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IMBSIR 80-2007

Annual Report 1979

Office of Nondestructive Evaluation

Harold Berger and Leonard Mordfin, Editors

Office of Nondestructive Evaluation

National Measurement Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

November 1979

Issued March 1980

Prepared for National Bureau of Standards

U.S. Department of Commerce

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80-2007

1980

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MATlOllAl. BUREAU

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UBBART

SEP ^ 9 1980

NBSIR 80-2007 0. ^ j

a-rANNUAL REPORT 1 979

OFFICE OF NONDESTRUCTIVE EVALUATION ^-07

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Harold Berger and Leonard Mordfin, Editors

Office of Nondestructive Evaluation

National Measurement Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

November 1979

Issued March 1980

Prepared for National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

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

Luther H. Hodges, Jr., Deputy Secretary

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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Preface

This report is the second in the series of annual reports on the

National Bureau of Standards (NBS) program in nondestructive evaluation

(NDE). These reports summarize the program's activities and plans. The

focus of the present report is on the program's activities in Fiscal Year

1979 and on its plans for the next five years.

It is hoped that this report will provide useful information to the

technical conmunity about the present directions of the NBS effort in non- destructive evaluation. We recognize that comments and suggestions from

manufacturers and users of NDE equipment can provide guidance for the NBS

program. We encourage readers to share with us their needs and interests

in the field of nondestructive evaluation.

Harold Berger

Chief, Office of

Nondestructive Evaluation
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Table of Contents

Page

Introduction 1

Personnel 4

Overview of the Technical Program 8

Acoustic-Ultrasonic Programs 8

Radiography 9

Electromagnetic Methods 9

Penetrant Testing 10

Wear Debris Analysis 10

Thermal -Infrared 11

Recent Progress in NDE 12

A. "Standards for Ultrasonic NDE," by D. G. Eitzen ... 13

B. "Pulse-Echo Instrumentation," by N. V. Frederick ... 15

C. "Ultrasonic Diffraction Technique for Characterization

of Fatigue Cracks," by S. Golan 16

D. "Ultrasonic Imaging," by M. Linzer 19

E. "Acoustic Emission," by N. Hsu 20

F. "Nondestructive Evaluation of Composites," by H. M.

Ledbetter, 0. C. Moulder, and S. K. Datta 21

G. "Polymer Sensor for NDE of Bearings," by S. C. Roth,

S. Edelman, J. F. Mayo-Wells, and J. M. Kenney .... 23

H. "Electrochemical Noise," by J. Kruger 24

I. "Magnetic Measurements," by L. Swartzendruber .... 27

J. "Eddy Current Conductivity Measurements," by G. Free . 29

K. "Eddy Current Imaging System," by B. Field 31

L. "Theoretical Modeling in Eddy Current NDE," by A. H. Kahn and R. A. Spal 34

M. "Optical Nondestructive Evaluation," by G. White and

A. Feldman 36

IV
N. "Optical Measurement of Surface Roughness," by E. C.

Teague 40

O. "Liquid Penetrant Flow Characteristics," by S. Deutsch 42

P. "New Image Quality Indicator," by R. C. Placious ... 43

Q. "Real-time Radiographic System Performance Measurements," by M. Kuriyama, W. J. Boettinger, and H. E. Burdette 45

R. "Neutron Radiography; Standard Measurements of the L/D

Ratio," by W. L. Parker and D. A. Garrett 50

S. "Resonance Neutron Radiography for NDE," by J. S.

Behrens, R. A. Schrack and C. D. Bowman 51

T. "X-Ray Residual Stress Evaluation in the Interior of

Materials," by M. Kuriyama, W. J. Boettinger and H. E. Burdette 54

U. "Wear Condition Monitoring," by A. W. Ruff, Jr. ... 59

V. "Image Metrology Facility," by E. C. Teague 61

W. "Safety Factors & Mathematical Modeling," by J. T. Fong 63

X. "Electric Power Research Institute/National Bureau of

Standards Acoustic Emission Program," by D. G. Eitzen 64

Y. "Acoustic Emission Transducer Cal ibration/EPRI , " by

F. Breckenridge 67

Z. "Acoustic Emission Theory/EPRI ," by J. A. Simmons and

R. B. Clough 69

AA. "Acoustic Emission Source Characterization/EPRI by

N. Hsu 76

BB. "Ultrasonic NDE Standards/DARPA," by G. Birnbaum ... 80

CC. "Reliability of Ultrasonic Weld Inspection/NRC ," by

D. G. Eitzen 81

DD. "Application of Nondestructive Evaluation to Construction/Army," by J. R. Clifton 82

EE. "NDE of Moisture in Roofing Systems/Air Force," by

L. I. Knab and R. G. Mathey 83

Appendix 85

A. Publications, September 1978 to Present 85

V
B. NDE Meetings at NBS 89

C. NBS Seminars on NDE 89

D. Adwards 91

E. NML Organizational Chart 92

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INTRODUCTION

Today, many material failures are prevented thanks to a system of test

methods that detects flaws and defects in materials before the failures

occur - in fact, before the materials are put into service. Called "nondestructive evaluation (NDE)," the system is potentially applicable to

inspection of such high technology products as nuclear reactors and supersonic aircraft as well as to inspection of more consumer-oriented products

such as pacemakers and parts of automobiles.

Actually, NDE is not a single method, but rather a name used to describe

a variety of techniques that can be used to examine materials without destroying or damaging them during the examination procedure. Some of these

methods, x-radiography for example, have been used for many years. Others,

such as neutron radiography and acoustic emission, are just now coming into

wider use as NDE methods. A comparison of the common NDE methods is given

in Table I.

The past year has brought about a striking upsurge in national awareness

of NDE. The problem of aircraft maintenance and inspection, as related to the

DC-10 airplane, attracted a great deal of attention to NDE. NBS was one of

several organizations interviewed by Science magazine to gather background

material for its important summaries of the NDE situation.*

A potentially serious national problem in which NBS has become deeply

involved concerns the probable use of "soft" ^aluminum in several air and

space craft. For the past 2-1/2 years, a major manufacturer has inadvertently produced aluminum-alloy plate that is believed to contain regions

of inadequate strength. It is suspected that some of this material has

already been fabricated and put into several commercial and military airplanes and the space shuttle. The problem that NASA brought to NBS involves metallurgy (identify the metallurgical problem and fabricate

wel 1 -characterized specimens for mechanical and nondestructive evaluation),

NDE (correlate the NDE measurements with the material parameters) and

statistics (assure a statistically valid conclusion from the tests).

This short-term project, now underway, will provide technical information

to help guide NASA. There is also a longer-term project planned; this

supports existing NBS-NDE plans to improve our understanding of (and con- tribution toward) NDE characterization of materials.

Other newsworthy events in the past year also helped to keep NDE in

the public eye. The accident at Three Mile Island pointed up deficiencies

in nuclear power plants. It is now recognized that nondestructive inspections to guarantee the integrity of the pressure boundary may not be adequate to prevent all accidents; nondestructive methods for verifying the

1. A. L. Robinson, "New Testing Methods Could Boost Air Safety," Science,

205 , 29-31 (July 6, 1979).

2. A. L. Robinson, "Making Nondestructive Evaluation a Science," Science,

205 , 477-479 (August 3, 1979).

1
inservice performance of pumps, valves and instrumentation are urgently

needed. The leaks that appeared in the Trans-Alaska oil pipeline (mainly

due to settling problems) were not the result of faulty girth welds. Yet,

undoubtedly, these leaks recalled to people's minds the NDE problems with

girth welds that occurred during construction. In this area, NBS has a continuing involvement; new DOT support for NBS, to study fracture and NDE

problems for the new gas line to come through Canada, has recently been

finalized.

There were other important, although perhaps less newsworthy, NDE

events. The Electric Power Research Institute (EPRI) initiated a new NDE Center to help transfer NDE research technology so it can be put to use by the electric utilities. A new emphasis on NDE is appearing at

Iowa State University and a major new commercial force in the field was set up in Albuquerque, as major changes took place in the Rockwell

International program in NDE.

It is reassuring that throughout these occurrences the NBS activity

in NDE has been recognized and called upon often. This makes it all the

more imperative that the NDE activity at NBS address real issues.

The principal emphasis in the NDE Program during Fiscal Year 1979

remained on standards and measurement activities that will provide near- term improvements in the major NDE methods. Thus, calibration services

or Standard Reference Materials (SRM's) are, or will shortly be, available

for ultrasonic reference blocks, ultrasonic transducers (total power,

radiation force as a function of frequency), electrical conductivity (ac

and dc), a penetrant sensitivity crack plate, measurements of fluorescent

brightness for penetrants and magnetic particles, radiographic film

density step tablets (SRM's to provide a density range beyond 4.0 are under consideration) and measurements of an inspector's visual acuity.

In addition, calibration of acoustic emission transducers is now being

offered on a limited basis. These efforts will improve the reproduci bi 1 i ty

of NDE measurements. On a longer-term basis, the program has begun to

address the nondestructive characterization of material parameters and

defects, in order to improve the quantitative nature of NDE measurements.

In this connection, a milestone for the coming year concerns the

underlying theory for an ultrasonic tomography system that will read out

in terms of ultrasonic velocity, attenuation and scattering. Such an instrument will be useful for characterizing both defects and material properties. This is one example to demonstrate that the program has initiated

work to address needs for quantitative NDE and characterization of materials.

These efforts will increase as we complete the task of providing improved

measurements and procedures for the well-used NDE methods. Future activities

will also address changes in NDE methods and standards that may come with

automated test systems.

2
Table I

COMPARISON OF COMMON NONDESTRUCTIVE EVALUATION METHODS

Method Characteristics

Detected

Advantages Limitations Example

of Use

Ultrasonics

Changes in acoustic

impedance caused by

cracks, nonbonds, in- clusions, or interfaces;

Can penetrate thick materials; excellent for crack detection; can

be automated.

Normally requires

coupling to material

either by contact to surface or immersion

in a fluid such as

water.

Adhesive as- semblies for bond integrity.

Radiography Changes in density

from voids, inclusions,

material variations; placement of internal

parts.

Can be used to inspect

wide range of materials and thicknesses;

versatile; film provides

record of inspection.

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

for penetration, inclu- sions, voids.

VisualOptical Surface characteristics

such as finish, scratches, cracks, or

color; strain in trans- parent materials.

Cften convenient; can

be automated.

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

Paper, wood,

or metal for surface finish and uniformity. Eddy

Currents Changes in electrical conductivity caused by

material variations,

cracks, voids, or in- clusions.

Readily automated;

moderate cost. Limited to electrically

conducting materials;

limited penetration

depth.

Heat ex- changer tubes

for wall thin- ning and

cracks.

Liquid

Penetrant Surface openings due

to cracks, porosity, seams, or folds.

Inexpensive, easy to use, readily portable,

sensitive to small sur- face flaws.

Raw must be open to surface. Not useful on porous materials.

Turbine

blades for sur- face cracks or

porosity.

Magnetic

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

voids, inclusions, material or geometry

changes.

Inexoensive, sensitive

both to surface and

near-surface flaws.

Limited to ferromagnetic material; surface

preparation and postinspection demagnetization may be re- quired.

Railroad

wheels for cracks.

3
PERSONNEL

The Office of Nondestructive Evaluation is a program office

coordinated within the NBS National Measurement Laboratory (NML). (An

organization chart for NML is given in the Appendix.) NDE projects,

however, are undertaken throughout the Bureau. Present NDE activities

involve all five centers in the National Measurement Laboratory and four

centers in the Bureau's National Engineering Laboratory. Work is done at

the Bureau laboratories in Gai thersburg , Maryland and in Boulder, Colorado.

NDE projects are started on the basis of need as determined by discussions with people from industry, technical societies and government

agencies. Once a project is decided upon, the work is initiated following

agreements on scope and schedule with NBS staff and Center or Division

management. Occasionally, projects are conducted or supplemented by outside

sources.

A diagram showing the personnel in the Office of NDE for the entire

period of FY1979 is given in Figure 1. During this past year our efforts

were supplemented by a visiting engineer, S. Golan of the Israel Institute

of Metals, by two guest workers, Sekyung Lee of the Korea Standards Research

Institute and Clifford Anderson of the Naval Surface Weapons Center in

Dahlgren, Va., and by a student trainee from the College of Notre Dame in

Baltimore, Amelia Nunn. All have returned to their host organizations.

In addition, our office staff was temporarily assisted by Diane Frizzell,

now assigned elsewhere at NBS.'

The leaders of the technical activities within the NBS Centers are listed in Table 11; the listing is given in terms of technical areas.

4
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personnel

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Table II

Tabular Summary of

NBS - NDE Personnel

Technique or Area Pri

A. Acoustic - Ultrasonic Application to:

Building Materials

Inorganic Materials

Metals

Polymers

Crack Characterization

Instrumentation

Standards

Reference Blocks

Transducers

Theory

3. Radiography

Neutron Radiography

Real-Time Systems

X-Radiography

C. Electromagnetic Methods

Electrical, Eddy Current

Methods

Theory

Conductivity Standards

Visual Acuity Standards

Magnetic Measurements

ipal Investigators

J. R. Clifton

R. G. Mathey

E. R. Fuller

J. A. Simmons

H. Ledbetter*

B. Fanconi

R. E. Green

D. J. Chwirut

M. Linzer

S. Edelman

N. V. Frederick*

D. G. Eitzen

N. N. Hsu

J. A. Simmons

R. B. Clough

D. A. Garrett

C. D. Bowman

M. Kuriyama

R. C. Placious

J. W. Motz

D. Polansky

G. Free

B. M. Field

A. H. Kahn

L. H. Bennett

G. Yonemura

L. Swartzendruber

6
Microwaves D. Ellerbruch*

Optics A. Feldman

E. C. Teague

D. Penetrants

Brightness, Fluid Properties B. F. Howell

K. D. Mielenz

R. Velapoldi

Crack Standard F. Ogburn

Flow Characteristics S. Deutsch

E. Wear Debris Analysis A. W. Ruff

F. Thermal Tests

Microcalorimetry E. J. Prosen

G. Fracture B. W. Christ*

M. B. Kasen*

J. H. Smith

H. Statistics J. T. Fong

I. Leak Testing S. Ruthberg

WAE, Part-time

* NBS Boulder Laboratories

Telephone Numbers:

NBS, Gaithersburg, Maryland, (301) 921-1000

NBS, Boulder, Colorado, (303) 499-1000

Office of NDE, (301) 921-3331

7
OVERVIEW OF THE TECHNICAL PROGRAM

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

are definite needs to improve the measurement methods and to relate measurements to the actual performance of the material. The Office of Nondestructive

Evaluation was established by the National Bureau of Standards to assist

industry and government agencies in improving the reliability of materials

and structures; NBS is working to help industry develop methods for accurate

and reproducible NDE measurements. This includes technical investigations,

development of standards (both measurement standards and procedural documents), characterization of instruments, and assessments of the meaning of

NDE measurements in relation to material performance. The main emphasis of

the NBS program is on the needs for improved measurements and calibration

standards and procedures for many of the NDE methods commonly used in

i ndustry

.

At the Bureau the NDE program is coordinated by the National Measurement Laboratory. Strong interactions with industry, technical societies,

and government agencies have been established in order to solicit their

advice on needs and to aid in technology transfer for developed methods and

standards

.

An overview of the NBS technical program in NDE is presented below.

More detailed reports of recent progress in selected areas of the program

are provided in the next section of this report.

Acoustic-Ultrasonic Programs

Work is in progress to develop methods for calibration of ultrasonic

and acoustic emission transducers. Spectral character! sties , beam profile,

and total sound power measurements are being studied. Some transducer

calibration services are now available.

