green's functions as a basis for comparison

and as a guide for feature extraction; and

(4) design of field applicable transducers with selected band width and sen- sitivity for specific applications.

As an example of the above approach, a prototype transducer for measuring

the thickness of concrete slabs up to a meter thick is shown in Figure 1 . The

transducer is a hollow thick-walled brass cylinder with a ring-shaped

piezoelectric ceramic disk on one end which serves as the detecting element.

A spherical tipped steel impactor, which is inserted into the hollow axis of

the cylinder, is used as a point-impact source. The impact occurs at the

center of the hole in the ring-shaped ceramic element. The detected echo is

digitized and further processed to yield the thickness information. Some

preliminary results indicate that the prototype is quite adequate for its

intended application. Further improvement to the transducer will be made by

modifying the shape of the brass cylinder to reduce the unwanted echoes from

the backing material.

88
SUMMARY

We have designed and constructed a transducer which generates and detects

deep penetrating spherical waves for measuring the thickness of high attenuation heterogeneous composite materials. The concept of the transducer design

is different from the conventional approach of generating planar waves. The

combination of theoretical Green*s functions and digital processing techniques

makes the interpretation of the signal tractable and reliable.

Figure 1. Picture showing the prototype point impact transducer for thickness/

velocity measurement of concrete.

89
NDE OF DISTRIBUTED DAMAGE IN METALS

R.J. Fields and H.M. Ledbetter

Fracture and Deformation Division

Progress in the NDE of distributed damage in metals has been made in

the following areas: wave velocity studies in creep damaged copper;

measurement of cavity size distributions in 30-4 stainless steel; preparation of a cast copper specimen for SANS evaluation; and ferromagnetic

susceptibility studies in creep damaged stainless steels.

ULTRASONIC STUDIES ON CREEP DAMAGED COPPER

Copper bars containing known amounts of creep cavities (oriented

cracks that are randomly distributed spacially) were prepared for elastic

wave velocity measurements. The preparation of the cavitated material was described in the previous Annual Report of ONDE (Ref. 1). A photomicrograph of the typical microstructure is shown in Figure 1. The elastic

wave velocities and moduli were determined as a function of density (or

void concentration) for the various specimens. The technique employed for

these determinations involved determining the time for an elastic wave to

travel from one end of a bar of known length to the other end, be reflected, and return. Standard ultrasonic transducers produced the pulse and

recorded its return. These results were monitored on an oscilloscope

whose time base could be determined with high precision.

For both axial (z) and transverse directions, . Figures 2, 3, and 4 show

C-j vs x

v.j vs x

C-j vs p

where v-j = longitudinal sound velocity

p = mass density

c-j = pv-j^ = longitudinal modulus

x = volume fraction of voids = 1 - p/p 0

The different intercepts show the effect of texture. Probably a <11 1> rod

texture that shall be verified by calculations.

The large slope suggests that the voids are not spheres. For

spheres, Hashin's (Ref. 2) model predicts, approximately,

1 dCj_

c-j dx

il

8

2.63

For the x-direction slope, we find, approximately,

90
7.87

1 dci

c-| dx

The difference in slopes (x and z directions) suggests that the discshaped voids do not orient randomly, but in some preferred way.

dc dc

That ( —) exceeds ( — ) suggests that the discs tend to align

dx z-dir dx x-dir

perpendicular to the z axis (the stress axis).

Thus, all these sound-velocity measurements are consistent with the

metallography and with the model of void growth (Ref. 3).

QUANTITATIVE MICROSCOPE STUDIES OF CREEP DAMAGED 304 STAINLESS STEEL

Creep damaged 304 stainless steel had been prepared for characterization by the SANS technique (Ref. 4) prior to ultrasonic NDE characterization. Some of the more highly damaged specimens contained cavities that are visible in the optical microscopy. It is not appropriate to use SANS

in this size range. These cavities have been measured using automated

quantitative microscopy.

We report here some of the measurements on a large number of creep

cavities in AISI type 304 stainless steel. The data were obtained through

the use of an automatic image analyzing computer, a device which is

capable of scanning large numbers of microscopic fields on polished metal

surfaces and making measurements on individual creep cavities in each

field. The techniques used, as well as some preliminary results, are reported in greater detail in [5]. All raw data is available on IBM-PC

compatible magnetic media (floppy disks).

The test program utilized flat, plane stress tensile specimens

fabricated from strip stock of a commercial heat of AISI type 304 stainless steel. All specimens were tested in air at 600°C under constant load

creep conditions. Two series of tests were conducted. The first was a set of replicate tests in which four groups of three specimens were tested

under conditions which were identical for each group. The second set of

tests involved a group of specimens which were tested at various loads and

test durations, analyzed, retested at the same load for an additional

period of time, and then reanalyzed. In all cases the central 3~4 cm of

the specimen test section was carefully polished after removal from the

testing machine. The specimens were then analyzed on an image analyzing

computer. With the magnification used in the present study f406x), this

device is capable of measuring cavity areas down to 1.7 ym^. A sufficient

number of fields were examined on each specimen so that at least 1000

cavities were measured per specimen. The results were corrected Tor the

presence of inclusions by measuring the inclusion size distribution on n

uncavitated specimen, and subtracting this distribution from the measure

cross-sectional area distribution.

91
Figure 5 is a histogram showing the measured distribution of cavity

cross-sectional areas on a typical specimen. A well-defined peak in the

distribution may be seen in the neighborhood of 15 pm 2

, with the distribution falling off fairly smoothly with increasing area. Figure 6 shows the same distribution plotted on Weibull probability axes. It can be seen

that the probability distribution function for the measured cavity

cross-sectional area is reasonably well represented by a Weibull cumulative distribution function over most of the range. Of interest is the

fact that the slope of the distribution appears to flatten towards the

extreme upper end of the curve. Because the coefficient of variation is

inversely related to the slope of the curve, this indicates a substantially greater degree of scatter in the size variations of the largest

cavities as compared to the much more numerous smaller cavities. We

believe that this result suggests that the small cavities can be treated

deterministically using models similar to those developed in Ref. 3* The

large cavities apparently behave stochastically and would require a different type of formalism.

The results of both test series indicate that the mean measured

cavity area (A) varies with time (t) and applied stress (o) according to

the relation A = Cto a where C and a are constants. Figure 7 shows the

results of the series of replicate tests, with the error bars indicating

the standard deviation of the measured vales. The correlation coefficient

for the linear fit is greater than 0.99. The hypothesis that the mean cavity area increases linearly with time is supported by some recent SANS

observations on type 304 stainless steel due to Fuller et al [3] and also

by earlier work on alpha-iron by Cane and Greenwood [6].

It should be noted that the above results were obtained on metallographic specimens. As such, they represent a two-dimensional cut through

a three-dimensional distribution. We have developed a computer program

which numerical converts the 2-D distribution to the 3~D distribution

using the theory of R.T. DeHoff (7) and the algorithm of Visscher and

Goldman (8). This program still requires further development to run correctly.

The present geometrical shape of the reference specimen of 304

stainless steel is not conducive to the same procedural approach applied

to the copper specimens. We are now evaluating the best NDE approach to

studying these reference specimens.

PREPARATION OF A CAST COPPER SPECIMEN FOR SANS CHARACTERIZATION

SANS studies on the creep damaged copper, reported in the previous

ONDE Annual Report (1), were complicated by a texture effect in the

original, copper bar stock. In order to quantify this effect, untextured

copper of the same purity would have to be analyzed in the SANS instrument. A copper cylinder 25 mm in diameter and 25 mm long was heated in a quartz vessel under a reducing atmosphere (CO) to 1200°C for one hour. The

resulting ingot was cut and polished to the same dimensions as the

preceding SANS specimens and given to the researchers in the Reactor

Division for evaluation. Their report on this specimen will be issued

92
separately.

FERROMAGNETIC SUSCEPTIBILITY OF CREEP DAMAGED AUSTENITIC STAINLESS STEELS

In the course of a routine investigation of several superheater tubes

from a coal-fired power plant, it was discovered that they were ferromagnetic in certain areas. These austentic stainless steel tubes had failed

after about 120,000 hours (13*5 years) service at 540°C, sustaining a steam pressure of about 1850 psi.

It is very significant that the magnetic regions were those that also

exhibited abundant creep cavities and cracks. Since austenitic steels are

not normally magnetic to the extent found here, further work was undertaken to detect the source of the ferromagnetism. Optical and electron

microscopy revealed the presence of sigma phase (non-magnetic) and ferrite

(magnetic) at grain boundary triple junctions (Figures 8 and 9).

Evidently, a certain percentage of the FCC alloy can transform slowly at

steam plant temperatures to the BCC structure. The interesting questions

are: why is the creep damaged regions much more ferromagnetic than the

sound areas of the tubes and can these observations be used to develop a simple NDE technique for steam plant opeators that will detect severely

degraded austenitic superheater tubes in situ? Such an NDE technique

would be useful because it would alert field engineers to the presence of

aged components during scheduled down-times rather than have them fail

during operation of the plant. A correlation between magnetic susceptibility and extext of optically visible creep damage in 321 stainless steel

is shown in Figure 10. Futher work has detected increased magnetic

susceptibility in crept 30-4 and 347 stainless steels.

SUMMARY

Progress in the NDE of distributed damage in metals has been made in

the following areas: wave velocity studies in creep damaged copper;

measurement of cavity size distributions in 304 stainless steel; preparation of a cast copper specimen for SANS evaluation; and ferromagnetic

susceptibility studies in creep damaged stainless steels.

REFERENCES

1. L. Mordfin, editor, "Office of Nondestructive Evaluation, Technical

Activities 1984," NBSIR 84-2944 (November 1984).

2. Z. Hashin "The Elastic Moduli of Heterogeneous Materials," J. Applied

Mechanics _29 pp. 143-150, (1962).

3. E.R. Fuller, Jr., R.J. Fields, T.-J. Chuang, and S. Singhal," Characterization of Creep Damage in Meals Using Small Angle Scattering," J. of Research of NBS , 89, pp 35-45, (1984).

93
4 . R.J. Fields, R.C. Dobbyn, and C.I. Glinka, "Microstructural Characterization by Small Angle Neutron Scattering,” to be published in In

Process, Nondestructive Microstructure Characterization , A.S.M.

Symposium, Sept. 1984.

5. T.S. Liu, R.J. Fields, D.G. Harlow, and T.J. Delph, "Statistical

Observations of Creep Cavitation in AISI Type 304 Stainless Steel,"

Scripta Metallurgies , J_9, pp 299-304, (1984).

6. B.J. Cane and G.W. Greenwood, "The Nucleation and Growth of Cavities

in Iron during Deformation at Elevated Temperatures," Metal Science 9_, pp 55-60, (1975).

7. R.T. DeHoff, "The Determination of the Size Distribution of Ellipsoidal Particles from Measurements Made on Random Plane Sections," Trans.

A.I.M.E., 224 , pp 474-477, (1962).

8. W.M. Visscher and A.S. Goldman, "Estimating the Distribution of

Spherical Particles from Plane Sections. An Optimal Algorithm for

Solution of the Abel Integral Equation," J. of Scientific and Statistical Computing, 4, pp 280-290, (1983).

94
Longitudinal

Modulus

C

I

0~I

I

Pa)

Figure 1. Creep damage in copper consists of cavities (or oblate

spheroidal voids) oriented

with the major axis perpendicular to the applied tensile

stress

EFFECT OF POROSITY ON MODULUS

Figure 2. Longitudinal modulus versus volume fraction of voids

in copper.

95
EFFECT OF POROSITY ON VELOCITY OF SOUND

Figure 3. Longitudinal sound velocity versus volume fraction of

voids in copper.

DEPENDENCE OF MODULUS ON DENSITY

Figure 4. Longitudinal modulus versus mass density in cavitated

copper.

96
Figure 5

200 v

1 80

1 60 i

2 4 6 8

NO . PER mm^

1 0

Histogram showing distribution of cavity cross-sectional areaa

on a typical specimen of cavitated stainless steel.

97
2

Figure 6 Distribution of cavity cross-sectional areas plotted on Weibull

probability axes.

98
LN

(<r~

MPa)

5.6

A C t <r 5.5h LEAST-SQUARES FIT

i

5.4 - r^o5.2

V t hr /

Figure 7. Evaluation data from numerous tests with model-based

equation results in straight line fit, thus supporting

model

Figure 8. Optical micrograph of degraded 321 stainless steel showing (a) ferrite and (b) sigma

phase.

99
Figure 9. Electron micrograph of degraded 321 stainless

steel showing ferrite (identified by electron

diffraction).

MAGNETIC VARIATION AROUND TUBE

Figure 10. Variation of ferromagnetic susceptibility (in terms

of equivalent % ferrite) around perimeter of failed

tube. Extent of visible creep damage is indicated.

100
CREEP CAVITIES IN COPPER: AN ULTRASONIC-VELOCITY

AND COMPOSITE-MODELING STUDY

H. M. Ledbetter and R. J. Fields

Fracture and Deformation Division

Institute for Materials Science and Engineering

When copper suffers tensile loading at high temperatures, voids nucleate

at grain boundaries. These voids grow, coalesce, and cause failure.

These voids (or creep cavities) pose problems for many people: the nde

specialist, who wants to detect them; the materials engineer, who wants to

improve resistance to failure; and the materials scientist, who wants to un- derstand the material behavior.

The present study used ultrasonic methods to determine longitudinal-mode

sound velocities and elastic constants in crept copper rods. We considered

two directions: axial and radial, that is, parallel and perpendicular to the

rod (stress) axis. We denote these directions x^ and x-j , respectively.

The study produced five principal conclusions:

1.

The copper rods contain considerable texture. To quantify this, we assume the usual [111] - [100] duplex rod texture observed in copper.

From copper's well-known monocrystal elastic constants, from an averaging

model given by Gairola and Kroner, and from the two sound velocities,

v^ and v^, one can calculate the relative [111] and [100] contributions.

For the as-received material, we obtained x ( 1 1 1 ) = 0.56, the volume fraction of grains with [111] orientations.

2. Heating the copper alters the texture. By the same analysis used above,

using values measured after heating, we found x ( 1 1 1 ) = 0.71. The proportion of [111] texture increases. Metallography shows grain growth

during heating. Presumably, this explains the texture transition.

3. The voids are not spherical. Figure 1 shows the variation of both v. anc

v^ with void volume fraction (determined by measuring mass density). The

figure also shows a theoretical line for spherical voids. Both other

theories and measurements support this prediction. The strong departure

of observation from this line suggests that the voids have oblatespheroidal (disc) shape. Datta and Ledbetter showed that disc-shaped

voids soften a material much more than do spherical voids. The extent or’ softening depends on the disc's aspect ratio: flatter discs cause nor-- softening. Metallography confirms that sets of small spherical voids

coalesce and form disc-shaped voids along grain boundaries.

4. The disc-shaped voids do not orient randomly. If they did, the slopes

dv.|/dx and dv^/dx would not differ.

101
5. Probably the disc-shaped voids tend to orient perpendicular to the stress

axis, x^. This accounts for the slope dv^/dx exceeding dv^dx. Again,

metallography confirms this orientation tendency.

We plan to use composite-property-modeling methods to verify quantitatively the void geometry described above. Our model will include several

variables: (a) copper’s elastic constants, (b) void volume fraction, (c) void

shape, and (d) void orientation.

In any related future studies, we want to consider two other properties:

(a) shear-wave sound velocity, and (b) internal friction.

Usually, both of these properties provide more information about internal

structure than the longitudinal-wave sound velocity used in the present study.

SUMMARY

By measuring longitudinal-mode ultrasonic velocity, we studied creep

cavities in copper. Using a model by Ledbetter and Datta, we interrelated

several variables: cavity volume fraction, cavity shape, and cavity orientation. Also, we made some deductions concerning texture.

c

Figure 1. Longitudinal modulus = pv^ versus volume fraction of voids in

creep-cavitated copper. The rod (stress) axis is denoted 3. Dashed

lines represent Ledbetter-Datta model calculations for (A) spherical

voids, (B) 10: 1-aspect-ratio disc-shaped voids oriented randomly,

and (C) identical discs oriented perpendicular to 3 axis. Symbols

show measurements.

102
NDE DATA ANALYSIS, RELIABILITY MODELING, AND PC-BASED SOFTWARE RESEARCH

J. T. Fong, R. S. Cramer, D. F. Redmiles, M. R. Knapp-Cordes

Mathematical Analysis Division, and

J. J. Filliben

Statistical Engineering Division

Center for Applied Mathematics

This project grew out of a consulting request in 1976 by the U. S.

Department of Transportation to the National Bureau of Standards (NBS) for

a comprehensive evaluation of the structural integrity of a large number

of girth welds in an oil pipeline then under construction at Alaska.

The study identified a research need on the development of an "acceptable industry standard" for analyzing round robin inspection data and for

estimating the detection, location, and sizing reliabilities of a field

nondestructive evaluation (NDE) procedure.

To address this need, the NBS Center for Applied Mathematics initiated

in 1977 a long-term research project with two specific goals as follows:

(a) To develop an analysis and modeling methodology for estimating the detection, location, and sizing reliabilities of ultrasonic and radiographic examination of weld flaws with or without post-examination sectioning data.

(b) To design a prototype archival database and personal-computer-based

software for collecting, evaluating, and disseminating field inspection

and round robin NDE data for on-line operational, maintenance, and

design decision support.

Since 1978, this work has also been supported by the NBS Office of

NDE. During 1982-84, an industry-based Pressure Vessel Research Committee

(PVRC) of the Welding Research Council in New York, NY, provided partial

support for the analysis of round robin and sectioning data of PVRC specimen

251J. Two technical reports, one for each of the above two goals, are being

prepared for discussion and publication during 1985-86. The titles of those

two reports are:

(a) "Reliability Analysis of Round Robin NDE Data for PVRC Weld Specimen

251J," by J. T. Fong, NBS Technical Report to Pressure Vessel Research

Committee of the Welding Research Council, New York, NY, Oct. 1985.

(b) "How to Manage Engineering Data with a Personal Computer (PC)," by J. T.

Fong, ASME Special Technical Publication for 1986 Joint PVP and Computer Engineering Conference Tutorial at Chicago, IL, July 1986.

103
TYPICAL ANALYSIS RESULTS

To illustrate the analysis methodology and the significance of a typical

result, the reliability of a flaw fabrication procedure used by PVRC about

20 years ago when specimen 25 1 J was made, is selected for discussion in

this report. As shown in Fig. 1, a block of A533 Grade B thick-section

steel (28 cm or 11 in thick) had 15 flaws of 4 different types built into

the butt weld during a 159-pass submerged-arc welding procedure. The actual

dimensions of those flaws, as determined by Yukawa in 1981 (Ref. 1), are compared with the intended dimensions in Table 1

To bring the data into a more manageable form for interpretation and

modeling, we consider a normalization procedure where the maximum dimension

of each intended flaw is assigned the uniform value of 1.00. The actual

dimensions of the 15 flaws as determined by Yukawa in his sectioning experiment are presented in a normalized box plot (Fig. 2) using a software package

known as DATAPLOT (Ref. 2).

A qualitative observation of Fig. 2 shows that the flaw fabrication

procedure is (a) dimensionalLy stable (up to 50% oversizing) for long slags

and short slags , (b) consistently exaggerating in dimensions by a factor

of 2.2 for cross cracks , and (c) generally unreliable for longitudinal cracks . This "inhomogeneity" in data provides an opportunity to conduct an analysis

of variance (ANOVA) (Refs. 2 and 3) and a more accurate assessment of the

fabrication reliability than hitherto attempted by previous investigators

(Ref. 4). A comparison of the traditional univariate analysis of 15 flaw

size data versus the use of ANOVA for 4 types of flaws is given an Fig. 3.

An interval estimate of the so-called mean amplification factor as a measure

of the effectiveness of the flaw fabrication procedure for confidence levels

between 50% and 95% is given in Fig. 4. The chi-square distribution of

the total variance using a one-way analysis of variance procedure for 50%

to 95% confidence levels is given in Fig. 5. More detailed results of the

reliability study of the flaw fabrication and detection procedures are given

in the Oct. 1985 NBS report to PVRC.

