r

Reference

NBS

Publi - cations

A 1 1 1 M NBSIR 78-1581

Annual Report 1978

Office of Nondestructive

Evaluation

Harold Berger and Leonard Mordfin, Editors

Office of Nondestructive Evaluation

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

November 1978

Issued January 1979

Prepared for: National Bureau of Standards

Department of Commerce

Washington, DC 20234

1 100

.1156

73-1581

BaWonaT Bureau of Standard* may i i nn

NBSIR 78-1581

<t+ I ANNUAL REPORT 1978

OFFICE OF NONDESTRUCTIVE

EVALUATION

Harold Berger and Leonard Mordfin, Editors

Office of Nondestructive Evaluation

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

November 1978

Issued January 1979

Prepared for: National Bureau of Standards

Department of Commerce

Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Preface

This report summarizes the activities of the National Bureau of

Standards (NBS) Nondestructive Evaluation (NDE) Program. It emphasizes

activities over the Fiscal Year 1978. However, since this is the

Program's first Annual Report, some material is included to summarize

activities since the Program was formally instituted in June 1975.

Although the NDE Program was not established until 1975, this does

not imply that no NBS attention was paid to NDE methods and problems

prior to that time. Indeed, some significant developments include the

recognition of the basic concepts of the magnetic particle test method

by Major William Hoke (U.S. Army) while he was working at NBS in the

1920's, the invention of the highly sensitive ultrasonic transducer

material PZT in the early 1950' s by NBS scientists B. Jaffe, R. S. Roth

and S. Marzullo and the development of the first ultrasonic velocimeter

by M. Greenspan and C. Tschiegg in 1957.

More recently, interest in NDE was furthered by the efforts of many

people who recognized the need for improved NDE measurements in terms of

reproducibil ity and in terms of quantitative results. Their efforts led

NBS to the establishment of the NDE Program.

Programs at NBS provide a focus for the activity both inside and

outside NBS. The programs provide funds and directions for needed

technical work that is done within NBS Centers. People remain attached

to a Center but are funded for specific activities in a matrix management approach. A program provides a central organization for outside

inquiries and for distribution of results. Often a program by its focus can provide improved assistance to outside agencies with measurement

probl ems.

In the case of NDE, the Program has functioned in the above manner. Related activities were recognized and additional activities were funded

to make a cohesive program.

Initial emphasis has been on short-range standards and measurement

problems that will impact the major NDE methods. Thus, attention is

given to such areas as ultrasonic reference blocks and transducers,

radiographic film classification, magnetic field leakage and electrical

conductivity standards. In the long-range plan for the Program, it is

recognized that additional techniques or modifications of existing

methods must also be developed in order to make NDE more quantitative

and in order to measure important material parameters such as hardness,

grain size and residual stress. Once all of these factors are in place,

attention can be directed usefully to performance criteria for materials

and structures.

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

technical community about the present directions of the NBS effort in

nondestructive 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
Table of Contents

Page

1 . Introduction 1

2. Personnel 4

3. NDE Technical Program - An Overview 8

A. Acoustic-Ultrasonic Programs 8

B. Radiography 9

C. Electromagnetic Methods 10

D. Penetrant Testing 11

E. Wear Debris Analysis 11

F. Thermal 11

G. Fracture-NDE 11

H. Material Property Studies 12

4. Some Examples of Recent NDE Progress 13

A. Ultrasonic Annular-Array Imaging 13

B. X-Ray Image Magnification 15

C. Theory of Eddy Cuttent Crack Detection 18

D. Use of Vibrational Spectroscopy for NDE 21

E. Safety Factors and Mathematical Modeling .... 25

F. Standards for Ultrasonic NDE 27

G. A Systematic Approach to Ultrasonic NDE Standards 33

H. Evaluation of Pipeline Girth Welds 35

I. Electric Power Research Institute/National Bureau

of Standards Acoustic Emission Program 35
5. Appendix 39

A. Publications 39

B. Publications in Press or Preparation 41

C. Talks by NDE Office Personnel 44

D. NDE Meetings at NBS 46

E. NBS Seminars on NDE 46

F. NML Organization Chart 51

-iv-
1 . Introduction

Nondestructive evaluation (NDE) represents a class of industrial

inspection techniques used for assessing the integrity of materials or assemblies without impairing their usefulness. NDE tests are designed

to reveal the presence of harmful defects such as cracks, porosity,

inclusions and similar inhomogeneities. In addition, NDE methods may

detect more subtle inhomogeneities such as those associated with grain

size or orientation, internal stress, compositional variations, cold

work, and the like, since these variations also may seriously influence

the useful life of the component. In each case, the goal of the NDE

test must be to identify the inhomogeneity in terms of size and location. In this way, the influence of the defect on materials performance

can be reliably assessed.

Nondestructive measurements yield information useful for:

o eliminating defective materials prior to expensive

machining or fabrication,

o assessing the condition of parts or assemblies during and

after fabrication,

o determining the condition of materials or assemblies

after a period of use,

o monitoring to detect signs of failure during operation,

and

o aiding effective failure analysis to minimize future

failure problems.

NDE has a strong impact on productivity, materials and energy

conservation, as well as safety. Improved, more reliable NDE measurements will lead to improved confidence in trade as measurements on goods

and materials are brought closer together. In the present climate of

product recalls and large judgements in the area of product liability,

improved NDE measurements and applications are of particular interest.

The NDE methods commonly used in industry include ultrasonics,

radiography, visual -optical tests, eddy currents, penetrants and magnetic particles. The methods tend to be complementary. Therefore, it

is not unusual to find more than one method used to inspect an object.

Vi sual -optical and penetrant methods are useful for the inspection of

surfaces and surface-connected defects. Magnetic particle and eddy

current techniques can reveal surface and shallow defects in ferromagnetic and electrically conducting materials. Radiography and ultrasonic methods are capable of probing deeply into various materials and

structures. Radiography offers advantages for confirming part placement

in complex structures. Ultrasonic methods tend to be sensitive for the

detection of cracks or any abrupt change in acoustic impedance. A

comparison of the common NDE methods is given in Table I.

1
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Table

I.

Comparison

of

Common

Nondestructive

Evaluation

Methods
The Bureau's NDE Program was formally initiated in June, 1975. The

program has grown in the intervening period by internal reprogramming

,

funds and personnel authorized by the Congress (following recommendations

by the Department of Commerce and the Office of Management and Budget),

and by funds transferred to NBS by other organizations to help solve

measurement and testing problems.

The objective of the Nondestructive Evaluation (NDE) Program is to

improve the reliability and durability of materials and structures

through standardized NDE measurement procedures. NBS works to help

industry develop methods for accurate and reproducible NDE measurements.

This includes technical investigations of standards (both physical

calibration standards and procedural documents such as recommended

practices), characterization of instruments, development of improved

techniques, and the assessment of the meaning of the NDE measurement

relative to material performance.

The Program is organized to address those needs. First, attention

is given to the measurement requirements of the presently used NDE

methods. Secondly, new or modified NDE methods are emphasized to provide more quantitative measurements and to provide measurement capability for performance-related material characteristics. Thirdly,

performance criteria will be emphasized in order to help provide better

information about the actual influence of defects and material parameters

on performance.

3
2 . Personnel

The Office of Nondestructive Evaluation is a program office

coordinated within the NBS National Measurement Laboratory (see

Organization Chart in 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 Gaithersburg, 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 of the Office of Nondestructive Evaluation for FY 1978 is

shown in Figure 1. During this past year, our efforts were supplemented

by two visitors, Dr. W. Sachse of Cornell University and S. Golan of the

Israel Institute of Metals, by a postdoctoral appointee. Dr. Stephen

Norton, and by two guest workers. Dr. Sekyung Lee of Korea Standard

Research and Mr. Yao-Feng Flo of the Institute of Nuclear Energy Research, Taiwan. M. Fahey and S. Norton have now been transferred to

other NBS activities. Wolfgang Sachse has completed his NBS assignment

and returned to Cornell. Yao-Feng Ho has returned to Taiwan.

Principal investigators in various NDE activities at NBS are listed

in the summary in Table II. Investigators named are active in the areas indicated on the basis of NDE program or other related support.