NBS researchers are studying ultrasonic test blocks, in a program

that had initial, partial funding from the Air Force, Army, and the

National Aeronautics and Space Administration, to determine the reasons

for variability of these metal calibration blocks. A calibration service

for aluminum ultrasonic reference blocks is available. Service for steel

ultrasonic reference blocks is planned for announcement in December 1979;

work on titanium blocks is progressing. Futher directions for this effort

include the development of material-independent test blocks and the development of well-characterized fatigue cracks that could serve as a calibration artifact for many NDE tests.

8
Instrumentation development work in both ultrasonics and acoustic

emission is also in progress. This includes development of improved

signal-to-noise ratio systems by methods such as signal averaging and

pulse compression. A program to characterize the important variables

in ultrasonic instrumentation is in progress. Imaging instrumentation

is also under development.

These NDE methods are being applied to metals, ceramics, polymers,

building materials, and electronic components. Specific application studies

involve ultrasonic inspection of pipeline welds for the Department of

Transportation and the analysis of ultrasonic inspection data for the

U.S. Nuclear Regulatory Commission.

A program to develop a theoretical basis for acoustic emission

spectral analysis to characterize moving cracks or defects is in progress,

partially funded by the Electric Power Research Institute. This program

includes work for improved transducer calibration.

Radiography

Current programs involve work in both neutron and x-radiography

.

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

of spatial resolution in radiographic systems, for the determination of

response of x-ray film and for the characterization of real-time fluoroscopic systems. Developments in progress include work on improved

x-ray screens and determination of scattered radiation content and its

effect on radiographic detectors and systems.

The neutron radiographic studies are made primarily with a thermal

neutron radiographic facility at the NBS research reactor. Work has

been carried out with a 3 MeV Van de Graaff accelerator and a 100 MeV

linear accelerator. A recommended practice for thermal neutron radiography is being developed in collaboration with the American Society

for Testing and Materials. Standards for characterizing neutron beams

for radiography and gaging are under investigation. MBS scientists

have investigated the use of three-dimensional thermal neutron radiography and have shown the application of this inspection procedure to

nuclear fuel subassemblies, batteries, and art objects. Recent work

for the U.S. Navy concerns an evaluation of practical neutron sources

for neutron radiography.

Electromagnetic Methods

° Visual. NBS scientists are examining methods for the measurement

of visual acuity under typical NDE inspection conditions. This includes

tha effects of subdued lighting common in radiographic reading rooms

and of the dark booth situations typically used in fluorescent penetrant

and magnetic particle inspection.

9
The program will characterize test methods used in NDE where the

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

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

defects will be identified. These accomplishments will lead to rec- ommendations for improved visual acuity measurement methods.

® Optical. Optical methods utilizing reflected and scattered light

are being investigated for the characterization of surface defects and for

the measurement of surface roughness. A review of optical NDE methods is

in preparation. Consideration is being given to the need for standards

in holographic NDE.

° Electrical, Eddy-Currents. Facilities for dc and ac electrical

conductivity measurements have been completed as the first stage of a new program in electrical and eddy-current methods. Procedures have been

established for the measurement of conductivity over the range of 1-100

percent of the International Annealed Copper Standard. Methods for the

calibration of eddy-current test equipment are under investigation.

® Magnetic Methods. This program is particularly concerned with

improving measurements for magnetic particle testing. The work includes

efforts to determine the uniformity of magnetization within the inspected

part and measurements of magnetic leakage flux.

® Microwave Methods. Microwave measurements are being used to

determine physical properties of materials. The NDE Program utilizes

microwaves to measure moisture content of concrete. These measurements

relate to the strength of the material. This represents one area in which

NDE methods are being explored for applications in the building industry.

Future work to measure moisture content of other building materials is

planned.

Penetrant Testing

NBS scientists are investigating the feasibility of preparing a master

crack calibration plate for the evaluation of penetrant sensitivity.

Electroforming methods are being used for the preparation of wellcharacterized, reproducible, inexpensive crack plates. The fluids and

particles used for penetrant testing are also of interest. Brightness

measurements of fluorescent penetrants are planned, along with work on measurements of key properties of the fluids.

Wear Debris Analysis

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

time for engine, bearing, and transmission overhaul. This method is now

10
being expanded in a current NBS program, partially funded by the U.S.

Navy, in which the wear debris particles in the lubricant are detected,

sized, and examined in order to determine where and by what mechanism

wear is occurring. Magnetic methods for obtaining size distributions of

wear particles are used. X-ray microanalysis techniques have been developed

for particles in the micrometer range. The techniques offer increased

sensitivity for engine condition monitoring compared to conventional SOAP

methods

Thermal -Infrared

A recently completed program resulted in the development of a method

for the nondestructive evaluation of batteries used in critical assemblies

such as cardiac pacemakers. A microcalorimeter capable of measurements in

the 0.2 to 1000 microwatt range is used to measure heat generated in

batteries and, in some cases, pacemakers under a variety of conditions.

Heat generation by new and partially discharged batteries is measured under

no-load conditions as a measure of self-discharge. The work has resulted

in a nondestructive method to determine power cell quality. Additional

work on infrared NDE systems is being considered.

11
RECENT PROGRESS IN NDE

This section is devoted to technical descriptions of the progress

achieved during the past year in selected areas of the NDE program. Before

presenting these descriptions, however, it may be well to briefly discuss

a few items that have particular significance from a program planning

standpoint.

An assessment of ultrasonic NDE standards in terms of present and

future needs was recently completed (see Section BB). This is an important

development because it lays out future directions for ultrasonic standards

development; directions that NBS and other organizations can follow to improve the reproducibility and quantitative aspects of ultrasonic NDE. In addition, the approach which was taken may offer a model for NBS to follow

in assessing standards needs relative to other NDE methods; this direction

is presently under consideration.

Another important item concerns a new NBS thrust into optical NDE.

Our new projects on light scattering and optical measurement of surface

roughness are described in Sections M and M, to follow. There are additional optical projects. One is concerned with a review and assessment

of standards needs for holographic i nterferometry . The review is presently

under way with the assistance of Professor Charles Vest of the University

of Michigan. A second project on laser techniques in NDE is also planned.

The first phase, a literature review, is well along; the work is being

done in collaboration with Johns Hopkins University.

A third important development is concerned with a metals characterization project that NBS is pursuing for the National Aeronautics and

Space Administration (NASA). The problem concerns improperly quenched

aluminum alloy plate; areas in these plates (thickness range about 2.5

to 15 cm) exhibit degraded mechanical properties. These soft areas exhibit lower hardness and changed conductivity values; these methods,

therefore, represent the main tools being used to sort aluminum plate

material now in the aerospace plants and vehicles. NBS involvement in

this important problem presents an opportunity to expand our capability

in NDE materials characterization. We are now pursing these opportunities

in materials characterization; methods involved include hardness measurement, eddy current conductivity and ultrasonic attenuation and velocity.

Several of the progress reports which follow contain information

which was developed without formal support by the NDE program; these

are included as part of the total NBS effort because of the NDE

orientation of the material.

12
A. Standards for Ultrasonic NDE

D. G. Eitzen

Mechanical Processes Division

Center for Mechanical Engineering and

Process Technology

The detection and evaluation of defects using acoustic emission and

pulse/echo ultrasonics relies heavily on comparative measurements.

While these techniques have great potential, they are sensitive to

measurement system characteristics and to the condition of the reference

artifacts used. An effort to improve the reliability and uncertainty of

these techniques is underway. Part of this effort has focused on the

development of measurement services for transducers and reference blocks.

The measurement services now available along with improvements, extensions

and applications are listed below:

1. Ultrasonic Transducer Power Output Versus Frequency

The absolute total power output of ultrasonic transducers is

measured versus frequency over any part of a range from about

1-20 MHz by means of a modified radiation pressure technique.

The uncertainty is frequency dependent but is nominally about

+ 5 %. In addition to its use in the calibration of ultrasonic

transducers for users, the system forms part of the basis for

traceability between the Food and Drug Administration and NBS

, ultrasonic power standards. This is important for determining

compliance of many ultrasonic products to FDA promulgated regulations. Work has been done on improving the vibration isolation

of the radiation apparatus. Although the present mounts have a very good isolation factor (about 50) at the working frequency of

the apparatus, a new, inertial mounting system has been designed

and is under construction and should improve the isolation even

further.

2. Ultrasonic Transducer and System Power Output by Calorimetry

The time-averaged total absolute power output of a transducer or system is measured by an ultrasonic calorimetric comparator for any

voltage input waveform in the range of 1-15 MHz. The uncertainty

is approximately + 7%.

3. Ultrasonic Reference Block Calibration

Sets of ASTM flat-bottomed hole-type ultrasonic reference blocks

are compared with an interim reference block and associated model

13
using a well -characterized measurement system. The service provides a mechanism for comparing sets of blocks through the NBS

ultrasonic system. In addition to the existing calibration

service for aluminum reference blocks, a service for the calibration of steel reference blocks has been established. Also, a more meaningful uncertainty statement has been developed based on

a thorough statistical analysis (with the help of the Statistical

Engineering Division) of the ultrasonic measurements of reference

blocks

4. 3y arrangement, carefully characterized ultrasonic source transducers and aluminum reference blocks can be made available for

loan. These can provide on-site calibration with the user's

system. Using the accurately measured ultrasonic source transducers, a user's power or frequency measurement system can be

calibrated in-situ. Four of these source transducers are currently

being used in an international intercomparison of ultrasonic power

measurement methods piloted by NBS. So far, measurements have been

made by six laboratories in four countries. The loaner aluminum

ultrasonic reference blocks, which have been carefully compared

with the NBS interim reference standards, provide a means for users

to compare their reference artifacts with those of NBS on their own ultrasonic systems. These loaner blocks have been used to help

establish the basis for a measurement assurance program. An intercomparison on aluminum reference blocks using the loaner blocks as transfer standards and an NBS-devel oped measurement protocol has

been completed to this end. Agreement within 3% has been achieved

between NBS and the participating laboratory. This agreement is a factor of 4 better than the existing ASTM method.

Additional work on ultrasonic measurement systems is in progress.

A technique for visualizing transducer beam profiles has been developed

and disseminated ( Materials Evaluation , in press). The technique was developed in response to a need for methods of transducer evaluation

suitable for use by the user community. The technique can also be used

as a modified C-scan for the inspection of material or parts to display

a three-dimensional plot of defects versus position. Work on improved

ultrasonic reference blocks has also continued.

14
B. Pulse-Echo Instrumentation Study

N. V. Frederick

Electromagnetic Technology Division

Center for Electronics and Electrical Engineering

Undesirable, sometimes unacceptable, uncertainties arise in pulseecho measurements when operators are changed or when an operator repeats

a measurement. Attempting to reduce these uncertainties, ASTM Committee E7

is preparing a document for calibrating ultrasonic pulse-echo equipment.

At NBS, through measurements on standard metal blocks, we are evaluating the ASTM E317 calibration document. To date, our studies

have suggested two innovations: a simple, inexpensive standard test

specimen and a transducer-probe modification.

The prototype standard test specimen consists of a right-circularcylinder brass block with lathe-finished ends. Identical gold-plated

quartz piezoelectric transducers are attached to each end with lowmelting-point solder (Rose's alloy). Test-range requirements determine

specimen length. A simple, rugged metal box with permanently attached

connectors houses the specimen. Use of this specimen permits the operator

to reproducibly evaluate several parameters: horizontal linearity for

short, medium, and long ranges; vertical linearity; receiver signal-to-noise

ratio; receiver-gain stability; and pulser performance. NBS will recommend

that the Committee request manufacturers to supply such a standard specimen,

or a set of them, as an integral part of each piece of test equipment. This

standard specimen will provide a means for maintaining an operator-bias-free

record of equipment performance.

A slight modification of existing transducer-probe design has practically eliminated the gross echo-pattern variations that arise from irreproducible transducer-specimen coupling. The modification also permits

rapid, unambiguous evaluation of various couplants. The modification con- sists simply of attaching three small feet to the transducer housing.

With a small pressure, these feet act as spacers between the transducer

and specimen surfaces, uniformly fixing the couplant layer thickness.

The feet do not ( must not) contact the transducer itself. The only tradeoff for cleaner, more stable, more reproducible echo patterns is a slight

attenuation due to a thicker couplant layer. For the feet, a prototype

design used metal shim-stock chips typically 0.8 mm x 1.0 nm x 0.1 mm thick, their surface area being approximately one percent of the transducerhousing surface area. A pressure-sensitive cyanoacrylate cement holds

the spacers on the housing.

15
C. Ultrasonic Diffraction Technique for

Characterization of Fatigue Cracks

S. Golan

Office of Nondestructive Evaluation

National Measurement Laboratory

A technique for the sizing and characterization of cracks with ultrasonic diffracted waves has been developed.

When an ultrasonic wave impinges on the tip of a crack, waves of

the shear and compression modes are diffracted in a circular form. From

measurements of the arrival time of the diffracted ultrasonic wave the

depth of the crack tip can be computed by applying a single or double

transducer technique (see Figure 2), provided the tip-diffracted signal can be detected. This technique involves time measurements only; therefore, sizing of cracks can be performed with high accuracy.

The amplitude of a diffracted wave is comparatively low, approaching

noise level; therefore, reliable results can be obtained only if optimum

conditions are established, and if the tip-diffraction signal can be

identified unambiguously in the noisy background. Various parameters

influencing the quality of the test, such as angle, mode, wedge efficiency,

double or single transducer technique, etc. have been investigated in

order to determine optimum testing conditions, and a technique was developed to identify the signal from its response to dynamic loading.

The technique was used to characterize fatigue cracks (in

collaboration with Oak Ridge National Laboratory and the University of

Tennessee). Very good correlation between ultrasonic and direct measurements were found (see Figure 3) and other important characteristics

such as crack closure and crack surface topography were evaluated.

16
17

Fig.

2.

Sizing

of

cracks

with

tip

diffracted

waves

(A)

single

transducer

technique

(B)

double

transducer

technique.
18

Fig.

3.

Ultrasonic

crack

profiling.
AMPLITUDE

D. Ultrasonic Imaging

M. Linzer

Signal Processing and Imaging Group

Center for Materials Science

Several studies to establish the theoretical framework for advanced,

computer-based, ultrasonic imaging systems have been completed. This

work has been directed, primarily, toward convol ution/backprojection

methods for producing ultrahigh-resolution reflectivity images through

the use of enclosing and partially-enclosing apertures. Circular arrays

for two-dimensional imaging and spherical as well as hemispherical

arrays for three-dimensional imaging were analyzed. Narrowband, wideband and optimum transmit waveforms were considered and detailed com- puter simulations were generated for a variety of potential experimental

situations. See for example. Figure 4. A preliminary investigation was made of approaches for correcting velocity, attenuation and reflectivity

images for ray refraction and of algorithms for frequency-dependent

time-gain compensation.

These studies are expected to guide the development of systems that

can provide images with greatly improved resolution and accuracy. This

development activity has begun with construction of a motor-control led scanner.

In related work, the sensitivity of our dynamically-focused annular

array system (described in last year's report) was improved by more than

20 dB. The system was successfully demonstrated in a clinical environment.

Fig. 4. Simulated point-spread function for computer

imaging using a spherical array and an optimum pulse having a width of 0.4 mm at

half amplitude. Note the absence of sidelobes.

