Technical Activities 1983

Office of Nondestructive

Evaluation

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Office of Nondestructive Evaluation

Washington, DC 20234

December 1 983

Prepared for U.S. DEPARTMENT OF COMMERCE

ationai Bureau of Standards

3CTM—ashington, DC 20234

100

J56

J4-2815

1933

NBSIR 84-2815

TECHNICAL ACTIVITIES 1983

OFFICE OF NONDESTRUCTIVE

EVALUATION

Leonard Mordfin, Editor

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Office of Nondestructive Evaluation

Washington, DC 20234

December 1983

Prepared for U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, DC 20234

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

S4-JS/

5

MS 5

TECHNICAL ACTIVITIES

TECHNICAL ACTIVITIES

Table of Contents

Introduction 1

LIQUID PENETRANT AND MAGNETIC PARTICLE METHODS

A New Fluorescent Glass Standard for Use in Dye ... . Penetrant Measurements 3

- R. W. Burke and M. V. Smith

Magnetic Measurements 5 - L. Swartzendruber

Magnetic Particle Inspection Standards 8

- L. Swartzendruber

RADIOGRAPHY

Development of High Optical Density Standards 9

- J. Hsia, C. H. Popenol and L. Fink

Radiographic Image Quality Evaluation at High Energies 12

- R. C. Placious and D. Polansky

Modulation Transfer Function Measurement of an Image

Intensified Solid State X-Ray Camera 13

- R. D. Spal, H. E. Burdette, W. J. Boettinger and M. Kuriyama

Digital Radiography 16

- R. C. Placious, D. Polansky and J. H. Sparrow

Advanced Radiography 13

- D. Polansky

NDT Support for the Fleet Missile System 19

- D. Polansky and J. H. Sparrow
NEUTRON METHODS

Nondestructive Characterization of Distributed Damage 20

- E. R. Fuller, Jr., K. Hardman- Rhyne, N. J. Tighe and R. J. Fields

Small Angle Neutron Scattering Study of Creep Damage in __

304 Stainless Steels * -3-*'

- S. P. Singhal, B. Mozer and R. J. Fields

Nondestructive Evaluation of Porosity in YCrCL by Small Angle ^

Neutron Scattering

- N. F. Berk, K. Hardman-Rhyne and E. Case

Green State Ceramics 45

- T. Negas, E. Fuller, K. Hardman-Rhyne and C. Robbins

Nondestructive Characterization of Subsurface Residual Stress . . . . 53

- N. J. Prask and C. S. Choi

ULTRASONIC METHODS

Theoretical Study of Acoustic Wave Scattering 57

- R. D. Mountain

NDE Terms and Definitions: Ultrasonics and Acoustic Emission 58

- D. Eitzen and M. Cadoff

Ultrasonic Reference Block Calibration Methodology 60

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

Transfer Standards for Ultrasonic Power Measurements 52

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

Ultrasonic Residual Stress Measurements 64

- G. V. Blessing, N. N. Hsu and T. M. Proctor

Evaluation of Residual Stresses in Inhomogeneous, Anisotropic

Materials using Horizontally Polarized Shear Waves 55

- R. B. King and C. M. Fortunko

Determination of the Elastic Moduli of Melt-Spun Metallic Glasses . . 67

- M. Rosen, C. L. Friant and H. N. G. Wadley

Effect of Composition on the Crystallization Kinetics and

Elastic Properties of Cu-Zr Alloys 69

- M. Rosen, F. Nadeau and H. N. G. Wadley

Nondestructive Characterization of Microstructurally Modified

Surface Layers by Means of Rayleigh Surface Waves 73

- M. Rosen, B. El kind and H. N. G. Wadley

XV
Determination of Phase Stability Criteria of Extended Solid

Solutions by Means of Nondestructive Characterization

- M. Rosen, R. J. Schaefer, J. J. Smith and H. N. G. Wadley

76

Ultrasonic Measurement of Solid/Liquid Interface Position

during Solidification and Melting of Metals !•••• 81

- R. L. Parker and J. R. Manning

Ultrasonic Steel Temperature Sensors 83

- S. J. Norton, M. Linzer, H. N. G. Wadley, C. Turner,

F. S. Biancaniello and S. D. Ridder

Cure Monitoring in Polymers and Composites via Nondestructive .... 86

Techniques

- D. L. Huns ton, B. M. Fanconi and F. I. Mopsik

Ultrasonic Applications to NOT and Materials Evaluation 89

- G. V. Blessing

Ultrasonic Imaging for Medical Applications 90

- M. Linzer and S. J. Norton

ACOUSTIC EMISSION METHODS

Acoustic Emission Theory Development 92

- J. A. Simmons and H. N. G. Wadley

Point Source Time Dependence in the Determination of Acoustic

Emission Green's Functions 98

- A. S. Carasso and N. N. Hsu

Calibration Activities for AE Transducers 102

- F. Breckenridge

MIL-Standard on Acoustic Emission Transducer Calibration 106

- D. Eitzen

Improvements to the NBS Conical Transducer for Acoustic Emission

Measurements 107

- T. M. Proctor

A Comparison of Simulated Acoustic Emission Sources 113

- M. P. Jones, N.N.. Hsu and R.E. Green, Jr.

A Simple Real-Time AE Source Location System 115

- N. N. Hsu and M. Barsky

Acoustic Emission Imaging 116

- S. J. Norton and M. Linzer

Acoustic Emission Studies of Rapid Solidification 113

- R. B. Clough, H. N. G. Wadley and R. J. Schaefer
Wear Condition Monitoring . - A. W. Ruff and E. Whitenton

122

EDDY-CURRENT AND ELECTRICAL METHODS

Eddy Current Standards 124

- A. J. McAlister

Traceability for Eddy-Current NDE Measurements 127

- G. M. Free

Eddy Current Coil Characterization ]_30 - F. R. Fickett

Theoretical Modeling in Eddy Current NDE 135

- A. H. Kahn

High-Frequency, Broadband Eddy-Current Probes for Improved

Flaw Characterization 14 0

- C. M. Fortunko, J. C. Moulder, J. Gerlitz, A. C. Bennett,

B. A. Auld and F. G. Muennemann

Electrical Noise 149

- U. Bertocci

OPTICAL AND THERMAL METHODS

Optical NDE: Light Scattering 150

- G. S. White

Optical Measurement of Surface Roughness 152

- E. C. Teague, T. V. V orburger, F. E. Scire, D. E. Gilsinn

and M. J. McLay

Holographic Nondestructive Evaluation 157

- C. M. Vest

Infrared Methods of Nondestructive Testing 161

- J. Cohen

NDE of Building Materials 162

- J. R. Clifton and M. E. McKnight

vi
SPECIAL REPORTS

Microhardness Reference Material Standard 164

- 0 . S. Lashmore

Nondestructive Evaluation of Nonuni formi ties in 2024 Aluminum

Alloy Plate - Relationship to Processing l69

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

S. D. Ridder, F. S. Biancaniello, R. C. Reno, S. Fick,

D. Ballard and R. Mehrabian

NDE Data Analysis, Reliability Modeling, and On-Line Decision

Making 174

- J. T. Fong

APPENDICES

A. Conferences Sponsored or Co-Sponsored 186

B. NDE Seminars at NBS 187

C. Invited Talks by ONDE Staff 188

D. NDE Program Publications 189

E. Awards 192

F. Technical and Professional Committee Participation and

Leadership 194

vii
.

c

'
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 in fiscal year 1983. Collectively, these

technical activities constitute the Bureau's Nondestructive Evaluation

Program, which is managed programmatically and administered on a Bureauwide basis by the Office of Nondestructive Evaluation.

Recognizing that modern NDE must be quantitative, and that NDE

measurements must be reproducible, the principal mission of the NDE

Program is to provide traceability for NDE measurements, i.e., traceability

to national standards of measurement. This mission calls for the

development and maintenance of calibration services, reference materials,

etc., as well as the formulation of recommended practices to help assure

that the means for traceability are implemented properly. The effective

accomplishment of this mission — traceability for NDE measurements —

requires concerted technical activity toward two other objectives as well. First, research must usually be carried out to achieve an adequate

understanding of the physical bases of the ND£ measurement techniques

and processes that need standardization. Second, the results of the

Bureau's research and development work on NDE measurements must usually

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. In summary, the technical activities of the NDE

Program can be thought of as comprising three tasks; research, standardization,

and applications.

A glance at the table of contents will reveal that the technical

reviews in this report have been categorized by NDE method. Within some

of the larger categories, e.g., ultrasonics, the reviews have been put

into an arrangement that reflects the three tasks set forth above, i.e.,

research first, then standardization and, finally, applications.

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

1978 and are commonly referred to as the "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 this report) and by the Office of Nondestructive Evaluation.

Either can be addressed in care of NBS, Washington, D. C. 20234, or reached by telephone via (301) 921-1000. Requests for further information

and suggestions for new NDE projects always receive prompt and careful

attention.
THIS PAGE IS INTENTIONALLY 3LANK

2
A NEW FLUORESCENT GLASS STANDARD FOR USE IN DYE PENETRANT MEASUREMENTS

R.W. Burke and M.V. Smith

Inorganic Analytical Research Division

Center for Analytical Chemistry

An investigation of a series of materials that were considered reasonable

candidates for use as fluorescent standards in dye penetrant testing has resulted

in the selection and recommendation of a terbium-doped phosphate glass for this

purpose. This glass was specially produced in the Inorganic Materials Division

and bulk stock is currently available in rod and bar forms. In making this

glass a number of problems had to be solved in order to obtain a product of

acceptable optical quality. Particularly troublesome was the severe tendency of

this glass to form bubbles in the melts and to develop cracks during the cooling

cycle. Ultimately the use of preheated graphite molds was found to offer the

best practical solution to both of these problems.

While the doping levels for terbium can exceed 40 percent by weight in

phosphate glasses, the glass on which most of the current analytical data have

been obtained was prepared by melting a blended mixture consisting of 20

Tb 2 0 3 , 40% A1(P0 3 ) 3 , and 40% NaP0 3 . The absorption and fluorescence emission

spectra of this glass are shown in Figure 1. A strong absorption band is

noted in the wavelength range between 330 and 390 nm whereas a strong fluorescence

band is observed between 525 and 560 nm. These two spectral regions correspond

closely to the absorption and fluorescence wavelength ranges of most of the

fluorescent dye penetrants now in common use.

In addition to its spectral characteristics, the unique properties of this

glass that enhance its use as a dye penetrant standard are the very small

dependence of its fluorescence on temperature and its long-term stability.

Based on measurements performed between 15 and 40 °C, the fluorescence was found

to decrease 0.05% per degree Celsius increase in temperature. For comparison,

the fluorescence temperature dependence of uranyl glass is about 20 times

larger. For the stability study, an accelerated test was used in which samples were exposed to radiation that had the same spectral distribution as the fluorescent

lighting of the laboratory but was 1000 times more intense. After being

subjected to the equivalent of 27,000 hours of continous normal laboratory

irradiation, no significant change in fluoresence was measurable (decrease

< 1.4%).

A portion of the bulk glass is currently being sized and polished to fit

adapters that will be used in Turner Models 110, 111 and 112 or Coleman Modal 12C

fluorometers in pending ASTM round- robin tests on the performance characteristics

of dye penetrants. Samples of this glass will be available on request for

use in these tests. Later this year this glass will also be available in a form

in which a graded series of fluorescent indications of known widths are produced by a combination of masking and overcoating with a nonreflective,

3
opaque metal film. This type of standard should be particularly useful

the reproduci bi 1 i ty and repeatability of comparative crack plate testing

penetrants and for also reducing operator bias in estimating the size of

actual surface defects.

WAVELENGTH, nm

Figure 1. Uncorrected excitation (solid line) and emission (broken

line) spectra of prooosed terbium phosphate fluorescent

glass standard.

n improvin

of

4
MAGNETIC MEASUREMENTS

Lydon Swartzendruber

Metallurgy Division

Center for Materials Science

Magnetic particle NDE is a simple and inexpensive, yet very

effective, NDE method and hence is in widespread use. However, the lack

of reliability of this method was graphically illustrated by a round

robin test reported by Gulley (ref. 1). In that test, eleven

laboratories inspected 24 specimens with known defects. Only one laboratory found more than 90 percent of the defects, while the majority

found less than 50 percent. The reason for the success of this one laboratory in presence of the failure of the others can be attributed to

the technique by which the presence of adequate magnetization of the

sample was determined. Our recent results (ref. 2) have shown the basic

reason for this and established the following principles:

1) The value of the applied magnetic field, H, in the vicinity of the

defect, rather than the B field within the material, is most

important for the magnitude of the force exerted on the magnetic

particles used in the NDE test.

2) The optimum applied magnetic field to use does not lie at the

point of maximum permeability of the material under test, as often

assumed, but is considerably larger than this field. The optimum

applied field is the largest field which will not cause the magnetic

particles to be too sensitive to surface conditions, cause excessive

“chaining" of the particles (hence reducing their mobility before

they are close to the defect), or give excessively large field

gradients due to “flux leakage" caused by sample geometry.

3) An empirical detection criterion can be established from which the

detectibility of a crack or defect can be determined. The minimum

applied field necessary to detect a defect can then be calculated

using suitable computer methods to determine the geometry of the

leakage field arising from the defect.

Using these principles it becomes possible to critically inspect the

effectiveness of various “rules of thumb" used in magnetic particle

inspection. These rules of thumb have, in the past, been based on a combination of what appears to work and what is practical to achieve.

These rules are being evaluated and modified according to the principles

mentioned above. Use of the current rules established an applied

magnetic field of between 1.3 kAnrl (16 Oe) and 11 kAnr1 (140 Oe) in

the vicinity of the defect. The rationale for this wide range of fields

is based on the experience that for very large parts (where the higher

fields are difficult to establish with available equipment) defects are

of less importance and hence lower fields are required, whereas for

smaller parts larger fields are required in order to detect the important

smaller defects. Also, the smaller parts generally have a smoother

surface and interference effects are not caused by using the larger

fields.
Another important aspect of our results (ref. 2) is that they

show how a Hall effect magnetometer may be used to determine

adequate magnetization in parts of arbitrary geometry. It is

necessary that the size of the probe be small in comparison to the

rate of change of the H field. It need not be small in comparison

to the size of the leakage field from the defects being tested. It

also must be arranged to measure the component of H parallel to the

surface of the part. This type of determination for adequate

magnetization can be expected to be especially useful in the case of

alternating current fields whose effects are much more dependent on the magnetic properties of the material under test than are inspections made with direct current.

Another important aspect of magnetic particle inspection relates

to the properties of the particles themselves. The optimum particle

size for magnetic particle inspection depends on a number of factors

but most important are the dimensions of the defect, the field

applied to the sample under test, and the surface roughness. To cover as wide a range of situations as possible, a range of particle

sizes is desirable and is usually present in most commercial

powders. Not only particle size, but also particle shape is

important. In this respect, there are two opposing factors. On the one hand particles should be spherical in shape to impart the

greatest mobility. On the other hand, needle shaped particles have

the greatest response to magnetic field gradient due to their

smaller demagnetizing factor (which is in most cases more important

than their permeability). There are also two opposing factors for

particle size. On the one hand, the smaller particles are the most

sensitive to fine cracks and small defects. On the other hand,

large particles have higher mobility and are less sensitive to rough

surfaces. Current magnetic particle specifications provide for a test of the magnetic particles on a test ring with artificial

sub-surface defects and a maximum size for the particles. That this

is an inadequate specification can be seen by examination of the

three particle distributions shown in Figure 1. The powders

represented by the curves A and B represent commercial powders from

two different suppliers. Powder C was formulated from comminuted

electrolytic iron. All three of these formulations meet the current

specifications yet are different in their response to different

defect situations. For detecting subsurface defects below a smooth

surface, as called for in the particle specifications, powder C was superior to A or B. Yet powder C would be of little use for most

magnetic particle NOE situations because of the lack of smaller

particles required for fine crack detection and the flake like shape

which gives poor mobility on a rough surface. Powder B could be

expected -to be better than A on a rough surface because the

increased amount of larger particles improves the overall mobility

of the powder, whereas the opposite situation would apply where fine

cracks on a smooth surface were of most interest. Practical tests

which could more clearly discriminate between the properties of

powaers A,S, and C could clearly improve the state of the art in
magnetic particle testing, and provide the nondestructive testing

engineer with a more rational choice of particle formulations geared

to specific applications.

1. l.R. Gully, “Proceedings of the Interdisciplinary Workshop for

Quantitative Flaw Definition", Air Force Materials Laboratory Report

AFML-TR-74-238, pp 5-67 (1974).

Z. C.L. Oehl and L.J. Swartzendruber, “On the Optimum Applied Field

for Magnetic Particle Inspection Using Direct Current1 ', to be

published in J. Nondestructive Evaluation , vol. 3, page 125.

S

=L

<ru

CL

\±i

o

<

iiLl o

Qt

LlI CL

Figure 1. Relative percentage frequency curve for three

magnetic particle formulations. For each formulation,

the ordinate indicates the percentage of all particles

in the formulation that are sized between n and n+1

micrometres

7
MAGNETIC PARTICLE INSPECTION STANDARDS

L. Swartzendruber

Metallurgy Division

Center for Materials Science

This project was initiated by the Specifications and Technical Data

Branch of the Army Materials and Mechanics Research Center, Watertown,

MA. Military specification MIL-M-11472, "Magnetic-Particle Inspection

Process for Ferromagnetic Materials", is being reviewed for proposed

revision or cancellation and replacement by Military Specification

MIL -STD-271, Military Specification MIL-I-6868, or American Society for

Testing and Materials Recommended Practice E709-80. The contents of

these documents have been compared with current state-of-the-art practice

in magnetic particle inspection as revealed by industrial practice,

available literature, current applicable Military Standards, Aerospace

Materials Specifications, and American Society for Testing and Materials

documents. A draft version of a revised MIL-M-11472 has been prepared

and circulated for comments by the intended users within the Department

of Defense. Comments have been received and the document is currently

being revised. In addition, a glossary of terms relating to magnetic

particle inspection has been prepared for inclusion in MIL-M-11472.

3
DEVELOPMENT OF HIGH OPTICAL DENSITY STANDARDS

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

Radiometric Physics Division

Center for Radiation Research

The anticipated change from the current ISO and ANSI standards (ref. 1) and

continuous demands for higher optical density standard materials require

proper action from NBS to meet the needs. Optical density standards are used

to calibrate densitometers. Densitometers are employed to measure exposed

X-ray films which are used for nondestructive 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 through development of hardware

and software for the Inverse Fourth Apparatus and characterizations of the

apparatus and high optical standards. Some electronic equipment and interface have to be replaced and software developed in order to achieve fully

automated measurements. See ref. 2.

HARDWARE

The computer system consists of a 64K microcomputer, two double sided

disk drives, a line printer and a CRT. Several interface boards have been

designed and constructed. The new high voltage power supply for the photomultiplier has been programmed to change voltages automatically.

The carriage which carries the flexible glass fiber is positioned by a new stepping motor with new power supply and the position of the carriage is

read by the computer by counting the moire fringes.

The current from the photomultiplier is converted to frequency with the

current-to-frequency converter. The frequency is counted by the counter and

read by the computer as measurement signals.

The integrating sphere for the detector has been fitted with a pressure

and vacuum system to create an air gap between the entrance aperture to the

integrating sphere and the sample when the sample slider is moving and to

press the sample tightly against the aperture when the sample is in the light

path during the measurement.

SOFTWARE

Many subroutines have been developed for the Inverse Fourth Apparatus.

These subroutines are for positioning the carriage and the sample holder,

collecting data, setting high voltages, and initializing the positions for

the carriage and sample holder.

Full computer programs have been developed to determine the zero position of the carriage and to determine optical densities of the x-ray and
photographic step tablets.

The optical density measurement procedures are as follows. The sample

holder is moved to the area of the sample to be measured. The carriage is

moved to a preselected position, dg, and several signals are measured and

averaged (S^). The sample is moved out of the light path. The carriage is

moved to a position so that the signal is slightly smaller then the average

signal S^. The carriage is then moved with small interval and the signals at

each position are measured. A linear least square fit is performed on the

set of data of signals vs positions. The carriage is moved back to distance

d£ and the sample is moved into the light path. Several signals are then

measured and averaged (S£). The average S£ of and S£ is calculated. The

signal and the equation of the fitted curve are used to calculate the

distance d-j . The transmittance, T, can be calculated by

where d

Q

is the 'zero distance'. The optical density is then

D

= -log T.

CHARACTERIZATIONS

Computer simulation has been performed to determine the optimum positions

which would give small uncertainty in determining 'zero distance'. These optimum positions were used to perform the measurements and the 'zero distance'

has been determined to be 112 mm ±0.5 mm. In determining optical density of

a film, the 'zero distance' was purposely varied from 112 mm to 110 mm and

114 mm. The resulting differences in optical densities were within the theoretical predictions.

The uniformity of the power law dependence at different carriage

positions was confirmed using the following method. The optical density of

a film has been measured at several positions of the carriage. The differences of optical densities were within the random noise of the measurements.

The lamp voltage was varied from 15 to 105 volts. The optical density

determinations were independent of voltages from 85 to 105 volts.

Optical densities of a photographic step tablet measured with the Inverse

Fourth Apparatus were compared indirectly with that of the Inverse Square

Instrument through a transfer densitometer. The results were within one percent of the values.

Preliminary direct intercomparisons on an x-ray step tablet between the

10
Inverse Fourth Apparatus and the Inverse Square Instrument were performed.

The agreements were also within one percent of the values.

Preliminary evaluation of low optical density samples indicated that the

receiver using the integrating sphere diffuser yielded higher optical density

than using the opal diffuser.

Several high optical density step tablets have been measured. These

step tablets, produced by an x-ray company, have seventeen steps. The sixteenth step has 5.45 optical density and the last step has optical density

higher than 5.8 and is beyond the measurement capability of the Inverse

Fourth Instrument.

Because of some hardware replacements and software development not

anticipated in our original plan, this project needs to be extended to the

next fiscal year in order to complete the remaining tasks: final intercomparison with the Inverse Square Instrument, intercomparison with other

national laboratories, pilot run with selected users, final selection of

standard reference materials and preparation of documentation.

REFERENCES

1. "Conditions for Diffuse and Doubly Diffuse Transmittance Measurements

(Transmission Density)'*, American National Standards Institute,

PH2. 19-1 976.

2. D. A. Swyt and J. G. LaRock, "Inverse-fourth apparatus for photometric

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

li
RADIOGRAPHIC IMAGE QUALITY EVALUATION AT HIGH ENERGIES

R. C. Placious and D. Polansky

Radiation Physics Division

Center for Radiation Research

The need for measuring x-ray system performance at high energies has led

to the design of an image quality indicator (IQI), and test protocol

similar to the one developed earlier for low energies (200 kV) (ref. 1).

Among the problems in developing a suitable IQI for high-energy x-ray beans

is the reduced image contrast per unit specimen thickness that is a property of such beams. In an attempt to produce a viable test object

having the required range of contrast sensitivity we have made four

modifications to the original design. After each modification it is

necessary to provide test exposures using high-energy x-ray sources. Most

of these exposures are being provided by private laboratories which are cooperating in this endeavor. The film readers include personal from

these laboratories as well as from NBS. All of the test data are being

evaluated here.

To date, exposures have been provided at 4, 7.5 and 8 MeV. Additional

exposures are to be made at 2 MeV and 15 or 25 MeV. While it is probable

that the test object and protocol will not be applicable over this entire

energy range, the inclusion of the latter ranges will allow a decision to

be made on where the limitations should be placed. The specimen thickness

and the multi -hole plaque used in all exposures are fixed.

REFERENCE

1. ASTM Standard E 746-80 "Standard Method for Determining Relative Image

Quality Response of Industrial Radiographic Film" 1982 Annual Book of ASTM

Standards, Part 1 1

.

12
MODULATION TRANSFER FUNCTION MEASUREMENT OF AN IMAGE INTENSIFIED SOLID

STATE X-RAY CAMERA

R. D. Spal, H. E. Burdette, W. J. Boettinger and M. Kuriyama

Metallurgy Division

Center for Materials Science

The goal of this work was to develop a simple procedure for measuring the

modulation transfer function of an image intensified solid state x-ray camera.

This is necessary for precise evaluation of the resolution of the existing

camera, and for comparing it to cameras under development. Previous work to

specify the camera performance involved one of two procedures, depending on the signal level. A strong signal is defined as one which produces a recognizable image at the standard video rate of 60 fields per second. For

strong signals, the resolution was estimated by viewing a test pattern of

bars of variable width and spacing. This qualitative method yields a limiting

resolution of about 100 microns. For weak signals, the quantum efficiency

and resolution were determined by computer processing the image of a uniform

beam of known intensity to reveal the number of photon images and their average

size. This quantitative method yields an average photo image diameter of

about 130 urn. However, it is difficult to extrapolate this result to

strong signals, especially since the distribution of photon image diameters

is broad and non-Gaussian. The present work uses strong signals.

The camera consists of a thin phosphor screen to convert x-rays to visible

light, an image intensifier tube to boost the light intensity, and a solid

state camera to convert the image into a video signal. The phosphor screen

and solid state camera are coupled to the entrance and exit windows of the

image intensifier with fiber optics. The image intensifier has a photocathode

deposited on the entrance window, dual microchannel plates, and a phosphor

deposited on the exit window. Its luminous gain is adjustable up to 500,000.

The solid state camera is a General Electric model TN2500 CID camera, consisting

of an area array of 244 by 248 pixels, each measuring 36 by 46 urn. Each

pixel is scanned 30 times per second.

The modulation transfer function (MTF ) is determined from the image of

the edge of a mask in an 8 keV beam. The beam is about 1 mm high, and wider

than the camera field of view. The mask is attached to the input phosphor

screen, with its edge oriented vertically and centered in the field of view

to obscure one half of the beam. The video signal is digitized by a 4 bit

frame grabber, and loaded into a buffer memory. An LSI 11/23 microcomputer

transfers the data from memory to disk, and later recalls the data from disk

for processing.

Since the pixel size is not much smaller than the resolution, Fourier

transform techniques are not used to determine the modulation transfer function.

Instead, it is assumed that the point spread function is a Gaussian with an unknown standard deviation a. Convolution of this point spread function with

a step function, representing the true mask image, yields the function representing

the actual mask image. Besides a, three adjustable parameters are included

in this function, to represent the position of the mask edge, the beam

13
intensity, and the background intensity. The method of nonlinear least

squares is applied to fit the parameters to the data. Each row of pixels is

analyzed independently, so that any deviation of the edge orientation from

the true vertical is not important.

Data were collected for luminous gains from 20,000 to 300,000. As the

gain was increased, the beam intensity was reduced to prevent overload. Some

results are presented in Figures la through lc. Figure la shows raw and fitted

data for a single row of pixels, with a gain of 20,000. The fitted value of

a is 190 um. It is customary to express resolution in line pairs per mm

(lp/mm) at a specified MTF value, usually .05. In these terms, the resolution

is 13 lp/mm. The value is nearly independent of gain over the range tested.

Figure lb shows the fitted value of a for many rows of one image, again with

a gain of 20,000. Finally, Figure lc shows the edge position for many rows

of two images, with gains of 20,000 and 150,000. The functional dependence

of the edge position on the row number is expected to be linear, with a slope

determined by the orientation of the edge. While this holds for the lower

gains, it fails for the higher gains. At high gain, the image is distorted,

even though the resolution, as determined from a, is not degraded. The

distortion is a bulging of the center of the edge beyond its true position

and into the shadow region. This effect is not presently understood, and

will be investigated further.

14
a

s. aa

jr

-- t 2

pm

ina

UI

C3a

UiX

ui<X

2. aa

i ’~T~

1

1

i ! !

• a "r

9 3

1 r _ , 1 ~-i -1--- '

’

1 3 3 J

° " f

ji

1

1 i

i 1 !

i i .

i 1 1

j

!

!

i

i . *9f» a rv

1

1

i 2 i kzr* ^n< rr.» r.*j

isua C

igure 1 a) Saw and fitted data, b) Fitted SIGMA and Mask edce j os :

•

i3

On .
DIGITAL RADIOGRAPHY

R. C. Placious, D. Polansky ana J. H. Sparrow

Radiation Physics Division

Center for Radiation Research

Digital imaging technology became feasible in the late iS70’s with

the advent of fast analog to digital converters coupled with relatively

inexpensive random access memory chips and a dedicated microprocessor

Detection equipment for radiography also became more readily available

so that it is now possible to take real time images and rapidly execute

some processing algorithm or transformation on the image and immediately view the result. Furthermore the displayed image can then have

operations oerfcrmed on it, such as scrolling or zooming, without loss

of the original image content.

One of the most useful processing operations is image integration which can

be done at TV frame rates. This is analogous to the image integration done by

film when exposures are fairly long due to low flux levels. Another useful

feature of the digital image processor is the ability to subtract one image from

another. This is quite often applied in medical radiology to make changes that occur between two images more readily apparent. Image subtraction is expected

to play a major role in a radiologic technique known as dual energy imaging

wherein two images are made with different x-ray spectra and compared.

Digital image processing can also be applied to film based radiograohs with

some degree of success. This is very useful for low contrast radiographic images

which can often be improved by a digital transformation which "stretches” the

available contrast range. The original radiograph .i s scanned and digitized in

the same way a real-time image is presented to the digital processor. The use of some of these techniques on film based images was discussed in a recent

symposium (ref. 1).

Part of the image processor memory is used to provide a graphics capability

for the system. In addition to the construction of lines, circles, souares,

alphanumeric text, etc., this capability allows for a presentation of histograms

which show the gray scale distribution of all pixels in the image of interest.

It is often on the basis of this knowledge of the gray scale range that one can construct or select a convolution or transformation which makes the image mere amenable to interpretation.

All of the ideas discussed above, along with many others, are being aoplied

to nondestructive inspections. Figure 1 demonstrates the effect of "contrast

stretching" applied to a low contrast slit image having a density change of 0.0-

less

REFERENCE

1. R. C. Placious, D. Polansky and J. H. Sparrow, "Digital Image Processing for

Improved Detection and Diagnosis of Hidden Flaws", Proc. 35 th mFPG Conference,

Phoenix, AZ, Dec. 1982 (Cambridge University Press, NY, in press).
Figure 1 . The upper half of this illustration is the original radiograph.

The lower half has been enhanced by a digital transformation

which greatly "stretches" available contrast.

17
ADVANCED RADIOGRAPHY

D. Polansky

Radiation Physics Division

Center for Radiation Research

The Test and Inspection Subcommittee of the DoD Manufacturing

Technology Advisory Group held a workshop on advanced radiologic programs

The workshop was held December 7-8, 1982 in Phoenix, Arizona with ASTM

Committee E-7 as co-sponsor. There were four sessions with papers on real-time imaging, computerized axial tomography, digital enhancement

and automatic image analysis. The writer was chairman of the workshop

on digital enhancement technology. A summary report* was written and

presented to the advisory group.

After lengthy discussion by the workshop participants, the following

were identified as vital needs for digital enhancement radiography:

a. The area of reprojection technology should be supported.

Tomographic systems that give data in the X-Y plane will require

the reprojection of data in the Z plane for analysis.

b. Sensor technology should be supported, and sensors should be

studied for optimization at different energy levels.

c. Inspection data should be used for process control.

d. Digital enhancement techniques should be used to promote

automatic evaluation of data, to eliminate the operator from

decision-making in the inspection process.

e. Develop small-area, high-sensitivity detectors.

The Aracor-Aerojet industry team is developing two computerized

axial tomographic systems for the Air Force. One unit is to be

used with a 300 kVp x-ray unit for the inspection of low density material

up to 70 cm in diameter while the second unit is for the inspection

of the Peace-seeker missile for the Air Force.

*MTAG Test and Inspection Subcommittee, "Manufacturing Technology

Advisory Group, Advanced Radiologic Planning Workshop, 7-9 December

1982," 18 + iii pp (US Army Armament Research and Development Command,

Dover, NJ, undated).

18
NOT SUPPORT FOR THE FLEET MISSILE SYSTEM

D. Polansky and J. H. Sparrow

Radiation Physics Division

Center for Radiation Research

The objectives of this program are to (1) provide technical engineering

support to the area of nondestructive testing of Trident missile components,

(2) recertify, twice yearly, all facilities involved in x-ray inspections of

Trident rocket motors, and (3) evaluate proposed changes in inspection

techniques. This work is supported by Strategic Systems Project Office,

Department of the Navy.

The two new ballistic missile systems being developed by the Department

of Defense are significantly larger than the presently deployed missile.