REFERENCES

1. S. Yukawa, "Sectioning of PVRC NDE Specimen 251 J," Progress Report to

PVRC dated Jan. 15, 1981 and May 25, 1983.

2. J. J. Filliben, "DATAPLOT - An Interactive High-Level Language for Graphics, Nonlinear Fitting, Data Analysis, and Mathematics," Computer

Graphics, 15 , No. 3, pp. 199-213 (1981).

3. H. E. Daniels, " The Estimation of Components of Variance," J. Royal

Statistical Soc., Supplement 6 , No. 2, pp. 186-197 (1939).

4. Buchanan, R. A., "Analysis of the NDE of PVRC Plate-Weld Specimen 251 J,"

WRC Bulletin 221 . Nov. 1976.

104
Table 1 Sectioning Results for PVRC 251J

Actual Flaw Intended Flaw

Location Coordinates (in.) Location Coordinates (in.)

Flaw Type* X Y Z X Y Z A CC 26.1-25.5 2. 4-4.

1.0-1.

25.5-25.3 3.0 1.0

a LS 26.3-26.4 16.1-18.1 0. 6-1.1 26.3 16.0-18.0 1.0

c LC 25.9-26.6 29.7-33.4 0.7-1.

26.3 30.0-32.0 1.0

a LC 25.1-25.6 2.2-5.

2.4-3.

25.0 2. 0-4.0 2.75

E CC 25.3-25.5 17.1-19.0 2. 3-3.

25.0-25.3 17.0 2.75

F SS 25.1-25 .2 30.6-31.8 1.9-2.

25.0 30.6-31.4 2.75

S LS 26.2-26.4 2. 2-4.

4. 5-5.26.3 2. 0-4.0 5.5

H LC 25.7-25.4 16.1-21.9 5.0-5.

26.3 16.0-18.0 5.S

I CC 26.0-26.4 30.2-31.9 5. 2-5.7 25.5-25.3 31.0 5.5

J CC 25.1-25.3 3. 1-4.

7. 7-8.

25.0-25.3 3.0 8.3

K SS 25.1-25.5 17.1-18.1 8. 0-8.

25.0-25.3 17.0 8.3

L LC 25.1-25.7 29.1-33.9 7. 6-8.2 25.0 30.0-32.0 8.3

M LC 25.7-26.3 1. 0-5.0 9.3-10.0 26.3 2. 0-4.0 10.0

N CC 25.3-25.3 16.7-18.7 9. 3-9.3 25.5-26.3 17.0 10.0

0 LS 26.0-25.2 29.8-32.2 9.5-10.2 26.3 30.0-32.0 10.0

•Type of Haw: CC * Cross Crack

IS * Long Slag

LC 3 Long Crack

SS * Short Slag

X

Figure 1 - Principal sectioning cuts of

PVRC 25 1 J . The block is

11 inches high (z-di rection)

by 36 inches long (y-direction)

105
Number

of

Flaws

Max.

Flaw

Dim.

(intended

4

2 -

(max., median, min., k 1/4-points)

- X

x r

- T X

1 X

Int. Max.

1

. db

^

Size —Jt-

”T " 1 i J C. CRACK

(5)

2 LCRACK

(5)

3

L.SLAG

(3)

4 S.SLAG

( 8 )

Figure 2. Box plot for four (4) types of flaws

Norm. Mu. Dim. (intended flaw dim. = 1)

Figure 3. A comparison, of univariate anal. vs. ANOVA with replicates

106
Confidence

Level

(C.L.)

Confidence

Level

(C.L.)

M = Sample Are. S2 = S.D. (ANOVA)

Figure 4. t-distribution limits mean amplif.

of intended flaw size

II = Sample Aee. S2 = s'd. (ANOVA)

0 12 3 4

Norm. Max. Dim. (intended = 1)

Figure 5. Chi-Sq distribution limits

107
108
III. NDE FOR INTERFACES AND COMPOSITES

The topics for this section, interfaces and composites, were chosen

primarily because of the major technical importance of interfaces and com- posites in modern engineered systems. They were also chosen because of the

continuing difficulty and scientific and technical challenge facing NDE

when applied to interfaces and composites. Although the focus of most of

the activities in this section are on NDE for process control, the work is

also important to in-service and post-manufacture inspection. In the first

group of six papers on composites, three papers of particular interest deal

with monitoring of polymer cure rate by fluorescence, dielectric and ultrasonic techniques. In the second group of five papers on interfaces, the

theoretical and experimental work on eddy current conductivity profiling

and the associated data inversion process deserve note.

109
110
CURE MONITORING OF COMPOSITES USING FLUORESCENCE SPECTROSCOPY

Bruno M. Fanconi, Francis W. Wang and Robert Lowry

Polymers Division

Institute for Materials Science and Engineering

The manufacture of polymer matrix composites involves complex

chemical and physical changes that must be adequately controlled to

produce desirable products. Monitoring of resin viscosity during cure is

a key step towards improved process control. A technique is under

development that uses the sensitivity of the fluorescence intensity of

some organic molecules to the local viscosity. Optical fibers are used to

bring the excitation light into the interior of a curing composite

component, as well as to collect and transmit the emitted light for

detection. The light in the fiber excites probe molecules that are located within the penetration depth of the evanescent wave. This

distance depends on the refractive indices of the waveguide and

surrounding matrix, as well as the angle of incidence that the propagating

light makes with the optical fiber-matrix interface. Thus, this approach

is particularly sensitive to the interfacial region that is of critical

importance in achieving desirable mechanical properties and performance.

The current focus of this work has been the identification of

suitable probe molecules, and calculations of the effect of viscosity

profiles on fluorescence intensities excited by evanescent waves. Two

types of probe molecules have been examined. The excimer-type

fluorescence probes are attractive owing to the presence of the monomer

fluorescence that can be used as an internal standard. This feature is

attractive since factors other than viscosity change can affect the

observed fluorescence intensities. Curing studies of amine-cured epoxy

resins had shown that the excimer-f luorescence technique was insensitive

to viscosity changes in the later stage of curing. For this reason, other

probe molecules with fluorescence sensitivity over a wider viscosity range

have been investigated. The lack of an internal standard for these probe

molecules lead to use of a second molecule which has a viscosity

insensitive fluorescence intensity at a frequency distinct from that of

the viscosity probe. Figure 1 shows the fluorescence intensities as a function of cure time of the probe molecule

1 -(4-dimethylaminophenyl)-6-phenyl-l ,3,5 hexatriene and the internal

standard 9 , 1 O-diphenylanthrancene dissolved in an epoxy resin. The ratio

of these two intensities is related to the viscosity developed at that

stage of cure.

An advantage of the use of probe molecules is that their

concentrations can be extremely low. The concentration of the probe

molecule and internal standard used to obtain the data shown in Figure 1 were 5*10 ^M and 2*10

- ^M, respectively. At these exceedingly low

concentrations the probe molecules are not expected to have an effect

the resultant mechanical properties of the composite part.

Ill
A significant advantage of waveguide spectroscopy for composites is

that the sampled material lies near the fiber-matrix interface, and by

varying the penetration depth of the evanescent wave it may be possible to

profile the viscosity distribution or chemical change in the interfacial

region. We have calculated fluorescence intensities excited by the

evanescent waves of the various cavity modes of thin-film waveguides. The

calculated intensities of the emitted light were evaluated for sensitivity

to distributions in the probe-molecule concentrations within the penetration

depths. Various concentration profiles were examined to include likely

distributions of viscosity and chemical effects in the interfacial region.

The calculations were conducted for thin film type waveguides in

which prisms are used to couple the light into the waveguides. The thin

film waveguide modes that can be activated depend on the refractive

indices of the film, substrate, and coupling prism, as well as the film

thickness, the wavelength of the excitation light, and the angle of

incidence. The electric field magnitudes within the matrix material were determined for these allowed modes, and together with an assumed

concentration profile of probe molecules, the relative fluorescence

intensities excited by the waveguide modes were calculated. The

concentration profile was assumed to be of the form C(x)=CQ

( 1-exp(a0 x^)

where x is the distance into the matrix from the waveguide-matrix surface,

C 0

in the concentration in the bulk and a0

is a parameter that controls

the distance near the surface over which the concentration differs

appreciably from that of the bulk. Figure 2 shows the ratio of the

fluorescence intensities of the two allowed modes assuming a substrate

refractive index of 1.46, a waveguide refractive index of 1.56, and an excitation light frequency of 488nm. The ratio is sensitive to the

concentration profile over a distance of about 30nm.

The model calculations support the notion that information about

viscosity profiles and chemical variability near the waveguide-matrix

interface can be elucidated using fluorescence spectroscopic studies of

probe molecules excited by the evanescent waves.

SUMMARY

Suitable probe molecules for monitoring viscosity changes occurring

during composite cure have been identified. Calculations of the

fluorescence intensity as a function of probe molecule concentration near

the waveguide-matrix interface indicated sensitivity over distances from 2 to 50nm.

112
0 20 40 60 80

Cure Time, Minutes

Figure 1. Fluorescence intensities of viscosity probe (top curve) and

reference standard (bottom curve) in an epoxy resin as a function

of cure time.

113
WAVEGUIDE FLUORESCENCE

Figure 2. Ratio of the calculated fluorescence intensities of two waveguide

inodes as a function of the distance from the waveguide-matrix

interface at which the concentration is 1/2 that of the bulk.

114
CURE MONITORING IN EPOXY RESINS BY ELECTRICAL MEASUREMENTS

Frederick I. Mopsik

Polymers Division

Institute for Materials Science and Engineering

The processing of epoxy resin based composites has been rapidly

expanding. These composites, especially those using high strength fibers,

are being considered as advanced, light weight replacements for metals in

many high technology applications. A major need in furthering the

application of these composites is a means for monitoring and controlling

the cure reaction so that it can be optimized for high cure rate and

better quality control. Monitoring of the cure cycle through dielectric

measurements offers the possibility of an easily implemented technique

that could readily be automated for on-line process control.

When this project was initiated last year, it was not clear as to

whether ionic conduction or dipolar relaxation would be the dominant

process in monitoring cure. An automated system for measuring AC

conductance over a very wide range of values as a function of time was developed to help resolve this issue. A reproducible, disposable

electrode set was also developed since the cured resin bonds very strongly

to any metal. In addition, a previously developed dielectric spectrometer

that used rapid time-domain measurements provided a basis for

investigating any dipolar loss mechanisms.

This past year measurements were carried out on several epoxy base

resins using an imidazole curing agent. The measurements at the beginning

of the cure were made at 50 Hz with the conductivity system where

conductance is clearly the dominant contribution to dielectric loss. As

the cure approached completion at constant temperature, the measurements

were extended both in frequency and in sensitivity using the spectrometer

Modifications were made to the spectrometer to allow a precise time

reference for the measurements.

A sample cure curve is shown in Fig. 1 . The solid curve shows the

data at 50 Hz with the extensions from the spectrometer shown as crosses.

The initial rise at short times is the increase in conductance as the sample was heated in the oven. The strong decrease is the result of cure.

The smooth monotonic decrease in conductance after the maximum indicates

that conductance is the main contributor to dielectric loss. If a dipolar

loss process that moved to lower frequencies during cure were important,

it would appear as either a shoulder or second peak in the conductance

curve, since for a given frequency the conductance is proportional to

dielectric loss and a dipolar loss process must have a maximum as a function of frequency. The data in Fig. 1 clearly show no shoulder or second

peak once the conductance starts to decrease.

115
There is, at the end of the cure, evidence of a relaxation process.

This is seen in Fig. 1 by the lower conductance values at 0.01 Hz taken

from spectrometer data. This loss is mainly at higher frequencies and is

relatively featureless. This can be seen in Fig. 2, where a complete

spectrum is presented in the complex plane. The points increase in

frequency to the left. The strong upsweep to the right is from

conductance. A relaxation would be definitely peaked and is not seen.

One unexpected result from these measurements was found when a sample

was preheated prior to filling the cell. The results for this cure are shown as the lower curve in Fig. 3 which is shifted by 50 minutes to the

right from the upper curve, the data from Fig. 1. The preheating

partially cured the sample as evidenced by the shorter cure time. What is even more significant is that the strong decrease in conductance at the

end of the cure is unaffected, since the two curves run in parallel. This

result suggests that a standardized conductivity measurement could be used

to evaluate the state of the resin prior to cure, establish its useful

life and help determine processing conditions.

For next year, more systems must be studied to establish firmly the

dominance of conductance as a contribution to dielectric loss. The

results already show that conductance can be used to follow the cure rate,

but it is possible that low conductance resins may show a relaxation

phenomenon near cure completion. Also, the use of conductance

measurements to establish shelf-life must be pursued. A series of

partially cured samples must be studied to confirm the results found this

year. Such a study could lead to a standardized test method for

monitoring the initial state of a cure. Also, a tie-in must be made to

other, more traditional measurements so that electrical measurements can

be related to more conventional measures of cure. Already, it has been

found that the conductivity decrease comes after the exotherm as measured

by DSC.

SUMMARY

Conductivity and dielectric loss measurements have been made on curing epoxy resin samples. Conductance as a function of time shows great

promise as an inexpensive and easily automated method for monitoring cure.

116
EPOXY

B3A2

60°C

CURE

(l-C)O

117

Figure

1.

Conductance

vs

time

for

a

curing

epoxy.

The

main

upper

curve

is

for

50

Hz

while

tlie

small

lower

curve

is

for

0.01

Hz.

The

crosses

are

data

taken

from

the

dielectric

spectrometer.
EPOXY

B3A2

60°C

270m

CURE

Qd) ..o

118

Figure

2.

Complex

plane

plot

for

the

complex

capacitance

measured

at

270

minutes

into

the

cure.

Frequency

decreases

to

the

right.

The

upsweep

is

due

to

conduction.
B3A2

60°C

CURE

119 I

igute

5.i

he

upper

curve

is

the

50

Hz

cure

data

of

Figure

1.

The

lower

curve

is

data

taken

tor a

preheated

sample

and

is

displaced

by

50

minutes

from

the

upper

curve.
ULTRASONIC CHARACTERIZATION OF POLYMERS

S. I. Rokhlin, K. Lewis, F. K. Graff

Department of Welding Engineering

The Ohio State University

Columbus, Ohio 43210

Thermosetting resins are widely used as matrices for advanced composite

materials and structural adhesives. Fabrication of composite materials or adhesive joining consists of curing (polymerization) under proper thermal

and pressure conditions of resin-impregnated fiber fabrics. During the

curing reaction, the thermoset resin transforms from the visco-liquid state

to the gel and then vitrified to the gelled glass. This transformation is

accompanied by strong changes of the viscoelastic properties of the materials which are related to the molecular network. Therefore, measurements of

velocity and attenuation of ultrasonic waves during cure may give important

information on the extent of the thermoset curing reaction and the mechanical properties of the material.

Several authors used ultrasonic waves for curing study of thermosetting

resins. In spite of these studies not much work has been done to understand

the nature of the ultrasonic wave interaction with thermosetting resins

during curing. The key issue here is the curing time-frequency-temperature

behavior of the ultrasonic wave velocity and attenuation during cure.

In this work we applied an ultrasonic spectroanalysis technique to measure the frequency dependence of the ultrasonic velocity and attenuation,

continuously during the cure of the epoxy resin. During the experiment we monitor amplitude and phase changes in the time and frequency domains of the

first signal transmitted through the epoxy resin in an experimental cell.

The three dimensional plot of the attenuation coefficient data is shown

in Fig. 1. From this data we come to a very important conclusion: the

attenuation coefficient behaves linearly with frequency at all stages of the

curing reaction from the viscous liquid to the solid state. The slope of

the attenuation factor as function of frequency is strongly dependent on time of cure (on degree of cure). The linear behavior of attenuation versus frequency suggests that the attenuation effect cannot be explained by classical viscothermal absorption or relaxation theory. Such type of behavior

(so-called hysteresis behavior) is poorly understood on the molecular level

and was found previously for some highly viscous liquids, for solid polymers

and for biological tissue.

The phase velocity data were evaluation from the phase spectrum of the

transmitted signal. These data are shown in Fig. 2. It is seen that there

are substantial changes in ultrasonic velocity changes with time and a moderate

dependency on the frequency.

The analysis of experimental data suggests that epoxy thermosetting

resin behaves as a polymer glass in the MHz frequency range in all stages of

the curing reaction. The ultrasonic wave feels the liquid-solid transformation during curing as a transformation in a glassy state, the rate of which

of course depends on temperature.

120
ATTENUATION SURFACE

Fig.l Attenuation coefficient versus frequency and ti me of curing.

121
SOUND VELOCITIES AND ELASTIC CONSTANTS

OF REINFORCED COMPOSITES

H. M. Ledbetter, M. W. Austin, and R. D. Kriz

Fracture and Deformation Division

Institute for Materials Science and Engineering

Our studies continue on sound velocities and elastic constants of reinforced composites. These studies involve both measurements and modeling.

A physical property of a composite material depends mainly on three

ingredients: matrix property, inclusion property, and phase geometry. Phase

geometry includes many variables: vplume fraction, inclusion shape, inclusion orientation, inclusion size, and inclusion distribution. For some com- posites, especially at higher temperatures, the inclusion-matrix interface

affects an apparent physical property.

Elastic constants enter many aspects of composite-material behavior:

stiffness-weight ratio, load-deflection, elastic instability, thermoelastic

stress, residual stress, sound-wave velocities, material characterization,

relationship to other physical properties (for example, thermal expansivity

and specific heat), plastic deformation, theoretical strength, and non- destructive evaluation.

Because one can measure elastic constants accurately, typically within

one percent, they- provide good tests of physical-property models. Although

isotropic materials possess only two independent elastic constants, a bulk

modulus and a shear modulus, composites (depending on their symmetry) possess

up to twenty-one elastic constants. Most composites exhibit at least orthotropic macroscopic symmetry, thus nine elastic constants. Uniaxial fiberreinforced composites exhibit transverse-isotropic (hexagonal) symmetry, thus

five elastic constants.

During the last year, we focused on several types of composites:

reinforcement matrix

1 . SiC particle AH

2 . SiC fiber AH

3. A& 2O

3

fiber AH

4. graphite cloth epoxy

5. glass fiber epoxy

6 . graphite ferrite, pearlite (cast iron)

7. voids Cu

SUMMARY

We continue to study, both by measurement and modeling, the sound velocities and elastic constants of various two-phase materials. The accompanying

figures show some selected results.

122
INTERNAL

FRICTION,

Q

_1

(10" 3)

Figure 1. Angular variation of Young’s modulus (in GPa) for a graphite-fabric-reinforced epoxy-matrix composite.

Curve through measurements represents theory.

co CLO

liT

C/3 D

_lZ>Q

C/3 b

z

3

o

>

Figure 2. Young's modulus along fiber direction, , and internal

friction, Q , versus fiber volume fraction, c. Straight

line assumes linear rule-of -mixture and represents lea^tsquares fit to three measurements. Curved line for 0

represents a free damped-oscillator model and linear

rules-of-mixture for mass, force constant, and resistance

constant. The model contains one adjustable parameter.

123
INTERNAL STRAIN (RESIDUAL STRESS) IN AN SiC/Al PARTICLEREINFORCED COMPOSITE: AN X-RAY DIFFRACTION STUDY

H. M. Ledbetter and M. W. Austin

Fracture and Deformation Division

Institute for the Materials Science and Engineering

expansion coefficients: 3-3 and 22.5*10 °K , respectively. Thus, one expects large internal strains and stresses in these composites because the

two constituents form interfacial bonds at high temperatures and are cooled

to ambient temperatures. The studied composite consisted of 30 volume

percent SiC particles, approximately 5 um in size, and shard-shaped.