4
Figure

1.

The

Office

of

NDE;

personnel

participation

during

FY

1978.

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Table II Tabular Summary of

MBS - NDE Personnel

Technique or Area Principal Investigators

Acoustic - Ultrasonic Application to:

Building Materials J. R. Clifton

Inorganic Materials E. R. Fuller

Metal

J. A. Simmons,

N. Hsu

H. Ledbetter*

Polymers R. W. Penn

R. E. Green

Crack Characterization D. J. Chwirut

Instrumentation M. Linzer

S. Edelman

Standards

Reference Blocks

Transducers

D. G. Eitzen

Theory J. A. Simmons

R. B. Clough

Radiography

Neutron Radiography D. A. Garrett

Real-Time Systems M. Kuriyama

X-Radiography R. C. Placious

J. W. Motz

Electromagnetic Methods

Electrical, Eddy Current

Methods G. M. Free

B. M. Field

Theory A. H. Kahn

Conductivity Standards L. H. Bennett

Visual Acuity Standards F. Yonemura

Magnetic Measurements L. Swartzendruber

Microwaves D. Ellerbruch*

6
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 L. K. Ives

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
3. NDE Technical Program - An Overview

In this section of the report, the NBS technical program in NDE is

described in general terms with specific information being given for the

many NDE techniques now under investigation. Progress during the past

year is discussed in some detail in selected areas under the heading,

Some Examples of NDE Progress.

A. Acoustic-Ultrasonic Programs

Ultrasonic testing is widely used in industry. The potential for

acoustic monitoring of structures is extremely attractive. The NBS

acoustic-ultrasonic effort is heavily standards-oriented but also includes work to improve these NDE techniques and to provide improved

understanding.

Work is in progress to develop methods for calibration of ultrasonic and acoustic emission transducers. Spectral characteristics, beam

profile, and total sound power measurements are being studied. Transducer calibrations on a limited basis are now available for ultrasonic

transducers in terms of total power (to values of about 15 watts; ac- curacy is estimated at about 5%) and radiation force as a function of

frequency (range is from microwatts to 20 watts in terms of power and to

about 30 MHz in terms of frequency). A full range of transducer calibration services is planned.

NBS researchers are studying ultrasonic test blocks in a project

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

National Aeronautics and Space Administration to determine the reasons

for variability of these metal calibration blocks. A calibration ser- vice for aluminum ultrasonic reference blocks is now available. Calibration services for steel and titanium reference blocks are planned.

Further directions for this effort include the development of materialindependent. test blocks and the development of well-characterized

fatigue cracks that could serve as a calibration artifact for many NDE

tests

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 and the development of piezoelectric polymer sensors.

A program to characterize the important variables in ultrasonic instrumentation is in progress. Imaging instrumentation, including

tomographic systems, is also under development.

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

building materials and electronic components. Specific application

studies involving advanced ultrasonic instrumentation are also being

conducted for the U.S. Nuclear Regulatory Commission (for steel reactor

8
components) and the National Institutes of Health (ultrasonic diagnostic

equipment for cancer detection). Ultrasonic inspection of pipeline

welds is planned as part of a weld performance study supported by the

Department of Transportation.

A project 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

project includes work for improved transducer calibration. The calibration work for acoustic emission transducers is now well advanced;

some initial calibrations have been accomplished.

B. Radiography

Current projects involve work in both neutron and x- radiography

.

The x-ray activity includes investigations of standards for the measurement of spatial resolution in radiographic systems, for the classification of industrial x-ray film and for the characterization of realtime fluoroscopic systems. Developments in progress include work on improved x-ray screens and grids and determination of scattered

radiation content and its effect on radiographic detectors and systems.

A study of the variables in field pipeline weld radiography and the

influence of those variables on the interpretation of the radiographs

and on the use of the radiographs to determine performance characteristics of the welds is part of the project now being pursued for the

Department of Transportation.

The neutron radiographic studies are made primarily with a thermal

neutron radiographic facility at the NBS reactor (a 10 MW, heavy water

research reactor). However, work has also been carried out with a 3 MeV

Van de Graaff accelerator and a 100 MeV linear accelerator; a Californium252 source is also available. A recommended practice for thermal neu- tron radiography has been prepared in collaboration with the American

Society for Testing and Materials, Committee E-7.05. Standards for

characterizing neutron beams for radiography and gaging are under investigation. In a collaborative effort with Argonne National Laboratory, NBS scientists have investigated the use of three-dimensional

thermal neutron radiography. This three-dimensional inspection, improved by image enhancement, is now being applied to the study of

lithium-type, pacemaker batteries, in a project partially funded by the

Food and Drug Administration. Recent work for the U.S. Navy concerns improved detection of corrosion in airframe structures by neutron

radiography; part of this study involves development of new, improved

scintillator screens for thermal neutron image detection.

9
C. Electromagnetic Methods

C.l Visual-Optical

NBS scientists are examining methods for the measurement of visual

acuity under typical NDE inspection conditions. This includes the

effects of the subdued lighting common in radiographic reading rooms and

of the dark booth situations typically used in fluorescent penetrant and

magnetic particle inspections.

The project 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 recom- mendations for improved visual acuity measurement methods.

Investigations of optical NDE methods are planned; these involve

measurement of surface roughness and the need for standards in holographic NDE.

C.2 Electrical; Eddy-Currents

Facilities for dc and ac electrical conductivity measurements have

been completed as the first stage of a new project in electrical and

eddy-current methods. In the future, work will include establishing

measurement procedures for conductivity standards over the range of

1-100 percent of the International Annealed Copper Standard and methods

for the calibration of eddy-current test equipment. Initial calibration

services will be offered to accuracies of 0.5%. It is expected, as experience is gained in the measurements, that accuracy can be improved

to 0.1%.

Current work includes theoretical studies that are leading to

improved understanding of the sensitivity of eddy current systems and new instrumentation development in which imaging techniques for eddy

current systems are under investigation.

A Workshop on Eddy Current Nondestructive Testing was held in

November 1977; a symposium on this topic is planned for September 1979.

C.3 Magnetic Methods

This project 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.

C.4 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 have been related 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

10
D. Penetrant Testing

NBS scientists are investigating the feasibility of preparing a master crack calibration plate for the evaluation of penetrant sensitivity. Electro-forming methods are being studied as an approach to the

preparation of wel 1 -characterized, reproducible, inexpensive crack

plates. Present methods offer the prospect for the preparation of

cracks as small as 0.1 ym in width and depths in the 10 ym range. 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. Surface tension,

wettability, viscosity and corrosive tendencies will be examined in an effort to characterize penetrants and to identify meaningful measures of

penetrant performance. The flow characteristics of penetrant systems

are also under study.

E. Wear Debris Analysis

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

time for engine, bearing and transmission overhaul. This method is now being expanded in a current NBS project 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 compared

to conventional SOAP methods for engine condition monitoring.

F. Thermal

This project is aimed at developing 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, fully assembled 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 will be done in combination with other nondestructive and destructive tests and will result in a nondestructive method to determine power

cell quality.

G. Fracture - NDE

Fracture mechanics analysis of pipeline girth welds to determine

what types and sizes of defects may lead to failure is under investigation as part of a project funded in part by the Department of

Transportation. Fracture mechanics models are being examined and future

plans include work to provide experimental verification of the model or

11
models that offer promise. Destructive tests of pipe weld samples

containing real defects are under way. One of the aims of these tests

is to determine whether or not fracture mechanics analysis is necessary

to evaluate all types of weld defects, particularly round, unsharp

defects such as porosity or slag. The accuracy of NDE procedures to

identify defects and to provide size and location information is also

being examined; emphasis is on radiography and ultrasonics.

Another effort in this area is directed at providing a rational

basis for selecting safety factors in structural systems.

H. Material Property Studies

It is recognized that variations in material parameters, such as texture and grain size can perturb NDE signals. Work to study effects

of material variables on acoustic signals is in the early stages. In addition, it is recognized that nondestructive measurements can be very

useful in detecting variations such as those mentioned above as well as characteristics such as hardness or residual stress. NBS plans call

for a substantial upgrading of nondestructive methods for measuring

residual stress through the development of improved measurement techniques and reference standards. This activity will address existing x- ray diffraction and ultrasonic approaches as well as some new nondestructive measurement concepts.

