Institute for Materials Science and Engineering

ONDESTRUCTIVE

EVALUATION

NISTIR 88-3839

U.S. Department of Commerce

National Institute of Standards

and Technology

Technical Activities

1988
Schematic of laser holographic

technique that is being used to

study the mechanisms of liquid

metal breakup into droplets during

the intelligent processing of

rapidly solidified metal powders.

See “Sensors for Metal Powder Atomization Systems” by S.D. Ridder,

F.S. Biancaniello, G. E. Mattingly

P. I. Espina, H. G. Semerjian,

C.Presser, and T. Hopp in this report.
4.

- ' u

y/ OIL ¥1V*

Institute for Materials Science and Engineering

NONDESTRUCTIVE

EVALUATION

H. Thomas Yolken, Chief

Leonard Mordfin, Deputy Chief

NISTIR 88-3839

U.S. Department of Commerce

National Institute of Standards and Technology

October 1988

Technical

1988

Activities

TECHNICAL

ACTIVITIES
Certain commercial equipment, instruments, or materials are identified in this

report in order to adequately specify the experimental procedure. In no case

does such identification imply recommendation or endorsement by the National

Institute of Standards and Technology, nor does it imply that the materials or

equipment identified is necessarily the best available for the purpose.

ii
INTRODUCTION

This report provides brief reviews of technical activities in nondestructive

evaluation (NDE) that were carried out by or for the National Institute of

Standards and Technology (NIST- - formerly the National Bureau of Standards) in

fiscal year 1988 (October 1, 1987, through September 30, 1988). Collectively,

these technical activities constitute the NIST NDE Program that is managed

programmatically on a NIST-wide basis by the Office of Nondestructive

Evaluation (ONDE)

Traditionally, the most common application of NDE is for the characterization

of cracks, voids, inclusions, and other kinds of flaws in materials, components, assemblies, and structures. This usage of NDE is the basis of modern

in-service inspection procedures as applied, for example, to aircraft, bridges,

pipelines, and pressure vessels. Recognizing that NDE measurements for inservice inspection must be reproducible and quantitative, a key component of

the NIST NDE Program is providing traceability for NDE measurements to national measurement standards. To this end, NIST conducts research to achieve an

adequate understanding of the physical basis of the NDE measurement techniques

and procedures that require standardization. Furthermore, the results of

NIST's research and development work on NDE measurements are applied to specific and meaningful problems in order to demonstrate the validity of the results and to help disseminate them to the user communities. Thus, it is possible to think of the NDE Program as comprising three types of activities:

research, standardization, and applications.

The most valuable effect of advances in NDE science and technology has been to

change NDE from a go/no-go system for the detection of flaws to a quantitative

system for the characterization of flaws and also for the nondestructive measurement of material properties and characteristics such as microstructural

texture, particle size and agglomeration, polymer cure state, density, surface

roughness, etc. The capability for reliable and reproducible nondestructive

measurements of this kind is vital to the national effort to raise the quality

of manufactured products. Clearly, the ability to monitor important material

properties or characteristics during a manufacturing process can often be used

to guide or control the process and, thus, to raise both the quality and the

uniformity of the product. In recent years, the NDE Program has placed its

major emphasis on the application of nondestructive measurement principles to

the evaluation of material properties and characteristics and on selected demonstrations of the applicability of these measurements to quality enhancement

in the processing of advanced materials.

The reviews in this annual report are arranged in the following sections that

reflect the NDE Program's four major activity areas: (1) NDE for Ceramic and

Metal Powder Production and Consolidation, (2) NDE for Formability of Metals,

(3) NDE for Composites Processing and Interfaces, and (4) NDE Standards and

Methods. Each of these sections is preceded by an introduction.

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

are commonly referred to as the "NIST NDE Annual Reports." A parallel series

of reports, also issued annually, presents bibliographies and abstracts for

the NIST's technical reports and publications on NDE and its supporting technologies. The purpose of both of these report series is to serve as an

introduction to NIST's NDE Program. Many readers will want further details on

specific aspects of the work or its outputs, and such inquiries are welcomed

and encouraged, both by the principal NDE investigators (whose names and

affiliation precede each of the articles in the report) and by ONDE. Either

can be addressed in care of NIST, Gaithersburg, Maryland 20899 or reached by

telephone via (301) 975-2000, FTS 879-2000, or AV 851-1285 ext. 2000.

Requests for further information and suggestions regarding the Program always

receive prompt and careful attention.

iv
TECHNICAL ACTIVITIES

TABLE OF CONTENTS

I. NDE FOR CERAMIC AND METAL POWDER PRODUCTION AND CONSOLIDATION. ... 1

Sensors for Metal Powder Atomization Systems 2

- S. D. Ridder, F. S. Biancaniello , G. E. Mattingly,

P. I. Espina, H. G. Semerjian, C. Presser, and T. Hopp

Nondestructive Characterization of Ceramic Sintering 7

- J. E. Blendell , J. F. Kelly, C. K. Chiang, G. V. Blessing,

and F. I. Mopsik

Thermal Wave Studies of Surface Finish (Machining Damage) 11

- G. White

II. NDE FOR FORMABILITY OF METALS 15

Eddy Current Temperature Sensing 15

- A. H. Kahn, M. L. Mester, and H. N. G. Wadley

NDE for Metal Texture 19

- A. V. Clark, G. V. Blessing, R. B. Thompson, D. Matlock,

and R. C. Reno

Ultrasonic Evaluation of Metal Surface Finishes 23

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

III. NDE FOR COMPOSITES PROCESSING AND INTERFACES 26

Measurement and Control of Polymer Processing Parameters Using

Fluorescence Spectroscopy 26

- A. J. Bur, F. W. Wang, and A. Lee

Guided Interface Waves 30

- H. N. G. Wadley, J. A. Simmons, and E. Drescher -Kras icka

Thermal Properties of Dielectric Films Using Thermal Wave

Techniques 32

- H. Frederikse, X. T. Ying, and A. Feldman

IV. NDE STANDARDS AND METHODS 35

Magnetic Methods and Standards for NDE 36

- L. J. Swartzendruber

v
Eddy Current Methods and Standards 39

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

Application of Capacitive Array Sensors to Processing of

Ceramics and Composites 42

- P. J. Shull and A. V. Clark

NDE Standards and Methods: Ultrasonics and Acoustic

Emission 45

- D. G. Eitzen and the Ultrasonic Standards Group

X-Ray Radiography 50

- T. A. Siewert

APPENDICES 53

1. NDE Seminars at NIST 53

2. Invited Talks by ONDE Staff 53

3. Publications 53

4. Awards and Appointments 60

vi
I. NDE FOR CERAMIC AND METAL POWDER PRODUCTION AND CONSOLIDATION

This activity is broadly concerned with developing approaches, sensors, and

procedures for nondestructively determining those properties of ceramic and

metal powders and of consolidated materials that relate to the quality and

performance of the materials and manufactured parts. The emphasis is primarily on measurements that can be made during the manufacturing process to sense

the pertinent properties of the product during critical stages of its formation and to provide the data required to control the process to optimize quality and productivity. Some of the effort is directed to determining machining

damage of ceramic materials. The activity includes development of sensors for

metal powder atomization systems; characterization of compacted and sintered

ceramics by AC spectroscopy, measurements of the complex dielectric constant

by time-domain spectroscopy, and ultrasonic velocity measurements; and determination of machining damage by thermal waves. Although these projects are

aimed at developing sensors for the manufacturing process, the project on metal powders represents the most complete approach to this end. It involves the

development of a process model, the investigation of a variety of sensors, the

study of their performance in an actual inert gas/metal atomization facility,

and the development of, and ultimately the use of, an expert system in process

control. This project, which is viewed as a model system to obtain experience

and insight on how to approach the complete problem of process sensing and

control, has been augmented by the formation of an industrial consortium.

Representative accomplishments in this activity during the past year include:

• In the program on the metal atomization system, progress was made toward

the development of (a) a fundamental understanding of the liquid jet breakup leading to droplet formation, (b) real-time sensing techniques for in

situ measurements of droplet size distribution and velocity, and (c) a process model and expert system for the control of the atomization process.

(a) A number of flow measurement techniques were tested and evaluated for

determining the salient features of the gas and liquid flows. These techniques included Schlieren and high speed photography, pressure and temperature surveys, and optical holography on a number of alloys and fluids.

Pulsed holographic studies of the gas-only and gas-liquid flows were initiated for characterizing these flow fields and for photographing single

liquid droplets. This work was initiated with water and metal alloys and

will be continued with stainless steel (1700 °C)

A comparative evaluation

of three point measurement techniques for particle sizing in the spray formation region downstream of the atomizer die and in the exhaust stream of

its exit section, was performed for liquid sprays. (b) Measurements were

made during several stainless steel atomization runs with a laser diffraction technique to obtain a representative measurement of mean particle size

and particle size distribution in the atomizer exit section. (c) The design of an intelligent control system has continued. The execution control

system on an Amiga computer was completed. The system program loads separate rule-based task modules, supports communication between them, and supports their operation in a multitasking environment. Software that permits

interfacing particle size to permit the retrieval of results via a remote

computer was developed.

• In the program on the NDE characterization of ceramic sintering, samples

were prepared of yttria stabilized Zr0 2 , sintered in air at temperatures

between 1200° and 1600 °C and annealed from 1 to 5 hours. AC spectra were
obtained on the sintered samples that indicated changes at the grain boundaries and in the grains themselves. Time-domain dielectric measurements

made on some of these samples were shown to be consistent and complimentary

with the impedance data. Features that are hidden in AC spectroscopy became apparent in dielectric spectroscopy and visa versa. Although the results showed a strong dependence on the process conditions, further work is

required to relate the various aspects of both measurements with the specific state of the ceramic such as grain size, interfacial polarization,

and density. Finally, preliminary ultrasonic velocity measurements were

made on some of the zirconia samples to assess the technique's sensitivity

to the firing temperature and time of the ceramic processing. Whereas a

definite trend was found that can be explained on the basis of increased

densif ication with sintering time, a consistent relationship with sintering

temperature was not observed. To help unravel these results, it would be

valuable to determine the porosity of all samples in future tests.

• Thermal wave studies on cutting tools made of hot pressed silicon nitride

were conducted to investigate machining damage in these specimens. These

samples were subjected to grinding (for 20 minute periods) with decreasing

roughness of SiC paper and measured after each grinding period. The average value of the thermal wave signals, when plotted as a function of signal

penetration depth, showed definite correlation with the surface damage resulting from the grinding. Although these results are essentially qualitative, they suggest that more quantitative thermal wave measurements may

provide a practical, nondestructive method for evaluating damage during

machining processes of ceramics.

Sensors for Metal Powder Atomization Systems

S. D. Ridder and F. S. Biancaniello

Metallurgy Division

Institute for Materials Science and Engineering

G. E. Mattingly, P. I. Espina, H. G. Semerj ian

and C. Presser

Chemical Process Metrology Division

Center for Chemical Engineering

T . Hopp

Factory Automation Systems Division

Center for Manufacturing Engineering

The research reported here is a continuation of research first supported by

ONDE in FY86 that has been aimed at developing an instrumentation system

capable of monitoring and controlling atomization processes to achieve the

desired particle size distribution. Interest in this project has since

attracted support from commercial metal powder producers and users whereby a

joint NIST/industrial consortium under ONDE management was initiated in FY88.

Work done in FY87 on developing in situ particle size analysis of a gas atomized metal has continued, but with certain modifications due to requirements

of the new consortium members. The major changes include (1) dropping the

2
"low" temperature Sn 5 wt% Sb system and using instead a 304 stainless steel

system, which has a significantly higher melting point than the Sn-Sb alloy;

and (2) the use of a new "consortium" gas jet die assembly.

The approach taken to develop the required sensor and control system remains

the same: (a) a fundamental understanding of liquid jet break-up processes

that lead to droplet formation; (b) real-time sensing techniques for in situ

measurement of droplet particle size distribution and velocity; and (c) expert

systems for control of the atomization process using process models developed

in task (a) and particle sensing techniques in task (b)

A. Process and Model Development:

The interactions produced by the specific "consortium" atomization die cause

liquid jet instabilities and break-up, followed by droplet formation. The

atomization die used in this study produces a circle of supersonic gas jets

that impinge on a central, downward flowing, molten liquid metal jet.

Detailed characteristics of the supersonic gas flow are critical in determining the nature of the liquid jet break-up and the size of the metal droplets

formed. The strategy adopted to produce the desired understanding of these

flow processes is to begin with the gas -only flow and continually change conditions and parameters toward the more harsh and hostile conditions present in

the actual atomization process.