In principle, one can measure the internal strain by conventional BraggBrentano-focusing and sin^-method x-ray diffraction and compute the internal

stress from the elastic constants. One determines the strain by measuring

the unit-cell dimensions of both phases, both unmixed and mixed in the com- posite. If a denotes the unit-cell dimension, then the linear strain is

e = Aa/a = (a

Q - a

Q )/a0

(1 )

where subscript o denotes the unmixed state and subscript c the composite

state. Table 1 gives the results of these measurements. Being face-centered

cubic, the aluminum alloy possesses one lattice parameter. Being hexagonal,

SiC possesses two. The table also contains the bulk modulus, B, and -the

stress, a, calculated from the isotropic hydrostatic-stress relationship

where aV/V denotes the volume strain, the sum of the three principal strains:

As expected from the relative thermal expansivities and an elastic

sphere-in-hole model, the aluminum matrix shows tensile stress, averaging

259 MPa. The SiC particles show a compressive stress, averaging -219 MPa.

The stress in the aluminum matrix amounts to approximately 95 percent of the

yield strength, 274 MPa.

Finally, we note that, based on transmission-electron microscopy, some authors suggest enormous dislocation densities in these composites. The

diffraction patterns in Fig. 1 do not support this claim. High dislocation

densities amount to a high distortion strain, which manifests itself as x-ray-dif fraction-peak broadening. Figure 1 suggests only moderate peak

broadening, thus only a moderate dislocation density. We intend to study

this question quantitatively.

o = BaV/V ( 2 )

aV/V = l (Aa/a)

i i - 1,3

(3)

124
SUMMARY

By x-ray diffraction methods, we studied the internal-strain/residualstress problem in a particle-reinforced SiC/ AS, composite. The particles

exist in compression, the matrix in tension, approximately 95 percent of the

yield strength.

Table 1. Measured strains and computed stresses for A1 and SiC

A1 SiC

Aa/a (10~3) 1.15 - 0.32

Ac/c (10~3) - -0.33

AV/V (10~3) 3.^5 -0.98

B(GPa) 74.9 223.4

a (MPa) 259 -219

a yield^ MPa ^ 274 -

Figure 1. X-ray diffraction pattern for the aluminum (111) line

(on right) and for the silicon-carbide (10.3) line. The

higher-intensity curves represent the unstressed cases.

125
EFFECT OF INTERFACE PROPERTIES ON WAVE PROPAGATION

IN A MEDIUM WITH INCLUSIONS

S. K. Datta (consultant to NBS

Department of Mechanical Engineering

University of Colorado, Boulder

Much current practical interest exists concerning wave propagation

through a composite medium with a random distribution of inclusions:

particles, flakes, or long continuous fibers in a homogeneous matrix.

Several theoretical studies report wave speeds and attenuation of coherent

plane elastic waves propagating through an elastic homogeneous medium con- taining spherical or ellipsoidal elastic inclusions. All these studies

assume that the inclusions bond perfectly with the surrounding matrix

material. Recently, Sayers [1] examined the effect of a distribution of

thin elastic spherical shells in a homogeneous matrix material of different

elastic properties.

In the present study, we analyze a problem different from the one con- sidered in [1]. We assume that the inclusions possess elastic properties

different from those of the matrix. Also, we consider the effect of a thin

boundary layer or material through which the elastic properties vary either

continuously or discontinuously from those of the inclusions to those of the

matrix. Results for the case without a thin layer are obtained by letting

the layer thickness go to zero.

The principal object of this study is to explore the practicality of

using ultrasound to characterize properties of interface layers in a particulate composite. Ultrasound is a practical tool for measuring properties of,

and characterizing the state of, a material with microstructure. References

to these various studies occur in [1]. We derive the equations governing

scattering by an inclusion surrounded by a thin layer of variable elastic

properties. (See Fig. 1.)

We find that the effective phase velocities and attenuation coefficients

can be modified substantially by the thin layer. For example, the effective

speed of propagation of a plane longitudinal wave is given by

k

2

(1 + 9cP ) (1 + 3cP ) {1 + -p- P, (2 + 3x

2

)}

!— _! 2 £ £ ( 1 ) k

2

1 - 15cP

2

(1 + 3gP

q

) + -JcP

2 (2 + 3 X 2

)

where P Q , p

1

, and P 2 depend on material properties. Considering the example

of SiC spherical particles in an AS, matrix, we find P

1 in this case is 0.02.

126
Thus, for small h/a we find that the percentage changes in P Q and P

2 are approximately 174(h/a)$ and 88(h/a)56, respectively. These changes should be

discernible in phase-velocity measurements. In Eq. (1), k denotes wavenumber, c denotes the volume concentration of inclusions, t denotes the

matrix-material wave-speed ratio, and subscript 1 denotes longitudinal wave.

SUMMARY

This study considers propagation of effective plane longitudinal and

shear waves through a medium with a random distribution of spherical

inclusions. We assume that inclusions and matrix possess different elastic

properties and that a thin layer of elastic material with still different

properties separates the inclusions from the matrix. Also, we assume samesize inclusions and same-thickness layers. We find that the layers substantially affect the phase velocities and attenuation of coherent plane waves

propagating through this composite medium.

REFERENCES

1. C. M. Sayers, Wave Motion, 7(1985) 95-104.

Figure 1. Schematic diagram showing spherical polar coordinates for a spherical particle of radius a surrounded by a layer of

thickness h.

127
CONDUCTIVITY PROFILING BY EDDY-CURRENT MEASUREMENTS

Arnold H. Kahn and Kevin R. Long

Metallurgy Division

Institute for Materials Science and Engineering

The purpose of this project is the development of a theoretical and

experimental basis for the determination of electrical conductivity profiles

of metallic materials by eddy current methods. Such conductivity profiles

are of interest because they are associated with surface hardening processes;

traditional eddy current testing, based on a comparison with selective

calibration samples is commonly used for quality control but measures only

some average depth. This research is aimed at introducing quantitative

profiling methods.

In solving the inverse problem of determining conductivity profiles, the

quantity of greatest interest, called the admittance function, ref. 1 , is

given by

c(u) = E(<u)/(iu)u 0

H(a)) )

( 1 )

where uj is the angular frequency of the ac currents, E(uO and H(<u) are respectively the electric and magnetic fields at the surface of the test

material, and u 0

is the permeability of free space. Impedance measurements

allow one to determine c(<d), as will be shown. By general methods of

electromagnetic theory, it may be demonstrated that for a finite sample c(oj)

has the form

c(uj)

oo E

n=1

(2)

where the A

n and A n are real. The A n are the inverse time constants of the

eddy current normal modes of decay; the An may be interpreted as the mode

strengths. These parameters characterize the test material. They are obtained by fitting the measured values of c(ui) to a truncated sum of the

form of Eq. (2). The truncated sets of A n and An are used to establish the

inversion profile.

The present approach is based on the observation that if c(oj) consists

of N terms, it represents the exact solution of a forward problem of N

conductive shells, ref. 1

The shell conductances and their spacings are given by the continued fraction expansion

c(ui) = -hi +

lu,*J o

T

1 + - h.

la)U 0

x 2

(3)

1

128
where the h^ are the spacings between shells with conductances t^. h0 is the

distance from the measuring point to the first shell. Finally, we recognize

that the model of shells is a discretized representation of a continuous

profile. The shells are then smoothed by spreading the conductances of each

shell half way to its neighbors, to give a step-like rendition of the

profile.

The proposed inversion process consists of the following steps:

1. Perform impedance measurements to obtain c(uO at numerous values

of the (real) frequency <*}, over a range such that the corresponding skin

depths span the dimensions of interest.

2. From the measurements of c (w), obtain a best fit to a truncated

series of the form of Eq. (2).

3. Transform c(oj) into the continued fraction form of Eq. (3), so as to

display the conductances and spacings of the shells.

4. Smooth the representation by shells into a quasi-continuous

distribution by spreading the conductances over the region between shells,

while keeping the integrated conductivity unchanged.

In testing the outlined inversion procedure, it is important to learn the

effects of the finite truncation of the series of Eq. (2). For this purpose

a computer simulation was performed for the profile reconstruction of a uniformly conducting slab, for which c(oj) is known exactly. The series was truncated for N = 4, 8, and 16 terms; the reconstructed profiles are shown in

Fig. 1. The data are appropriate for an aluminum slab 1 cm thick. The input

conductivity is shown as a dashed line.

Several characteristics seen in Fig. 1 are generally observed in

inversions by this method. The profiles are ragged at the outer surface,

then they are true for roughly half the region, and finally the accuracy

deteriorates near the midpoint of the slab. The deterioration is understood

to be caused by the symmetry induced vanishing of the interrogating electric

field at the midpoint. Since the exciting field is weak in this region,

there is little information to be obtained there from a small number of terms

in the series.

To demonstrate the inversion process, we performed computer experiments

for the inversion of data corresponding to a non-uniform profile. As an example, we present the case of a profile with a step in the conductivity.

(In principle, the method could be applied to any profile.) The forward

problem was solved and the admittance calculated at 20 frequencies from 1 s.y.z to 200 kHz. These data were then used as input to the four-step inversion

process outlined above. In Fig. 2 we show the results. The input

conductivity is drawn as a dashed line. The best fit to the data was obtained with 9 terms in the series of Eq. 2. The horizontal steps give tr.

reconstructed conductivity profile and the vertical lines show the location,

of the shells. This is typical of the best performance by this method, '-'or-' subtle deviations from uniformity would be poorly detected.

129
The approach has been extended to cylindrical geometry. When the

following substitutions are made the complete calculation algorithm still

applies

c(uO *> Rc(cj)

-h . - (R?-R i 2

1 )/ 2>

where R is the sample radius, the R^ are the shell radii, and the are the

cylindrical shell conductances.

The admittances are obtained from the experimental data by the

following relation

. 2 • (Z (oj) ~ Z (oj) )a^

Roto,) = *1 ar - (4)

where

Z ( uj) = impedance of empty coil

Z ( oi) = impedance of coil with sample

R = radius of sample

a = radius of coil

L

Q

= inductance of empty coil.

Experimental tests using cylindrical coils have been performed. It was found that the results determine the positions of conductivity change with

good accuracy, but that the magnitudes are only qualitatively represented.

While this work initially had been intended to address the

characterization of surface modification processes, the methods are generic

and may be used for the study of a conductivity profile, no matter how

produced. One area of emerging interest is that of temperature profiling,

since in many materials the conductivity is a unique strong function of

temperature. Discussions with the Aluminum Association have indicated that

such an approach could be very useful for determining temperature profiles

during the extrusion of aluminum.

SUMMARY

The method of depth profiling the electrical conductivity of a sample

material by measuring the frequency dependence of a surrounding coil's

impedance has been studied and tested by computer simulation. The theory was extended from planar to cylindrical geometry. Experimental verification was undertaken

REFERENCES

1. R. L. Parker, J. Geophys. Res. 85, 4*121 (1980).

130
Conductivity

(10 7Q

-1m

-1)

‘g

conductivity

<io'Q-«m-'>

(a) (b) (O

Depth Z (mm)

e 1. Profile reconstruction of a uniform slab of 1 cm thickness, using

exact but incomplete data in Eq. (2). Graphs (a), (b)

and (c)

have 4, 8, and 16 terms. The vertical lines show the locations

of the computed shells; horizontal solid lines show the computed

conductivity. The dashed line gives the input conductivity.

Figure 2. Results of inversion

computation for a profile with a step in the

conductivity. Input data

were for 20 frequencies

between 1 kHz and 200 kHz.

131
ULTRASONIC MEASUREMENT OF SURFACE ROUGHNESS

G.V. Blessing and D.G. Eitzen

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The purpose of this research is to study the effect of surface part

roughness on the scattering of incident ultrasonic waves; and then in turn to

address the inverse problem of evaluating surface part condition by means of

the scattered wave. Related studies were initiated several years ago in

support of an ASTM project to evaluate the relationship of roughness to

(apparent) material attenuation in steel plate . The program has since

evolved to developing the ultrasonic technique for monitoring roughness features on static and moving parts. Both liquid and air-coupled schemes are being investigated. While the amplitude of reflected echoes at normal incidence is being given principle attention, off-angle and multi-transducer

schemes are also being investigated.

Figure 1 illustrates recent ultrasonic results on a flat aluminum strip

with five increments of roughness ranging from to 0.8 to 37 pm rms. Each

roughness section was nominally 5 cm square on the 25 cm long specimen. The

peak-detected echo amplitudes of the back scattered pulses are recorded as a function of transducer position along the sample length. (The time for this

transducer sweep was a few seconds.) The sharp (step) boundary between roughness sections is evidenced by the sudden drop in signal amplitude due to

boundary scattering. The pulse-echo measurements were made at normal incidence, with a water squirter system coupling transducer and part via a one

cm water jet path (0.6 cm diameter) between nozzle exit and part surface. The

ultrasonic frequency was 5 MHz, for a wavelength of 0.3 mm in water.

This approach has also been successfully applied to curved surfaces, on stationary and rotating cylindrical parts with roughnesses comparable to the

strip values above. In the case of the (7 cm diameter) rotating part, the

detected echo amplitude faithfully recorded the same scattered amplitude as was obtained on the stationary part, up to the tested rotation rate of 200

rpm.

SUMMMARY

A good correlation between rms surface roughness and reflected ultrasonic

echo amplitude has been obtained. The coupling medium can be air, water

immersion, or a squirter (similar to a machine tool coolant stream). The

interrogated surface can be flat, curved, stationary, or moving. We will seek

to direct the work toward in-process control of the surface finish of parts

produced by automated machining.

REFERENCE

1. G.V. Blessing, P.P. Bagley, and J.E. James, "The Effect of Surface

Roughness on Ultrasonic Echo Amplitude in Steel," Materials Evaluation 42,

pp 1389-1400 (Oct. 1984).

132
100

apnijiduiv oqog SA|ie|ay

133
OPTICAL MEASUREMENT OF SURFACE ROUGHNESS

T. V. Vorburger, D. E. Gilsinn, E. C. Teague, M. J. McLay,

F. E. Scire and C. H. W. Giauque

Mechanical Production Metrology Division

Center for Manufacturing Engineering

Optical scattering techniques are being used extensively to study and

monitor the surface roughness of a variety of optical, semiconductor, and

mechanical components produced by industry. However, the successful development

of these techniques carries the need for a better understanding of the physics

of optical scattering from rough surfaces as well as for standardization of some

of the more practical approaches for on-line measurement.

Our research in optical scattering is directed along two lines. First, we are performing basic research into the quantitative understanding of the

relationship between rough surface topography and the resulting optical

scattering patterns. Second, we are working on practical approaches for the use

of the optical scattering method in an automated inspection station and as a manual tool for inspecting the roughness of components with unusual shapes.

On the basic research side, we have completed a study of the inverse

scattering problem for six sinusoidal surfaces with varying amplitudes and

spatial wavelengths. Table I. shows a comparison of values for roughness average

R and spatial wavelength D calculated from the optical angular scattering

measurements with R and D values measured by a stylus instrument on samples

machined in the same batch runs as those measured optically. The agreement

between the results is well within the uncertainties of the measurements which

were on the order of 1-3 percent. Our main conclusion fhom these results is

that for the wide range of wavelengths and roughnesses represented by these

surfaces the straightforward optical theory that we used is sufficiently valid

to be useful for measuring geometrical roughness parameters of surfaces. We

have now begun the work of building a surface statistical model that will allow

for successful application of inverse scattering techniques for measuring

realistic, random rough surfaces.

On the applied research side, we are developing instruments for measurement

of surface roughness in the two practical situations mentioned above. Both of

these use a commercial optical sensing unit with a 20 element detector array to

measure the optical scattering distribution. Figure 1 shows the on-line optical

instrument (termed the ragun) for monitoring surface roughness in operation at

the Automated Inspection Station in the NBS Automated Manufacturing Research

Facility. The robot moves each part to be measured in' front of the ragun for

roughness inspection. The instrument is at an early stage of development. At

later stages we plan to direct the optical alignment of the part with data

presented to the robot controller by the ragun and to quantify the measured

scattering results in terms of standard roughness parameters.

Towards that end, we have compared results measured with this instrument

with measurements of rms roughness R using the stylus profiling instrument and

with angular distributions measured Sy our research optical instrument named

134
DALLAS,

1 that has been discussed in previous reports. Measurements were taken

on three hand lapped stainless steel specimens of varying roughness.

The scattering geometry of the on-line instrument is somewhat different

from that of the DALLAS instrument (Fig. 2). In both cases the surface is

oriented with respect to the instrument in such a way that the detector array

intercepts the planar pattern of scattered light. The on-line instrument has

been discussed by Brodmann, et al. and is shown schematically in Figure 2a. It

consists of an optical source with an infrared wavelength of about 800 nm and a 20-detector photodiode array that spans a scattering angle (2 <j>) of 30°. The

angle of incidence a is equal to 8.4°, just far enough off normal so that the

optics for collecting the scattered radiation do not interfere with the incident

beam. Under proper alignment, the long axis of the detector array is parallel

to the roughness direction on the surface, i.e., perpendicular to the lay of the

machining marks. In the DALLAS setup, the angle of incidence 8, which may be

varied, was set at 40°, and the roughness direction and the plane of the

semicircular detector yoke were oriented in the plane of incidence. The

detector yoke consists of 87 detectors separated by 2°, which span a total

scattering angle of ±86° with respect to the surface normal. Therefore, the

scattering angle range of the DALLAS detection system is a little less than

three times that of the on-line instrument.

The two sets of angular scattering results are shown in Figure 3* As the

rms roughness measured by the stylus instrument increases, the angular

scattering pattern broadens for both instruments. In particular, the DALLAS

result for the surface it 14 with 0.078 pm R clearly shows a strong specular beam

at a scattering angle of -40°. This peak disappears and the diffuse scattering

curve broadens for the two rougher surfaces. The on-line sensor data do not

show a narrow specular beam because the angular resolution of this instrument is

broader owing to the finite convergence angle of the incident beam.

Nevertheless, these scattering patterns also show increasing width as R

increases. In addition, a scattering pattern index, shown as S , tracki the R^

roughness values. is a nonstandard parameter introduced by the manufacture?

of the on-line instrument, that is directly proportional to the variance of the

bell-shaped scattering pattern. In Figure 3, the value tends to increase

with the rms roughness. Figure 3, therefore, shows a clear correlation between

roughness and scattering for this small number of specimens and this correlation

may be exploited to measure the roughness of hand lapped specimens.

Our future work in this area will include research on the appropriate

statistical model for optical scattering from industrial surfaces and continued

development of the on-line instruments.

For practical use of the on-line instrument we are working to obtain a reliable relationship between and one of the standard profile parameters.

For the manual version of the on-line instrument, we must develop mechanical

adapters that will enable it to be aligned with curved surfaces.

We also plan to interface the on-line instrument to a desktop computer and

perform the inverse calculation with the appropriate statistical models to

derive the surface roughness parameters directly.

135
SUMMARY

During FY 85 we have completed a comparison of optical and stylus

measurements of roughness parameters on sinusoidal surfaces and find excellent

agreement between them. We have also installed an optical scattering instrument

in an on-line system to monitor surface roughness on parts manipulated by a robot and correlated results from this instrument with results obtained from a research angular scattering instrument and from a stylus instrument.

REFERENCES

1. T. Yolken and L. Mordfin, editors, "Office of Nondestructive Evaluation - Technical Activities 1984," NBSIR 84-2944 (Nov. 1984) p.3.

2. R. Brodmann, 0. Gerstorfer, and G. Thurn, Opt. Eng., "Optical Roughness

Measuring Instrument for Fine-Machined Surfaces," Opt. Eng. £4, No. 3.

pp. 408-413 (May/June 1985).