Their nondestructive inspection poses new problems and one avenue being

pursued is the use of computer aided tomography (CAT). The NBS task is to

follow the technology being developed and advise the Navy Department

of its applicability to a specific missile.

The qualification of the real-time inspection systems at all facilities

requires a review team. NBS is a member of that team which recently reviewed

the quality of inspections at Pomflant* The team found that some of the

inspections did not meet requirements and recommended that corrective action

be taken. Another review of this facility is planned in the near future to

evaluate their missile inspection performance.

The calibration of the radiation output of the 15 MeV linear accelerator

was conducted at two facilities. The x-ray beam profile in the horizontal

and vertical directions were measured so that the position of the laser

alignment beam relative to the radiation beam could be checked.

Equilibrium caps made of polystyrene will be supplied to all of the

facilities for use with their ionization chambers; they can then routinely

check the li natron's x-ray output to verify that it remains above the

minimum specified for the real-time inspections. The recertification

program of all testing facilities is carried out semi-annually by an audit

that consists either of visits to the installations or the submittal of test

data to the auditors for evaluation. The purchase of a tape recorder on this

project, that is the same as those used by the testing facilities, now makes

it possible to evaluate real-time inspections at NBS. Copies of magnetic

tape recordings of missile inspections will be routinely supplied to NBS for

evaluation of the quality level of inspection.

* Polaris Missile Facility, Atlantic, located in Charleston, SC.

19
NONDESTRUCTIVE CHARACTERIZATION OF DISTRIBUTED DAMAGE

E. R. Fuller, Jr., K. Hardman-Rhyne and N. J. Tighe

Inorganic Materials Division

Center for Materials Science

R. J. Fields

Fracture and Deformation Division

Center for Materials Science

INTRODUCTION

In a number of instances, failure of a component results not from the

formation and growth of a single macrocrack, but rather from the accumulation

of damage, distributed homogeneously throughout the component. An example of

such a situation is the nucleation and growth of creep cavities in metallic or ceramic components- used in high-temperature applications under stress. An

important design consideration for such components is an assessment of the

material’s creep life. However, of equal importance in service is a nondestructive assessment of the total amount of accumulated creep damage and,

hence, of remaining lifetime. Another example of distributed damage might be

distributed inhomogeneities (such as, microcracks, impurity phases or porosity) that can develop during or following ceramic processing. Although

this damage does not necessarily accumulate during service life,

nondestructive assessment of these distributed defects during in-line

processing is of importance both for quality control and for early rejection

of defective components to reduce later processing costs.

To address these issues, the objective of this research program is to assess nondestructively this accumulation of distributed damage and to

correlate that assessment with microstructural defects in the material. As

part of this objective various model material systems with distributed defects

are being developed. Such "standard" systems allow the comparison of various

nondestructive inspection techniques both amongst themselves and with direct

observational measurements of size and abundance of defects, thereby

increasing the scientific base for these NDE methods. The research effort

during the past year has encompassed three such material/damage systems. The

first, which is a continuation of research from last year, is a system of

distributed creep cavities in metallic specimens at various fractions of their

creep life. The second is an analogue damage system in high- temperature

,

advanced structural ceramics. This ceramic research is supported in part by

the Army Materials and Mechanics Research Center, Watertown, MA. The third

system is distributed porosity in ceramic materials at various stages of

sintering during the processing cycle and is a collaborative effort with a project on green state NDE.

CREEP CAVITATION IN METALS

Research has continued this year in the production of metallic specimens

with distributed creep cavities. Two systems are being studied. One, 304

stainless steel, is a commercial alloy of practical importance; the other,

OFHC copper (99.99% pure), is a material that is being considered as a model

20
material/ damage system, because it is easily cavitated in a short period of

time. These studies are described below. When completed, the results of

these studies will be used to assess the correlation between the degree of

cavitation at equivalent life fractions in the stainless steel and in the

copper, thus establishing a rational basis for nondestructive evaluation of

creep damage and other forms of distributed damage in structural metals and

alloys.

304 Stainless Steel

304 stainless steel used in high-temperature applications consists of

metal carbides in an austenite matrix. The carbide-austenite interface at a grain boundary becomes a preferential site for cavity nucleation, which at

elevated temperatures can be readily activated with low applied stresses by

creep deformation and/or grain boundary sliding. The resulting cavities then

grow, link and ultimately cause failure. The early stages of this process are extremely slow and the creep cavities, due to their small size, are not easily

detectable or quantifiable. It is these early stages of nucleation and cavity

growth that are examined in this research.

Since carbide precipitates, as well as creep cavities, give rise to

neutron scattering, two requirements must be satisfied for a quantitative

evaluation of cavitation damage: (i) The volume fraction of carbide

precipitates should not change significantly during creep; and (ii) A

reference sample with equivalent carbide structure should be measured and

subtracted from the scattering spectrum of the crept sample. The first

condition was achieved in the present study by a "stabilizing" heat treatment

of approximately 40 hours at 775 °C prior to initiation of the creep

experiments at temperatures of 600°C and below. This allowed a complete

precipitation of carbide and thereby stabilized the volume fraction of

carbides. The second condition was satisfied by using a reference specimen,

which was only heated (and not stressed), along with the crept specimen.

A number of specimens have been crept thus far in this study. Most of

these experiments have been conducted at 600°C with applied stresses from 124

to 262 MPa and with accumulated times under stress from 50 to 2300 hours. A

list of the nominal stress levels and the times under stress is given in

Table 1. Some of these specimens are being studied using small angle neutron

scattering (SANS) by researchers in the Reactor Radiation Division. Results

of this work will be reported by that group.

A few specimens listed in Table 1 fractured under load. These have been

examined metallographically . As shown in Figure 1, these specimens exhibit

abundant creep cavitation. Therefore, the assumption in last year's work that

the small angle neutron scattering is due to cavitation appears to be

justified. The lack of such evidence earlier in this project was viewed as a potential limitation of the work. However, this difficulty is now eliminated.

We are now ready to begin density measurements and a sonic resonance

determination of the elastic properties of selected bars from these tests.

Pure Copper

A large quantity of OFHC copper (99.99% pure) has been acquired. Creep

specimens having dimensions suitable for both SANS and ultrasonic measurements

21
have been fabricated, and testing has begun. We have determined that this

material fails at 600°C in vacuum in approximately 24 to 30 hours under an applied stress of 7.7 MPa (1100 psi) . As shown in Figure 2, these specimens

are full of distributed damage.

A series of interrupted tests are currently in progress. These tests

will be conducted at nominal applied stresses of 7.7 MPa (1100 psi) and 5.8

MPa (840 psi) . In all cases an unstressed control specimen is exposed at

temperature along with the creep specimen. The density of the 50 mm gage

section will be determined as a function of elongation and time under stress,

and compared with that of the control specimen. These specimens will then be

reduced to 8 mm long cylinders for SANS studies, ultrasonic elastic modulus

determinations and internal friction studies.

DISTRIBUTED DEFECTS IN STRUCTURAL CERAMICS

Advanced ceramics, such as silicon nitride, silicon carbide, SiAlON's,

etc., are being considered for a number of high-temperature applications

because of their excellent high-temperature properties (high strength,

corrosion resistance, and thermal conductivity, for example). These

applications include heat exchangers and heat engines to mention only two,

where numerous components (turbine blades and rotors, combustor chambers,

diesel cylinder liners and piston caps, etc.) are being fabricated from

ceramics. Long-term reliability of these components will most likely be

governed by the same type of creep cavitation failure as for metals. In

addition, distributed defects, such as impurity phases, microcracks and

porosity, which enter these ceramics during the processing cycle, can also

influence reliability. To characterize nondestructively these distributed

defects in ceramics two research studies have been undertaken this year. One

study examines distributed, submicrometer impurity phases and microcracks in

nonoxide ceramics. Small angle neutron scattering (SANS) in the diffraction

regime and transmission electron microscopy (TEM) are used for this study.

The other study extends SANS techniques to the multiple refraction regime to

elicit information about distributed porosity in the size range from

micrometers to tens of micrometers. In the coming year both of these SANS

techniques and TEM will be applied to elucidate the nature of creep cavities

in ceramic materials over an extended size regime.

Inclusions and Microcracks in Nonoxide Ceramics

Small angle neutron scattering (SANS) in condensed matter is a nondestructive technique that can measure distributed defects approximately

2 to 100 nm in size. Defects and impurities that lead to detrimental

structural reliability in advanced silicon nitride and silicon carbide

materials are generally submicrometer in size and difficult to measure until

they have reached an advanced stage of growth, which often leads to failure of

the material. SANS techniques are being explored as a nondestructive probe

for characterizing these distributed defects, with TEM observations being used

to verify the microstructural nature of these defects.

A previous study (ref. 1), using SANS to characterize a hot-pressed

silicon nitride material, concluded that neutron scattering in their material

was refractive in nature. This is not necessarily a general conclusion for

dense ceramics, but rather indicates that the nature of the neutron scattering

22
needs to be determined for each material system, and if possible verified by

alternate techniques. In the present studies, which were supported in part by

the Army Materials and Mechanics Research Center, two high-temperature,

advanced ceramics [magnesia-doped, hot-pressed silicon nitride (NC 132) and a pressureless sintered silicon carbide (Hexoloy SA) ] were examined with SANS

and by transmission electron microscopy (TEM)

For the silicon nitride material SANS measurements were made for

°-l °-i scattering vectors, Q, in the range of 0.005 A to 0.17 A and at

O wavelengths of 5.45, 7.6 and 9.0 A. Figure 3 shows the scattering data for

Si^N^ plotted as the logarithm of intensity versus scattering vector, Q, in

reciprocal angstroms. Two regions are particularly useful in analyzing the

data. Region 1, shown in Figure 3 and expanded in Figure 4, is the Guinier

2 region where the logarithm of the intensity has a Q behavior. The intensity

-4

in region 2, called the Porod region, has a Q dependence, and is shown

expanded in Figure 5.

A Guinier fit to region 1 yields a radius of gyration of 18.6 nm, which

is related to the average radii of the iron and tungsten inclusions in this

material, as confirmed by TEM. In this scattering region the neutron

intensity is limited by the larger dimensions of the scattering particles. In

particular, scattering by large pores or extensive porosity (on the order of

0.8 to 10 uni) could be easily measured, but no such evidence was seen for this

high-density material either by SANS or TEM. The SANS results are shown in

Figure 6 by comparing the direct beam scattering (blank sample) with the

scattering from the Si^N^ sample at several wavelengths. If large pores were

present there would be significant broadening of these scattering patterns

(compare with Figure 10 below)

The Porod region is more sensitive to the smaller dimensions of the

scattering centers, and results in a characteristic Porod length which

measures a volume to surface ratio. The ratio obtained for this material was

21.2 nm. This result in conjunction with the Guinier analysis suggests an average inclusion radius of 11 to 14 nm.

Data have also been collected for two samples of a sintered alpha silicon

carbide. One sample is as-received and the other has been treated at 1370°C

for 3500 hours. Initial results indicate microcracks or microvoid healing

during the heat treatment, however, analysis is still in progress. TEM

observations confirm the presence of microcracks in the as-received samples

(Figure 7)

Porosity in YCrO^

Porosity is a critical aspect in the densif ication process of a sintered

ceramic material. To elucidate the extent of such porosity, a quantitative

study is being conducted with small angle neutron scattering (SANS) to

determine average pore size. Rather than restricting the SANS measurements to

the typical submicrometer size regime of neutron diffraction, this study has

explored multiple neutron refraction as a means of extending the SANS

characterization into the tens of micrometer size regime. Although this study

23
is conducted jointly with a project to characterize neutron scattering and a project to characterize "green-state" NDE (see articles by N. Berk et al. and

T. Negas et al. in this report) , similar techniques are expected to apply to

creep cavities and other forms of distributed damage. This extension of SANS

techniques to larger sizes is an important result because it allows a greater

overlap of SANS characterization with other NDE techniques.

In the present study, two samples of YCrO^ were fabricated from pure

powders by isostatic pressing at 207 MPa (30,000 psi) ; one sample was then

sintered. The density of the "green" compact was approximately 55% of

theoretical density and that of the sintered material was approximately 93%.

To explore multiple neutron refraction, SANS measurements were taken at five

O wavelengths: 5.45, 6.25, 7.0, 8.0 and 9.0 A. The results revealed a striking

difference between the two samples as illustrated in Figures 8 and 9, which

are SANS spectra for the "green" compact and sintered specimens, respectively.

In particular, a strong dependence on wavelength is seen in the data for

the "green" compact. This dependence is illustrated in Figure 10 by plotting

the normalized intensity versus scattering vector, Q, for all five

wavelengths. By fitting these data to a Gaussian distribution, the full width

at half maximum, FWHM, could be determined and was found to increase linearly

with wavelength. Figure 11. This behavior is characteristic of multiple

neutron refraction from large particles or voids and is consistent with the

porosity of the "green" ceramic compact. The sintered material shows no wavelength dependency indicating either the lack of pores or voids, or that

they are very large and beyond the detection limits of our instrument.

Although the qualitative aspects of the data clearly demonstrate a strong

effect of ceramic processing on the population of neutron scatterers in these

materials, quantitative measures of the void size and void size distribution

are less straightforward. If one assumes that the neutron scattering is

described by multiple refraction and edge diffraction of voids, the estimate

of the average pore radius is approximately 2.5 um which is physically

reasonable for the green compact of YCrO . For the wavelengths of these

measurements, however, this corresponds to scattering phase shifts well within

an intermediate range of values for which the neutron scattering is not

expected to be analyzable by multiple refraction behavior alone. Therefore, a generalized theoretical technique is being developed by N.F. Berk of the

Reactor Radiation Division to provide a quantitative analysis of the SANS data

for densified ceramics, and other distributed defects in this size regime.

REFERENCE

1. P. Pizzi, "Analysis of Microvoids in Si^N^ Ceramics by Small Angle

Neutron Scattering," in Fracture Mechanics of Ceramics , Edited by

R.C. Bradt, D.P.H. Hasselman and F.F. Lange, Vol. 3, pp. 85-98 (Plenum

Press, New York, 1978).

24
Table 1. Nominal stress levels and total elapsed times for creep cavitation

tests of 304 stainless steel at 600°C.

Material Nominal Stress Elapsed Time

(MPa) (103 psi) (hours)

NBS 304 SS 207 30 102

312

2113

2303

221 32 335

1116

234 34 141

336

407

461

262 38 50

100

166

ORNL 304 SS 124 18 1537

(Reference-heat) (interrupted at

789 hours)

145 21 1493

(interrupted at

745 hours)

25
"V*

26

Fig.

1.

Creep

cavitation

in

a

304

stainless

Fig.

2.

Creep

cavitation

in

a

pure

copper

steel

specimen

that

failed

at

600°C

specimen

that

failed

at

600°C

in

in

1116

hours

unde^an

applied

stress

vacuum

(<10°

torr)

after

24

hours

of

221

MPa

(32

x

10

psi)

.

under

an

applied

stress

of

7.7

MPa

(1100

psi).
LN

INTENSITY

Scattering Vector Q (A*

1 )

Fig. 3. Logarithm of neutron scattering intensity versus scattering vector,

Q, in reciprocal angstroms. The two regions (1. and 2.) denote the

Guinier and Porod regions, respectively.
INTENSITY

Fig. 4. Plot of the Guinier region from Figure 3.

Fig. 3. Plot of the Porod region from Figure 3.

23
o<

in

A1ISN31NI

O

o

in

o

o

o

o

o

o

CD

„<r

29

Fig.

6.

Comparison

of

direct

beam

scattering

(blank

sample)

with

the

scattering

from

the

Si^N^

sample

at

several

wavelengths.
Fig. 7. Transmission electron micrograph of microcracks in the as-received

silicon carbide material. Cracking occurs at the intersection of

faults in the silicon carbide grains with the grain boundary.

30
-a

4)

CM

CO

<J

o

00

o<

00

CM

fO

co

OJ

CO

0)

ao

CO

0<

CD

in

ax

00

OJ

ro

co

LU

X

Q_-

o

>h a) Su flj

9

CC

SANS

spectra

for

a

"green"

compact

of

YCrO^

at

three

wavelengths:

5.45,

7.0

and

9.0

A.

Js

the

scattering

intensity

versus

a

linear

slice

through

the

neutron

scattering

plane

Indicated

by

pixel

number).
o

cu

<M

CO

O)

O

GO

o<

CD

CVJ PO

CD

LU

><

Q.

CD

O

00 o<

ID

00

CM

ro

co

( £ 0IX)A1ISN31NI

o

32

Fig.

9.

SANS

spectra

for

a

sintered

compact

of

YCrO^

at

three

wavelengths:

5.45,

7.0

and

9.0

A.

P

is

the

scattering

intensity

versus

a

linear

slice

through

the

neutron

scattering

plane

(as

Indicated

by

pixel

number).
Fig. 10. Normalized scattering intensity versus scattering vector Q, for

neutron scattering from a "green" YCrO^ compact at five wavelengths.

YCr 03 Greenstate (Unfired)

Fig. 11. Full width at half maximum, FWHM, versus wavelength squared for a "green" YCrO^ compact. The FWHM is characterized by the scattering

angle e = arcsin [XQ/2 t] for scattering vector Q.

33
SMALL ANGLE NEUTRON SCATTERING (SANS) STUDY OF CREEP DAMAGE IN 304

STAINLESS STEELS

S. P. Singhal and B. Mozer

Center for Materials Science

Reactor Radiation Division

R. J. Fields

Center for Materials Science

Fracture and Deformation Division

304 stainless steel used in high-temperature applications consists of

M-.C, (M stands for Cr and other metallic elements in the carbide) type of

23 0

carbides at the grain boundaries. The carbide-austenite interface is a preferential site for the nucleation of cavities during high-temperature

degradat ion--a phenomenon called cavitation. The structure after cavitation

consists of three phases; namely, austenite, carbide, and cavities. The

attempt to use SANS as a reference method to nondestructively evaluate the

evolution of creep cavities from very early stages of cavity growth

(inaccessible to conventional methods) requires that the creep induced changes

in volume fraction, size distribution, and spacial distribution of carbides do

not contribute significantly to the scattered intensity. At this point there

is no theoretical or experimental study to indicate that this limitation is

not important, yet by adapting special experimental procedures, the effects

due to such changes could be minimized. The following two procedures were

employed:

a. All samples were given a stabilizing heat treatment of 100 hours at

600 °C prior to the initiation of creep thereby precipitating out

the entire volume fraction of carbides.

b. A control sample (undeformed) was heat treated along with the crept

samples over the period of creep deformation. SANS spectra from the

undeformed sample were used as a baseline to delineate the cavity

contribution from the deformed samples. The creep parameters of two

samples (x-6, x-8), which fulfilled these requirements in this and a previous study, are described in Table 1 . This report describes

recent results on these samples and compares them with the previous

study (ref. 1 )

.

The SANS studies were carried out on the MBS reactor facility using a converging coliimation and a neutron wavelength of 6.25 With the choice of

collimation and wavelength parameters, a scattering vector (Q) range of

0.005 ft"' to 0.15 X

' could be measured in these experiments. This Q range

measures the scattering contribution of the inhomogeneities in the size range

of approximately 40 % to 1200 2. By using converging collimation we have been

able to measure the scattering intensity at Q values about a factor of three

lower than a previous preliminary study (ref. 1).

34
Detailed theory and procedures for analyzing the SANS data have been

described by Kostorz (ref. 2). A few salient features will be discussed here.

If scattered intensity is denoted by Z, then the macroscopic differential

scattering cross section of the scattering entities is given by

^ - CZ/tMT (1)

dfl

In this equation, t is the sample thickness, M is the total monitor count, T

is the sample transmission, and C is a combination of experimental constants

for the instrument. Creep damage as related to the evolution of cavities and

changes in carbide size, shape, and spacial distribution is measured by the

difference in the de/dft for the deformed (D) and undeformed sample (U), i.e.,

Ktamage ' (“)D

‘ (“)u

' ' WuV (2)

d e In further discussion, we have assumed that contribution to (-77 ds , , damage

comes predominantly from creep cavities. Figures 1 and 2 show scattering

patterns for the deformed and undeformed samples of x -6 and x-8 , respectively.

We can see that in these (also, in all other samples measured) the deformed

sample always showed higher scattered intensity than the undeformed, thereby

emphasizing cavity contribution to the scattering. Figures 3 and 4 show only

cavity contribution, i.e., after substracting the spectra for the undeformed

sample from the deformed one. The steep fall of scattering intensity in

figure 3 is indicative of very narrow size distribution of cavities.

One parameter of major interest is the growth of average cavity size as a function of creep deformation at constant stress. A Guinier analysis was

performed on these spectra (figures 3 and 4) to obtain an average cavity size.

Guinier (ref. 2) showed that for a randomly distributed, monosized, spherical

heterogeneity, the intensity (Z) and scattering vector (Q) relationship can be

described by the equation

Z (3)

Here R is the radius of gyration of the particles and is related to their

S

diameter (D) by the equation

D = /I 0/3 • R (4)

S

Z is the constant related to the volume and number density of the cavities,

oIf heterogeneities are not monosized, then the utility of Guinier

approximation is limited to only a very small Q range near zero. Figures 5

35
. . -2

and 6 represent Guinier plot [Log Z vs. Q ] for cavities in samples x-o and x8. It is clear from these plots that cavities must have a size distribution

as a straight line in these plots can be fitted only in the narrow Q region

near the peak. The cavity diameter obtained by this procedure normally overestimates the contribution of large cavities, yet it is a very useful

parameter to study cavity growth as a function of creep time while degradation

is in progress. Using a least square fit subroutine, equation (3) was fitted

to the data points in the relevant Q range of figures 5 and 6. The

experimental data points and the fit line are shown in figures 7 and 8. A

reasonably accurate fit was obtained in the selected Q range for both cases.

The average cavity sizes derived from these fits for the two samples are

and

<D .. > % cavity 770 $ for x-6

<D .. > % 763 2 for x-8. cavity ^

Table 1 shows that doubling the creep time at the same stress has the

effect of doubling the average cavity size for sample x-6. Figure 9 shows the

growth of cavity size as a function of creep time in the two samples assuming

that at the initiation of creep, the cavity size is negligible. If we include

the point at the origin, there appears to be a linear time dependent size

growth of the cavities in x-6; but in the absence of more data points, only a limited significance can be attached to the trend in figure 9. In the

previous report (ref. 1), we concluded that x-6 has higher average cavity size

despite the longer creep time because x-6 was stressed at 21 ksi as opposed to

18 ksi for x-8, therefore resulting in the enhanced stress induced coarsening

of cavities. In this study we find that average cavity size in the two

samples is not very different. This indicates that for longer creep times the

size growth of cavities is perhaps less sensitive to the small changes in

appli-ed stress. This is because the stress difference between these two

samples is only about 3 ksi. The other possibility as debated by Weertman

(ref. 3) is that when a large fraction of cavities grow large enough to

scatter at the Q values below minimum Q in the experiments, the average size

and volume fraction parameter from the standard SANS analysis are highly

underestimated and also the Guinier region is inaccessible. The confirmation

that this has taken place at a certain stage of the creep requires the void

size and volume fraction determinations by TEM and density measurements,

respectively. Such measurements are currently in progress. To refine the

general application of SANS as a reference method to quantify creep cavity

growth in alloys, further work must be performed on simpler metals or model

alloys to absolutely identify the contribution of interacting microstructures

and defects in structural alloys.

REFERENCES

1. E. R. Fuller, Jr., R. J. Fields, E. D. Case, S. Singhal, and C. J. Glinka,

"Nondestructive Evaluation of Distributed Damage," Annual Report, Reactor

Radiation Division, N3S (1983).

36
2. G. Kostorz, "Neutron Scattering in Materials Science,” Chapter 5 in

Treatise in Materials Science and Technology 15 , ed. G. Kostorz, (Academic

Press, New York, 1979).

3. J. R. Weertman, M. Yang, and M. Roth, "Grain Boundary Cavitation in Copper

Subjected to High Temperature Creep,” Annex to Annual Report, Institut

Laue- Langev in, Grenoble, France, p. 263 (1982).

Table 1 . Growth of creep cavities as a function of time at constant stress in

304 stainless steel.

Sample # Creep

Parameters

Average Cavity Diameter from

Guinier Approximations

(2) (nm)

745 at 21 ksi

(144.3 MPa)

346 34.6

x-6

1493 at 21 ksi

(144.8 MPa)

770 77.0

789 at 18 ksi

(124.1 MPa)

266 26.6

x-8

1537 at 18 ksi

(124.1 MPa)

763 76.3

37
10.00

8

8.75 —

7.50 -

>

<75 ~ 5.25

cio 5.00

O

. • Deformed

0 Undeformed

O

o

o

o

3.75

2.50

8

0 • 0®.

- 5.60 - 5.19 - 4.78 - 4.37 - 3.95 - 3.54

Log Scattering Vector

3.13

Figure 1. SANS spectra on deformed and undeformed x-6. Deformation

under 21 ksi stress was carried out at 600°C for 1493 hours.

Log Scattering Vector

Figure 2. SANS spectra on deformed and undeformed x-8. Deformation under

18 ksi stress was carried out at 600°C for 1537 hours. The

undeformed sample was heat treated at 600°C for 1537 hours.
Intensity

(Counts)

2800

2330Hq

1860

1390-

820

o

450 fO Deformed Minus Underformed

20

O

o

0.05 0.10 0.15

Scattering Vector (A

Figure 3. SANS spectra showing the scattering due to creep-induced cavities

for x-6.

Log Scattering Vector

Figure 4. SANS spectra showing the scattering due to creep-induced cavities

for x-8.

39
Loy

Intensity

’

Loy

Intensity

Figure 6

8.00

6.67

0.08 0.17 0.25 0.33 0.42 0.50

(Scattering Vector) 2 (A' 2

) x 10 3

Guinier plot showing the scattering contribution of creep cavities

in sample x-6.

7.20 fOo o

'o O

6. OS

4.97 —

3.85 —

2.73 —

1.62 —

0.50

O Deformed Minus Undeformed

0.12 0.23 0.35 0.47 0.58 0.70

(Scattering Vector)'l2 (A'

2

) x 10 3

Guinier plot showing the scattering contribution of creep cavities

in sample x-8.

40
Intensity

(Counts)

Intensity

(Counts)

Least square fit of the Guinier function of the data in the

selected range of figure 3 for sample x-6.

Scattering Vector (A

1

) x 10

Least square fit of the Guinier function to the cavity scattering

data in the selected Q range for the sample x-8.

di

Figure 8.
1000

Figure

833

_ 666

<

03 * 500

>

>

£0 o

333

166

• X-6

OX-8

O

0c 1 1 1 0 333 666 1000

Creep Time (Hrs)

•O

1333 1666

. Size growth of creep cavities as a function of creep time at

600°C for samples x-6 and x-8.

42
NONDESTRUCTIVE EVALUATION OF POROSITY IN YCrO- BY SMALL ANGLE

NEUTRON SCATTERING 6

N. F. Berk

Reactor Radiation Division

Center For Materials Science

and

K. Hardman-Rhyne

Inorganic Materials Division

Center for Materials Science

and

E. Case

University of California, Berkeley

We are undertaking a quantitative study of porosity in YCrCL and other

ceramics using small angle neutron scattering (SANS). The goal of the

investigation is to provide reliable data on average pore size in ceramic

materials at different stages of densification, including the highly porous

green state compact. Detailed understanding of the densification process

is vital to the ceramics industry since the strength and refractory behavior

of the final product depend on properties of its microstructure and

especially on the distribution of pores and defects. While large pores are visible by electron microscopy of suitably prepared thin sample specimens,

scattering methods generally provide the best means of obtaining statistical

information from the bulk and may be the only technique available for fragile or otherwise difficul t-to-handle materials. Moreover, the interaction of thermal

neutrons with condensed matter is so weak that the method, unlike electron

microscope techniques, is totally nondestructive, even in the green state.

The usefulness of SANS for nondestructive evaluation of ceramics has

already been demonstrated at NBS by an innovative application to the study

of microcracking in YCrCL made recently by Case and Glinka, who were able to

subtract the intrusive background scattering from voids and other defects by

combining data from samples having different thermal histories. The study

of scattering produced by pores themselves, however, requires a different

technique. In particular, multiple scattering and refractive effects become

increasingly important as average void size increases. This entails

qualitative changes in the nature of the SANS intensity which alone can

signal significant alterations in the distribution of pores as density is

increased, as shown below. Quantitative determination of pore size is less

straightforward, however, and requires the comparison of measured intensities

with theoretical predictions over a range of parameters for which practical

theory has generally been lacking. The derivation and numerical implementation

of appropriate multiple scattering theory applicable over a wide range of

average pore sizes and neutron wavelengths has thus been stimulated by these

researches and has become an important component of the overall program to

obtain dependably quantitative SAMS characterizations of densification.

43
In the preliminary phase of the experimental study we have obtained

SANS data from two samples of YCrO^ which were similarly prepared pure

powders, isobarically pressed at 3 TPa (30,000 kbar) . One, a green

state compact has 55% theoretical density; the other, a sintered sample,

has 93% theoretical density. Measurements were made at several neutron

wavelengths and are shown for the green state compact as a function of

scattering wavevector in Fig. 10 on page 33. The full widths at half

maximum of these curves were determined by approximate Gaussian fits and

increase linearly with wavelength in the range shown, a behavior characteristic

of multiple refraction from large particles and thus consistent with the

evident porosity of the green state. In contrast, the scattering from

the sintered sample (not shown) exhibits no wavelength dependence on this scale, indicating the absence of comparably large pores. Clearly, even a qualitative analysis of such data reveals a strong effect of

processing on the population of neutron scattering in these materials.

Moreover, if the scattering in Fig. 10 on page 33 is assumed to be

describable only as multiple refraction and edge diffraction by voids

then an estimate of average pore radius gives a value of approximately

2pm, which appears to be physically reasonable for the green state

compact. This estimate is based on a fit of a preliminary version of

the theory to experiment at several wavelengths. As example is shown

below; the curve is approximately Gaussian except in the tail. The

extent to which the whole shape of measured intensity curves can be

accounted for by theory will be a crucial factor in setting the limits

of dependable void size determinations using SANS.

Figure 1. Comparison of preliminary theory (solid line) with experimental

data (open circles)

.

44
GREEN STATE CERAMICS

T. Negas, E. Fuller, K. Hardman -Rhyne, and C. Robbins

Inorganic Materials Division

Center for Materials Science

INTRODUCTION

Rejection of ceramics after densifi cation, and their failure inservice, are due primarily to defects that influence the physical/

chemical properties of the materials. Increased demands for higherperformance advanced materials have imposed more stringent requirements

on the processing industry. Proven reproducibil ity and reliability of

ceramic components are needs that can only be accomplished by a combination of processing controls and NDE procedures (ref. 1) together with a fundamental understanding of how defects arise and evolve within the

processing cycle. This program focuses on the early stages of ceramic

processing, the "green state", which consists of an assemblage of particulates loosely consolidated by forming methods and often containing

binders, moisture, and other additives that normally are "burned out"

during a preliminary calcination step. The green part, therefore,

constitutes a reservoir of accumulated processing flaws and imperfections (voids, pressure or particle packing heterogeneities, fissures,

agglomerates, inclusions, etc.) that persist and/or generate new defects

during subsequent processing. Ideally, characterization and rejection

of parts should begin at this stage, but virtually no work has been done

on the properties of green compacts. Reliable methods to detect and

relate initial flaws to final structural imperfections, therefore, have

not been demonstrated.

This work consists of the following related elements:

(a) processing of generic green ceramics containing flaws of controlled

size and distribution;

(b) characterization of these compacts through final microstructura

evolution, primarily by microscopy and small angle neutron scattering (SANS); and

(c) evaluation of potential NDE methods cross correlated with characterization measurements.

PROJECT ACTIVITIES

During this year, a cooperative program was established among MBS,

Argonne National Laboratory (ANL), and a guest worker, Dr. Eldon Case,

Univ. of Calif., Berkeley. NBS is responsible for all aspects of green

state processing and pertinent characterization measurements. ANL is

conducting exploratory NDE measurements based on ultrasonics, microfocus

radiography, and NMR on the green compacts and on those also subjected

to binder burnout and final densification.
Processing

Two classes of green ceramics are under investigation. YCr03 -based

compacts, when fully densified , provided the first model ceramic materials used to apply diffractive mode, SANS techniques, and theory (see

NBS, NDE Annual Report, 1982) to the detection and characterization of

finely distributed defects (microfissures) in the 2-200 nm size range.