A range of flow measurement techniques have been tested and evaluated for

determining the salient features of these gas and liquid flows including water

and metal alloys. Schlieren photography, pressure and temperature surveys,

and optical holography have been used to measure and characterize these flows.

The waveforms (shown in the FY87 report using Schlieren photography) are due

to the gas expansion phenomena. Those distributions may be used to calculate

Mach number along the centerline of the jet. When static temperature

measurements are made and used to calculate local sound velocities, the Mach

number distributions can then be used to calculate local gas velocities. When

the liquid jet is present, the gas jet pattern is altered because of the

interactions which occur at, and downstream of, the gas -liquid contact point.

Upstream of this contact point in the actual atomization process, the gas flow

should closely resemble that occurring in the gas-only flow.

Holographic surveys of the gas -only and the gas -liquid flows have been

started. This technique offers considerable promise both for characterizing

these flow fields and for photographing single liquid droplets. A typical

holographic record of the gas -liquid flow in the near jet region is shown in

Figure 1. The 20 nanosecond exposure is sufficiently rapid to "freeze" the

motion. Also visible in Figure 1 are the contortions on the liquid jet column

as well as the density variations in the turbulent gas flow surrounding the

liquid. It may be feasible to use pulsed holography to determine drop velocities. In this way both droplet size and speeds can be determined in the gasliquid flows where this technique can be used.

As previously mentioned the atomizer has been modified to operate at the

elevated temperatures necessary to process 304 stainless steel (1700 °C)

,

and

a series of atomization runs for repeatability and parameterization data have

3
commenced using this alloy. Off-line particle size measurement of the powder

produced during these runs will be used to determine how gas jet velocity,

molten metal superheat, and metal flow rate affect the particle size.

Future activities will include surveys of the pressure and velocity over the

cross-section of the gas-only flows. These results will extend our current

results obtained along the jet centerline and will produce more complete

descriptions of the gas flow field. This will include the oscillations and

instabilities present on the outer edges of the gas flow. Holographic surveys

and analyses will be continued both to explore the use of this technique in

obtaining gas density distributions, the initial break-up mechanisms of the

liquid jet column, and the determination of liquid droplet sizes and speeds.

The atomization repeatability and parameterization study will be completed in

the next year as well as the installation of a higher capacity crucible to

allow us to determine steady state conditions.

Figure 1. Hologram of water being atomized (20 ns exposure time). Ligament

and primary droplet formation are clearly evident.

4
B. Sensor Development:

Particle sizing techniques are being studied for diagnostics in two sections

of the inert gas atomizer facility; viz., (a) in the spray formation region

downstream of the atomizer die, and (b) in the exhaust stream of the atomizer

exit section. The jet breakup and droplet formation processes in the atomization chamber will be studied by providing detailed measurements of droplet

size, number density, and velocity. A comparative evaluation of three-point

measurement techniques was performed in previous measurements in liquid sprays

these include (a) polarization ratio, (b) scattering light intensity deconvolution, and (c) phase/Doppler interferometric techniques. Results indicate

that the first two techniques are more sensitive to the smaller particle size

range (d < 5 yum) , whereas the third one provides more reliable measurements

for larger droplets (d > 3 /zm)

1 Plans are underway to obtain data with these

devices in the liquid-metal atomizer. 2,3 Experiments will be carried out

initially with the phase/Doppler instrument, which will be leased within the

next several months

A line - of - s ight measurement technique was selected to obtain a representative

measurement of mean particle size in the atomizer exit section. The instrument operates on the principle of laser Fraunhofer diffraction, in which particles diffract laser light onto a calibrated multi - element ring diode. The

particle size distribution, averaged along a cross section of the process

stream, can then be used to determine mean particle size and other statistical

properties. The instrument also has the capability to provide input for process feedback and control. The instrument can provide good time resolution

for the high process flow rates and particle concentrations, and short run

times encountered during atomization (typically 2 min)

To date, measurements were made during several metal atomization runs with the

Fraunhofer device. The particle size distribution was generally found to be

multimodal and included a wide range of sizes. Sieve measurements for each

run indicated that the mean size during a typical run is D 0 5 ~ 40 ^m.

Discrepancies in these particle sizes can be attributed, in part, to the range

detected by each technique, and to coating of the test section windows with a fine layer of metal powder. The window arrangement has been modified to purge

argon over the inner window surface; however, a fine layer of powder still

coats this surface. Other modifications are currently being studied, but will

be carried out in an off-line facility that provides a continuous flow of

metal powder.

The continuous metal powder flow facility was used to monitor the response of

the laser diffraction apparatus to changes in stream flow conditions; this was

accomplished with a pressure-atomized water spray. It was found that as water

pressure decreased droplet size increased, as expected; the measured mean

droplet diameter matched well the data obtained with a similar laser diffraction instrument, supplied by the nozzle manufacturer. The facility was also

used to eliminate laser beam steering effects due to window imperfections and

nonparallel surfaces. Currently, fused-silica quartz windows are being used,

which enable quick alignment of the laser diffraction instrument at the

atomizer test section.

5
Future activities will include continued operation of the laser diffraction

system in the exit section of the atomization chamber. Off-line studies will

also be used to evaluate system problems and capabilities, and to carry out a

parametric investigation with different metal powders. The phase/Doppler sizing apparatus will be available to obtain data in the metal spray and in the

off-line atomization die facility. Experiments will also continue with a laser

sheet beam to illuminate the spray jet, and with high speed cinematography to

observe the dynamic features of the metal powder spray.

C. Intelligent Control System Development:

In the past year we continued the design of the intelligent controller and

implemented several of the supporting services which it will require. In

particular, we completed the execution control system (ECS) on the Amiga

computer. This program loads separate rule -based task modules, supports

communication between them using a common memory implementation, and supports

their operation in a multitasking environment.

Currently, the atomization process is controlled and monitored through the

Azonix data acquisition system (DAS). An analysis of the project's requirements indicated that the Azonix is inadequate for the real-time control needs

of the controller. We have begun to define the specifications for a system to

replace the Azonix that will allow direct access to the sensor and control

signals. We also developed software routines to interface to the Malvern

particle sizer that permit the retrieval of results via a remote computer.

A preliminary version of a controller simulator of the atomization process was

demonstrated at the Metal Powder Consortium's annual meeting.

Future activities include acquiring a new DAS, installing the controller

computer at the atomizer site, and integrating the DAS system to the atomizer's instrumentation. Based on experiments performed with the installed

system, we will refine the implementation of the intelligent controller.

References

1. C. Presser, A. K. Gupta, R. J. Santoro, and H. G. Semerjian, "Laser

Diagnostics for Characterization of Fuel Sprays," Proc . 5th Inti. Congress

on Appl. of Lasers and Electro-Optics (ICALEO 1986), Vol. 58, pp. 160-167,

Arlington, VA (1986).

2. H. G. Semerjian, M. R. Zachariah, and C. Presser, "Laser Diagnostics for

Investigation of Particle Formation Processes," presented at the Materials

Research Society Spring Meeting, Reno, NV, April 5-9, 1988.

3. C. Presser, "Analysis and Measurement of Process Particles," presented at

the Alcoa Laboratories Centennial Symposium on Sensor Technology,

Nemacolin Woodlands, PA, June 15, 1988.

6
Nondestructive Characterization of Ceramic Sintering

J. E. Blendell , J. F. Kelly, and C. K. Chiang

Ceramics Division

Institute for Materials Science and Engineering

G. V. Blessing

Automated Production Technology Division

Center for Manufacturing Engineering

F. I. Mopsik

Polymers Division

Institute for Materials Science and Engineering

The ability to nondestructively monitor the microstructure of a ceramic

material during sintering is important for improving the reliability of

ceramics. Determining during sintering when the microstructure has achieved

a specific condition would allow control of the sintering conditions to

reproducibly obtain the desired microstructure. Several techniques including

electrical and ultrasonic measurements are being investigated for this

purpose

A. Sample Preparation and Impedance Spectroscopy:

Sintering of ceramics involves the removal of porosity and, at later stages,

grain growth. Because grain boundary energy is less than half that of a free

surface, initially the system energy is lowered by increasing the area of contact of the grains from point contacts to finite areas. This leads directly to

a reduction of porosity. When the pore size is small enough, usually at porosities of less than 10 percent, a further reduction in energy can occur by

allowing the grain boundaries to move and with a growth in grain size. While

this later stage is occurring, there is a still further reduction in porosity.

To monitor this process, we have previously looked at the use of AC impedance

spectroscopy to characterize both the porosity and grain size of a sintered

sample. The data showed distinct arcs in the complex resistivity plane that

were identified with grain, grain boundary, and electrodes as one goes from

high to low frequencies. However, lack of reproducible conditions and well

characterized samples prevented a direct correlation with sample

microstructure

To achieve such a correlation, we prepared samples of yttria stabilized Zr0 2 , sintered at temperatures between 1200° and 1600 °C in air, annealed for times

from 1 to 5 hours. The densities measured, using the geometric volume, varied

from 74.4 to 96.7 percent of theoretical density (6.082 gm/cm3 ). We are

currently measuring the grain size and porosity on polished sections of these

samples

7
AC impedance spectra were obtained at 350 °C in a dry oxygen atmosphere for

samples sintered at 1200° and 1600 °C for both 1 and 5 hours. The electrodes

were evaporated platinum. Resistivity arcs previously associated with the

bulk grains and the grain boundaries were observed. The results showed a

large decrease in magnitude (a factor of 2) in going from 1200° to 1600° with

the arc associated with the grain boundaries decreasing the most. This indicated not only a change at the grain boundaries but also in the grains proper.

B. Time-Domain Dielectric Spectroscopy:

Most of the work was aimed at assessing the use of impedance spectroscopy for

evaluating the state of Yttria stabilized Zirconia ceramics. Towards this

goal, time-domain dielectric measurements were made on some samples that were

fired for 1200° and 1600° for 1 and five hours. The samples, with guard rings

added, were identical to those used in the impedance measurements. The results, taken at 35 °C for the complex dielectric constant, e* = e'-ie", in the

complex plane, covering seven decades of frequency are shown in Figure 1. The

same data were then replotted as impedance spectra (complex resistivity,

p * = p'-ip") using the transformation p* = l/(iwe 0 e*) as shown in Figure 2.

Instrumental limitations prevented complete determination of the arc to the

right. Within the limits of the data, and allowing for the large change in

measuring temperature, the results with AC impedance spectroscopy were

consistent, were those of dielectric measurements.

For the data measured in this study, it has become clear that both

representations can be useful in evaluating the ceramic. The limiting value

at high frequencies, e h , is hidden in a p plot. For the samples studied here,

c h was definitely a function of the density, and, for this particular material, also the composition. The low frequency tail of the e" vs. e' plot, seen

in Figure 1 as the beginning of an arc curving to the right, from its magnitude is clearly due to interfacial polarization. The minimum in the p" vs. p'

plot, clearly seen in Figure 2, maps into the inflection point of the e" vs. e'

plot that is however difficult to find. The minimum in p" vs. p' plot corresponds to a bulk conductance that is related to several material properties.

This number has a strong dependence on the processing conditions. There also

appeared to be some changes in the total data with the changes in the ceramic

grains, but the data are still incomplete.

Future work should include an attempt to more rigorously tie together the

impedance and dielectric representations of the data. The data are clearly

complementary and definitely show promise for sinter monitoring. A more well

defined as well as a more important system, Al 2 0 3 , will allow a more satisfactory comparison. Also, such studies should be conduced with well characterized system, such as alumina, where the basic material properties are well

defined

8
0 1000 2000 3000

c‘

Figure 1. The imaginary

component of the complex

dielectric constant (e")

versus the real component

(e') for yttria-stabilized

zirconia. Each point is

for a given frequency with

the decades marked by ()

Frequency decreases from

left to right. The marked

point corresponds to a

similarly marked one in

Figure 2.

Figure 2. The imaginary

component of the complex

resistivity (p") as a

function of the real component (p') for yttriastablized zirconia. The

frequency points are marked

as in Figure 1 with frequency decreasing to the

right

9
C. Ultrasonic Velecity Measurements:

Preliminary ultrasonic velocity measurements were made on zirconia samples to

assess the technique's sensitivity to specific ceramic process parameters.

These parameters were the firing temperature (1400, 1500, and 1600 °C) and the

firing time (1 and 5 hrs . ) , which in combination yielded six distinct process

states for the material sample sets. The 1.5 cm diameter samples varied in

thickness from 0.5 to 2.8 mm. The thinnest (0.5 to 1.1 mm) and the thickest

(1.0 to 2.8 mm) samples were chosen from each of the six sample sets to also

evaluate the possible influence of sample volume on processing.