12
4. Some Examples of Recent NDE Progress

A. Ultrasonic Annular-Array Imaging

D. Dietz, S.I. Parks and M. Linzer

Signal Processing and Imaging Group

Center for Materials Science

A dynamically- focused ultrasonic array system has been developed.

The design is based on a constant F-number approach (Figure 2) whereby,

at short focal lengths, the aperture is increased in proportion to the

focal length. The approach allows the use of larger area array elements, thus increasing the sensitivity of the system. Other major

advantages include a substantial reduction in the delays and refocusing

rates required for the lens synthesis with a corresponding reduction in

the electronic complexity of the system. The initial design employs an array operating at 2.25 MHz with four annuli active at the near focal

length of 1.5 cm. As the focal length increases, the array expands to a maximum of twelve rings with 4.0 cm outer diameter for focal lengths

greater than 12 cm. A single, tapped delay line with 1 vs total

duration provides the time delays for focusing on receive. A variable

point or line focus is provided on transmit. Preliminary results of

water-bath scans of stainless-steel components show that the system is

capable of providing high-resolution imaging of flaws in practical NDE

appl ications

.

A combined theoretical and experimental study of the effect of

bandwidth on the focal plane response of a circular lens and annular

array was also undertaken. The wideband response of a lens and single

annulus was calculated by convolving the impulse response of these

imaging devices with the driving function. For a circular lens, the

beam width in the focal plane, as well as the position and height of the

sidelobes, was analyzed as a function of bandwidth and aperture weighing. The wide bandwidth model of an annulus was used to calculate the

response of an annular array. Excellent agreement was obtained between

this model and the experimentally measured response of the array operating at 2.25 MHz with 40% bandwidth.

13
Q

14

Figure

2.

Principles

and

schematic

diagram

of

expanding

aperture

annular

array

used

for

dynamic

focusing

on

receive.
B. X-Ray Image Magnification

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

Metal Science and Standards Division

Industrial applications of radiography presently demand the early

real-time detection of small flaws such as tight cracks in materials.

The live images of flaws or structure are recorded (or viewed) usually

on a detector (an electro-optical imaging system) with similar size as the image itself. In order to detect small objects, an improvement in

the resolution of real-time imaging systems is required, hopefully

without loss of image brightness. However, attempts to improve the

resolution usually result in a significant loss of intensity. Thus, the

detectability (or intensity sensitivity) of small signal changes caused

by flaws will be lost due to a lack of brightness. Any approach in the

improvement of resolution for real-time imaging always encounters two

opposing problems; if one improves the resolution, then the brightness

generally decreases, and vice versa. Present commercial image intensifies have resolution limits determined by the multistage configuration and the fiber diameter in fiber optic plates. They may be about

50 pm, down to 10 pm at best.

We have developed a technique which enables us to magnify an x-ray

beam containing structure information (radiography or topographic images)

before it reaches a detector. This magnification capability can be used

either to improve the overall resolution of existing x-ray radiographic

techniques which are limited by the detector or to permit the use of

less complex (and high gain) imaging systems to attain resolutions

already possible. In our demonstration an x-ray magnifier displayed a detailed image of 1000 mesh gold grid (25 pm spacings) with good con- trast on a real-time basis on an ordinary image intensifier of 100 pm

resolution. In order to magnify an x-ray beam which contains structure

information (such as one containing radiographic images), the beam is

successively diffracted from two silicon crystals. The first diffraction magnifies the beam horizontally and the second in a perpendicular

direction.

This magnification technique makes use of Bragg diffraction from a nearly perfect silicon crystal free from dislocations. This type of

Bragg diffraction, often called dynamical diffraction , has unique features which are essential for making x-ray image magnification possible. When an x-ray beam diffracts from the surface of a crystal and the

diffracting planes are not parallel to the crystal surface, the diffraction is termed asymmetric. There are three aspects of asymmetric dynamical diffraction which are important for the x-ray magnifier; beam

magnification, reflectivity and the acceptance angle for the diffraction. Figure 3 shows schematically the asymmetric diffraction geometry.

An incident parallel monochromatic beam of x-rays is magnified in one dimension by a factor m as shown in Figure 3, where and e

^ are

15
the angles between the crystal surface and the incoming and outgoing

beams respectively. Obviously, high magnifications are obtained when

0. is very small. The "quantum" efficiency of an x-ray magnifier is

determined by reflectivity under Bragg conditions. The ratio of the

diffracted total flux (photon/sec) to the incident total flux is called

the reflectivity and is a function of the deviation from the Bragg

condition. For a thick perfect crystal with negligible absorption, this

ratio is unity for a range of angles centered about the Bragg condition

and falls to zero rapidly for larger deviations from the Bragg condition. Because the reflectivity is unity regardless of the diffracting

plane, the intensity (photons/sec cm2

) of a parallel beam magnified in one dimension by asymmetric diffraction from a perfect crystal is decreased by a factor (1/m) only because of the magnification of the beam

area. Since refractive indices for any materials cannot be larger than one for the ordinary x-ray energy range, the unity reflectivity is the

highest efficiency, that is no loss, which one can expect in x-ray

optics. As shown in Figure 3, the maximum divergence of the outgoing

beam, Ae

Qut , is related to the quantity oo s

, which is determined by the

crystal property of silicon, and is of the order of 6 arc second. This

small value of 0 ^ guarantees the one to one correspondence of the

details between the unmagnified images and the magnified images.

16
A$out

igure3.

Asymmetric

Bragg

diffraction

showing

one-dimensional

magnification

ot

an

x-ray

beam.

The

cross-section

of

the

incoming

beam,

d.,

is

magnified

bya

factor,

fii,

to

produce

the

outgoing

beam d

The

extrerMhy

narrow

divergence

of

the

outgoing

diffracted

beam

created

by

dynamical

diffraction

guarantees

the

faithful

magnification

of

x-ray

images

present

in

the

incoming

beam.
C. Theory of Eddy Current Crack Detection

Arnold Kahn

Ceramic, Glass and Solid State Science Division

Eddy current inspection methods at frequencies of the order of 5 to

200 kHz are very commonly used for the detection of cracks and flaws.

However, there has been relatively little attention given to the fundamental analysis of the sensitivity of the method. To contribute to what

we consider to be an important element in this field, we have performed

rigorous calculations on the eddy current distribution in a model problem. The results are now being prepared for publication.

The case studied is that of a cylinder with a longitudinal, radial

surface crack. A detecting solenoid surrounds the cylinder. The effect

of the crack is to modify the impedance of the surrounding coil. This

modification is shown in Figure 4> where the arrows indicate the shift

of the complex impedance due to the crack. The figure shown is for a depth of one half the radius, a large value selected for demonstration

purposes. The change of impedance is largest in the vicinity of a/6

(radius/skin depth) equal to 2, and the change is mostly in the reac- tance component. The calculations have been executed for varying crack

depth at selected values of a/6. We obtain the results that for small

crack depth, the relative reactance change is proportional to (crack

depth/radius) 2 with a constant of proportionality that depends on the

ratio a/6 . The results are shown in Figure 5. In the region of greatest sensitivity, a/6 - 2.0, we find that in the limit of small crack

depth the optimum detectability is given by

A ImZ = 0.70 ImZ

Q

(d/a) 2

,

where A indicates the change duetto the presence of the crack and ZQ

is

the impedance in the absence of the crack. Application to laboratory

measurement capability will be carried out in the near future.

18
SOLID CURVE - WITH NO CRACK

ARROWS - INDICATE SHIFT DUE TO CRACK

REAL PART OF

NORMALIZED IMPEDANCE

a=CYLINDER RADIUS

6=SKIN DEPTH

Figure 4. Impedance Diagram for a cylinder with crack depth

equal to 0.5 x radius.
tt a

d

d=CRACK DEPTH

a=CYLINDER RADIUS

8=SKIN DEPTH (= )

Figure 5. Plot of ira/d x relative change of reactance vs. crack depth

for varying ratio of cylinder radius (a) to skin depth (6).
D. Use of Vibrational Spectroscopy for NDE

Darrel 1 Reneker - — - Polymer Science and Standards Division

The structural soundness of an object can be evaluated if its

vibrational spectrum can be compared with that of a like object of known

mechanical integrity.