19
E. Acoustic Emission

N. Hsu

Mechanical Processes Division

Center for Mechanical Engineering

and Process Technology

An acoustic emission (AE) detection system, be it a simple single

channel system or a multi-channel computer-based system, requires a simulated AE source for checking general system performance and for

setting amplifier gains and threshold levels. Commonly used simulation

techniques such as pulsed piezoelectric transmitters, sparks, and helium

gas jets have the disadvantages that their signatures have never been

precisely determined and that the control of these simulated sources is

rather difficult and arbitrary.

The concept of using a breaking pencil to generate a simulated AE was first reported by this author more than three years ago. Since then it

has received wide acceptance as a simple and effective field system

calibration device. In the past year the device has been further refined

in that independent and direct measurement of the peak breaking force is

made with a static force load cell incorporated in the construction of

the device. Consequently, an AE system can be calibrated with a physically known quantity as the input source. A report is being prepared

which provides details of the design and test results of correlation

studies between the monitored input force measurement and various empirical AE parameters. The device is now expected to see even wider use

and should contribute substantially to the standardization of the present

generation of AE detection/processing systems.

Also, a systematic study of the problems and possible solutions

associated with AE source location using triangulation methods has been

initiated during the past year. The objective of the study is to devise

system calibration techniques to make the methods reproducible and re- liable. A detailed error analysis of some of the source location computation algorithms has defined the limitation of specific algorithms and

sensor configurations. Included in the study are the characterization

of the various modules of a triangulation system and the development of

laboratory experiments and theory to analyze transient wave propagation

in structures. The system characterization and the transient wave analysis are essentially an extension of the study of a wel 1 -characterized

AE system developed and reported previously.

20
F. Nondestructive Evaluation of Composites

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

Fracture and Deformation Division

Center for Materials Science

Ultrasonic waves provide a powerful nondestructive tool for studying

a solid's general mechanical state. Well-known solid-state ultrasonic

applications include determinations of thickness, residual stress,

elastic properties, texture, and phase transitions. Variously polarized

ultrasonic velocities provide such information. Wave-scattering measurements furnish information on the location, size, and geometry of flaws.

Wave-attenuation measurements yield information on internal friction

(absorption) and scattering (inhomogeneities). All internal defects,

even phonons, interact with elastic waves and attenuate them. Attenuation applications include determinations of defect types, defect

density, and grain or particle size. For isotropic homogeneous materials

the theory and practice of ultrasonic velocities in solids is reasonably

advanced.

Composi tes--being by nature inhomogeneous, anisotropic, densely

flawed, and residually stressed--provide attractive media for theoretical,

experimental, and applied ultrasonic-wave studies. Partially offsetting

this attractiveness, exact theories and measurements on composites are precluded by the uncertainty and complexity of the distribution of the

reinforcing particles or fibers. Besides the properties of the constituent fibers and of the matrix, it is this distribution function that

determines the composite's macroscopic properties.

We propose to study, both experimentally and theoretical ly , elastic

waves in a single composi te--boron-al uminum--to understand its macroscopic anisotropic elastic-constant and internal -friction properties.

Despite obvious needs for such basic comprehensive studies, none have

been reported to date. Thus, an opportunity exists for applying fundamental theory and measurement techniques to strengthen our understanding

of elastic waves in composites and to provide a firmer base for non- destructive-eval uation technology.

Our specific current research goals include combined experimental

and theoretical studies:

I. Determine orientational dependence of ultrasonic velocity for

both longitudinal and transverse polarizations. Develop the

velocity tensor. Use a MHz-frequency pulse-echo technique.

Consultant, Mechanical Engineering Department, University of Colorado,

Boulder, Colorado 80309.

21
$

2. Combine these results with mass density to develop the C.

.

elastic stiffness tensor.

3. Similar to 1 and 2, using a kHz-frequency technique, develop

velocity tensor and S. . elastic-compliance tensor.

J 4. Examine 1 and 3 results for dispersion. If discovered, try to

explain.

5. Model the anisotropic macroscopic elastic properties such as Young's modulus, shear modulus, bulk modulus, compressibil ity

,

and Poisson's ratio in terms of constituent elastic properties.

6 . Develop graphical representation surfaces for all the elastic

constants listed in 5 and for the sound velocities.

7. Measure attenuation and damping as a function of orientation

using both pulse-echo and resonance methods. Develop representation surfaces for internal friction.

8 . Determine anisotropy of Rayleigh-wave velocity in laminae

plane. Launch waves by laser excitation. Detect by laserbeam deflection, a technique to be developed in our laboratory.

Items 1 through 4 are complete, and items 5 and 6 are underway.

To a very good approximation, the boron-aluminum composite can be

represented by five independent elastic constants: Cii = C 22 > C 33 , C 44 = C 55 , C 66 > snd V 31 = V 32 - The remaining elastic constants are computed from the relationship: C 12 = Cn-2 C 66 ^nd

^13 = C 23 = V 31 (Cii+Ci 2

)- Using theories due to Hashin and Rosen (1964)

and Bose and Mai (1973, 1974), we find excellent agreement between

constituent and composite elastic constants. In these latter two papers

the authors consider (for a random fiber distribution) the in-plane

problem of waves moving perpendicular to the fibers and also the

antiplane-strain problem of a wave polarized along the fiber direction

but moving in a transverse direction.

The five independent elastic constants were determined by measuring

eighteen differently polarized wave velocities along [ 100 ]-type and

[110]-type directions, [001] being the fiber direction. Agreement

within a few percent was achieved, both in internal consistency and in

terms of microscopic-macroscopic models mentioned above. These results

may represent state-of-the-art measurements on metal -matrix composites.

They were obtained with a custom pulse-echo system featuring narrow

pulses, wide bandwidth, a simple impedance-transforming amplifier, and

an FET transmission gate.

22
G. Polymer Sensors for NDE of Bearings

S. C. Roth, S. Edelman, J. F. Mayo-Wells, J. M. Kenney

Polymer Science and Standards Division

Center for Materials Science

The NDE work of the Bulk Properties group emphasized a comparison

of the usefulness of polymer sensors and conventional accelerometers for

monitoring the condition of bearings (see publication in the Proceedings

of the 28th Meeting of the Mechanical Failures Prevention Group, NBS

Special Publication 547, pp. 303-314, July 1979).

In the study a horizontal shaft supported on ball-bearings was used; a quiet bearing was at one end and a noisy bearing at the other.

An isolated electric motor was coupled to the shaft by a flexible belt

so that only the bearings contributed measurable noise to the structure

supporting the shaft. A polymer sensor was fixed to the stationary race of each bearing and a miniature piezoelectric accelerometer was mounted

on the supporting structure as close to each bearing as practicable.

It was found that polymer sensors have several advantages. The

principal advantage derives from the flexibility and low density that

allow the polymer sensor to be mounted directly to the bearing. So

mounted, it responds only to the bearing noises. Conventional accelerometers are relatively massive and require specially prepared mounting

surfaces of appreciable area. These characteristics require them to be

mounted some distance from the bearing where they can be affected by

noise from other sources. This extraneous noise can cause uncertainty

as to which of several bearings is bad.

It has been suggested that polymer sensors could provide a non- invasive means of detecting cracks of the kind recently affecting DC-10

airplanes. A polymer gage cemented to a metal surface responds to sur- face strain in all directions and detects a signal which can be analyzed

into a spectrum of resonances of the metal panel. A change in the

structure of the metal preliminary to cracking (and certainly, development

of a crack) will cause a significant shift in resonance frequencies and

amplitudes. Polymer sensors are cheap so that one can be attached to

each critical surface. The sensor and lead constitute a continuous thin

sheet of polymer that would not affect the behavior of the panel. All

resonances of the panel would be excited any time the engines were

operating. Before each take-off, a superposition of the current spectrum on a spectrum recorded when the plane was known to be in good shape

would detect any change in the integrity of the panel.

Other proposed NDE work consists of the use of polymer sensors to

detect broken strands in airplane control cables and the use of polymer

sensors in a nonresonant method to measure the real and imaginary parts

of the elastic moduli of long, thin rods as continuous functions of

frequency and static load.

23
H. Electrochemical Noise

J. Kruger

Chemical Stability and Corrosion Division

Center for Materials Science

The detection and analysis of small amplitude fluctuations of the

current and/or potential of galvanic cells can give some information

concerning the processes occurring at the electrodes. The measurement

of electrochemical noise is being investigated as a means to detect the

onset of localized corrosion.

For the purpose of studying corrosion processes, it is often con- venient to control the potential of the electrode under study. This is

accomplished by means of a potentiostat. Commercial instruments, however, tend to introduce unacceptable noise levels in the circuits,

preventing the study of the signals of interest. For this reason, a special low-noise potentiostat was developed at NBS with the cooperation

of the Special Analytical Instrumentation Group, Center for Analytical

Chemistry. The instrument is designed for the detections of fluctuations

in the frequency range between 0.1 and 2000 Hz. The internal noise is

of the order of 3 • 10"^V//Hz. Figure 5 shows the noise current produced by the potentiostat on different resistive loads. It can be seen

that current fluctuations in the nA range caused by changes in the

electrode characteristics can be detected above the instrumental noise.

Noise measurements are now being made on various electrodes. For

aluminum in neutral solution, for instance, pitting is correlated with a large increase of the noise current, as shown in Figure 6. When the

electrode potential is brought above the pitting potential (about

-650 mV vs SCE), the noise current increases by almost three orders of

magnitude below 100 Hz.

Other electrode systems are being studied in order to assess the

sensitivity and range of application of this novel tool for the study of

corrosion.
o

zH/v/V ‘}U0jjno asiofsi

=

i

25

Noise

current

produced

by

the

potentiostat

on

different

resistive

loads.
Current

Density,

A/CMVHz

Fig. 6. Aluminum In neutral solution; pitting is correlated with a large increase of the noise current.

26
I. Magnetic Measurements

L. Swartzendruber

Metal Science and Standards Division

Center for Materials Science

The magnetic particle method is a relatively simple and inexpensive,

yet effective and rapid method; it is currently in wide use for both

production and field testing of ferromagnetic components. Despite its

apparent simplicity, a large number of variables influence the process

and need careful control in order to obtain repeatable and reliable

results. To aid in this control, use of a test ring with artificial

subsurface defects is often specified. The extent to which such a test

ring evaluates the properties of the particle being used rather than a combination of operator skill, proper particle densities, proper magnetization levels and other contributing factors, is poorly understood.

An evaluation of the importance of the various contributing factors

requires the development of a mathematical model to describe the formation of magnetic particle indications. To this end, the development

of indications on the test ring currently specified in MIL-E-6868E (and

proposed for inclusion in the ASTM magnetic particle recommended practice)

is under investigation.

In developing a model to describe indication formation on a test

ring, a description of the leakage field from the artificial defects is

required. Because of the non-linearity of a ferromagnetic material such

a description poses formidable mathematical difficulties. However, we have shown experimentally that, to a good approximation, a simple linear

dipole model can be used to describe the leakage field from cylindrical

defects provided that a proper equivalent depth, which is less than the

true depth, is used. A calculated leakage field is illustrated in

Figure 7. Measured and calculated fields are compared in Figure 8.

Using the observed leakage field strengths and the known number of

defects that form indications on the test ring at various current levels,

a detection criterion has been suggested in terms of the force experienced by an isolated spherical particle. An extension of this criterion to other situations would be very useful and might allow the

calculation of required magnetization levels and detectable defect size,

parameters which must now be determined empirically.

27
Distance, inches

Fig. 7. Calculated components of the magnetic leakage field at the

surface from a subsurface cylindrical defect in a linear

isotropic magnetic medium of high permeabil ity. m refers

to the dipole moment per unit length of the defect an h to

the height above the center of the defect.

40

<u 20 O

o>

(Do* I

-20

-40

1

1

Hole No. 2

I =2400 A

measured values

dipole field

1

1 1

/ ^

/ •

/

! o • ° 'N /

\

\

\o ^

1 1

o y o

/ o

/ o ' / /

/ 'o

1 1 1 -4-20 2

Distance, mm

Fig. 8. Experimental transverse, and perpendicul ar , Hj_ , leakage

fields for hole number 2 of the test ring specified in MIL-E6868E with an applied magnetizing current of 2400 amps. The

dotted lines are calculated for a dipole with an m of 607

Oe mm2 and an h of 2.6 mm.

28
J. Eddy Current Conductivity Measurements

G. Free

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

The objectives of this project are (1) to develop a calibration

service for electrical conductivity standards in the range 10% - 100%

lACS and (2) to produce electrical conductivity standards which would

become NBS Standard Reference Materials (SRMs), in a joint effort with

the Metal Science and Standards Division.

The calibration service project can be divided into three distinct

areas in which work has been done: (1) the development of a DC measurement system to measure resistance at the microohm level, (2) the design

and construction of an eddy current bridge to test primary standards for

uniformity and to compare test samples with the primary standards and

(3) the development of primary conductivity standards.

The DC measurement system has been completed and tested on several

test bars. The stability and sensitivity of the system is within the

requirements of measuring at the microohm level. The total accuracy and

precision of the system is not as yet known due to the lack of a uniform

sample needed to determine these quantities.

An eddy current bridge has been developed which is based on a new concept in eddy current measurement. A paper discussing the theory,

construction and operation of the bridge was presented at the "Symposium

on Eddy Current Characterization of Materials and Structures" held at

NBS, September 5-7, 1979. The principle of operation is that all measure

ments are made at a constant skin depth instead of the usual measurements

made at a constant frequency. Advantages of the system are that all

conductivity measurements can be based on a single standard (usually a minimum of ten standards are needed to cover the range 1-100% lACS) and

lift-off is automatically resolved in the system. The bridge circuit is

a modified Maxwell bridge with a grounding network. The range of this

instrument is .1-10 mH inductance and 2-200 ohms for the series resistance. The instrument works in the frequency range 5 kHz - 100 kHz.

Initial testing of the system has shown that the accuracy of the system

is .01% of the conductivity being measured.

The eddy current bridge has been used to scan the primary standard

bars at different skin depths. From the scans it was determined that

only one of the test bars has the uniformity necessary to be used as a primary standard. The use of this one bar will necessitate increasing

the NBS total uncertainty because even this bar has areas in which the

conductivity varies by approximately 0.1%a. All NBS bars were heat

treated to improve the uniformity of the electrical characteristics but

the improvement was not sufficient to qualify the remaining bars as primary standards.

29
The second objective of the project, the development of electrical

conductivity standard reference materials is being done jointly with

the Metal Science and Standards Division. This project was initiated

during the current fiscal year. Responsibilities for various areas of

the project have been defined. It was decided that SRM's in the con- ductivity range of aluminum alloys would be the first produced. The

geometry of the samples has been set. The dimensions of the standards

will be 1 1/2" X 1 1/2" x 1/2". The alloys have also been chosen so that the approximate conductivity of the standards will be 20%, 30%, 40%

and 50% lACS.

During the next fiscal year more bar samples will be fabricated.

The bars will be cut from larger metal plates in an area of the plate

that has been determined to have uniform electrical characteristics.

More primary standards are necessary to establish NBS measurements and

to lower the total uncertainty that will be used in the NBS calibration

service.

Development of the NBS eddy current bridge will continue. A voltage

follower network will be built and tested to determine if such a network

can be used in the grounding network of the bridge. If phase change in

the follower can be held to a negligible amount it would replace the

grounding network of the present bridge. The voltage follower network

would simplify the bridge balance and reduce the time spent in balancing

the bridge by approximately half. The ranges of inductance and resistance that can be measured will be increased to provide for the measurement of a wide variety of coils.

The calibration service will be initiated as soon as the primary

bars can be machined and calibrated. It is planned that the service

would be announced in December, 1979.