Green compacts of these materials were characterized by NDE (at ANL) and

by SANS (at NBS) methods. As a result of promising preliminary results

(see below), emphasis was turned to a broad range of generic green state

defects that encompass agglomerates, impurity inclusions, and heterogeneous packing of particles. These features can all be simulated in one type of green composite ceramic consisting of a relatively uniform

matrix of fine particles containing a distribution of densified, large

spheres. MgAl 2 04 (spinel) was selected for both the matrix and_ "hard"

spheres to maintain constant chemistry, thermal expansion, and thermal

conductivity for subsequent processing and characterization. Table 1 sumnarizes the processing cycle for these compacts. Three sets (ten

specimens each) of these materials having 0, 2, and 20 percent volume

fractions of agglomerates in the 75-100 urn range were fabricated for

investigation. In addition, specimens from each set were calcined at

700 °C to remove organic binders and then sintered at 1500-1550 °C to

obtain final densification. Measurements on these latter materials

permit monitoring of the evolution of flaws from the green state to the

finished microstructure. Figure 1A illustrates a typical green comDOsite as processed. After densification, Figure IB, new flaws (pores)

have developed, adjacent to the spherical agglomerates, indicating that

the matrix phase detaches due to faster densification (greater shrinkage). The detrimental effect of these defects also is reflected by

final bulk density. Without agglomerates, green compacts densify to near 98 percent of theoretical, while the materials loaded with two and

20 percent attain approximately 94 and 85 percent, respectively

.

Characterization by SANS

Small angle neutron scattering from materials is characterized by

two dominant regimes, diffractive (DS) and multiple refractive scattering (MRS). The DS mode yields microstructural information for the 2-

200 nm size range. However, the MRS mode is potentially more useful for

the green state as larger, micron-size defects can be detected. In cooperation with Dr. E. Case and the Reactor Division staff, numerous exploratory measurements have been made on YCr0 3 and MgAl 2 0u green

compacts (ref. 2). 0 Using six neutron wavelengths (A = 4.85, 5.45, 6.25,

7.0, 8.0, and 9.0 A), it has been demonstrated that MRS is the dominant

mechanism. The specimens show typical beam broadening (full width at

half maximum FWHM) with a linear dependence on A 2 and a circularly symmetric

Gaussian profile. A comparison of neutron scattering data from densified

YCrO-, (shown in Fig. 3, page 31) with data from green state YCrO„ (shown

in Fag. 9, page 32) illustrates the observed phenomenon and basic differences

46
o between DS and MRS.* Figure 2 shows observed MRS (9.0 A) for green

compacts of MqAl 2 0i+ with (20 percent) and without hard agglomerates.

The data demonstrate remarkable reproducibil ity and the ability to

detect changes in scattering intensity from different samDles. Processing history and microstructure evolution also can be followed by these

changes in MRS, as shown in Figure 3. Here, the curves display a progressive increase of scattering centers at small scattering vector, Q,

for a MgAl 2 04 green compact (no agglomerates, plus binder) after calcination at 700 °C and at 975 °C.

To date, SANS experiments using green compacts are yielding preliminary information that demonstrates differences among materials

(ref. 2). Future research will be devoted to a critical analysis of

these data combined with an evaluation of existing and new models and

theory for MRS, especially linked to the specific type of scattering

centers (defects) in green ceramics. A high temperature furnace for

SANS also has been constructed to continuously monitor microstructural

flaws in-si tu throughout the processing cycle. It is recognized that

SANS techniques have limited application for in-line process control for

manufacturing conditions. However, they provide a powerful laboratory

tool to follow defects through processing cycles, and they constitute a unique laboratory standard with which alternate NDE methods can be

compared.

NDE Characterization

In collaboration with Dr. D. S. Kupperman, ANL, ultrasonic studies

of YOO3 and MgAl 2 04 -based green ceramics are in progress (ref. 3). Two

YOO3 specimens were examined with both longitudinal and shear waves. Surprisingly, no liquid couplant was necessary to propagate these waves,

and the shear-wave velocity varied with polarization, indicating elastic

anisotropy. The latter observation may be due to the fact that the

compacts were first hard-die, uniaxially pressed before isostatic compaction. This result could be most significant if it can be established

that density gradients from the former processing step are carried into,

and "imprinted" within, the latter. The results of the measurements

are:

V

1 = 1.43 X 10

3 m/s; V

t = X 10

3 m/s

where the two values of V t

show the variation with polarization.

*The profile of the multiply refracted beam should be given by the

Fourier convolution of the incident beam with the n-fold refraction. As

n is large, detailed information from the main beam profile is lost in

the MRS process, leaving only information on scatterers present in the

specimen.

47
Table 2 summarizes data for ultrasonics measurements of MgAl 2 04 green compacts (ref. 3). Five points on each specimen were probed, and

sample- to- sample variability is now under investigation. Preliminary

results show that the frequency spectrum for these materials is within

0-2.0 MHz and that the spectra, as in SANS, are di fferent for each

material measured, suggesting anomalous microstructure. Additional

research is necessary to determine sensitivity of ultrasonics using

green compacts containing smaller flaw sizes and populations, as well as sintered materials. In addition, microfocus x-radiography techniques

will be examined using NASA equipment.

CONCLUSIONS

Generic green ceramic compacts can be processed to contain a variety of controlled flaws and heterogeneities. Preliminary SANS and

ultrasonics measurements have shown the ability to detect microstructural anomalies in these materials. The sensitivity and selectivity of

these techniques to controlled defects require future research efforts.

REFERENCES

1. A. G. Evans, "Structural Reliability: A Processing-Dependent

Phenomenon", J_. Am. Ceram . Soc . 65, No. 3, pp. 127-37 (March 1982).

2. K. Hardman-Rhyne and E. Case, "Small Angle Neutron Scattering Measurements on Green Compacts of YCr0 3 ", presentation at TMS-AIME

Fall Meeting, Philadelphia, PA, October 1983.

3. W. A. Ellingson, D. S. Kupperman, T. Negas, and E. Fuller, "Initial

Results of Nondestructive Evaluation Methods Applied to Green

Ceramics", presentation at TMS-AIME Fall Meeting, Philadelphia, PA,

October 1983.

48
Table 1

Processing of MgA^O^-Based Green Ceramics

MgAl^O^ powder

\s

wet-milled to 2.0 urn average particle size

v

spray dried with

polyvinyl alcohol (PVA)

plus glycerol additives

to obtain spherical,

"soft" agglomerates,

5-150 pm

mechanical

bl ending

/\

\>

agglomerates densified

at 1500 °C

isostatic pressing to

67.5 MPa (10,000 psi

)

of composite, green

compact (disks, 30-

37 mm diam. and 3-

20 mm thick)

"hard" agglomerates

classified by screening

to a selected size

range

49
Velocity

of

Sound

vs.

Agglomerate

Concentration

</) c o o o f— r-*

1/1 4J • • • to <a o o o •r- ac o

Q_

>>

4-1

—

s_ r— to

<TJ

U x. rx LO 3 o E LO (X

J3 1CT 00 CO CO 3 — > >3a LO CO o «- *—

4-> CO

l/l ~E

to . 4-> CO CM

O

K 3 Q- CO CO

O > CO CO CO

4-J < LO 1— i— i—

•r- '—• Oo

1— LO o o a r— CO ^3- > LU cn CO CM f— r— r— i —

fO CO o o c CO LO CO

•I—

a cn CO CM

-aC p— r— 3 o 4-> to o o CT LO CM o CT 3 o CO CO CO C ac 1— p— o

—1 <3" r— o OO CM 1—

CO CO CO CO t- 1—

CO CO o CO LO

C CO CO CO 3

<3

O ^—v

4-> •t— E m +-> s_ <TJ 3 S- o s< E +-> o o CM o o c 1^ CM r— 3 1 CT a LO

CT 3 lx < O —

c_> X

a- S- • + 3 u CM

O) •sr -a •r— •r— CM rx r—

r— o e -3 -3 1 i 1 C. CM f- 4-> CO CO CO c CO — ir z 2: (5 c s —

W) CT < s: > to 

C_ CO <o —

o

II>»3e33

CT

CU

S- u_* co

r33C

<D

4->

<13

ct

50
50 yxm

Figure 1 Line reproductions of SEM micrographs illustrating spherical

agglomerates in green state MgAlzOi* (A) and generation

of new pores (darkened) after densification at 1500 °C (B).

51
l?rtN5!TY

-n

IMTEMSITf

Figure 3 Neutron scattering profiles (X = 9.0 A) for a green compact

of MgAl 2 04 (lower curve, no agglomerates), fired at 700 °C to remove binders (middle curve), then calcined at 975 °C (upper

curve) before fully densifyinq at higher temperature.
NONDESTRUCTIVE CHARACTERIZATION OF SUBSURFACE RESIDUAL STRESS

H. J. Prask and C. S. Choi

Energetic Materials Division

U. S. AMCCOM, Dover, NJ

and

Reactor Radiation Division

Center for Materials Science

In earlier work it was demonstrated that the precision and

reproducibility of the neutron diffraction method were sufficient for

residual stress measurements (ref. 1). It was also found, however,

that for the differential volumes of interest in technological applications

(less than about 20 mm as defined in Figure 1) and employing conventional

0-29 scans, texture could produce shifts in apparent peak positions greater

than any expected from residual stress.

To minimize the role of texture in residual stress measurements we have

adopted an energy dispersive approach (ref. 2), utilizing a three-axis

spectrometer, in which sample orientation remains fixed with respect to

incident and diffracted neutron beam directions, and monochromator and

analyzer wavelengths are matched and scanned.

Initial measurements have centered on an aluminum alloy (2024-T351 ) ring-plug sample fabricated for use as a reference sample for ultrasonic

measurements (ref. 3). In this shrink-fit type of cylindrical sample the

theoretical stress distribution is given by*

PR

radial stress. r > R

1 (1)

tangential stress. r > R-j (2)

and

where D =

- Rf )«

5

r<R] 13)

(4)

R-j is the plug radius, R^ is the ring outer radius, E is Young's modulus, and

6 is the differential radial interference. In the aluminum reference sample
E = 73100 MPa, Poisson's ratio is 0.33, R, = 12.7 ram, R~ = 38.1 mm, with

a thickness of 25 ram.

The measurements were made using the (200) reflection and a differential

volume of 1 .5 x 1 .5 x 20 mm at a scattering angle of 90°. If the unstressed

lattice spacing Cd

Q

J is known, residual stresses for the three principal

directions could be obtained directly by three strain measurements at each

point of interest in the sample. Alternatively, (a

p

- a

Q

J can be obtained

at each point of interest without a knowledge of d

Q

(ref. 4). Values for

a

r and a

Q can then be extracted by application of the overall equations

of equilibrium and the use of an analytical model.

In Figure 2, measured - a

Q

values are shown for selected points in the

sample. These are compared with a

r

- a

Q

values calculated with the use of

eqns. (1) - (4) and the measured, pre-assembly dimensions of the sample. We

have also calculated a stress distribution in the sample independent of any

model except for the assumptions shown in Figure 2. With the application of

the local equilibrium conditions, also shown, the adjustable parameters

B (= 443 ± 19 MPa • cm

)

and C (= 3.01 ± 0.1) are evaluated from a fit to the

data in the ring region. Finally, applying the overall equilibrium condition

for force on a principal plane, P is evaluated to be -122 ± 5 MPa, to be

compared with -129 ± 2.4 MPa from measured dimensions and the variance thereof.

In view of the success with the aluminum ring-plug sample, the energydispersive neutron diffraction method is being applied to a material which

has posed serious difficulties for conventional residual stress measurement

techniques; depleted uranium. Initial results on two 25-mm diameter extruded

cylinders with quite different thermomechanical histories show markedly

different strain distributions. It is anticipated that unstressed lattice

spacings and three-dimensional stress profiles will be obtained at selected

points in the samples in the very near future with existing instrumentation.

REFERENCES

1. C. S. Choi, et al_, in "NBS Reactor: Summary of Activities - July 1977

to June 1978," F. J. Shorten, editor, NBS TN 995, p. 34 (1979).

2. L. Pintschovius, et al_, "Determination of Residual Stress Distributions

in the Interior of Technical Parts by Means of Neutron Diffraction,"

Residual Stress and Stress Relaxation, E. Kula and V. Weiss, editors,

pp. 467-482 (Plenum Press'," N. Y., 1982).

3. N. N. Hsu, T. M. Proctor, Jr. and G. V. Blessing, "An Analytical

Approach to Reference Samples for Ultrasonic Residual Stress Measurement,"

ASTM J. Testing & Evaluation 10 , No. 5, pp. 230-234 (Sept. 1982).

4. See, for example, J. 3. Cohen, H. Dolle and M. R. James, "Determining

Stresses from X-Ray Powder Patterns,'' Accuracy in Powder Diffraction , S. Block and C. R. Hubbard, editors, NBS SP 567, pp. 453-477 (1980).

54
Figure 1. Upper: Perspective schematic of differential volume defined by

source-side and detector-side collimation at a scattering

angle of 90°.

Lower: Plan view of sample movement in beam for examination of

different regions.

55
Assume:

Figure

2.

Experimental

results

and

equations

for

ring/plug

sample

analysis

(as

described

in

text).
THEORETICAL STUDY OF ACOUSTIC WAVE SCATTERING

Raymond D. Mountain

Thermophysics Division

Center for Chemical Engineering

The scattering of low frequency sound waves is one way to

investigate inhomogeneities in a material. In principle, the

details of the scattered wave (relative intensity, polarization,

directional variation) contain a great deal of information about

the scatterers. Earlier, we developed within the framework of

the Born approximation , a formal relation between the intensity

of the scattered power and a novel set of moments of the scatterer

which provide information about the size and shape of the inhomogeneity,

ref. 1

In order to apply these results to easily realized laboratory

situations, it is necessary to reanalyze the scattering problem in the

time 'domain. This has been done along the lines outlined by Rose and

Richardson in ref. 2 where the scattering of a unit impulse is examined.

Our results may be expressed as follows. From the measured amplitude of

the scattered signal, the second and fourth temporal moments may be

determined. Then, one immediately obtains the ratio of the fourth to

the second moment, which is theoretically shown to be proportional to

the square of the ’’radius” of the scatterer. In order that instrumental

affects not obscure the signal, the duration of the incident pulse must

be short compared with the transit time across the scatterer.

REFERENCES

1. R.D. Mountain and G. Eirnbaum, "Inhomogeneity Size and Shace

Determination from Scattering of Low-Frequency Sound Waves",

Journal of Applied Physics 53, No. 5, op. 3581-3584 (May

1982).

2. J.H. Rose and J.M. Richardson, "Time Domain Born Approximation",

Journal of Nondestructive Evaluation 3, No. 1, po. 45-53

(1982).' ,
NOE TERMS AND DEFINITIONS: ULTRASONICS AND ACOUSTIC EMISSION

Donald Eitzen and Marilyn Cadoff

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The Army Materials and Mechanics Research Center (AMMRC) has asked that

NBS assist them in developing terms and definitions on general terms and on ultrasonics suitable for use in MIL-Standards. The specific objectives of

the current phases of this activity are to:

1. Develop appropriate terminology for the broad NQTI primary terms,

including: Nondestructive Testing, Nondestructive Inspection,

Nondestructive Evaluation, and Nondestructive Examination.

2. Develop appropriate terminology for some of the general terms

associated with nondestructive methods, including: Reference

Standards, Calibration Standards, Reference Slocks, and Calibration

Slocks. The metrological use and implications of these terms will

be taken into account in this terminology.

3. Develop appropriate and precise terminology for ultrasonic test

methods and procedures using resources such as ASNT, ASTM, ASMS, and

military publications with definitions of ultrasonic terms. Also,

identify terms that are necessary but not yet defined. -

4. Develop additional general terms associated with nondestructive

methods. The metrological use and implications of these terms will

be taken into account. Also, develop precise terminology for those

specific terms for ultrasonic methods identified earlier as needing

definition.

In carrying out these tasks well over 30 draft or published documents

were reviewed and competing terms and definitions were organized. A number

of internal workshops were conducted with NBS experts on metrology and on

.'IDE. As a result, four terms were proposed for the broad “IDE primary

terminology such as "Nondestructive Testing." General terms such as "reference standards" were studied and, as a result, 23 general terms were

proposed. Also 115 terms were proposed for ultrasonic test methods. This

pnase of the project is essentially complete, however, additional editing of some terms was undertaken in order to maintain consistency between this

effort and seme recent NBS comments on proposed MIL-STD-13GSC , "Definition

of Terms for Test, Measurement and Diagnostic Equipment." Input is being

received on the terms from the other armed services as the draft MILglossary is in the "coordination" phase,

all coordination inputs.

C, rtner revisions await receipt or

The 115 terms on ultrasonic methods have also been used as the basis

for a new ASTM ultrasonics glossary. At the request of ASTM E7.G6 and of

AMMRC the definitions were reformatted and have been balloted within the

ultrasonics suocommittee of ASTM. The terms are currently being revised

based on the results of the ASTM ballot.

53
A further objective relating to terms for acoustic emission (AE) has more recently been defined by AMMRC:

5. Develop acceptable, precise, and consistent terminology for

acoustic emission test methods and procedures.

In working on this task over 16 draft or published documents were reviewed and used to develop a data base for terms and for input to

definitions. Approximately 37 terms were selected and draft definitions

composed. The chairman of ASTM E7.04.01 on AE Glossary has begun reviewing

the drafts for input to the MIL-document and for use in the ASTM glossary.

A class of terms relating to "source severity" has not been defined because

they seem to be application/material dependent. A class of terms on equipment-specific AE parameters has also not been defined to date.

59
ULTRASONIC REFERENCE BLOCK CALIBRATION METHODOLOGY

G.V. Blessing and D.G. Eitzen

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The NBS, as part of its calibration mission, has an on-going program to

evaluate and improve ultrasonic reference block calibrations. A review of

the state of the art of those calibration practices, especially as they have

been guided by the ASTM, has been recently completed (ref. 1). In that

review, the principal system variables of the calibration procedure are identified, and recommendations for reducing their associated measurement

errors are presented. Quantitative evaluations of the limitations to

improving measurement precision are made in light of present technology.

Finally, suggestions for improving present practices are given, and

extensive reference to the relevant technical literature is made.

The ultrasonic transducer is identified as a significant variable in

the calibration system, even though much effort has been expended to design

a reproducible unit. As a result, correction factor approaches have been

studied to compensate for the responses between different transducers. In an effort to apply correction factors to a ceramic element transducer in

order to bring it into compliance with the ASTM E127 quartz standard (ref.

2), the following tests were performed. A ceramic transducer with like

dimensions and fundamental frequency as. the quartz standard was used. The

center axis far-field responses of two transducers were then compared

(Fig. i), and the necessary correction factors determined. The calibration

results on a block set before and after applying these correction factors to

the ceramic transducer were then compared with those obtained using the

quartz standard. The results are plotted in Figure 2 relative to the

quartz data represented by the solid horizontal line. Of special note is

the improvement in the agreement between the ceramic and the quartz data by

simply using a block target to set system sensitivity.

REFERENCES

1. G.V. Blessing, “An Assessment of Ultrasonic Reference Block

Methodology," NBSIR 83-2710 (Jun. 1983).

2. Anon., “Standard Practice for Fabricating and Checking

Aluminum Alloy Ultrasonic Standard Reference Blocks", E 1 27 -81 in

the Annual Book of ASTM Standards, Part 11. Philadelphia, PA:

American Society for Testing and Materials, 1982.

60
100.0 I I

I

I I I

I

Far-field center axis beam profiles of a ceramic (dashed line) and a quartz transducer (solid line).

UJa

3

a.5

<

O

X

o

UJ

UJ>

<

UJac

20

10

0

- 10

-20

Quartz

Ceramic Ball Target

Block Target

* Bl. Tar. Corrected

* * * * * * * * * *

A :

t t :\ H

V

A A

—

.

A

i ] ! 1

1

i ! 0 1 2 3 4 5 6 METAL PATH, in.

Reference-block-echo amplitude data taken with a ceramic transducer

(discrete points), relative to that taken with a quartz transducer

(solid line), as a function of metal oath aistance for a No. 5 hole se Ceramic values using two distinct targets before the apolicaticn o*

correction factors (diamonds and triangles), compared with tne correct

values (stars) using a block target.
TRANSFER STANDARDS FOR ULTRASONIC POWER MEASUREMENTS

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

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The characterization of ultrasonic transducers by measurements of total

radiated output power is motivated by the needs of such diverse applications

as medical ultrasonics and quantitative nondestructive testing. In the

interest of improved transfer of calibrations based on these measurements, a new series of standard ultrasonic sources has been developed. Design

criteria included the improvement of overall performance and the elimination

of certain operational difficulties often encountered during field use. While proof tests were underway on early prototypes, research was also

conducted involving the feasibility of a "universal source" capable of

operation at many frequencies. (The availability of a "universal" source would greatly reduce the number of standards needed by client

1 aboratories. ) Successful feasibility tests were followed by proof tests

now almost complete. Fabrication of the first lot of units to be

distributed by the Office of Standard Reference Materials will begin upon

delivery of transducer element raw materials.

The principal use envisioned for the new transducers is the transfer of

NBS measurements of total radiated ultrasonic power in liquid media. In

transfers involving earlier standard sources, errors arising from the use of

the sources were significant compared with those of the underlying

measurement of ultrasonic power. By allowing elimination of two

calculations and two measurements of rf voltage in the transfer procedure,

the inclusion of built-in metering circuitry in each transducer reduces this

added error to insignificance. Additional advantages of this feature of the

new design include reduction of the equipment needed by the user and

preclusion of substantial errors sometimes inherent in high frequency rf

measurements. Impedance matching networks customized for these transducers

will be offered so that optimal use can be made of readi ly-avai 1 abl e 50 ohm

rf sources, and to allow operation at higher power levels than are usually

possible with matching networks commonly used in the field.

Operation at the higher power levels needed in seme medical

applications is facilitated by the use of 36-degrees Y-cut lithium niobate

in place of the quartz used for transducer elements in earlier designs. By

drastically reducing (by 95 percent) the rf drive voltage needed to attain a given level of output power, use of this element material reduces the

complexity of the accompanying matching network and allows the use of

elements of lower fundamental frequency. The new "universal" sources have a fundamental frequency of nominally 0.5 MHz. Overtone operation is at 1 MHz

intervals; this spacing is adequate for most currently-known applications.

Shown in Fig. 1 are the results of a swept-frequency measurement of output

power. Equipment limitations prevented graphically recording test results

for frequencies higher than 30 MHz; manual tests have been successfully made

at 78 MHz.

62
At present, transfer calibrations have been^at power levels between 5

,nw and 500 mW at frequencies between 1 MHz and 15 MHz.

Continuing research includes studies of the long-term stability of the

new transducers (which has so far been indistinguishable from the stability

of the earlier quartz units) and of the possibilities of further refinements

of mechanical and electrical design.

Figure 1. Swept-frequency measurement of ultrasonic outout power of new "universal" source.

53
ULTRASONIC RESIDUAL STRESS MEASUREMENTS

G.V. Blessing, N.N. Hsu, T.M. Proctor

Mechanical Production Metrology Division

Center for Manufacturing Engineering

A reliable means to nondestructi vely evaluate the residual stress

state of an object is of much interest to materials scientists, design

engineers, and safety officials. While substantial research has been

expended to apply ultrasonic techniques to this problem, practical

difficulties of measurement precision and unknown sample stress have

limited its application. This work focuses on both of these problems by

using new transducer technology on a sample designed with a known stress

state.

Ultrasonic shear wave time-of-fl i ght measurements were made at a nominal frequency of 4 MHz on a shrink-fit disk sample of 2024 aluminum

alloy (ref 1). The stress state of the sample was produced by shrinkfitting a plug and ring to produce a calculated 130 MPa region of uniform

compression in the plug, and a concomitant nonuniform tension and

compression in the ring. Time-of-fl i ght measurement scans across sample

diameters were made using a piezoelectric shear, transducer with a viscous

couplant, and were repeated using a contactless electromagnetic acoustic

transducer (EMAT). The ultrasonic results were then compared with

elasticity theory, assuming the acoustoelastic relationship between sound

velocity and material strain.

Figure 1 illustrates the pattern obtained using the EMAT

transducer to traverse specimen diameters respectively in stressed

(asterisks) and non-stressed (solid line) samples. The time difference

relates to the sound velocity difference between orthogonal wave

polarizations for one round trip of the ultrasonic wave pulse measured

from the first to the second echo. The data are in good qualitative

agreement with elasticity theory. Of special note is the dramatic

improvement (by about a factor of ten as compared with the piezoelectric

transducer scans) that was obtained in measurement precision due to the

absence of coupling effects between transducer and sample. Measurement

repeatability of the time difference was nominally + 1 ns, limited

principally by a low si gnal -to-noi se ratio for the observed echoes.

Future plans for the ultrasonic measurement of residual stress

include the use of hybrid transducer techniques, fabricating a ring-plug

specimen from steel, and fundamental data analysis for the zero stress

state.

REFERENCE

1. G.V. Blessing, N.N. Hsu, T.M. Proctor, "Ultrasonic Shear Wave

Measurements of Known Residual Stress in Aluminum," Proceedings of the

Symposium on Nondestructive Methods for Material Property Determination,

Hershey, PA (April 6-3, 1983).

64
TIKE

DIFFERENCE

(us)

150. 0

100 . 0

SO. 0

0 . 0

-50. O'

-100. O'

* *

a *

a

a a

a *

-40 -30 -20 -10 0 10 20 30

HELA1T7S POSITION (mm)

40

Figure 1. Time-of-f li ght differences between orthogonal ultrasonic-wave

polarizations across a diameter of a stancard specimen (asterisks)

and an unstressed specimen (solid line).

oc
EVALUATION OF RESIDUAL STRESSES IN INHOMOGENEOUS, ANISOTROPIC MATERIALS

USING HORIZONTALLY POLARIZED SHEAR WAVES

R. B. King and C. M. Fortunko

Fracture and Deformation Division

Center for Materials Science

A new acoustoelasticity theory was developed for horizontally polarized

shear waves (SH-waves) propagating at arbitrary angles with respect to the

normals to the surfaces of plate geometries (ref. 1). Based on this theory

a new experimental procedure was developed and experimentally verified. This

procedure involves making two sets of relative velocity measurements at two

different propagation angles with SH-waves. It was shown that from these

measurements the difference of in-plane principal stresses (To-T,) cou l d be

evaluated even in the presence of unknown material anisotropy.

The theory presented in ref. 1 was limited to the special case when the

principal directions of stress are parallel to the basis vectors which define

the material symmetry. While this is valid in certain circumstances (e.g.,

butt-welded plates with symmetric weld preparations) it is unnecessarily

restrictive. The theory was extended in ref. 2 to the case where the

principal stress directions are at an arbitrary angle with respect to the

material basis vectors. It was demonstrated that the experimental procedure

described in ref. 1 was still applicable in the more general situation.

Based on the theory of refs. 1 and 2, it is expected that SH-waves

propagating at grazing incidence in a plate are completely insensitive to

material anisotropy but are sensitive to the difference of the in-plane stress

components ("^-T-j^). Tbe insensitivity to anisotropy was confirmed using a plate of rolled aluminum alloy 606T-T6. It was found that relative measurements

with grazing-incidence SH-waves were approximately fifty times less sensitive

to material anisotropy than are conventional birefringence measurements with

normally incident shear waves.

REFERENCES

I 1. R. B. King and C. M. Fortunko, "Determination of In-Plane Residual Stress

States in Plates Using Horizontally Polarized Shear Waves," J. Appl

.

Phys. 54 , No. 6, pp. 3027-3035 (1983).

2. R. B. King and C. M. Fortunko, "Evaluation of Arbitrary Plane Residual

Stress States in Nonhomogeneous, Anisotropic Plates," U1 trasonics (in

press)

.

56
DETERMINATION OF THE ELASTIC MODULI OF MELT-SPUN METALLIC GLASSES

M. Rosen, C. L. Friant and H. N. G. Wadley

Metallurgy Division

Center for Materials Science

Metallic glass formation and subsequent crystallization upon annealing

has recently become an active research area. Rapidly solidified alloys

exhibit a variety of desirable physical, chemical and mechanical properties

of particular interest in the electronics and power industries. The enhanced

development of rapidly solidified metallic glasses has been accompanied by an extensive body of research concerning both material characterization and

processing. Microstructural characterization applying nondestructive techniques,

e.g., contact or noncontact (laser) ultrasonics, may be attractive for the

contribution to understanding the kinetics and mechanisms of transformations

occurring in the melt-spun ribbons, and for its ultimate application for online feedback control of materials processing variables.

A novel approach was developed and reported last year for the determination of sound velocity in thin metallic ribbons employing contactless

laser generation and either piezoelectric or laser-interferometri c detection

of the propagating ultrasonic waves (ref. 1). The Young's modulus can be

readily calculated from the experimental ly-determined sound wave velocity,

assuming one-dimensional extensional waves propagating in a homogeneous,

isotropic, linearly elastic solid of known density. Determination of the

variation of Young's modulus with annealing time and temperature yielded

important kinetic information on the stability of the glassy metals, PdCuSi

and Cu-Zr alloys, against relaxation processes and crystallization (refs. 2-4).

The present work was concerned with the development of an experimental

procedure and theoretical analysis whereby, in addition to the Young's modulus,

the second independent elastic modulus (shear modulus) can be derived. By

knowing both independent moduli, the others can also be calculated, e.g.,

adiabatic compressibility, Poisson's ratio, Debye temperature. Several features

of guided waves which propagate in bounded elastic media, such as plates, sheets,

foils, ribbons, and thin cylinders, distinguish tnem from bulk waves. Guided

waves show dispersion of wave velocity with frequency and plate thickness, or

rod diameter. The only nondispersi ve guided wave is the fundamental horizontally

polarized shear wave SH (0). The SH (0) mode can therefore be very useful in

the determination of the shear modulus. However experimental difficulties had

to be surmounted before the SH (0) velocity could be measured in thin metallic

ribbons. Among others, the orientations of the generating and receiving

transducers relative to the ribbon proved to be important considerations (ref. 5).

Using a specially developed goniometric device for the determination of

the shear wave velocities in thin metallic ribbons, and applying the theoretical

considerations mentioned above, both the longitudinal and shear wave velocities

in thin ribbons were measured directly for the first time. Table I shows the

67
velocities. Young's and shear moduli, adiabatic compressibility and Poisson's

ratio for PdCuSi, Cu-Zr, "Metglas" 2605 -SC and aluminum foil. Noteworthy is

the unusually high compressibility and Poisson's ratio for PdCuSi in its

glassy state. Work is in progress to analyze the composition dependence of

the adiabatic compressibility and shear moduli of Cu-Zr alloys in terms of

the relative stability of the glassy state against crystallization.

REFERENCES

1. C. H. Palmer, S. Pick and M. Rosen, "A Dual -Probe Laser Interferometer

for Contactless Determination of Ultrasonic Wave Velocities and

Attenuation", in preparation.

2. M. Rosen, H. N. G. Wadley and R. Mehrabian, "Crystall i zation Kinetics

Study of Amorphous PdCuSi by Ultrasonic Measurements", Scriota Metal!

.

]±, 1 231 (1981 ).

3. J. C. Chang, F. Nadeau, M. Rosen and R. Mehrabian, "Crystal! i zation

Kinetics Study of Amorphous CusoZrso by Means of Ultrasonic Measurements

and MicroHardness ", Scripta Metal 1 . 16 , 1073 (1 982).

4. M. Rosen and E. Horowitz, "Ultrasonic Nondestructive Characteri zati on (NDC) of Metallurgical Mi crostructures and Transformations", Johns

Hopkins University, Report CMR-NDE-7 (September 1982).

5. C. L. Friant and M. Rosen, "Ultrasonic Materials Characterization of

Melt-Spun Metallic Ribbons", Proc. Symposium on Nondestructive Methods

for Material Property Determination, April 1983, Hershey, PA (in press).

TABLE I

Alloy V E{cm/s) c(dynes/cm 2

) V s (cm/s) G (dynes/cm 2) V,(cm/s) K (dynes/cm 2

) V

Pd-Cu-Si 2.97 x 10 s 9.45 x 10 11 1.737 x iq5 3.36 x ion 4.495 x IQS 16.73 x ion 0.41

Cu-Zr 3.30 x 105 7.98 x 10” 1.98 x 1 0

5 2.37 x ion 4.67 * 10 s * 12.15 x ion 0.39

Metglas

2605-SC 4. 54 x 10 5 15.72 x ion 2.86 x 105 5.97 x io 11 5.56 x 10 s * 14.56 x 10 11 0.32

Aluminum

Foil 5.12 x 1Q5 7.09 x IQ 11 3.13 x 10 5 2.65 x 10 ii 6.36 x 10 s 7.19 x 10 ii 0.34

•Longitudinal velocities calculated from experimentally observed extensions! and

shear velocities.