Table 1

Comparison of Stylus and Optical Measurements

of Roughness Parameters

(D « surface wavelength, all units in pm)

Deduced From

Measured by Optical

Surface Stylus Scattering

R D R D a a Brass 1 1.02 40.1 1.013 40.0

Brass 2 1 .02 100.2 1 .013 100

Brass 3 1 .01 801 0.98 794

Nickel 1 1.03 100.2 1 .01100

Nickel 2 0.31 100.2 0.311 100

Nickel 3 2.98 100.1 3.008 100

136
137
Collimating Lens

4-3 1—

03 £. 03 <0 SC

CO •a c 03 £ Li (H co cn co SC O v ^ a. < a 4-> —4 4-3 Q. -J 03 4J 3 £ co -J £ £ O O i-C < 4J O SC O C

CD Cl co £. 4-3 a. <0 E T3 -C —4 0

03

C <13 -U <0 3 £ £

cn <0 c 4-3 a. £

.£ E- 03 <0 >4 03 <0 r—

T3 r4 03 Li c £ <0 £ —4 Li

1-4

O • o 03 <0 <0 i—

4-i 03 03 SC 03 za 1 £ 4-> E cn £ >-n <13 C3 —4 60 O o E *4 03 1—

X E

<£ £ <0 03 •—4 03 DO O £ 03 -O O £

j£

—t 03 4-> £ 03

C 03 jJ £0.-4 03 4-3 —4 4-3 W 03 £ C Li 4-3 £ CO 3 O 60 <0

4-3 4-3 03 60 <—

£ C3 —4 £ 03 O 03 CL -4 03 3 03 03 i-H •a £ £ £ 3 03 03 03

<n 3 JE co 4-3 £ 4->

C

m £ 60 —4 <0 4-3 4-3 C 4-> 3 C £ <0 < 03 O O 60 4-3 0 <U £ £ <0 E 03 O 4 -4 -a E 03 CO (—4 03 £ 03 03 o cn <i3 4.3 £4 3 SC O < 03 4-3 0 £ E- £

4J

J 4_>O Li <0

a

—— 03 »

1 03 03 —4 o C Cl £ £ • £ C 03 03 —4 >4 03 X3 03 03 O 4-3 >

03 0) 03 £ £ 0) -4 £.£.-i<oo£0303 3 4-3 £ —I C .£ • 0] ^ (5 I) H ® 4J C

(0 T3 to 4J > I £> <0 ©c-unJ-^ccoaj z flj n *o «-* o-^-us

on

<u£3

60

Ct.

>.

COwv= <

(0

<0 2

<u £

4-> £o

<4-1

T3 • C ^

co

n CM

n co

03

—

-4£ 4-> •U c

co co s i O 3

<0 £

60 J_> cn 60 c c —c —4

5. <0

(0 c

4-3 -4

4-3 CO I o c

cn o

OJ

CO£3

(30 —4

Cxa

4-3 <4-1 C 0)

<u aceo£

1-4 c

<0 ss

CO

4-3

03 .£ CO

4-3

w

138
NONDESTRUCTIVE EARLY DETECTION OF CORROSION AND DELAMINATION UNDER PROTECTIVE

COATINGS USING THERMAL WAVE MICROSCOPY

T. Nguyen and M. E. McKnight

Building Materials Division

Center for Building Technology

Thermal wave (TW) microscopy has proven to be an excellent method to image

microfeatures beneath the surface of both transparent and opaque samples. The

main objectives of this study are to determine the feasibility of thermal-wave

imaging as a sensitive nondestructive method for detecting early corrosion and

defects at the steel/coating interface and to propose a procedure for using the

method. The information obtained, can, however, be applied to numerous areas

of materials science. In 1984, the research results demonstrated that thermal

wave microscopy is capable of imaging the microstructure of steel with or without a corrosion layer. The results also showed that TWM could be used to

image corrosion spots of > 5pm in size under a clear coating. In 1985, we utilized the technique to 1) detect corrosion of metal under an opaque

(pigmented) coating and 2) investigate how far thermal waves can penetrate

through a protective coating to detect the corrosion of metal underneath.

In addressing the first area, both rough and polished cold-rolled, SAE

1010 steel samples, which had been corroded during exposure to 90 % RH and 40° C, were employed. The thermal wave imaging system used has been described

previously (1,2). The scanning electron microscope backscatter (SEM) and TW

images of these corroded (uncoated) steel samples are shown in Figure 1 and 2.

As shown in these figures, both SEM backscatter and TW were able to image

regular type of corrosion on both polished and rough steel. However, close

examination of these micrographs reveals that it is quite difficult to distinguish between the corrosion from the surface roughness features in the SEM

backscatter images (Figure la). Indeed, our computerized image analysis

was not able to distinguish differences in gray levels between the corrosion

and surface roughness on this image. As a result, the area and the percentage

of corrosion could not be computed. In contrast, corrosion clearly stands out

in the TW images; and this is most pronounced at 142 kHz frequency. Based on

this image, the thickness of the corrosion layer was estimated to be about

7pm. The sharp contrast on the TW images also allowed rapid and reliable

calculations of the area and percent of corrosion on steel by image analysis.

After taking the images, the uncoated samples were washed repeatedly with

acetone and ethyl alcohol (to ensure a wettable surface), then dried with hot

air before application of the pigmented coating. An orange alkyd coating

(125 cps viscosity) was flooded on these specimens and spun horizontally using i spin coater to obtain uniform opaque coatings of ^ 2.5pm in thickness (thickness

was calculated based on spin speed and coating viscosity). The samples were

cured at 150°C for 30 minutes. TW and backscatter SEM images of the samples,

which were taken after conditioning for two weeks at room temperature, are shown in Figures 3 and 4. These figures demonstrate clearly that TWI is

139
capable of imaging very early corrosion of steel under an opaque coating. The

contrast due to corrosion is also visible in the SEM image. In the SEM image,

however, the image is due to the contour of the corrosion spot (where the resin

follows as a result of the spinning action) rather than to a difference in

thermal properties between the corrosion products and steel substrate (as is

the case with TWI)

To address the problem of the depth of penetration of thermal waves in

organic coatings, a clear, crosslinked network epoxy coating on rough, corroded

cold-rolled steel samples was employed. 25 mm x 25 mm steel samples were

divided into 6 sections. After covering one of the 6 sections with a pressure

sensitive adhesive tape, a coating layer of 2pm thick was applied. The

thickness was estimated based on a calibration curve established by using

ref lection/absorption Poirier transform infrared technique. The coated sample

was then cured at 180° C for 30 minutes. The taping and coating procedure was repeated until coating thickness of 0, 2, 4, 6, 8, and lOym were obtained

on 25 mm x 25 mm corroded samples (Figure 5). Gold coatings of 200 and 400 A°

were evaporated on the samples to protect the organic coatings because our preliminary investigation indicated that organic coatings of > 3ym thick

on steel substrate underwent charging and/or burning at 30 kv power. Representative TW and SEM images of these samples are shown in Figures 6-10. The

micrographs showed that corrosion under coatings, up to lOym thickness,

could be imaged by TWI. It should be noted, however, that in some cases bubbling

and charging were observed on gold coatings (Figure 11) and that there was no noticeable difference of these effects between the 200 and 400 A° Au films.

These burning and bubbling problems could affect the "effective thickness" to

be imaged above the corrosion spots. Nevertheless, SEM micrographs of the same area of some imaged sections did not show the corrosion, indicating that

the organic coatings on these sections were still preserved. We shall investigate the use of lower power (20 and 25 kv) and/or carbon coating in place of

gold as possible solutions to eliminate the gold bubbling problem. We will

also investigate the use of laser thermalwave, thereby possibly eliminating

the elaborate specimen preparation requirements and also possibly providing

imaging to greater depths. The results obtained indicated that TWM is capable

of imaging corrosion of steel beneath an opaque, - 2.5ym organic coating

and quite thick clear coating. However, for complete assessment of the potential of TWI as a nondestructive method to detect corrosion under protective

coatings and paints, additional studies on the effects of type of coatings

(organic, inorganic and metallic) and particle size and type of pigments on the imaging capability of TWM are needed.

SUMMARY

The results obtained indicated that TW provides sharper contrast of the

corrosion of steel than conventional SEM. The results also showed that TW can image the corrosion under both clear and pigmented coatings. For clear coating,

TW was able to image corrosion of steel under organic coating up to lOym thick.

For both clear and pigmented coating of greater than 3ym, a gold film must be

employed to protect the organic coating from burning or charging. However,

gold films do not seem to always protect effectively the organic coatings. The

140
use of lower power or laser thermal waves should be considered to alleviate the

burning problem caused by electron TW at high power.

REFERENCES

1. T. Nguyen and M. E. Mcknight, "Office of Nondestructive Evaluation,"

NBSIR 84-2946, pp. 17 - 24 (Nov. 1984)

2. T. Nguyen and A. Rosencwaig, "Thermal-wave Microscopy and Its Applications

to Imaging the Microstructure and Corrosion of Cold-rolled Steel," Appl.

Surface Sci., 24 , No. _1 (1985).

3. T. Nguyen, "Thermal-wave Imaging of the Microstructure and Corrosion of

Cold-rolled Steel under Protective Coatings," J. Industrial Engineering

Chemistry Product R and D , Accepted for publication, June/ 1985.

ACKNOWLEDGEMENT

We wish to thank Craig Olson, Metallurgy Division for helping to obtain

the backscatter SEM and TW images.

141
Surface relief

features

Corrosion products

Figure 1. Images of corrosion on uncoated, rough, cold-rolled steel

a) SEM b) Thermal Wave (TW) at 79 kHz modulation frequency, and c)

TW at 142 kHz, showing well-resolved contrast between corrosion

products and surface roughness by TW.

142
Figure 2. SEM (a) and TW (b) images of corrosion of uncoated, polished,

cold-rolled steel, showing less constrast of the corrosion products

on polished steel by TW.

143
Figure 4. As figure 3 but on polished steel sample.

Figure 3. SEM (a)

under a imaging

by TW.

D

and TW (b) images of corrosion of rough, cold-rolled steel

2.5pm pigmented (orange) organic coating, showing the

capability of corrosion underneath an opaque coating

144
25 mm

uncoa+ed

ZfJ -thick

dear cros?-

1 inked epwy

coa-fcirv^

4-M

6H 8 N 10 )Li

25 mm

Figure 5. Corroded steel sample with different organic coating thickness

for studying the effect of coating thickness on the TW imaging

of. corrosion beneath coating.

Figure 6. SEM (a) and TW (b) images of corrosion of steel coated wiM

a 200 A

0 Au film.

145
Figure 7. SEM (a) and TW ( b and c) images of corrosion of steel underneath

a 8yni organic coating which was protected by a 200 A° Au film

on top, showing very well the corrosion under rather thick,

organic coating by TW.

146
Figure 8. As figure 7 but Che thickness of organic coating is l 'Jura. The corrosion products are visible in the SEM image indicat ini' Chat probably some gold and organic coatings have been burne

100x

147
Figure 9. SEM (a) and TW ( b and c) images of corrosion of steel underneath

a 6um organic coating which was protected by a 400 A° Au film on

top.

148
Figure 10. As 9 but the thickness of the organic coating is LOun.

149
I

Figure 11. Polarized light microscopy at 600x showing the bubbling and cracking

of gold films on some of the imaged sections. (Gold films were employed to protect the thick organic coatings).

150
THERMAL WAVE MICROSCOPY FOR USE IN NEAR SURFACE

CRACK DEPTH AND ORIENTATION DETERMINATION IN

METALLIC MATERIALS

Peter J. Blau and Craig D. Olson

Metallurgy Division

Institute for Materials Science and Engineering

INTRODUCTION

The purpose of this project is to develop and examine metal calibration

specimens containing near-surface cracks using the Thermal Wave Microscope

(TWM). The TWM uses a pulsed electron beam in a specially-modified Scanning

Electron Microscope (SEM) to generate near surface thermally excited regions.

Within these regions, acoustic signals due to thermal expansion are generated.

These can be detected with an acoustic transducer on which the sample is mounted.

Differences from place to place on the specimen surface in thermal conductivity,

microstructural homogeneity, and thermoelastic properties affect the contrast in

the TWM image. The FY'85 work on this project involved the fabrication of

specimens containing detectable defects and produced a study of the TWM operating conditions required to detect and characterize these defects. Associated

with this work were investigations of specimen mounting and beam damage to the

surfaces being examined in detail by the TWM.

RESULTS

Several types of candidate specimens for TWM calibration were obtained and/or

fabricated. The most instructive one was produced by drilling small holes in a brass coupon and rolling them closed to form a closed "crack". Fig. 1 shows how

this was done. The simulated defect specimen (SDS) was systematically examined in

the TWM while operating conditions were varied. Only certain specific operating

conditions resulted in satisfactory images. These are given in Tables 1 and 2.

For other types of specimens with different shapes, mounting methods, and materials compositions it is likely that another set of imaging conditions would be

found. The reasons why some specific conditions worked better than others in

producing images are not yet known.

Figure 2 presents a curve of thermal diffusion length versus frequency for

brass using an expression given by Rosencwaig [1]. The frequencies giving

satisfactory images for the brass SDS on the TWM have been indicated on the

plot.

Figure 3 shows that the TWM could detect the direction of inclination of the

subsurface crack if it were oriented properly with respect to the electron beam

scanning direction. The "shadow" in the image was clearly observed when the plao.<-

of the crack in the SDS was at 90 degrees to the scanning direction (the bean

scanned from left to right on the photograph.) A similar effect of defect ->r lactation was obtained for operating frequency and phase and is shown in FI rur<- •. Tilting the specimen surface away from normal to the electron beam also i

r

• - - r

•

i the ability of the TWM to obtain satisfactory images.

151
Figure 5 shows the nature of the scanned area after prolonged examination

(about 20 hours on the same area at various raster sizes - i.e. magnifications.)

A film of carbon was apparently deposited on the heated examination area. Attempts

at chemically etching this area to study whether beam damage (such as recrystallization of the brass) had occurred were not successful due to the presence of the

deposited film. There were no obvious signs of heating effects in the microstructures surrounding the area of prolonged beam rastering.

CONCLUSIONS

The following conclusions were drawn based on TWM studies of a brass simulated

defect specimen:

(1) The ability of the TWM to detect and image subsurface defects was affected by beam voltage and current, specimen tilt, and specimen

orientation.

(2) The presence of a subsurface crack and the fact that it was inclined

in a particular direction to the surface plane was detectable. The

angle of its inclination and depth of the crack at a given surface

location could not be ascertained.

(3) TWM worked better on the metallic specimens than on other materials

investigated during the course of the year. These included specimens

of partially stabilized zirconia, glass, and polymers.

(4) There was no clear evidence for beam heating damage to the microstructure because etch-resistant carbon films were deposited in the scanned

regions of the brass specimen after prolonged exposure to the beam.

RECOMMENDATIONS

Based on results for the metallic specimens examined during the past year,

TOM may aid in the detection, location, and orientation of defects, but would

require substantial improvements and significant progress both in instrumentation

and theory in order to become more quantitative. Because related work using the

TOM on wear specimens during the past year [2] has shown some promising results

in detecting the locations of phase boundaries, areas of elastic incompatibilities,

and the density of compressed compacts, it is recommended that work be redirected

from the quantification of crack depths into another area of considerable technological importance. This new effort involves the detection of localized areas

of residual stress in metallic assemblies.

REFERENCES

1. A. Rosencwaig, Science 218 (1982) 223.

2. P. J. Blau and C. D. Olson, Proc. Wear of Materials, ASME, NY, (1985), 424.

152
TABLE 1. THERMAL WAVE IMAGING CONDITIONS FOR BRASS

(SIMULATED DEFECT SPECIMEN)

Accelerating Voltage

( kV ) Current

(M A)

Imaging Frequencies

( kHz )

20 1.9 143, 144, 150, 211, 214

30 1.8 64, 72, 74, 76, 81, 83, 84,

86, 87, 97, 140

30 1.9 64, 72, 74, 85, 87, 106,

143, 144, 209, 213, 214

TABLE 2. BEST PHASE SELECTIONS FOR IMAGING AT FREQUENCIES OF EITHER

143 or 144 KHZ ON THE BRASS SIMULATED DEFECT SPECIMEN

Accelerating Voltage Current Phase

kV ) Cm A) (degrees)

20 1.9 002, 091, 188, 308

30 1.9 001,

100,

002, 008,

160, 170,

060,

181

068,

300

153
MACHINE

and

DRILL

COUPON

154

Figure

1.

Fabrication

method

for

the

brass

simulated

defect

specimen-
( T T T T—

j |

i i 50 100 200 500 KHz

FREQUENCY

Figure 2. Calculated thermal diffusion length in brass (solid

and specific values of the imaging frequency which

satisfactory results.

line

gave

155
IMAGE DATA IMAGE DATA

kV 30 Curr 1.8 j-iA k V 30 Curr 1.8 jj A

Mag 40 X Mag 40 X

F r e q 76 - kHz F r e q 7fc kHz

Phase 097 Phase 097

Date 2 1 85 Date 2 1 85

m a 1 1 Brass Mat! BRASS

Figure 3. Orientation of the crack with respect to the beam scanning

direction (left to right) affected defect detectability.

156
IMAGE DATA IMAGE DATA

K V 30 Currl.8 jjlA • k V 30 Currl.8 jj.A

Mag 40 X Mag 40 X

F r e q 87- kHz F r e q 97 kHz

Phase 097 Phase 002.

Date 2 i 85 Date 2 1 85

Matl BaaSS Mati Brass

Figure 4. Ability to detect the simulated crack was affected by both

frequency and phase settings on the TWM.

157
(a) (b)

Figure 5. Carbon deposition during prolonged examination was observed.

(a) specimen surface as-removed from the chamber, (b) after

etching to reveal the grain structure in the vicinity of the

crack area.

158
IV. NDE FOR PROCESS CONTROL

NDE for process control is the focus for this section of the report. In

contrast to Section Ill’s focus on interfaces and composites, this section

emphasizes NDE of metals and ceramics for process control. The five

reports on ceramic processing NDE document an advance in this important

application of process technology. The report on ultrasonics in metallurgy

also is notable in that important progress has been made in developing an ultrasonic internal temperature sensor for hot metals. The work on developing an ultrasonic technique to evaluate thermal insulation both during

manufacture and for inspection after installation is also notable. This

technique (patent applied for) is expected to find widespread application

in the building industry.

159
160
NONDESTRUCTIVE EVALUATION OF DISTRIBUTED DAMAGE IN CERAMIC MATERIALS

USING SMALL ANGLE NEUTRON SCATTERING TECHNIQUES

K. A. Hardman-Rhyne

Inorganic Materials Division

Institute for Materials Science and Engineering

The problem- of measuring pore size distributions as a function of

sintering conditions has long plagued material scientists. A non-destructive

small-angle neutron scattering (SANS) technique, sensitive to defects (sizes

up to 3 um) and their size distribution has been developed at NBS.

Theoretical advances relating to those problems are reported by N.F. Berk in

the Reactor Radiation Division [1], however, the experimental and material

issues are addressed here.

The sintering process for ceramic materials includes studies of both

unfired compacted powder samples ("green" ceramics) with 50 percent porosity

and sintered materials with 2 percent porosity (generally consisting of

closed pores). These volume fractions and pore sizes (-1.0 um) are much

larger than can be seen with traditional single particle diffraction

techniques in small angle scattering. Multiple scattering techniques have

been employed to elucidate microstructural information including pore size,

size distribution, porosity, and surface areas [2,3]* The analysis procedure

utilizes the strong wavelength dependence of the small Q incoherent multiple

scattering data to determine the scattering radius of curvature, r

c at Q-0.

In addition a Porod analysis is used to determine the total surface area of

the pores from the large Q data.

Multiple Scattering arises from thick samples or a high concentration of

powder particles or voids in the material. The scattered neutron intensity

is measured on a two dimensional detector. Since the neutron intensity

contours are generally circular in multiple scattering experiments, the

intensity data are circularly averaged and plotted as a function of the

scattering vector, Q where in the small angle limit Q * 2ir9/X for 0, the

scattering angle and X, the neutron wavelength. Q is proportional to the

distance on the detector between the incident and and scattered beam. The

shape of the curve is described by the scattering radius of curvature r

c at Q

- 0, and is related to the full width at half maximum, q, as q

- 2.355r~.