Testing of electical conductivity SRM's will start in the spring of

1980. The initial tests will determine the uniformity of these metal

blocks. Eddy current tests will be done at different frequencies to

determine if surface hardness causes error in eddy current measurements.

The magnitude of the error will be determined.

30
K. Eddy Current Imaging System

B. Field

Electrical Measurements and Standards Division

Center for Absolute Physical Quantities

The objective of this project is to develop an eddy current flaw

detection system with a more meaningful display and to demonstrate the

feasibility of such a system for determining the type and shape of

flaws. Work on this aspect of the project started with a literature

search for papers concerning defect detection or characterization using

eddy current techniques. A promising approach for a sensor was reported

by McMaster ( Met. Eng. Quart. , pp. 32-48, May 1966) using a Hall effect

detector. A similar sensor was built and several experiments were performed. As a result of these experiments (and later discussions with

McMaster) it was learned that pickup of extraneous signals by the leads

introduced significant problems. Adequate shielding of the leads proved

difficult and appeared to be impractical for a large array of sensors, and

thus it was felt that the sensor design could be better met by a differential

coil arrangement.

A probe assembly of our own design, consisting of an array of small

pickup coils (probably about 50 coils) with four large driving coils

arranged in a square around the array of pickup coils has been proposed

as a possible flaw detector. The present implementation of this idea is

shown in Figure 9, a drawing of a prototype probe assembly; this is

placed on the flat surface to be analyzed. Driving coils on opposite

sides of the array will be excited simultaneously but with current signals

180 degrees out of phase with each other. By varying the relative

signal strength of the two coils, we should be able to detect conductivity

discontinuities with high spatial resolution. Information about the

shape of the discontinuity can be determined by separately energizing

the orthogonal pair of driving coils. This idea, as yet, is untested,

but, preliminary experiments indicate that this is a feasible concept.

Potential advantages of this concept are:

1) the assembly allows high spatial resolution of discontinuities

with a relatively small number of pickup coils.

2) a reasonably large area (approximately 80 sq. cm in the

prototype) can by analyzed with no mechanical scanning

requi red.

3) the system will be able to provide limited information about

the shape of the discontinuity, e.g., distinguishing between

cracks and pits.

4) the test is most sensitive to surface discontinuities, but

limited information about sub-surface discontinuities

and the depths of discontinuities may be available.

31
DRIVING

COILS

CONFORMAL

COATING
5) the prototype probe is designed for flat surfaces, but a modification of the probe will also allow testing of

slightly curved surfaces.

A desktop computer will perform experiment control, data logging, and data

reduction for the system. The computer has been interfaced successfully

with a frequency synthesizer (for energizing the driving coils) and a general purpose interface crate of our own design. The interface crate

will allow us to easily interface a variety of instruments to the computer. We have the ability at present to perform data logging of eight

analog channels (with 0.025% accuracy) and to control a mechanical

scanner. Several computer programs have been written to perform a onedimensional scan of an aluminum plate, digitize the signals from the

pickup coils, and graphically display the results. A lock-in analyzer

is used to amplify and phase-detect the in-phase and quadrature com- ponents of the pickup coil signals. These mechanical scanning experiments were used as a convenient method for examining eddy current fields

to produce an improved design for the pickup coils.

33
L. Theoretical Modeling in Eddy Current NDE

A. H. Kahn and R. A. Spal

Ceramics, Glass and Solid State Science Division

Center for Materials Science

We have completed the calculations of the impedance of a coil which

contains a conducting cylinder with a long radial surface crack. The

calculations were performed by two independent methods. The first

method employed an eigenfunction expansion of the magnetic field in the

conductor, with the expansion coefficients determined by the fitting of

boundary conditions on the surface and in the crack. The second method

of calculation was conversion of .the problem to an integral equation for

the eddy current density on the surface of the conductor. The advantage

of the second approach is that it is applicable to any two-dimensional

shape of cross section of the conductor; in addition, it offers an independent check on the first method of calculation.

The results of the calculations for the cylinder with a crack are shown in the following figures. The fractional change of the real

(resistive) and imaginary (inductive) parts of the impendence are shown

plotted against the ratio of crack depth to radius (d/a) for a wide

range of values of the ratio of radius to skin depth (a/5). For the case of a tight crack these calculations represent a complete solution

of the problem. Open cracks can be treated as individual cases by the

integral equation method.

The results described above are all related to the detection of

long flaws in bodies of uniform two-dimensional cross section, such as rods, cylinders and strips. With this accomplishment as a start, we plan to go on to three-dimensional problems which are of greater interest. A possible problem for attack is the configuration in which an eddy current probe is passed above a conducting plane with a crack or other defect on or beneath the surface. Such problems have, in the

past, been treated under the approximation that the defect size was

small with respect to the skin depth. By extension of the integral

equation method we plan to treat such problems more generally.

34
ReZ

‘O

O

O

QJ IB c

&- o «+- (B O

O O. -M +J u to 5n c 0) Ol 3 3 3 <B «+- r—

“O

C IB

iB >

a; cn

cn IB to *o c s iB CD

(T3 •1— 4-> x: 0> O a OJ O (U xz c r—

p>— +J (B (U <o •o to c M- O) o O a. &.

“r— E o4- o o

(B iB (1) IB S- S- —

Ll.

u 4-> -o

CD

<u ~a ^ fC <u

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t/y

u

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(U <v

IV (J IM 3 C

•o <0 S- o o

(1) <U ‘4- cn a. c E «

fO ‘f” • JZ -a K3 O <u ^ I^- (O r- 4-> O

fOC 4- c o o o o

*r- •»— to +J ^ 4-J OI u a u 3

fO fO c 1

i- S- 3 IB U. O ‘V- >

cn

LU
M. Optical Nondestructive Evaluation

G. '^ite and A. Feldman

Ceramics, Glass and Solid State Science Division

Center for Materials Science

The use of optical techniques for nondestructive evaluation of

materials is growing in importance. For example, holographic inter-

•^erometry has become a standard procedure for detecting flaws in tires.

Optical scattering techniques are in use for detection of flaws in

hypodermic needles and artillery shell casings. Speckle interferometry

is being developed as an optical NDE tool to complement holography. It

is the purpose of this project to provide a sound scientific basis for

optical NDE methods.

At present, the focus of our program is on the study of light

scattering from surface flaws. A scattering apparatus, shown schematically in Figure 12, has been constructed for this purpose. In preliminary scattering experiments conducted with this apparatus, the

beam from a CO 2 laser source was propagated normal to the surface of a brass specimen containing a groove. The groove with dimensions approximately 50um wide, 50ym deep and 1 cm long was produced by spark erosion.

Scattered light within a solid angle of 2 x 10"^ was measured as a function of the angle between the scattered beam and the incident beam

in a plane perpendicular to the specimen groove. These measurements

define a scattering function.

Representative data for an angular scan are shown in Figure 13.

The structure in the scattering function resembles the diffraction

pattern of a single slit, which is to be expected by application of

Babinet's principle. From the spacing of the minima in the curve and

the use of the formula for single slit diffraction, one calculates that

the width of the groove should be 52um, in close agreement with the

approximate dimension given above.

An interesting feature in Figure 13 is the double peak to the right

that appears near the scattering angle 0 = 1_71- This structure appears

to be a property of the groove because, when the specimen is rotated

130® about the normal to the specimen surface, the double peak shifts to

the left near 9 = -17® . This suggests that the scattered light contains

more detailed information about the groove structure.

In the course of setting up the scattering experiment, it was found

that the system alignment was a more critical than initially suspected.

For example, if the groove was not normal to the scattering plane but

deviated by only 0.3®, the scattering function would become grossly distorted and asymetric. Furthermore, asymmetry was observed in the

scattering function when the axis of rotation of the detector did not

coincide with the groove.

36
TARGET

37
38
Improvements of the scattering system are being made. A greater

emphasis is now being placed on alignment. A special alignment system

has been constructed so that the axis of rotation of the detector can

be made to coincide with the groove to within 50um. A further improvement we are making is the replacement of a manual rotation mechanism,

which made measurements extremely time consuming and tedious, with a stepper motor rotation mechanism. This latter improvement should make

possible future automation of the system by microcomputer. Furthermore, we

plan to monitor the output wavelength of the CO 2 laser and the output

intensity.

r

39
N. CDt'‘cal Measureirent of Surface Roughness

1 . C. 'eague

Vecnanica' Processes Division

Cencer ^or Mechanical Engineering and

Process "ecnnology

We are :naking progress toward the establishment of a basis for the

aevelopment of recommended methods for optical measurement of surface

roughness. ’We have completed an extensive literature search and analysis of the resulting papers on optical methods for measuring surface

rougnness. 7ne analysis ha^s included a distillation of these methods

“or *he ones most suitable ror NOE. 'We are presently in the early draft

stage of writing a review paper on NOE and on-line surface roughness

measurement which will be published in the fall of 1979 in a new international journal entitled "Precision Engineering." An excerpt from the

rcugn draft of the introduction to this paper follows.

"In this review, we consider alternative techniques to the stylus

primarily in terms of their potential for NOE and on-line surface measurement as tney may be applied in the metal working industry. We distinguish

here between on-line measurements by which we mean real-time, high speed,

automated measurements that can be performed routinely and without disruption between stages of manufacturing , and in-process measurements which

we define as measurements that can be made while the part is being machined

or formed. In-process measurement offers the potential for adaptive control to opiimize the finished parts automatically, but it must deal with

the environmental problems of part vibration, debris, and surface coolants

and luoricants thai are generally present during the forming process.

"There is currently great interest throughout industry in the

cevelooment of on-line surface measurement techniques because of the

potential economic benefits in manufacturing. On-line surface inspection facilities would bypass the high labor costs of the stylus technique and would allow for rapid, ICO-percent quality control of finished

carts. There are, in fact, working on-line surface inspection systems.

One example is used at the Ford assembly plant in Puerto Rico, where a laser-based system is used to inspect the surface roughness of the shafts

O'^ power steering pumps.

"In this review, we will concentrate on optical techniques for

surface topography measurement. Non-optical techniques, which include

capacitive and inductive techniques, thermal comparators, and pneumatic

gauges, also show some promise and are discussed elsewhere. We will

discuss each technique in terms of the criteria of speed, ease in producing an electrical signal, resolution and range, its suitability for

studying isotropic and non-isotropic surfaces, its sensitivity to part

vibration, its capability for quantitative measurement of surface

parameters, and limitation of the types of part geometry which can be

studied.

40
Also, a prototype ultra-high precision mechanical stage has been

designed and machining of the stage parts is nearing completion in the

MBS machine shop. Assembly, testing and interfacing of the X-Y drive

components and stylus transducer to the Image Metrology Facility (described in Section V) should be complete by the end of FY1979. This X-Y

stage development is an essential element to achieve the objective

because stylus instruments have been and remain the most quantitative

technique for measuring surface roughness. Thus, in order to establish a firm basis for the optical measurement of surface roughness, light

scattering from surfaces must be compared with area measurements and

characterization of surface topography. This stage in conjunction with

the Image Metrology Facility will enable the first such comparison to be

done for typical industrial surfaces.

The initial design of this stage will employ monolithic flexure

pivots as used in the "Piezo-Flex"* stage within a novel "dynamic

flexure" conf iguration that will ensure straight line motion. By using

the monolith construction technique, a host of other problems associated

with conventional long range stages can be eliminated. A few of the

problem areas are:

1) stick-slip friction (horizontal vibrations);

2) bearing noise (vertical roughness of travel);

3) ultra-high vacuum (oil and high vapor pressure lubricants are required). -

To adequately meet the requirements of these measurements, the

objective of the stage development is to produce a device with the

following performance:

Travel

Trajectory of Motion

Roughness of Trajectory

Resolution of Driving

Mechanism

Resolution of Position

1 cm X 1 cm Less than 1 urn over full range

Less than 10 nm p-p

0.1 urn

Resolution of feed-back loop

F. E. Scire and E. C. Teague, "Piezodriven 50-um Range Stage With

Subnanometer Resolution," Rev. Sci . Instrum., 49 (12), Dec. 1978.

41
0 .

I

Li Quid Penetrant Flow Characteristics

5. Ceutsch

-luia Engineering Division

Center for Mechanical Engineering and

Process Technology

Liquid penetrants are frequently employed to locate microscopic,

surface accessible defects in solid, non-porous materials. Initial work

concentrated on identifying and quantifying the factors which affect the

rate and extent of penetration.*

-or small defect width to depth ratios, in which defect widths

range from roughly 0.01 to lOum, it was determined that gravitational

and non-continuum affects may be ignored. In addition, the axial

velocity _ was found to be governed by the Poisson equation

+ G/u = 0

where G is the applied pressure gradient and u the viscosity. Penetration time then, was shown to follow the Ri deal -Washburn relation

2 t ^ i u/ciRcos0

where t is time, i defect depth, a surface tension, R defect width and 9 the static contact angle. The proportional i ty constant, however, was ^ound co^depend strongly on defect geometry and penetrant application

procedure.

The work summarized above ignored the existence of a moving line of

contact between liquid penetrant and air. This moving contact line has oeen the subject of a good deal of theoretical work over the past decade.**

One consequence of the moving contact line is that attempts to use the

traditional no-slip boundary condition there inevitably lead to an infinite force on the boundary. Currently a slip boundary condition is

used as a way around this problem. However, it is not clear that the use of the slip condition is on firm physical ground. In addition, its use leads to a singular pertubation problem, the solution of which is

oractical for only a few simple configurations.

Work will concentrate then, on examining the boundary conditions

at the moving contact line. In parallel, computer codes capable of

handling the problem in more complex geometries will be developed.

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

Penetrant Testing," Journal of Research , Vol . 34, No. 4, July-August 1979.

E.3. Dussan 7., "On The Spreading of Liquids on Solid Surfaces:

Static and Dynamic Contact Lines," Annual Review of Fluid Mechanics,

Vol. 11, 371-400, 1979.

42
P. A New Image Quality Indicator

Robert C. Placious

Radiation Physics Division

Center for Radiation Research

Staff of the NBS X-Ray Physics Group played key roles in the

development, by ASTM Committee E-7, of a new image quality indicator

(IQI) for assessing industrial radiographic film capability. This

device, sometimes referred to as the "Splettstosser plaque," is a multi

hole plaque-type penetrameter which offers promise for quantitative

evaluations of other parts of the x-ray image-forming system as well.

This IQI consists of an orderly array of holes in thin plates. The

plate thickness varies from .015 in. (0.38 mm) to .005 in. (0.13 mm).

The design of this IQI is shown in Figure 14. It is normally used by

placing it on a 3/4-in. (1.9-cm) thick steel plate whose maximum surface

roughness is prescribed. For the conditions stipulated here, the IQI

plus the test plate form a system whose equivalent penetrameter sensitivity (EPS) can be calculated. The actual EPS values vary from 0.94%

up to 1.92% and it would be simple to extend this range if needed. A

series of round-robin tests was performed which indicate that it is not

only feasible to measure EPS using this device but that limiting values

of EPS are directly related to film type. It may, therefore, provide a quantitative index of film capability provided all other parameters and

conditions are maintained constant.

Many other uses for the device have been suggested. As an EPS

indicator it is now undergoing evaluation in our laboratory by comparing

it with commercially available devices designed for measuring unsharpness. Tests on such devices for assessing radiographic definition

(unsharpness) have been completed and the results are expected to be

available shortly.

The advantages of this type of image quality indicator lie not only

in its potential for measuring radiographic parameters but also in its

simple concept and ease of construction. It can be fabricated in a machine shop with a modicum of equipment by any careful investigator.

It is also possible that it will be commercially available provided it

is accepted by the industrial community.