58
EFFECT OF COMPOSITION ON THE CRYSTALLIZATION KINETICS AND ELASTIC PROPERTIES

OF Cu-Zr ALLOYS

M. Rosen, F. Nadeau and H. N. G. Wadley

Metallurgy Division

Center for Materials Science

As-spun metallic glasses, e.g., Cu-Zr alloys, are not thermodynamically

stable. They tend to structurally relax and finally crystallize when the

thermomechanical conditions are appropriate (ref. 1). The resulting more stable

structures exhibit a drastic reduction of the initially superior mechanical,

physical and chemical properties. The factors governing the thermal stability

of amorphous alloys and their effects on properties are not well understood.

A very prominent change in properties upon crystallization is the increase,

by about 40 percent, in the elastic moduli of the material, accompanied by a drastic reduction in the plastic behavior (ref. 1). The objective of the

present study was to investigate the compositional dependence of the elastic

properties in the Cu-Zr system by means of ultrasonic measurements (ref. 2).

Five Cu x -Zri_ x alloys (x = 0.3, 0.4, 0.5, 0.6, 0.7) were prepared by

melt-spinning in the form of ribbons 2 mm wide, and 25 urn thick. X-ray

diffraction indicated no crystal linity . The ribbons were isothermally annealed

at different temperatures for different time periods. Some samples were held near the crystallization temperature for more than 24 hours to assure complete

crystallization.

The sound wave velocity was determined by measuring the transit time of

a single pulse generated by a Nd:YAG laser and detected either by a piezoelectri

transducer (ref. 3) or by the dual-laser interferometer described last year.

The total estimated error in the calculated value of the Young's modulus was

± 0.2 percent. Ribbon densities were determined by means of a float and

wire technique.

The extensional wave velocity. Fig. 1, and the Young's modulus vary in

a sigmoidal manner as a function of annealing time, characteristic of a thermally activated process. Crystal! ization occurs by nucleation and

diffusional growth. Analysis of the kinetics of the crystallization yields

activation energies of 37 6 kJ mole"^ for compositions up to 50 w/o Cu. For

higher concentrations of Cu, the activation energy increases continually up

to 451 kJ mole"^ (Fig. 2). The increasing activation energy can be related

to changes in the configurational entropy of the alloy as the population of

the Cu-Cu pairs increases (ref. 4).

Young's modulus of amorphous Cu-Zr varies with composition in the form

of a smooth S-curve (Fig. 3). Higher values of the Young's modulus are obtained for higher Cu concentrations. In the present investigation, a functional relationship has been found between the variation of the Young's

modulus with composition and that of the glass transition temperature. The

behavior of Young's modulus versus composition of the glassy alloys (Fig. 3) was found to be in qualitative agreement with the behavior of the glass

69
transition temperature, Tg, Fig. 4. This relationship is particularly

interesting since it may indicate a connection between variations in

the cohesive energy of the alloy and its glass forming capability. The

analogous behavior may be due to changes induced in the bonding strength

between constituent atoms as the composition is varied. Should such a relationship indeed exist between the elastic properties and the glass

transition temperature, then the elastic properties might be a figure of

merit of the glass formation ability of the alloy. In this case, a non- destructive ultrasonic capability exists to characterize and predict the

glass formation ability. More work is necessary to establish the validity of

this assumption.

REFERENCES

1. J. C. Chang, F. Nadeau, M. Rosen and R. Mehrabian, "Crystallization

Kinetics Study of Amorphous CusgZrso by Means of Ultrasonic Measurements

and Microhardness", Scripta Metal! . 16 , pp 1073 (1982).

2. F. Nadeau, M. Rosen and H. N. G. Wadley, "Effect of Composition on the

Elastic Properties of Cu xZr-j_ x Glassy Alloys", in preparation.

3. M. Rosen and E. Horowitz, "Ultrasonic Nondestructive Characterization

(NDC) of Metallurgical Mi crostructures and Transformations", Johns

Hopkins University Report CMR-NDE-7 (September 1982).

4. M. Rosen, C. L. Friant, F. Nadeau, J. J. Smith and E. Horowitz, "Ultrasonic

Nondestructive Materials Characterization of Rapidly Solidified

Microstructures", Johns Hopkins University Report CMR-NDE-8 (August

1983).

70
Figure 1

igure 2

. Variation of the extensional sound wave velocity as a function of tine at three isothermal holding temperatures

during recrystallization of Cu^Zr^ glassy metallic alloy.

! 20

i UJO

2

o

u

>

o

<r^

ICO

UJ2

O

a

<

/

/

/

/ / /

/

50 60

AT % Cu

Effect of composition on the activation energy of crystal! i zation

in Cu-Zr amorphous alloys.

71
Figure 3. Variation of Young's modulus with copper content in amorphous

and crystalline Cu-Zr alloys.

9

foJ2

UiH

2

O

K

<n2

<

q:

hcn

</> <

_ic

Figure 4. Variation of the Yeung's modulus and glass transition temperature

with copper content in amorphous Cu-Zr alloys.

72
NONDESTRUCTIVE CHARACTERIZATION OF MICROSTRUCTURALLY MODIFIED SURFACE

LAYERS BY MEANS OF RAYLEIGH SURFACE WAVES

M. Rosen, B. Elkind and H. N. G. Wadley

Metallurgy Division

Center for Materials Science

Directed energy source irradiation by means of high power lasers and

electron beams is being extensively applied for the modification of surface

properties of metallic surfaces. Significantly improved wear, corrosion and

fatigue properties have been achieved by rapid melting and quenching of

peripheral surfaces of metals. Modification of surfaces may also involve

incorporation of alloying elements into the surface layer, or localized

thermomechanical treatment of the desired characteristics. In nearly eutectoid

steels, the martensitic layer at the irradiated and rapidly-quenched surface

will be followed by layers of bainite and pearlite. Control of the developing

microstructures and their nondestructive characterization are crucial in

understanding the operating mechanisms. However, the modified surface zones

are not readily amenable to conventional nondestructive ultrasonic characterization. The objective of the present research task is to develop a non- destructive characterization method using Rayleigh surface waves that enables

the determination of the elastic moduli of the modified layer and the depth

of penetration of the heat-affected zone into the bulk.

The present report provides preliminary results of the effect of electron

beam glazing on aluminum alloys and steel samples. The nondestructive method

involves generation of Rayleigh surface waves and their detection by means of

a specially designed device based on piezoelectric transducers, as well as laser generation and laser-interferometric detection of the Rayleigh waves (refs.

1,2). Choice of an appropriate frequency range enables determination of the

elastic properties of the microstructural ly modified layers. From the frequency

analysis of the "apparent” Rayleigh wave velocities, it is feasible to determine

the depth of penetration of a homogeneously modified surface layer into the

bulk of the sample.

Electron beam glazing has been applied in the course of this research to

develop modified metallurgical microstructures on PdCuSi, Fig. 1, age hardened

aluminum alloys 2024, 5052 and 6061, as well as formation of martensitic and

bainitic layers on pearlitic steel substrates. Fig. 2. In all the steel

samples the Rayleigh wave velocity of the modified layers was lower than the

bulk values, by about 2 percent (ref. 2). In PdCuSi the Rayleigh velocity of

the amorphous layer was found to be 30 percent smaller than in the crystalline

substrate (ref. 1). The results in aluminum can be explained in terms of

annealing of the surface age hardened layer. This assumption is corroborated

by the lower hardness values of the glazed aluminum surfaces. The results of

this investigation are being analyzed in terms of the elastic properties of

the specific phases involved.

73
Work is in progress to measure the apparent Rayleigh velocity as a function

of frequency, thus enabling thickness gauging of the layer affected by the

electron beam irradiation.

REFERENCES

1. M. Rosen and E. Horowitz, "Ultrasonic Nondestructive Characterization

(NDC) of Metallurgical Microstructures and Transformations", Johns

Hopkins University Report CMR-NDE-7 (September 1982).

2. M. Rosen, C. L. Friant, F. Nadeau, J. J. Smith and E. Horowitz, "Ultrasonic

Nondestructive Materials Characterization of Rapidly Solidified

Microstructures", Johns Hopkins University Report CMR-NDE-8 (August 1983).

Figure 1. Modified metallurgical microstructure on PdCuSi.

74
Figure 2. Martensitic and ba ini tic layers on pearl i tic steel substrate

75
DETERMINATION OF PHASE STABILITY CRITERIA OF EXTENDED SOLID SOLUTIONS BY

MEANS OF NONDESTRUCTIVE CHARACTERIZATION

M. Rosen, R. J. Schaefer, J. J. Smith and H. N. G. Wadley

Metallurgy Division

Center for Materials Science

Extension of the solid solubility of alloys under nonequilibrium conditions

by means of rapid cooling has great scientific and technological potential in

terms of the ability to predict and design the metallurgical properties of

alloy systems. Extended solid solutions of aluminum with transition metal

additions have been shown to possess excellent mechanical properties, corrosion

resistance and improved fatigue life. At the present time, there is no widely

accepted model or set of criteria that permits predictions to be made concerning

the amount of extension of the solubility as a function of quenching conditions.

By attaining the necessary supercooling, suppression of the decomposition of

the alloy can be controlled, thus preventing segregation, solute clustering

or subsequent aging. The objective of the research is to undertake a systematic

investigation of aluminum-base alloys that are known to possess extended

solid solubilities upon rapid cooling from the melt. These aluminum systems

include additions of first row transition metal elements such as Cr, Mn and Fe.

Nondestructive evaluation techniques, e.g., sound velocity, ultrasonic attenuation,

compressibility, and electrical resistivity, will be used to characterize

the physical properties of the alloys as related to the heat treatments of the

alloys. The NDE data can be correlated with the mechanical properties and

thermal stability of the alloys. Corroborating evidence from x-ray analysis,

optical and electronic microscopy, and strength and hardness measurements

provides additional aspects that cannot be covered by nondestructive ultrasonic

methods.

The first phase of the research program dealt with the Al-Mn system

(refs. 1-3). Samples were prepared in ribbon form by melt spinning and by

electron beam surface melting of bulk samples. The samples were evaluated by

several experimental techniques in the as-quenched condition and after annealing

for different times at 450°C. The measurements gave consistent indication of

the high degree of supersaturation attained in the rapidly-solidified materials

and showed changes in several physical properties as decomposition of the

supersaturated phase progressed. At low supersaturations, the precipitates

were localized at the grain boundaries. At high manganese concentrations,

the precipitates were abundantly dispersed through the matrix, and the lattice

supersaturation decreased more rapidly.

The maximum equilibrium solubility of Mn in A1 is 1.82 w/o. In the

supersaturated condition the aluminum lattice accommodates up to 13 w/o, as found by x-ray diffraction of the as-spun Al-Mn ribbons. At 15 w/o Mn, x-ray

diffraction showed that additional peaks appear. The electrical resistivity

76
of the ribbons, determined by means of a standard four-probe potentiometric

method, shows a strong increase in resistivity with increasing concentration

of manganese. Fig. 1. Annealing at 450°C strongly affects the resistivity.

By means of a nucleation and diffusion controlled growth process, Al-Mn

particles are formed, thus diminishing the number of effective electron

scatterers from the aluminum matrix.

The velocity of ultrasonic waves. Fig. 2, was determined by measuring

the transit time of a single pulse generated by a Nd:YAG laser and detected

by a piezoelectric transducer (ref. 4). Rayleigh surface waves were used to

characterize the supersaturated solid solution generated by electron beam'

surface melting of a slab of Al-7 w/o Mn. The 2 percent difference in Rayleigh

velocity, with that of the untreated face being the greater one, is due to

the presence of Al-Mn precipitates in the equilibrium structure.

The elastic moduli of both annealed and unannealed ribbons exhibit a prominent minimum at 2.5 w/o Mn. It is believed that . the minimum in the

elastic moduli is of intrinsic importance, and is related to changes in the

bonding strength as manganese is added to the aluminum lattice. The behavior

of the lattice parameter. Fig. 3, and electrical resistivity, Fig. 1 , as a function of manganese concentration, corroborates the significance of the

minimum in the elastic properties. Work is in progress to investigate the

behavior of the elastic properties, electrical resistivity and lattice parameter

of aluminum-base alloys with Cr and Fe.

The present phase of the research also indicates a measurable difference

in the sound velocity between annealed and unannealed samples. The difference

increases with increasing manganese content. The difference in sound velocity

indicates that nondestructive measurements are feasible for in-process dynamic

monitoring and determination of the supersaturation range of rapidly-sol i di fi ed

alloys.

REFERENCES

1. R. J. Schaefer, M. Rosen, J. J. Smith, D. Shechtman and R. Mehrabian,

"Nondestructive Characterization of Rapidly Solidified Al-Mn Alloys :i , Proc. 3rd Conf. on Rapid Solidification Processing , R. Mehrabian, M.

Cohen and B. Kear, editors (in press).

2. M. Rosen, C. Friant, F. Nadeau, J. J. Smith an-d E. Horowitz, "Ultrasonic

Nondestructive Materials Characterizati on of Rapidly Solidified

Mi crostructures ", Johns Hopkins University Report CMR-NDE-8 (August

1983).

3. J. J. Smith, M. Rosen and H. N. G. Wadley, "Effect of Composition on the

Elastic Properties of Rapidly Solidified Al-Mn Alloys of Extended Solid

Solubility", in preparation.

77
4 . M. Rosen and £. Horowitz, "Ultrasonic Nondestructive Characterization

(NDC) of Metal lurgi cal Mi crostructures and Transformations " , Johns

Hopkins University Report CMR-NDE-7 (September 1982).

F i cu re 1

Weight Percent Manganese

Variation of the electrical resistivity in rapidly

Mn alloys as a function of Mn concentrati on in the

and annealed conditions.

78

(U

u\
igure 2

5800 r-r

5600- A As-Spun • Annealed (@ 450°C,3 hr)

^ 5400 (-

I

1 ' 4600 i—i—!—i—I—!—i—i

i—!

I—:—:—

0 5 10

Weight Percent Manganese

Variation of the extensions! sound wave velocity in rapidly

solidified Al-Mn alloys as a function of Mn concentration in the

as-spun and annealed conditions.
i gu re 3 Variation of the lattice parameter in rapidly solidified Al-Mn

alloys as a function of Mn concentration in the as -spun and

annealed conditions.

30
ULTRASONIC MEASUREMENT OF SOLID/LIQUID INTERFACE POSITION

DURING SOLIDIFICATION AND MELTING OF METALS

R. L. Parker and J. R. Manning

Metallurgy Division

Center for Materials Science

Ultrasonic techniques are being developed to provide real-time in -situ , nondestructive measurement of the position, motion and shape of solidification interfaces in opaque materials.

The use of pulse-echo ultrasonic flaw detectors to detect the presence and

location of cracks, voids, and other flaws in metals and non-metals is well

known. The solid-liquid interface in a melting or freezing metal should

also produce a reflected echo, in that there is a measurable difference

in both sound velocity and density across the interface. For normal incidence of longitudinal waves, about 10% of the pressure amplitude, or 1% of

the energy, would be expected to be reflected from a planar solid-liquid

interface in a pure metal. Such a technique would be useful for feedback

and closed-loop process control of solidification to achieve improved quality

control and productivity —such as in warning of potential breakouts in con- tinuous casting of steel, ref. 1. The technique can be regarded as real-time

ultrasonic metallography.

A paper on this subject (ref. 2) was presented at the Army Research Office

Tri-Service Conference on Manufacturing Research held at Leesburg, Virginia

May 31 - June 2, 1983, and appears in the Proceedings of that meeting. It summarizes our earlier work in this area, including measurements on solidliquid tin in a resistance-heated Bridgman furnace; the use of computer

spatial averaging in room-temperature modelling tests on large-grain

stainless steel, in order to improve signal/noise ratios in the presence

of strong Rayleigh scattering; a survey of earlier tests by others; and

current NBS tests on hot steel and iron.

The tests on hot steel have been made with an RF induction furnace in the

Bridgman geometry, in argon, with the transducer coupled to the cool end

of the 12 cm long specimens. Using 1 MHz longitudinal waves, we have

made measurements of the solid-liquid interface location and motion in

pure iron rods 2 cm 0D by 12 cm long, and in 304 stainless rods 3 cm 0D

by 12 cm long, in the presence of substantial grain growth. These are

the first such measurements on these materials. This grain growth both

attenuates the incoming beam and introduces back-reflected noise signals.

In the case of alloys, the changes in acoustic impedance as the beam

enters the mushy zone are much less abrupt than is the case for a pure

metal, and therefore the reflected signal is further reduced. Thus,

digital signal processing is necessary for reliable test results with

alloys, using spatial averaging. In the Bridgman geometry, this can be

accomplished by rotating the transducer followed by signal averaging.

Rotation alters the interference patterns from the grains (much as in the

parallel translation case) because there are variations in the cylindrical

symmetry of the sound field produced by variations in the PZT element. A

stepper motor, computer-controlled, provides the rotation.

81
To develop a reliable pulse-echo system for determining skin thickness in

continuous casting of steel, it is essential to determine the degree of

transmission through bulk, hot steel and the degree of reflection from

the solid-liquid interface. These quantities are frequency dependent,

and can be time-dependent in the case of grain growth and interface

motion. An apparatus has been constructed to do this, and measurements

are underway on iron and steel. Computer signal processing is necessary

to improve signal/noise ratios in the case of alloys.

1. R. L. Parker, "Ultrasonic Measurement of Solid/Liquid Interface

Position during Solidification and Melting of Metals," AIP Conference

Proceedings No. 84 (Physics in the Steel Industry), New York, 1982.

2. R. L. Parker, "Ultrasonic Measurement of Solid/Liquid Interface

Position During Metal Solidification," Proc. Army Res. Off. Conf. on Mfg. Res., June 2, 1983.

82
ULTRASONIC STEEL TEMPERATURE SENSORS

S. J. Norton, M. Linzer, H. N. G. Wadley, C. Turner, F. S. Biancaniello

and S. D. Ridder

Metallurgy Division

Center for Materials Science

An investigation was undertaken of the feasibility of determining the

internal temperature distribution within a cylindrical steel billet from

ultrasonic time-of-fli ght measurements along different paths penetrating the

billet. From these measurements, the internal sound-velocity distribution

can be reconstructed by tomographic techniques. Using an empirical relationship

between sound velocity and temperature, the velocity profile can then be

converted to a map of the internal temperature distribution.

Heat flow modelling was included in the study to investigate the spatial

and temporal characteristics of the internal temperature distribution in a cooling cylindrical billet. As a first step in measuring temperature, a tomographic algorithm was developed for reconstructing the internal sound

velocity distribution from time-of-fli ght measurements along a minimum number

of paths penetrating the billet. By representing the unknown velocity distribution in a suitable orthogonal basis set, only a minimum number of terms in

the basis expansion need be retained for a sufficiently accurate representation

of the velocity distribution. The basis set can- also be chosen to satisfy

automatically the geometric constraints of the boundary, as well as any

boundary conditions known a priori, such as surface temperature. In this

way, a proper choice of basis functions can greatly reduce the number of

measurements required for an adequate representation of the velocity. The

reconstructed velocity distribution is then converted directly into a temperature

distribution using the known velocity-temperature relationship for steel.

To test the reconstruction theory, time-of-f 1 i ght measurements were

simulated by computing the transit times of pulses along particular paths

through an assumed temperature distribution in a cylinder, where the temperature

profile was obtained from heat flow theory. The simulated time-of-f 1 i ght

data were then used as input to the tomography algorithm and a velocity

reconstruction generated. The velocity distribution was in turn converted to

temperature, and finally compared to the assumed temperature distribution.

In the absence of measurement errors, the simulated reconstructions closely

matched the original temperature profile when only three or four transit-time

measurements were used.

Preliminary reconstructions were also obtained using actual time-of-fl i ght

measurements through a hot six-inch steel cylinder. When the number of terms

in the basis expansion of the sound velocity is kept small, the reconstruct!' on was found to compare to within 10 percent of the measured temperature distribution

(Fig. 1). When more terms are included, which are responsible for higher

83
spatial resolution, the reconstruction process becomes increasingly sensitive

to measurement errors, and as a consequence, the reconstructed temperature

was in poorer agreement with the measured temperature profile. The effects

of measurement errors and their relationship to spatial resolution and accuracy

in the reconstructed temperature distribution are now being investigated.

An investigation of transducer technology suitable for ultrasonic detection

at high temperatures was undertaken. It was concluded that piezoelectric

devices, such as PZT, would be much more sensitive than electromagnetic

transducers (EMATs) and many orders of magnitude more sensitive than laser

interferometer detectors. A scheme for coupling piezoelectric transducers to

surfaces at high temperatures was devised, using a fused silica buffer rod

and a glass couplant between the rod and hot surface. This coupling scheme,

combined with the use of a 500 kHz ultrasound frequency, allowed very sensitive

detection of ultrasonic energy propagating through steel up to 1320°C, the

highest temperature obtainable in our furnace.

A first-order mathematical theory of the inverse dimensional resonance problem was also developed. Dimensional resonance represents another approach

to reconstructing internal temperature in steel by measuring ultrasonic

resonances in slabs of rectangular geometry. In this approach, sound-velocity

inhomogeneities arising from spatial temperature variations are reconstructed

by exciting the resonance modes in the steel slab and measuring the resultant

shifts in the resonance frequencies. When the inhomogeneities are relatively

small, the theory shows how the perturbed resonance frequencies can be used to

reconstruct the velocity variations within the slab. Again, exploiting the

known temperature-veloci ty dependence, the internal temperature distribution

may then be recovered.

84
TEMPERATURE

(°C)

400

Figure 1

160

120

v ( r ) = v (R ) +

°l J 0

(k

! r)

II MEASUREMENTS

(Least Squares Solution)

30 —

40 —

0 0.4 0.8 1.2 1.6

NORMALIZED RADIAL DISTANCE

2.0

Temperature profiles in hot cylindrical billet. The solid line

is a 8essel function fit to the true internal temperature measured

with thermocouple probes. The dashed line is a reconstruction

of the temperature computed by estimating the parameter a] in a least squares sense from 11 time-of-f 1

i ght measurements. ~ne surface temperature is assumed known.

35
CURE MONITORING IN POLYMERS AND COMPOSITES VIA

NONDESTRUCTIVE TECHNIQUES

Donald L. Hunston, Bruno M. Fanconi , and Fred I. Mopsik

Polymer Science and Standards Division

Center for Materials Science

The rapidly expanding use of polymers in structural applications

has generated much interest in the new field of polymer processing with

chemically reacting (i.e. polymerizing) materials. The comnercial importance

of these polymer systems combined with the general lack of knowledge in this area has produced an urgent need to investigate the basic science of

processing with reacting polymers and to develop nondestructive test methods

to explore this area. These needs include both laboratory test techniques

which permit the study and optimization of the processing reactions and

on-line techniques that can be used to monitor and adjust processing

variables.

A fundamental approach to this problem, however, requires a variety

of measurement techniques since important events occur on the molecular

level, the morphological level, and the mechanical properties level.

The approach taken in the program currently underway in the Polymers

Division is addressing this difficulty by combining techniques from three

different areas: spectroscopy, dielectrometry , and mechanical characterization. The spectroscopic technique (Fourier transform infrared measurements)

have the potential to examine curing (polymerization) reactions at a molecular

level indicating what the reactions are and how rapidly they proceed. The

mechanical characterization technique involves the ultrasonic test method

developed previously in the NDE program, refs. 1 and 2. In this method an ultrasonic shear wave is propagated in a thin quartz strip that is coated

with the sample to be tested. By measuring the wave in the quartz,

information related to the mechanical properties of the coating can be

obtained. Consequently, this method provides data directly relevant to

processing and performance. The dielectric experiments, which utilize the

unique NBS time domain dielectric spectrometer, provide information on mobilities at a morphological level, i.e., a size scale intermediate to

the other two methods. By combining these three techniques, it will be

possible to obtain a much more complete understanding of the transformations

that occur during reactive processing of polymers.

During the past year a feasibility study was conducted to determine

if all three of these techniques could be used to monitor cure in similar

chemically reacting polymer systems. These tests confirmed that such

measurements could be made ana thus demonstrated that an in-depth development

of each technique as a cure monitoring tool would be advantageous. In

86
previous years the ultrasonic technique has been shown to be a valuable

cure monitoring device which has a unique capability to nondestructive!

y

follow changes that occurred during the curing of polymers in thin films

or restricted layers. In addition to this the technique has the potential

for quantitatively determining mechanical properties. Over the past year

this latter capability has been implemented. Since no other technique

can provide equivalent measurements the only way to validate this capability

for highly viscoelastic materials is to compare the results from the

ultrasonics test with extrapolated values obtained by applying timetemperature superposition to low frequency data from torsional oscillation

experiments on a thermorheologically simple material. Such tests were

conducted using a polyvinyl chloride plastisol and the results are shown

in Table I. In light of the large extrapolations involved (5 decades),

the agreement between the two sets of results is excellent.

Table I: Validation of Ultrasonic Technique

Method Shear Storage Shear Loss

Modulus (MPa) Modulus (MPa)

Ultrasonic Tests 0.70 1 .8

Estimate from Superposition 0.78 2.1

The successful development of this technique has led to a desire by a number of other groups to implement a similar device for addressing their

particular problems. For example, NBS is currently constructing such a device for the Bureau of Engraving and Printing so they can use it to

study drying of printing inks, ref. 2.

Future work in this program will focus on the development of the time

domain dielectric spectrometer as a cure monitoring device. This instrument,

which was developed at NBS, has the capability to measure the dielectric

constant of a material over a very wide range of times (or frequencies)

in a single experiment. Preliminary studies on the latter phases of cure

have shown that this capability makes it possible to follow changes in

molecular mobilities that would otherwise be very difficult to detect

because they appear only in the very low frequency range. This is illustrated

in Figure 1 which shows the complex dielectric constant (real part minus

a background level of 100 pF, A C', and the imaginary part, C") for an epoxy -derivative solid film before and after a post cure heat treatment.

This type of information is particularly useful since the final degree of cure is often a critical parameter in processing. As a result further

development of this technique is highly desirable and will be a major goal

next year.

87
REFERENCES

1. D. L. Hunston, "Cure Monitoring of Thermosetting Polymers by an Ultrasonic Technique, Review of Progress in Qua ntitative Nondestructive

Evaluation , Vo 1 . 2 , D . (77^ ~

Corp., 1983).

q-- » rivjMi =33 in uuanu lauve Mu naestruc

2* D- U. Thompson, ed., pp. f/ i i - i 730 (Plenum Pub.'

2. D. L. Hunston, "Relationship between Mechanical Properties and

Performance of Inks as the Basis for Quality Control Techniques",

MBS I R -83 -2691 (April, 1983).

Bia-GMA/TEG DMA

Figure The real part of the complex dielectric constant

minus a background level, AC '

,

and the imaginary

part, C" , as a function of frequency for an epoxyderivative solid film before, , and after,

a post cure thermal treatment.

38
ULTRASONIC APPLICATIONS TO NOT AND MATERIALS EVALUATION

u. V. Blessing

Mechanical Production Metrology Division

Center for Manufacturi ng Engineering

Miscellaneous small projects were performed in response to other

agency requests and committee round-robin efforts.

1. Mi Alloy 3ond Q-efects : A diffusion-bonded nickel alloy sample possessing

unbond artifacts was evaluated using ultrasonic C-scan and continuous

amplitude scan techniques for Pratt & Whitney, West Palm Beach, FL.

2. Residual Stress Round-Robin : The elastic anisotropy of both stainless

steel and carbon steel samples were evaluated as part of a round-robin effor

for residual stress standard development sponsored by the Society for

Experimental Stress Analysis (SESA).

3. Fused Quartz Sound Speed : The transit times of shear and longitudinal

waves were precisely measured in a fused quartz disk. This disk is being

evaluated as a candidate for an ASTM round robin effort for making sound

speed measurements.

4. Metal Matrix Composite Scans : Several sample sheets of graphitereinforced metal matrix composites, developed by the Army, were

ul trasoni cal ly scanned for their scattering amplitude profiles.

5. Carbon/Carbon Turbine Composite : A variable thickness carbon/carbon

composite sample was ul trasonical ly scanned for possible del ami nations . The

turbine material was developed by the Vought Corp., Texas, for a DARPAsponsored project.

5. DOT Steel Support Weldments : The welded regions of f ailed support roas were ul trasoni cal ly evaluated using a surface wave technique. These

specimens were taken from the scene of the highway ramp sucport failure

which occurred in Chicago, 1932.

3a1
ULTRASONIC IMAGING FOR MEDICAL APPLICATIONS

Melvin Linzer and Stephen J. Norton

Metallurgy Division

Center for Materials Science

Work for this program in the past year consisted of theoretical analysis

and development of imaging technques, organization of the "Eighth International

Symposium on Ultrasonic Imaging and Tissue Characterization " and editing of

the journal Ultrasonic Imaging .

In the imaging area, a proof of convergence of the iterative reconstructionf rom-projections algorithm was derived (ref. 1). This proof, for the first time,

separates rates of convergence for different spatial frequency components in

the image. An in verse-scattering approach for generating separate highresolution, quantitative images of the variations in density and compressibility

in tissue was also developed (ref. 2).

The Eighth International Ultrasonic Symposium attracted 225 attendees,

one of our largest audiences to date. Seventy-seven papers were presented,

covering a wide variety of ultrasonic imaging and characterization techniques.

The journal Ultrasonic Imaging has become recognized as the leading journal

concerned with ultrasonic techniques. Subscribers now exceed 500 for the

first time. A large increase in the number of submitted papers occurred last

year and we are planning to increase the number of pages by 25 percent in

1984. The subject most widely discussed in the journal in 1983 was the

development of techniques for measuring attenuation in reflection.

In the accounts that follow, the theoretical work on imaging is reviewed:

1. Iterative Reconstruction Techniques: Convergence as a Function of Spatial

Frequency

The convergence of two well-known iterative reconstruction-f rom- projections algorithms, ART (algebraic reconstruction technique) and

SIRT (simultaneous iterative reconstruction technique) was analyzed.

The analysis reveals how individual spatial frequency components in the

image converge at different rates to their respective object components.

The functional form of this convergence is also revealed. The analysis

proceeds by considering the continuous versions of the ART and SIRT

algorithms in the limit of continuous sampling along the projections and

in angle. From the continuous versions, explicit convergence formulas

are derived which show that the continuous ART and SIRT algorithms indeed

converge to the correct solutions, that the convergence is geometric,

and how the rate of convergence varies with spatial frequency. The rate

of convergence as a function of spatial frequency could well represent

information of practical importance in establishing stopping criteria

90
for these iterative techniques (ART and SIRT), particularly when prior

information about the inherent bandwidth of the projection data is known.

Once these limits are given, the number of iterations needed to achieve a given amount of error reduction for a particular spatial frequency could,

in principle, be estimated in advance.

2. A Method for Imaging Separately Density and Compressibility Variations

in Tissue

A method was developed for reconstructing separate images of the

variations in density and compressibi 1 ity in the same tissue sample.

The images can be obtained from near-field scattering measurements using

only two long, rectangular transducer elements. As in diffraction

tomography, 180° access around the region of interest is required. This

approach differs from conventional diffraction tomography, however, in

that no transducer arrays are required and broadband illumination is

used. A flat transducer, assumed long relative to the extent of the object,

is used as a source of broadband, plane-wave illumination, and as a receiver of the backscattered sound. A second transducer, oriented at a different angle with respect to the first, is used as a receiver only.

The two transducers are rotated together 180° around the object directly,

backscattering measurements are performed during the rotation. This

arrangement can be shown to sample the plane-wave spectrum of the object

directly and provides sufficient information to reconstruct independent

images of the variations in both the density and compressibility of the

scattering medium. Image resolution is limited by the bandwidth of the

illuminating sound.

REFERENCES

1. S. J. Norton, “Iterative Reconstruction Techniques: Convergence as a Function of Spatial Frequency", in preparation.

2. S. J. Norton, "A Method for Imaging Separately Density and Compressibility

Variations in Tissue", Ultrasonic Imaging 5, No. 3, p. 240-252, 1983.

91
ACOUSTIC EMISSION THEORY DEVELOPMENT

J. A. Simmons and H. N. G. Wadley

Metallurgy Division

Center for Materials Science

Theoretical efforts on acoustic emission during the past year have

concentrated on two main areas: 1) completion of the deconvolution program

required for tranducer calibration and underlying multichannel acoustic

emission inversion. The results of this research have been submitted to the

IEEE Journal on Acoustics, Speech and Signal Processing (ref. 1).