Qualitatively, the shape dependence of the multiple scattered curve can "be

called beam broadening. This beam broadening effect is strongly wavelength

dependent and is most apparent at greater wavelengths. If multiple

scattering is not present the shape of the intensity (r

Q

) as a function of Q

exhibits no wavelength dependence.

161
Compacts of sub-micron spray-dried spinel (MgA^Oij) powder

(approximately 0.76 ym in size) were uniaxially pressed at 69 GPa and then

isostatically pressed at 207 GPa. The "green” pressed disks were calcinated

at 700 °C to remove organic binders and will be referred to as the "green"

state (G.S.) sample. This sample was fired at 1300°C for 12 hours to obtain

a partially sintered material referred to here as the sintered sample.

As expected, the small-Q scattering from the G.S. compact showed a strong wavelength dependence due to the high porosity. Analyses of the

samples indicated that the G.S. sample is 53. 6 $ dense (or 46.4$ porosity) and

the sintered sample is 97$ dense (or 3 $ porosity)

The small-Q regime of the scattering curves were fit to a gaussian

function and the incident beam values were substracted to obtain r

c [Q] (the

notation means radius of curvature at the origin in Q units) as a function of

wavelength. The R

eff(0) or effective void radius measured from the small-Q

data [3] for the G.S. and sintered samples are 440 and 800nm, respectively.

The theoretical and experimental values of r

c [Q] versus wavelengths are shown

in Figure 1 . The error bars are shown or are less than the size of the

symbol. Excellent agreement of the data with theory can be seen. The R

eff(®)

or effective void radius measured by the large-Q data [ 3 ] and surface area of

the voids were determined from the analyses of the Porod regime. The R

eff(“)

for the G.S. sample is 1 60nm and for the sintered material, 690nm. The

surface area for the G.S. sample is 4.5m

2

/gm which is in good agreement with

gas adsorption results.

SUMMARY

The two values obtained for the "green" state could suggest a distribution of void sizes but the large difference here suggests that two

different size characteristics are being measured; that of "neck" and

"bottles" of ink-bottle type connected porosity. In the sintered material

the SANS measures both closed and open porosity. With the completion of the

cold source at the reactor this year, higher wavelengths will be obtainable

which will allow measurements of pores or inclusions up to 30 ym. This is

particularly significant in that the size range of 5 to 30 ym will allow SANS

results to be compared with other techniques such as thermal waves and

ultrasonics which can be used as sensors for on-line process control.

REFERENCES

1. N. F. Berk, 1985 Annual Report submitted to 0NDE.

2. N. F. Berk and K.A. Hardman-Rhyne , J. Applied Cryst. 1_8, in press 1985.

3. K. A. Hardman-Rhyne and N. F. Berk, J. Applied Cryst. 18, in press 1985.

162
>.c

KG

.0

.0

.0

.0

.0

.0

.0

.0

0

0

O NO AGGLOMERATES

—THEORY NO AGGLOMERATES

/

/

/ r/

/

/ o/

/ GREEN STATE

4/ /

4 4 /

/

4

4 4O

44

4

SINTERED

0.6 0.8 1.0

NEUTRON WAVELENGTH X ( nm )

1. The theoretical (dotted lines) and experimental

(squares) r [Q] versus neutron wavelength both

green state and sintered spinels.

163
THE PHASE SHIFT AND MULTIPLE SCATTERING IN SMALL ANGLE NEUTRON

SCATTERING: A THEORY FOR NDE OF CERAMICS .

N.F. Berk

Reactor Radiation Division

Institute for Materials Science and Engineering

Small angle neutron scattering (SANS) from ceramic materials in early

stages of processing, including the powder and green state, usually is

characterized by the observation of "beam broadening” —an apparent

broadening of the incident beam well beyond instrumental resolution and the

absence of a weakly scattered component, in contrast to the typical SANS

diffraction experiment. Since this behavior is generally observed to depend

strongly on the wavelength, A, of the incident beam it is sometimes assumed

to be describable as multiple refraction. In fact, A-dependent beam

broadening is a signature for incoherent multiple scattering which, in terms

of the underlying single-particle cross-section, may be far removed from the

refractive regime of very large single-particle phase shifts. Indeed, for

particle or void sizes of typical concern in such materials, say radii, R,

encompassing the range 0.1-10 pm, the phase shift

v = 2Rp A

, . (1)

where p is the scattering length density, will tend to lie in a regime (0.1—

10) not evidently characterized as either refraction, v * 00

, or diffraction,

v -*• 0. Thus it is important to incorporate the v-dependence of the singleparticle scattering into a formalism for incoherent multiple scattering

(MSANS) from a population of particles or voids [1]. While such an approach

falls short of the complete dynamical scattering theory ultimately required

for such complex systems, it does provide a powerful quantitative tool for

nondestructive evaluation of ceramics processing and distributed damage

[ 1

, 2 ].

We have assumed that the MSANS intensity is the result of incoherent

multiple scattering from monodisperse, randomly distributed, structureless

spheres in a uniform background. Then, the neutron cross-section per unit

of area from a sample of thickness z and area A, as a function of wavevector

Q in the plane of a two-dimensional, position sensitive detector, and with

pinhole collimation, is [1,3,4]

W(Q,z) = e‘

Z 5(Q) + “f ?J 0 (QRc)[e'z(1 " q(c) - e _Z

]d?, (2)

where q(?) in the exponent is

v-dependent, cross-section,

o (Q, v) k

2 R

4 fj 0 (xu) [

J 0

iv/1 - e

completely determined by the single-particle,

1 ]udu

2

(3)

In lowest order, 0(v 2 ), the right hand side of (3) easily reduces to the

Born approximation or diffraction limit. Also in (2), the scattering power

z = z/i, where i is the scattering mean-free-path

164
Numerical evaluations of q(?) are shown in Fig. 1 for a range of v. For v £ 1 the curves are indistinguishable to within 0.1$ from the

diffraction limit (v * 0 )

q°U)= 0 ( 2

-

5 ) { (

+ C/ 2 )/T""I - 2£(1 - £/4)ln [^(

+ /T"= 'I]}, (4)

2

with e; = 5 /4. Even for v = 2 the Born approximation is effectively stable

but breaks down quickly for larger values, as shown. The leading

singularity of q(?) at 5 = 0 is determined entirely in 0 (v 2

) and is thus the same as in the diffraction limit, which from (4). is given by 1/2^ 2 ln^. It

is this singularity which fixes the asymptotic fall of 0 ( Q ) as Q

-*• ® and

gives the Porod law, which is thus seen to be invariant in v [1,6].

Moreover, the N-fold single-particle limit, where N is the number of

particles, defines the Q

+ ® behavior of the multiple scattering since the

asymptotic behavior of ( 2 ) is determined by the leading singularity of the

integrand at the origin. Since q(^) -» 1 as 5

-* 0, this is established in

0(z) and is the singularity of q(^) [1]. Thus, for Q

-* ®, NAW(Q,z)/V -* No(Q,v)/V - P/Q 1*, where P = 2ir(S/V) is the Porod constant, and S is the

total surface area of the N particles.

These ideas have been successfully applied to a SANS beam broadening

study of high purity alumina (A1 2 0 3

) powder [2]. Eq. (2) was used to fit

the curvature k of measured intensity curves at Q = 0 for several incident

neutron wavelengths, allowing the determination of <j> and Reinterpreted as an effective radius, see below. Parameters were in the ranges: X = 0.45-1.0

nm, z = 2.0-10.0 mm, <p = 0.25-0.33, and z = 5-400. The corresponding phase

shifts, v = 0.15-.0.30, were well within the limit shown above, Fig. 1, to

justify analysis as multiple diffraction. To apply the method to

polydispersed powder, the radius measured from the small-Q data was interpreted as an effective radius, R(0), defined by the extension,

z = No/A -<• Z(j)< 0 >/ < v> -* z<j)v

2 A2 R(0 ) , (5)

where <•> denotes the average over the particle-size distribution (PSD).

The last equivalence in (5) applies only to the diffraction regime, where 0 - o° = (1/2 )^r2 and R(0) = <R->/<R 3 >. The best-fit value of R (0

)

from all data was found to be 265 nm within a 2-5$ uncertainty. Once R(0)

is known, all the small-Q data can be represented on a universal curve for

multiple diffraction, r [QR] vs_ z, where r [QR] = }/'/-< is the radius of

curvature of the scattered intensity at Q = 0 in dimensionless units and is

effectively a measure of the width of the intensity curve near the origin

[1]. This is shown in Fig. 2, comprising the results from 25 data sets,

where the theoretical curve is well-approximated in the range shown by

r

c [QR] = 0.92 [Iln 0.852] 0,5

( 6 )

For the limit of single-particle scattering by a sphere, r [QR] = /'5 \ . Large-Q data were analyzed using the Porod law, expressed in terms of

effective particle radius R(<=°) = <R 3 >/<R 2 >, which results from its ext- r

. . r to polydispersed systems. The result [2] was R(«) = 232 nm within l. values of R ( 0 ) and R(®) were rationalized by assumption of a lognormal 11 , from which <R> = 171 nm and dimensionless width parameter 8

= 0.382 w- • • derived. These results were found to be in very good agreement wi tr. size determinations by laser light scattering and by x-ray sedi grits

165
methods. Application to MSANS NDE of unfired "green" state compacts and

sintered materials is also in progress [7].

SUMMARY

Significant progress has been made toward the development of an analytical methodology for deriving quantitative particle-size information

from multiple small angle neutron scattering (MSANS). Application to

alumina powder has indicated the potential of the approach for reliable NDE

of ceramic materials, and ongoing measurements also point in this direction.

Theoretical work continues with emphasis on extending the formalism,

analytical methodology and computer software to the determination of larger

particle-size ranges and the development of more systematic approaches to

data analysis.

REFERENCES

1. N.F. Berk and K.A. Hardman-Rhyne (1985). J. Appl. Cryst., J_8_, in

press .

2. K.A. Hardman-Rhyne and N.F. Berk (1985). J. Appl. Cryst., J_8_, in

press .

3. H.S. Snyder and W.T. Scott (1949). Phys. Rev. 76_, 220.

4. H. A. Bethe (1953). Phys. Rev. 89, 1256.

5. R.J. Weiss (1951). Phys. Rev. 83_, 379.

6. N.F. Berk and K.A. Hardman-Rhyne (1986). Proceedings of the

International Conference on Neutron Scattering, 1985, Santa Fe ; Physica

B, to. be published .

7. K.A. Hardman-Rhyne, K.G. Frase, and N.F. Berk (1986). Proceedings of

the International Conference on Neutron Scattering, 1985, Santa Fe;

Physica B, to be published

166
q(C)

£

Figure 1. The function q(£) for several values of the phaseshift v.

167
Scattering

Radius

of

Curvature

(QR)

Figure 2. Radius of curvature of multiple scattering intensity at Q

168
ULTRASONIC MEASUREMENTS OF CERAMICS

G.V. Blessing

Mechanical Production Metrology Division

Center for Manufacturing Engineering

and

M.P. Jones

Inorganic Materials Division

Institute for Materials Science and Engineering

Substantial materials research interest continues for the development of

effective ceramic processing procedures, and for the nondestructive evaluation

of ceramic properties both during and after processing. This is evidenced by

the expanded efforts at NBS in the ceramics area, and has led to a collaboration between the Institute for Materials Science and Engineering and Manufacturing Engineering to nondestructively monitor specific ceramic properties at

various processing stages. The approach being taken for the ultrasonic non- destructive technique is presented here.

The purpose of this study is to relate pertinent material properties of

sintered ceramics to their green-state elasticity using ultrasonic methods.

This relationship would be useful to monitor and control ceramic processing,

permitting the rejection of ceramics possessing poor green-state elastic

properties and thereby avoid further costly processing. While many ultrasonic

studies have been made on sintered ceramics, few have been made on the green

state, and apparantly none have systematically correlated green-state elasticity with final sintered properties.

By means of ultrasonic longitudinal and shear wave velocity measurements,

the degree of isotropy, homogeneity, and inter-sample elasticity variations

will be determined as a function of processing parameters on both the green

and sintered states for a series of alumina ceramic samples. To evaluate

material elasticity in particular as a candidate for a process-control

parameter, dynamic modulus values will be calculated from these velocity

measurements on samples in which the' binder has been removed (producing hard

agglomerates and subsequent low strength materials) before pressing and

sintering. These green-state elastic values will then be compared with those

obtained on samples that yield good (high strength) properties. It is conjectured that hard agglomerates will act as elastically uncoupled particles due

to a lack of binder, and lead to lower sample moduli. The lower green-state

moduli would then be expected to correlate with a low-strength sintered state.

To avoid sample contamination by couplant absorption into the porous

ceramics (especially in the green state), dry coupling techniques have been

developed for use with both longitudinal and shear waves. A novel polymer: : coupling material permits dry coupling of shear waves to fragile green-stitand sintered ceramics with minimal pressure in a two-transducer throughtransmission technique. With these techniques, order-of-magnitude

169
differences in elasticity have been observed between green-state and sinteredstate samples.

SUMMARY

A joint CME/CMS study designed to relate ultrasonic measurements of

green-state elasticity to the final sintered properties of ceramics was undertaken in mid FY 85 . Dynamic modulus measurements have been identified as one possible process-control parameter. A novel coupling technique necessary for

dry coupling to green-state ceramics has been developed using a special

polymeric material. Initial measurements showing an order-of-magnitude difference in elasticity have been carried out.

170
THERMAL WAVES

Grady White, Lorretta Inglehart, Marty Jones, Anne Wilson,

and Christie Nguyen

Inorganic Materials Division

Institute for Materials Science and Engineering

The technique of thermal waves involves the periodic application of heat

to a specimen and the monitoring of the resulting heat flow. Periodicity not

only increases the signal to noise ratio but also allows the heat flow

process to be treated as a highly damped traveling wave. The physics involved

in the generation and detection of thermal waves has been studied by a number

of groups over the past several years but the systematic application of

thermal waves to the investigation of NDE applications is a recent

development. Because thermal waves scatter from thermal discontinuities in a manner analagous to the scattering of sound waves from elastic

discontinuities, thermal waves should provide an alternate probe for the NDE

of materials. Therefore, we are beginning to apply the thermal wave technique

to the study of certain well defined defects in brittle materials.

The work this year has been divided into three categories porosity

investigation, equipment construction and development, and cement

investigation. Each of these topics will be considered separately below.

POROSITY INVESTIGATION

The major thrust this year has been the investigation of porosity in

alumina. Porosity in ceramics has long been a source of concern, but no practical techniques for determining porosity in a reliable nondestructive

manner have yet been developed. Microscopy, both optical and SEM , and

porosimitry measurements have been used in the past but these approaches are both time consuming and destructive to the specimens being investigated.

Moreover, porosimitry measurements detect only the open, or connected, pores

in the material. Therefore, closed, or isolated, pores are not detected by

this technique. In addition, there have been several papers in the literature

reporting correlations obtained between ultrasonic velocities and porosity in

ceramics. However, the specimens in these papers generally have been poorly

characterized both in terms of sample preparation and porosity analysis.

Therefore, it has not been possible for a model to be developed accurately

relating the velocity and the porosity. For these reasons, we have chosen to

study porosity in a well controlled, well characteri zed manner. We chose

thermal waves as our probe both because we expect changes in porosity to oe strongly reflected in variations in thermal conductivity and because we wish

to understand better the relationship between thermal waves and materials. In this work, we are collaborating with various people at NBS: Gerry Blessing in

the Fabrication Technology Division, and Carl Robbins and Kay Rhyne in the

Inorganic Materials Division.

171
The specimens were made from alumina powders which had been spray dried

by Carl Robbins of the Inorganic Materials Division and were pressed at

30,000 psi. The first set of specimens were then divided into three

categories: green state, bisque fired, and dense fired. The temperature

treatments for the three categories were, respectively, no firing, 1100 C for

20 hours, and 1500 C for 20 hours. Density measurements using the Archimides

Principle, light scattering measurements at 10.6 um wavelength, and

ultrasound velocity measurements were then made on the specimens. Table 1 summarizes the results.

Table 1 . Specimen Parameters

% density I/I (dense

velocity

long.

(xE5 in/s)

trans

green .58 .142 .661 .422

bisque .60 .200 1.482 .902

dense .98 1 .000 4.492 2.010

A second set of specimens is currently being pressed and fired at

conditions duplicating those described above. In addition, a set of specimens

is being made up of alumina powder which has been calcined (fired at 1000 C

for 12 hours) after being spray dried. The calcined powder is expected to

provide specimens which maintain their porosity through various firing

treatments. This will allow us to test porosity in two materials which are nominally the same but in which the network of aluminum oxide surrounding the

pores has been fired at different temperatures. Table 2 lists the thermal

treatments for the second batch of specimens.

Table 2. Thermal Treatment

Uncalcined Calcined

powder

green

bisque

dense

RT

RT

1100 C/20 hr

1500 C/20 hr

1000 C/12 hr

RT

1100 C/20 hr

1500 C/20 hr

The thermal wave measurements have been made in a photoacoustic system

(ref. 1 ) in a modified cell which allows measurements to be made upon all

three types of specimen, green, bisque fired, and dense fired, without

unsealing the cell. This eleminates a major source of error in the

photoacoustic effect (PAE). The measurements are being made with a carbon

dioxide laser since, at 10.6um, alumina absorbs very strongly, providing a heat source localized at the surface of the specimen. The specimens are mounted at a position where the laser beam diameter is '2mm rather than at

the focus of the beam. This not only reduces the chances of thermally

damaging the specimens but provides a signal which is averaged over a range

of pore sizes.

172
Figure 1 is a plot of the PAE signal for the three uncalcined specimens

as a function of frequency. There is a clear distinction among the three

specimen treatments as viewed by the PAE which we are beginning to study. The

linear dependence of signal magnitude on 1 /oj, Fig. la, is consistant with

thermally thick, optically opaque specimens, as modeled by Rosencwaig and

Gersho (ref. 2). The increase in signal magnitude as the interrogated

specimen is changed from the green to the dense specimen is expected since

the increasing porosity should increase the resistance to heat diffusion.

However, in the plot of the signal phase, Fig. 1b, the turn over for the

dense fired specimen which occurs at low frequency is unexpected. This effect

is currently under investigation to determine if it is an anomaly of the PAE

system or is a real effect.

EQUIPMENT CONSTRUCTION AND DEVELOPMENT

We are constructing a mirage thermal wave system at NBS which is

designed to be compact and self contained, except for the laser heat source.

We have now obtained a 4-watt argon ion laser, a 1.5 watt carbon dioxide

laser, a vector lock-in amplifier, optical beam steering equipment, an acousto-optic modulator, and a position sensitive detector. The two lasers

give us the ability to operate at widely different wavelengths to take

advantage of the optical absorption properties of various specimens which we wish to investigate.

The mirage system will provide a noncontact thermal wave capability and

will be free of the constraints imposed by the PAE cell. In addition, the

mirage system is designed to be completely computer controllable, which is

necessary if mapping or imaging is to be done on any regular basis. We expect

the mirage system to be operative near the beginning of FY86.

CEMENT INVESTIGATION

We have also used the PA system to investigate epoxy impregnated cement

samples fabricated in the Center for Building Technology. The initial purpose

of this work was to determine if the photoacoustic effect (PAE) could map out

defects, in particular microcracking , in such a complicated structure of

varying materials and voids.

The experimental procedure consisted of mounting the cement specimen

onto the PA cell as outlined in reference (1). Twenty scans of 7mm in length

were made at 50ym separations. The signal was processed in a vector lock-in

amplifier and then fed into a chart recorder. The phase information was used,

rather than the magnitude information, to minimize contributions from optical

and surface effects. The change in phase of the signal is related to the time

delay of the thermal wave and, therefore, to the depth the signal penetrated

into the specimen. The data from the chart recorder was hand digitized and

entered into a computer from which a two dimensional map of the interrogated

surface was obtained. After comparison of this map with an investigation

the surface made with an optical microscope, we determined that changes

the thermal wave signal in this specimen were due to variations in the epoxv

filler rather than to structural variations in the cement. However, lata :'r t. this work have not yet been fully analyzed and further investigations

specimens which have not been epoxy impregnated are planned in an attempt t find surface microcracking.