We have developed a method for making such observations that combine

the use of a piezoelectric polymer transducer, a synchronized method for

mechanically exciting the test sample, and a small computer capable of

making digital Fourier transforms. We initially applied this technique

to a bar of poly-methylmethacrylate, exciting vibrations by dropping a steel ball or striking the end-surface with a glass bob pendulum.

Impact points were varied, and an electromagnet was used to release the

ball so that time and point of contact were reproducible.

The electrical signal from the transducer was complicated, oscillatory, and decaying. It was amplified and applied to a digitizer. The

digitizer was triggered by an electrical signal from the electromagnet

for the vertical xirops or by .-the positive slope of the signal for the

pendulum hits;. The analog signal was filtered by a 20 kHz 4-pole

Butterworth filter and then'digitized at a rate corresponding to a spectral width of 20 kHz. Digital resolution was 10 Hz per point. The

power spectrum of the signal in the frequency range 0 to 20 kHz was obtained using a fast Fourier transform algorithm in a computer with an 8k memory. A series of such spectra were obtained for varying modes of

exci tation.

These spectra were compared with those obtained from corresponding

experiments conducted after the bar was altered, first to simulate mass defects and then cracks, and again after temperature-induced changes in

modulus were produced. See Figures 6 and 7.

The data indicate that there are defects to which the modes

observed in a particular experiment are insensitive, but in principle

there exist modes of vibration sensitive to every aspect of the me- chanical integrity of the sample. This method requires that the sample

support, excitation, and transducer position be chosen so that the

observed spectrum is in fact sensitive to the important aspects of the

mechanical integrity of the part tested.

Although we have demonstrated this NDE technique on plastics, it is

also applicable to metal or ceramic objects and even to assemblies of

the same or different materials involving several parts in good mechanical

contact. The spectra are sensitive to changes in modulus or density,

both of which may vary significantly in plastics due to differences in

cooling rates or additives.

21
INTENSITY

(ARBITRARY

UNITS)

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000

FREQUENCY, Hz

Figure 6. A typical spectrum for a ball drop excitation (solid line) and

for a pendulum impact at the center of the end face (dotted

line). The peaks labeled v> n are due to modes that bend the

long axis and those labeled are due to longitudinal modes

along the long axis. The amplitude of the Vj peak was reduced

by 1/4 with respect to the others so it could be plotted con- veniently. The vi peak of the dotted curve lies almost exactly

beneath the peak of the solid curve.

22
Figure 7. The positions of the peaks assigned to the n=l and n=3 bending

modes shown on an enlarged scale. The displacements and nodes

associated with each mode are indicated schematically in the

insets. The demonstrated sensitivity to optimally placed mass

defects was about 2 % of the mass of the bar. On the diagrams

at the right the impact point of the ball is indicated by an \,

the impact point of the pendulum by an arrow, the position of

the supports by a small vertical bar, and the points at which

pieces of wax were added to increase the mass by black dots.

In all cases the active area of the transducer was at the center

of the broad face of the bar as indicated by the small open

circle inside the schematic outline of the transducer. The

mass was added in two equal and symmetrically placed pieces.

The total mass added was 8.2 grams for E, 12.7 grams for F,

and 2 grams for J, K, L, P, and Q. The peak positions ^

were

strong peaks observed in most experiments but were not assigned

to normal modes.

23
Defects may cause frequency shifts, changes in amplitude of modes,

or the introduction of new modes. Some defects have little effect on a particular mode, and observation of a single mode can be regarded as a test for only certain kinds of defects at certain points in the sample.

Since a number of modes can be observed by varying the point of excitation (and even more by attaching additional transducers), a reasonably

complete examination of the sample can be made. Higher order modes are expected to be particularly useful for detecting periodically distributed defects.

The method described here can be used to survey and then to observe

those modes of greatest interest in detail. Related vibrational NDE

methods, specialized to particular objects, do not have such broad

capability for survey. The fact that data are processed in digital form

facilitates comparison of spectra from a test object and an object known

to be good. This reduces, or in many cases eliminates, the need to

identify the displacements associated with a particular peak.

24
E. Safety Factors and Mathematical Modeling

Jeffrey T. Fong

Mathematical Analysis Division

The objective of this project is to propose a mathematical

framework (model) to integrate all available quantitative and qualitative information about an engineering system such that the uncer- tainties in the so-called engineering data could be transformed into

"rational" factors of safety for design 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. Typically, a sizable amount of NDE data and en- gineering test data are generated with varying degrees of uncertainties,

and the problem is to integrate all available information for a "rational" decision involving the safe operation of a specific system.

Mathematical modeling becomes the natural vehicle to accomplish this

task.

This project will consist of three phases:

Phase I Conceptual Modeling and Design of Data Structure,

Phase II Modeling of Data Uncertainties and Their Integration,

Phase III Testing of Models on Specific Applications.

In carrying out Phase I, care must be taken on the quality and the legal

implication of a large body of engineering data currently available on mechanical components. This requires the collaboration of many knowledgeable engineers and managers in both the industry and the government

where data are generated and evaluated. Phase II requires the expert

collaboration of material scientists, statisticians, NDE specialists,

and computer scientists to formulate a workable model. To test the

validity of a class of models, we intend to apply them selectively to

critical systems for which the engineering data are sufficiently welldocumented.

During FY78, the first year of this project, we undertook several

small steps on the Phase I aspect of this work; progress was achieved in

two major areas as described below:

1. Safety factors for fatigue life prediction - a proposed

definition based on test data uncertainties and sampling

theory.

In an invited paper soon to appear in Nuclear Engineering and

Design, the concept of safety factors for fatigue life prediction is

discussed using both the well-known Gaussian and the not-so-well -known

25
Weibull statistics on a typical set of data as available in the

literature. Attention was given to the inherent uncertainties of any

set of test data as well as the interpretation of the data based on elementary results of a sampling theory. The importance of using en- gineering judgement to interpret failure data is illustrated by ranking

the uncertainties of some engineering data on U.S. pipelines. A new definition of safety factors for design under uncertainties is proposed.

2. NBS to co-sponsor an International Symposium on Inservice Data

During the Winter Annual Meeting of the American Society of

Mechanical Engineers, San Francisco, December 10-15, 1978, a two-session

symposium on Inservice Data Reporting and Analysis for Pressure Vessels,

Piping, Pumps and Valves will be held to discuss both the current status

and some new approaches to the collection of engineering data on critical components. This symposium is co-sponsored by four ASME divisions

(Pressure Vessel & Piping, Design Engineering, Materials, and Nuclear

Engineering), two ANSI committees, two research institutes (EPRI and

SwRI), and two government agencies (NRC and NBS). A total of 13 written

contributions from U.S. and abroad have been received for presentation

and discussion at the conference. A special publication containing the

full text of all those contributions will be available to symposium

participants and the public prior to the December meeting. To promote more

incisive discussion during the one-day symposium, the organizing

committee has initiated the preparation of a preview containing the

abstracts of all papers as well as one or more official discussions of

each paper by invited experts in the field of data collection and re- liability analysis. The symposium organizing committee is chaired by

this author, who also serves as the editor of the ASME Special

Publication on the Symposium.

26
F. Standards for Ultrasonic NDE

Donald 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 un- certainty 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 are indicated

below:

1. Ultrasonic Transducer Power Output Versus Frequency

Using a modulated radiation pressure technique, the absolute total

power output of ultrasonic transducers is measured versus frequency

over any part of a range from about 0.1 - 20 MHz. The uncertainty

is frequency dependent but is nominally about ± 5%. In addition

to this frequency information the measurement provides the value

of the radiation conductance used to calculate absolute power output levels. The apparatus, procedure, error analysis and results are discussed in "Ultrasonic Transducer Power Output by Modulated

Radiation Pressure" by Greenspan, Breckenridge and Tschiegg, J. Acoust. Soc. Am., 63(4) (Apr. 1978).