A new concept of causal boundary roots was developed using the roots of a slightly modified Z-transform of a time series (called the Y transform)

obtained from new programs which can solve polynomials in excess of degree 800.

If a causal time series has non-zero elements a], a2» a 3 , ... one considers

the roots of the polynomials

NL a

ny

n = 0

n=l

As N becomes large (typically in excess of 100) the roots with absolute value

less than 1 of this series become fixed and can serve as a recognizable

signature for the initial or transient part of the time series.

The roots of the Y transform also provide a powerful new technique for

deconvolution in the presence of noise. The most advanced methods hitherto

available for treating deconvolution treat it as an ill-conditioned but wellposed problem in linear algebra. This approach was applied here previously

using a new and efficient singular valued decomposition (SVD) technique.

However, that technique was not particularly robust and it was often difficult

to guess which candidate estimate to the deconvolved inverse was best. By

modifying the formulation of the deconvolution problem to give a well-conditioned

but ill-posed problem, it has been possible to develop a completely new method based on Y transform roots in which “a priori" information can be used

to produce comparable noise reduction to that obtained by SVD techniques

while providing more accurate frequency information about the deconvolved

inverse.

However, this method, too, suffers from lack of robustness. By combining the

SVD and the Y transform root methods in a cross-cutting algorithm in which

each method is used to refine the errors of the other, a new level of robustness

and accuracy was achieved for deconvolution which finally appears to be

powerful enough to deal with typical transducer calibration and multichannel

AE inversion problems. An example applied to a model deconvolution problem

is shown in the accompanying figures. The transducer response taken from an empirical waveform filtered at 2.5 MHz upper frequencies is shown in Figure

1. The model transducer response is shown in Figure 2 and the composite data

92
with added noise is shown in Figure 3. No conventional methods we have

found can be applied to even approximately deconvolve the curve in Figure 1 from that in Figure 3 to obtain the curve in Figure 2. The estimate from the

cross-cutting algorithm overlaid with the correct answer is shown in time

representation in Figure 4 and in frequency representation in Figure 5. As can be seen in Figure 5, the recovery of frequency information up to 1 MHz is

almost exact. Only above 2.5 MHz is there essentially no information about

the answer, as would be expected due to the low frequency content of the curve in Figure 1.

The second area of effort in the theory of AE has centered on detailed forward

modelling of the thermoelastic emission from laser heating with diffusion effects

and comparison with acoustic emission to be expected from vertical cracking

at and near the plate surface (ref. 2).

Because of the large flat surfaces of the plate, the dynamic Green’s functions

for motion due to a monopole force function are characterized by Heaviside

and logarithmic jumps occurring at discrete arrival times associated to multiple

wave reflections. The Green's functions associated to the force dipoles

characteristic of thermoelastic and crack sources then have delta function

components and cannot be accurately modeled using ordinary moment expansions

without proper filtering either in space or time. However, because of the

presence of these discrete components for the Green's function in a plate, it

becomes possible to resolve certain dynamic near-surface aspects of material

processes. For instance. Figure 6 shows the predicted AE from a half-penny

crack growing in a self-similar mode at 1 mm/ps for one microsecond in a 22.25 cm plate of stainless steel. The first moment corrections associated

to the particular crack growth model clearly differentiate it from the modelinsensitive zeroth moment curve. Similar calculations have been carried out

for predicting the AE to be expected from the heating due to thermal expansion

from a laser pulse. Figure 7 shows the predicted AE versus an experimentally

measured AE waveform on 37.46 ram thick 2024-T6 aluminum plate. The effects of

thermal diffusion are too slow, even in aluminum, to be detected in the AE

signal. Thus AE from a laser pulse tends to be model independent, although

there are some small discrepancies which are still being investigated.

REFERENCES

1. J. A. Simmons, "New Results for Deconvolution and Signature Analysis of

One-Sided Time Series", in press.

2. H. N. G. Wadley, J. A. Simmons and C. Turner, "Predictive Modelling of

Quantitative Acoustic Emission Waveforms", Review of Progress in Quantitative NDE, Plenum Press, 1983.

S3
94

Figure

I.

Inference

transducer

response

figure

2

-

Unknown

-

transducer

response

for

mode 1

deconvolution

for

inodel

deconvolution

piobleiu.

problem.
o«

cl a

LUa

23

Z

O

Q»

aanuidwv

acninawy

Fiyure

4.

Deconvolution

estimate

for

Output

da

La

with

noise

for

"unknown"

transducer

response

Model

deconvolution

problem.

as

produced

from

cross-cut

algorithm.
o

(uiu) luauiaseidsiQ jBsujeA jaiuasidg

Q CM 9 o 9 o « c* C« (X *• 9

d d 6 O 6 O o d

aanmdnv ivui33ds

96

Figure

f>.

Spectral

plot

tor

deconvolution

Figure

6.

Predicted

AE

from

half-penny

estimate

in

model

deconvolution

crack

showing

effects

of

problems

.

moment

corrections.
Epicenter

Vertical

Displacement

(nm)

Time in Microseconds

Figure 7 Comparison of theory and experiment for laser generated AE in

2024-T6 aluminum.

97
POINT SOURCE TIME DEPENDENCE IN THE DETERMINATION OF ACOUSTIC EMISSION

GREEN’S FUNCTIONS

Alfred S. Carasso

Mathematical Analysis Division

Center for Applied Mathematics

and

Nelson N. Hsu

Mechanical Production Metrology Division

Center for Manufacturing Engineering

INTRODUCTION

In acoustic emission CAE) testing, it is often necessary to determine the

Green's function for an elastic structure experimentally. This involves

using a known point source with a prescribed time dependence, and detecting

the signal generated by this source (ref. 1). In the idealized case of a Dirac

6-function time dependence, the detected signal is proportional to the exact

dynamic Green's function. If a general arbitrary time dependence is prescribed,

however, the detected signal is a convolution of the Green's function with

the source time dependence. It should be noted that AE Green’s functions are typically not smooth; rather, they exhibit sharp discontinuities in their

time derivative, and these discontinuities carry information regarding the

times of arrival of various components of the solution (see Figure 1), As a rule, the convolution process smooths out these sharp features, so that the

detected signal bears little resemblance to the structure Green's function.

In that case, an ill-posed deconvolution problem must be carefully solved

in order to arrive at an accurate reconstruction of the Green's function.

While a Dirac 5-function time dependence is impossible to realize

physically, a smooth (/infinitely differentiable) time dependence of short

duration, concentrated near t = 0, can be realized. Such a function may be

viewed as an approximation to the Dirac 5-function. An important example is

the inverse Gaussian distribution (ref. 2), defined for all values of t by

k(a , t) =

2 tt t

c

if t < 0,

exp (- ) , t > 0,

where a is a fixed positive constant. See Figure 2. The size of c controls

the "duration" of the time function k(a,t), and convolution with k(<x,t)

smooths out sharp features at an increasing rate, the larger a is chosen.

Compare Figures 1 and 3.

98
DECONVOLUTION

The above kernel is intimately related to heat conduction theory and

deconvolution with such a kernel can be reduced to solving an appropriate

initial value problem for a partial differential equation in two independent

variables. This theory was previously developed by one of the authors

(.ref. 3). Applied to the acoustic emission problem, it offers the possibility

of a powerful and reliable algorithm for reconstructing sharp features in the

structure Green's function. Highly successful numerical simulations were

carried out on some typical AE Green's functions in recent computer-based

feasibility studies. Figure 4 shows the result of deconvolution of the

function in Figure 3 using the above algorithm; this should be compared with

the exact Green's function shown in Figure 1. Further work in this direction

is contemplated.

REFERENCES

1. N. N. Hsu, "A Mechanical AE Simulator for System Calibration and

Wave Form Analysis'1 16th Meeting of the U. S. Acoustic Emission

Working Group, Williamsburg, Virginia, October 1976.

2. M. T. Wasan, "On an Inverse Gaussian Process", Skandinavisk

Aktuerietidskrift , pp. 69-96, 1968.

3. A. Carasso, "Determining Surface Temperatures from Interior Observations", SIAM J. Applied Mathematics 42 , pp. 558-574 (1982).

99
0 1 2 3 4 5

tioe in rusecs

D

IS

P

L

A

CEnE

riT

Figure 1

.

Exact dynamic Green's function for a structure

.

D

IS

P

LA

C

E

n

ENT

0 1 2 3 4 5

:::e in nusecs

D

Is

p

LA

C

c

inCN

T

Figure 2. Inverse Gaussian time deoe.ndence with ~ = 0.5.

100
pi3fnoj>m«>Ho

0 1 2 3 4 5

I i i t i ,

S

D

IcP

L 4 A

C

£

£ 2

N

T

0

-2

0 1 2 3 4 5

Tine in nusecs

Figure 3. Convolution of Figures 1 and 2. Simulated detected Green's

function with c = 0.5.
CALIBRATION ACTIVITIES FOR AE TRANSDUCERS

F. Breckenridge

Mechanical Production Metrology Division

Center for Manufacturing Engineering

In January 1980, we implemented a calibration service for acoustic

emission transducers using surface pulses on the surface of a 2100-kg steel

block. A brief description of the calibration technique appears in the NDE

annual report for 1982. Since the inception of the calibration service, 352

calibrations have been performed on the steel block facility. Of these, 97 were performed for paying customers of the service, 73 were experiments having

to do with the calibration system, 155 werecal i brati ons of experimental

transducers, and 27 were for other laboratories at NBS.

As mentioned in the NDE annual report for 1982, a comparison was carried

out between the reciprocity calibration implemented at the Nippon Steel

Corporation in Japan and the NBS surface-pulse calibration. These results

indicated very close agreement between the two methods, and they were presented

to the Sixth International Acoustic Emission Symposium in Susono, Japan,

November 1982.

Further comparisons have been carried out between the Nippon Steel

reciprocity calibrations and the NBS calibrations. The new comparisons used

six different transducers, of Japanese manufacture, some of which were of a special type designed to have low response to Rayleigh waves. Comparisons were

made between the NBS surface-pulse type of calibration and the Japanese

Rayleigh type of reciprocity calibration and also between the NBS through-pulse

type of calibration and the Japanese longitudinal type of reciprocity

calibration. Figures 1 through 4 show the excellent degree of the agreement.

The previously noted systematic bias between calibrations on the steel

block done by surface pulse and those done by through pulse has been eliminated

in our recent and more careful experiments. In the more recent through-pulse

calibration experiments, the source is a capillary break on the bottom surface

of the steel block, and the transducer under test is located on the epicenter

of the source on the top surface. The force required to break the capillary is

measured and used to calculate the magnitude of the through-pulse waveform at

the location of the transducer under test. An experiment was done using the

standard capacitive transducer as the transducer under test, and, within the

limits of the estimated accuracy of the experiment, no discrepancy was indicated between the surface-pulse and the through-pulse calibrations. The

agreement between the through-pulse calibration and the longitudinal

reciprocity calibrations is taken as a further indication that the

through-pulse calibration is not biased.

Computer software has been written to enable the through-pulse calibration

to be used as a customer service.

102
The design of a secondary calibration system for users to transfer primary

calibrations (performed at NBS) to other transducers is in the initial planning

stage. Preliminary experiments indicate it should be feasible to use tone

burst signals on a steel transfer plate, and to electrically drive an NBS

conical transducer to produce the mechanical input for the calibration.

103
013:

RAYLEIGH 3 4-> 1 C •4* 3 o I 31 > u 3 •4— <3 3; s- i/i 4-1 <+- 3 r—

s- 3 •<— *3 </1 3 *— =

</) 4J 3 J- 3 u 3 yi T3 U

C3 2 C 3 .2

-3 4-1 -0 3) 31

r— i/l • f— 3 a a 2 3 O o O .-3 —

+3 •i« 5_ $_ >1

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(/» 3 3 3

•4—

u ct> 3 = 3>

(3

(/I 3 aC 3 2 ” *— >1 a 2. 3 3 — X o o 2. 3

CM2

s_3

104
NRIS

2215H.

610;

LONG I

TUD I

NHL

10-2-3,

013;

LONG 1

TUD 1

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(/I *3

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MIL-STANDARD ON ACOUSTIC EMISSION TRANSDUCER CALIBRATION

Donald Eitzen

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The Army Materials and Mechanics Research Center (AMMRC) has asked that

NBS assist them in developing a MIL-document describing a method for the

primary (and a later document on secondary) calibration of acoustic emission

transducers.

In working on this objective, internal and archival literature on the

NBS calibration method, the Nippon Steel Corp. method, the NBS Standard

Transducer, the NBS Conical Transducer, and Simulated AE Sources were reviewed in preparation for the writing of a procedural document for the

primary calibration of acoustic emission transducers. An outline for this

procedural document' has been developed. Portions of existing documentation

nearly suitable for the procedural document have been identified.

Drafting of a "strawman" document has begun and is proceeding well.

106
IMPROVEMENTS TO THE NBS CONICAL TRANSDUCER FOR

ACOUSTIC EMISSION MEASUREMENTS

Thomas M. Proctor

Mechanical Production Metrology Division

Center for Manufacturing Engineering

The original model of the NBS conical transducer, which received an IR-100

Award in 1981, had been shown to measure dynamic normal pi cometer displacements

in the range from tens of kilohertz to above a megahertz thus making it an ideal

transducer for acoustic emission measurements. The physical shape of the early

model was approximately a cylinder 25 mm high and 37 mm in diameter (see Figure

13 of last year's report). Significant size reduction has been accomplished.

The new version (Figure 1) has a backing that is filled with an absorptive mix

of copper and tungsten powders and epoxy. The back wave from the active element

is effectively dispersed by not only scattering as in the original models but

also by absorption. The response of this version is shown in Figure 2.

Because the high fidelity of these devices depends in part on the direct

contact of the small face of the active element, the problem of front electrode

wear has presented itself. Older versions of this device which had silver

plated electrodes have suffered from significant front electrode wear. We have

been able to recondition these transducers by replacing the front electrode with

evaporated nickel. Nickel not only forms a strong bond to the PZT element but

also has much better wear characteristi cs than the silver electrodes frequently

used on PZT elements.

Other protective layers have been developed. A few transducers have been

made that have a very thin steel shim (0.17 mm) cemented to the tip of the

conical element. Another method which has been successful is the use of very

thin (0.17 mm) lead shim between the transducer tip and the working surface.

These small shim pads are placed at the point where the transducer is to be

placed. They are not cemented to the tip but are used only once and thrown

away. A grease couplant is used on both faces of the shim. These protective

layers do degrade the flat response characteri Stic somewhat but their

performance is still quite good.

To satisfy requests from other laboratories and from the ASTM Acoustic

Emission Subcommittee for a secondary standard, a Standard Reference Material

project was undertaken for NBS to offer for sale standard AE transducers for

comparison purposes. The transducer design to be used is one commonly known as the polyhedron version which was shown in Figure 14, and its response in Figure

15, of last year's report. First versions of this device will be offered for

sale later this year.

107
The work begun last year on experimental measurements of the displacement

of a plate due to stress waves generated by a point force step function has

continued. The results of these experiments and a comparison with the plate

theory is described in a paper which has been submitted by 3reckenridge, Pao and

Proctor. These results are for a number of different source/recei ver geometries. The agreement is quite good; an example is given in Figure 3.

The NBS conical transducer is sensitive almost exclusively to motion

normal to the surface. It produces virtually no signal due to tangential

surface motion. However, much of the information that is contained in every

acoustic emission event is carried by the tangential component. Thus we have

undertaken the development of a transducer sensitive to tangential surface

displacements as a complementary element to the vertically sensitive NBS conical

transducer. Some progress in the development of a tangential transducer has

taken place this year. Figure 4 shows a promising candidate for a high fidelity

tangential transducer. Figures 5, 6 and 7 are, respecti vely , the theoretical

horizontal displacement on an infinite half space, the time response of the

transducer we are developing and the frequency response of this transducer as compared to the theoretical displacement wave form. The time response indicates

some ringing after the main large spike. This shows up in the frequency

response as minima at 300 and 1500 kHz. Work continues on improving this new AE

transducer.

Protective

Nylon

Skirt

Figure 1. Small version of NBS conical transducer.

103
MAGNITUDE

(

dB

Figure 2. Frequency response or the MBS conical transducer mocel

shown in Figure 1.

109
DISPLACEMENT

Figure 3. Measured and theoretically predicted surface displacements due

to a point force step function on a plate two thicknesses away

and on the same surface.

Figure 4. Horizontal displacement transducer (upside down).

110
Figure

b.

Theoretical

horizontal

di

splacement

of

Figure

b.

Waveform

measured

by

the

transducer

tiie

surface

of

a

half

space

due

to

a

shown

in

Figure

4

(compare

with

the

point

force

step

function.

theoretical

waveform

in

Figure

5).
MPIGNI

TUDE

(dB)

Figure 7. Frequency response of the tangential transducer determined

by comparing Figures 5 and 5.
A COMPARISON OF SIMULATED ACOUSTIC EMISSION SOURCES

M. P. Jones and N. N. Hsu

Mechanical Production Metrology Division

Center for Manufacturing Engineering

and

R. E. Green, Jr.

Material Science and Engineering Department

The Johns Hopkins University

Although the phenomenon of acoustic emission has been the subject of an ever-increasing number of scientific investigations and technological

applications for a number of years, it has not optimally fulfilled its

promise as a nondestructive testing technique since the precise

characteristics of the stress waves emitted from specific sources remain

unknown. In order to assure that a selected, experimental, acoustic

emission source-identification system can be successfully used to detect and

record the unknown waveforms of acoustic emission signals which are characteristic of real structural or microstructural materials alterations,

it must first be shown that the system is capable of faithful detection and

recording of waveforms produced under carefully controlled experimental

conditions which correspond to known theoretical waveform solutions.

One method of characterizing an acoustic emission system is to generate

a stress wave possessing known features and propagate it through the

structure being monitored. The distortion of the stress wave by the

structure and/or the sensors can then be ascertained by systematically

changing the structure or sensor while the source remains constant. Since

it is impossible at the present time to have a real acoustic emission source which is precisely reproducible and which can be generated at will,

simulated acoustic emission sources must be used. A prerequisite to

utilization of any simulated source is that its characteristics be

established and compared with real acoustic emission sources.

In the present work a well -characterized system was used to obtain the

dynamic force-time function at the source. The system consisted of an aluminum plate with sensor at the epicenter; the sensor measured the

vertical displacement of the surface of the plate. In this configuration,

the experimental and theoretical surface displacement waveforms were found

to be in excellent agreement when a glass capillary fracture was used to

approximate a step-force unloading source. Furthermore, the step-force

function was recovered from the detected signal using deconvolution

techniques. Two other sources approximating a step-force unloading were

also investigated. One of these was the fracture of a brittle pencil lead

and the other was a new type of piezoelectric transducer developed at the

113
National Bureau of Standards. The rise time, the time needed for each source to unload the plate, was approximately 0.1 us, 0.3 us, and 0.5 us

for the glass capillary, the pencil lead, and the pulsed transducer,

respectively. Three faster rise-time sources were developed using transient

local heating to generate thermoelastic stress waves. One source used a 50-

ns, 30-mJ Nd:YAG laser pulse. Another was produced when a 25-ns, 100-A

current was passed through a junction consisting of an electrode and the

plate. Finally, an electric spark was discharged directly onto the plate.

A discussion of all these simulated sources and the associated surface

displacement waveforms and their respective deconvolutions were reported at

the Ultrasonics International 33 Conference at Dalhousie University,

Halifax, Canada, July 1983.

114
A SIMPLE REAL-TIME AE SOURCE LOCATION SYSTEM

N.N. Hsu and M. Barsky

Mechanical Production Metrology Division

Center for Manufacturing Engineering

Flaw location by the acoustic emission (AE) technique has many

advantages. It is a real-time, whole-field, passive monitoring technique;

it can determine the location of an active flaw while the structure is under

load; and it requires relatively few sensors attached to the structure for

monitoring an area.

In an effort to optimize the effectiveness of the technique, we have

performed detailed system error analysis and found:

(1) available source location systems require a computer,

(2) computation and display of source location are computer time

shared with the acquisition and computation of other

AE parameters during the AE test,

(3) AE source location cannot be very precise unless the details

of individual waveforms of the detected AE are analyzed (the

uncertainty of dispersive wave speed of AE propagating in a structure contributes large errors to the source location

calculation), and

(4) the available computer based AE systems are not only

expensive but also inefficient as far as source location is

concerned.

From a systems engineering point of view and in many AE monitoring

applications, it is the rapid display of the approximate location of an AE source that is of greatest importance. Rather than refine the numerical

algorithm for computing the source location with time-of-arri val data of

limited precision, we resolved to maximize the effectiveness with minimum

cost. A prototype was designed, constructed and demonstrated. It

consisted of the following features:

(1) It uses a simplified algorithm for converting delta-time to

x-y coordinates.

(2) It monitors a square area with four sensors.

(3) It displays the location of an AE source in a 16x16 grid.

(4) It is self contained as a modular system.

(5) It was constructed with readily available low cost parts.

Details of the design were given at the June 33 AEWG Meeting and will

be reported in the open literature.

115
ACOUSTIC EMISSION IMAGING

S. J. Norton and M. Linzer

Metallurgy Division

Center for Materials Science

During the past year, an examination was made of the problem of recon- structing a two-dimensional random source distribution from measurements of

the emitted radiation recorded on the ci rcumference of a circle surrounding

the source region (ref. 1). An analytical inversion formula for the

two-dimensional random source problem and the analogous solution to the

three-dimensional inverse problem were derived. For tractabi 1 i ty, the analysis

was restricted to random sources that are spatially incoherent, i.e., where

the radiation emitted from distinct points in the source distribution is

statistically uncorrelated. Sources that can. be reasonably modeled as random

and spatially incoherent are common in nature. In optics, thermal or blackbody

sources are notable cases. Acoustic emission, arising from cracking or other

material transformations, sometimes satisfies these conditions. The importance

of the latter example derives from the fact that acoustic emission is often

an accurate indicator of the potential of a material to fail under stress.

Mechanisms that give rise to acoustic emission sources consistent with the

assumptions of a random and incoherent source model are distributed microcracking

and martensitic transformations.

Devaney (refs. 2-4) has shown how the far-field correlation function of

the radiated source field bears a multiple Fourier transform relationship to

the incoherent source distribution. This relationship is mathematically

analogous to the Born inversion procedure in inverse scattering, and is based

on the usual assumption that the radiation is recorded in the far field of

the source. In this study, closed-form inversion formulas were derived that

are valid for the near field, i.e., no far-field approximations are employed.

The derivation for the two-dimensional source consists of inverting an integral

equation with the aid of a Green's function expansion in a set of basis

functions suitable for the geometry of interest. An efficient method for

performing numerical reconstructions of the source intensity using the fast

Fourier transform algorithm was developed.

The three-dimensional generalization of the two-dimensional inversion

formula was also derived. The 2-D problem consists of reconstructing a 2-D

random source distribution from emitted radiation on a circular detecting

array surrounding the source region. The analogous three-dimensional problem

assumes a bounded 3-0 source enclosed by a spherical detector array. This

problem was solved by making use of Devaney 's observation (refs. 2-4) that the

inverse-scattering and inverse-source problems are mathematically similar

when the source is random and spatially incoherent. Under these conditions,

both problems reduce to solving integral equations of identical form. In the
corresponding 3-D inverse-scattering problem, a scattering region replaces

the source region and the elements in the spherical array are used as spherical

wave transmitters as well as receivers. Ball, Johnson and Stenger (ref. 5)

have recently reported a near-field solution to the inverse-scattering problem

in this spherical geometry. Their inverse-scattering solution was used to

solve the corresponding 3-D inverse-source problem.

A backprojection approach to the inverse-source problem was also investigated.

Although some approximations are made in generating the image, this technique

is more efficient computationally and less restrictive with respect to source

characteristics and transducer array geometry than the exact inverse-solution

outlined above. In this approach, the signals recorded by transducers surrounding

the source region are correlated pair-wise, filtered, and then backprojected

into image space. This process of filtering and backprojection bears some similarity to image reconstruction algorithms used in medical x-ray tomography.

The backprojection method may make it practical, for the first time, to image

acoustic emission sources and to detect acoustic emission signals below the

random electronic noise in the receiving system.

REFERENCES

1. S. J. Norton and M. Linzer, "Reconstructing Spati ally-incoherent Random

Sources in the Near Field: Exact Inverse Formulas for Circular and

Spherical Arrays", in preparation.

2. A. J. Devaney, "The Inverse Problem for Random Sources", J. Math. Phys.

20, pp 1687-1691 (1979).

3. A. J. Devaney, "Inverse Source and Scattering Problems in Optics", Qpti cs

in Four Dimensions - 1980 , Chap. 15, pp 613-626 (Proceedings #65, Am. Inst,

of Phys., New York, 1981).

4. A. J. Devaney, "A New Approach to Emission and Transmission CT", 1980 IEEE

Ultrasonics Symposium Proceedings , pp 979-983, Cat. No. 80CH1602-2.

5. J. S. Ball, S. A. Johnson and F. Stenger, "Explicit Inversion of the

Helmholtz Equation for Ultrasound Insonifi cation and Spherical Detection",

Acoustical Imaging , Vol . 9_, pp 451-461 (Plenum Press, New York, 1980).

117
ACOUSTIC EMISSION (AE) STUDIES OF RAPID SOLIDIFICATION

R. B. Clough, H. N. G. Wadley and R. J. Schaefer

Metallurgy Division

Center for Materials Science

Rapid solidification is a new technique used for producing metallic

glasses, which provide low loss transformer core material, and is also used

to produce superior surface coatings and long wearing bearing surfaces. AE can be used to monitor rapid solidification surface modification to detect

flaws produced during processing. It also promises to provide dynamic information on the solidification process itself, since a typical solidification

time for a surface melt is on the order of 10 ms and stress waves can be

monitored over considerably shorter times (~ 100 ys). Very little work

has been done in this area and due to the potential of AE to shed light on this subject, NBS and DARPA are sponsoring research on AE monitoring of rapid

solidification processing.

Two types of directed energy source are being used, an electron beam and

a Nd-glass laser.. The former can provide an energy pulse over 10 ms in

duration and the latter can have a pulse duration of about 100 ys to 5 ms. Metallographic examination was made of resolidified electron beam surface

melts of an Al/Cu (2219) alloy and a commercially pure (1100) aluminum. There

are no cracks in the resolidified 1100 aluminum, and very little AE during

resolidification. In contrast, there are numerous cracks in the 2219 aluminum

alloy, and large amounts of AE. This indicates that AE monitoring of electron

beam surface modification may be used for detecting cracking during processing.

As a partial explanation for such cracking, and/or plastic deformation; a preliminary stress analysis of rapid surface solidification suggests that

large tensile forces can be produced during cooling, which could generate

cracking and/or plastic deformation. Cracks can be formed or run into the

region directly outside of the melted layer, such as in the heat-affected

zone of the substrate. This is shown in Fig. 1, which depicts a typical

"mushy zone" microstructure in a resolidified layer of 2219 aluminum. A hot

tear can be seen to run down into (or out from) the heat-affected zone of the

substrate. Thus it is not surprising that the AE can be dependent on the

heat treatment of the bulk material as is shown in Table I. This variation

is presumably caused by differences in thermoelastic and plastic deformation

and/or cracking during cooling in highly stressed regions both within and

outside of the resolidified microstructure. To study such effects, it is

essential to eliminate experimental variability due to inadequate measurement

precision.

In order to minimize the variability in results produced by the measurement

system, an improved specimen holder has been fabricated which minimizes

rincdown and the influence of specimen geometry. This has been calibrated

(Fig. 2) with a Nd-YAG laser, yielding the result that the measured AE energy

(the sum of the squares of the signal voltages) is proportional to the absorbed

energy. An identical proporti onal ity holds true regardless of source type or

118
orientation, an advantage to using the energy approach. It is also possible

to use this method to make absolute determinations of source strength;

equivalent dipole moments are given for an Al/4% Cu alloy. This method, thus,

is a quantitative acoustic emission method.

AE has also been monitored during the drilling of holes by a Nrl-glass

laser in 2024-T4 aluminum plate. Here the AE energy from the entire process

is calculated and preliminary results indicate that AE energy increases

monotonically with hole depth. This is an important result, since there can

be a large variability in hole depth for a given set of laser control

parameters, which may be due to material variability, surface condition, or instabilities inherent in deep penetration. From these initial results, AE

shows promise for monitoring of laser drilling or surface modification, for

feedback control of hole depth or depth of penetration.

TABLE I

Acoustic Emission After Beam Cut-off as Affected by Substrate Material Condition

Material

and

Condition

Rockwell B

Hardness

AE Energy (Relative Units)

£a_< 1 .5x1 05 W/m C£>1 .5x10^ W/m Total

2219- 39 0.008 0.013 0.021

Solutionized

2219-T6 77 0.056 0.117 0.173

q

= absorbed heat flux

a = melt radius

119
Figure 1

0.5mm

*

/

Melt

> ' V v« *-•

:

-

•» • •» »

- . \ f-M ' i'- \ <J:

".

: \CV '

' A ’V ' Mushy Zone,

100m m

Substrate

Optical micrographs of 2219 aluminum alloy surface melted at

qa = 2.7 x 10^ WrrH showing detailed microstructure of the

region of the "mushy" zone at the bottom of the melt pool.

120
Absorbed qa, (W/m) x 10~7

.4 .6 .8 1.0 1.2 1.4 1.6 1.8

0 .1 .2 .3 .4 .5 .6 .7 .8

Dipole Moment/mNm

F i cu ra 2 Relationship between input energy end acoustic emission energy in

rapid solidification AE apparatus.

121
WEAR CONDITION MONITORING

A. W. Ruff, E. Whitenton

Metallurgy Division

Center for Materials Science

The principal thrust of this project is concerned with the application

of acoustic emission monitoring to wear under laboratory conditions. The

experiments are done under well -control led and simple conditions so that some

of the fundamentals of the phenomena involved can be identified. Actual

application in the future to real field conditions will involve much more complex conditions. However it is hoped that by achieving some basic

understanding of the phenomena, application in certain selected instances

will be possible. The problem being studied is that of delamination wear

under high stress, lubricated conditions. This wear process has been very

extensively studied (ref. 1), and involves the progressive development of subsurface cracks as a result of the normal applied load and surface tractions

due to friction. At some critical size, the crack propagates quickly to the

surface and a wear particle is formed. These particles can be 10 urn thick

and 100 um wide and long, in the case of steels. Since all but the final

stages occur below the specimen surface, a technique for monitoring crack

growth, such as acoustic emission, would be extremely useful. Some studies

of contact fatigue using acoustic emission have already been reported (ref. 2).

Studies have been carried out this year on a quenched 0-2 tool steel that

was intentionally treated to achieve low toughness. Studies on this same

steel (ref. 3) have characterized the emission resulting from hardness

indentations, so that some detail is known already. The wear test system

involves a block-on-ring geometry. The ring is machined to have a small bump

on the surface so that once in every revolution a load increment is applied

to the block specimen. This load increment should cause an incremental

advance in the subsurface cracks that are susceptible to growth. The signal

detection electronics are synchronized with the load increment so that observation of acoustic emission pulses can be done at the optimum time. The AE

system consists of a standard PZT detector, preampl ifier, amplifier, and

display oscilloscope. Built-in filtering restricts the system band pass from

100 kHz to 1.2 MHz. A number of experiments carried out on the 0-2 tool

steel have revealed pulses that correlate with some of the load increment

events. The pulses display a ring-down characteri sti c that is probably

determined by the specimen geometry. There are several possible explanations

for the sporadic nature of the detected emission pulses: (1) small emission

events may not be identified because of the noise level present, (2) crack

advance may not occur to the same extent on each load increment pulse, (3)

each crack advance event may produce basically different emission events. It

is also necessary to positively identify the detected pulses as originating

from subsurface cracks (even though they are synchronous with the load increment pulse). Subsurface metallography has been carried out on some of the

specimens and cracks are found. However it has not been possible to identify

the particular cracks that grow during the wear experiment. Metal lographi

c

subsurface studies are destructive to the specimen and preclude further wear
studies on the same block. Therefore another technique will be needed to

monitor the crack growth during wear. It is planned to use ultrasonic pulse

scattering methods to do this in a different test geometry, that of two

crossed cylinders. A new test machine has been obtained and will be instrumented this year. The AE detector will be mounted on the stationary 12.7-mm

diameter steel cylinder. The orthogonally mounted 12.7-mm diameter cylinder

rotates under lubricated conditions and at contact pressures over five times

larger than the block-on-ring system. These higher pressures should accelerate

the wear and crack growth processes. An ultrasonic pulse transducer will be

mounted on the end face of the stationary cylinder and should indicate changes

in crack size (area) durirrg the wear test. This additional source of information should overcome some of the interpretation problems experienced so far. These experiments will begin in FY84, and will be closely coordinated

with other efforts on acoustic emission and ultrasonic pulse characterization

at NBS.