The ultrasonic velocities were determined by measuring the transit- time of

short duration (0.1 /is) high frequency (15 MHz) dilational elastic wave pulses

echoing between the parallel sample faces. A dry-coupling elastomer was used

between the transducer and samples to avoid sample contamination. The velocities, obtained from the ratio of sample thickness to average transit- time

using successive echoes, were precise to 0.2 percent. The results on the thick

samples are plotted in Figure 3 as a function of firing temperature for the two

firing times. Two meaningful trends with implications for process monitoring

were observed. (1) The velocity of all samples increased with increasing firing temperature, and (2) the velocity of the longer-fired (5 hrs.) samples were

greater in velocity at a given temperature than the shorter- fired (1 hr.) samples. Both trends can be explained on the basis of increased densification

with increased sintering time and temperature. The results on the thin samples

showed that their velocities also increased with increasing firing temperature.

However, a consistent relationship as a function of firing temperature was not

observed, possbly due to the unknown sample porosity.

(0

E

E

£O

HI

>

o

Z3

o

CO

Fired 1 hour • Fired 5 hours

Figure 3. The ultrasonic

velocity as a function of

firing temperature for two

sets of zirconia samples

respectively fired for one

and five hours.

FIRING TEMPERATURE (°C)

10
In conclusion, we note that the ultrasonic velocity, a measure of the material

modulus of elasticity, is a sensitive monitor of sample densification as a

function of firing time and temperature. To further evaluate this relationship, it would be valuable to precisely determine the porosity of all samples

in future tests.

Thermal Wave Studies of Surface Finish (Machining Damage)

G. White

Ceramics Division

Institute for Materials Science and Engineering

The investigation of machining damage effects on high performance ceramics was

undertaken with thermal wave measurements; specifically, with the mirage detection technique. The term "thermal waves" is used to describe the diffusion

of heat in a material during periodic heating. The resulting thermal signal

is sensitive to variations in the thermal properties of the material. The

thermal probe length is /x (micrometers), the thermal diffusion length, and is

a function of the period, or the modulation frequency, of the heating source

M = [a/irf]* (1)

where a is the thermal diffusivity of the specimen and f is the frequency.

Because of the critically damped nature of thermal waves, /x also corresponds,

to the distance the signal will travel, i.e., changing f corresponds to changing the depth and lateral range of the thermal wave signal. Therefore, the

sensitivity to very near surface defects is increased at higher frequency.

Accomplishments during FY 1988 are divided into two categories: mirage system

improvement and machining damage assessment.

Mirage System Improvement:

Variations in frequency vary the depth that is probed. Previously, frequency

was varied manually, greatly restricting the type and range of experiments

that were feasible. This year, a function generator and acousto-optic modulator were added to the mirage system, and software was incorporated that

allowed computer scanning of the frequency. A second improvement was the development of a method of transferring the data from the system in use to other

computers for analysis. Previously, the mirage system was capable of providing a listing of the data or of plotting single frequency curves. However,

obtaining multi- frequency curves and statistical analysis of the data was not

possible. The ability to transfer the data to computer systems, which already

contain data handling software, expands the capability of the mirage system

without a major investment in software development. The practical effect of

these two changes is that data can now be taken in a day that previously would

have required a week.

Machining Damage:

NDE needs in high performance ceramics were discussed with ceramists at the

Norton Company. They were particularly concerned with potential damage from

11
their machining procedures, i.e., cracks, microcracks, and residual stress.

Consequently, they provided 12 x 12 x 6 mm hot pressed silicon nitride cutting

tool specimens for determining the sensitivity of thermal waves to machining

damage. Machining damage in these specimens can be viewed in two ways: first,

the damage can be considered as a set of discrete flaws, each of which affects

the flow of heat in its vicinity; second, the damage can be viewed as a thin

layer of material that has a thermal diffusivity that is different from that

of the bulk material. In the first case, effort was directed to detection of

individual flaws in the material, particularly on detection of critically

large flaws. In the second case, the approach was to consider the damaged

layer as a second material and to relate the degree of damage to the degree of

change in the thermal behavior of this material.

Two-dimensional maps of specimen surfaces were used to look for discrete

damage as a function of surface preparation. To evaluate the material in

terms of a uniform damage layer, measurements of the thermal wave signal magnitude and phase from multiple positions on the specimen surface were averaged. In both the discrete and the averaged approaches, measurements were

made as a function of frequency to provide depth information. In addition,

a third measurement was used that combines the discrete and the average approaches. The standard deviation of the averaged magnitude and phase were

calculated and plotted as a function of frequency. This approach recognizes

that the damage layer is composed of a large number of discrete flaws and

assumes that, as the number and severity of the flaws increases, the standard

deviation of the averaged signals will increase. Therefore, as frequency is

increased, the probe samples material nearer the surface and, as the damaged

region makes up a larger fraction of the material tested, the standard

deviation will increase.

The specimens from Norton Company were examined in as-received condition,

using all three of the approaches outlined above. They were subjected to

grinding for 20 minute periods with decreasing roughness of SiC paper (180,

240, and 320 grit) and remeasured after each grinding period. Figure 1, a

three dimensional plot of the phase of a specimen surface after the 240 grit

grinding, clearly shows grinding grooves remaining in the material. The asreceived material, in contrast, did not exhibit coarse groove structure, but

did exhibit other discrete defects ranging from 20 to 110 /im. As Figure 1 shows, such defects would be undetectable after coarse grinding, but would

appear as the surface was polished to finer finishes. The average value of

the thermal wave signals, when plotted as a function of penetration depth,

shows a systematic deviation correlated with the surface damage resulting from

grinding. The standard deviation of the thermal wave signals also shows a

large increase as the frequency was increased above 500 Hz. These results

show that the averaged thermal wave signals are sensitive to the level of

grinding

In addition, thermal diffusivity measurements of the specimen after grinding

show a clear change from the bulk value of a. In the as -received specimens,

a is constant up to f = 3500 Hz. After grinding with 180 grit paper, the

values of a deviate from this value for f > 600 Hz. This deviation decreased

after the specimen was ground with 240 grit paper and decreased further after

grinding with the 320 grit paper, showing that it was related to the grinding

12
process. These results are particularly interesting since they do not require

an "ideal” specimen for comparison. At low frequencies, the thermal diffusivity is that of the bulk while at higher frequencies, apparently related to the

degree of surface damage, a deviates from the bulk value. The amount of

deviation increases as the frequency increases.

Figure 1 . Thermal wave phase measurement of the surface of a hot-pressed

silicon nitride specimen showing effects of grinding grooves from 240 grit

paper. The horizontal axes are in mm. The vertical axis has arbitrary units.

While the results achieved thus far are qualitative, they suggest that

quantitative thermal wave measurements of machining damage may provide a practical method for evaluating damage during machining processes.

Finally, evaluation of the thermal diffusivity of ceramic dielectric

specimens, which have undergone different processing treatments, has just

begun. Previously, photoacoustic measurements 1 of thermal diffusivity were

made on a set of typical barium titanate based capacitor materials. The new

set includes specimens that have undergone different firing treatments and

that may have lamination defects. The specimens were supplied by the AVX

13
Corporation as part of a collaborative effort to understand the properties of

capacitor materials.

Future work lies in two areas. The first of these is a continuation of the

present effort to finer levels of surface damage to find the sensitivity

limits of the techniques. The second area is to explore residual stresses

that pose a severe problem in ceramics and result from most machining processes. We intend to determine whether thermal wave measurements are sensitive to surface stresses and to relate thermal wave signals to the level of

the surface stress.

References

1. G. S. White, C. Nguyen, and B. Rawal, "Young's Modulus and Thermal

Diffusivity Measurements of Barium Titanate Based Dielectric Ceramics,"

Nondestructive Testing of High-Performance Ceramics , pp . 371-379 (American

Ceramic Society, Westerville, OH, 1987).
II. NDE FOR F0RMA3ILITY OF METALS

The goal of this activity in the NDE Program is to develop generic approaches,

sensors, and procedures for characterizing metals during the forming process.

The emphasis is on measurements that can be made on the production line to

improve process control rather than developing inspection techniques for postmanufacturing inspection.

Current efforts in this activity include the development of NDE temperature

sensors based on eddy current techniques for determining the internal temperature distribution in hot metal objects, developing an in-process ultrasonic

monitor for metal grain texture in manufacturing of steel products, and utilizing ultrasonics for on-line monitoring of both metal surface roughness and

cutting tool wear during machining. Representative accomplishments in this

activity during the past year include:

• The formability of sheet metal, which in large part depends on grain

texture or grain orientation, is a significant process variable in the manufacture of such diverse items as beverage cans, appliances, and automotive

panels. In order to improve process control, a noncontacting ultrasonic

method was developed last year for on-line monitoring of texture in aluminum sheet. This year's research, in collaboration with the Advanced Steel

Processing and Products Research Center, demonstrated that the technique is

also applicable to thin ferritic steel sheet.

• The determination of surface roughness during machining of bulk metal parts

is desirable for both quality control of the finished product and control

of the cutting or grinding process. An ultrasonic NDE sensor was developed

two years ago for on-line monitoring of surface finish and last year's research successfully demonstrated that the same ultrasonic sensor could be

utilized to detect on-line worn or damaged cutting tools. This year's research shows that a finely focused ultrasonic beam can be used to map the

topography of a surface in a fashion analogous to the contacting stylus

profilometry technique.

Eddy Current Temperature Sensing

A. H. Kahn, M. L. Mester,* and H. N. G. Wadley

Metallurgy Division

Institute for Materials Science and Engineering

^Research Associate, The Aluminum Association

The principal objective of the NIST-Aluminum Association joint project on

temperature measurement is the development of a temperature sensor for control

of extrusion processing. In Phase I, the first year of the project (1986-87),

an eddy current system was assembled and prepared for testing in plant operation, as described in last year's report. At the end of Phase I the plant

test was successfully carried out at the Cressona Aluminum Co., Cressona, PA.

15
The sensor coil system used for the tests was installed in one quadrant of a

four channel canister. The canister was mounted horizontally in the extrusion

press and four extrusions passed through it, one through the sensor. In the

series of tests a total length of approximately one mile of products passed

through the sensor; the temperature was measured and recorded every 1.25 seconds. Figure 1 shows a recording of the data collected during the extrusion

of one billet. The breakout temperature is low because the starting metal

comes from the cooled end of the billet; the temperature rises with time as

the inner part of the billet is extruded and also because the die becomes

heated. After 60 seconds the billet was exhausted and the cooling of the static aluminum remaining in the sensor was observed. Figure 2 shows the temperature measurements on a billet for which the speed of extrusion was varied in

order to demonstrate the ability of the sensor to follow the temperature under

widely varied conditions.

RUN ID R0UN01D.DAT

1100

O>i050

CD

T3

LlJ

QC3 1000

\—

<

QL

LlJ

CL

2 950

LU

h~

900

TIME (sec)

Figure 1. Measured temperature as a function of time for a typical 1-in round

aluminum rod during extrusion processing.

In the trials at Cressona the encircling coil described in the previous report

was used. This sensor was used for solid round, solid square, and hollow

square extrusions. It would also be satisfactory for round tubing.

16
3/4 X 3/4 SQUARE AT VARIED SPEEDS

Figure 2. Measured temperature as a function of time for 3/4- in- square

aluminum stock during extrusion. The speed was intentionally varied to

demonstrate heating effects.

In the Phase II period of this project (1987-88) the eddy current sensor

system is being extended to other shapes of interest such as flat strips and

sheets, U-channels, and I-beams. In these cases the geometric shape presented

for measurement is that of a thin flat wall. An appropriate testing method

employs through- transmission techniques in which an exciting coil is placed on

one side of the test material and the response of the material is received by

a secondary coil on the opposite side. We have prepared a laboratory model of

such a coil system for operating at room temperature with test materials of

various thicknesses and conductivities, simulating the properties of aluminum

products at elevated temperatures. For flat sections of less than a skin

depth, the measured complex impedance points for a given coil configuration

fall on a single universal curve, with each point corresponding to a unique

value of the parameter X = aQt, where a is the electrical conductivity, Q is

the angular frequency, and t is the thickness of the plate. Data taken on the

through- transmission system are presented as transfer impedance values, i.e.,

the ratio of output voltage to input current, with the result divided by the

reactance in the absence of the test sample. A plot of through- transmission

for several samples of various thicknesses and conductivities at various

17
frequencies is shown in Figure 3. The tendency of the curves to separate at

the high frequency end signifies breakdown of the large skin- depth approximation and is used to establish the limit of validity of the approximation.