2. Ultrasonic Transducer and System Power Output by Calorimetry

Using a twin, series flow ultrasonic calorimetric comparator, the

time-averaged total absolute power output of a transducer or system is measured for any voltage input waveform in the range of 1-15

MHz. The uncertainty is approximately ± 1 %. The system, procedures and uncertainties are described by "Ultrasonic Calorimeter

for Beam Power Measurements" by Zapf, Harvey, Larsen and Stoltenberg,

NBS TN 686 (1976).

3. Aluminum Ultrasonic Reference Block Calibration

Sets of ASTM E-127 type ultrasonic reference blocks are compared

with an interim reference block and associated model using a wellcharacterized measurement system. The service provides a mechanism

for comparing sets of blocks with the NBS data base and with other

reference blocks through the NBS ultrasonic system. The system and

detailed procedures are described in "Procedures for the Calibration

of ASTM E 127-Type Ultrasonic Reference Blocks" by Chwirut, Sushinsk\

and Eitzen, NBS TN 924 (1976).

27
4. Loaner Services for Transducers and Reference Blocks

By arrangement, carefully characterized ultrasonic source transducers and aluminum reference blocks can be made available for

loan. These can provide on-site calibration with the user's system. Using the accurately measured calibration ultrasonic source transducers, a user's power or frequency measurement system can

be calibrated in-si tu. The loaner aluminum ultrasonic reference

blocks, which have been carefully compared with the NBS interim

reference standards, provide a means for users to compare their

reference artifacts with those of NBS on their own ultrasonic

system.

Additional work on ultrasonic measurement systems is in progress.

An expansion of the NBS artifact system for ultrasonic reference blocks

to steel and titanium reference blocks is being developed. The feasibility of developing improved steel and titanium reference blocks is to

be established by mid FY 1979. Also under consideration are materialindependent reference blocks made of amorphous, low attenuation material;

these could replace much of the present multiplicity of reference

arti facts

The influence of changes or adjustments to instrumentation on the

variations in the amplitude of response from reflectors has also been

studied in some detail. For example, changes in the pulse length

adjustment of a flaw detector result in amplitude response changes from

a reference block by over 13%, even after normalization. A study of the

effects of different (but very similar) transducers was also conducted

("The Evaluation of Search Units Used for Ultrasonic Reference Block

Calibrations" by Chwirut and Boswell, NBSIR 78-1454). The study showed

variations of over 26% in response due to different transducers,. This

study has important implications; one of the key issues is: what are

the necessary tolerances on the instrumentation in order to obtain the

required reliability and uniformity in ultrasonic NDE?

Another important area of study is the development of methods for

determining the directivity pattern of ultrasonic transducers. A

mathematically well-founded method called planar scanning is being

developed as a laboratory method. It is capable of determining all of

the important field point parameters of transducers. Work is also

proceeding on the development of techniques more appropriate for the user community.

A calibration capability is being developed for acoustic emission

(AE) transducers and will shortly be offered as a measurement service.

This activity is partially supported by the larger EPRI/NBS Acoustic

Emission Program described in section 4.1 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 accomplished by obtaining

28
time histories from the transducer under test and 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.

The simulated source and transfer block produce a vertical surface

displacement that is theoretically calculable (Figure 8). The displacement measured by the first candidate standard transducer is shown

to faithfully reproduce the actual displacement as shown in Figure 9.

A newly designed and constructed standard tranducer has resulted in

further accuracy; it provides measurements of dynamic absolute displacement of the order of angstroms with an uncertainty of about 3%

(Figure 10).

There is also a substantial, associated theoretical effort. Theoretical developments using the scattering matrix description of electroacoustic transducers has impacted work on determining directivity patterns

of transducers. Two recent theorems on the nature of the radiated field

of generalized acoustic sources suggest future calibration techniques

for users. A recent theoretical description, which more accurately

describes actual transducers, is making possible more realistic standards procedures (NBS and ASTM). Theoretical developments in dynamic

elasticity are making possible the development of primary and secondary

acoustic emission calibration methods.

29
to• • cm• o

Z/UrilL . (-L)m

CM

t

i M"

I

r

=

ct/r

Figure

8.

Theoretical

./aveform

of

vertical

displacement

on

the

transfer

block.
f+-H H-H H-H H-H H--H1 H-H H-H H-H

Figure

9.

Displacement

of

transfer

block

measured

with

model

1

NBS

transducer.

New

NB5

transducer

gives

even

better

agreement

(not

shown)

with

theory.
STEEL BLOCK JAN. 12.1978

APPLIED FORCE (div)

Figure 10. Plot showing about 3% agreement in dynamic surface

displacement between theory and measurement using new NBS standard transducer.
Figure

9.

Displacement

of

transfer

block

measured

with

model

1

NBS

transducer.

New

NBS

transducer

gives

even

better

agreement

(not

shown)

with

theory.
STEEL BLOCK JAN. 12.1978

APPLIED FORCE (div)

Figure 10. Plot showing about 3 % agreement in dynamic surface

displacement between theory and measurement using

new NBS standard transducer.
G. A Systematic Approach to Ultrasonic NDE Standards

George Birnbaum

Office of Nondestructive Evaluation

NBS has undertaken a study, supported in part by DARPA, to assess

the current status of NDE ultrasonic standards and calibrations and to

determine current and future needs in this area. The source material

for this study includes surveys of the literature and patents, a study

of foreign practice, surveys of NBS and consensus standards (e.g. ASTM)

programs, discussions, visits and letters, and a Workshop on Ultrasonic

NDE Standards: "Current Needs and Future Directions," held October 17-

18, 1977 for the purpose of implementing the objectives of this study.

This resource material is being critically analyzed to determine: I. what needs to be done to improve existing standards or standards for

existing systems; II. to select for further evaluation proposed

standards and calibration methods; and III. to assess the requirements

for standards and calibration for developing ultrasonic systems.

Following this analysis, we will make recommendations for work in parts

I to III which should provide the basis for an approach to a system of

ultrasonic NDE standards. In part I, we recognize that improvement of

accepted standards, e.g. those proposed by ASTM, traceable to NBS, or those widely used in practice, will have an immediate and cost effective

impact on improving the reliability and more quantiative use of current

methods. It is also clear that improvements in these standards and in

the underlying theory, and in their relation to practice will have

significant, direct impact on future systems. Part II deals with proposed methods which are new, rather than improvements to those considered

in Part I. The emphasis here is not on unexplored ideas but rather on the examination and possible implementation of the concepts for specific

standards needs. Part III deals with standards and calibration needs

for evolving and future NDE methods.

Recommendations for improvement in existing standards will impact

primarily on conventional pulse echo systems and include work on transducers, the electronic system and reference blocks. The fields produced by transducers are complex and the variability is high. Thus an important aspect of the transducer characterization problem is the need

for a better understanding of the experimental and theoretical nature of

transducers to develop minimum specifications to obtain reproducible

results in flaw evaluation. Similar considerations apply in the electronics characterization. What are the right things to be measured and

how should they be measured? The electronics and transducer calibration

problem is not so much how to do it but what. In the areas of blocks,

the development of quartz blocks free of the material problems of metal

blocks is a promising future direction. However, a new problem, that of

transferring the calibration to metal components, must be solved.

33
Many methods of standardization and calibration have been proposed

which seem to offer logical or practical advantages over currently

accepted features but are not widely used or used at all. These methods

should be completely analyzed with a proper set of criteria and promoted

if they indeed prove to be significantly advantageous. As an example of

this process we have examined the possibility of using theoretically

characterized scatterers such as spheres where the theoretical knowledge

of the scattering cross section is to play a crucial role in the calibration process. Although this feature would appear to be attractive,

we find that some of the advantages claimed for the method are really

not important in practice and that further work is necessary. On the

other hand, this study indicates that theory may play a significant role

in aiding the transfer of a calibration to different conditions, for

example, frequency and bandwidth.

We finally consider the standards needs for developing techniques.