43
IMAGE QUALITY INDICATOR

Shim thickness Hole Size:

Step Step Hole Hole

Identification Size Identification Size

15 .38 nim ( .015") 32 .31 mm (.032")

10 .25 mm ( .010") 31 .79 mm (.031")

8 .20 mm ( .008") 28 .71 mm (.028")

5 .13 mm ( .005") 25 .64 mm (.025")

23 .58 mm (.023")

20 .50 mm (.020")

Fig . 14, Design of IQI

.

44
Q. Real-Time Radiographic System Performance Measurements

M. Kuriyama, W. J. Boettinger and H. E. Burdette

Metal Science and Standards Division

Center for Material Science

Currently the characteristics of a real-time radiographic system

are described by individual laboratories for their own convenience. The

resolution claimed to be attained by one laboratory using a single

isolated small object does not necessarily provide the desired reso- lution for other laboratories which, for example, deal with a collection

of such small objects distributed in materials. In addition to reso- lution, there are two other important factors for characterizing radiographic systems; speed of obtaining diagnostic results and contrast (or

detectability) of objects. The present work describes a method for

evaluating the above parameters in a real-time radiographic system. The

feasibility of this method is demonstrated using an actual x-ray source

for a radiographic system.

The resolution of real time radiographic systems is often considered

to be dominated by the resolution of viewing detectors. This is true,

if only one can prepare either a mathematical point source or a truly

parallel beam. In real-time radiography, unlike films, detectors cannot

be placed in direct contact with or very close to object materials; the

divergence of the beam, or exactly speaking the apparent source size,

cannot be ignored. The resolution of any radiographic (or x-ray optical)

system is intimately related not only to optical slit and detector

systems but also to the characteristics of x-ray sources. It is,

therefore, best to evaluate the quality of radiographic systems including the radiation source as they are in use. The method proposed is

based on the following theoretical consideration. The source emits

radiation non-uniformly ; the radiation from a point of the source has a different angular distribution (divergence) from radiation emitted from

different points. This non-uniform property, including different degrees

of divergence, is represented by I<-(x), where x indicates a point in the source. A detector which usually nas a finite opening sits at the

position y.

The objective in evaluating the quality of optical systems is to

determine such an expanded quantity Ir(x) for the overall system as accurately as possible. For real radiographic systems, this quantity

K(x) obviously includes the effects due to the slit systems before, and

viewing detectors (image intensifiers, films or counters) after, the

object.

45
Among many possible ways, we choose the two simplest modes of the

evaluation of I^(x). As shown in Figure 15, we use here as an object a plate which consists of two regions of different thicknesses. In mode

I, this heaviside object is set at a stationary position and the intensity profile is obtained as a function of position. In mode II, the

object is moving at a constant speed, while the intensity is recorded at

a fixed position in space as a function of time. For both modes, the

intensity is given by

i(y;z) =/ dx[a(x)+6(x) H (z - ^

X

b-a M -

b (1)

where a(x) = I^(x) exp [-uL], (2)

6(x) = I^Cx) [exp {-u(L+aL)> 1

—

1

_i 1 X Q. 1 OJ (3)

and H(x) _ 0 if X < 0

1 if X > 0 (4)

Here the distances a and b between an object and a detector and between

the object and a source, respectively, are assumed to be large compared

with the thickness of the object L and L + aL. The observed intensity

distributions are schematically shown in Figure 15. It should be noted

here that the characteristics of the radiographic system Ir(x) are truly

contained in a(x) and s(x).

If we differentiate I(y,z) with respect to the variable y or z, we obtain

iil^=(^)|dx3(x)6(z-|x-^y) (5)

for mode I with a fixed z and

= Jdx 6(x) 6(z - |x - ^y) (6)

46
INTENSITY

MODE I MODE re

POSITION TIME

F1g. 15. Possible ncthods for cveluoclng the optical performance properties

of radiographic systems, such as resolution, dctcctabiliC/

speed

.

I 47
for mode II with a fixed y. Here 5(x) is Dirac's delta function. The

right hand sides of Eqs. (5) and (6) are both simply related to the

function 3, and thus I^(x). The left hand sides of Eqs. (5) and (6) are

the derivatives of measured data. It is usually easier to employ mode

II, because the detector is in a fixed position and the intensity is

recorded continuously as a function of time as the object moves at a constant speed.

Figure 16 shows the intensity distribution expected from an ideal

uniform source and an actual intensity distribution observed from our radiographic system. Using a mini-computer on site, we can differentiate

the observed intensity to obtain I<-(x) and further to obtain the Fourier

transform of I^(x), which is the modulation transfer function (or more

exactly the optical transfer function.) Also, as seen from Eq. 3, one can obtain the minimum detectable image from this measurement. The details

of the application of this method including reproducibility, reliability

and convenience have been documented in the past year. This technique also

provides simultaneous information on the detectability of objects and the

measure of speed required for diagnosis.

48
INTENSITY

INTENSITY

Fig. 1

IDEAL SOURCE

REAL SOURCE

The ideal intensity distribution from an ideal system and an intensity distribution from a real system, using the proposed

Heaviside technique.

49
R. Neutron Radiography; Standard Measurements of the L/D Ratio

W. L. Parker and D. A. Garrett

Reactor Radiation Division

Center for Materials Science

The purpose of this work is to evaluate two standard methods of

measuring the L/D ratio of a neutron radiographic facility, where L is

the distance between the neutron source and the image plane and D is the

diameter of the neutron source, assuming that the source possesses a finite diameter. In general, an ideal nuclear reactor-based system

consists of a distributed neutron source, a defining aperture, and an imaging system.

Next to the flux, probably the most important parameter to be

specified for a neutron radiographic facility is the L/D ratio, since

it, to a large extent, determines the quality of a neutron radiograph

that can be made.

The determination of L/D should involve only the independent

measurement of L and D, two well-defined distances. However, beam nonuni

formity and scattered neutrons may combine to give an effective L/D

ratio which differs from the simple geometrical ratio.

The method employed is a combination of methods proposed to ASTM by

groups at Aerotest and the IRT Corporation. It involves the measurements

of widths of radiographic shadows of identical neutron-opaque objects

which are placed at different distances from the cassette housing the

converter and film, as shown in Figure 17. As the object is moved from

the image plane toward the source, the width of the shadow increases

while that of the "umbra" decreases.

A series of eight radiographs were made, using cadmium wires as the

objects, for apertures of 1 in. (2.54 cm) and 2.5 in. (6.35 cm). 3y

mathematical analysis of the radiographic data, it was found that the

effective diameter of the aperture, D, was approximately 80 percent of

the actual size. The cause of this phenomenon is presently under investigation, but possible explanations are variations across the beam,

reflections from the collimator sides and the circular geometry.

Fig. 17. Cadmium wire test object.

50
S, Resonance Neutron Radiography for NDE

J. W. Behrens, R. A. Schrack, and C. D. Bowman

Nuclear Radiation Division

Center for Radiation Research

A technique called resonance neutron radiography is being developed.

To demonstrate and test the method a broad energy spectrum of neutrons

and a linear position-sensitive proportional counter were used with timeof-flight techniques to determine the distribution of silver between two

sil ver-soldered metal disks and to measure the thickness of the solder.

A test facility for resonance neutron radiography has been established; experiments completed confirm the scientific validity of the

method. The apparatus is illustrated in Figure 18. The NBS linear

accelerator was used to produce a pul sed-neutron beam spread over a wide

band of neutron energy. This beam was collimated by a narrow vertical

slit and passed through the object to be radiographed. The transmitted

intensity was detected in a linear position-sensitive proportional

counter which contained 4-atm ^He and 6-atm argon. Position sensing was accomplished by charge division from the resistive electrode. The

object under study was moved horizontally by a precision-driven tray.

The data on position of the tray (x-direction) and position of neutron

detection (y-direction) were fed into a data processor. This system

processed the data to form pictures for particular neutron energies of

interest. The neutron energy was determined by measuring the time-offlight of the neutron between source and detector. The method takes

advantage of the unique resonance structure characteristic of a given

isotope of a given element and, therefore, can determine the position

distribution with both elemental and isotopic selectivity.

Testing of the method involved radiographing a brass disk machined

to contain a steel disk. The two disks were silver soldered together.

Solder was omitted from about a 20-deg portion of the full circle. The

objective of the experiment was to determine the distribution of the

silver solder and to measure its thickness.

The results of the measurament are shown in Figure 18. The inner

darkened circle is the inner hole of the disk and the outer circle

represents the boundary of the steel. In looking at Figure 18 it is

clear that the distribution of the silver was not uniform and the "-20-

deg slot is clearly visible. The thickness of the silver in the more

uniform regions averages about 0.025 mm. These results were obtained in

a 24-h run using the 5-eV resonance of the isotope ^°°Ag. Tne resolution

is about 5 mm and the sensitive length of the detector is 20 cm.

51
SOURCE

DYNAMIC

RESONANCE NEUTRON RADIOGRAPHY

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1

»"ig. 18 . NEUTRON RADIOGRAPH

IMAGE OF SILVER DISTRIBUTION
The present experiment centered on determining the presence of

silver within an object. Clearly, other elements and isotopes can be

similarly identified through their characteristic neutron resonances.

The method is useful for elements with resonances below 1 keV and,

therefore, permits measurements on elements as light as Mn and Co. The

detector special resolution can be improved into the submillimeter range

for a smaller sensitive length. Improvements to achieve a higher counting

rate also are possible.

4

53
T. X-Ray Residual Stress Evaluation in the Interior of Materials

M. Kuriyama, W. J. Soettinger and H. E. Burdette

Metal Science and Standards Division

Center for Materials Science

One of the nondestructive methods currently used for measurements

of residual stresses in industrial materials involves the application of

x-!^ay analysis for stress measurement. X-ray diffraction phenomena are used to determine macroscopic residual stresses in engineering components.

The methodology of analysis and its basic principles are well known.

Briefly, when materials are under stress, x-rays are diffracted with a Bragg angle which is si ightly ^different from the Bragg angle expected in

unstressed materials. The change in the Bragg angle is related to the

alteration of atomic interplanar spacings when the crystal lattice of

the materials is strained. As a measurement system, the essential part

of this x-ray technique is the accurate measurement of lattice constants

(or their changes) in materials by use of well -refined Bragg diffractometry. The surface residual stress can be evaluated from the strains

measured by x-ray diffractometry using a set of assumptions regarding

material elasticity and homogeneity. Although the accuracy obtained by

this technique is, in principle, superior to that of any other method, an obvious shortcoming lies in its incapability of detecting strains (or

stresses) in the interiors of bulk materials.

Currently, improved quality control of industrial components

demands quantitative information concerning the stress distributions near cracks and residual stress distributions after different types of cold

working and heat treating. These demands naturally lead to the necessity

of measuring residual strains in the interiors of materials. Ordinary

Bragg diffractometry will not be sufficient to respond to these demands.

There is an entirely different approach to the x-ray evaluation of

residual strains although the approach makes use of the principles of x- ray diffraction. This approach involves the use of energy dispersive

solid-state detectors with high-energy x-ray photons. The use of solid

state detectors has been introduced very effectively in the fields of

scanning electron microscopy (microanalysis) and x-ray fluorescence

analysis of materials in the past ten years. It is called energydispersive spectroscopy. Unlike these successful applications, this

technique has not been applied to the residual stress (strain) measurements of materials. Extremely high resolution and accuracy are required

for strain measurements in comparison with other applications. If one

can improve the resolution sufficiently and overcome other important

technical problems, this new system would be ideal for residual stress

measurement in industry; the equipment will display visually and almost

instantaneously, and analysis of the data will be made on site by a computer. Also, this system, in general, works better for high-energy

photons. High-energy photons also make practical the use of the transmission geometry, since the x-ray absorption coefficient of materials is

approximately inversely proportional to the third power of the energy of

x-rays

.

54
The use of an energy dispersive system for possible residual stress

evaluation was tested in 1973 by Leonard^ who concluded, however, that

this system did not have sufficient accuracy for this purpose. We have

proven that his conclusion was premature and it is still too soon to

dismiss the possible industrial use of this technique for the evaluation

of residual stresses. In doing so, we have proposed^’ ^ a method for

determining a strain tensor in predetermined volumes in the interior of

a material, as shown in Figure 19. In energy dispersive spectroscopy,

one is concerned with the energy spectral profiles and peak positions at

different energy values, instead of Bragg angles which play a key role

in Bragg diffractometry . Lattice constant will be measured in energy

dispersive spectroscopy by the energies of diffracted photons:

d(A) = ( 6.199 x sine ^

1 E(kev) ’ ( 1 )

where d is an atomic interplanar spacing related to lattice constants, E is the energy of diffracted photons measured from peak positions of the

spectra, and the coefficient including half the scattering angle e is

constant for a given scattering geometry. For our purpose, the scattering

angle should be smaller than 30° to ensure complete transmission geometry.

One may claim then that the energy resolution of current solid

state detectors is not small enough to reduce the resolution for the

evaluation of residual strains. It has been known fortunately that each

diffraction profile in the energy spectrum obtained from a solid state

detector is very close to Gaussian. If the mathematical shape is

known for a spectral profile, then the claim mentioned above can be

circumvented: mathematically filling the observed peaks with Gaussian

functions, one can determine the centroids (or peaks) of the profiles

far more accurately than the aE/E value stated above would indicate. As

shown in Figure 20, one can improve by a factor of 100 the accuracy of

determining the centroid positions.

Figure 20 shows an example of the observed spectral profile which

has been fitted by a Gaussian curve with a linear background. The

accuracy of determining the centroid (or peak) position has been found

to depend simply upon the counting statistics. Reproducibility of those

positions has also been tested; as long as the same predetermined volume

is viewed, the centroid position remains identical within the statistical

error. As a reference to possible instrumental instability, the Ag Ka

line spectrum in each run has been fitted with a Gaussian curve. (White

radiation was obtained using a Ag target tube.) The Ag Ka line result

55
SAMPLE

DETECTOR

Fig 19 .

six independent secs of rr.easureticncs vich two detectors. T1

mapping of strains throughout the volune of the sample is

achieved by translations.

56
30'1

Stainless

Steel (

220 ) IIiii I o


 a>

vS> CO

COo

CD

COO

CO


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COoo

CO

QC

UJ

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r~\

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cu

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57

An

example

of

the

observed

diffraction

profile

fitted

with

Gaussian

curve

with

linear

background.
indicated that the instability, if any, is not sufficient to jeopardize

the accuracy in the determination of diffraction peak positions. Our

result demonstrates that strains of 5 x 10"^ can be detected with re- liable reproducibility, if sufficient counting statistics are established,

and strains of 3 x

10"^^ can be detected even with moderate counting

statistics.

In conclusion, an energy dispersive diffraction system has demonstrated its capability as a useful tool for the determination of residual

stresses inside materials when the curve-fitting technique is used

simultaneously. The present demonstration has been carried out with lowenergy photons. The use of high-energy photons certainly makes more

practical the use of these energy dispersive systems for residual stress

evaluation. More penetration and increased energy resolution of detectors will improve the resultant accuracy and detectability of strains.

Since the energy dispersive system can be made simple and compact,

without any delicate moving parts, the system is quite ideal for industrial use on site, particularly when data are handled by a mini-computer.

By no means has the energy dispersive system such as used here reached

the ultimate resolution; further improvements on x-ray optics and detectors

should be made, particularly with high-energy photons.

•Leonard, L., Franklin Institute Research Lab (Philadelphia) Report

F-C3454 July (1973).

^Xuriyama, M. , Boettinger, W. J. and Burdette, H. E., ASNT National

Fall Conference, October, Denver, CO, p. 49 (1978).