“O

<D

N• —

O

£

o

N

ZTMReal Normalized

Figure 3. Impedance plane plots of frequency- sweep through- transmission

signals measured on seven flat plates of various thicknesses and conductivities. Symbols are placed at every twentieth frequency point for each sample.

Each point on the curve corresponds to a unique value of the product of frequency, conductivity, and thickness. In all cases the samples are thin

relative to the skin depth.

On the basis of these results, we have designed a set of through- transmission

coils for placement in an extrusion canister for on-line testing. Construction of the system in the canister, with water cooling, is now in progress.

During the planned tests simultaneous comparison with radiometric methods will

be carried out.

18
NDE for Metal Texture

A. V. Clark

Fracture and Deformation Division

Institute for Materials Science and Engineering

G. V. Blessing

Automated Metrology Division

Center for Manufacturing Engineering

R. B. Thompson

Center for Nondestructive Evaluation

Iowa State University

D. Matlock

Advanced Steel Processing and Products Research Center

Colorado School of Mines

R . C . Reno

Metallurgy Division

Institute for Materials Science and Engineering

The formability of sheet metal is a significant process variable in the

manufacture of such diverse items as beverage cans, appliances, and automotive

panels. A typical example is press -shop operation in the automotive industry.

Here, sheet segments are cut ("blanked") from a coil and fed into a production

line. The blanks are then formed into components such as door panels. If

variability in material formability occurs, the parts may not have the desired

shape. On automated production lines this may result in line shut-down. This

may occur because a robot arm is programmed to go to a specific location, grip

the part, and move it elsewhere; if the part has the wrong shape, the arm may

not be able to secure the part. It appears, especially in the automotive industry, that users of sheet steel will soon be requiring both higher formability and tighter bounds on variation in formability. Therefore, it would be

highly desirable to develop a rapid, nondestructive method for characterizing

formability of sheet before it enters a production line.

One method in current off-line use is the so-called "modul-r" technique 1 that

is based on an experimental correlation between ultrasonic measurement of

Young's modulus, E, and a commonly used (destructive) measurement of formability, the r- value. The r- value is typically obtained by cutting tensile

coupons at 0°, 45°, and 90° to the rolling direction, and then measuring the

ratio

r = + €tt)

where and c tt are the longitudinal and thickness strains, respectively,

at a significant level of plastic deformation. As currently implemented, the

"modul-r" method requires small specimens to be cut from the end of a coil (at

0°, 45°, and 90°) and inserted into an ultrasonic instrument that measures E

by magnetostrictively inducing a sound wave in the specimen. However, this

19
approach is destructive, will work only on magnetic materials, and can only be

used in a practical sense on specimens removed from the end of a coil.

Since the work of Reference 1 there have been several theories developed that

relate velocities of bulk, guided, and surface waves to the texture of polycrystalline, rolled sheets of cubic metals. There also exists a relation

between texture (degree of preferred orientation of the polycrystals) and the

sheet formability. Consequently, there are now several candidate methods for

nondestructive ultrasonic formability measurement.

We have recently been focusing our efforts on the use of noncontacting

ultrasonic transducers for both on- and off-line measurement of sheet formability. 2-5 In this work, we are primarily using electromagnetic-acoustic

transducers (EMATs) which induce ultrasound in the sheet without the need for

an intervening couplant. We have obtained a well-characterized set of steel

sheets having a wide range of the average r-value, r. Measurements of bulk

and guided wave arrival times have been made. For bulk waves, we used longitudinal and shear waves propagating through the plate thickness. For guided

waves, we used both the lowest-order shear-horizontal wave (SH0 -mode) and the

lowest-order symmetrical Lamb wave (S 0 -mode). From theory, various combinations of arrival times should be proportional to r. These combinations are

listed in the table below:

Wave Type Arrival Time Combination

Bulk T^ATg + TS1 + Ts2 )

Guided S 0 -mode [T(0°) + T(90°) + 2T(45°)]/4

Guided SH0 -mode [T(0°) + T(45°)]/2

Here T^ , Ts

and Ts

are arrival times of longitudinal waves and shear waves

polarized parallel and perpendicular to the rolling direction. T(0) is the

arrival time of a guided wave propagating at angle 6 to the rolling direction

A comparison of ultrasonic arrival time combinations revealed that all three

combinations were indeed proportional to the average drawability r. An example is shown in Figure 1, where <TS0 > refers to the arrival time combination

for the S 0 -mode. The range of r. in Figure 1 is typical of the drawability

desired of sheet for automotive applications.

As mentioned above, the "modul-r" technique relies on the correlation of r with E, the average Young's modulus in the plane of the sheet. There is an

approximate relation between the low-frequency limit VLIM of the S 0 -mode

velocity and the Young's modulus:

V

2

(«)

LIM

E(J)

p(l-i/

2

)

20
Here 0 is the angle relative to the sheet rolling direction and u is Poisson's

ratio. The S 0 -mode data were analyzed using the above relation, and the E

calculated from

E = [ E(0° ) + E(90° ) + 2 E(45° ) ]/4

Figure 1. Relation between averaged arrival time of S 0 -mode, <TS0 >, and

average r-value, r.

When the resulting ultrasonic values of E are plotted versus r, the results

are as shown in Figure 2. Here the solid line represents the best fit to the

data of Reference 1 and the open circles represent the S 0 -mode data. These

data are within the scatter band of the data of Reference 1. This indicates

that the ultrasonic technique gives results comparable to the modul-r

technique currently in use.

Consequently, an EMAT-based acoustical array, propagating S 0 -mode waves at 0°

,

90°, and 45° could be placed at a small liftoff above sheet to characterize

formability on-line. As a first step in technology transfer an EMAT system

21
has been constructed whose signal- to-noise ratio on thin ferritic steel sheet

is comparable to conventional (piezoelectric) transducers. As currently configured, this system consists of a single transmit-receiver EMAT pair, which

measures arrival times (with EMATs in situ) with a precision of 1 ns or better

when 100 arrival times are measured and averaged. At the current pulse repetition rate, the system reads out an averaged arrival time about once a second. One possible application for an array would be in the press -shop, where

blanks having unacceptable formability could be rejected before proceeding

through the production line. Another application would be on-line in a steel

rolling mill.

E (MPa)

Figure 2. Comparison of correlation of r with E made with EMATs (open

circles) and correlation made with experimental setup of Reference 1 (solid

line)

In addition, the NIST participants in this program are now collaborating with

researchers in the Advanced Steel Processing and Products Research Center

(ASPPRC) , a joint government-business -academia consortium involved in research

to produce better sheet, bar, and plate stock. The prototype EMAT system

described above was demonstrated to representatives of steel and automotive

companies in the Center and received a favorable reception. It was decided,

as part of this collaboration, that a larger data base would be obtained by

measuring r both ultrasonically and by destructive means. A number of sheets

covering a large range of r will be supplied by Center members who will measure r destructively. These will then be compared with nondestructive values

obtained ultrasonically.

If the correlation for this larger data base appears good, NIST researchers

will explore various means of technology transfer. These include guest workers who will learn EMAT-based measurement technology and give guidance on how

22
systems need to be configured for production environments; possible development

of improved prototype systems which could be demonstrated in pilot projects at

participating ASPPRC laboratories.

References

1. C. A. Stickels and P. R. Mould, "The Use of Young's Modulus for Predicting

the Plastic-Strain Ratio of Low-Carbon Sheet Steels," Met . Trans

1,

pp. 1302-1312 (1970).

2. A. V. Clark, R. C. Reno, R. B. Thompson, J. F. Smith, G. V. Blessing,

P. P. Delsanto , and R. B. Mignogna, "Texture Monitoring in Aluminum

Alloys: A Comparison of Ultrasonic and Neutron Diffraction Measurement,"

Ultrasonics 26 . pp . 189—197 (1988).

3. A. V. Clark, Jr., "Ultrasonic Characterization of Texture and

Formability," MRS Bulletin XIII . pp . 40-42 (1988).

4. A. V. Clark, G. V. Blessing, R. B. Thompson, and J. F. Smith, "Ultrasonic

Methods of Texture Monitoring for Characterization of Formability of

Rolled Aluminum Sheet," Rev, of Prog, in Quant. NDE 7B . pp . 1365—1373

(1988) .

5. R. C. Reno, R. J. Fields, and A. V. Clark, "Crystallographic Texture in

Rolled Aluminum Plates: Neutron Pole Figure Measurements," Rev, of Prog,

in Quant . NDE 7B . pp . 1439—1445 (1988).

Ultrasonic Evaluation of Metal Surface Finishes

G. V. Blessing and D. G. Eitzen

Automated Production Technology Division

Center for Manufacturing Engineering

The measurement of surface finish is important in many areas of manufacturing.

Sensor development for on-line monitoring of a material's surface condition

is, therefore, of much interest for controlling automated manufacturing processes. In order to provide such a sensing capability, we have been applying

noncontacting ultrasonic scattering and reflection techniques utilizing the

machining coolant stream to couple the ultrasonic signal to the part. This

technique provides for the evaluation of both average surface roughness and

detailed surface profilometry on parts in situ during the manufacturing

process

1 ’ 2

In the last years' reports we presented results on the application of an

ultrasonic sensor to monitor the surfaces of rapidly rotating cylindrical

parts (e.g., during machining at a turning center) and to scan the surfaces of

flat and curved stationary parts (e.g., during machining at a milling center).

In both of these applications the ultrasonic probe produced an area- averaging

beam. In this report we present results obtained using a finely focused

ultrasonic beam to map the topography of a surface in a fashion analogous to

the (contacting) stylus profilometry technique.

23
The potential of the ultrasonic sensor as a profilometer was evaluated using

30 MHz focused ultrasound on a precisely shaped sinusoidal aluminum surface

with a unidirectional lay. The average surface roughness Ra was 1.0 /xm, and

the surface periodicity A was 800 /xm. 3 Both echo -amplitude and transit-time

measurements were made, traversing perpendicular to the surface lay at a focal

distance of 2 cm with the specimen immersed in water. The echo -amplitude data

provided a measure of A, while the transit- time data provided a measure of

local surface height.

Figure 1 compares the results of a contacting stylus scan3 with an ultrasonic

echo -amplitude scan perpendicular to the lay on the sinusoidal specimen. It

is important to note that the received echo signal is a convolution of the

incident beam dimension, the surface topography, and the transducer. For

example, the echo amplitude signature in Figure 1(b) by itself provides no

surface height information. The transducer used here was a broadband (highly

damped) spherically focused element of diameter 6 mm, focal length 20 mm, and

a half -amplitude beam width of 200 /xm in the focal region.

(a) Stylus

1 mm

(b) Ultrasonic

Figure 1. Profilometry scans of a 1.0 /xm Ra sinusoidal aluminum surface by

(a) a contacting stylus, and (b) a noncontacting ultrasonic echo -amplitude

technique

In contrast with the ultrasonic amplitude scan of Figure 1(b), Figure 2 is a

transit- time scan of the sinusoidal surface. Discrete measurements of relative transit time for the round-trip distance between transducer and surface

were taken at 100 /xm steps perpendicular to the lay. A sinusoidal pattern of

periodicity 0.8 mm is readily observed. (The negative slope superposed on the

sinusoidal pattern is an artifact caused by the changing temperature of the

water coupling medium during the scan.) Compensating for the slope artifact,

and knowing the sound speed in water at room temperature (1.49 mm//xs) , a nominal surface peak- to-valley distance of 2.5 /xm was calculated from the data of

Figure 2. However, the correct peak- to-valley dimension of the 1.0 /xm Ra surface is 7T /xm. This discrepancy is attributed principally to the finite beam

24
width of the incident ultrasound. The effect of beam width, which was

nominally 25 percent of the surface periodicity in this case, was to average

surface feature distances, thereby reducing the apparent peak- to-valley dimensions. For these surface and beam dimensions, a deconvolution of the data

(based on the beam width) would be required for an accurate measurement of

surface height.

1 -

o I 1

1

1 •— o 0.5 1.0 1.5 2.0 2.5

Position (mm)

Figure 2. Profilometry scan of the same surface scanned in Figure 1 using an

ultrasonic transit- time echo technique.

Future plans include increasing the ultrasonic frequency to profile finer

dimensions, studying ground surfaces and perhaps the grinding wheel itself,

and measuring specific surface features by means of ultrasonic surface waves

that would follow the surface contour details.

References

1. G. V. Blessing and D. G. Eitzen, "Surface Roughness Sensed by Ultrasound,"

to be published in Proceedings of Metrology and Properties of Engineering

Surfaces International Conference held at NIST, 13-15 April 1988.