Two of the major needs which motivate these developments are quantitative measurements of flaw geometry, orientation and size and a decrease

in the dependence on operator interpretation. The coupling of minicomputers to NDE equipment, and the use of adaptive and imaging systems,

appear to make such hopes real. What are the standards requirements of

such systems? Do such systems need standards? Our analysis of the

problem leads us to suggest that more complex systems will require more

careful characterization and more complex reference standards, Exactly

what these will be is the subject of further research. However, it

appears even at this stage that some of the necessary standards might

not be too different from many that are in current use.

34
H. Evaluation of Pipeline Girth Welds

Leonard Mordfin

Office of Nondestructive Evaluation

The Department of Transportation (DOT) is sponsoring work at NBS on the inspection and evaluation of girth welds of the kind used in cross- country pipelines for oil and gas.

Recent advancements in NDE and fracture mechanics have led to a widely held contention that the existing quality standards for pipeline

welds are too stringent. In particular, the contractor for the now- completed Trans-Alaska Oil Pipeline asked DOT to waive these standards

for a substantial number of defective welds on the grounds that a fracture-mechanics analysis showed that they would not diminish the

performance of the pipeline. Acting in a consulting capacity to the

Department's Office of Pipeline Safety Operations, NBS evaluated the

technical merits of that waiver request. This proved to be a difficult

task because the contractor's application provided insufficient data for

a rigorous assessment.

In order to provide a more efficient procedure for future evaluations of this type, the present NBS effort is designed to furnish DOT

with some of the technical information it would need to establish guidelines governing the content of such waiver requests.

The NBS effort has both fracture-mechanics and NDE components. In the former, experimentally verified fracture-mechanics models and other

predictive approaches for pipeline girth welds are being developed in

order to identify the kinds of data needed to properly assess the performance of flawed welds. The NDE part of the work seeks to identify

the kinds of radiographic information which are needed to properly assess defect dimensions, and will also develop improved inspection

procedures (radiographic and ultrasonic) that will enhance the

characterization of weld defects.

This three-year project was initiated quite recently (February

1978), but substantial progress has already been achieved. Literature

surveys and test method evalutions are under way. The most visible

results involve the fabrication of girth welds, containing intentional

defects of various kinds, in full-scale pipe of a commonly used type.

These welds have been inspected radiographically and ultrasonically and

will be cut into laboratory-sized samples for mechanical testing

eval uations.

35
I. Electric Power Research Institute/National Bureau of Standards

Acoustic Emission Program

Donald 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 already proved a valuable tool in materials research studies.

AE techniques are relatively new and significant problems remain in

their application. 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. Techniques such as threshold counting, energy measures, peak detection

and straight-forward spectral analysis often fail to yield the critical

information. 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 of 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 stated objective of

this joint project is

To develop and demonstrate the theoretical basis,

measurement techniques and calibration procedures required

to evaluate the technical feasibility of using acoustic

emission spectrum analysis for characterizing moving

cracks or defects. To provide the electric power industry with an acoustic emission transducer calibration

36
capability referred to national standards, and evaluated

spectral analysis methods for retrieving acoustic emission source signals, and for demonstrations of the feasibility of the spectral method for predicting defect

velocity in structural materials representative of power

plant structures through controlled experiments.

While the objective is stated in terms of the electric power industry,

the impact of this effort is clearly much broader than a single industry

or agency.

The project elements, progress and plans are briefly described

below.

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. Some initial results of this calibration effort are described

in this report, Section 4.F.

Task 2 - Develop theoretical basis for moving defects

This work will result in a theoretical base for methods of retrieving acoustic emission source signals and for distinguishing between

defect motion and spurious signals. The generalized transfer function

approach for describing a theoretical basis for AE analysis developed

and disseminated in the project has received further acceptance in the

technical community and forms standard language. Significant refinements have been theoretically developed which permit quantitative separation of the source characteristics from the signal coloration due to

the propagation medium and transducer. Their numerical implementation

is being pursued.

The theoretical solution for elastic wave propagation in a plate

has been carried out, based on a new Fourier Inversion technique. This

development, equivalent to determining a new Green's Function, has

created significant interest in the theoretical community. The results

have been reported to the Acoustic Emission Working Group and are being

prepared for formal publication.

Significant theoretical direction for the other tasks has been

accomplished and groundwork for new signal processing techniques and for

specialized theories of AE signals from defect mechanisms have been

developed.

37
Task 3 - Correlation of theory and experiment using transparent

material

The objective is to correlate experimental AE results from 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.

The computer data handling analysis, transform and plotting routines were developed and have found considerable use. Several experimental

configurations for obtaining AE from glass have been developed. These

include a ball impact, indentor, wedge opening of a surface crack and

pressurized cracked (rehealing) plate configuration. A library of AE

signals and associated Fourier spectrums has been developed for cracks

in glass using these configurations. The data indicate that crack

velocities in glass are exceedingly fast. Time and frequency data can

be used to discriminate between fracture and no fracture in the ball

impact configurations. Most recently a decomposition of the surface

traction (which defines the source) has been postulated. Experimental

verification will lead to characterization of the defect using AE

measurements, the plate theory and the decomposition.

Task 4 - AE measurements in structural steels

The objective is to perform exploratory tests for measuring crack

characteri sties in structural steels, particularly those important to

the electric power industry. The experiments should determine the

feasibility of AE analysis for determining defect characteristics in

structural steels.

Significant effort has been spent developing, recording and processing systems for AE from structural steels. Recording systems and

transducers have been characterized. Signal processing programs such as time domain deconvolution, spectral analysis, digital filtering, and

signal averaging and enhancement have been written and checked. Explicit force-time functions of simulated signal sources such as breaking

glass capillaries and pencil leads, ball impact, electric arc and pulsed

ultrasonic transducers have been determined. These results, very important for Task 1, also ready the AE testing laboratory for experiments

on defects in structural steels.

Several experimental configurations and concepts for controlled

defects in the steel specimens are being investigated. The sensitivity

of the analysis to specimen configuration and to specimen structure and

internal "geometry" e.g., weld zone, is being determined.

38
5. Appendix

A. Publ ications-September 1977 to Present

(1) "The Nondestructive Evaluation Program at the National Bureau

of Standards," H. Berger, NDT International, Vol . 10, pp. 277-279

(Oct. 1977).

(2) "Neutron Radiographs Using the Ionographic Process," P. B. Scott,

S. E. Johnson, G. W. Watson, Xonics, Inc., and H. Berger, NBS,

J. Appl . Phys., Vol. 49, 5078-5080 (Oct., 1978).

(3) "Nondestructive Testing Standards - The Role of NBS," H. Berger,

Trans. ANS, Vol. 28, pp. 124-125 (1978).

(4) "Innovative and Advanced NDT," H. Berger, NDT International,

Vol. 10, No. 6, pp. 337-340 (Dec. 1977).

(5) "Californium-252 Source Technology, H. Berger, Scientific and

Industrial Applications," Dept, of Energy Report C0NF-760436,

Vol. II, PP. V-l to V-14 (1978).

(6) "Calibrations and Standards for Nondestructive Testing," H. Berger

and L. Mordfin, Materials Evaluation, Vol. 36, No. 11, pp. 36-39

(Oct. 1978).

(7) "NDE," H. Berger and L. Mordfin, National Bureau of Standards

LC 1080 (April 1978).

(8) "Report on the Symposium on Nondestructive Testing Standards,

G. Birnbaum, Proceedings of the ARPA/AFML Review of Progress in

Quantitative NDE, Sept. 76, P. 158 (Sept. 77).

(9) "The Evaluation of Search Units Used for Ultrasonic Reference

Block Calibrations," D. J. Chwirut and G. D. Boswell, NBSIR

78-1454 (Feb. 1978).

(10) "Acoustic Emission in the Nuclear Industry--The State of the

Art," Roger Clough, ASM Proceedings of 2nd International

Conference on NDE, Feb. 1978, Salt Lake City, Utah.

(11) "Ultrasonic Transducer Output by Modulated Radiation Pressure,

M. G. Greenspan, F. Breckenridge and C. Tschiegg, JASA, Vol. 3,

No. 4, (April 1978).

(12) "Ultrasonic Resolution," E. Miller, Letter to the Editor,

Physics Today (June 1978).