^Kuriyama, M. , Boettinger, W. J. and Burdette, H. E., Symposium on Accuracy in Powder Diffraction, June (1979).

58
LI. Wear Condition Monitoring

A. W. Ruff, Jr.

Metal and Science Standards Division

Center for Materials Science

This project is concerned with the nondestructive monitoring of

the operating capability (health) of mechanical systems in which wear is

a significant life-limiting process. This monitoring can take several

forms in the field. The most common methods involve measurement of

system operating parameters, e.g. temperature, speed, pressure or vacuum,

etc. Frequently, these parameters are insensitive to the onset of

failure problems and do not offer adequate early warning. More recently

efforts have been directed toward vibration monitoring of rotating

machinery and systems in order to increase sensitivity. This approach,

while promising, is hampered by difficulty in properly interpreting

changes in the vibration or acoustic spectrum of a system. Further

research is needed in understanding the complicated signal spectrum

obtained in such an approach.

In the last several years, considerable effort has been placed in

developing wear debris recovery and analysis methods for system con- dition monitoring. The Navy Department has led these developments

although such programs now extend throughout the DoD. These methods

generally extract the wear debris from oil lubrication systems and

provide a nearly continuous measure of wear metal formation rate. The

debris method is frequently combined with spectrochemical methods of oil

analysis in the diagnosis of system condition, although the two methods

are sensitive to wear products in a different way. Debris can also be

recovered from non-oil -1 ubricated systems, e.g. gas turbine engine

ducts. Some of these techniques are being applied in the private

sector, e.g. several major airlines and truck fleet systems. Relatively

little understanding of the trends in wear characteristics and in debris

generation mechanisms exists so far. This lack of a firm basis hampers

the further development of debris monitoring methods no matter how

promising. Standards of method application and wear debris analysis are needed to properly apply the techniques on a broad scale. This project

is oriented to assist in these problem areas through method development,

the provision of fundamental understanding, and assistance in standardization activities.

Research efforts have continued in the study of wear debris formation mechanisms in steel and copper metals. The emphasis has been on rubbing (adhesive) wear and on abrasive wear. Abrasive wear is a major

cause of failure in lubricated systems, generally the result of particulate contamination from outside the system (seal problems) or from

recirculation of wear debris particles (filter problems). We have

59
examined the type of wear debris removed from steel surfaces under

various abrasive conditions. Particle size and shape distributions have

been obtained. In the case of wear of copper (whose alloys form the

usual commercial bearing materials), wear debris studies have been

combined with surface and subsurface microstructure studies. Findings

include the tendency for abrasive particles to fragment and become

imbedded in the ductile metal surface. The identification of cutting

chip particles in debris collections does not appear to be a satisfactory indicator of system wear mode. In fact, many debris particles

are produced by plastic deformation processes during abrasive wear and

must be distinguished from normal rubbing wear particles.

Standardization activities involve the ASTM Committee G-2. A wear

debris analysis activity has been started by project staff involving

about ten laboratories. Work will be carried out toward possible refer- ence methods of recovery and analysis. A Navy Department meeting is

scheduled at which worldwide standardization of ferrographic methods

will be discussed. Possible NBS input concerns the area of reference

debris particles. The fall meeting of the Mechanical Failures Prevention

Group involved a session on on condition monitoring of lubricated systems

organized by project personnel.

A Ferrograph system is now available at NBS, purchased through

Recycled Oil Program funds. Once established, that capability will be

applied to engine condition monitoring in several planned projects.

Plans for next year also include the application of acoustic monitoring

methods to bench wear systems where debris recovery and analysis will be

carried out. In this way, two different methods can be simultaneously

applied and compared to indicate system condition. The acoustic monitoring work will be carried out in collaboration with other NDE projects

concerned with acoustic methods.

60
V. Image Metrology Facility

E. C. Teague

Mechanical Processes Division

Center for Mechanical Engineering and Process Technology

With funding support from ONDE and other NBS sources, the NBS Image

Metrology Facility, a system of computer hardware and software has been

developed, principally from commercially available modules, to enable

Bureau staff to obtain dimensional and other analytical information from

a variety of image data. The facility can now be used to acquire and

store images from photographic transparencies via a scanning microdensitometer and will in the future be capable of obtaining images from a vidicon camera, a scanning electron microscope and surface microtopography

instruments.

Images may be stored for analysis and processing in either the

three refresh memories of the display processor, two disc drives or a nine track magnetic tape unit. The display processor allows a user to

analyze and process the data in three 512 by 512 eight-bit images.

Additional features of the processor are a unit which calculates the

histogram of all 260,000 data values in 1.15 second, a feedback unit

which enables iterative operations to be performed on image data at

video rates, i.e., one frame in 1/30 second, and three sets of look-up

tables which may be loaded from the host computer which allows the user

to perform a wide variety of radiometric transformations and point-bypoint algebra on image data.

A large software package of FORTRAN callable subroutines is

available from which users may build specialized programs. The package

consists of a set of 40 subroutines which perform "primitive" operations

with the display processor and a set of utility subroutines. Typical

operations which may be performed with these subroutines are:

Calculate and plot the histogram of an image.

Draw a graph of the intensity variation along the line joining

two cursor locations specified by the user.

Calculate the distance between two cursor locations specified

by the user based on a user defined metric.

Perform a histogram radiometric transformation on an image.

61
Magnify an image by two, four and eight times and select

magnified area from original with continuous trackball

positioning from user.

Shift one image vertically and horizontally to bring it into

registration with a second image.

Pseudocolor an image according to a user specified correspondence

between gray level and color.

Development of this facility continues. A number of application

studies are now in progress.

#

62
W. Safety Factors and Mathematical Modeling

J. T. Fong

Mathematical Analysis Division

Center for Applied Mathematics

The objective of this project is to propose a mathematical framework

(model) to integrate all available quantitative and judgmental information about an engineering system such that the uncertainties associated

with the information are transformed into "rational" safety factors for

engineering and regulatory decision-making. The framework should be

flexible enough to allow experienced engineers and NDE scientists to

fine-tune their judgment as more information becomes available.

During the first year of this project (FY 78) a statistical concept

of a "rational" safety factor, which incorporates "engineering judgment,"

was proposed in an invited paper which susbsequently appeared in Nucl ear Engineering and Design (Vol. 51, pp. 45-54, 1978).

During FY 79 the statistical concept of a "rational" safety factor

was applied to the uncertainty estimate of weld defect dimensions from

field radiographs. A correspondence was developed between two estimates, one based on field radiographic readings, and the other on care- fully conducted laboratory "calibration" experiments. In the case of

the 1976 Trans-Alaska Pipeline Girth Weld Data on Defect Depth, an adhoc factor of 2.5 which had been proposed, was correlated with a variability analysis of three sets of readings of the field radiographs. The

essence of this accomplishment was reported at an international con- ference (Post-SMiRT-5) held in August 1979 at Berlin.

The Bureau's initiative in calling attention to the need to

standardize certain aspects of NDE and inservice data reporting practice

resulted in an invitation to present a paper at an international seminar

on structural reliability (Berlin, August 1979). The paper, "Inservice

Data Reporting Standards for Engineering Reliability and Risk Analysis,"

will appear in a future volume of Nuclear Engineering and Design .

63
X. Electric Power Research Institute/National Bureau of Standards

Acoustic Emission Program

D. G. Eitzen

Mechanical Processes Division

Center for Mechanical Engineering and Process Technology

Acoustic emission (AE) is a new nondestructive evaluation technique

for monitoring structural integrity. It is a passive ultrasonic technique for detecting and locating active structural defects. When a defect in a structure is stimulated, for example by loading in a preservice test or by the actual operating conditions, the defect may emit

high frequency stress waves. The detected signals from the stress waves

are processed in an attempt to locate and evaluate the significance of a flaw. Applications of AE include its use in determining the structural

integrity of aerospace and petrochemical structures, bridges and power

plant components, detection of leaks and loose parts and the monitoring

and control of on-line welding. AE techniques have also proved a valuable

tool in materials research studies. Significant problems, however,

remain in the application of AE. One problem is in the reliability of

detection of defects. There is a significant potential for false calls

since noise sources other than structural defects often exist. Methods

for source discrimination and identification are needed to minimize this

problem. Another problem is one of extracting the necessary information

from the signals in order to determine the character and severity of the source. A third problem area is in interpretation, intercomparison, and

repeatability of AE test results. Methods of determining system or subsystem (e.g. transducer) characteristics have not been adequately

developed and agreed upon. Methods of calibration and standardization

of AE systems and tests are needed.

The need for the development of basic calibration capabilities,

theories for AE and experimental verification was jointly recognized by

the Electric Power Research Institute and the National Bureau of Standards.

A jointly supported project was developed to answer some of the basic

questions regarding the use of AE techniques. The objectives of this

program are:

To develop and demonstrate the theoretical basis, measurement

techniques and calibration procedures required to evaluate the

technical feasibility of using acoustic emission signal analysis

for characteri zing moving cracks or defects. To provide an acoustic

emission transducer calibration capability referred to national

standards, and evaluated signal analysis methods for retrieving

acoustic emission source signals, and for demonstrations of the

feasibility of the methods for predicting defect velocity in structural materials through controlled experiments.

64
The project elements, progress and plans are briefly described

below. Extended discussions of several elements of these tasks follow

this review.

Task 1 - Develop calibration capability for AE transducers

The calibration capability for the ultrasonic sensors used for AE

measurements is to be referred to national standards and offered as a service. The capability is also to be used to characterize the transducers for the experimental phases of the project.

A theoretical base for the calibration is provided by the exact

dynamic elasticity solution to the halfspace with a point force step

function. A new dynamic absolute displacement transducer makes implementation of a calibration service possible. Some results of this

calibration effort are described in Section Y. Also, recent experiments

seem to show the feasibility of developing new piezoelectric transducers

significantly better than those presently available.

Task 2 - Develop theoretical basis for moving defects

The objective of this work is to provide a theoretical framework

for predicting acoustic emission from specific defects, for the analysis

of received signals to determine source information and for discriminating between spurious signals and those from defects. An extended

discussion of the results follows in Section Z.

Much of these frameworks, such as the basic transform approach and

the Green's function for the infinite plate, have been previously developed and reported within this program. More recent efforts have

focused on more specific singal processing problems associated with

source deconvolution and calibration problems. Many concepts and algorithms for filtering and deconvolution have been pursued. Decimation

techniques and an adaptive integration method have been pursued for

deconvolution. A faster, more accurate numerical method for calculating

the wave propagation in an infinite plate is being investigated. A new Fourier transform-type algorithm with less distortion than other algorithms has been developed. Some of the processing work is aimed at

deconvolution in the presence of noise. Some specific theoretical

source and propagation problems still need to be solved.

Task 3 - Correlation of theory and experiment using transparent

material

s

The objective is to correlate experimental AE results from growing

defects in transparent materials with the theoretical analysis of moving

defects. These controlled experiments will demonstrate the feasibility

of the AE analysis methods for predicting defect characteristics.

65
Three experimental configurations for producing cracks in glass

have been fully developed: ball impact, indentor and local thermal

tension. Independent verification shows the glass crack event occurs in

less than a microsecond so that measurement of velocity by AE is not

feasible in this material. On the other hand a characterization of the

event in terms of a force time history at the source through deconvolution

of the measured displacement (absolute AE signal) has been demonstrated

in collaboration with Task 4. The AE events in glass were shown to

agree well with the existing theory. Further comparison awaits additional

specific theoretical solutions.

Task 4 - AE measurements in structural steels

The objective is to perform exploratory tests for measuring crack

characteristics in structural steels, particularly those important for

nuclear reator pressure vessels in the electric power industry. The

experiments should help determine the feasibility of AE analysis for

determining defect characteristics in structural steels.

The signal acquisition and digital data processing systems were further developed. Deconvolution methods for two sensor-source geometries were implemented (see Section AA for details and some results).

A large sample of A535B steel was obtained. Data are being taken on this

and similar steels using several configurations, including a bolt-loaded

stress corrosion specimen and cracking of an embrittled plate with an indentor. Further work on deconvolution of simulated and defect events

in plain and welded steel specimens is planned.

66
Y. Acoustic Emission Transducer Cal ibration/EPRI

F. Breckenridge

Mechanical Processes Division

Center for Mechanical Engineering and Process Technology

A calibration capability is being developed for acoustic emission

(AE) transducers and is ready to be offered as a measurement service.

This activity is partially supported by the larger EPRI/NBS Acoustic

Emission Program described in the preceeding section and by ONR. The

objective is to determine the sensitivity versus frequency of AE transducers over the approximate range of 100 KHz to 1 MHz. This is accom- plished by obtaining time histories from the transducer under test and

from the NBS standard transducer, both mounted on a large (4800-lb) steel

transfer block. The input is a simulated source on the same surface of

the block as the transducers. The resulting time histories are digitized

and processed in frequency space to obtain the desired measure of spectral

response.

Additional physical aspects of the calibration have been recently

explored by means of several experiments:

1. Repeating the same configuration of source and test transducer to determine precision.

2. Varying the test transducer's angle of orientation to determine the effect on transducer response; the dependence of

the response on orientation is small but observable indicating

the presence of horizontal sensitivity in commercial transducers.

3. Varying the location of receiver in an arc around the source;

this yielded no significant dependence of test transducer on arc position.

4. Varying the source-to-receiver separation showed no significant deviation from the expected 1/r relationship.

Calculated aspects of the calibration were also checked by means of

computer experiments. We found that time deconvolution methods and the

FFT method gave equivalent transducer responses. Deconvolution of a wave form from the standard transducer by the calculated surface pulse

waveform yields a total system impulse response as an indicator of

combined errors in the system. These wavefonns showed the errors to be

minor. The spectrum of the surface pulse was obtained. As a check, the

original waveform was reconstructed from this spectrum. An inverse with

respect to convolution was obtained for the surface pulse.

67
The data collecting system has been upgraded to increase the sampling

rate by a factor of four.

It was observed that transducers having a circular area of contact,

when excited by wave motion travelling in the surface, exhibit a circular

aperture type of interference which introduces zeros in their frequency

response. If these zeros occur in the range of interest, the transducer

is not likely to be useful as a calibration transfer standard. This

suggests work is needed on the development of more appropriate transfer

standards. Initial feasibility experiments already conducted indicate

that transducers which could better serve as transfer standards (and,

perhaps, as event sensors) could be developed.

The calibration method described has a number of caveats. Some of

these could be resolved by also developing an epicenter measurement of

transducer response, which is our plan.

68
Acoustic EmissionTheory/EPRI

J. A. Simmons and R. B. Clough

Metal Science and Standards Division

Center for Materials Science

This activity is part of the joint EPRI/NBS program on acoustic

emission. Work in the theory of acoustic emission has been divided into

four parts:

1. Deriving the transfer function formalism

2. Dealing with the plate geometry

3. Signal processing and deconvolution

4. Modelling AE from defect sources.

1) The transfer function formalism which may be summarized by the

equation:

allows one to express the voltage frequency response from a given AE

signal received at a given transducer in terms of a transfer function

containing the material geometry and tranducer characteristics and a •A

mean stress drop tensor, a_ , associated to the emission event. The

transfer function representation is not generally valid, but requires

both restrictions and assumptions. However, it appears likely that this

formalism may well be valid in many technological important applications.

If one wished to invert the AE information to find the source

stress drop tensor, the transfer function formalism leads to certain

important implications: 1) Unlike scalar transfer function problems

where inversion information can be obtained directly from power spectra,

to find from V(w), multiple transducers yielding complex spectra with

phase information are generally necessary. Generally, six separate

observations are needed to separate the six stress components. 2)

Bandpass filtering to eliminate the defect size effect may also be

required, which together with other filtering to eliminate noise, can,

at best, yield band limited information about the source.