2. D. G. Eitzen and G. V. Blessing, "Ultrasonic NDE for Surface Roughness,"

MRS Bulletin XIII . No. 4, pp . 49-52 (April 1988).

3. G. V. Blessing and D. G. Eitzen, "Ultrasonic Real-Time Monitoring Device

for Part Surface Topography and Tool Condition In Situ," U.S. Patent No.

4,738,139 (issued 19 Apr 1988).

25
III. NDE FOR COMPOSITES PROCESSING AND INTERFACES

The goal of this activity is to develop generic approaches, sensors, and

procedures for quantitative NDE of composites and interfaces. As in the two

previous activities, the emphasis is on measurements that can be made during

the manufacturing process to sense the properties of the product during critical stages of its formation and to provide the data required to control the

process to optimize quality and productivity. Since the knowledge base on composites characterization is far from complete, we expect that a portion of this

activity will be concerned with relating important composite characteristics

with performance and then developing NDE monitoring methods.

This activity includes research on utilizing fluorescent spectroscopy to

monitor the processing of polymer matrix composites; applying ultrasonic techniques to improve the understanding and ability to monitor interfaces; and

utilizing photothermal radiometry (thermal wave NDE) to monitor the quality of

ceramic coatings on metals. Noteworthy accomplishments in this activity

include

• A major barrier to the implementation of advanced polymer composite

materials in many applications is that the processing lacks the desired

reliability. To improve the reliability, nondestructive evaluation measurement techniques need to be developed to improve process monitoring and

control. Last year's research showed that fluorescence spectroscopy appeared to be feasible to monitor the non-Newtonian shear viscosity of polymer melts during processing. This year's research extends the technique's

application to the monitoring of polymer molecular orientation, velocity,

and flow characteristics. These parameters play a key role in determining

the properties of composites.

• The characterization of interfaces is of vital importance in designing and

manufacturing advanced composites. Theoretical and experimental research

over the last two years has shown that ultrasonic waves radiate a fraction

of their energy into the surrounding matrix, in the form of leaky ultrasonic waves, as they propagate along a fiber. Research this year experimentally confirmed the quantitative aspects of the model for iron/aluminum

and silicon carbide/aluminum metal matrix composites.

Measurement and Control of Polymer Processing Parameters Using Fluorescence

Spectroscopy

A. J. Bur, F. W. Wang, and A. Lee

Polymers Division

Institute for Materials Science and Engineering

The need for improved monitoring of polymer processing has escalated in recent

years because of the large demand and market for advanced polymer materials

that require tight controls on processing conditions over a broad range of

variables. To satisfy these new requirements, we are developing sensors based

on fluorescence spectroscopy to monitor process conditions on-line at the molecular and microscopic level . 1,2 The objective of our program is to utilize

26
these new measurement techniques in conjunction with processing models to

predict and control the materials properties and performance of the final

product

Work during FY88 has focused on four areas: the design of experiments to

measure fluorescence anisotropy and non-Newtonian viscosity as a function of

shear rate; the chemical synthesis of a polymeric chromophore that is being

used in experiments to measure fluorescence anisotropy; the development of a

mathematical model to describe fluorescence photobleaching recovery and its

relationship to velocity and flow characteristics; and negotiation with industrial laboratories for the purpose of carrying out collaborative research and

development programs on polymer processing problems of mutual interest.

Fluorescence Anisotropy and Synthesis of a Polymeric Chromophore:

Fluorescence anisotropy measurements are being carried out using a capillary

flow apparatus and a Weissenberg rheometer. The capillary flow apparatus is

used in conjunction with a commercial fluorimeter so that fluorescence and

viscosity can be measured simultaneously. A capillary is positioned vertically in the sample chamber of the fluorimeter and the shear rate experienced

by the specimen is controlled by adjusting the pressure applied at the top of

the capillary. We recently completed optical instrumentation of the

Weissenberg rheometer and we are using it to carry out fluorescence and rheological measurements. The range of shear rates covered by these instruments

is approximately 10' 2 to 102 s' 1

Fluorescence anisotropy measurements are being conducted on a low molecular

weight polybutadiene specimen doped with a polymeric chromophore. The polymeric chromophore, which was synthesized in our laboratory, consists of polybutadiene tagged with f luorescently active anthracene so that the anthracene

is situated at the center of the polymer chain. Infrared and gel permeation

chromatography verify that anthracene has been placed in the central position

and that the resultant number average molecular weight is approximately

12,000, as expected.

Our working hypothesis for the anisotropy experiments is that, for a

non-Newtonian fluid, the fluorescence anisotropy increases (and the viscosity

decreases) with increasing shear rate, and that the underlying cause of this

effect is molecular orientation. The fluorescence anisotropy experiment is

designed to measure this molecular orientation. In our first experiments we

tested the converse of this hypothesis, i.e., for a Newtonian fluid fluorescence anisotropy is independent (as is the viscosity) of shear rate. Low

molecular weight polybutadiene, = 2800, which was doped with the tagged

polybutadiene (10' A molar concentration), was observed to be Newtonian and to

have constant anisotropy in the shear rate range 1 to 100 s” 1

. We conclude

that, within the sensitivity of our measurement, molecular orientation of the

tagged polybutadiene does not occur. Experiments using non-Newtonian

polybutadiene, = 22,000, are now in progress.

27
Velocity and Flow Characteristics;

A sensor to measure velocity, velocity gradient, and wall slip near the wall

of a processing machine was designed and a mathematical model to describe its

behavior was formulated. The sensor operation is based on fluorescence photobleaching recovery (see Figure 1). The design consists of an optical fiber

that is fitted through the wall of a processing machine and is flush with the

inside wall. Polymeric material, which contains a photobleachable dye, flows

past the end of the optical fiber and the fluorescence properties in a defined

region at the end of the fiber are observed. At a given instant, the dye in

the probed volume is photobleached by a short pulse of ultraviolet radiation.

As a function of time, f luorescently active material flows into the probed

volume and the detected fluorescence intensity increases. In the model, we

analyze this fluorescence recovery and derive a functional form for intensity

versus time. From the equations, it is possible to distinguish between laminar flow and wall slip and, in the case of laminar flow, to obtain values for

velocity and velocity gradient. Experiments to test this model will be

carried out in FY89.

Interactions with the Polymer Processing Industry:

Considerable effort was exerted in order to increase the amount of industrial

interaction and participation in our polymer processing program. A news

release, which was issued from the NIST Public Relations Division, generated

over thirty responses from major polymer processing companies. We responded

to each request and are in active negotiation with a half dozen companies

concerning the establishment of research associateships . The contacts that

were developed via the news release were invited to participate in the NIST

Intelligent Processing of Materials Workshop, August 31, 1988.

References

1. A. J. Bur, F. W. Wang, and R. E. Lowry," Fluorescence Monitoring of

Polymer Processing: Mixing and Zero Shear Viscosity," Proc . Soc. Plastics

Eng., Annual Tech, meeting, April 1988.

2. F. W. Wang, A. J. Bur, R. E. Lowry, and B. M. Fanconi, "Fluorescence

Monitoring of Polymer Processing," Polymer Materials Science and

Engineering 59 (1988).

28
HALL SLIP LAMTNAR FLQH

VA VB

photobleached regi on

2a = fiber diameter

Figure 1 . The principle of operation of the velocity sensor is fluorescence

recovery after photobleaching . The shaded region at the end of the optical

fiber is a photobleached region of a flowing material, whose movement is

monitored by the fluorescence recovery. The results of a model calculation of

the fluorescence recovery are plotted as a function of reduced time T. For

equal average velocities <v>, recovery for wall slip is much faster than for

laminar flow.

29
Guided Interface Waves

H. N. G. Wadley, J. A. Simmons, and E. Drescher-Krasicka

Metallurgy Division

Institute for Materials Science and Engineering

Research this year has focused on using leaky ultrasonic waves to interrogate

physically inaccessible interfaces of metal matrix composite (MMC) fibers.

Our research exploited our earlier discovery of elastic waves that radiate a

fraction of their energy into the surrounding matrix as they propagate along a

fiber. 1 Progress has required a close coupling of experimental and theoretical work. The general quantitative description of modes in composites was

reported 1 and the specific equations describing leaky waves in MMC without an

interface zone have been carefully analyzed. 2 The results of these calculations indicate four families of waves in a single fiber composite. A direct

linkage has also been established between these families and the rod modes of

the fiber. The existence of leaky waves from two of the branches has been

experimentally confirmed in Fe/Al and SiC/Al MMC during this year's research.

In experiments on the Fe/Al system, surface type rod modes were used for

generation and detection of interface waves. For the experiments, a surface

acoustic wave was transmitted along a steel rod (the model fiber) ; see Figure

I. After passing into the aluminum matrix, this mode converted to a combination of leaky modes. The receiving transducer was placed at different points

of the matrix and the acoustic response was measured. The resultant signal

was decomposed into its component modes, identified by their peaks, to permit

comparison with the theory. All modes whose leakage angles permitted measurements were detected. We have drawn a practical conclusion from these experiments: the modes with low leakage angle and low attenuation are convenient

for measuring the average velocity along a fiber; those with higher ieakage

angle are more convenient for local velocity measurements along the fibers.-

Studies were also conducted on the SiC/Al system using an SiC rod. Some of

the modes, which arise from a different type of rod than that used in the

Fe/Al specimens, were experimentally confirmed. This part of the research was

partially done in cooperation with Professor B. T. Khuri Yakub of Stanford

University. A scanning system was built in order to increase the applicability of ultrasonic interface waves to a direct interface characterization. The

schematic diagram of the experiment is shown in Figure 1 . A movable conical

transducer, later changed to a monofrequency pinducer, was placed against the

outer surface of the composite SiC/Al sample. The receiver was moved along

the specimen surface while the transmitter excited an interface wave that

propagated along the interface. The phase velocities of different leaky modes

were measured directly by monitoring the changes of the receiver positions

Ax = x2 -Xj and related changes of the travel time At = The results,

the phase velocity of interface leaky wave Vj = Ax/At, were compared with the

calculated dispersion curves for each particular SiC/Al interface mode.

Figure 2 draws the calculated dispersion curve together with the experimental

results for one of these modes. The dotted lines on this figure show the

attenuation of this mode.

30
AV|

Vi

0 3 i0.2 -

Figure 1. The schematic diagram of the ultrasonic measurements on SiC/Al

interfaces

It is worth noting that the maximum phase velocity of this mode of 18564 m/sec

represents the fastest ultrasonic wave ever measured. This velocity is about

twice that of the longitudinal velocity in SiC and about three times that of

the longitudinal velocity in aluminum. While infinite velocities are theoretically possible for rod modes near their cutoff frequencies, we are not aware

of any technique that permits the experimental observation of these rod waves

modes at high phase velocity.

This mode was also used in our approach to measure the local variations in

velocity over a section of SiC/Al interface. Changes in the velocity of MMC

31
interface waves are expected to be related, through inverse techniques, to the

changes in the elastic moduli near the interface.

Figure 2. Comparison between calculated (continuous line) and measured

(points) dispersion curve for SiC/Al interface leaky mode. The dotted line

shows the calculated attenuation.

References

1. E. Drescher-Krasicka, J. A. Simmons, and H. N. G. Wadley, "Guided Interface

Waves," Rev, of Prog, in QNDE 6B. pp . 1129-1136 (1987).

2. H. N. G. Wadley, J. A. Simmons, R. B. Clough, F. Biancaniello

,

E. Drescher-Krasicka, M. Rosen, T. Hsieh, and K. Hirshman, "Composite

Materials Interface Characterization," 1st Progress Report for SDIO,

NBSIR 87-3630, March 1988.

Thermal Properties of Dielectric Films Using Thermal Wave Techniques

H. Frederikse, X. T. Ying,* and A. Feldman

Ceramics Division

Institute for Materials Science and Engineering

*Guest Scientist from Fudan University, Shanghai,

Peoples Republic of China

The purpose of this project is to inspect the thermal behavior and mechanical

integrity of non-metallic coatings using the propagation of thermal waves.

Such coatings play an important role in many technological areas: optical

32

ATTENUATION

IN

DB/

(MM

X

MHZ)
components, engines and combusters, corrosion protection, electronic devices,

etc. Thermal wave techniques have gained considerable attention and popularity during the last 10 to 12 years. Especially thin and thick layers, from a

few microns to several millimeters, can be probed conveniently by thermal

waves because the thermal diffusivity length can be adjusted to these depths

by varying the modulation frequency. Several detection schemes can be used to

determine the temperature variations in time or in space; a number of these

techniques do not require contact with the material being probed and, hence,

lend themselves well for nondestructive evaluation.