173
FUTURE PLANS

We plan to continue the work on the porosity, including developing a model to interpret the interaction of thermal waves with porous materials. We

also intend, in collaboration with Drs. John Murphy and Grover Wetsel of the

Johns Hopkins Applied Physics Laboratory and Prof. Robert Green of Johns

Hopkins University, to place inclusions in alumina specimens to determine the

sensitivity of thermal waves to the detection of such flaws. Finally, we intend to use the mirage system to try to detect and quantify surface and

near surface defects which serve as sources of failure for brittle materials.

All three defects, pores, inclusions, and cracks pose serious problems for use of ceramics in load bearing applications.

SUMMARY

We have used the PAE system built last year to obtain preliminary signal

magnitude and phase data upon alumina specimens which are 58$, 60% t and 98%

of theoretical density. Clear differences in both magnitude and phase are observed among all three specimens. The specimens are being made at NBS and

are being characterized by a number of tests, e.g. light scattering, SANS,

porosimitry, and ultrasound, in addition to the thermal wave measurements, to

provide as thorough an understanding of their properties as possible. Such an understanding is vital to the developement of a quantitative model relating

thermal waves to the measurement of porosity.

A mirage thermal wave system is being built at NBS to provide imaging

capabilities. The mirage system is designed to be computer controlled and

will allow detection and mapping of closed vertical cracks, inclusions, and

other localized defects.

REFERENCES

1. T. Yolken and L. Mordfin, editors, "Technical Activities 1984

Office of Nondestructive Evaluation," NBSIR 84-2944

(Nov. 1984).

2. A. Rosencwaig and A. Gersho , J. Appl . Phys . 47, 64-69

(1976).

174
o

3anuN9virt

>

o

z

LUo

O

LUcc

lira

0)

00

175

Kiot

Of

PAE

magnitude

vs

1/aj

for

three

alumina

specimens:

green,

bisque,

and

dense.

Straight

lines

are

In

agreement

with

the

theory

of

Kosencwalg

and

Gersho

(ref.

2).
aSVHd

176

Figure

1b.

Plot

of

PAE

signal

phase

vs

ui

for

the

three

alumina

specimens

in

Fig.

la.

The

turn

over

for

the

dense

fired

specimen

is

currently

under

investigation.
NONDESTRUCTIVE EVALUATION-GREEN STATE CERAMICS

C. Robbins, W. Coblenz and M. Jones

Inorganic Materials Division

Institute for Materials Science and Engineering

INTRODUCTION

"The ability to form advanced ceramics with the required level of

reliability requires extreme levels of microstructural control over powder

characteristics, particle packing, and pore size uniformity.

"It is

increasingly evident that the starting powder characteristics and the

details of the consolidation process (prior to densif ication) are the

origins of many of the limiting defects that are found in these

technologically important ceramic materials.

The task of this project is to prepare "green" (unfired) and

selectively sintered ceramic compacts with known flaws for exploratory

study and characterization by nondestructive and destructive analytical

methods. Powders selected for the compacts must be thoroughly

characterized, processing conditions documented and some destructive tests

made on the ceramic compacts at selected intervals between "green" and

fully densified states.

During this year, work was continued at NBS and at Argonne National

Laboratory (ANL) on a group of spinel (MgA^O^) compacts, and work was initiated on a new group of AI 2O

3 compacts.

SPINELS (MgAl

2 0

4

)

These materials were characterized both at NBS and at ANL. At NBS the

pore size distribution was measured using small angle neutron scattering

(SANS). Both green and sintered specimens were measured. Experimental

results are presented elsewhere in this annual report by K. Hardman-Rhyne.

Initial results from Argonne National Laboratory have detected density

gradients in some of the green compacts using both x-ray tomography and

x-ray microradiography. Surface scratches produced during processing,

which were visible by light microscopy, were also seen by rnicrorad iography

as slight density differences.

ALUMINA COMPACTS (AlgOj)

A high purity alumina powder (purity, 99.9955) from Baikalox was selected to prepare green compacts with known flaw sizes and number

density. Particle size distribution by x-ray sedigraph shows a median

particle diameter of 0.55 urn (Figure 1). Measurements of surface area g.m

177
adsorption technique of Brunauer, Emmett, and Teller [BET]), porosity

(mercury porosimetry) , and crystallite size (x-ray analysis) are currently

in progress on this powder.

Three sets of compacts prepared from the as-received powder were bisque

fired at 1000°C for 18, 42, and 66 hours in an initial study. These

specimens have been examined at NBS by SANS and ultrasonic methods.

Ultrasonic data for the compacts are given in Table 1 . The samples have

been returned for porosimetry measurements for correlation of the

ultrasonic results.

A large quantity of the powder has been spray dried to produce soft

agglomerates (Figure 2) for die pressing 100-150 compacts. In addition, a quantity of this spray-dried powder has been calcined to produce hard

agglomerates. Green compacts prepared from the soft agglomerates should

have interconnected pores. Compacts prepared from hard agglomerates should

have large interagglomerate pores and when sintered at low temperatures

should produce a bimodal pore size distribution (interparticle and

interagglomerate)

Microstructure will be documented by microscopy and porosimetry.

Currently, on the order of seventy compacts have been prepared for the

following studies: SANS measurements; thermal wave studies; acoustic

measurements; and microscopy and mercury porosimetry studies.

SUMMARY

Initial work at ANL on spinal samples provided by NBS demonstrate that

x-ray tomography and microradiography may be used to detect flaws in green

ceramics. These samples have been characterized at NBS for pore size

distribution using SANS. Work at NBS on alumina has shown that ultrasonic

methods are sensitive to initial sintering in near green state ceramics. A

quantity of soft agglomerates of A^O^ has been prepared for die pressing

100-150 green compacts. The compacts are currently being studied by NDE

and DE methods.

FUTURE PLANS

Plans are to introduce controlled flaws in the form of highly sintered

A^O^ spheres into the green die pressed compacts prepared from the soft

agglomerates. It is also planned to generate spherical voids of known size

in the compacts by the addition of styrene spheres to the powder before die

pressing, and then removing the former by low temperature calcination. We

have demonstrated that this is a feasible method of sample preparation.

178
Table 1

Wave Speeds in Bisque Fired Al^^, Die Pressed at 28 MPa (4,000 psi)

Treatment

Thickness

(mm)

Longitudinal

(mm/ us)

Shear

(mm/ us)

Green 8.02±.03 0.823 0.620

1000 °C-1 8 hrs. 7.95±.02 1 .882 1 .341

1000 °C-42 hrs. 7.88±.08 2.360 1 .519

1000 °C-66 hrs. 7.87±.06 2.324 1.651

REFERENCES

1. H. K. Bowen, "Basic Research Needs on High Temperature Ceramics for

Energy Applications," Mat. Sci. and Eng, , 44, 1-56 (1980).

2. M. Yelazquez and S.C. Danforth, "Pressure Filtration of Monosized

Colloidal Silica," to be published in "Proceedings of the Symposium on Surface and Colloid Science in Computer Technology," Potsdam, NY,

June 1985.

Figure 1. X-ray sedigraph of A1.-0- showing a median particle size

of 0.55 ym.

179
Figure 2. SEM photograph of spray dried agglomerates of

Al^O^ before die pressing. Long scale bar = 10 um.

180
ULTRASONICS IN METALLURGY

Bernard Droney*, Melvin Linzer, Jeffrey Martinez, Floyd Mauer

Stephen Norton, Kurt Sandstrom, Christian Turner and Haydn Wadley

Metallurgy Division

Institute for Materials Science and Engineering

INTRODUCTION

In FY 85, significant progress was made in perfecting measurement

techniques and obtaining velocity-temperature data needed for accurate

reconstruction of temperature profiles in hot steel by ultrasonic tomography.

Ultrasonic tomography involves determining the time of flight and path

length along a number of paths within one cross section of a hot steel body.

Techniques based on computerized tomography are then used to reconstruct the

ultrasonic velocity profile. Theory has recently been extended to include

reconstructions in square as well as circular cross sections and to make use

of heat flow constraints in order to reduce the number of measurements

required. The velocity-temperature dependence for each type of steel under

investigation is then needed in order to convert velocity profiles to

temperature profiles. Progress in obtaining this type of data is reported

here

VELOCITY-TEMPERATURE MEASUREMENTS

Last year we described an improved method for obtaining ultrasonic

velocity data at high temperatures for steel samples. A one-piece, stepped

rod was used to provide both a test section and buffering rod. An ultrasonic

wave could be generated by focusing a laser pulse onto the outer end of the

test section or the step where it joined the buffering section. The

difference in time of flight gives the TOF in the test section, which is at a uniform temperature in the hot zone of an argon-atmosphere furnace. This

method, which was first used for obtaining velocity-temperature data on 304

stainless steel, has now been used for measurements on AISI 1018 plain-carbon

steel (0.18 wt % C, 0.74 wt % Mn) . This being a ferritic steel, the results

are complicated by the bcc to fee phase transition and the magnetic

transition at the Curie point, as well as microstructural changes associatec

with precipitation/dissolution of carbon. In particular, it is not possible

to use handbook values of the thermal expansion when making the necessary

corrections for changes in the length of the test section. We have,

therefore, modified our equipment to obtain dilatometer measurements on tne same test section and under the same heating and cooling conditions usee ultrasonic measurements. Curves for thermal expansivity and longituaina*

velocity are shown in Figure 1 and Figure 2.

* AISI Research Associate from Bethlehem Steel Corporation

181
The transition temperatures determined by thermal analysis are also shown.

A-| and A

3 represent the low-temperature and high-temperature limits of the

two-phase region over which the alpha phase (bcc) and gamma phase (fee)

coexist. To differentiate between heating and cooling, the letters c for

"chauffage" and r for "refroidissement" are added.

On heating, the expansion is nearly linear until the A^ boundary is

crossed and austenite begins to form. The reduction in volume accompanying

the bcc to fee transition results in contraction of the sample until the

transformation to austenite is completed at the A^ boundary. Above the A

3 temperature, the curve is again linear. On cooling, there is considerable

hysteresis, causing a 50° to 60° C shift in the transition region.

Ultrasonic velocity, on the other hand, shows surprisingly little effect due

to the crystallographic transformation. What it does show is considerable

nonlinearity starting about 250° C below the transition. The curve is

remarkably reproducible on successive heating and cooling cycles. In fact,

within the heating and cooling rate limitations of our furnace, it is

difficult to show any hysteresis. These observations indicate that

limitations on ultrasonic temperature sensing that might have resulted from a non-unique velocity-temperature relation in ferritic steels are not as serious as once thought.

The origin of the steep velocity-temperature gradient between about 720°

and 820° C is unclear. One explanation advanced by Papadakis et . al.

(reference 1) is based upon the dissolution of carbides. However, data of

Kurz and Lux (reference 2) on high-purity Armco iron show the same phenomenon

over a similar temperature range even though this material contained no carbides. They also show that the bcc-fcc transition at 910 °C has a negligible effect on the velocity-temperature relation. The Curie

temperature for iron is 768° C and the possibility exists that the effects we observe are a manifestation of the loss of the magneto-strict ion contribution

to the modulus.

A source of high purity iron is now being sought to enable us to

unambiguously isolate the effects of phase transitions from those associated

with magnetostriction and carbide formation.

SUMMARY

Reference data relating ultrasonic velocity to temperature has been

obtained at temperatures up to 1110 0 C for AISI 1018 plain carbon steel. The

uncertainty in these measurements is roughly 1 part in 10 ^, which corresponds

to an uncertainty of 17° C in temperature. The data will be used in

reconstructing temperature profiles in hot steel bodies from time-of-flight

measurements

182
REFERENCES

1. E. P. Papadakis, L. C. Lynnworth, K. A. Fowler, and E. H. Carnevale,

"Ultrasonic Attenuation and Velocity in Hot Specimens by the Momentary

Contact Method with Pressure Coupling, and Some Results on Steel to

1200° C, " The Journal of the Acoustical Society of America 52 No. 3 (Part 2)

pp. 850-857 (1972).

2. W. Kurz and B. Lux, "Die Schallgeschwindigkeit von Eisen und

Eisenlegierungen im festen und flussigen Zustand," High Temperatures-High

Pressures 1 pp. 387—399 (1969).

Figure 1. Linear expansion in percent for AISI 1018 carbon steel.

The transformation range on heating (Ac1-Ac3) and cooling

(Ar1-Ar3) was determined by thermal analysis.

183
6000

4600 -

_L _L _L

30 90 150 210 270 330 390 450 510 570 630 690 750 810 870 930 990 1050 1110 TEMPERATURE/^ •

Figure 2. Ultrasonic velocity versus temperature for AISI 1018 carbon

steel. T

c

is the Curie temperature, 768° C for iron.

184
ACOUSTIC EMISSION AS AN NDE TECHNIQUE FOR CHARACTERIZING

MARTENSITIC TRANSFORMATIONS

Y. Berlinsky 1

, H. N. G. Wadley, R. B. Clough, J. A. Simmons and M. Rosen *1

Nondestructive Characterization Group

Metallurgy Division

Institute for Materials Science and Engineering

Acoustic emission is an elastic transient generated by a change of

stress within a body. As such this technique has remarkable potential in

monitoring and characterizing various microscopic phenomena such as dislocation motion, microcrack growth and martensitic phase transformations.

Traditional acoustic emission instrumentation measures, among other

things, the acoustic emission energy of an event. The measured energy of an acoustic emission signal cannot as yet be theoretically related to the

elastic energy of source. Therefore, to quantitatively measure this

quantity, we have used calibration sources of known strain energy to relate

the data measured during experiments with traditional instruments to the

energy of the natural sources.

Two types of energy calibration sources, whose time dependences bound

those of most natural sources, have been used. One is that of a dropping

ball and the second is the absorption of an infrared laser pulse. The

calibration system is described in Figure 1 . By varying the height of the

dropped ball or the energy of the laser pulse, [ref. 1], a calibration curve

is obtained. This calibration curve relates the envelope strength (relative

energy units) of a commercial acoustic emission system with the source

elastic energy. The envelope strength is corrected for bandwidth due to the

difference between the source spectrum and the AE system response. Such a curve is shown in Figure 2.

Once having calibrated our measurement system, we were then able to

proceed with an investigation of the kinetics and mechanisms of martensitic

phase transformations. The Fe-30.5 wt. % Ni system was chosen as a model

alloy system because its transformation conveniently began just below ambient

temperature and the transformation itself has been intensively studied by

numerous other techniques. It was found from the acoustic emission signals

emitted that upon cooling this alloy just below room temperature, a few

martensitic plates were formed. The stress field induced by these plates

the surrounding matrix then catalytically induced a "burst" of martens:*:: - transformation with concomitant more intense emission. This was then foil.-* on further cooling, by numerous emissions as the sample underwent a com pi -ttransformation to martensite. A typical acoustic emission activity is

in Figure 3*

^Guest Worker from Israel, Ministry of Defense

Guest Worker from the Johns Hopkins University, Material Selene- • and Center for NDE

185
Interestingly, the M

s temperature (martensitic start temperature) is

very clearly defined by acoustic emission and is substantially higher than

that reported in the literature from electrical resistivity measurements.

Using the calibration procedure described earlier, the elastic energy of an acoustic emission could be converted to that of the source from whence it

came, i.e., a martensitic lath. We are presently investigating the

relationship of this energy to the shape change of a martensitic plate - a key parameter in the description of a martensitic transformation.

Work has also begun to investigate the martensitic phase transformation

of rapidly solidified ribbons of Fe-30.5 wt. % Ni. A typical acoustic

emission activity (events rate) of the ribbon is shown in Figure 4. Being more

sensitive than electrical resistivity, the acoustic emission technique

detects the early stages of a martensitic transformation. That is because

only a few martensitic plates do not cause a detectable change in the

electrical resistance of the sample.

By comparing the acoustic emission activity of the bulk and the ribbon

samples, a different transformation mechanism was evident. It was found

that the M

s temperature in the ribbon was lower than that in the bulk sample.

There was no burst at the early stages of the transformation, and the activity

had only one distinct envelope, in the temperature range of -50 °C to -100 °C.

Future efforts will be directed towards getting a better understanding

of the energy calibration procedure, and its sensitivity to various

parameters. Also the kinetics and mechanism of martensitic phase

transformations will be investigated, using the calibrated acoustic emission

technique.

SUMMARY

New calibration methods are being developed to facilitate quantitative

use of acoustic emission data recorded with traditional instrumentation. The

procedures are based upon calibration and standardization of analysis

methods. They have been applied to the study of martensitic transformations

and show promise of quantifying the dynamics of this important class of

metallurgical transformations.

REFERENCES

1. Y. Berlinsky, R. B. Clough, H. N. G. Wadley, and M. Rosen. "Acoustic

Emission as an NDE Technique for Characterizing the Martensitic Phase

Transformation in a Fe-Ni Alloy," to be published in the proceedings of

the conference: Reviews of Progress in Quantitative NDE, June 23 “ 28,

1985.

186
X

>> V)

•j

sb

187
-

15

(AE)

CM

X

ina CD

II

(A Hi

E

mO

>

O

GC

LU

Z

LU

o

H

cn

<

o

cn

coCO

003

01

0)a

0

r43

>

s

01 'O3a

3

3

j-j • 0 >> a oo

1 sI 0) e c

3 a)

4-1 CO CJ PS -H

CO 4-1 CO w ca <

3

3

j=

4-1 3

a

>4

>4-1 3

O O

CO 3

O 3

•H J=

44 4-1 CO

54 <44 £> O

•HfH C

CO O

O *H

44 >< cj oo c

i4 3

0) >44 3W co

CN3

i43

00

•H

&4

[SlINn W31SAS 3V]

3V ‘HlONaaiS 3d033AN3 031030000

188
BURST

AT

[siiNn Advaiiauv]

31Vd 3V

189

TEMPERATURE

[°C]

Figiiru*

3.

Typical

AE

activity

during

cooling

of

Fe

-30.5

wt.

/

Ni

from

room

temperature

Lo

-170

°C

. A

sharp

burst

is

observed

at

-5

°C.
700

foo/SlN3A3l

A1IAI10V 3V

190

Figure

4.

Event

rate

during

cooling

of

rapidly

solidified

Fe

-30.5

wt.

%

Ni

ribbon

from

room

temperature

to

-140

°C.
DYNAMIC MICRO INDENTATION EVALUATION OF MATERIALS

Robert S. Polvani

Metallurgy Division

Institute for Materials Science and Engineering

Facing many different end uses, designers of industrial parts and equipment

need data bases and test methods for measuring the mechanical properties of metals,

especially their dynamical capabilities. Structural supports and piping require

creep strengths, while bearing, cams and gears involve impact and sliding wear

strengths. A sensitivity to the rate of loading is found in all polymers and some

metals. A new and nondestructive approach to dynamic mechanical testing is being

developed. Derived from conventional "hardness” there are two important innovations. The indentation is described in terms of the instantaneous applied load

and penetration depth. Secondly, indentation can be performed over a range of

loading times, from hours down to milliseconds.

The Dynamic Microindentation Tester was extensively revised to improve three

features of its dynamic capability. First, the test event recorder, a storage

oscilloscope, was replaced with a transient digital oscilloscope. Doing this re- quired completely revising the system software, but markedly increased the detailing

of the test event. Potentially, a 10X improvement is available. Second, the load

and displacement transducers were revised; the measurements are now directly coupled

to the sample itself. Before displacement was measured with respect to the main

frame, and converting to penetration required correction for the compliances of the

sample and main frame. Lastly, as a means of determining the extent of anelastic

recovery, a pause of variable duration was introduced between the recording of the

test event and measurement of the residual indentation depth.