39
(13) "Eddy Current Losses Due to a Surface Crack In Conducting

Material," A. H. Kahn, R. Spal and A. Feldman, 3. Appl

Phys. 48, 4445 (Nov. 1977).

(14) "Development of High-Sensitivity Ultrasonic Techniques for

In-Service Inspection of Nuclear Reactors," M. Linzer,

D. R. Dietz and S. I. Parks, NRC Annual Report, October 1976 - September 1977, Contract No. B-5680.

(15) "An Ultrasensitive Ultrasonic System with Applications to

Nondestructive Evaluation and Medical Diagnosis," M. Linzer,

Ultrasonics International 1977 , IPC Science and Technology

Press, London, U.K., pp. 28-29 (1977).

(16) "Acoustic Emission in Brittle Materials," A. G. Evans and

M. Linzer, Ann. Rev. Matls. Sci. 7_, 179 (1977).

(17) "New Method for the Experimental Evaluation of X-Ray Grids,"

C. E. Dick and J. W. Motz, Medical Physics, Vol . 5, No. 2 (Mar/

April 1978).

(18) "Image Information Content and Patient Exposure," J. W. Motz

and M. Danos, Medical Physics, Vol. 5, No. 1 (Jan/Feb 1978).

(19) "X-ray Scatter Data for Diagnostic Radiology," C. E. Dick,

C. G. Soares and J. W. Motz, Phys. Med. Biol., Vol. 23,

No. 2, pp. 235-244 (March 1978).

(20) "A Standard Method for Determining the Efficiency of Fluorescent

X-ray Intensifying Screen: A Status Report," R. C. Placious,

E. S. Moser, R. S. Holland and F. Masi , SPIE Vol. 127, Optical

Instrumentation in Medicine VI (1977).

(21) "Characterization of Debris Particles Recovered from Wearing

Systems," A. W. Ruff, WEAR 42, pp. 49-62 (1977).

(22) "Quantitative Methods of Wear Debris Analysis," A. W. Ruff,

WEAR 46, No. 1, pp. 263-272 (1978).

(23) "Debris Analysis of Erosive and Abrasive Wear," A. W. Ruff,

Proceedings of the International Conference on Fundamentals

of Tribology, MIT (June 1978).

(24) "Materials Failure Analysis," J. H. Smith, Proceedings of 9th

Synthetic Pipeline Gas Symposium," October 31, 1977, American

Gas Association.

(25) "An Approach to Acoustic Emission Signal Analysis - Theory and

Experiment," N. N. Hsu, J. A. Simmons, S. C. Hardy, Materials

Evaluation, 35, No. 10, pp. 100-106 (Oct. 1977).

40
(26) "The Macroscopic Detection of Corrosion in Aluminum Aircraft

Structures With Thermal Neutron Beams and Film Imaging Methods,"

Donald Garrett, NBSIR 78-1434 (Dec. 7, 1977).

(27) "Elastic Properties of Zinc: A Compilation and a Review,"

H. M. Ledbetter, J. Phys. Chem. Ref. Data 6, pp. 1181-1203

(1977).

(28) "Recent Low- temperature Elastic-constant Measurements On

Technological Materials at NBS," H. M. Ledbetter, Advances

in Cryogenic Enqineerinq, Vol. 24, Plenum, New York,

pp. 103-119 (1978).

(29) "Temperature Dependence of the Elastic Constants of an NbTi/Cu

Superconducting Composite," D. T. Read and H. M. Ledbetter,

Composites 9, pp. 100-104 (1978).

B. Publications in Press or Preparation

(1 ) "Improving the Reliability of Ultrasonic Measurement: Recent

NBS Progress," D. J. Chwirut and D. G. Eitzen, ASNT Proceedings.

(2) "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

Testing , Vol. 6.

(3) "Sizing of Cracks With Scattered Ultrasonic Waves," S. Golan,

Proceedings First International Symposium on Ultrasonic Materials

Characterization, June 1978, ASNT.

(4) "The Characterization and Calibration of Ultrasonic Transducers

Used in NDT and Materials Testing," W. Sachse, Proceedings First

International Symposium Ultrasonic Materials Characterization,

June 1978, ASNT.

(5) "Ultrasonics Transducers for Materials Testing and Their

Characterization," W. Sachse and N. N. Hsu, Physical Acoustics

14 , (W. P. Mason and R. Thurston, eds.) 1978.

(6) "Eddy Current Workshop Proceedings," G. Free, National Bureau

of Standards, Gaithersburg, Maryland, November 3-4, 1977.

(7) "Review of Ultrasonic Techniques for Measuring Residual Stress,

N. Hsu and W. Sachse, 39th National ASNT Fall Conference - Residual Stress Measurement, Denver, CO, October 2-6, 1978.

(8) "Visualization of Transducer - Produced Sound Fields in Solids,'

W. Sachse, N. Hsu and D. Eitzen, 1978 IEEE Ultrasonics Symposium,

Cherry Hill, NJ

.

41
(9)

"A Comprehensive Ultrasonic Tissue Analysis System," M. Linzer,

S. I. Parks, F. P. Higgins, S. J. Norton, D. R. Dietz, T. H. Shawker and J. L. Doppman, Ultrasonic Tissue Characterization II , NBS Special Publication (1978).

(10) "The SonoChromascope: A State-of-the-Art System for the Digital

Acquisition, Processing and Display of Ultrasonic Images," (Invited

Paper), S. I. Parks and M. Linzer, Proceedings of the TC-4 Working

Conference on Computer Aided Tomography and Ultrasonics in Medicine , North Holland Publishing Co., Amsterdam, Netherlands, (1979).

(11) "Ultrasonic Tissue Characterization II ," M. Linzer, NBS Special

Publication (1978).

(12) "Nondestructive Tests Used to Insure the Integrity of Semiconductor

Devices with Emphasis on Passive Acoustic Techniques," George G. Harman, Proceedings of NATO Advanced Study Institute on Nondestructive Semiconductor Materials and Devices.

(13) "'New' Candidates for Ultrasonic NDE Standards and Calibrations,"

G. Birnbaum, ARPA/Rockwel 1 Cornell Conference Proceedings.

(14) "Internal Friction and Sodium Transport in Beta Alumina,"

J. H. Simmons, A. D. Franklin, K. F. Young, and M. Linzer,

J. Am. Ceram. Soc.

(15) "Electromagnetic Theory and Its Relationship to Standards,"

A. H. Kahn and R. D. Spal , Proceedings of the Eddy Current

Workshop, NBS, Nov. 3-4, 1977.

(16) "Ultrasonic Transducer Characterization at NBS," E. Miller and

D. G. Eitzen.

(17) "A Method for Calibrating Electroacoustic Transducers by

Measuring the Total Near-Field Force," E. Miller and A. D. Yaghjian.

(18) "An Ultrafast Signal Averager," R. S. Shideler and M. Linzer,

To be submitted to Review of Scientific Instruments.

(19) "Expanding-Aperture Annular Array," D. R. Dietz, S. I. Parks and

M. Linzer. To be submitted to Ultrasonic Imaging.

(20) "Tomographic Reconstruction of Reflectivity Images," S. J. Norton

and M. Linzer. To be submitted to Ultrasonic Imaging.

(21) "Wideband Annular Array Response," D. R. Dietz, S. J. Norton and

M. Linzer. To be submitted to Proceedings of 1978 Ultrasonic

Symposium , and in a more elaborate version to the Journal of

Acoustical Society of America.

42
(22) "Attenuation and Velocity Dependence of Chirped Ultrasound

Signals," A. C. Kak, M. Fatemi and M. Linzer. To be submitted

to IEEE Trans, on Sonics and Ultrasonics.

(23) "Basic Limits in Real-Time Industrial Radiographic Systems," by

Masao Kuriyama, W. J. Boettinger and H. E. Burdette, to be

published in an ASTM special publication.

(24) "X-ray Magnifier," by W. J. Boettinger, H. E. Burdette and M.

Kuriyama, to be published in Review of Scientific Instruments.

(25) "Amplitude-Matching Dynamic Focusing for Imaging in Inhomogeneous

Media," T. Sato and M. Linzer. To be submitted to Ultrasound

in Medicine and Biology.