A second thrust of the project concerns wear debris particle characterization

using ferrographic techniques. Efforts this year are concentrating on the

development of two standard reference materials for this method, and are funded by the Office of Standard Reference Materials. However, contact has

also been maintained with other laboratories doing these measurements. Two

methodologies have been developed by the Joint Oil Analysis Program laboratory,

Pensacola, FL, and the Air Force Materials Laboratory, Ohio. Interlaboratory

tests using these methods are being organized for the near future, and NBS

will participate in these. Based on those results, one consensus method may

develop for use by all DoD laboratories, and for possible standardization

through the SAE committee. NBS input to this process will be provided.

REFERENCES

1. Delamination Wear , N. P. Suh, editor, (Elsevier Pub!., 1977).

2. T. Yoshioka and T. Fujiwara, "A New Acoustic Emission Source Locating

System for the Study of Rolling Contact Fatigue," Wear 31 , 183-186 (1982).

3.

Private communication, R. B. Clough (NBS).
EDDY CURRENT STANDARDS

A. J. McAlister

Metallurgy Division

Center for Materials Science

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

nonferrous metals industries for nondestructive detection of flaws such

as cracks, inclusions, and variations in composition and microstructure

in metals and metal parts via local changes in electrical conductivity.

Primary conductivity standards are needed for reliable execution of this

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

necessary range of conductivity for industrial testing is from 0.585 to

58.5 MSm"! (1 to 100 percent I ACS).

The properties desired in a primary conductivity standard are long

term stability, durability, and low magnetic susceptibility. (In testing

of high susceptibility steels, normal practice has been to apply a saturating magnetic field to reduce the differential permeability to a value near that of vacuum.) Hence, elemental metals and alloys of

equilibrium phase composition, upon which stable nonconducting surface

layers can be formed, are desirable. The surface properties are important not only for durability, but for reproducible lift-off behavior

as well.

Our overall aim, the selection of metals and alloys and demonstration

of their suitability for primary conductivity standards is now essentially complete. Pertinent results are summarized in the following

table. Magnetic permeability is expressed as the difference in

permeability in units of the vacuum value and one.

Target Observed Magnetic

Conductivity Conductivity Permeabi 1 ity

{% IACS

)

Material (wt.%) Condition {% IACS) U/uq-1) Max

101 OFHC Cu annealed 101.9 * 0.1

unannealed 99.5 * 0.1

85 1.3 Zn + Cu as cast 81.1 * 1.0

+ 1 x 10"4 75 2.4 Zn + Cu 900 *C HT 70.4 * 1.0

60 A1 1100 F finished 60 * 0.05

48 A1 2024-0 finished 47 * 0.10

41.5 A1 6061-T finished 41.5 * 0.05

29 A1 2024-T-351 finished 29 * o.lO

23 21 Zn, 2.5 A1 + Cu 900 "C HT 20.5 * 2.0 + 8 x 10“5

23 3.0 A1 + Cu

17 7 A1 + Cu 900 *C HT 15.0 * 0.01 - 6 x 10-5

as cast 15.0 * 0.01

- 1 x 10-4 12 1.5 Si + Cu as cast 12.7 * 0.01

7 3.0 Si + Cu as cast 7.4 * 0.02 + 2 x lO-4

3.5 Ti , Grade 4 as received 1.9 * 0.02

1 6 Al, 4V + Ti as received 0.97* 0.005

124
The nonlinear spacing of target conductivities is necessitated by the

nonlinear variation of probe coil impedance with sample conductivity.

Commercial alloys in as-received condition proved suitable for the A1 and Ti

based standards. Observed conductivity variations over smooth surfaces of

these materials are adequately small and appear to be random. Magnetic

permeability is not a significant question with these materials, since

transition metal impurities do not carry a local moment in either metal.

High levels of transition metal impurity could result in the formation of

ferromagnetic compounds in A1 . However, as a practical matter, their

occurrence would be revealed in calibration as an apparent change of

conductivity with frequency. The higher conductivity and reduced

conductivity variation of annealed vs unannealed Cu is due to the removal of

cold work damage. Annealing did not improve either Ti or the Ti alloy.

The decision to focus on Cu-based alloys outside the A1 and Ti ranges,

and to prepare special melts, was not made lightly. As a practical matter,

it is essential that the magnetic permeability of an eddy current

conductivity standard be very close to the vacuum value. Only Cu-based

alloys are potentially capable of meeting this criterion in the needed

conductivity ranges. Special melts are indicated because current industrial

practice is to add significant quantities of Fe, Co, and Mn (which can develop full magnetic moments or form magnetic precipitates in Cu) as grain

refiners or to improve mechanical properties. Currently available

Si-bronzes contain 0.8 w/o Fe; Cupronickels, 1.0 w/o Fe; brasses, 0.05

percent Fe. Yet the brasses, for example, must contain less than 0.03

percent Fe if Fe precipitation is to be avoided during stress relief.

Cupronickels, otherwise attractive, were rejected because of the tendency of

Ni to form superparamagnetic clusters in Cu.

Castings (alloy additive content indicated in weight percent) of 1.3 Zn,

2.4 Zn, and 21 Zn + 2.5 A1 in Cu, and of 7 Al, 1.5 Si and 3.0 Si in Cu were made in-house. OFHC Cu and alloy additives of 99.995 purity or better were

employed. Due to the higher vapor pressure of Zn, the Qrasses were formed

by melting the components in sealed, He-filled vycor tubes; consequently,

the ingots were slow cooled. The Al and Si bronzes were melted in graphite

crucibles and quickly cooled. As the table shows, the brasses achieved

target conductivity and good magnetic permeability ratios, but showed

unacceptably large conductivity variation. This fault is due to porosity,

probably arising from the slow cooling. It should not be regarded as a disqualifying defect, however, since with appropriate commercial foundry

practice, using hot isostatic compaction if necessary, such porosity can oe avoided or eliminated. The bronzes performed quite well, electrically and

magnetically, in as-cast condition. Two ingots of 7 Al oronze were

prepared, one homogenized at 900 "C, the other left as cast. No difference

could be detected in their performance.

125
Magnetic susceptibility measurements were made in-house on five of the

Cu-based alloys by the Thorpe-Stenftle method. Pieces were sawn from the

interior of the ingots, etched, and stress relieved at 200 “C prior to

magnetic measurements. As indicated in the table, levels of magnetic

impurity in the starting materials are low enough to make standards quite

satisfactorily from the magnetic standpoint. Such impurities are present

however. Three of the samples were slightly paramagnetic; extremely pure

alloys would be slightly diamagnetic.

One final alloy, 3 A1 in Cu with target conductivity of 23 percent IACS,

is being prepared and will be tested as the last phase of this project.

126
TRACEABILITY FOR EDDY-CURRENT NDE MEASUREMENTS

George M. Free

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

The eddy-current project to develop nonmagnetic electrical conductivity

standards and to initiate a calibration service for electrical conductivity

standards is nearing completion. Measurement systems for both dc and eddycurrent measurements are in final form. The methodology of calibration

has been established and documentation is being completed. Standard

Reference Materials (SRMs) at various points in the range 1-100 percent

I ACS will be offered as the materials become available and we complete

the required certifications. The calibration service for electrical con- ductivity standards will be announced sometime in 1984.

The electrical conductivity calibration service and the certification

of electrical conductivity standard reference materials have a common factor:

the instrumentation developed to measure electrical conductivity. The

instrumentation consists of a direct-current measuring system by which the

dc conductivity of metal samples is determined. These metal samples then

become the primary conductivity standards at NBS. Using an eddy-current

bridge developed at NBS comparison is made between the primary conductivity

standards and either customer samples or SRMs to determine their electrical

conductivities.

The dc measurement system has been modified so that four-point measurements

can be made on small samples. The feasibility of using a four-point measurement

in conjunction with the relations betwen conductivity, sample resistance, and

sample thickness, i.e., the relationship developed by Van der Pauw, has been

tested. Measurements were made on aluminum discs. These samples were 2.0 cm

in diameter and varied in thickness from 0.15 cm to 0.6 cm. The resistance

of the test samples can be measured with an accuracy of + 0.01 percent of

value. The initial measurements were difficult to make due to noise in the

measurement system generated by thermal EMFs. To reduce this noise the oil

bath in which the test samples are submerged must have better temperature

stability and more uniform flow of oil past the contacts. A new temperature

controlled oil bath has been purchased and is now being tested for temperature

stability. The bath controls temperatures between 15°C and 30°C to approximately

+0.002 C. Over periods of 20 minutes the stability is +0.001 C. Future

measurements will be made in this bath. The accuracy of the dc measurement

should be improved by an order of magnitude. This improvement is possible

since resistivity is a function of sample thickness instead of sample crosssectional area. The smaller metal standards will be macnined using techniques

developed for making optical flats. The measurement of the thickness of the

standards will also oe improved.

127
Development work on the eddy-current bridge is focussed in two

areas; simplifying the measurement and increasing the frequency range

of the bridge. In the typical Maxwell inductance bridge there are two

sets of balances that must be made, the primary circuit balance (which

determines the values of R and L of the inductor) and the group circuit

balance (which reduces the error due to stray capacitance). To simplify

the measurement either the ground circuit can be eliminated or the

number of balances between the two circuits can be reduced. Both

approaches are being tested but at present elimination of the ground

circuit is not possible. The present approach is to match components

in the primary and ground circuits and use common inductive dividers

to drive the components. Using this scheme the measurement had been

greatly simplified. The main circuit is balanced, a slight adjustment is

made to the ground circuit at the highest detector sensitivity, and then a final balance is made of the main circuit. In most cases three circuit

adjustments are all that are necessary to obtain final balance.

To increase the frequency range of the bridge it was necessary to use new broadband operational amplifiers in the ground network. The bridge frequency

range has been increased so that it now covers the range 100 Hz to 100 kHz.

The final configuration of the ground circuit, to obtain minimum noise and

drift and high phase accuracy over the frequency range, is being completed.

The errors in the eddy-current measurement due to lift-off and coil

heating (which changes the resistance of the coil) have been reduced. A

sample holder has been built which automatically varies coil-to-metal

separation in increments of 0.1 urn. It is now possible to measure a standard

with a number of known values of lift-off. These measurements with different

lift-off settings become part of the calibration data. An algorithm has been

written to determine, from the measurements on the standard and on the

unknown being calibrated, what coil-to-metal separation is present in the

measurement of the unknown. The separation is then varied until it is the same

as the initial measurement of the standard sample. By interspersing measurements of the standard with measurements of the unknowns it is possible to

determine changes in coil resistance due to coil heating. These changes are calculated and corrections are then applied to all measurements. Measurement

repeatability is now at + 0.005 percent of value.

The following summarizes the principal accomplishments during FY83:

(1) The dc measurement circuit was modified to make measurements of resistance

at the 10 microohm level. (2) A holder for small metal samples was constructed

and the feasibility of making measurements using Van der Pauw's relationship was tested. The major sources of error in the new measurement were determined and

steps are being taken to eliminate them. (3) The frequency range of the eddy

current bridge was extended to cover the range of 100 Hz and 100 kHz. (4)

Measurements with the eddy-current bridge have been simplified so that in most

cases three adjustments of circuit parameters are all that are necessary to

achieve final balance at the highest sensitivity. (5) A new sample holder

has been constructed for eddy current measurement. Coil-to-metal separation

distance can be varied by increments of less than 0.1 micrometer. (6) A new

128
calibration scheme has been devised which incorporates the capabilities

of the sample holder. Measurement repeatability has been improved to + 0.005 percent of value. (7) A method has been devised to determine the

frequency error in the calibration of the test coil. This has not been

tested as yet. (8) A document on the measurement of electrical conductivity

by eddy currents, written for ASTM, has passed the main committee ballot and

will be published in the ASTM book of standards. (9) Documentation of the

dc and eddy-current measurement systems will be completed for possible

publication as a NBS Technical Note. CIO) 100 SRMs of conductivity 100 percent

I ACS have been certified. These will be issued as electrical conductivity

SRMs.

Plans for FY84 include Cl) Calibration of all primary standards using the new dc method. (2) Determination of temperature coefficients of primary standards

over a broader range of temepratures , i.e., 15-30°C. (3) Certification of a new SRM at the 1 percent IACS level. (4) Announcement of the calibration

service for eddy current conductivity standards. (5) Determine those ferromagnetic materials for which SRMs would have the greatest impact. (6) Initial

design of an eddy-current bridge for the calibration of ferromagnetic

materials.

129
EDDY CURRENT COIL CHARACTERIZATION

F. R. Fickett

Electromagnetic Technology Division

Center for Electronics and Electrical Engineering

The overall goal of this program is the development of experimental

techniques for accurate characterization of eddy current test coils and the

determination of the effect of various mechanisms, such as heat or mechanical

motion, on the coil signature. An important 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 work, the field evaluation of

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

rapid evaluation of coil performance and, in the second, a technique for

accurate mapping of the near-field of the coil. In this first year of the

program we have concentrated our efforts on the investigation of techniques to

evaluate the basic electrical parameters of prototype coils. Initial work

evaluating various field mapping techniques has also been done.

ELECTRICAL CHARACTERIZATION STUDIES

Measurements of the basic electrical parameters have been made on a variety of coils by several techniques that showed promise of capability for

precision measurement based on our preliminary study of the problem in FT 82.

We have made measurements with: 1) a lock-in detector system; 2) a vector

voltmeter; 3) a digital processing oscilloscope; and 4) a commercial digital

LF impedance analyzer. The major source of imprecision in all these measurements is the determination of the phase between the current and voltage

signals. Thus, part of our work has involved the investigation of low-inductance resistors and Rogowski coil devices. Calculations of inductance and

distributed capacitance have been made for conventional resistors, foldedstrip precision resistors, and a Rogowski coil. Inductances are on the order

of 3 nH for the conventional resistors and about an order of magnitude lower

for the other two. Capacitance values are in the nF range, not a problem for our work here.

The commercial LF impedance analyzer mentioned above should solve many of

these problems, at least over a limited range of parameters, but at the time

of this writing we have just taken delivery of the analyzer and are still in

the initial stages of evaluation. However, it appears almost certain that

this instrument will be the workhorse of the program in the next year.

Preliminary frequency dependence curves for impedance and phase shift of a surface- type coil, both with and without a ferrite core are shown in Figs.

1-2. Data for an encircling coil are shown in Fig. 3. The data from which

these were drawn should have a relative uncertainty of a part in ten thousand

on impedance and a part in a thousand on phase angle. These claims are under

evaluation.

Analysis of measurements made with the lock-in system led to that system

being removed from consideration because of a lack of phase accuracy and

stability, even when a precision phase option was incorporated. The vector

130
voltmeter technique was also discarded due to its lack of sensitivity at the

relatively low frequencies used in most commercial eddy current applications.

The digital processing oscilloscope is used in the configuration indicated

in Fig. 4. It offers the advantage of a waveform processing capability,

waveform storage, and noise reduction by software processing of stored signals. The system does have a limited frequency range and uses discrete values

which can contribute to zero-crossing errors. Lack of simultaneity of the

separate channels is a potential source of error as are phase shifts in the

input amplifiers. We have measured these shifts and incorporated the corrections into our data processing. The parameters of interest can be determined

from the acquired waveform data by two methods: integration of the product of

the coil voltage and a signal proportional to the current, or measurement of

the time between zero crossings of the two signals. In either case, the

ultimate accuracy of the measurement is determined by the total effective bit

capacity of the instrument. Development of software to control the processing, to account for variations in dc levels, and to accurately determine the

location of zero crossings has required a significant effort. Figure 5 shows

processed 10 kHz data from this system for the same coil for which data are shown in Fig. 2. Those data give a phase angle of 86.54 degrees. Our measurements indicate that, with further refinement, we can expect to achieve an accuracy of 0.040 degrees and a precision of 0.01 degrees under rather ideal

conditions and using 16 bit processing. This is well in excess of what would

be required in most commercial applications, but the apparatus is also far

more sophisticated than that available to most commercial operations. It is

still more than an order of magnitude less accurate than the phase calibrator

developed by the Electrosystems Division. We are refining the measurement and

the data processing software. We are also looking at higher frequency digital

oscilloscopes in hopes of extending the frequency range of our measurements

without serious degradation of accuracy, but some tradeoff is inevitable.

At this writing, a selection of commercial coils has been ordered and is

due to be delivered within a few weeks. The characterization of several of

these and determination of the effect of temperature on the electrical parameters of at least one will be completed before the end of the year.

MAGNETIC CHARACTERIZATION STUDIES

Determination of the best method to use for measuring the field configuration in the near-field region of a typical coil is another aspect of the

program. We have constructed a device that allows precise orientation of a subject coil in the vicinity of a detector. Measurements using conventional

small-area Hall probes are underway and a detection system making use of a Superconducting Quantum Interference Device (SQUID) has been designed.

Discussions are being held with M. Ma of the Electromagnetic Fields Division

regarding the potential for using a TEM cell (ref. i) for evaluation of the

coils. This system offers some Interesting possibilities, but it is more of a far-field device. However, it is still worth considering because of the large

amount of information that can be obtained with a relatively easy-to-operate

apparatus. Other techniques for microscopic measurement of ac and dc magnetic

fields are also being investigated such as the application of high-permeability

disk-reading heads and optical methods involving polarization by magnetic

stress.

131
INTERACTIONS

We have been increasing our familiarity with the problems of eddy current

NLE by attendance at the DARPA workshops and by interaction with industry, the

military, and universities. These interactions have been most productive and

have given us much information regarding the actual problems faced in the

day-to-day application of standard eddy current probes in industry and the

special problems associated with the more complex new probe designs.

Acknowledgment is due L. F. Goodrich, who assisted in much of the early

work on this project and has continued to serve as a helpful source of information on aspects of instrumentation.

REFERENCES

1. M. T. Ma and G. H. Koepke, "A Method to Quantify the Radiation Characteristics of an Unknown Interference Source," NBS Tech Note 1059 (1982).

132
IMPEDANCE,

kfl

IMPEDANCE,

flk

«

o

o

wa

a

•o

UJ* -Jo

z

<

UJ

CO<

z

CL

Figure 1. Impedance and phase shift of a surface— type coil measured as a function

of frequency in free space and in contact

with a high-conductivity copper sheet.

Figure 2. Free-space impedance and phase

shift for a coil of the same type for which

data are shown in Fig. 1, but with a ferrite

core. Note the higher values on the impedance axis.

90

60

-30

«

©

9

a

9

13

UJ

-Ia

z

<

Ul05<

Z

a.

90

-60

-|30

Figure 3. Impedance and phase shift data

for a coil of the encircling type, both

empty and containing a copper tube sample.

—*0

FREQUENCY, kHz 132

PHASE

ANQLi:.

dogroefl
Figure 4. Block diagram of the digital processing oscilloscope system. Phase

shifts due to the input amplifiers and the separate system channels are determined and corrected out with the processing software.

B20729 01x02303 O

K *req Shi -ft angl e Resi st Induct

Hz deg deg ohm henry

1 10020.27 0. 000 86.624 298.777 . 080443

2 10020.22 0.000 86.614 298.669 .oeoisi

10020. 17 0.000 86.568 304. 076 .080343

4 10020.22 0.000 86.393 301. 181 . 080403

3 10020.23 0.000 86.372 303.032 .080347

average 10020.22 0.000 86.393 301. 131 • 080383

upper 10020.27 0.000 86.624 304.076 . 080343

1 oxer 10020. 17 0.000 86.368 299.669 .080181

pts/wave 494.43 Ptm shi-f t 0.00

Vrms 2.691 Irms .000331

Figure 5. Typical data from the digital processing oscilloscope system.

These are taken at 10 kHz on the same coil for which data are shown in Fig. 2.

134
THEORETICAL MODELING IN EDDY CURRENT NDE

A. H. Kahn

Metallurgy Division

Center for Materials Science

The purpose of this project is to provide theoretical support for the

development and improvement of electromagnetic methods of NDE. The principal

activity in the past year has been the development of a theoretical model for

the detection of a surface crack in metallic material by the interpretation

of impedance signals in an excitation coil. Previous calculations of the

magnetic field in the vicinity of a crack had either neglected the role of the

dimensions of the exciting coil or had taken it into account in an approximate

way. In this work, a model was developed and computational methods assembled

which allow calculation of the impedance signal, taking into account coil

dimensions, elevation and position, and crack dimensions. The model used

gives the impedance per unit length of a pair of wires oriented parallel to a V-groove crack in the surface of a slab of metallic material. The calculations

may also be performed for the same configurations, but without a crack, and

the crack signal obtained by subtraction. The model is illustrated in Figure 1.

An example of the calculated fields in the absence of a crack is shown in

Figure 2, where the complex Poynting vector (energy flux) is plotted as a function of position on the surface of the slab. For the case illustrated,

the wire center separation and liftoff are both one skin-depth 6 (= 2/awu

where a is the conductivity of the test material, u is the angular frequency,

and u the permeability ). (For aluminum at 100 MHz excitation, 5 is 0.25 mm).

In the figure, the real part of the Poynting vector, corresponding to dissipative

loss, is marked by squares; the imaginary part, corresponding to inductively

stored energy flux, is marked by circles. With a crack present the curves

are modified, as may be seen in Figure 3, where the crack depth is 2.06 and

the opening is 0.5 (corresponding to 0.5 mm depth and 0.13 mm opening in the

example for aluminum). In Figure 4, the coil is positioned at 0.35 from

the crack center. These curves give a physical picture of the electromagnetic

fields and also show the quality of the level of approximation used.

From the calculations which produce the fields over the surface of the metal

it is also possible to obtain the impedance modification of the wires, which

is the principal measured quantity in a testing situation. From a series of

these calculations, the impedance was obtained for a scan of the coil over the

region of the crack. The results are shown in Figure 5, where the phase and

magnituqe of the impedance of the wires, per unit length, are shown as a function of distance, P, from the crack.

The extension of these calculations to cover a range of frequencies is now in progress. The results will be compared with the experimental and

theoretical investigations of Dr. C. M. Fortunko at NBS Boulder, and of Dr.

3. A. Auld of Stanford University.

135
D Crack Depth A Wire Separation

2F Crack Opening H Wire Elevation P Y/ire Position Relative

to Crack

Figure 1 Schematic drawing and nomenclature for the model used for the

calculation of eddy current crack signals.

Figure 2 Poyncing vector at the surface of a metal slab with no crack

.

Parameters are as described in the text. The real part (energy

loss) is shown by squares; the imaginary part (energy stored; by

ci rcles

.

-0 0
on

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cj jz

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13 7
C3 x ^ 3 -c0! t_ U O Xu

(J

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J= (J

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138
Impedance

(

)J

0

<ox

10' 2

)

Phase

Angle

-

(degrees)

Phase of Coil Impedance

Figure 5

Magnitude of Coil Impedance

Computed phase and magnitude of coil impedance as a function

coil center position, P.

129
HIGH-FREQUENCY, 3 ROADBAND EDOY-C’JRRENT PROBES FOR IMPROVED FLAW

CHARACTERIZATION

C. M. Fortunko, J. C. Moulder, J. Gerlitz, and A. C. Bennett

Fracture and Deformation Division

Center for Materials Science

and

3. A. Aula and F. G. Muennemann

Edward L. Ginzton Laboratory

Stanford University

INTRODUCTION

Eddy current techniques for nondestructive evaluation have been used in

industry for many years, but current practice is largely qualitative and

empirical in nature. Flaw identification and sizing usually are based on comparisons of the observed flaw signal with an atlas of measurements on kncv/n

flaws of the type expected. This approach has been dictated by the lack of a firm theoretical basis for inferring flaw characteristics f rom actual eddy

current signals. In recent years, however, theoretical interest in the eddy

current inversion problem has quickened, stimulated by the increased interest

in quantitative MCE that the concepts of f i tness-for-purpose and retirementfor-cause have engendered.

Progress in modeling the interaction of an eddy current probe with a flaw

has been rapid during the last five years, advancing from early studies of

idealized two-dimensional flaws in a uniform field (ref. 1) to recent detailed

analyses of three-dimensional flaws interrogated by a nonuniform probe field

(refs. 2,3). The acvances in theory have led to the design of procecures for

extracting flaw parameters from mul tipcsiticn . mu I ti frequency eddy current

data and have created a need for critical experimental measurements to verify

model predictions.

The present collaboration between N3S and Stanfcrc University was begun

last year in order to address the need -or measurements of eddy current flaw

responses to verify theoretical predictions. The work at Stanford nas focused

on theoretical modeling of flaw responses as a function of flaw parameters,

probe geometry, material properties, and frequency of operation, as well as experimental measurements at very high (microwave) frequencies . The NES

effort has been directed towards developing arc characterizing new highfrequency, broadband eddy-current probes. Curing F'r£2, a broadband probe

design was developed and a prototype version was constructed an c used to make

measurements on a series of well character! zee calibration specimens. The

theoretical model and the results of these preliminary measurements are summarized in reference 3.

140
During FY83, N8S efforts emphasized further development and

characterization of broadband eddy-current probes and new experimental

measurements. Specific accomplishments this year included: 1) a coil-winding

fixture was developed that improves considerably our ability to fabricate

eddy-current sensor coils; 2) a computer model for the broadband probe was devised and used to optimize and characterize the probes; 3) two new eddy-current probes were developed covering the frequency range of 100 kHz to

1 MHz and 20 to 80 MHz; 4) the eddy-current apparatus was improved by

interfacing it to a digital voltmeter controlled by a hand-held computer; 5) a series of measurements were made on an Inconel 718 calibration specimen

supplied by Rockwell International to verify and characterize the

high-frequency probe response. Progress in these areas is described below.

BROADBAND EDDY-CURRENT PROBE DEVELOPMENT

A novel coil -winding fixture was developed to facilitate the fabrication

and matching of flat, spiral-wound, pancake coils for eddy current probes.

The fixture considerably reduces the amount of time required for fabricating a coil and produces flat, uniform coils reproducibly from smaller gauge wire

than it was possible to use with previous manual techniques. The fixture has

made it possible to produce coils of sufficiently high impedance (10-50 ohms)

that transformers are no longer required to match the coil impedance to the

input impedance of the four-port hybrid, resulting in a significant

simplification of the hybrid design. The possibility of patenting this

coil -winding fixture is currently being explored.

A significant improvement was made in the design of the four-port hybrid

used as the inductance bridge for the broadband eddy-current probe. By

optimizing the inductance of the balun transformer, it was possible to

minimize the inherent imbalance signal while maintaining sensitivity to flaw

signals. Optimization was accomplished through the use of extensive computer

simulations described below. A circuit diagram of the improved broadband

eddy-current probe is shown in Figure 1 . Using the new design, a new high-frequency eddy-current probe was constructed for operation in the 20 to

80 MHz band. This new probe is particularly well suited for detecting very

small flaws in highly resistive materials such as Inconel 718. In addition to

the new high-frequency eddy-current probe, a new four-port hybrid was constructed for use with commercial eddy-current probes in the 100 kHz to 1 MHz frequency range.

In order to efficiently design and characterize broadband eddy-current

probes, it is advantageous to have a model of the probe circuit that can predict the response of the probe to changes in such circuit parameters as coil impedance, component values, or frequency of operation. Unfortunately

,

the circuit is too complex for an analytical approach to be tractable, so that

numerical modeling is required. Although there are several commercial circuit

analysis programs available for laocratory minicomputers, these programs

invariably use a form of nodal network analysis not readily adapted to

transformer circuits. So an effort was undertaken to develop a simplified

circuit model that could be solved with standard numerical techniques.
The lumped-parameter circuit model that was developed is shown in

Figure 2 . Several simplifying assumptions were made in order to make the

problem more tractable. Using Kirchoff‘s law to write the loop equations for

the 4 currents shown in the figure yields the following complex matrix

equation:

^1 + *2 + Z3 + R

0

) J«(M2 + Hj) (z

3 * R

0

) -1

0 “ V

«' z2

* Z

3

) Z

3 j.(m

2

0

*

l z j«(M

2 + Z

3 (Zj + Z

3 + R

0

) <*0 + -wy Vo h

(Z3

R0

> J.IMj Aj) (R

0 J-Mj) «2 * z5 * 2R„> _

V o_ U_

This equation is readily solved with standard methods for the four unknown

currents, given the appropriate values for the impedance matrix and input

voltage, V . The output voltage of the probe may then be found from the

expression 0

V

1

i 4

) r 0

( 2 )

A computer program was developed to solve Equation 1 by Gauss-Jordan

elimination. Inputs required for the program are the measured impedances of

actual circuit components and the input voltage. By holding the impedance of one coil fixed while varying the impedance of the other coil and solving

Equations 1 and 2 iteratively, the probe response to a simulated flaw may be

determined. The results of two such simulations, are shown in Figure 3 .

EXPERIMENTAL MEASUREMENTS

In order to verify and characterize the performance of the new highfrequency eddy-current probe, a series of measurements were undertaken on a calibration specimen of Inconel 718. Each measurement was repeated 15 times

to provide adequate data for statistical analysis. In addition, it was hoped

that the data would prove useful for verification of theoretical predictions

in the important region of a/5 = 0.5 to 1.5, where a is the flaw depth and 5 is the skin depth.

The experimental apparatus used for these measurements was essentially

the same as that used last year. In order to improve the precision of the

measurements, a digital voltmeter controlled by a hand-held computer was used

to monitor the analog output of the vector voltmeter. The use of the handheld computer also facilitated data analysis.

The calibration specimen used in the experiments consisted of an Inconel

718 bar, 13 x 75 x 300 mm, with a number of slots el ectro-discharge machined

into one surface. Three flaws were chosen for the measurements; the flaw

dimensions are given in Table I. The specimen was prepared by the Rocketdyne

Division of Rockwell International and loaned to NBS for this study by Mr. J.

L. Nummelin.

142
As discussed in last year's report, the new broadband eddy-current probe

does not include any provision for nulling the bridge circuit. Thus, the

probe has an inherent imbalance signal, even when placed over unflawed metal.

When the probe is placed over a flaw, the output signal is the sum of this

bridge imbalance and the actual flaw signal. In order to determine the flaw

signal, it is therefore necessary to independently determine the bridge

imbalance so that it may be subtracted from the composite signal. The

following procedure was developed for making measurements on the Inconel

specimen. The composite signal is obtained by centering one of the

eddy-current sensor coils over a flaw using fiducial marks on the probe and

the specimen. The probe is firmly clamped in place and measurements taken at

the target frequencies. The probe is then removed from the flaw, repositioned

in a good area adjacent to the flaw, and reclamped. Measurements are then

taken at the same frequencies to obtain the bridge imbalance signal. The

entire procedure was repeated 15 times in order to establish the

reproducibil ity of the measurements. The liftoff signal was determined in

separate experiments by inserting a series of spacers under one of the

eddy-current coils and measuring the output of the probe at the target

frequencies.

The data for each frequency were analyzed by averaging the 15 bridge

imbalance measurements to obtain an average bridge imbalance signal. This

average bridge imbalance was then subtracted vectorially from each of the

composite "flaw plus imbalance" signals to obtain 15 independent measurements

of the flaw signal. These 15 flaw signals were averaged to yield the average

flaw signal. All averages were computed by separately averaging the in-phase

and quadrature components of each signal.

The results of this series of measurements are shown in Table II,

together with the liftoff phase angle. The results clearly show the ability

of the probe to detect very small flaws in highly resistive material, such as Inconel 718. Unfortunately , the depth-to-width ratio is too close to unity

for these flaws for a meaningful comparison with theoretical predictions, as

is evidenced by small angles between the liftoff phases and the observed flaw

signal s

.

THEORETICAL MODELING

As mentioned in the introduction, there has been rapid progress recently

in theoretical modeling of two- and three- dimensional flaws interrogated by

non-uniform probe fields. All such models require as an input a detailed

description of the probe magnetic field distribution in both phase and

amplitude. Such a field distribution is highly dependent on a number of

parameters which are independent of the physical and electrical characteristics of the probe, e.g., conductivity of the test piece, probe liftoff,

operation frequency, etc. For this reason, much of the theoretical effort

during FY83 was directed to the development of a rationalized calibration

scheme, together with analyses which allow the computation of probe fields

under different circumstances. This procedure requires only the distribution

of the probe's tangential magnetic field on a single liftoff plane, measured

(or calculated) in air, to compute magnetic field distributions for any

143
liftoff and test sample conductivity. Such a procedure is also very valuable

in the probe calibration effort, since it provides a basis for reproducible

measurements which can be made on a variety of different samples.