Figures 1 a and b report actual test data for a typical dynamic test. The

specific result is for a test of an 0-2 hardened and tempered tool steel. Figure

1 b is the load-displacement curve for the indent; it combines the results of both

the up-loading and downloading of the sample. Figure 2 is a schematic explanation

of this curve. Because the two results are reported, load-displacement curves can serve two different and important functions. First, the indentation deformation

energy can be partitioned into its elastic, plastic and anelastic components. For

example the total work to indent the 0-2 steel was 430 gf-um; of that total 26 percent was elastically recoverable. This partitioning of the indentation energy has

been used as a means of understanding the wear resistance of "hard" coated net il , and should be even more useful if a different property, formability for example,

were the primary interest.

Second, the load-displacement curve is interchangeable with the s t res r - ; . curve. The convertibility has been already shown for copper, but except r >r ific cases cannot be generally made. A primary goal of this task is to !<••••: • way for making that general conversion.

191
Lastly, Table I offers preliminary data illustrating the importance of

using a dynamic loading. The sample is a metal matrix composite of 6061 aluminum

and 15 volume percent SiC particulate. These are dynamic Knoop hardness data, and

show an effect of loading time on the apparent hardness. The determinations were

all made in the loaded condition, and reflect both the elastic and plastic deformation responses of the material.

TABLE I. A comparison of the Knoop Hardness as a function of the duration of the

applied loading.

LOAD DURATION (SECONDS) 100 10 1 0.1 0.01

KNOOP HARDNESS (kg/mm2

) 80 156 160 147 113

To explain the relative softening at the extremes of the duration requires

conjecture. At the slowest rate, creep is a significant factor that has the time

necessary for an observable effect. At the highest rate, the input of deformation

energy is dissipated as both plastic deformation and local heating. For near

impact conditions, theory predicts about an 80 percent conversion of the deformation

energy into local heating.

SUMMARY

The apparatus has been extensively revised for improved dynamic performance

and preliminary testing has been performed. Samples are now being prepared for

a demonstration of the general dynamic capabilities.

192
Applied

Load

(20

gf/dlv)

Penetration Depth (1 um/dlv)

>

-ooCVJ

o

”8

J

Figure 1. Dynamic results for a 100 gram Knoop indentation of a hardened and tempered 0-2 tool steel.

(a) Applied load. A, and penetration depth, B, curves versus time.

(b) The load-displacement curve for loading, L and

unloading, U.

Figure 2. Schematic representations of the load-displacement curve.

(a) Hard materials have smaller indentation energies, Ap.

(b) After up- loading, 0, recovery can be largely elastic,

1 , or plastic, 2.

(c) This characteristic can be quantified by the relative

elastic energy, Ae and plastic energy, Ap, or area under the curves.

193
USE OF A COMMERCIAL HARDNESS TESTING INSTRUMENT AS A

NONDESTRUCTIVE PROBE OF MECHANICAL PROPERTIES

D. S. Lashmore and J. L. Mullen

Metallurgy Division

Institute for Materials Science and Engineering

The microhardness indentation process involves a sampling of a very

small volume of material in the region of the indentor. The kinetic values of

hardness and load displacement characteristics provide information related to

microdeformation and contain information related to the elastic properties and

yield strength of the material(l). This project was designed to develop the

instrumentation to characterize this process and to measure microindentation

charcteristics of important alloys. Characteristic of this project is the use

of commercially available instruments because of the desirability of rapidly

transferring to industry a new technology. The development of this kind of a NDE technique is particularly important to the electrodeposition area because

of the typically small volumes of material available for the measurement of

mechanical properties.

As in many instrumentation projects, one of the more serious problems is

signal to noise ratio. In the system described here two sources of noise

exist; the first is the signal to noise ratio of the analog signals from the

displacement and the load measuring instruments and the second is the digitizing noise or uncertainty in the voltage resulting from limitations in the

digitizing equipment. The ideal system should not be digitizing noise limited.

Unfortunately, at the start of this project onlv an II bit A/D converter was

available. As the signal was about 1 volt, this yielded a digitizing

uncertainty of about 400u volts. By making some changes in the hardware, it

became possible to obtain a full 12 bits which improved the situation to an uncertainty of about 240p volts. This error in the ability to read the signal

is marginally acceptable; however, converting to a 16 bit A/D converter would

give us a noise value of about 15p volts, which is below the analog noise.

Major improvements in signal to noise were made with the advice of John

Mandel whose scheme to improve the raw data involves fitting of the raw data

and determining the standard deviation of the collection of data. Then each

data point is compared with a statistical value which incorporates the

residual standard deviation, a noise factor, and the difference between the raw data and the fitted data.

Other important developments in the instrumentation included the

procurement of a commercial hardness testing instrument specifically for this

project. In the past, all the development of instrumentation and software has

to be on a shared instrument which severely limited the time available. Major

improvements were made to the apparatus to improve its rigidity. A load

displacement curve for a NBS standard reference material of copper is shown in

Fig. 1. Simple hardness values using this instrumentation compared with the

traditional technique are shown in Fig. 2 and the instantaneous Vickers

harbdness as a function of displacement is shown in Fig. 3. The latter curve confirms Tabor's statement (1), that the Vickers hardness number is

independent of displacement and that the strain will always be 8% which is

exactly what was measured.

194
The unloading curve provides a means of determining the modulus of the

material. For the copper specimen we have been indenting, the slope

corresponds to 1,4100 kg/mm 2 (20 million psi) which is consistent with the

literature values. Significantly the strain measured was exactly 8% in

agreement with the empirical value assumed by Tabor (1) for a Vickers

indentor. An estimate of the Ultimate Yield Stress can also be obtained from

the data using a value of 2.9 for ratio of Vickers Hardness to Ultimate

tensile strength, then

UTS= 135 Kg/mm 2/2. 9=46 kg/mm

2 (65,320psi). (1)

This value is in good agreement with the values reported by Lamb(2) for copper

electrodeposited from the same electrolyte as the sample we are using.

SUMMARY

It has been demonstrated that commercial hardness testing instruments

have the potential to provide important information concerning ultimate

tensile strength and elastic modulus. This capability is important for those

concerning with coatings or alloy development where only small amounts of

material are available for testing. When existing limitations in equipment

are overcome, then data will be obtained on copper single crystals to confirm

and further develop the theory of the microindentation process.

REFERENCES

1. D. Tabor. J. Inst. Metals 1951 Vol 79, pg. 1-18.

2. V. Lamb, C. Johnson and D. Valentine. J. Electrochem. Soc.

Vol. 117, No. 9, (Sept. 1970).

195
r~

®'S?I c

0)Sccn 'O

03cou

•HEC

•He jj

<u c

cj 0)

CO T3

<-i c a -h

03 •H 03

~a eo

«4-l s O (0 •H C T> O

•H 03 U M U <U C ^ 3 O

<4-1 -H>

CO CO

CDCO J3u

03 *H E 3

COM

U

qd aja, c a.

•H

Oa

a

CO t-i o o

!—1 <4-1

oju3

00

196
(

00IS )

NHA

Fig. 2 Vickers Hardness Measured by the Automated Hardnes:

Measurement System as a Function of the Optical Vickers

Hardness. The error bars represent + 1 Standard Deviation.

197
I

1 1 1 T“

arasr arnr aru mm aor

cad ssaNayuH

s

B

\h 2

IU

.z

u

CE

fll

in

H

8

°

198

Figure

3.

Vickers

hardness

as

a

function

of

indentor

displacement

in

microns
NONDESTRUCTIVE EVALUATION OF TOOL WEAR AND CHIP FORMATION

Kenneth W. Yee and Laurie Evans

Automated Production Technology Division

Center for Manufacturing Engineering

and

David Dornfeld

University of California, Berkeley

INTRODUCTION

With the upswing in automated manufacturing - especially untended

manufacturing - the detection of worn or dull tooling, and the maintenance of small, manageable chips become very important elements in the

machining process. The continued use of worn or dull tools can result in

the production of unfit parts, or broken tools, and the formation of

continuous chips can cause entanglement and clogging of the machining

center. This means that in an untended operation, where there is no operator to stop and check the machining center, tool and chip management

is extremely Important since the machining center itself can be damaged

by worn tooling and chip congestion.

Progress In tool wear prediction In milling operations is described

in this report as weli as continued work in the area of chip form

management

TOOL WEAR

On-line tool wear sensing is more important now than ever in

automated manufacturing. Without an operator to determine when tooling

must be changed, an imprecise method in itself, worn tools must be

changed based on the amount of cut or the number of parts made. This is an inefficient method since the life of tools, even from the same lot,

varies significantly. This means that tools would have to be changed

after the shortest life expectancy of any tool in a lot. Much of the

useful life will be wasted for the majority of tools, and there is a loss

of time and money in making excessive tool changes due to the additional

time required to change tooling. Worse still, a machine tool might not

have enough locations in the tool magazine to operate untended for the

required length of time.

Drill-Up is an instrument which was originally designed at the

National Bureau of Standards to prevent breakage of sma II -d i ameter dr 3 used on automatic-feed drilling machines. This application and the

measurement methods involved are described in reference 1; a description

of the use of Drill-Up to monitor tool wear in large diameter drills is

199
given in reference 2. Based on time-domain analysis of vibration, DrillUp has a calibration routine which automatically adjusts to the amplitude

of the vibration signal due to normal machining. Large amplitude ac- celerations, synchronous with the tool rotation, have been found to be

Indicative of improper machining, and it is this increase in signal level

which Drill-Up monitors as the tool wears to detect worn-out tooling.

The use of Drill-Up as an alternative to monitoring feed force and

spindle power consumption has been investigated for detecting tool wear

in end-milling in three hardnesses of steel; this has been described in

reference 3. Because they are commonly-employed tools, 1/2 in. (approx.

12 mm) diameter high speed steel end mills were used in heavy cuts in

A I S I 4150 (290 Brinell Hardness Number, BHN), 4130 (245 BHN) , and 1015

(180 BHN). Drill-Up parameters were altered to provide two instruments,

an original circuit and a more sensitive circuit, for monitoring end-mill

wear. Feed force and spindle cutting power, defined as total spindle

motor power consumption while machining minus spindle motor power con- sumed while the spindle motor is rotating but not cutting, were also

examined as tool wear detection parameters. The results of the experiments conducted are shown in Figure 1. Linear regression fits of feed

force and cutting power are plotted versus maximum flank wear of the four

cutting flutes, for the average of four tools in each of the three

steels. The wear values at which the Dr Ill-Up circuits determined worn

tooling are plotted on the feed force versus wear plot. It can be seen

that the change In the cutting power with Increasing flank wear (the

slope of the curve) Is very similar for all three steels, and is large

enough that cutting power might be a viable method for detedtlng wear. The change in feed force with flank wear varies with the Increasing

hardness of the steel. This means that feed force may be less applicable

than cutting power for a wide range of materials, but may not be ruled

out as a wear monitoring method yet. The original Drill -Up circuit was

found to be capable of detecting wear in the two harder steels, and the

sensitive circuit was able to detect a suitable degree of wear in the

softer steel. (A worn-out tool is considered to have roughly 5-7 mi Miinches, or 125 to 175 micrometers flank wear.) The performance of DrillUp in these experiments indicates that it is a useful method of

determining tool wear for one size of end mill in several steels.

Feed force and cutting power methods show promise in the area of

tool wear detection for end-milling. Drill-Up has shown potential in

detecting tool wear in drilling, has been successful in preventing

breakage of small diameter drills, and with minor modifications can predict tool wear In end-milling.

CHIP FORMATION

The goal of this research is to investigate the applicability of

acoustic emission (AE) to the study of chip formation in single-point

turning. The results of this research have both theoretical and practical Interest since some of the limitations of present untended

manufacturing operations are related to a lack of knowledge of the chip

conditions. In some metal operations this can lead to deterioration of

the surface finish, dimensional variation, or severe damage to the

workpiece and tooling due to chip tangle.

200
In order to predict chip formation, an acoustic emission event

(rate) counter was constructed which was designed expressly as an experimental tool to be used for the counting of acoustic emission (AE)

signal bursts which exceed a selectable threshold voltage during a predetermined time interval. Tests using this device were performed on a turning center with coated carbide Insert tooling. An AE transducer was mounted at the rear of the tool holder. The mater la Is machined were

6061-T651 aluminum rod, and two types of steel rod: AISI 1215 and 4340.

The AE signal was analyzed using the acoustic emission event counter.

Each significant burst event in the AE signal can be related to the chip

breaking process due to the Instantaneous large energy release at chip

fracture compared to the AE generated during normal cutting. The count

rate of burst events above a certain threshold excludes the continuoustype AE signal contributed by normal cutting and is a good indicator of

the chip-breaking frequency. This is shown In Figures 2 and 3 which are plots of the events per second versus the feed rate for the two types of

steel bars. The transition from continuous to discontinuous chip formation occurs at about 0.006 Inches per revolution for the 4340 and, for

the 1215, at around 0.004 Inches per revolution. For the alloy steel

there Is a detectable change in slope; for the low carbon steel there is a less dlscernable change. For two materials (the aluminum and the alloy

steel) one can predict the formation of chips; it may also be possible to

predict chip formation In the low carbon steel although with less

certainty. Further development is needed in this area with a wider range

of materials In order to produce suitable chip management algorithms.

SUMMARY

During FY85, progress has been made in tool wear monitoring via

development of power, force, and time-domain vibration (Dr Ill-Up)

methods, as applied to end-mil ling. Chip formation detection in turning

has proceeded In several new materials. Including low carbon steel (AISI

1215) and mild alloy steel (AISI 4340).

REFERENCES

1. K. W. Yee, and D. S. Blomqulst, "An On-Line Method of Determining

Tool Wear by Time-Domain Analysis,” Technical Paper MR82-901 , Soc.

Mfg. Eng'rs, Dearborn, Ml, 1982.

2. K. W. Yee, "On the Use of Dr Ill-Up for On-Line Determination of Drill

Wear," Technical Paper MR84-914, Soc. Mfg. Eng'rs, Dearborn Ml

1984.

3. K. W. Yee, and L. Evans, "Dr Ill-Up, An Alternative for On-Line

Determination of End-Mill Wear," Proc. of the 13th N. A. M. R. c.,

Berkeley, CA, Soc. Mfg. Eng'rs, Dearborn, Ml, May, 1985.

201
0.0 2.0 4.0 6.0 8.0 10.0 12.0

WEAR (IE-3 INCHES)

Figure 1 . Feed Force and Cutting Power vs. Wear for Three Steels

202
©

CN

o

ooo

CD

o

q

<N

o

o

o

ooo

o

CO

o

o

o

o

CM

o

o

03 c

<r

cn<

u

0)

0) AJ

03u

CNv

co

(ZM) 3V JO SI/MU JO ojea juaAg

203

Feed

Rate

(in/rev)
o

CM

o

CO

©

co©

©

CM

To

o

©a

CO

o

oa

CO

o

oa

OOa

CMO

o

>

CDC

CD

(0 cc

(zm) 3V jo Sl/Md *0 0;ey IU0A3

204

Figure

3.

Event

rate

of

AE

vs.

feed

rate

for

AISI

1215

steel
ULTRASONIC MEASUREMENTS ON THERMAL INSULATION

G.V. Blessing and D.R. Flynn

Mechanical Production Metrology Division

Center for Manufacturing Engineering

A recent request from the thermal insulation sector of the building

industry to NBS, for innovative methods to measure insulation quantity, has

resulted in feasibility tests using ultrasonic waves. The scattering sen- sitivity of air-borne ultrasound at 40 kHz to the average density of

commercially available fiberglass batt material has been demonstrated in these

tests.

A two transducer transrait-receive continuous wave system was used, with

the transmitter facing the receiver and separated by about 15 cm. Figure 1 illustrates the received amplitude obtained at 40 kHz respectively for (a) no insulation, (b) one R-1 1 batt thickness, and (c) two R-1 1 batt thickness

between transmitter and receiver. The R-value is the commercially-used

measure for heat flow resistance. Home ceiling insulation values may range

from zero to R-40 or greater, depending on the region of the country and other

factors

Two significant features may be observed for the signals in Fig. 1 as a function of increasing R-value. The most prominent is the (expected) reduction in signal amplitude with increasing insulation due to increased

ultrasonic scattering. Less evident, but perhaps of equal significance as a practical measurand, is the phase shift (later in time) with increasing

insulation. It may be conjectured that this shift is due to an increased

sound path the waves must travel on the average through the multiplyscattering fiberglass medium. This is based on the assumption that

fiberglass, possessing a significantly different acoustic impedance from air,

acts to scatter rather than absorb the wave front.

A patent application covering this technique for inferring thermal insulation values from ultrasonic measurements has been submitted to DOC. It is

expected to be useful for process control in manufacture of insulation and for

determining the value of installed insulation.

SUMMARY

The feasibility of a new method of inferring the R-value of installed

attic insulation using air-borne ultrasound has been demonstrated. The technique promises to be orders of magnitude faster, less expensive, and less

intrusive than other methods. It may also be used for process control of

insulation manufacture.

205
co no

<N ° ^

(s}|oa) epnindiuv peAiooey

206

Figure

1.

The

received

40

kHz

ultrasonic

wave

amplitude

as

a

function

of

time

for

three

quantities

of

fiberglass

insulation

between

transmitter

and

receiver:

(a)

none,

(b)

one,

and

(c)

two

R-ll

batts.
APPENDICES

A. NDE SEMINARS AT NBS

Dr. Erkhardt Schneider , Fraunhofer Institut fur Zerstorungsfreie

Priifverfahren, Saarbriicken, FRG

"Evaluation of Stress States with Ultrasonic Techniques"

October 16, 1984

Mr. James J. Yavelak , Babcock & Wilcox Co., Alliance, Ohio

"Sensing Residual Stresses and Microstructure with Magnetic Barkhausen

Noise Analysis"

December 10, 1984

Dr. David A. Hutchins , Queen’s University, Kingston, Ontario, Canada

"Non-Contact Ultrasonic Transducers for NDE"

March 11, 1 985

Ms. Susan N. Vernon , Naval Surface Weapons Center, Silver Spring, Maryland

"Eddy Current Inspection of Composites with Conducting Fibers in a Non-Conducting Matrix"

March 28, 1985

Dr. Eva Krasicka , University of Illinois

"Ultrasonic Study of Tunneling of Trapped Hydrogen in Niobium"

May 23, 1985

Dr. B. N. Ranganathan and associates, Martin Marietta Aerospace, New Orleans,

Louisiana

"Nondestructive Evaluation at the Michoud Division of Martin Marietta

Aerospace"

July 16, 1985

Professor Richard Klaus , Virginia Polytechnic Institute and State Uni ver-: . - y

Blacksburg, Virginia

"NDE of Composite Materials Using Optical Fibers"

August 6, 1985

207
Dr. William N. Reynolds , Atomic Energy Research Establishment, Harwell,

United Kingdom

’’Ultrasonic and Thermographic Characterization of Composite Materials"

August 13. 1985

B. INVITED TALKS BY ONDE STAFF

"NBS Research on NDE Sensors for Manufacturing Process Control,"

H. T. Yolken, Bethlehem Steel Corporation, Research Seminar, Bethlehem,

Pennsylvania, October 18, 1984.

"Quantitative NDE and Quality Improvement," L. Mordfin, Fairmont State

Section, American Society for Nondestructive Testing, Fairmont, West

Virginia, November 8, 1984.

"Quantitative NDE and Quality Improvement," L. Mordfin, Hampton Roads

Section, American Society for Nondestructive Testing, Newport News, Virginia,

January 8, 1985.

"International NDE Standards and the GATT Code," L. Mordfin, 7th

International Conference on NDE in the Nuclear Industry, Grenoble, France,

February 1, 1985.

"Quantitative NDE and Quality Improvement," L. Mordfin, Lynchburg Section,

American Society for Nondestructive Testing, Lynchburg, Virginia,

February 20, 1985.