2) Stress wave propagation in an isotropic plate has been solved

in this program based on a new Fourier transform technique developed in

collaboration with Prof. John Willis of Bath Univeristy, England. This

technique allows one to compute the transient response in an elastic

plate due to various stress sources located up to about ten plate thick- nesses from the detector. Examples of the response to various point

69
sources applied as step functions in time at five plate thicknesses from

the detector are shown in Figures 22 and 23; the geometry is indicated

in Figure 21. Some of these curves, such as G 31 , also directly yield

dipole response functions. Other dipole responses are obtained by

numerical differentiation. Note that G 31 tends to have opposite values

when the source is changed from the top to the bottom surface. This

fact, which is much more pronounced when the source is somewhat nearer

the detector, may allow the determination of source depth for such

defects as mode I cracks oriented perpendicul arly to plate faces. Other

theoretical consequences of the plate solution are being studied. These

results are accurate to better than 6 digits. The apparent jumpiness of

the curves is due to multiple reflected wave arrivals.

3) In order to invert the signals received from the transducer to

obtain information about the AE source, it is necessary to carry out a numerical deconvolution procedure. A formally similar deconvolution

procedure is required to produce a transducer calibration. Because of

the high priority associated to this latter need, work was temporarily

suspended on the plate solution results to look at deconvolution algorithms. Most of the ordinary algorithms in use today were found to be

non-robust, frequently yielding incorrect answers to deconvolution with

the type of signal needed for tranducer calibration. The problem occurs because of numerical noise amplification produced by deconvolution

algorithms. New algorithms were developed. Two of these require more

extensive computer facilities. One of these methods is being explored

for s#ignature analysis potential. The third, developed in cooperation

with Dr. Diane O'Leary at the University of Maryland, is still being

studied. Since there are a great number of fields where deconvolution

is used, the importance of these new algortihms extends well beyond

acoustic emission.

4) The theory for acoustic emission from expanding planar dislocation loops has been developed. An example of the AE signals from a circular loop expanding with constant velocity for a fixed period of

time in an infinite body is shown in Figure 24.

The need to study real defects as opposed to simpler calibration

type sources introduces a number of requirements due to the generally

lower signal level of real defects and the tensor nature of the defect

signal. The high speed data acquisition system and its associated minicomputer system are now being procured. Low noise preampl ifiers are being built to mount directly on the back of wel 1 -characterized capacitive transducers, each of which will be recorded by a separate highspeed anal og-to-digi tal converter. The current A-to-D converters have

only 3-bit resolution with concommitant lack of dynamic range, and we

70
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71
detector on the same plate surface. Elastic constants chosen at typical stee^

values. Time units are dimensionless. As indicated in Fig. 21, the first ^

f: index on the G refers to the direction of motion of a surface particle while*

the second index gives the direction of the applied force. All other componei

of G are zero in this configuration. Small "TR" on the time axis is the RayT wave arrival time.

72
Fig. 23. Response of infinite plate to step function point source with source and

detector on opposite plate surfaces. Elastic constants chosen at typical

steel values. Time units are dimensionless. As indicated in Fig. 21,

the first index on the G refers to the direction of motion of a surface

particle while the second index gives the direction of the applied force.

All other components of G are zero in this configuration. Small "TR" on the time axis is the Rayleigh wave arrival time.

73
+1.00 X lO’’'^

cm

U(t)

DISPLACEMENT

0

-0.10 X lO"''^

Fig. 24.

ACOUSTIC EMISSION SIGNALS FOR TRANSIENT.

CONSTANT VELOCITY DISLOCATION LOOP EXPANSION

IN ALUMINUM

Vo = c/100 = 1.2 X lO-’cm/s

T = 10'® s h

CLIMB SLIP

<213 SIGNAL PRESENT

CH3 NO SIGNAL

Acoustic emission from a circular loop expanding for lysec with con- stant velocity. The only two non-zero emissions from slip are the san The tv/o radial motions from climb also coincide. The normal motion

response in the X

3 direction is not shown but resembles the radial

motion with a stronger peak at the longitudinal wave arrival time and secondary response of opposite sign to that of radial motion.
are currently studying means for increasing the dynamic range. The

outputs from the analog-to-digital converters are dumped at very high

speed into a remote high-speed peripheral making it possible to record

multiple emissions in a single test in a laboratory environment separated

from the computing facility.

We have chosen to study experimental acoustic emission signals in

steel plate specimens, and are currently studying indentation loading

methods under a variety of conditions to select the most promising

experimental configurations. Our goal is to study microcracking under

controlled conditions where the cracking mechanism will vary from ductile

to brittle. While not yet fully evaluated, brittle type cracks have

been produced at the surface in the heat-affected zones of welds (both

continuous and spot) and in high carbon steel which was given an em- brittling heat treatment.

75
AA. Acoustic Emission Source Characterization/EPRI

N. Hsu

Mechanical Processes Division

Center for Mechanical Engineering and Process Technology

One of the objectives of our work on acoustic emission (AE) is to

determine the source characteristics of the AE event by analyzing the

leading part of the detected AE signals. While detected AE signals

contain potentially useful information about the deformation source mechanisms of a structure under load, signal processing techniques such

as threshold counting, RMS recording, energy measurement, peak detection,

and spectral analysis often fail to extract such information unambiguously. The difficulty lies both in the inherent complexity of the

deformation mechanism and in the lack of understanding of the source mechanism, the wave propagation details, and the physics of the sensor's

mechanical -to-el ectri cal conversion process.

Instead of taking an empirical approach to establish the correlations

between the detected AE and the observed possible deformation mechanism,

we approach the problem by constructing a simple test system which

consists of three main ingredients: a true displacement sensor (capacitive transducer), a simple structure (either a large block or a plate),

and known theoretical impulse-response functions for specific sensor- source relative locations. We first establish the validity of these

ingredients by testing with simulated AE of known step- function time

dependency generated by breaking glass capillaries. Unknown sources are then introduced, one at a time, into the system for determination of

their time functions. Consequently, the difficult problems of the

evolution of an AE signal can be studied separately as three parts: the

calibration of a sensor, the transient wave propagation in a structure

and the source mechanism. This approach thus provides a base for the

quantitative analysis of all aspects of problems related to AE sensor,

structure and source.

In the past year we have further developed a signal processing

scheme which essentially resolves the inverse problem— to find the

source time function from the detected AE signal. We have constructed

explicitly the inverse impulse response functions with respect to con- volution for two source/sensor geometries; one of these is shown in

Figure 25. For the first time any unknown vertical force time function

resulting from impact opening can be determined simply by recording the

displacement at the epicenter (or on the same surface) and convolving

the recorded displacement with the inverse function. Many simulated AE

signatures have been determined and signatures of some AE from brittle

fracture have also been obtained. Two examples of the source recon- structed from the measured displacement are shown in Figures 26 and 27.

This inversion technique not only demonstrates the possibility of

characterizing AE sources completely and absolutely but also has applications in the measurement of force-time functions such as impact, a measurement that is required in many experimental mechanics problems.

76
77

Fig.

25.

Inverse

function

G"

(t)

at

the

epicenter

of

a

large

plate.

The

curve

is

obtained

by

direct

inversion

of

the

impulse

response

function.

Physically,

the

curve

is

the

force

function

required

to

produce

a

displacement

at

epicenter

of

delta

function

time

dependency.
BREAKING

GLASS

CAPILLARY

78

Fig.

26.

Source

force-time

function

of

breaking

glass

capillary

obtained

by

time-domain

deconvolution

of

recorded

epicenter

displacement.

Insert

trace

is

the

recorded

epicenter

displacement.
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BB. Ultrasonic NDE Standards/DARPA

G. Birnbaum

Office of Nondestructive Evaluation

National Measurement Laboratory

An NBS interagency report to the Defense Advanced Research Projects

Agency on "An Appraisal of Current and Future Needs in Ultrasonic NDE

Standards" has been completed. This work, supported also by NBS, assesses

the current status of NDE ultrasonic standards and calibrations and

attempts to determine current and future needs in this area. In addition

to many specific recommendations, the following are some of the broader

recommendations and conclusions: (1) The most important need in current

and future ultrasonic NDE measurement methods is for transducer characterization. (2) New and more quantitative techniques will not in general make obsolete current standards and calibrations; in many cases these

will continue to be useful with relatively minor changes. (3) Because of

the wide variety and requirements of ultrasonic NDE techniques, it is important to deal with standards needs from the viewpoint of an integrated

system rather than as isolated and individual requirements.

In addition to the above report, the following work was completed

as part of the same study. (1) A Comparison of American and European

Ultrasonic Testing Standards, S. Golan, NBSIR 79-1790, which reviews 27

documentary standards from nine industrialized countries and two international organizations. (2) "Ultrasonic Transducers for Materials Testing

and Their Characterization" , by W. Sachse and N. Hsu, Physical Acoustics , Vol . 14, Academic Press (1979). A sunmary of the literature on ultrasonic

NDE standards is being prepared for publication as an NBS interagency

report. It is expected that those reports as well as the report to DARPA

will serve as resource documents for ultrasonic NDE standards.

80
CC. Reliability of Ultrasonic Weld Inspection/NRC

D. G. Eitzen

Mechanical Processes Division

Center for Mechanical Engineering and Process Technology

The Pressure Vessel Research Council (PVRC) performed a round robin

on the ultrasonic inspection of reactor welds. Twelve inspection teams

inspected three large weld specimens which simulate the nozzle area of a reactor pressure vessel. The specimens were welded with an attempt made

to introduce defects at specific locations. A small study, funded by the

Nuclear Regulatory Commission, concerns an evaluation of the procedures

and data resulting from the round robin to see if the probability of finding flaws can be determined in a statistically meaningful way. The actual

analysis of the data is possible future work.

There are several problems associated with the determination of the

reliability of defect detection from the information and data presently

available. There are some questions regarding the design of the round

robin and the inspection procedures and serious questions about the true

condition of the specimens. Any errors in introducing the defects into

the weld region as to location or size result in serious coloration of

the inspection data; the true locations and sizes of the defects are not

known

.

The first analysis of the data indicated a very low probability of

defect detection. However, there was reason to suspect that deviations

between actual and assumed flaw locations account for part of this low

probability. A difference between actual and assumed flaw location

results in two apparent inspection errors: one miss call and one false

call. A second analysis of the data which used the data itself as criteria for flaw location (a two-coincidence method) yielded a somewhat

higher probability of defect detection but still not as high as the

method seems capable of yielding.

To date the raw data have been obtained from the PVRC and discussions

with some participants and experts have been accomplished. The data and

methods are being evaluated by NBS experts in ultrasonic NDE and statistics.

Alternate data analysis schemes are being considered.

81
DD. Application of Nondestructive Evaluation to Construction/Army

J. R. Clifton

Structures and Materials Division

Center for Building Technology

The use of NDE methods in construction is being studied for the

U.S. Army Construction Engineering Research Laboratory. At present,

when the military has a building constructed, it largely depends on the

contractor to use materials meeting the design specifications and to

adhere to acceptable construction practices. As a check on the performance of the contractor, construction inspectors have been used by

the military. However, often these inspectors do not have the necessary

skills and experience to be effective. Therefore, the military plans to

modify this approach. A modification being considered is the incorporation of quality assurance testing of the building materials prior to

acceptance of the completed building. The quality assurance testing

will be based upon NDE techniques.

NDE techniques applicable to concrete quality assurance will be

identified and assessed. Assessment of the NDE techniques will be based

on considerations of usefulness of information obtained, reliability,

level of expertise required to use the equipment and to interpret the

results, and cost-effectiveness. Then, the use of NDE for the quality

assurance of certain other building materials will be assessed.

Important factors which should be part of quality assurance testing

of concrete, and NDE methods which can be used to assess them, have been

identified. These factors include strength, uniformity, density, surface

finish and thickness of concrete, and conditions and location of steel

reinforcement. Applicable NDE methods have been divided into two categories. First are those methods which have proven to be reliable and

whose results are generally accepted by concrete technologists. In the

second are NDE methods that are either being developed or whose reliability needs to be demonstrated.

A report is being prepared which gives the principles, cost,

advantages and limitations of applicable NDE methods. In addition, the

feasibility of combining NDE methods to obtain an improved assessment is

being explored. A field demonstration of selected NDE methods will be

carried out by making tests on actual structures. The purpose of this

demonstration is to convey, to military personnel responsible for design

and construction of military facilities, the usefulness of NDE in

quality control and quality assurance programs.

32
EE. NDE of Moisture in Roofing Systems/Air Force

L. I. Knab and R. G. Mathey

Structures and Materials Division

Center for Building Technology

Moisture in insulated built-up roofing (BUR) systems causes many

premature roof failures. Moisture in the insulation will reduce the

useful life of a membrane by causing blistering, splitting, wrinkling,

and deterioration of the membrane.

Early detection of moisture in roofing is needed if rapid

deterioration is to be prevented. The usual methods of inspection,

however, are slow, costly, require cutting samples from the roof, and

seldom provide conclusive results. The best hope for improvement of

inspection and maintenance procedures is through nondestructive evaluation (NDE) which could possibly provide reliable identification of wet

areas of insulation and membrane.

There are currently a number of promising NDE methods, such as nuclear backscatter gages, electrical capacitance instruments, and

infrared thermography, being used to measure the amount of moisture in

roofing systems. Because the state-of-the-art is such that many un- certainties exist, a comprehensive study was conducted to compare the

accuracy, validity, and applicability of these methods so their proper

role in roofing inspection, maintenance, and repair programs can be

established. The research results obtained in this study were performed

in conjunction with a program to determine the effect of moisture and

its distribution on the thermal conductivity of insulated roofing systems.

A state-of-the-art report describing the NDE methods currently

available, their technical mechanisms of operation, and the currently

published NDE laboratory and field data (1979) is near completion in

work being done for the Air Force.

Laboratory NDE tests were conducted to assess the performance and

response of two nuclear meters, three electrical capacitance instruments, one infrared themography apparatus, and two types of microwave

equipment. With the exception of the microwave equipment, the instruments (or service including the instrument) are sold commercially. The

two types of microwave equipment are in developmental stages; one type

is being developed by the NBS/Boulder Electromagnetics Division and the

other at the U.S. Army Cold Regions Research Engineering Laboratory

(CRREL).

83
NDE laboratory measurements were taken on a total of seventy, 60 cm

by 60 cm (two feet by two feet) roofing specimens, each consisting of a roofing insulation board with an attached, four ply, BUR membrane. The

seventy specimens included five common roofing insulations, each tested

in one- and two-inch thicknesses.

Both gravel and smooth surfaces were evaluated; two thicknesses of

asphalt were included. NDE responses were taken with the specimens

placed on concrete, steel, and wood decks.

Moisture was induced in the two feet by two feet specimens by means

of a water vapor pressure difference. This was accomplished by maintaining the insides of two large chambers, measuring 244 cm by 488 cm (eight feet by sixteen feet) in area, at 38°C (100°F) and 100 percent

relative humidity while keeping the outside of the chambers at 10°C

(50®F) and 25 percent relative humidity. Some of the insulations, such

as fiberboard, gained moisture rapidly while the foamed plastics absorbed

moisture at a much slower rate.

To determine the distribution of moisture, 275 cores were taken

from the wet insulation. The cores were sectioned and oven dried to

determine the moisture content and distribution. The coring data will

be used to study the effect of the distribution of moisture on the NDE

responses.