Last year we developed photothermal radiometry (PTR) as a noncontact method to

monitor the thermal quality of ceramic coatings at room temperature. During

the present reporting period we have investigated the heat resistance of a

number of oxides at elevated temperatures up to 900 °C. The oxide coatings,

deposited by plasma spraying to a thickness of 50 to 100 /j.m , were chromia,

zirconia, and alumina; the substrates were stainless steel plates in all

cases. This work was done in collaboration with Grady White of the Ceramics

Division who is also doing thermal wave research (see report on page 32).

The experimental set up is pretty much the same as that described in last

year's report. The only difference is that the sample is positioned inside a

horizontal cylindrical furnace, some 6 to 8 cm from the opening at one end.

Measurements were made at six temperatures between 20 and 900 °C. . Two infrared detectors were employed over this temperature range: a liquid nitrogen

cooled InSb detector for temperatures up to 500 °C and a germanium photodiode

for temperatures between 500 and 900 °C. This change of detectors was dictated by the fact that the InSb detector saturates above 500 °C due to the

d.c. thermal signal. Even in the range of 200 to 500 °C small apertures had

to be inserted to limit the amount of radiation falling on the sensitive InSb

area. Similar considerations applied to the Ge photodiode.

At every temperature the magnitude of the signal, |s|, and the relative phase,

A<f>

,

were measured as a function of the modulation frequency from 9 to 30 Hz.

Analysis of the A<£-vs-y f plot yielded the desired results for the thermal

diffusivity a and the thermal conductivity k, of the coatings. The values of

a and k are about a factor two smaller than the handbook data for bulk specimens (and much smaller than the single crystal values). This is not surprising considering the high degree of disorder and the relatively low density of

plasma sprayed coatings. Another indication of the large scatter is the temperature dependence; a and k show a nearly constant behavior rather than the

predicted 1/T dependence.

In the last few months we have turned our attention to the thermal properties

of diamond films. Since about two years ago there has been a sudden surge in

interest in diamond coatings produced by chemical vapor deposition or sputtering techniques. NIST has launched a program in this area including both preparation and characterization. One of the properties of great importance is

the high thermal conductivity of diamond. Consequently it is important to

determine this property both as a guide for applications and as a measure of

the quality of the diamond films. In recent months we have studied several

thermal wave techniques in order to determine the most suitable method for

33
diamond coatings. Results have been obtained on a 1/2 -mm- thick film (obtained

from GE) . In this case PTR was the preferred method. Other promising

approaches are the longitudinal method, propagation of the heat wave along a

film of diamond deposited on a narrow strip of thermally insulating ceramic,

or a variation of the optical beam deflection technique (mirage effect)

Plans for FY 1989 are focused on the diamond films and the appropriate thermal

wave techniques for their evaluation.

34
IV. NDE STANDARDS AND METHODS

The objective of the Standards and Methods activity in the NDE Program is to

provide the scientific understanding of NDE measurement methods and to

develop, maintain, and disseminate effective standards for NDE measurements

that are traceable to national standards.

Five project reports from the NDE Standards and Methods activity are presented

this year dealing with ultrasonics and acoustic emission, eddy currents, magnetic methods (primarily Barkhausen) , real-time radiology, and the capacitance

array sensor. Two of these reports cover two of the largest efforts in the

NDE Program but all five of the reports document significant progress. It is

fair to say that the NDE Standards and Methods activity is the cornerstone of

the entire NDE Program, as it continues to serve as the basis for intensive

standardization and consultation services provided to the nation's NDE

community

The reduction in the number of reports presented this year (there were nine

last year) is due, in part, to retirements by some of the NDE Program's senior

researchers. Thus, for example, the Program's long-term project on standards

for film radiography was terminated following Robert Placious' retirement.

However, ONDE's continuing interest in radiation methods is apparent in the

new project on real-time radiology (or radioscopy) that was started a year

ago. This redirection reflects ONDE's ongoing effort to anticipate the NDE

community's changing needs for standards as technology advances.

Elsewhere, the recent retirement of Julius Cohen brought a halt (hopefully

temporary) to the Program's project on thermographic NDE. It is intended to

resume the project next year with replacement talent. Similarly, progress in

the Program's leak testing project had to be put on hold this year due to

staffing problems in the Center for Basic Standards. This important work will

also be resumed next year.

Despite these interruptions, productivity in the NDE Standards and Methods

activity in fiscal year 1988 was good. A few brief examples of this year's

accomplishments follow:

• Thomas Siewert of the Fracture and Deformation Division and Leonard Mordfin

of the Office of Nondestructive Evaluation negotiated an agreement with

representatives of the Army Materials Technology Laboratory (MTL) and the

General Electric Aircraft Engines Quality Technology Center for a joint

effort to develop document standards (military and ASTM) on real-time x-ray

radioscopy (RTR) for nondestructive evaluation. Under the terms of the

agreement GE will develop drafts on the basis of their company standards

and MTL will provide funding to NIST to incorporate measurement considerations into the documentary standards. As a corollary benefit to NIST,

Siewert has been granted access to MTL's and GE's RTR laboratory facilities

for research purposes. GE's facilities in Cincinnati, in particular, are

among the most advanced in the country.

35
• A new "Standard Test Method for Minimum Detectable Temperature Difference

for Thermal Imaging Systems," which was developed in the NDE Program, is

proceeding through the ASTM balloting process. This document represents

the second of three test methods that will define the critical performance

parameters of thermographic NDE instruments. (The first standard, on

minimum resolvable temperature difference, was adopted by ASTM last year.)

• ONDE's long-term contract from the MTL to develop new and improved

military standards for NDE was especially fruitful this year. A standard

fieldworthy method for verifying the performance of acoustic emission (AE)

testing systems is described in MIL-HDBK- 786 , prepared by Donald Eitzen of

the Center for Manufacturing Engineering (CME) . A key feature of the method

is the simulated AE event developed earlier by Nelson Hsu of CME and for

which he received an IR-100 award. Standard glossaries of terms and definitions for ultrasonic testing procedures and for radiographic testing were

prepared by Eitzen and by E. H. Eisenhower of the Center for Radiation

Research and were issued as Military Standards 371 and 369, respectively.

• ASTM has initiated work on the development of a new standard test method

to assess the visual acuity of inspectors and others who read and interpret radiographs. The basis of the standard is a set of 72 reference radiographs of artifacts containing tight discontinuities (artificial cracks)

in different locations, orientations, contrasts, etc. The set was developed by Robert Placious of the Center for Radiation Research, following a

scheme conceived earlier by Gary Yonemura, formerly of the Center for

Building Technology. This development was accomplished in the NDE Program

with partial support from the MTL. Although intended originally for radiographic applications, it is now anticipated that the new test method will

also prove useful to practitioners of other NDE disciplines, such as

visual inspection and liquid penetrant testing, where visual acuity is a

critical factor.

Magnetic Methods and Standards for NDE

L. J. Swartzendruber

Metallurgy Division

Institute for Materials Science and Engineering

A variety of magnetic methods are currently used in nondestructive evaluation,

both for detecting defects and for verifying material properties. Some of

these methods, such as magnetic particle inspection, magnetic flux leakage

testing, and magnetic permeability measurement, are widely used in industry;

the first two for defect detection, and the latter for property determinations

such as ferrite content in stainless steel welds. A number of methods (Barkhausen noise, magnetoacoustic emission, magnetomechanical damping, and ac magnetometry) have been used on a limited scale but require further development

to increase their reliability and make them more widely applicable. Finally,

some magnetic property measurements (e.g., saturation magnetization, coercivity, and initial permeability) contain a wealth of information concerning

36
material properties that have barely begun to be exploited. Effort on this

project during the year has been primarily directed to Barkhausen noise

analysis

Progress

Many workers have shown that measured properties of Barkhausen noise can be

related to material properties such as hardness, grain size, internal stress,

and defect density. When usable, the Barkhausen method is very attractive

because high production rates are possible. However, the relationship between

the observed noise and a material property is always heuristic and is generally poorly understood from a fundamental point of view; this could lead to

erroneous conclusions.

There are many ways to characterize Barkhausen noise, including (1) the noise

pulse amplitude distribution profile, (2) the power spectral density, (3) the

pulse number spectrum, and (4) the total noise power. Commercially available

equipment uses one or another of these methods to produce a "Barkhausen number" that changes when a material property changes. The same method does not

appear to be used by any two pieces of equipment. Our purpose has been to

develop an experimental arrangement that will have the flexibility to calculate these "numbers" from the characteristics of the observed noise as well as

to allow a detailed analysis of the noise from a fundamental point of view.

This will be accomplished primarily by software analysis of digitized noise

signals

The experimental arrangement is illustrated in Figure 1. A computer is used

to control a high speed, dual channel digitizing oscilloscope, a frequency

synthesizer, and a bipolar power supply. The bipolar power supply is used to

energize a yoke which swings the sample through a hysteresis loop with a frequency and amplitude controlled by the synthesizer. An offset current from

the power supply can be set by the computer in order to trace out minor loops

on the hysteresis curve of the sample. Two pickup coils are placed on the

sample; an encircling coil A and a pancake coil B. Both coils can be used to

observe Barkhausen noise. In addition, coil A can be used to measure the

total flux density in the sample, thereby tracing out the hysteresis loop of

the sample. The noise from one or both pickup coils is amplified by a preamplifier and then digitized by the oscilloscope. The digitized information

is transferred to the computer via an IEEE-488 bus. By using direct memory

access, transfer rates up to 400 kbaud can be realized.

With the loop being traced at a frequency of 0.1 Hz, a complete noise spectrum

in the frequency range 0 to 25 kHz can be transferred to the computer for a single loop in 10 seconds, with the total amount of information being 500

kilobytes. This noise frequency range is adequate for almost all applications. (Much higher noise frequency ranges, up to about 1 MHz, could be used

with the present equipment but much longer times would be required for

obtaining and analyzing the data.) Much of the basic software required to

operate the equipment and analyze the noise has been developed and installed

with the aid of a guest worker from Israel. This guest worker is also

attempting some fundamental modeling of the elementary Barkhausen jumps.

37
Figure 1. Experimental system for detailed analysis of Barkhausen noise

characteristics

A second version of the military standard for magnetic particle inspection

(MIL-STD- 1949) was prepared and coordinated (work supported by the U.S. Army

Materials Technology Laboratory) . Valuable comments were obtained from over

fifty companies. We also are participating in conversion of this standard to

an ASTM document. As part of this work, a round robin on the use of standard

artificial flaw shims in magnetic particle inspection was conducted. The

response to this round robin was inadequate to establish the validity of the

use of these standard shims. The poor response is believed due to the large

effort required by participants in the round robin. Important as these standards are, most organizations are simply too busy inspecting to put forth the

required effort. A new round robin is being planned that will provide more

limited, though useful, results with much less effort on the part of the

participants

Effort during the coming year will focus on further development of our

Barkhausen system and associated software and on obtaining and analyzing

Barkhausen noise from selected steels with a variety of microstructures. The

goal will be to develop materials with very well characterized noise properties that can be used as standards to compare the outputs from different types

of noise analyzers. As an important part of this effort, optimization of the

38
pickup coil-preamplifier combination will be pursued with the aid of a new

guest worker.

Eddv Current Methods and Standards

T. E. Capobianco and F. R. Fickett

Electromagnetic Technology Division

Center for Electronics and Electrical Engineering

Coil Construction-Factor Study:

Because of the statistical analysis requirements of empirical modeling, the

coil construction- factor study described in our last report has undergone

substantial modification this year. The study has been redesigned to allow

use of modern statistical design techniques and to account for the scatter

winding of commercial coils. The initial study design complicated the statistical analysis of potential interactions between construction factors, and

the selection of coils was not based on statistical principles which allow us

to optimize the amount of information from a minimum number of data points.

The new design, developed with the help of the Center for Applied Mathematics,

is based on the statistical concept of multi-dimensional response surface

modeling and uses sophisticated software which can place design points so as

to produce the most information with the fewest number of points. In our

case, each design point in the study is a coil to be wound, so efficiency of

experimental design is a major consideration. One of the appealing features

of this new design is that placement of the design points is independent of

the criteria to be optimized. Thus, response surfaces can be determined for

inspections on high or low conductivity alloys, and for different crack

geometries using a single coil set.

For such empirical statistical models it is desirable to have an overdetermined data set. For the six factors (listed in Table 1) varied at three

levels each (ferrite diameter is at two levels) 40 to 50 coils would be both

an achievable number to wind and an adequately overdetermined set.

The additional factor of coil repeatability, or homogeneity of the set, is

also a concern. The coil set determined using the statistical design software

has 40 different constructions to be wound, with 10 repeats at selected points

to provide a measure of the winding homogeneity, for a total of 50 coils.