Fourier methods were used to perform this calculation. First, the

tangential magnetic field is transformed to the two-dimensional Fourier

domain; each spatial frequency component of this transformed field is then

multiplied by a propagation factor of the form

exp[-k (zg-z^] (3)

where k is the magnitude of the spatial frequency, and z. and z2 are respectively the measured and desired liftoffs. To accommodate^samples having

different conductivities, one also multiplies by a reflection factor, (1 - r),

which is given by

r(k) * o>u[ur^uc“k^] (4)

For most metals, this can be expressed in terms of the skin depth, 5, as

r(k) = [2/ 16] [1 + k

2

S

2

]

1/2

. (5)

The resulting field distribution is the spatial transform of the original

field, but in a new reference plane and in the presence of a conducting plane.

A two-dimensional inverse Fourier transform is then performed to recover the

actual field.

A preliminary test has been performed on this numerical procedure. The

magnetic field distributions for horizontal and vertical dipoles were calculated, using an analytic formula for the spatial-transform field, for a given distance from the point dipole source. These were then transformed,

using the above procedure, to a different plane, and the result compared to

the value calculated directly from the analytic formula. These were in very

good agreement, showing only numerical round-off errors. The comparison for

the full transformation procedure is presently underway.

One limitation with this theory is that the transformed liftoff distance,

z

2

, must be larger than the measurement liftoff z.. It is therefore most

advantageous to make calibration measurements as close to the probe as possible.

FUTURE STUDIES

From the results of this year's work, several areas that would be

fruitful for future work have been identified. First, in order to facilitate

the comparison of experimental measurements with theoretical predictions, it

will be necessary to make measurements on flaws with much higher

depth-to-width ratios, perhaps actual fatigue cracks. Second, a means to

calibrate the probes is required so that the actual flaw impedance may be

determined from measured flaw signals. Third, since eddy current inversion

protocols involve multiposition, as well as multi frequency, data, it is

144
necessary to systematically study the probe response for various probe-flaw

configurations to understand in detail the probe behavior in the scanning

mode.

REFERENCES

1. A. Kahn, R. Spal , and A. Feldman, "Eddy Current Losses Due to a Surface

Crack in Conducting Material," J . Aopl . Phys . 48 , pp. 4454-445S (1977).

2. B. A. Auld, F. G. Muennemann, M. Riaziat, and D. K. Winslow, "Analytical

Methods in Eddy Current NDE," in Review of Progress in Quantitative

Nondestructi ve Eva! uation , (D. 0. "Thompson and D. £. Chimenti , eds.),

pp. .363-368 (Plenum, 1982)

.

3. F. G. Muennemann, B. A. Auld, C. M. Fortunko, and S. A. Padget,

"Inversion of Eddy Current Signals in a Nonuniform Probe Field," to be

publ ished.

Table I. Flaw

spec

dimensions for rectangul

imen.*

ar E.D.M. notches in Inconel 718

Flaw Number Lenath Depth Width

mm (in) mm (in) mm (in)

A - 1 6.396 (0.2518) 0.1245 (0 .0049) 0.0314 ( 0 .0026

)

A - 4 2.619 (0.1031) 0.1270 (0 .0050) 0.0940 (C .0027)

A - 7 1.298 (0.0511) 0.1168 (C.CG46) 0.0965 (0.0028)

* Measurements made by A. Smith, Rocketdyne Metrology Lab.

1^5
Table II. Average flaw signals for three rectangular E.D.M. notches in an Inconel 718 specimen. Flaw dimensions are given in Table I.

Average Flaw Signal

Frequency

(MHz)

Flaw Number Magnitude

(mV)

Phase

(deg.)

Angle to liftoff

(deg.)

20 A-l 0.044 66.3 5

A-4 0.045 70.6 0

A-7 0.029 74.0 -3

25 A-l 0.032 167.7 3

A-4 0.041 164.6 6

A-7 0.030 165.3 6

30 A-l 0.053 164.9 5 A-4 0.063 161.2 9

A-7 0.046 162.1 8

35 A-l 0.061 169.5 -7

A-4 0.086 154.0 8

A-7 0.067 153.6 8

40 A-l 0.187 150.8 -3

A-4 0.227 140.5 7

A-7 0.158 142.9 5

I

146
Figure 1 Improved broadband eddv-cu»*rent nynK. a T

] and T

2 are identical transformers^recl^TM

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2 ^ the edd^*currsnt

and i- is the balun transformer "

, P rect> ion-wound on ferrite ccr=s‘

voltage is supplied to ?he TMoo~ nri X“nd ? a ferr1te we. Excitation

the A-port.

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, '

I gu r s 2 . Lumped-oaraner Lumped-paranerer circuit model for the broadband eddy-r urr*-- c(VM preceedmg ngure. y — D '- C6 s.ncwn n
<aw) 3o*i”ioa indino 3“!3Nd 3S*Hd indino

£

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148

Figure

3

.

Results

from

computer

simulations

of

broadband

eddy-current

probes.

(A)

Results

obtained

using

original

design

parameters.

(B)

Improved

response

obtained

after

optimizing

design

parameters.

Sensitivity

of

the

probes

is

proportional

to

the

slopes

of

the

response

curves.
ELECTROCHEMICAL NOISE

Ugo Bertocci

Metallurgy Division

Center for Materials Science

Localized corrosion is a serious practical problem caused by the

breakdown of the passive film, and affects most corrosion-resistant

materials. Its detection is often difficult, particularly at an early

stage. Electrochemical noise analysis, that is, the analysis of the random

fluctuations in electrochemical cells, has shown promise to become a method for observing film breakdown, since there is correlation between

the amplitude of the noise and the magnitude of the localized corrosion.

The method might have applications for monitoring the onset of localized

corrosion and for the study of the stability of protective films. At the

present time little is known on the sensitivity of the method or on its

applicability to different corroding systems.

Over the past year, a study has been made of the breakdown of the

passive film on aluminum in neutral solutions. The stability of the film

was checked by measuring the fluctuations of the passive current in the

absence and in the presence of chloride ions at different potentials. The

results obtained are quantitatively similar to those obtained for Fe-Cr

alloys, since breakdown was detected only where Cl" ions were present.

This indicates that this method can be applied for the monitoring of

passivity breakdown also in the case of A1 . Current transients during

the induction period were recorded, together with their amplitude spectra.

The amplitude of the transient is quite small, of the order 10 to 30 nA,

and the slope of the spectra is consistent with repassivation times of the

order of one second.

The relationship between noise amplitude and degree of localization

of anodic attack has been investigated. The correlation between localized

attack and the NDE method of measuring electrochemical noise levels, and

the independence, on the other hand, of noise amplitude or the rate of

anodic dissolution was confirmed by measurements during the transpassive

dissolution of glassy Fe-Ni-Cr alloy, which has no tendency to pitting;

very low current noise was observed even when the anodic dissolution

proceeded rapidly at more than 1 mA/cm^. An alloy of the same composition

but in crystalline form, which is subject to localized attack, showed a much higher level of current noise. In the course of this research,

characteri zation of the electrode behavior by measurement of the ac impedance was carried out employing white noise as input signal with

excellent results. These measurements, giving both the real and imaginary

parts of the electrode impedance, were taken both in passive and in

transpassive conditions, and ranged from 24 mHz to 5 kHz, showing that

white noise is a convenient means for ac impedance measurements.

149
OPTICAL NDE: LIGHT SCATTERING

G.S. White

Inorganic Materials Division

Center for Materials Science

Light scattering measurements have been made upon grooves with

trapezoidal cross sections in order to determine if the observed scattering

could be described by a simple Fraunhofer calculation and to compare the

observed scattering with that from grooves of simple cross section (shallow

rectangular and V-shaped)

.

The simple Fraunhofer approach which worked well for describing

scattering from the shallow rectangular groove (ref. 1) has not been amenable

to expansion to the trapezoidal case. The calculated scattering has

consistently been more complex than the observed scattering, although the

envelope of the calculated scattering has approximated what is observed. It

appears that the model used is too local for it to provide realistic

scattering. Because the narrow two trapezoids have dimension A = 50 um, a = 20.2 um, h = 21 um, and A = 68.9 um, a = 21 um, h = 27 um, where A and a are the top and bottom widths of the trapezoid, respectively, and h is the

depth, these two grooves lie in or near the resonance domain. In this region

where the dimensions of interest are about the same as the wavelength being

used, a local theory would be expected to be inadequate. The vector theory of

Maystre (ref. 2), developed for the resonance domain, describes the observed

scattering much more closely although discrepancies remain. As shown last

year in the work with the V-shaped grooves (ref. 3), most of the discrepancy

can be attributed to variations in the precise shape of the trapezoid cross section over the region of illumination. This is a combination of the

Gaussian cross section of the incident beam and the departure from ideal

uniform groove shape of the trapezoid. The latter is caused, not only by

variations in A, a, and h across the illuminated area but also by metal

displaced during the grooving process and left piled up along the length of

the groove. As has been shown, this metal residue does not alter the number

or spacing of the diffraction peaks but can change dramatically the relative

peak heights.

Comparison of the scattering from the trapezoidal V-shaped grooves and

shallow rectangular grooves produced clear differences. The scattering from

the shallow rectangular groove was identical to that from an ideal single

slit. Scattering from the V-groove produced a much different pattern with

large narrow maxima at small angles, small maxima next and intermediate

height, broad maxima at the largest angles. These large angle, large maxima

must result from a combination of diffraction effects with specular scattering

from the angled walls of the groove. However, because scattering in the resonance domain must be treated by fitting solutions to Maxwell's equations

across the entire region of interest, it is clear that assigning specific

scattering features to specific features of the groove is impossible. The

trapezoidal groove produced scattering which appeared to be a combination of

the other two patterns, due possibly to the fact that the trapezoidal shape

contains flat regions corresponding to the rectangular groove and slanted

150
walls corresponding to the V-groove. Most interesting, however, is that these

patterns seemed to scale with groove size. That is, a narrow trapezoid

produced a scattering pattern clearly more closely related to that from a large trapezoid than to that from a narrow V-groove. Since the narrow grooves

are in the resonance domain while the wider grooves are approaching the

geometric scattering region, this scaling feature is somewhat surprising and

is not yet understood.

REFERENCES

1. G.S. White and A. Feldman, "Diffraction from a Shallow Rectangular

Groove," Appl. Opt. 20 , No. 14, pp. 2585-2589 (July 1981).

2. D. Maystre, "Scattering from Perfectly Conducting Rough Surfaces in the

Resonance Domain," IEEE Trans. Antennas and Propagation, submitted for

publication.

G.S. White and J.F. Marchiando, "Scattering from a V-Shaped Groove in

Resonance Domain," Appl. Opt., 22 , No. 15, 2308-2312 (Aug. 1, 1983).

3. the
OPTICAL MEASUREMENT OF SURFACE ROUGHNESS

E.C. Teague, T.V. Vorburger, F.E. Scire, D.E. Gilsinn,

and M.J. McLay

Mechanical Production Metrology Division

Center for Manufacturing Engineering

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

the U. S. and the rest of the world to use light scattering

rather than the traditional stylus instrument for nondestructive

evaluation of manufactured parts. The theory of light scattering

from surfaces whose irregularity heights are comparable to and

larger than the wavelength of the light is more difficult and

much less developed than that for highly polished surfaces.

Light scattering has therefore been used primarily for comparison

measurements of surface roughness. Our work has been directed

towards building the experimental capability and theoretical

expertise to investigate the behavior of light scattering

measurements in terms of their use for both comparator and

absolute determinations of surface roughness.

Our apparatus for performing angular distribution measurements,

Detector Array for Laser Light Angular Scattering (DALLAS), has

been described in previous ONDE annual reports. During the past

year we have been analyzing the first sets of data and seeking to

interpret^ the measured angular scattering distributions in terms

of surface roughness properties, as determined by stylus

measurements, and in terms of theoretical models of the

electromagnetic scattering processes. Towards this end we are

performing both direct and inverse scattering calculations.

In the direct scattering approach, the optical angular distributions and stylus roughness profiles are measured for the

same rough surface. Typical angular distributions for lapped

stainless steel surfaces are shown in Figure 1 . The corresponding stylus profiles of these surfaces are shown in Figure 2. A

theoretically predicted angular distribution is then calculated

by substituting the digitized stylus profile into the integrand

of an optical phase integral calculation based upon a simplified

Kirchhoff solution for the scattering of electromagnetic waves,

ref 1 . Although the calculation involves only elementary scalar

theory for optical scattering, the agreement between experiment

and calculation is fairly reasonable.

Figure 3 shows one comparison. The data, solid line, which show

scattered light intensity vs. scattering angle, were taken for a highly two dimensional specimen with a roughness of 0.20 pm, as measured with a stylus instrument. The angle of incidence was

+30 degrees. Theoretical intensity values were calculated for

the 87 angles that correspond to the angles of the detectors for

DALLAS. Each calculated intensity value was obtained by

averaging over 3even closely spaced scattering angles within the

angle subtended by the detectors of DALLAS and ten surface

profiles

.

152
The calculations in Figure 3 were performed after we had first

attempted to obtain agreement between theoretically predicted and

measured angular distributions for surfaces that were slightly

three-dimensional in nature, i.e., surfaces with randomly shaped

grooves that had a dominant direction but with some directional

randomness. We have not yet been successful in obtaining a procedure to account for the directional randomness of these

surfaces

.

Agreement between theory and experiment for the inverse approach

has not been as good as for the direct calculations. Here we

attempt to calculate the rms roughness parameter Rq and the

autocorrelation length T of the scattering surface. The

calculation proceeds by assuming that the surface may be

described by a statistical model characterized by these two

parameters; a Gaussian height distribution function and an exp(-

x/T) autocorrelation function are assumed. A two-parameter nonlinear least squares fit between the measured and theoretical

angular distributions is then calculated. Figure 4 shows the

relatively poor agreement between the data and the calculated

results which have been obtained with this model of this surface.

The results, therefore, strongly suggest that the model is inappropriate for this surface. This is borne out by the fact that

the autocorrelation function for this surface, as computed from

stylus profile measurements (see Figures 5 and 6), is quite

different from the exponential form assumed in the model.

Our plans for future work are to explore the use of more complex

models of the surface topography, to explore alternative means

for solving the inverse problem and to compare the direct

scattering results obtained with different models for the electromagnetic scattering processes. Specific models to be compared

are the Beckmann-Spizzichino model (used in the work described in

this report), May st re-Meecham projection distance approximation,

Rayleigh model and possibly the geometric optics slope model for

the larger roughnesses. Our work this year has clearly shown

that, for scattering from rough surfaces, attempts to practically

solve the inverse scattering problem must iteratively improve

upon both the direct scattering model and the algorithm used for

obtaining its inverse.

REFERENCES

1. P. Beckmann and A. Spizzichino, The Scattering c f

Electromagnet ic Waves from Rough Surfaces (Pergamon, New York,

1 963 ) .

153
Intensity

Scattering Angle

Figure 1. Angular scattering data for three lapped stainless steel

specimens. The angular distributions are normalized so that

each has the same total intensity. The total intensity is

obtained by summing the signals from all the de rectors. Note

that the intensities are plotted on a logarithmic scale.

i r i r

OJ

1 mM 0.06 um Ra

id

! yjir*" ”

0.24 um Ra

u

I I 0 100 200 300 400 500 600 700

Distance (^m)

Figure 2. Stylus profiles of the surfaces used for the angular

scattering measurements shewn in Figure 1.

154
Fi gure

F i gure

Scattering Angie

Comparison between theory and experiment for direct scattering

calculation. The scattering surface haa a roughness of 0.20

micrometers, as measured with a stylus instrument, and was a highly two-dimensional surface with a profile and an autocorrelation function as shown in Figures 5 and 6, respective

ly. The distributions were normalized in the same way as those

in Figure 1.

Scattering Angie

4. Comparison between theory and experiment for inverse calculation

optimized two-parameter fit. The scecimen surface 'was the same one used for the direct calculations shewn *n Figure 3.
f

Figure 5. Stylus profile 0 f surface used for calculations of Figures 3

0 100 200 300 400 500

Figure 6.

Shift Distance l^m)

Autocorrelation function for the surface usee for the direct and inverse calculations shown in Figures 3 and 4.

136
HOLOGRAPHIC NONDESTRUCTIVE EVALUATION

Charles M. Vest

Department of Mechanical Engineering and Applied Mechanics

The University of Michigan

During this year our exploration of the applications of optical holography

to nondestructive evaluation was continued. This program was initiated a few

years ago by preparing an extensive evaluative review of the technical literature of holographic nondestructive evaluation. Based largely on the results

of that review a number of experimental investigations have been carried out

in the areas of quantitative nondestructive evaluation and flaw detectability.

During the past year we emphasized three areas. The first area was the use of

moire techniques to enhance flaw detectability, the second area was development

of a real-time technique for simultaneously measuring displacement and tilt in

the neighborhood of a point on an object surface; the third area was updating

of the evaluative literature review.

Two-exposure holographic interferometry produces a fringe pattern

indicative of the surface displacement of an object. In its application to

nondestructive evaluation, the presence of a flaw can be noted by comparing

the fringe pattern produced by the flawed object with that produced by a nominally identical object with no flaw. Often, the defect may include only

a small perturbation of the pattern and, therefore, it may be difficult to detect.

Moire phenomena can be used to detect small pertu-rbations in periodic patterns.

If we superimpose a transparency of the interference fringe pattern of a flawed

object upon the inteference pattern of a similar, but flaw-free, object, a moire pattern can be formed that is indicative of the presence of the flaw.

In a typical interferogram, the fringe pattern varies over the surface of the

object, so the application of moire techniques to flaw detection is less

straightforward than application of these techniques to error detection in

gratings that have constant periods. In particular, the clamping and stressing

of the test and the flaw-free objects must be nearly identical if ambiguous or confusing moire patterns are to be avoided. In holographic nondestructive

evaluation this is difficult to achieve. However, a practical testing scheme

should present a clear indication of the flaw, unencumbered by extraneous

moire fringes. For this reason we studied three techniques for improving moire

detections of flaws in such interferograms (ref. 1):

1. Introducing a small relative magnification of the transparencies

of the interferograms of the flawed and flaw-free components in order to

compensate for small differences in stress level.

2. Forming a moire pattern by superimposing two transparencies of a single interferogram of the flawed component that differ only by a small relative

magnification.

3. Utilizing digital image orocessing $o form and enhance the moire

patterns of techniques 1 and 2 above.

157
The goal of the application of each of these techniques us to produce

a clear display of a flaw. In fact, our goal was to produce a closed moire

fringe roughly outlining the flaw. The interferograms used were all formed by

pressurizing an aluminum disk, which had blind-drilled holes or slots in its rear

surface. The first experiments were done using superposition of photographic

transparencies of the fringe patterns. Introduction of the relative magnification

was very cumbersome to achieve. This led to the introduction of digital -image

processing. A single interferogram of the flawed object was digitized and

stored in a computer. A second magnified image of this interferogram was formed computationally. These two images were then multiplied and enhanced by

the computer to produce the moire pattern. An example is shown in Figure 1.

The flaw is clearly indicated by a light region on the left-hand side of the disk.

We believe that the application of digital -image processing to forming and

enhancing moire patterns has great potential and may be useful in industrial

applications of NDT.

In recognition of interest in monitoring of small surface motions, we investigated a technique in which real-time holographic interferometry

was performed with two very thin, parallel, closely-spaced object illumination

beams in order to produce a time-varying irradiance which, when incident on a photodetector, gives a signal whose analysis indicates both the normal displacement and tilt at a point on an object surface (ref. 2). Figure 2 is a schematic

diagram of the experimental system. P and Q are points on the object surface.

The imaging system is composed of lenses and l^. The hologram is recorded

in plane H, and the points P and Q are imaged onto detector D. The output signal

from the photodector has a function of time and is shown in Figure 3. A detailed

analysis of the interference and detection process led to the interpretation

of such signals. In essence, the fine structure of this signal indicates

the normal displacement. (In this particular example a shift of one fringe

corresponds to a displacement of 0.3 um.) The zero crossings of the modulation

of this signal indicate the tilt of the object. (In this particular example each

pair of zero crossings corresponds to a tilt of 0.16 mrad.) It is hoped that this

technique will be useful for monitoring motions due to transient phonomena such as stress wave propagation in solids.

REFERENCES

1. X.Youren, C. M. Vest and E. J. Delp, "Digital and Optical Moire Detection

of Flaws Applied to Holographic Nondestructive Testing," Optics Letters 8 , No. 8, pp. 452-454 (Aug. 1983).

2. Y. Xu and C. M. Vest, "Holographic Technique for Simultaneous Measurement

of Displacement and Tilt," Applied Optics 22 , No. 14, pp. 2137-2140

(July 15, 1983).

138
Fig. 1. Digitally-formed moire pattern. A flaw is

indicated by the light region on the left side of the disk.

159
3 V'*

“1

z

Fig. 2. System for real-time monitoring of surface

displacement and tilt.

Fic. 3. Typical output signal of system shown in Fig.

160

CV.
INFRARED METHODS OF NONDESTRUCTIVE TESTING

J. Cohen

Radiometric Physics Division

Center for Radiation Research

The purposes of this project, initiated last year, are 1) to develop

expertise and maintain an awareness of infrared methods of NOT, especially

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.

An intensive study of thermal imaging, including theory and system

engineering was made, and a need for performance standards for thermal

imaging systems was identified and brought to the attention of ASTM. As

a result, a task force within ASTM subcommittee E7.10 has been formed,

dedicated to the development of the performance standards.

NBS Technical Note 1177, "Elements of Thermography for Nondestructive

Testing", was issued. This is intended to be a tutorial report in thermography, especially as it relates to NDT. It includes a treatment of performance measures, which likely will serve as a basis for an ASTM standard.

Further, this investigator has begun to provide consultation service.

161
NOE OF BUILDING MATERIALS

James R. Clifton and Mary E. McKnight

Building Materials Division

Center for Building Technology

The determination of the engineering properties, quality, and uniformity of building materials is necessary to reliably predict service

lives of materials in-place in both buildings under construction and in

existing buildings. The technical feasibility of using NOE methods in the

inspection of in-place materials is being assessed by laboratory and field

studies. During the past year the use of NDE in improving quality assurance programs for building materials was explored. The state-of-theart of quality assurance (QA)/quality control (QC) of building materials

was addressed in a Federal Workshop (ref. 1). The most troubling quality

problems with materials appear to be those resulting from on-site construction activities, as contrasted with fabricated components. The economic

loss due to lack of QA/QC in the construction industry appears to amount to

billions of dollars yearly. NDE methods which can be used in the quality

acceptance of building materials were described in two publications (refs.

2 and 3). In another publication (ref. 4), results of research on the

detection of cracks in concrete were presented. Future activities will be

directed toward identifying improvements in the QA/QC NDE inspection of

building materials which can be obtained by computer applications.

The development of an NDE method using scanning infrared thermography to

evaluate the state of degradation of organically coated metal substrates

was continued during the past year in a project sponsored by the Center for

Building Technology. Information contained in the thermograms was quantified by digitizing the signal, associating degradation (ref. 5), i.e.,

blistering and corrosion, with gray level, and determining the fraction of area represented by each gray level. Further work to obtain size and location maps of the deteriorated areas is planned for next year.

REFERENCES

1. Federal Workshop on Quality Assurance of Building Materials, October

1982, NBS,

2. J.R. Clifton and N.J. Carino, "Nondestructive Evaluation Methods for

Quality Acceptance of Installed Buildinq Materials", J. Res. NBS,

87 (5), pp. 407-436 (1982).

3. J.R. Clifton, "Nondestructive Evaluation Methods for Quality Acceptance

of Building Materials", Proceedings of 31st Defense Conference on Nondestructive Testing , pp. 95-109 (Nov. 1982).

162
4. L.I. Knab, G.V. Blessing, and J.R. Clifton, "Laboratory Evaluation of

Ultrasonics for Crack Detection in Concrete", ACI Journal, 80 (1),

pp. 17-27 (1983).

5. M.E. McKnight and J.W. Martin, "Nondestructive Corrosion Detection Under

Organic Films Using Infrared Thermography" , Proceedings of the 14th

National SAMPE Technical Conference (Oct. 1982).

163
MICROHARDNESS REFERENCE MATERIAL STANDARD

David S. Lashmore

Metallurgy Division

Center for Materials Science

The Electrodeposition Group has developed two microhardness standards under

contract with the Office of Standard Reference Materials. We hope that we can make 200 of these standards available to the public through OSRM by October 1983.

The hardness ranges of these standards are 125 and 550 KHN and they will be

certified at loads of 25, 50 and 100 grams. Preliminary results indicate that

it may be possible to certify the standards to within _+ 5 percent at all loads with

both Knoop and Vickers indentors.

The standards were made using electroforming technology which yields

an extremely uniform microstructure, and hence a uniform hardness. A comparison

between a commercial standard and an electroformed standard is shown in Fig. 1 which shows the hardness variation with position.

Significant efforts in the packaging have resulted in a standard whose

top and bottom faces are parallel to within 0.115 degrees and whose top

face is metal lographical ly polished flat. This packaging allows the standard to

be used without an auxiliary leveling stage on the hardness tester. The standards

have also been designed to withstand prolonged use in a corrosion laboratory envi ronment.

Development of the certification procedures for these standards is now in

the last stages. The procedure is in conformity with ASTM E92, B578, E384,

but it has been necessary to go beyond the ASTM specifications to ensure that:

(a) the load actually applied by the indentor is the lead specified; (b)

there is no impact (kinetic) loading or other artifact introduced by the testing

machine; and (c) the optical measurement of the hardness impression is accurate.

One of the problems that came up during the certification process is illustrated

in Fig. 2a. In this load-time trace from a commercial hardness tester one can observe both an artifact at lOg, and some impact loading amounting to approximately

3 grams. The slope of the load-time curve is much too steep in this machine.

It turns out that these phenomena are both independent of the applied load and

independent of the cycle time, which is adjustable on this particular model.

This error in loading might, in turn, produce errors as high as 12 percent at 25g.

As we are aiming at +. 5 percent accuracy for the standards, clearly this machine

is unsuitable. A much improved lead-time characteristic is shown in Fig. 2b.

Note the more gradual slope as the load is slowly increased, and the much reduced

impact loading.

Vibration can introduce significant errors into the hardness measurement. An

example of vibrational 'noise' is shown in Fig. 3a. Load errors can be extreme

if someone 'taps' on the table. Fig. 3b, or slightly less if acoustic noise is

present (e.g., a vacuum pumpl. In order to minimize these types of errors

we have mounted the hardness tester on a heavy granite block and, in turn, mounted the block on a thick rubber pad.

164
Another source of error is introduced by using the low power (0.65 NA) objective

lens normally supplied with the hardness tester to measure the hardness impression. This effect is illustrated in Table I.

A summary of the errors made in the complete measuring process is shown in Table

2. It would seem possible to certify the hardness numbers (both Vickers and

Knoop) at 25, 50 and 100 grams at _+ 5 percent accuracy and, for most cases, still

maintain a factor of 2 for safety.

TABLE 1: COMPARISON OF 0 .65 NA LENS WITH, 0.95 NA LENS

0.65 NA 0.95 NA

Position V i cKers Knoop Vi ckers Knooc

1 61 2.3 626.4 593.3 J . O . vj 2 6U7 .9 619.0 598.1 dp4

3 507 .9 611 .8 598.1 597 .

7

4. 612.8 622.7 o93 .3 5ul .2

6 607.9 622.7 503 .1) 608.2

6 698.1 626 .4 598.1 604

.

7

7 617.8 608.2 588 .5 594.2

8 6u3 .0 604 .

7

o93 .3 594.2

u 607 .9 597.7 570.3

10 612.8 601.2 K kj < J • w 597 .

7

1 1 693.3 615.4 £ U ^ T 59 7 .

7

12 607.9 61 6.4 50 7 .

9

5uc .2

13 622.9 619.0 693.3 “94.2

Average 608.6 614.5 w ^ ^ • 1 407 v j, - ' •

Note that when measured with the 0 .95 "A, Vi dors anc Knoop agree almost exactly,

sc that any deviation between one measurement and another is certainly a result

of standard non-uni formity

.

1 n ^
KNOW'

HARDNESS

NtlMDL-H

C/lMO

TA6LE 2: POSSIdlE MARGINS FOR ERROR IN CERTIFICATION PROCESS

DEVICE B DEVICE A

(0.95 NA) (0.65 NA)

Measuring process + 2.5%

Vibration effects +_ U

.

Loading impact + U.5%

+ 4.0%

+ 1 . 0%

f 25.0%

i-i. . sa

i

i

|-1.53

DXSTnNCS —N r* \ i'i

Fi^. 1. Variation of roicrohardness with position on the substrata comparing the electro forrr.ed

'•3S scandard with the best coirmerciallv available standard.
Fig. 2a. Load-time trace:Device A w/ 0.65 NA;

50 g load at approx. 45 sec. dwell

SO 0 m\l 1 S

Fig. 2b. Load-time trace: Device B w/ 0.65 NA;

50 g load at approx. 45 sec. dwell

167
10

9

03

Fig. 3a. Vibrational 'noise 1 incurred during

normal operation of Device A.

to

3

Q

*

Fig. 3b. Vibrational 'noise' incurred when

table mounting is tapped.

168
NONDESTRUCTIVE EVALUATION OF NONUNIFORMITIES IN 2024 ALUMINUM AllOY

PLATE - RELATIONSHIP TO PROCESSING

L. K. Ives, L. J. Swartzendruber, W. J. Boettinger, M. Rosen, S. 0.

Ridder, F. S. Biancaniel lo, R. C . Reno, S. Fick, D. B. Ballard and

R. Mehrabian

Metallurgy Division

Center for Materials Science

This task was initiated at the National Bureau of Standards at the

request of the National Aeronautics and Space Administration shortly

after the announcement in August 1979 by the Reynolds Metal Company tnat

about 31 million pounds of aluminum were suspected of containing "soft"

spots due to a possible malfunction in the water cooling system at one manufacturing plant. Some of these "soft" spots were reported to be as much as 45 percent below the strength specifications used for the

purchase of the aluminum by aircraft manuf acturers and suppliers.

The initial concern of this task was the 2219-T87 aluminum alloy used

extensively on the space shuttle. The results of our investigations on this alloy were used by the sponsoring agency to ensure that the testing

necessary to prove structural integrity had been accomplished prior to

launch. The results also had the fortunate effect of expediting the

space shuttle launch by eliminating a large amount of unnecessary testing.

Following the effort on 2219 attention was focused on 2024, an alloy

which is widely used in the construction of commercial aircraft. Because

our results established that better nondestructive evaluation techniques

are needed for quickly judging the strength of an aluminum plate

throughout its thickness rather than simply on the surface as given oy

hardness and electrical conductivity, investigation of the feasibility of

using an ultrasonic technique as an alternative were carried out on both

the 2219 and 2024 alloys.

The goal of this task, which is now essentially complete, was to

develop specific relationships between processing variables used during

ingot casting, mechanical properties, and NOE responses. The detailed

blend of metallurgical examination of the alloy with its NOE response was necessary not only to attacx the specific problem at hand but also to

gain a fundamental knowledge of the features of metallurgical

microstructures which cause changes in NDE parameters.

The investigation included the following:

i. Studies on as-received material. This included a 15.24 cm (6

in) thick plate of 2Q24-T351, a 0.635 cm (1/4 in.) thick plate

of 2024-F, and a direct chill cast ingot for 2024, all obtained

from industry.

16 ?
2. Investigation of the phases and inclusions present in cast 2024

aluminum alloy with the aim of determining the degree of microand macro-segregation and identifying the inclusions present in

the as-cast ingots.

3. Determination of a set of C-curves which can predict the

mechanical and NOE properties for any type of quench following

the solution heat treatment. Two tempers, T851 and T351, were investigated.

4. Transmission electron microscope studies of the stable and

metastable phases present and an attempt to relate the observed

microstructural changes to the measured changes in mechanical

properties and NDE measurements.

5. A study of the ultrasonic wave propagation as a function of

thermomechanical treatment of the alloy with the objective of

establishing a correlation between ultrasonic data and mechanical

properties and of providing an additional NDE method to improve

the characterization of the material.