With the exception of the infrared themography method, NDE measurements were taken at about fifteen moisture content levels for each

specimen. For all the combinations (insulation type and thickness,

surface, and asphalt thickness) and including replication, about 75,000

NDE readings were taken.

The NDE data have been computerized and are currently being

analyzed. An unbiased technique of comparing the ability of each of the

NDE methods to detect moisture is being developed.

Based on an extensive analysis of the NDE data the accuracy,

validity, and applicability of the NDE methods will be evaluated.

Guidelines and recommendations will then be established for the

selection of the most effective methods of determining moisture

in built-up roofing systems.

34
APPENDIX

A. Publications, September 1978 to Present

(1) "Calibrations and Standards for Nondestructive Testing", H. Berger and L. Mordfin, Mater. Eval . 3^, No. 11, pp 36-39

(Oct. 1978).

(2) "Annual Report 1978 - Office of Nondestructive Evaluation",

H. Berger, L. Mordfin, Eds., NBSIR 78-1581 (Nov. 1978).

(3) "The Need For Better Nondestructive Evaluation Technology",

H. Berger, Dimensions, 63, No. 3 (inside cover) March 1979.

(4) "Timber Pilings: Maintenance and Inspection —Summary of a Panel Discussion", H. Berger, Proceedings from 4th Nondestructive Testing of Wood Symposium, Vancouver, WA, August

1978, pp 155-159 (1979).

(5) "An Appraisal of Current and Future Needs in Ultrasonic NDE

Standards", G. Birnbaum, D.G. Eitzen, NBSIR 79-1907 (1979).

(6) "X-Ray Magnifier", W.J. Boettinger, H.E. Burdette, M. Kuriyama,

Rev. Sci. Instrum. No. 1, pp 26-30 (Jan. 1979).

(7) "Piezoelectricity and Pyroel ectrici ty in Polyvinyledene

Fluoride - A Model", M.G. Broadhurst, G.T. Davis, J.E. McKinney,

R.E. Collins, J. Appl . Phys. No. 10, pp 4992-4997 (Oct.

1978).

(8) "Recent Improvements to the ASTM-Type Ultrasonic Reference

Block System", D.J. Chwirut, NBSIR 79-1742 (Feb. 1979).

(9) "Toward the Development of Improved Reference Fatigue Cracks

for Use in Ultrasonic Nondestructive Evaluation", D. J. Chwirut

and D. G. Eitzen, International Advances in Nondestructive

Testi ng , Vol . 6, pp 179-197 (Aug. 1979)

.

(10) "Mechanical Properties of Adobe" , J.R. Clifton, F.L. Davis,

NBS TN 996 (May 1979).

(11) "Electric-Field-Induced Phase Changes in Poly(vinyl idene

fluoride)", G.T. Davis, J.E. McKinney, M.G. Broadhurst, S.C.

Roth, J. Appl. Phys. No. 10, pp 4998-5002 (Oct. 1978).

(12) "A Preliminary Study of the Fluid Mechanics of Liquid Penetrant

Testing", S. Deutsch, J. Res. NBS No. 4, pp 287-292

(July-Aug. 1979).

(13) "Wideband Annular Array Response", D.R. Dietz, S.J. Norton, M.

Linzer, Proc. 1978 IEEE Ultrasonics Symposium, pp 206-211

(IEEE Cat. No. 78 CH 1344-1 SU , 1978).

35
(14) "Expanding-Aperture Annular Array" , D.R. Dietz, S.I. Parks, M.

Linzer, Ultrasonic Imaging No. 1, pp 56-75 (Jan. 1979).

(15) "Neutron Flux Intercompari son at NBS", K.C. Duvall, M.M.

Meier, O.A. Wasson, V.D. Huynh, J. Res. NBS 8^, No. 6, pp 555-

561 (Nov. -Dec. 1978).

(16) "Measurement of the Photoelastic Constants of Optical Materials",

A. Feldman, Opt. Eng. 17_, No. 5, pp 453-462 (Sept. -Oct. 1978).

(17) "Uncertainties in Fatigue Life Prediction and a Rational

Definition of Safety Factors", J.T. Fong, Nucl . Eng. Des.

pp 45-54 (1978).

(18) "Inservice Data Reporting and Analysis," J.T. Fong, Ed., PVPPB-032 (ASME, 1978K

^ ^

(19) "Inservice Data Reporting and Analysis, Vol . II", J.T. Fong,

B. M. Johnson, Eds., PVP-35 (ASME, 1979).

(20) "Inservice Data - The Missing Link in the Exercise of Judgment

in Engineering Decision-Making", J.T. Fong, Inservice Data

Reporting and Analysis, Vol II, PVP-35, J.T. Fong, B.M. Johnson,

Eds. , pp 153-158 (ASME, 1979).

(21) "A Comparison of American and European Ultrasonic Testing

Standards", S. Golan, NBSIR 79-1790 (June 1979).

(22) "Piston Radiator; Some Extensions of the Theory", M. Greenspan,

J. Acoust. Soc. Am. 6_5, No. 3, pp 608-620 (Mar. 1979).

(23) "Nondestructive Tests Used to Insure the Integrity of Semiconductor Devices with Emphasis on Passive Acoustic Emission

Technigues", G. G. Harman, Proceedings of NATO Advanced Study

Institute on Nondestructive Semiconductor Materials and

Devices, NBS SP 400-59 (Sept. 1979).

(24) "Loose-Particle Detection in Microelectronic Devices", J.S.

Hilten, P.S. Lederer, J.F. Mayo-Wells, C.F. Vezzetti , NBSIR

78-1590 (Jan. 1979).

(25) "Review of Ultrasonic Technigues for Measuring Residual Stress",

N. Hsu and W. Sachse, Proceedings of the 39th National ASNT

Fall Conference - Residual Stress Measurement, Denver, CO

October 2-6, 1978 (1979).

(26) "Ultrasonic Tissue Characterization II", M. Linzer, Ed., NBS

SP 525 (Apr. 1979).

(27) "A Comprehensive Ultrasonic Tissue Analysis System", M. Linzer,

S. I. Parks, S.J. Norton, F.P. Higgins, D.R. Dietz, R.W. Shideler,

T. H. Shawker, J.L. Doppman, Ultrasonic Tissue Characterization II , NBS SP 525, M. Linzer, Ed., pp 255-260 (1979).

36
( 28 ) "Dynamic Elastic Modulus and Internal Friction in Fibrous

Composites", H. M. Ledbetter, in Nonmetal lie Materials

and Composites at Low Temperatures, pp 267-281 (Plenum,

New York, 1979).

(29) "Laser-Induced Rayleigh Waves in Aluminum", H.M. Ledbetter

and J.C. Moulder, J. Acoust. Soc. Amer. No. 3, pp 840-

842 (1979).

(30) "Low-temperature Magnetically Induced Elastic-constant Anomalies

in Three Manganese Stainless Steels", H.M. Ledbetter and

E.W. Collinqs, in Metal Science of Stainless Steels, pp. 22-40,

(Met. Soc. AIME, New York, 1979)

.

(31) "Sound Velocity Anomalies Near the Spin Glass Transition In

An Austenitic Stainless Steel Alloy", H.M. Ledbetter and

E.W. Collings, Phys. Lett. 72A , pp 53-56 (1979).

(32) "Dynamic Elastic Modulus and Internal Friction In 6-lOCR and

G-llCR Fiberglass-Cloth-Epoxy Composites", H.M. Ledbetter in

NBSIR 79-1609 (June 1979).

(33) "The SonoChromascope" , M. Linzer, S.I. Parks, Proc. IFIP TC-4

Working Conf. on Computer-Aided Tomography and Ultrasound in

Medicine, J. Raviv, J.F. Greenleaf, G.T. Herman, Eds., pp 73-

76 (North Holland Publishing Co., Amsterdam, 1979).

(34) "Piezo- and Pyroelectricity of Poly( vinyl idene fluoride) from

Plasma Poling", J.E. McKinney, G.T. Davis, Organic Coatings

and Plastic Chemistry pp 271-277 (1978).

(35) "Ultrasonic Transducer Characterization at the NBS", E.B.

Miller, D.G. Eitzen, IEEE Trans. Sonics & Ultrasonics SU-26,

No. 1, pp 28-37, 63-64 (Jan. 1979).

(35) "NDE Publications: 1972-1977'. L. Mordfin, Ed., NBSIR 78-1557

(Nov. 1978).

(36) "Ultrasonic Reflectivity Tomography: Reconstruction with

Circul ar Arrays" , S.J. Norton, M. Linzer, Ultrasonic Imaging

I, No. 2, pp 154-184 (Apr. 1979).

(37) "Ultrasonic Reflectivity Imaging in Three Dimensions: Reconstruction with Spherical Arrays", S.J. Norton, M. Linzer,

Ultrasonic Imaging 1_, No. 3, pp 210-231 (July 1979).

(38) "Flat-Cone Diffractometer Utilizing a Linear Position-Sensitive

Detector", E. Prince, A. Wlodawer, A. Santoro, J. Appl . Cryst.

II, pp 173-178 (1978).

87
(39) "A Fracture Mechanics Evaluation of Flaws in Pipeline Girth

Welds", R.P. Reed, H.I. McHenry, M.B. Kasen, Welding Research

Council Bulletin No. 245 (Jan. 1979).

(40) "The Scattering of Elastic Pulses and the Non-Destructive

Evaluation of Material s" , W. Sachse, S. Golan, Proc. ASME

Winter Annual Mtg., San Francisco, Dec. 1978, pp 11-31 (1979).

(41) "Engineering Aspects of Medical Ultrasonic Imaging: A Few New

Directions" (in Japanese), T. Sato, M. Linzer, Japanese J.

Clin. Med. No. 1, pp 148-152 (1979).

(42) "Neutron Radiographs Using the lonographic Process", P.B.

Scott, S.E. Johnson, G.W. Watson, H. Berger, J. Appl . Phys.

No. 10, pp 5078-5080 (Oct. 1978).

(43) "Light and Vision", G.T. Yonemura, Chapter 2 in Developments

in Lighting - 1 , J.A. Lynes, Ed., pp 25-45 (Applied Science

Publishers, Essex, England, 1978).

(44) "Resonance Neutron Radiography Using A Position-Sensitive

Proportional Counter", J.W. Behrens, R.A. Schrack, and

C.D. Bowman, Trans. Am. Nucl . Soc. 207 (1979).

(45) "Acoustic Emission of Polymers Under Tensile Load", A. Peterlin,

P robing Polymer Structures , Advances in Chemistry Series 174 , Jack L. Koenig, Ed., pp. 15-23 (1979).

88
B. NDE Meetings at NBS

The NDE program has been active in sponsoring NDE meetings, both

symposia and workshops. The purposes behind this significant meeting

activity include (1) drawing attention of the industrial community to

NDE, (2) providing a good record of the state-of-the-art, (3) providing

a forum for information exchange, (4) helping our NBS staff meet individuals active in NDE and learning the status of current work in the

field, and (5) providing a mechanism for NDE people to discuss their NDE

standards needs.

During this past year, NBS sponsored a Symposium on Eddy Current

Characterization of Materials and Structures. The meeting, held in

cooperation with ASNT, ASTM and IEEE, was held at NBS on September 5 to

7, 1979.

C. NBS Seminars on NDE

A list of NBS-NDE seminars held during the past year is given in

Table VII.

89
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D. Awards

There were several recognitions of NBS-NDE people during this past

year. Awards include the following:

Industrial Research, IR-100 Award:

NBS was recognized for work on the x-ray magnifier. NBS scientists

involved in this development include M. Kuriyama, W. J. Boettinger and

H. E. Burdette.

NBS Applied Research Award:

M. Linzer was cited in recognition of his development of a highly

sensitive ultrasonic system - a major development imbodying new technology, improving technological and theoretical approaches - immediately

applicable to medical diagnosis and nondestructive evaluation of materials.

Department of Commerce Silver Medal:

Two NDE people were presented the DoC Silver Medal in ceremonies

at DoC on October 30, 1979.

J. T. Fong is recognized for technological contributions in

mathematical analyses for materials science and engineering.

H. Berger is recognized for his outstanding leadership and

scientific contributions in the field of nondestructive evaluation

and for having attained national prominence in this area.

Department of Commerce Gold Medal:

G. G. Harman, Jr., was recognized for his outstanding

contributions to the field of interconnection bonding of

semiconductor microelectronic devices. His nondestructive

bond pull tests and his acoustic emission measurements have

been widely adopted and acclaimed by industry and government.

Hugh M. Huffman Award of the U.S. Calorimetry Conference:

E. J. Prosen was cited for his outstanding work in

calorimetry and chemical thermodynamics which included

microcalorimetry of cardiac pacemaker batteries.

91
NML Organizational Chart

OFFICE OF THE DIRECTOR

NATIONAL MEASUREMENT LABORATORY

Office of Senior Science Adviser Senior Executive Officer

Associate Director

for Planning

Office of

Advanced Scientific

Research

Associate Director

for Measurement

Services

Office of Oomestic ana

International Measurement

Stanaaras

Office of Weights and Measures

Office of Measurement

Services

Deputy Director

for Programs

Deputy Director

for Resources

and Operations

Office of Nondestructive

Evaluation

Office of Environmental Measurements

Office of Standard Reference

Materials

Office of Standard Reference Data

Office of Measurements for Nuclear Safeguards

Office of Recycled Materials

Center for H Absolute Physical

Quantities

. emoerature

-4 Measurements and Standards Division

Electrical Measurements and

Standards Division

i.engtn and Mass

Measurements and Standards Division

T'me and F^eduency

Division

Quantum Physics

Division

r

Center for Radiation Research

Atomic and Plasma

Radiation Division

Nuclear Radiation

Division

Radiation Physics

Division

Radiometric

Physics Division

Radiation Source

and Instrumentation

Division

Center for Thermodynamics and

Molecular Science

Surface Science

Division

Chemical Kinetics

Division

Chemical

Thermodynamics

Division

Center for Analytical

Chemistry

Inorganic

Analytical Research

Division

Organic Analytical

Research Division

Gas and

Particulate Science

Division

Tharmoohysics

Division

Molecular Spectrcscooy

Division

92

Canter for Materials Science

Chemical Stability and

Corrosion Division

Fracture and

Deformation

Division

Polymer Science

and Standards

Division

Metal Science and

Standards Division

Ceramics, Glass,

and Solid State Science Division

Reactor Radiation

Division
NBS-114A (REV. 9- 78 )

U.S. DEPT. OF COMM,

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 80-2007

3.

4. TITLE AND SUBTITLE

Annual Report 1979, Office of Nondestructive Evaluation

5. Publication Date March 1980

Code

7. AUTHOR(S)

Harold Berger and Leonard Mordfin, Editors

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS CSfreef, City, state, ZIP) 13. Type of Report & Period Covered

Final - FY 1979

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200~word or leas factual aummary of moat significant information. If document includes a significant bibliography or

literature survey, mention it here.)

This report is the second in the series of annual reports on the National

Bureau of Standards (NBS) program in ^nondestructi ve evaluation (NDE). These

reports summarize the program's activ^'ties and plans. The focus of the present

report is on the program's activities in Fiscal Year 1979 and on its plans for

the next five years.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Acoustic; annual report; eddy currents; inspection; magnetic particles;

nondestructive evaluation; penetrants; radiography; statistics; ultrasonics;

visual -optical tests.

18. AVAILABILITY QUnlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF

PRINTED PAGES

[ For Official Distribution. Do Not Release to NTIS UNCLASSIFIED

FH Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

20. SECURITY CLASS

(THIS PAGE)

22. Price

Rj Order From National Technical Information Service (NTIS), Springfield,

VA. 22161 UNCLASSIFIED

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