(26) "Ultrasensitive Ultrasonic Techniques" (Invited review article),

M. Linzer. To appear in Research Techniques in Nondestructive

Testing , Vol . 4, R. S. Sharpe, ed. , (Academic Press, Inc.,

London, 1979).

(27) "Ultrasonic Materials Characterization," H. Berger and M. Linzer,

eds. American Society for Nondestructive Testing.

(28) "Bispectral Analysis of Random Signals and Its Applications,"

T. Sato, M. Linzer and K. Sasaki.

(29) "Reconstruction and Optical Interferometric Visualization of

Ultrasonic Fields," F. P. Higgins, S. J. Norton and M. Linzer.

(30) "Ultrafast Signal Averaging and Pulse Compression Techniques

for Sensitivity Enhancement," M. Linzer, R. S. Shideler and

S. I. Parks.

(31) "Three-Dimensional Radiographic Imaging," W. A. Ellingson and

H. Berger, to appear in Research Techniques in Nondestructive

Testing , Vol. 4, R.S. Sharpe, ed., (Academic Press, Inc.,

London, 1979).

43
C . T alks by NDE Office Personnel

(1) Nondestructive Methods of Corrosion Testing and Monitoring.

Air Force Workshop, School of Engineering, University of Florida,

St. Augustine, FL.

Harold Berger, September 1977.

(2) A Review of the NBS Program in Nondestructive Evaluation.

Aerospace Industries Association, Subcommittee #4, Cincinnati, OH.

George Birnbaum, September 1977.

(3) Some Novel Methods for Neutron Image Detection.

37th National ASNT Fall Conference, Detroit, MI.

Harold Berger, October 1977.

(4) Calibrations and Standards for Nondestructive Testing.

37th National ASNT Fall Conference, Detroit, MI.

Leonard Mordfin, October 1977.

(5) Radiographic Measurements for the Trans-Alaska Pipeline Girthwelds.

Long Island Sections of American Society for Nondestructive Testing

and American Welding Society, Westbury, NY.

Harold Berger, February 1978.

(6) Scattering of Ultrasonic Pulses by Obstacles in Elastic Solids.

Physics Department, Catholic University, Washington, DC.

Wolfgang Sachse, February 1978.

(7) The Disposition of Elastic Waves and the NDT of Composite Materials.

5th Conference on Composite Materials Testing and Design, ASTM,

New Orleans, LA.

Wolfgang Sachse, April 1978.

(8) Techniques in Quantitative Ultrasonic NDE.

Mohawk-Hudson Section of ASNT, Bunthill, NY.

Wolfgang Sachse, April 1978.

(9) Sizing of Cracks with Scattered Ultrasonic Waves.

National Bureau of Standards NDE Seminar Series, Gaithersburg, MD.

Shmaryahu Golan, April 1978.

(10) Sizing of Cracks with Scattered Ultrasonic Waves.

Department of Materials Science and Engineering, Northwestern

University, Evanston, IL.

Shmaryahu Golan, April 1978.

44
(11) Sizing of Cracks with Scattered Ultrasonic Waves.

Department of Metallurgy and Mining, University of Illinois,

Urbana, IL.

Shmaryahu Golan, April 1978.

(12) Ultrasonic NDE of Materials.

Conference of What is New in Materials, Engineering College, Cornell

University, Ithaca, NY.

Wolfgang Sachse, May 1978.

(13) Welcoming Remarks

First International Symposium on Ultrasonic Materials Characterizations,

National Bureau of Standards, Gaithersburg, MD.

Harold Berger, June 1978.

(14) The Characterization and Calibration of Ultrasonic Transducers Used

in NDT and Materials Testing.

First International Symposium on Ultrasonic Materials Characterization

,

National Bureau of Standards, Gaithersburg, MD.

Wolfgang Sachse, June 1978.

(15) Sizing of Cracks with Scattered Ultrasonic Waves.

First International Symposium of Ultrasonic Materials Characterization,

National Bureau of Standards, Gaithersburg, MD.

Shmaryahu Golan, June 1978.

(16) Nondestructive Testing Standards - The Role of NBS.

American Nuclear Society Annual Meeting, San Diego, CA.

Harold Berger, June 1978.

(17) Determination of the Size of Flat Defects with Diffracted Ultrasonic Beams.

Air Force Materials Laboratory, Wright-Patterson AFB, OH.

Shmaryahu Golan, June 1978.

(18) Visualization of Transducer Produced Sound in Solids.

ARPA/AFML Review of Progress Meeting in Quantitative NDE, La Jolla, CA.

Wolfgang Sachse, July 1978.

(19) Crack Size Measurements with Ultrasound.

Dept, of Physics, University of Tennessee, Knoxville, TN.

Shmaryahu Golan, August 1978.

(20) The NBS Program in NDE - Opportunities in NDE. Engineering Foundation

Conference, The Role of Education in NDE.

Franklin Pierce College, Rindge, NH

Harold Berger, August 1978.

(21) Ultrasonic Characterization Sizing.

Naval Research Laboratory, Washington, D.C.

Shmaryahu Golan, September 1978.

45
D. NDE Meetings At NBS

The NDE program has been active in sponsoring NDE meetings, both

symposia and workshops. A list of these meetings is given in Table III.

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.

E. NBS Seminars On Nondestructive Evaluation

A series of seminars at NBS on the subject of NDE started in 1973-

1974. Approximately one seminar has been arranged each month during the

period September to May. The series has served to bring many recognized

authorities to NBS to describe their work and to discuss with the staff

the NDE activities under way or planned at NBS. The seminars are open

and advertised locally; visitors usually attend.

A complete listing of the past two seasons' seminars is given in

Tables IV and V. The speakers come from both academic and industrial

backgrounds and the topics have ranged from very advanced research to

practical testing.

Speakers and topics in previous seminar seasons followed a similar

trend. Among the speakers in the 1975-1976 series were Gerald Gardner

(Southwest Research Institute), Donald Kettering (Grumman), H. C. Kim

(University of London), Shmuel Mardix (University of Rhode Island), Paul

Packman (Vanderbilt University) and Amos Holt (Babcock and Wilcox).

Previous series included William Baxter (General Motors Technical Center),

Bill Yee (General Dynamics), William Ellingson (Iowa State University)

and Roy S. Sharpe (NDT Centre, Harwell).

There are, of course, many closely related seminars at NBS. Recent

examples include a Fracture and Deformation Division seminar on, "Current

Status of Pressure Vessels and Their Steels in Japan," by Michio Inagki,

National Research Institute for Metals, a Metal Science and Standards

Division seminar on "Ultrasonic Investigation of Radiation Damage in

Al-Mn and Al-Fe Random Dilute Alloys," by Gordon Setser, University of

Illinois; and the NBS Colloquium, "A Review of the NDE Program at

Stanford University," by Gordon Kino of Stanford.

46
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Date

Topic

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Hagemaier,

Sept.

12,

NDE

at

McDonnel 1

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as

McDonnell

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F. NML Organizational Chart
NBS-1 14A (REV. 9-78)

U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. Aic«*«lon No. 3. Recipient's Accession No. BIBLIOGRAPHIC DATA

SHEET NBSIR 78-1581

4. TITLE AND SUBTITLE 5. Publication Date

Annual Report 1978, Office of Nondestructive Evaluation

1978

7. AUTHOR(S) Editors

Harold Berger and Leonard Mordfin

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS PfoJ#eS/Ta

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, ZIP) 13. Type of Report & Period Covered

Final - FY1978

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.)

This reprot summarizes the activities of the National Bureau of Standards

(NBS) Nondestructive Evaluation (NDE) Program. It emphasizes activities over

the Fiscal Year, 1978. However, since this is the Program’s first Annual Report; some material is included to summarize activities since the Program was formally

instituted in June 1975.

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)

Annual report; nondestructive evaluation; ultrasonics, radiography; visual -optical

tests; eddy currents; penetrants; magnetic particles; inspection; acoustic;and

statistics.

18. AVAILABILITY [X] Unlimited

| | For Official Distribution. Do Not Release to NTIS

[~] Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003- PH Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

51

22. Price

$5.25

USCOMM-DC