Additional ferrite cores were needed to build this set. Unfortunately, the

desired shapes and sizes are not commonly available over the entire range of

permeabilities necessary for our study and, thus, the lead time for manufacturing the ferrites turned out to be over ten weeks. Also, at the beginning

of the year we had expected that another 12 to 15 coils, in addition to the 18

finished last year, 1 would yield a complete set on which an empirical model

could be based. Instead, we're facing the task of winding 50 new coils in a

completely redesigned experiment. Therefore, construction of the model relating coil fabrication to inspection sensitivity will not be completed until

next year. The coils already constructed will enable us to evaluate relative

39
sensitivities of the precisely layered coils compared to similar scatter-wound

coils in the new set.

Table 1 . Construction Factors

Factor Levels

Ferrite diameter (mm) 0.89, 1.40

Number of turns 90, 120, 180

Winding distance from end (mm) 0.38, 0.76, 1.14

Ferrite permeability 800, 1500, 6500

Aspect ratio 0.5, 1.0, 2.0

Wire gauge (AWG) 40, 44, 48

Next year this newly designed study will result in a sound empirical model

that will allow us to move on to the next logical extension of this work,

namely a manufacturability study which implements this model in a production

environment and enlists the participation of commercial probe manufacturers.

Stanford Delta Z Program:

Provisions for the NIST installation of the Stanford/ONDE developed eddy

current AZ calculation computer program have been completed. A contract was

arranged with the program's author, Steve Jefferies. Mr. Jefferies visited

NIST-Boulder in August and installation, preliminary checkout, and training

were completed. The program will assist in modeling and evaluation of coil

geometries and flaw interactions.

Artifact Standards:

We are exploring a new technique for producing eddy current artifact standards

that involves tightly closed artificial discontinuities of an exactly known

size. Although this work was not a part of the proposed plan this year, the

idea evolved as a result of interactions on our probe characterization standard and the accompanying round robin. 2 The initial results look promising

and, if subsequent work confirms our expectations, we intend to pursue a

patent on the technique. Some of these results were presented at the QNDE

conference in August, 3 and further refinement of the technique is now in progress. If the preliminary results are proved correct, we envision using these

artifacts in conjunction with a "standard probe" and offering the set as a

probe and system characterization package.

40
NDE Application of SQUIDs:

As a result of interest generated by our presentation at the Navy SQUID NDE

Workshop, 4 we attempted a collaborative effort with Argonne National Laboratory to measure manufactured and actual defects in nuclear reactor heat exchanger tubing using an ASTM specified artifact. Our approach was to keep the

apparatus as simple as possible since this was to be an exploratory study. We

used the SQUID in an unshielded arrangement with a pair of superconducting

coils configured as a first order gradiometer as the input. Our hope was that

this type of input would partially compensate for running unshielded. The

coils were adjacent and coplanar and wound in series opposition. This gradiometer was mounted in a fiberglass -epoxy tube which was fitted with a pair of

copper saddle coils that provided a field normal to the gradiometer coils.

The tube was made to fit inside the ASTM sample and to look for defects from

the inside wall. Unfortunately, the electrical noise in our lab is severe and

the SQUID was barely able to maintain lock. This indicated the need for extensive shielding, or perhaps higher order gradiometer coils. Neither arrangement

could be realized in the actual environment anticipated for these tests. We

suggested that more conventional magnetic NDE techniques would be more

appropriate for this application.

Two Axis Positioner and Data Acquisition System:

This year we purchased, with Division funds, an AT-class computer as the

foundation of a sophisticated eddy current data acquisition system utilizing a two axis positioning apparatus and our existing impedance analyzer. This system represents a major change in direction regarding both hardware and software. In the past we have relied on a borrowed positioning system, but when

the coil parameter study grew to its present proportions, it became obvious

that this system was no longer adequate.

The new system gives us significant advantages in mass storage, computational

speed, and flexibility. Our software is being developed in Pascal, which

offers the advantages of being faster and more powerful than BASIC and the

code can be written with greater clarity. Using the serial interface, this

computer controls a two axis positioner. The tables ride on recirculating

ball bearings over the 46-cm (18 in) range of each axis and have a minimum

step size of 0.013 mm (0.0005 in) and repeatability of ± 0.0013 mm (0.00005 in).

Eddy current probes will be carried by a counterweighted , articulated, fiberglass-epoxy arm, which is presently under construction. Probe data from the

impedance analyzer will be read into the computer over a GPIB-488 bus.

References

1. T. E. Capobianco and D. F. Vecchia, "Coil Parameter Influence on Eddy

Current Probe Sensitivity," Review of Progress in Quantitative NDE 7A,

pp . 487-492 (Plenum, NY, 1988).

2. L. L. Dulcie and T. E. Capobianco, "New Standard Test Method for Eddy

Current Probes," Proc . of the 36th DoD Conference on NDT . pp . 154-160

(U.S. Army Aviation Systems Command, St. Louis, MO, 1987).

41
3. T. E. Capobianco and J. C. Moulder, "Standard Flaws for Eddy Current Probe

Characterization," Proc . of the Review of Progress in Quantitative NDE,

La Jolla, CA, August 1-5, 1988.

4. F. R. Fickett, "Review of NBS Work in SQUID -Based NDE," SQUID/NDE

Workshop, Harper's Ferry, WV, April 13-15, 1988.

Application of Capacitive Array Sensors to Processing of Ceramics and

Composites

P. J. Shull and A. V. Clark

Fracture and Deformation Division

Institute for Materials Science and Engineering

B. A. Auld

Ginzton Laboratory

Stanford University

Capacitive array probes are attracting increased attention because of their

potential for robotic sensors and for nondestructive evaluation, especially

for cure monitoring of composites. In most applications, the probe is noncontacting and scans the workpiece; in composites, the probe is usually

inserted inside the composite layup.

Here we report on two new applications of these sensors: noncontacting

characterization of (a) sintering of ceramics and (b) curing of composites.

Both applications depend upon the fact that the complex dielectric constant

changes during material processing.

For noncontact applications, the probe impedance (or its reciprocal, the

admittance) depends upon several factors: probe geometry, distance to specimen

(liftoff), and the electrical properties of the specimen (dielectric constant,

e). Thus, it is necessary to have a theory that can be used to deduce e from

admittance measurements, in the presence of liftoff.

In general, the liftoff is unknown. In fact, even if the probe is placed on

the workpiece, there will still be an unknown amount of liftoff due to effects

such as protective covering over probe electrodes, nonuniform electrode thickness, etc. These effects, while seemingly small, can have an influence on

admittance, especially for small probes with closely spaced electrodes. For

example, we have found a liftoff of approximately 100 /xm can cause a change in

AY approaching 100 percent; the worst case we have measured. AY is the

difference between the probe admittance in air, and the admittance in the

presence of the specimen.

In our work on sintering of ceramics, we have constructed probes of different

geometries and tested them on a variety of ceramics with different e . Our

initial idea was to multiplex the electrodes to vary the probe's electrical

geometry, and use an elementary theory to predict both e and liftoff, d, from

our admittance measurements. One problem with this theory is illustrated in

42
Figure 1, where we show AY versus d for a material having a relative dielectric constant of 50. The theory (curve A) predicts a monotonic decrease of AY

with liftoff whereas the measurement (curve D) shows a sharp drop followed by

a recovery. Similar results were obtained on other ceramics.

Figure 1. Liftoff response for different probe geometries and boundary

conditions: A — theoretical, B - 2-D probe to reduce edge effects, C - miniaturized probe with ground plane approximately 100 mm from the specimen, D — miniaturized probe with specimen on the ground plane.

We have identified several causes of the discrepancy between theory and

experiment. The elementary theory requires that the probe have a sinusoidally

varying potential which averages to zero. We have found that our impedance

measuring instrument creates a probe potential field that has both a spatially-varying component and a constant component. We refer to these as the

non-zero and zero spatial frequency components, respectively. The potential

fields created by these components are calculated by the finite element method

and shown in Figure 2. Figure 2a shows the resultant potential field from the

sinusoidally-varying component of the electrode configuration. This indicates

very little interaction with the ground plane. In contrast the potential field

of the constant component, Figure 2b, is greatly distorted by the presence of a

ground plane. We have made measurements which show that the capacitance to

ground for the constant component is about ten times the capacitance predicted

if the probe were part of a parallel plate capacitor with the same area.

We are developing techniques to suppress these measurement artifacts.

Increasing the distance between electrodes having opposite polarity (decreasing spatial frequency) is a partial solution, as is increasing the distance

between specimen and conductors in the environment. The latter effect is

shown in Figure 1, curve C, where the specimen is 100 mm from a ground plane.

Further suppression of the "recovery" occurs when the electrodes are designed

to reduce charge concentration and when they are mounted on a low e substrate.

See Figure 1, curve B.

We have also made experiments to demonstrate proof -of -concept of noninvasive

cure monitoring of composites. Here a major concern (for graphite -epoxy

composites) is the shielding that occurs due to specimen conductivity. (This

43
is not a concern for probes embedded in the composite). For example, we have

monitored the cure of a thin plate of commercial ("5 minute") epoxy that was

placed on one side of a 6-mm thick panel of unidirectional graphite - epoxy ; our

probe was placed on the opposite side. Results of our experiment are shown in

Figure 3. We found that the magnitude of the impedance changes dramatically

with curing. The percentage change is larger at 1 kHz than at 100 kHz. The

phase angle, while close to —90° (indicating primarily a capacitive coupling

between probe electrodes) , does show a change due to conductivity of the

epoxy. The percent change is again higher for 1 kHz than for 100 kHz.

(a) (b)

Figure 2. Finite - element calculation of the potential field showing the

probe -sample -environment interaction - (a) the non-zero spatial frequency

component and (b) the zero spatial frequency component.

We have developed a mathematical model of the interaction of the probe's

electrostatic field (in air) with the electrodynamic field in the conducting

composite. The resulting equations are being developed into a finite element

code that will be used to calculate the field in the composite and also the

probe admittance, as the dielectric constant and conductivity vary during

cure. This will give insight into means of extracting information about the

state of cure in thick composites. The depth to which the electrodynamic

44
field penetrates can be varied by changing either probe geometry or the

frequency of probe excitation.

Figure 3. Probe response -- impedance magnitude and phase vs. time- -to a curing

epoxy with a 6-mm thick conductive material (graphite -epoxy composite) place

between the probe and the epoxy.

NDE Standards and Methods: Ultrasonics and Acoustic Emission

D. G. Eitzen and the Ultrasonic Standards Group

Automated Production Technology Division

Center for Manufacturing Engineering

The objective of this project is to develop and disseminate artifact and

documentary standards, develop and maintain measurement and calibration services, and develop new or improved methods for acoustic emission and ultrasonic NDE techniques. The documentary standards are typically guided through

ASTM and then promoted as international standards. The calibration services

for acoustic NDE methods are essential to the NDE community and referenced

around the world.

Our transducer development work is motivated by the need for devices to

transfer calibrations to sensor users/suppliers and for precision dynamic

motion measurement for new or advanced acoustic methods. The development of

new ultrasonic and AE methods also relies heavily on theoretical analysis to

gain a better understanding and new insight into the physics of the soundstructure interactions that lead to the development of new generic methods

or adaptations for specific applications.

Our documentary standards activities in the last year were again very

productive. With partial support from the Army MTL, two new MIL documents

were published; MIL-STD-371

,

1 an ultrasonics glossary, and MIL-HDBK- 786

,

2 an

AE system field assurance guide using the Hsu pencil source for producing simulated AE. An article on "AE Sensors and Their Calibration" was published as

45
a chapter in the ASNT handbook on acoustic emission testing. 3 The article

provides user information on AE sensors and disseminates information on primary calibration and on NIST-developed tools for secondary calibration. Standards activities through ASTM and ISO continue to grow. Data and techniques

are being developed to revise four ASTM standards, and significant effort is

directed at two new ISO standards. The chairmanship of ISO/TC 135/SC 3 continues to require significant effort. Also, responsibility (joint with ONDE)

has been assumed for organizing a joint ASTM/NIST/ASNT symposium on NDE

standards to be held in the fall of 1989.

Methods for secondary calibration of AE sensors are under development. The

objective of this effort is to devise an inexpensive and convenient system for

transferring the calibration of acoustic emission transducers. A priori, any

system that would place a source transducer in face-to-face contact with the

receiving transducer, has been rejected. It has been established that the mechanical impedance of a receiving transducer interacts significantly with that

of the driving object on which it is mounted. The mechanical impedance of a

transducer is likely to be a complicated function of frequency, and there is

no known way to calculate or measure this impedance. Therefore, the interaction between the mechanical impedances of two transducers placed face to face

would produce results that would be impossible to analyze.