6. A nondestructive evaluation of the age hardening sequence by means of dynamic eddy-current conductivity measurements.

7. Use of heat flow modelling to calculate almost all conceivable

heat flow conditions anticipated during the quench of 2024

aluminum alloy plate from the solution heat treatment

temperature of 495

- C. The calculated time-temperature data were

then coupled to the C-curves and the variations in properties

across different thickness plates for the "worst case" heat flow

conditions were predicted.

Predictable macrosegregation was obtained in laboratory ingots of

2024 aluminum alloy. It was found that macrosegregation of copper and

other alloying additions in direct chill cast ingots of 2024 aluminum

alloy cannot be completely eliminated by chill face scalping and

subsequent thermomechanical treatment. Although good scalping practice

should maintain compositions within specified limits with no deterioration in mechanical properties, the macrosegragation remaining in

the finished plate product will contribute to the scatter observed in NDE

measurements. Further, because of the large copper content variation

near the chill face, surface hardness and eddy-current conductivity

measurements are necessarily very sensitive to scalping depth in their

ability to evaluate the condition of finished alloy plates.

A large number of samples were taken from a 0.635 cm thick plate of

2024 aluminum alloy in the f temper and processed to the T851, T351 or T4

temper. During processing to these tempers, the quench following

solution heat treatment was varied, giving a series of samples with a wide range of microstructures and hence mechanical properties. Two types

of "pre-aging" treatment, labelled sequence A and sequence 3, were used.

170
The hardness, eddy-current conductivity, yield strength, ultimate tensile

strength, elongation, and area reduction of these samples were measured.

The accumulated data were used to establish a set of statistically _

significant C-curves from which the alloy properties can be predicted

for any time-temperature cycle of the quench following heat treatment.

The C-curves can also be used to generate correlations between mechanical

and NOE properties. The ultimate tensile strength vs. hardness and vs. conductivity determined for 2024-T351 are shown in Figures 1 and 2.

Based on such calculations and measurements it was concluded that

eddy-current conductivity alone cannot be used as a reliable predictor of

the mechanical properties of 2024-T351 or 2Q24-T851. It must be combined

with other information such as hardness and yield strength measurements

on the same Tot (same ingot or plate) of material.

The C-curves were combined with time-temperature data from a computerized heat flow model to predict the variations in properties

across plates of different thickness for both sequence A and sequence B type "pre-aging" heat treatments. It was found that the ultimate tensile

strength falls below specification for the "worst case" quench conditions

for rather thin plates (~ 1 cm thick).

TEM studies were carried out on a large number of specimens in a 120

k V instrument equipped to operate in scanning transmission (STEM) mode as well as in the conventional transmission mode. The instrument was equipped with an x-ray energy dispersive spectrometer. A major objective

was to identify those microstructural changes that were responsible for

the mechanical and physical properties delineated in the C-curve

representations. Although the microstructure as a function of

"pre-aging" treatment is complex, it appears that "pre-aging" induced

precipitates can contribute to the strength and are subject to overaging

during further heat treatment. This provides a mechanism for the loss of

strength which can account for the fact that the strength of the TS51

temper is actually reduced below that of the T351 temper given the same "pre-aging" heat treatment (rather that being raised as occurs for

properly quenched material).

The objective of the ultrasonic studies was to determine the extent

to which a correlation exists between the mechanical and ultrasonic

properties. For this purpose, the absolute, rather than the relative,

values of the sound velocity and ultrasonic attenuation are required.

The absolute values of sounds velocity and ultrasonic attenuation were determined to within ± 1 ms~- and * 0.02 dB, respecti vely. A parabolic

relationship was found between hardness and sound-wave velocity, whereas

ultrasonic attenuation decreases with increasing hardness.

Detailed results of the project have been published in a final report

(ref. 1).

REFERENCES

1. "Processing/Microstructure/Property Relationships in 2024 Aluminum

Alloy Plates", N8ISR 83-2669, U. S. Department of Commerce, N.3.S.,

January 1983.

171
zd

tin

^

<j

>

»-»

HARDNESS, HRB

Figure 1. Comparison of ultimate tensile strength vs. Hardness data for

2024-T351 with the correlations predicted by the C-curves. The

dashed lines are the scatter band (^95^ confidence level) obtained

from a least squares quadratic fit to the data. The solid and

dotted lines were calculated from the C-curves.
80

70

60

50

40

20

CONDUCTIVITY, XIACS

Figure 2. Comparison of ultimate tensile strength vs. conductivity daca for

2024-T351 the correlations predicted by the C-curves. The dashed

lines are the scatter band (^SSf® confidence level) obtained from

a least squares quadratic fit to the data. The solid and dotted

lines were calculated from the C-curves.
NDE DATA ANALYSIS, RELIABILITY MODELING, AND ON-LINE DECISION-MAKING

J. T. Fong

Mathematical Analysis Division

Center for Applied Mathematics

In October 1982, NBS responded to a request by an industry-based

research group to conduct a two-year study on the analysis and reliability

modeling of five sets of flaw-sizing and location data. The request resulted

from the recognition by the Pressure Vessel Research Committee (PVRC) of

the Welding Research Council that a computer-assisted data analysis methodology

has been under development at NBS since 1978 and that it would be beneficial to

collaborate in applying that methodology to some specific NDE data generated

by PVRC.

Since 1965, PVRC has supported an industry cooperative program on NDE

reliability by having twelve plate-weld specimens containing intentional

flaws fabricated and inspected by several teams using either existing or improved NDE methods. To calibrate the efficacy of the ad-hoc flaw fabrication

procedure, one of the specimens, PVRC 251 J, was sectioned after it completed a round-robin NDE program. More importantly, the sectioning data were expected to

provide an "absolute" estimate of the reliability of NDE procedures used for

251 J as well as a qualitative assessment of all round-robin NDE tests where

the actual location and sizing of flaws were not available.

Specimen 251 J was fabricated by welding two 11-in. thick plates of ASTM

A-533-65, Grade B, low-alloy steel (80,000 psi tensile strength), using the

submerged arc welding process. The 36-in. long by 1-1/4-in. wide butt weld, as shown in Figures 1 and 2, contained 15 intentional flaws of four types (5 long

cracks of 2-in. nominal length, 5 cross cracks of 3/4 in. nominal length, 3 long

slags, and 2 short slags).

The NBS-PVRC joint project on the analysis of PVRC round-robin NDE data calls

for the development of specific computer software for, and the application

of NBS-developed graphics and analysis software to, the following sets of data

on specimen 251 J:

Set 1 Sectioning Data (Yukawa, 1983) vs. Assumed Geometry of Intended Flaws.

Set 2 Ultrasonic Test Data (5-team, 1968), using an existing PVRC procedure.

Set 3 Ultrasonic Test Data (3-team, 1970), using a "new" PVRC procedure.

Set 4 Ultrasonic Test Data (4-team, 1971), using the "new procedure on cladding.

Set 5 Radiographic Test Data (6-team, 1976).

This summary report describes the progress made during the first ten

months of the project.

174
ENGINEERING DATA ANALYSIS METHODOLOGY

To assist engineers in meeting their information needs for both crisis

and normal modes of work, credible and affordable sources of engineering

data such as handbooks and databases exist with varying scopes of coverage and

depths of analysis. A computer-assisted methodology had been developed where

the process of analyzing any engineering data is broken down into five distinct

phases:

1. Data structure and representation.

2. Data completeness and quality check.

3. Data simplification for parametric studies.

4. Data analysis and variability modeling.

5. Critical evaluation of assumptions and results of analysis.

This conceptual scheme is being implemented for two specific applications,

namely, (a) the round-robin NDE data of specimen 251 J , and (b) the elastic,

yield strength, ultimate strength, creep, and fatigue properties of a class

of steels with corresponding microstructural data during mechanical testing.

ANALYSIS OF 251 J SECTIONING DATA - Interim Report

Dr. S. Yukawa of the General Electric Materials & Processes Laboratory made

available, on behalf of PVRC, a large number of drawings and mTcrograph-1 ike

images of 15 flaws of specimen 251 J as observed and intrepreted following

sectioning. A summary of the sectioning data (ref. 2) is reproduced in Table 1.

Pictures of the flaws in either projected or sectioning forms were received by NBS

for digitizing and 3-dimensional representation.

As shown in Figures 3 and 4, the manual drawings of the projections

of one such crack, flaw H, revealed a lot of geometric information which

may or may not be detected or relevant to a specific a

p

d 1 i cation. Of the

13 sections provided for this flaw, two typical ones appear in Figures

5 and 6 as test problems for exercising the digitizing software initially

developed by David Redmiles of the NDE Mathematical Analysis Division. Using

Dataplot, another NBS-developed software (ref. 3), the digitized images

of the two sections are displayed in Figures 7 and 8. A 3-dimensional

representation of the two sections in a perspective view is given in Figure

9. New software is being developed to connect those sections to form a continuous solid body for viewing at arbitrary angles to facilitate a comparison with ultrasonic test data at different beam angles.

QUALITY CHECK FOR NDE DATA AND THE CONCEPT OF A QUALITY INDEX

In collaboration with H. Berger of Industrial Quality, Inc., Gaithersburg,

MD, a list of thirteen criteria for checking the quality of radiographic data,

and a system of weights on those criteria to arrive at a measure known as the

"data quality index", were developed. A graphical display of the index in

the form of a rosette is given in Figure 10. Eighteen criteria for ultrasonic data are being develooed together with Berger and D. Eitzer. of the NBS

175
Mechanical Production Metrology Division. Details of both lists are given in

ref 1

.

PVRC 251 J FLAW FABRICATION RELIABILITY - Interim Report

To demonstrate the value of an erstwhile variance decomposition technique

(ref. 4), we chose one parameter, the maximum flaw dimensions as revealed by

sectioning and normalized by the intended length, as a sample parameter for

reliability analysis. As shown in ref. 5 and Figure 11, there are 15 data

points for the normalized maximum dimensions that range from 1.0 to 2.9 with

a mean of 1.89 and a standard deviation (SD) before analysis equal to 0.53.

Because of the replications in the 15-data structure, it is possible to obtain

additional information by applying the so-called one-way analysis of variance

(ref. 5) such that the flaw fabrication procedure can now be characterized

by an SD equal to 0.60. Using this new information and the condition that we allow the actual maximum dimension to exceed the intended by no more than

50 percent, the reliability of the fabrication procedure is now estimated at

25 percent.

INTERNATIONAL NOE RELIABILITY SYMPOSIUM

In June 1983, more than a hundred NDE scientists and engineers from Europe,

Japan, and North America met in Portland, Oregon to review and discuss the use of

round robin NDE of flawed specimens for estimating inspection reliability (ref. 6)

The symposium, which was chaired by the writer, was organized by the American

Society of Mechanical Engineers (ASME), the American Society for Nondestructive

Testing, the U. S. Pressure Vessel Research Conmittee, and NBS. Among the co- sponsors were the Japan -PVRC, the Plate Inspection Steering Committee of the

Commission of European Communities, the U. S. Nuclear Regulatory Conmission, the

U. S. Department of Energy, the Electric Power Research Institute, and others.

The symposium reviewed the history of an international round robin NDE

program that was spearheaded by the U.S. PVRC more than ten years ago,

summarized the technical accomplishments of all participating laboratories

and companies including work in progress, discussed data analysis methodologies

including one developed at NBS, and examined open problems at panel sessions on future directions in NDE research. A significant finding of the symposium

was that research in NDE measurements and parametric studies in round robin

testing have led to systematic improvements in inspection procedures and a more

sound basis for decision-making in both the industrial and the regulatory sectors

NDE DATABASE FOR ON-LINE ENGINEERING DECISION SUPPORT

Looking beyond the analysis and modeling of NDE data for reliability

estimation, we began a computer software effort to integrate the NBS-PVRC

database on NDE with five additional engineering databases to demonstrate

the feasibility of bringing credible and up-to-date information on line to

engineers for crisis decision-making (ref. 7). The five additional databases

are:

(a) Materials Property Database.

(b) Design Loads and Stress Analysis Software Package Access Database.

(c) Inservice Inspection and Failure Database.

176
(d) Human Factor Database.

(e) Case Studies, Economics, and Directory of Experts for Critical Review.

This demonstration project is sponsored by the ASME Committee on Research

Needs and is administered by a task force of 20 members with the writer as its chairman. The first on-line demonstration of the project is scheduled

for June 1984.

REFERENCES

1. J. T. Fong, "A Data Analysis Methodology as Applied to the PVRC Round

Robin NDE Test Program," Proc. International Symposium on NDE Reliability , Portland, Oregon, June 1983 , in preparation.

2. S. Yukawa, "Sectioning of PVRC NDE Specimen 251 -J," Progress Reports to

PVRC dated Jan. 15, 1981 and May 25, 1983.

3. J. J. Filliben, "Dataplot - An Interactive High-Level Language for Graphics,

Nonlinear Fittinq, Data Analysis, and Mathematics," Computer Graphics 15,

No. 3, pp. 199-213 0981).

4. H. E. Daniels, "The Estimation of Components of Variance", J. Royal

Statistical Soc. Supplement 6 , No. 2, 136-197 (1939).

5. J. T. Fong, "Analysis of Sectioning Data of PVRC-J for Estimating Flaw

Fabrication Reliability," to appear in Proc. International Symposium on NDE Reliability, Portland, Oregon, June~1"983 , in preparation.

6. J. T. Fong, S. H. Bush, and 0. F. Hedden, eds., A Symposium Preview on NDE Reliability through Round Robin Testing , a 193-page document prepared

for the pre-registants of an international "symposium on NDE reliability,

Portland, Oregon, June 19-21, 1983.

7. J. T. Fong, "Computer Software Needs of Materials Property Data Bases for

Selected Engineering Applications," to appear in An On-Line Materials

Property Data Base , Proc. of a symposium sponsored by ASME Pressure Vessels

& Piping Division and the Metal Properties Council, Inc., Sheraton Boston

Hotel, Nov. 15, 1983, during the 1983 Winter Annual Meeting of the .Am Soc

of Mechanical Engineers.

177
Table 1. Sectioning Results for PVRC Specimen 251

J

Flaw

Actual Dimensions** Intended Dimensions

Type* X Y Z X Y Z A CC 26.1-26.5 2. 4-4.

2

1.0-1.

3

25.5-26.3 3.0 1.0

Q 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.

2

26.3 30.0-32.0 1.0

D LC 25.1-25.6 2. 2-5.

5

2.4-3.

1

25.0 2. 0-4.0 2.75

E CC 25.3-25.5 17.1-19.0 2. 8-3.

2

25.0-25.8 17.0 2.75

F SS 25.1-25.2 30.6-31.8 1. 9-2.7 25.0 30.6-31.4 2.75

G LS 26.2-26.4 2. 2-4.

8

4. 6-5.

4

26.3 2.0-4.

0

5.5

H LC 25.7-26.4 16.1-21.9 5. 0-5.

7

26.3 16.0-18.0 5.5

I CC 26.0-26.4 30.2-31.9 5. 2-5.

7

25.5-26.3 31.0 5.5

J CC 25.1-25.8 3. 1-4.

6

7. 7-8.

2

25.0-25.8 3.0 8.3

K SS 25.1-25.5 17.1-18.1 8. 0-8.

3

25.0-25.8 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 25.8-25.3 16.7-18.7 9. 3-9.8 25.5-26.3 17.0 10.0

0 LS 26.0-26.2 29.8-32.2 9.6-10.2 26.3 30.0-32.0 10.0

*Type of Flaw: CC = Cross Crack

LS = Long Slag

LC = Long Crack

SS = Short Slag

** Dimensions: Coordinates of the flaw extremities; coordinate system as per

Figs. 1 and 2; dimensions in inches as per ref. 2.

178
X

f

Figure 1. Dimensions of Specimen 251 J.

x

Figure 2. Principal sectioning cuts.

179
Z.C~)

i

ov VO tO r- VO o cn <o m CO C4 o CO

tn o a\ o o rH o pH o rH o rH

• • • • • • • • • • • • • pH rH o o o cn CN CO 00 vO

<s CN CN CV| CM <N rH pH pH rH pH rH pH

Figure 4. Plan view of Flaw H.

Presumed tip of

intentional flaw

ISO
181

Figure

5.

Section

C-C

of

Flaw

H.

Figure

6.

Section

D-D

of

Flaw

H.
9*S2 L' S3 8* S3 6*S3 0*93 1*93 3*93 8*93 V93

8*S

*S

S*S

9*S

2.*S

• 8 * S

Figure 7. Digitized image of Section C-C of Flaw H.

9* S3 £*S3 8*S3 6* S3 0*93 1*93 3*93 8*93 **93

Figure 8. Digitized image of Section D-D of Flaw H.

182
Three-dimensional representation of Flaw H between Sections A-A

and 0-0, as viewed from a perspective. (The separate element a the upper left corner of Section 0-0 has been omitted for clari

Figure 9.

ft

rt
DATA qCAUrf INDEX - 0.0 DATA QUAUrr INDEX - O.0T

Figure 10. Data quality index for a 13-criterion radiographic data check

list, shown before (left) and after (right) some of the criteria

are weighted by a data source.

analysis)

car analysis)

Figure 11. Reliability of the flaw fabrication procedure for one parameter

(flaw length) based upon a one-way analysis of variance.

13 £
appendices
A. Conferences Sponsored or Co-Sponsored

Eighth International Symposium on Ultrasonic Imaging and Tissue

Characterization, June 5-8, 1983, Washington, D. C.

International Symposium on Reliability of Nondestructive Evaluation

through Round Robin Testing, June 19-21, 1983, Portland, Oregon.

Gordon Research Conference on Nondestructive Evaluation, August 21-26,

1983, Andover, New Hampshire.

NDE in Materials Processing Meeting, ASM Metals Congress, October 3-5,

1983, Philadelphia, Pennsylvania.

136
B. NOE Seminars at NBS

Dr. Allan Rosencwaig , Therma-Wave, Inc., Fremont, CA

"Thermal Wave Detection and Imaging"

March 21, 1983

Dr. Fred E. Stanke , Stanford University, Stanford, CA

"Elastic Wave Propagation in Polycrystall ine Materials"

April 11, 1983

Dr. James E. Gubernatis , Los Alamos Scientific Laboratory,

Los Alamos, N. M.

"The Role of Elastic Wave Scattering Theory in Ultrasonic

Nondestructive Evaluation"

April 15, 1983

Dr. L. S. Fu , Ohio State University, Columbus, OH

"Ultrasonic Evaluation of Mechanical Properties"

June 23, 1983

Professor Dr. Paul Hoeller , Director, Fraunhofer Institut fur

Zerstorungsfreie Prufverfahren, Saarbrucken, W. Germany

"Nondestructive Testing for Materials Characterization and Stress

Analysis"

September 12, 1983

187
C. Invited Talks by QNDE Staff

"Nondestructive Evaluation for Materials Characterization," L. Mordfin,

IAEA Seminar on Nondestructive Testing Technology — Current Development

and Future Trends, Singapore, March 11, 1983.

"New Directions in the National Bureau of Standards' NDE Program,"

H. T. Yolken, 14th Symposium on Nondestructive Evaluation, San Antonio, TX.

April 20, 1983.

"The Role of NDE in Manufacturing Science," H. T. Yolken, 1983 Conference

and Workshops on Mission Assurance: Industry/AF Space Di vis ion/ NASA,

Los Angeles, CA., June 15, 1983.

"Reliability of Industrial NDE," H. T. Yolken, Review of Progress in

Quantitative NDE Sponsored by the Center for Advanced NDE at the Ames

Laboratory (USDOE) with cooperation from the Air Force Wright Aeronautical

Labs., the Naval Sea Systems Command, and DARPA, Santa Cruz, CA.,

August 8, 1983.

"Developments in Sensor Technology for Microstructure Monitoring and

Process Control," H. T. Yolken, (co-authored by R. Mehrabian), ASM

Metals Congress, Philadelphia, PA., October 3, 1983.

18S
D. NDE Program Publications

H. Berger and L. Mordfin, Comparison of Common Nondestructive Evaluation

Methods, Quality Progress 16 , No. 2, p. 17 (Feb., 1983).

G. V. Blessing, An Assessment of Ultrasonic Reference Block Calibration

Methodology, NBSIR 83-2710 (June, 1983).

G. V. Blessing and D. G. Eitzen, Variables Affecting Ultrasonic Reference

Block Calibration, 19S2 Paper Summaries, ASNT National Conferences,

287-291 (1982).

D. A. Bracher, D. A. Garrett and C. 0. Heller, Theory ana Design of

Instrumentation for Bridge Investigation, Failure Prevention in Ground

Transportation Systems , NBS SP 621, 143-150 (Oct., 1982).

G. Birnbaum, H. Berger and D. G. Eitzen, Traceable NDE Standards,

Can. Soc. NDT J 4, 47-49 (Jan., 1983)..

J. C. Chang, F. Nadeau, M. Rosen and R. Mehrabian, Crystallization Kinetics

Study of CucnZrcg by Means of Ultrasonic Measurements and Microhardness,

Scripta Met 16 , p. 1073 (1982).

J. R. Clifton and N. J. Carino, Nondestructive Evaluation Methods for

Quality Acceptance of Installed Bui 1 di nq Materials, J. Res. NBS 87, No. 5,

407-436 (1982).

J. R. Clifton, Nondestructive Evaluation Methods for Quality Acceptance of

Building Materials, Proc. 31st Defense Conf. on Nondestructive Testinq,

95-109 (Nov., 1982).

R. S. Clough, ed.. Quantitative NDE in the Nuclear Industry (Proc. 5th

Inti. Conf. on NDE in the Nuclear Industry, ASM, 1983).

R. B. Clough and H. N. G. Wadley, Indentation Loading Studies of Acoustic

Emission from Temper and Hydrogen Embrittled A5 33 B Steel, Metallurgical

Transactions 13A , 1965-1975 (Nov., 1982).

J. Cohen, Elements of Thermography for Nondestructive Testing, NBS TN 1177

(May, 1983).

S. K. Datta, C. M. Fortunko and R. B. King, Sizing of Surface Cracks in a Plate using SH Waves, Review of Progress in Quantitative Nondestructive

Evaluation 1 , 227-231 (Plenum, NY, 1982).

D. Eitzen, F. Breckenriage, R. Clough, N. Hsu, T. Proctor, C. Stockton

and H. Wadley, Fundamental Developments in Acoustic Emission Measurements:

The NBS Program, Quantitative NDE in the Nuclear Industry , R. 3. Clough, ed.,

315-325 (ASM, 19837:

189
D. G. Eitzen and J. R. Quinn, Electric Power Research Institute/National

Bureau of Standards Joint Program on Acoustic Emission, Nondestructive

Evaluation Proqram: Proqress in 1982, G. J. Dau, et al , eds.. Report

NP-272S-SR, pp. 40-1 to 40-16 (EPRI, Feb., 1983).

D. L. Hunston, Cure Monitoring of Thermosetting Polymers by an Ultrasonic

Technique, Review of Proqress in Quantitative Nondestructive Evaluation 2,

1711-1730 (Plenum, NY, 1983).

D. L. Hunston, Relationship Between Mechanical Properties and Performance of

Inks as the Basis of Quality Control Techniques, NBSIR 83-2691 (April, 1983).

N. N. Hsu, S. F. Fick and T. M. Proctor, Recent Developments in the Design

of Piezoelectric Ultrasonic Transducers for Nondestructive Evaluation,

1982 Paper Summaries, ASNT National Conferences , p. 54 (1982).

N. N. Hsu, T. M. Proctor, Jr., and G. V. Blessing, An Analytical Approach to

Reference Samples for Ultrasonic Residual Stress Measurement, J. Testing

and Evaluation 10 , No. 5 r 230-234 (Sept., 1982). ^

L. K. Ives, L. J. Swartzendruber, W. J. Boettinger, M. Rosen, S. D. Ridder,

F. S. Biancaniello and R. Mehrabian, Relationship between Process Variables

and NDE in 2024 Aluminum Alloy Plate, 1982 Paper Summaries, ASNT National

Conferences , 480-481 (1982).

A. H. Kahn, Impedance Changes Produced by a Crack in a Plane Surface,

Review of Proqress in Quantitative Nondestructive Evaluation 1 , 369-373

(Plenum, NY, 1982).

R. 3. King and C. M. Fortunko, Determination of In-Plane Residual Stress

States in Plates using Horizontally Polarized Shear Waves, J. Appl. Phys. 54 , No. 6, 3027-3035 (1983).

L. I. Knab, G. V. Blessing and J. R. Clifton, Laboratory Evaluation of

Ultrasonics for Crack Detection in Concrete, ACI J. 30 , No. 1, 17-27 (1983).

R. D. Kriz, Monitoring Elastic Stiffness Degradation in Graphite/ Epoxy

Composites, 1982 Paper Summaries, ASNT National Conferences , 160-164 (1982).

M. Linzer, ed.. Ultrasonic Imaging 5 (1983).

M. Linzer and S. J. Norton, Ultrasonic Tissue Characterization, Ann. Rev.

Biophys. Bioeng. 11 , 303-329 (1982).

M. E. McKnight and J. W. Martin, Nondestructive Corrosion Detection Under

Organic Films using Infrared Thermography, Proc. 14th Natl. SAMPE Tech.

Conf

.

(Oct. , 1982)

.

L. Mordfin, ed., NDE Publications: 1981, NBSIR 83-2741 (May, 1983).

S. J. Norton, Generation of Separate Density and Compressibili ty Images in

Tissue, Ultrasonic Imaging 5 , No. 3, 240-252 (1983).

190
S. J. Norton and M. Linzer, Correcting for Ray Refraction in Velocity and

Attenuation Tomography: A Perturbation Approach, Ultrasonic Imaging 4 , No. 3, 201-233 (July, 1982).

C. L. Oehl and L. J. Swartzendruber, On the Optimum Applied Field for

Magnetic Particle Inspection using Direct Current, J. Nondestructive

Evaluation 3 , p. 125 (1983).

R. L. Parker, Ultrasonic Measurement of Solid/Liquid Interface Position

During Solidifcation and Melting of Metals, Physics in the Steel Industry

(AIP Conf. Proc. No. 34), 254-271 (1982).

T. M. Proctor, Jr., Introduction to Papers Presented at the Symposium on Ultrasonic Measurement of Stress, J. Testing and Evaluation 10 , No. 5,

199-201 (Sept., 1982).

T. M. Proctor, Jr., Some Details on the NBS Conical Transducer, J. Acoustic

Emission 1 , No. 3, 173-178 (Sept., 1982).

M. Rosen, S. Fick, E. Horowitz and R. Mehrabian, An Ultrasonic Investigation

of Precipitation Hardening Phenomena in 2219 Aluminum Alloy, Review of

Proqress in Quantitative Nondestructive Evaluation 1, 625-628 (Plenum, N. Y.,

1982).

S. Ruthberg, Leak Testing of Hermetically Sealed Electronic Components,

1982 Paper Summaries, ASNT National Conferences , 431-436 (1982).

R. A. Schrack, J. W. Behrens, A. D. Carlson, C. D. Bowman and R. D. Johnson,

Recent Developments in Resonance Neutron Radiography, Quantitative NDE in

the Nuclear Industry , R. B. Clough, ed., 158-163 (ASM, 1933). ~~

C. Tschiegg, M. Greenspan and D. Eitzen, Ultrasonic Continuous-Wave BeamPower Measurements; International Comparison, J. Res. NBS 88 , No. 2

(Mar. - Apr. , 1983)

.

H. N. G. Wadley, C. K. Stockton, J. A. Simmons, M. Rosen and S. D. Ridder,

Quantitative Acoustic Emission Studies for Materials Processing, Review of

Proqress in Quantitative Nondestructive Evaluation 1, 421-431 (Plenum, N. Y.,

1982T

G. S. White and J. F. Marchiando, Scattering from a V-Shaped Groove in the

Resonance Domain, Appl. Opt. 22 , No. 15, 2308-2312 (Aug. 1, 1983).

Y. Xu and C. M. Vest, Holographic Technique for Simultaneous Measurement of

Displacement and Tilt, Appl. Opt. 22 , Mo. 14, 2137-2140 (July 15, 1983).

H. T. Yolken, ed.. Technical Activities 1382 Office of Nondestructive

Evaluation, NBSIR 32-2617 (Dec., 1982).

X. Youren, C. M. Vest and E. J. Delp, Digital and Optical Moire Detection

of Flaws Applied to Holographic Nondestructive Testing, Optics Letters 3,

No. 8, 452-454 (Aug., 1983).

191
E. Awards

Acoustical Society of America Gold Medal

Mr. Martin (Moe) Greenspan was awarded the Gold Medal of the Acoustical

Society of America in the Spring of 1983. This award, the Society's

highest, is given annually to a member who has made major contributions in

the field of acoustics. Mr. Greenspan was cited "for wide ranging and

superlative contributions to experimental and theoretical physical

acoustics, including induced cavitation in liquids and sound propagation

in solids, liquids, and gases.

1 '

Engineer of the Year

Dr. Nelson N. Hsu of the Mechanical Production Metrology Division, a principal investigator for acoustic emission in the NDE Program, was named

Engineer of the Year for his contributions to the science and technology

of experimental mechanics. The award was given by the National Society

of Professional Engineers on February 24, 1983, during Engineers Week in

Washington, D. C.

ASTM Awards of Merit

Mr. Daniel Polansky of the Radiation Physics Division, a principal investigator for radiography in the NDE Program, received the ASTM Award of Merit

and designation as a fellow of the Society in June, 1983. He was cited

for his years of outstanding service to ASTM in the development of

Committee E-7 on Nondestructive Testing and the standards it produced.

Dr. Jeffrey T. Fong of the Mathematical Analysis Division was also a 1983

recipient of the ASTM Award of Merit. Dr. Fong, who has provided

mathematical and analytical support to the NDE Program for several years,

was recognized for his leadership and dedicated service in fatigue research.

ASM Fellow

Dr. A. William Ruff of the Metallurgy Division, principal investigator for

wear-debris analysis in the NDE Program, was elected a Fellow of the

American Society for Metals in October, 1983 in recognition of distinguished

contributions in the field of metals and materials.

ISHM Best Paper Award

Mr. Stanley Ruthberg of the Semiconductor Materials and Processes Division,

a longtime principal investigator for leak testing in the NDE Program,

received an award in November, 1983, for the best paper presented at the

International Society for Hybrid Microelectronics Annual Symposium last year.

Ruthberg' s paper, "Hermetic Testing of Large Hybrid Packages," discussea

the special problems posed by hermeticity tests for microelectronics

packages having volumes on the order of tens of cubic centimeters.

192
NTA Award

Mr. Jimmy James, a cooperative student in the Mechanical Production

Metrology Division, won first place in a regional paper competition for

undergraduates in Albuquerque, N. M. This cash award was presented by

the National Technical Association for his paper on measuring residual

stresses by ultrasonic methods. The paper was based on work performed at

NBS under the direction of Dr. G. V. Blessing and supported by ONDE.
F. Technical and Professional Committee Participation and Leadership

Participants in the NDE Program and the staff of ONDE have continued

their participation and leadership in standards committee and professional

society activities relating to NDE. The following appointments or elections to leadership positions occurred during the past year.

G. V. Blessing Chairman, Washington Area Chapter

IEEE Sonics/Ultrasonics

D. G. Eitzen Chairman, ASTM E7.06.02 on Aluminum

Ultrasonic Reference Blocks

L. Mordfin Chairman, ISO/TC 135/SC 3 on Acoustic

NOT Methods, for the Sept. 15, 1983

meeti ng

.

i

194
NBS-i I4A irev. 2-«q) U.S. DEPT. OP COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE ANO SUBTITLE

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

NBSIR 84-2815 January 1984

Technical Activities 1983

Office of Nondestructive Evaluation

5. AUTHOR(S)

Leonard Mordfin, editor

6. PERFORMING ORGANIZATION (If joint or other than N8S, see instructions) 7. Con tract/ Grant No. national bureau of STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

S. Type of Report & Period Covered

Annual , FY 83

9.

SPONSORING ORGANIZATION NAME ANO COMPLETE ADORESS (Street. City. State, ZIP)

10.

SUPPLEMENTARY NOTES

I

1 Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual Summary of most significant in formation. If document includes a significant

bibliography or literature survey, mention it here)

A review of the Nondestructive Evaluation Program at MBS, for FY 1983,

is presented in this annual report.

12. KEY WORDS (Six to tw eive entries; alphabetical order- capitalize only proper namips; and separate kev wqrds.oy semicolons)

Acoustic emission; calibration; eddy currents; magnetics; neutron metnods;

nondestructive evaluation; optics; penetrants; radiography; standards,

thermal testing; ultrasonics

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