"The Challenge of Advanced NDE," H. T. Yolken, luncheon address, 1985 Spring

Conference, American Society for Nondestructive Testing, Washington, D.C.,

March 11, 1985.

"Advanced NDE for Manufacturing Process Control," H. T. Yolken, 17th

Symposium on Nondestructive Evaluation, San Antonio, Texas, April 24, 1985.

"NDE Sensors for Manufactur ing Process Control: Developing National Strategy

and Policy," H. T. Yolken, Review of Progress in Quantitative NDE,

Williamsburg, Virginia, June 25, 1985.

"Automated Materials Processing," H. T. Yolken, National Science Foundation,

Planning Workshop for Senior Management, Washington, D.C., July 15, 1985.

C. PUBLICATIONS

Following is a partial listing of NBS reports and publications on NDE and

related topics that have been issued since last year’s Technical Activities

report was prepared. A more complete compilation will be presented in ONDE's

annual bibliography with abstracts.

B. A. Auld, G. McFetridge, M. Riazat and S. Jefferies, "Improved Probe-Flaw

Interaction Modeling, Inversion Processing, and Surface Roughness Clutter,"

Review of Progress in Quantitative Nondestructive Evaluation 4 a, pp. 623-634

(1985).

208
M. Barsky and N. N. Hsu, "A Simple and Effective AE Source Location System,"

Materials Evaluation 43, No. 1, pp. 108-110 (Jan. 1985).

H. Berger, D. C. Cutforth, D. A. Garrett, J. Haskins, F. Iddings and

R. L. Newacheck, "Neutron Radiography," Nondestructive Testing Handbook 3,

2nd edition, Section 12, pp. 532-563 (ASNT, 1985).

G. Birnbaum, G. S. White, and C. M. Vest, "Laser Generated and Detected

Ultrasound and Holographic Methods," Pressure Vessel and Piping Technology

1985 —A Decade of Progress , pp. 661-669 (ASME, NY, 1985).

P. J. Blau, "Investigation of the Nature of Micro-indentation Hardness

Gradients Below Sliding Contacts in Five Copper Alloys Worn Against 52100

Steel," J. Materials Science 19 , p. 1957 (1984).

P. J. Blau, "Relationship Between Scratch and Knoop Micro-indentation

Hardness and Implications for Abrasion of Metals," Microstructural Science

J_2, p. 293 (1985).

P. J. Blau and T. R. Shives, "Microindentation Hardness Testing," ASTM

Standardization News 13 , No. 1, pp. 47-51 (1985).

G. V. Blessing, N. N. Hsu and T. N. Proctor, "Ultrasonic-shear-wave

Measurement of Known Residual Stress in Aluminum," Experimental Mechanics 24 , No. 3, pp. 218-221 (Sept. 1984).

G. V. Blessing, P. 0. Bagley and J. E. James, "The Effect of Surface

Roughness on Ultrasonic Echo Amplitude in Steel," Materials Evaluation 42 , No. 11, pp. 1389-1392 (Oct. 1984).

T. E. Capobianco and F. R. Fickett, "Precision Measurement of Eddy Current

Coil Parameters," Review of Progress in Quantitative Nondestructive

Evaluation 4A , pp. 491-498 (1985).

A. S. Carasso and N. N. Hsu, "Probe Waveforms and Deconvolution in the

Experimental Determination of Elastic Green's Functions," SIAM J. Appl. Math.

45_, No. 3, PP- 369-383 (June 1985).

A. S. Carasso and N. N. Hsu, "The Inverse Gaussian Pulse in the Experimental

Determination of Linear System Green's Functions," ARO Report 85-1,

pp. 389-404 (Army Research office, Research Triangle Park, NC, 1985).

E. L. Church, T. V. Vorburger and J. C. Wyant, "Direct Comparison of

Mechanical and Optical Measurements of the Finish of Precision Machined

Optical Surfaces," Opt. Eng. 24 , pp. 388-395 (1985).

R. B. Clough, H. N. G. Wadley and F. S. Biancaniello , "Acoustic Emission

Studies of Electron Beam Melting and Rapid Solidification," Nondestr ^ct

Evaluation: Application to Materials Processing , pp. 27-40 (ASM, 198- .

R. B. Clough and H. N. G. Wadley, "Acoustic Emission Monitoring of

Dislocation Motion and Microfracture During Electron Beam Melting ini . Solidification of Aluminum Alloys," Review of Progress in Quant 1 tat : v- Nondestructive Evaluation 4B, pp. 661-669 (1985).

209
K. L. Eckerle, J. J. Hsia and V. R. Weidner, "Transmittance MAP Service," NBS

SP 692, 44 pp. (1985).

[D. G. Eitzen], "Glossary of Terms and Definitions for Acoustic Emission

Testing Procedures," Military Standard MIL-STD-1 945, 5 pp. (DOD, 24 October

1 984) .

D. G. Eitzen, N. Hsu, A. Carasso and T. Proctor, "Deconvolution by Design —An

Approach to the Inverse Problem of Ultrasonic Testing," Review of Progress in

Quantitative Nondestructive Evaluation 4 a , pp. 179-188 (1985).

F. R. Fickett and T. E. Capobianco, "Magnetic Field Mapping with a SQUID

Device," Review of Progress in Quantitative Nondestructive Evaluation 4 a , pp. 401-410 (1 985)

C. L. Friant, M. Rosen, R. E. Green, Jr. and R. Mehrabian, "Ultrasonic NDE of

Rapidly Solidified Products and its Application to Process Control,"

Nondestructive Evaluation: Application to Materials Processing , pp. 51-59

(ASM, 1 984).

C. L. Friant and M. Rosen-, "Ultrasonic Materials Characterization of Melt

Spun Metallic Ribbons," Nondestructive Methods for Material Property

Determination , pp. 301-314 (Plenum Press, NY, 1984).

D. E. Gilsinn, T. V. Vorburger, F. E. Scire, E. C. Teague and M. J. McLay,

"Surface Texture Characterization by Angular Distributions of Scattered

Light," Review of Progress in Quantitative Nondestructive Evaluation 4B,

pp. 779-788 (1985).

M. Gvishi, M. Rosen and H. N. G. Wadley, "Acoustic Emission Characterization

of the Martensitic Phase Transformation in NiTi," Review of Progress in

Quantitative Nondestructive Evaluation 4 b , pp. 651-659 (1985).

K. Hardman-Rhyne, N. F. Berk and E. D. Case, "Porosity Study of Sintered and

Green Compacts of YCrO^ Using Small Angle Neutron Scattering Techniques,"

Nondestructive Evaluation: Application to Materials Processing , pp. 103-108

(ASM, 1984).

N. N. Hsu and D. G. Eitzen, "Analytical Approach to Acoustic Emission Signal

Processing: Problems and Progress," Proc. 7th International Acoustic

Emission Symposium, pp. 326-334 (Japan Soc. Non-Destructive Inspection,

1 984)

S. Kim, J. R. Weertman, S. Spooner, C. J. Glinka, V. Sikka and W. B. Jones,

"Microstructural Evaluation of a Ferritic Stainless Steel by Small Angle

Neutron Scattering," Nondestructive Evaluation: Application to Materials

Processing , pp . 169-176 (ASM, 1984).

D. S. Kupperman, H. B. Karplus, R. B. Poeppel, W. A. Ellingson, H. Berger,

C. Robbins and E. Fuller, "Application of NDE Methods to Green Ceramics:

Initial Results," Nondestructive Evaluation: Application to Materials

Processing

pp. 89-101 ( ASM, 1 984 )

210
H. M. Ledbetter, S. K. Datta and R. D. Kriz, "Elastic Constants of an Anisotropic, Nonhomogeneous Particle-Reinforced Composite," Acta Metallurgies

32, pp. 2225-2231 ( 1 984)

M. Linzer, editor, Ultrasonic Imaging 7 (Academic Press, 1985).

T. S. Liu, R. J. Fields, D. G. Harlow and T. J. Delph, "Statistical

Observations of Creep Cavitation in AISI 304 Stainless Steel," Scripts

Metallurgica 19 , pp. 299-304 (1984).

R. Mehrabian and H. N. G. Wadley, "Needs for Process Control in Advanced

Processing of Materials," Review of Progress in Quantitative Nondestructive

Evaluation 4B , pp. 839-858 (1985).

L. Mordfin, editor, "Office of Nondestructive Evaluation: Technical

Activities 1984," NBSIR 84-2944, 163 pp. (Nov. 1984).

L. Mordfin, editor, "NDE Publications: 1982," NBSIR 85-3183, 32 pp

(May 1 985)

J. C. Moulder, J. C. Gerlitz, B. A. Auld, M. Riaziat, S. Jefferies and

G. McFetridge, "Calibration Methods for Eddy Current Measurement Systems,"

Review of Progress in Quantitative Nondestructive Evaluation 4 a, pp. 411-420

(1985).

T. Nguyen and A. Rosencwaig, "Thermal-wave Microscopy and Its Applications to

Imaging the Microstructure and Corrosion of Cold-rolled Steel," Appl. Surface

Sci. 24, No. 1 (1985).

S. J. Norton and H. N. G. Wadley, "Tomographic Reconstruction of Internal

Temperature," Review of Progress in Quantitative Nondestruc tive Evaluation

4A, pp. 309-318 (1985).

R. L. Parker, "Ultrasonic Measurement of Solid/Liquid Interface Position

During Solidification and Melting of Iron and Steel," Nondestructive

Evaluation: Application to Materials Processing , pp. 23-25 (ASM, 1984).

T. M. Proctor, F. R. Breckenridge and D. G. Eitzen, "The Development of High

Fidelity Acoustic Emission Transducers," Proc. 6th Inti. Conf. on NDE in the

Nuclear Industry , pp. 329-337 (ASM, Metals Park, OH, 1984).

R. E. Schramm and J. C. Moulder, "EMAT/Synthetic Aperture Approach to

Thick-Weld Inspection," Review of Progress in Quantitative Nondestructive

Evaluation 4A, pp. 225-232 (1985).

J. J. Smith, M. Rosen and H. N. G. Wadley, "Nondestructive Character i zat ion

of Rapidly Solidified Al-Mn Alloys by Ultrasonic and Electrical Methods,"

Nondestructive Evaluation: Application to Materials Processing , op. oi-6 < (ASM, 1 984).

J. J. Smith, "Nondestructive Characterization of Rapidly Solidified

Aluminum-Manganese Alloys," Report CMR-NDE-1 4, 48 pp. (Johns Hopkins

University, Baltimore, MD, 1984).

211
P. L. Swanson, "Subcritical Fracture Propagation in Rocks: An Examination

Using the Methods of Fracture Mechanics and Non-Destructive Testing,”

NBS-GCR-85-491 , 268 pp. (April 1985).

L. R. Testardi, S. J. Norton and T. Hsieh, "Determination of Inhomogeneities

of Elastic Modulus and Density Using Acoustic Dimensional Resonance," Review

of Progress in Quantitative Nondestructive Evaluation 4B , pp. 877-880 (1985).

H. N. G. Wadley, chairman, "Acoustic Emission—Open Discussion," Review of

Progress in Quantitative Nondestructive Evaluation 4B , pp. 727-737 (1985).

H. N. G. Wadley, S. J. Norton, F. S. Biancaniello and R. Mehrabian,

"Ultrasonic Measurement of Internal Temperature Distribution," Nondestructive

Evaluation: Application to Materials Processing , pp. 3~11 (ASM, 1984).

H. N. G. Wadley, editor, Proceedings, 6th International Conference on NDE in

the Nuclear Industry (ASM, Metals Park, OH, 1984).

H. N. G. Wadley and R. Mehrabian, "Acoustic Emission for In-Process

Monitoring and Microstructure Control?," Nondestructive Methods for Material

Property Determination , pp. 207-236 (Plenum Press, NY, 1984).

H. T. Yolken and L. Mordfin, "Strategic Plan for Nondestructive Evaluation

for the Period 1985-1989," 41 pp. (Office of Nondestructive Evaluation, NBS,

December 1 984)

D. AWARDS

AEWG Publication Award

Frank Breckenridge , Carl Tschiegg and Martin Greenspan, all associated with

the Center for Manufacturing Engineering, received the coveted Publication

Award of the Acoustic Emission Working Group for their landmark paper,

"Acoustic Emission: Some Applications of Lamb’s Problem," which appeared in

the Journal of the Acoustical Society of America, Volume 57. The citation

states, in part, that the paper "... laid the foundation for the standardized calibration of acoustic emission sensors and stimulated the development

of quantitative theories of the wave-propagation aspect of acoustic

emission."

Department of Commerce Silver Medal

Department of Commerce Silver Medals, which are bestowed for meritorious

contributions of unusual value to the Department, were awarded to

Dr. Bruno M. Fanconi of the Polymers Division, Dr. Frederick R. Fickett of

the Center for Electronics and Electrical Engineering, and

Dr. Hassel M. Ledbetter of the Fracture and Deformation Division. All three

are principal investigators in the NDE Program.

212
Industrial Commission on Illumination (CIE)

Dr. Jack Hsia of the Center for Radiation Research was named associate

director of CIE Division 2 on ’’Physical Measurement of Light and Radiation,"

by the Council of the Commission. A principal investigator in the NDE

Program, Hsia has been developing measurement standards for the fluorescence

of liquid penetrant and magnetic particle materials, and for the light

transmittance of high-density radiographs.

Department of Commerce Bronze Medal

Dr. Anna C. Fraker of the Metallurgy Division and Dr. Maurice B. Kasen of the

Fracture and Deformation Division were recipients of the Department of

Commerce Bronze Medal Award for superior federal service. Fraker is the NDE

Program's principal investigator for NDE of corrosion; Kasen was cited, in

part, for "... his innovative, definitive studies on how defects affect

pipeline structural integrity. ..."

NBS Unit Safety Award

The Office of Nondestructive Evaluation is proud to announce its receipt of

the NBS Unit Safety Award, "for an exceptional safety performance record for

a continuous period beginning July 1, 1979." Dr. George Birnbaum has served

as the Office’s safety officer for this entire period.

E. PRINCIPAL INVESTIGATORS

Berk, Norman F. Small-angle neutron scattering

Condensed matter theory

Berlinsky, Yoram Acoustic emission

Wave propagation and instrumentation

Blau, Peter J. Thermal waves

Tribology

Blessing, Gerald V. Ultrasonics

Experimental physical acoustics

Breckenridge , Franklin R. Acoustic emission and transducers

Transducer calibration

Capobianco, Thomas E.

Carasso, Alfred S.

Carino, Nicholas J.

Clark, Alfred V.

Eddy current NDE

Electromagnetic technology

Acoustic emission

Applied mathematics; inverse problems; imag’?

analysis; deconvolution

Pulse echo

Concrete technology and structural anal y. . -

Ultrasonics and eddy currents

Mechanical properties

213
Clough, Roger B. Acoustic emission

Mechanical properties

Cohen, Julius Thermography

Fourier optics

Droney, Bernard Steel processing sensors

Metallurgy

Eckerle, Kenneth L. Fluorescence

Spectrophotometry

Ehrlich, Charles D. Calibrated leaks and leak detection

Surface physics

Eitzen, Donald G. Acoustic emission

Engineering mechanics

Fanconi, Bruno M. Optical wave guide techniques

Polymer science

Fick, Steven E. Specialized measurement

Electrical engineering

Fickett, Frederick R. Electromagnetic methods

Solid state physics, superconductivity, and

magnetism

Fields, Richard J. Quantitative metallography

Mechanical metallurgy

Fong, Jeffrey T. Reliability

Mathematical analysis

Fraker, Anna C. Microstructures , microscopy, and standards

development

Corrosion processes

Free, George M. Eddy current measurements

AC impedance measurements

Hardman-Rhyne , Kay A. Small-angle neutron scattering

Ceramics

Hsia, Jack J. Spectrophotometry

Spectrophotometry and thermal radiation

properties

Hsu, Nelson N. Acoustic emission and ultrasonics

Experimental solid mechanics

Hunston, Donald L. Ultrasonics

Polymer science

214
Inglehart, Lorretta Thermal waves

Physics

Kahn, Arnold H. Eddy currents

Solid state physics

Kriz, Ronald D. Ultrasonics and fiber optics

Mechanical properties of composites

Kuriyama, Masao X-ray diffraction

Solid state physics

Lashmore, David Microhardness measurements and micromechanical

properties

Alloy deposition

Ledbetter, Hassel M. Elastic properties and internal friction

Physical properties of solids

Linzer, Melvin Ultrasound instrumentation

Signal processing

Mauer, Floyd Ultrasonic temperature sensing

Ultrasonic measurement

Mielenz, Klaus D. Fluorescence

Optical instrumentation and optics

Mopsik, Frederick I. Electrical measurements

Dielectrics

Moulder, John C. Eddy current; ultrasonics using EMATS

Materials research

Mountain, Raymond Acoustic scattering

Statistical physics

Norton, Stephen J. Ultrasonic imaging

Inverse modeling

Nguyen, Tinh Thermal wave imaging and infrared thermography

Corrosion under coatings

Placious, Robert C. Radiological imaging

Radiation physics

Polansky, Daniel Radiographic inspection of materials

Physics

Prask, Henry J. Neutron diffraction

Residual stress

Proctor, Thomas M. Acoustic emission, transducers

Transducer calibrations and design

215
Robbins, Carl R.

Rosen, Moshe

Ruff, Arthur W.

Simmons, John A.

Spal, Richard D.

Swart zendruber, Lydon W.

Teague, E. Clayton

Tilford, Charles R.

Vorburger, Theodore V.

Wadley, Haydn N. G.

Wang, Francis W.

White, Grady S.

Yee, Kenneth W.

Ceramic powder preparation and

characterization

X-ray diffraction

Ultrasonics, eddy currents

Materials characterization

Wear condition monitoring

Tribology/metallurgy

Defects and elastic propagation; materials

characterization

Applied mathematics and theoretical mechanics

X-ray imaging

Synchroton radiation

Surface methods

Physical metallurgy

Non-contacting optical measurements of surface

roughness

Surface metrology and physics

Leak and pressure standards

Vacuum technology

Optical scattering techniques

Surface roughness measurement

Acoustic emission

Fracture and deformation

Fluorescence spectroscopy

Polymer characterization

Thermal waves

Mechanical properties of brittle materials

Machine tool sensors

Electronic instrumentation

216
ftfiSl114A (RKvu a-#c> U.S. OCFT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR- 85/31 87

2. Performing Organ. Report No. 3. Publication Date

November 1985

4. TITLE AND SUBTITLE

Institute for Materials Science and Engineering

Nondestructive Evaluation - Technical Activities 1985

S. AUTHOR(S)

Yolken, H.T., Mordfin, L., Birnbaum, G. (Editor)

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL' BUREAU OF STANOAROS

DEPARTMENT OF COMMERCE

WASHINGTON. D.C. 2*234

7. Contract/Grant No.

I. Type of Report & Period Covered

Annual , FY85

5. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Bureau of Standards

Rte. 270 & Quince Orchard Road

Gaithersburg, Maryland 20899

It. SUPPLEMENTARY NOTES

f I Document describes a computer protram; 5F-I85. FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or lass factual summary of most significant information. If document includes a significant

bibliography or literature Murrey, mention it here)

A review of the Nondestructive Evaluation Program at NBS, * for fiscal year 1985, is

presented In this annual report.

II KEY WORDS (Si* to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon t/ acoustic emission; eddy currents; leak testing; magnetics; neutrons; nondestructive

evaluation; optics; penetrants; radiography; standards; thermal testing; ultrasonics

13. AVAILABILITY

Ifr I Unlimited

I I For Official Distribution. Do Not Release to NTIS

1 I Order From Superintendent of Documents. U.S. Government Prmtinf Office. Washington. D.C

20402.

1 Order From National Technical Information Service (NTIS). Springfield. VA_ 22161

14. NO. OF

PRINTED PAGES

22S

15. Price

S22.95

uico< “OC
.