The choice of a (calibration) block to be interposed between source and

receiving transducers is dominated by the necessity that the propagation modes

in the block be calculable and that the block have a mechanical impedance that

matches that of the medium on which the transducer is to be used.

As a first attempt, a steel plate 3.3 cm thick by 90 cm square was tried as a

calibration block. Elasticity theory predicts the transfer function for the

plate, and experimental results using a capillary-break source and an NIST

conical transducer receiver agree remarkably well with the theory. (See last

year's report for this project, Figure 1.) Two alternative schemes were considered for the secondary calibration system. Both schemes use a source on

the surface of the block, and two receivers equally spaced from the source.

One of the receivers is the reference transducer (RT) and the other is the

transducer under test (TUT). In one scheme, the source is a capillary breatc

and the receivers feed transient recorders followed by Fourier analyzers. In

the other scheme, the source is an NIST conical transducer driven by a tone

burst. The receiver signals are gated to remove reflections and other unwanted signals, and the transfer function at each frequency is measured directly

by means of a variable attenuator and detector. In both schemes, the transfer

function obtained using the TUT is divided by that obtained using the RT,

frequency by frequency.

Scheme 1 and scheme 2 were both tried on the 3. 3 -cm- steel plate using a TUT

having a wear face diameter of approximately 1.5 cm. Results of both tests

(Figures 1, 2) can be compared with the normal calibration (Figure 3) for the

TUT, and it can be seen that both schemes give poor results. However, if the

large NIST calibration block is substituted for the 3.3-cm-steel plate, then

the results are in reasonable agreement with the normal calibration.

46
FREQUENCY (MHz)

Figure 1. Test of

secondary calibration

performed according to

scheme 1 on a 1.5 -cm

diameter AE transducer

using a 3.3 cm thick by

90 cm square steel plate

as the transfer block.

The reference transducer

was an NIST SRM 1856

conical transducer; the

source, a glass capillary

break.

FREQUENCY (kHz)

Figure 2. Test performed on 3.3 cm by 90 cm square steel plate similar to

scheme 2. The source was an NIST conical transducer, and the transducer under

test was the 1.5 -cm diameter AE transducer.

47
FREQUENCY (MHz)

Figure 3. Primary calibration of the 1.5 -cm diameter AE transducer.

The explanation for the failure of the 3.3-cm plate as a calibration block

lies in the complicated interaction between the motion of the surface of the

plate and the aperture effect of the transducer. The fact that a point transducer, such as the NIST conical transducer, produces a correct waveform for

the plate indicates that point transducers could be calibrated on the plate,

but the extended transducer does not calibrate correctly. The features of the

plate waveforms resulting from a step function force source vary markedly with

distance from the source and travel with different speeds. The aperture

effect of the transducer is different for each feature of the waveform.

The results obtained using the extended transducer on the steel plate impugn

all experiments in which extended transducers are used to measure motion on

plates. For meaningful results it is essential to use point transducers.

We believe that a steel block 20 cm thick by 40 cm square would be a good

compromise; working time would be sacrificed, with attendant loss of low frequency accuracy, but the surface pulse waveforms would replicate those of the

large block within the working time.

Simulated acoustic emission sources have been studied theoretically and

experimentally. The interest is in enhanced tools for calibration and field

tests, in tools for point impact/point receiver methods, and in tools to develop remote measurement techniques. Consider, for example, the ball impact

48
source. Hertzian theory provides the dynamic stresses for an elastic ball

colliding with an elastic half space. Combining this theory with elastic

plate theory, one can calculate displacements in a plate resulting from collision with a ball. The result is a source with reasonably known characteristics. Ball bearings between 1/16 inch and 3/8 inch have been dropped onto

an 8 . 9-cm- thick glass plate from a height of 3 cm. An NIST conical transducer

located on the bottom of the plate opposite the source was used to measure the

dynamic normal displacement at that point. The transducer had been calibrated

by a capillary-break experiment on the same plate.

The experimental waveforms from the dropping ball experiments were convolved

with the inverse Green's function of the plate in an attempt to recover the

source waveforms. Comparison of these source waveforms and those calculated

from Hertzian theory shows some discrepancy that we attribute to the fact that

it has not yet been possible to compensate completely for the transducer's

transfer function. Resolving this discrepancy is an important goal of this

effort

We have also considered repetitive transient sources. Electronically

triggered sources which act to apply mechanical transient forces are desirable

for several reasons; signal averaging may be applied to increase signal- tonoise ratio and accuracy, and Fourier analysis can be applied to obtain

transient waveforms without using a digital transient recorder.

A piezoelectric device which applies a static load to a surface and then

suddenly removes that load (like the capillary break) has been designed but

not yet built. In the design, a parabolic interface between steel and brass

acts as an acoustic lens to focus a rarefaction wavefront onto the point of

contact between the device and the driven object.

The tangential transducer, reported in 1986, has a patent pending and a

detailed article describing it was submitted for publication. 4 Construction

of replicates has begun in order to assure manufacturability and efficient

technology transfer. Data are also being collected to demonstrate the agreement between the measured waveforms and theory and to depict the added AE

information available.

References

1. Anon., "Glossary of Terms and Definitions for Ultrasonic Testing

Procedures," MIL-STD-371 (15 October 1987).

2. Anon., "Field Assurance of Acoustic Emission System Operation Using

Simulated Acoustic Emission Events," MIL-HDBK-786 (1 October 1987).

3. D. G. Eitzen and F. R. Breckenridge , "Acoustic Emission Sensors and Their

Calibration," Nondestructive Testing Handbook . 2nd edition, Vol. 5,

Section 5, pp. 121-134 (ASNT , Columbus, OH, 1987).

4. Thomas M. Proctor, Jr., "A High Fidelity Piezoelectric Tangential

Displacement Transducer for Acoustic Emission," submitted to J . of

Acoustic Emission.

49
X-Rav Radiography

T. A. Siewert

Fracture and Deformation Division

Institute for Materials Science and Engineering

Image quality standards designed for conventional radiography are not adequate

for real-time radioscopy systems, whose use is increasing. Development of new

radiation transfer standards was the preeminent need determined in the 1987

workshop on real-time radioscopy; improved measurement of overall system performance also ranked high. By cataloguing the uses of these systems and

designing appropriate standards (devices placed in the specimen location to

measure such characteristics as contrast and resolution) , this program is

addressing these needs.

Questionnaire

To obtain the data upon which an appropriate radiation transfer standard could

be developed, a questionnaire was distributed to users and producers of realtime systems at the January 1988 meeting of the ASTM Committee on Radiology;

it requested information on industrial usage of these systems. Chairmen of

ASTM subcommittees involved with real-time systems helped design the questionnaire and will receive a summary of the responses. A preliminary assessment

of the fifteen replies received to date reveals certain trends:

• The energy range reported for the real-time systems varied widely, but a

histogram (Figure 1) of the replies shows a plateau between 100 and 150 kV.

This plateau in energy indicates the range for an initial design, a transfer

standard which would serve the majority of users.

Figure 1. Histogram of potentials used in RTR systems.

50
• Aluminum was mentioned most often as a material examined by real-time

systems. A histogram of the material thickness revealed a plateau near

10 mm; this correlates well with the penetrating capability of the plateau noted for system energy. Thus, a standard made of aluminum in this

thickness range would satisfy the needs of most users.

• Steel was second in usage. Its histogram had a plateau between 6 and

30 mm. The 6-mm thickness could also be effectively penetrated by a 100

to 150 kV system. Polymer-matrix composites, silicon electronic circuit

substrates, plastics, ceramics, titanium, and gold were also mentioned.

• A histogram was developed from responses to the resolution required by

these systems; a plateau occurred between 2 and 10 line pairs per millimeter. This resolution range should be incorporated into the radiation

transfer standard.

Replies to the questionnaire are expected from ASNT members who learned of our

program at a July 1988 topical meeting on real-time radioscopy, 1 as well as

the members of ASTM subcommittees. To obtain representative data for the

spectrum of domestic usage, cooperation with additional industry and standards -making groups is being sought. A final report, which will be completed

in late 1988, will describe the use of real-time radioscopy systems and form

the basis for the design of a prototype standard.

New Image Quality Indicators:

New designs of image quality standards that will be fully compatible with the

capabilities of real-time radioscopy systems are being developed. For example, conventional image quality indicators have been designed for the specimen

oriented orthogonal to the beam, but real-time systems should accommodate

rotation of the specimen.

The concept of an image quality standard with rotational symmetry has been

developed; as the specimen rotates, image quality can be constantly measured.

The initial concept includes spheres (with two degrees of rotational symmetry)

or rods and cones (with one degree of rotational symmetry) that have a lowdensity core and a high-density coating. Figure 2 shows a cross section

through one of these and its radiographic projection. Since the core is lowdensity material, it causes little attenuation of the beam, and the projection

is primarily that of the coating.

The effective radiographic thickness of the central region is twice that of

the coating. With proper choice of coating material and thickness, this

region might function as a contrast standard. For thin coatings, the edge of

the projection forms a sharp peak, which might be used to evaluate the modulation transfer function. The overall diameter of the projection provides a

standard dimension for determining the magnification of microfocus units. For

spherical shapes, the circular edge of the projection could reveal variations

in width due to focal spot asymmetry, or it might be used to evaluate the

effect of specimen movement during evaluation.

51
Figure 2. Cross section through a sphere or rod with low density core and a

high density coating, and its radiographic projection.

Lucite spheres of 3 -and 6 -mm radius have been plated with copper to evaluate

this concept. Coating thicknesses up to 0.03 mm have been achieved with

electroless plating solutions; greater thicknesses have been achieved with

subsequent electroplating. Preliminary radiographs show good edge definition

at 60 kV. Evaluation of the other attributes is underway through cooperative

programs with industrial laboratories.

References

1. T. A. Siewert, "Standards for Real-Time Radiography — National Bureau of

Standards," Paper Summaries . Real-Time Imaging III Topical Conference , pp. 21-24 (American Society for Nondestructive Testing, Columbus, OH,

July 1988).

52
APPENDICES

APPENDICES

1 . NDE SEMINARS AT NIST

Professor R. H. Cole . Brown University

"Dielectric Measurements of Material Properties"

November 9, 1987

NDE Poster Session

November 23, 1987

Professor Mack A. Breazeale . University of Tennessee

"Physics and Engineering Principles of Nonlinear Acoustics"

February 2, 1988

Professor Robert L. Thomas . Wayne State University

"Thermal Wave Imaging Using IR Video Techniques with Synchronous Heating"

May 27, 1988

Professor B. A. Auld . Stanford University

"Integrated Sensors for Robotics and Manufacturing Process Control"

J une 10, 1988

2. INVITED TALKS BY ONDE STAFF

"Automated Materials Processing," H. T. Yolken, Welding and Testing Technology

Conference, Knoxville, Tennessee, February 17, 1988.

"Nondestructive Evaluation of Monolithic Shipping Casks for Spent Nuclear

Fuel," L. Mordfin, Lynchburg Section, American Society for Nondestructive

Testing, Lynchburg, Virginia, February 17, 1988.

"Overview of the Nondestructive Evaluation Program at NBS , " G. Birnbaum,

Nondestructive Inspection/Evaluation Ad Hoc Working Group, Alexandria,

Virginia, May 24, 1988.

"Intelligent Processing of Materials: A New Challenge for NDE," H. T. Yolken,

Fall Conference, American Society for Nondestructive Testing, Anaheim,

California, September 20, 1988.

"New Challenges for NDE," H. T. Yolken, Second Regional Congress for NDT for

Latin America and the Caribbean, Lima, Peru, September 26, 1988.

3. PUBLICATIONS

Following is an incomplete listing of NIST reports and publications on NDE and

related topics that have become available since last year's Technical

Activities report was prepared.

Anon., "Glossary of Terms and Definitions for Ultrasonic Testing Procedures,"

MIL-STD-371, 11 pp . (15 October 1987).

53
Anon. , "Field Assurance of Acoustic Emission System Operation Using Simulated

Acoustic Emission Events," Military Standardization Handbook MIL-HDBK- 786

,

8 pp . (1 October 1987).

Anon., "Glossary of Terms and Definitions for Radiographic Testing,"

MIL-STD-369 , 46 pp . (15 October 1987).

Anon., Six NBS Projects Win 1987 I-R 100 Awards," NBS Research Reports . NBS SP 735 . pp. 20-22 (Dec. 1987).

T. C. Bagg, "Digitizing Documents: Guidelines for Image Quality," Inform 1 , No. 11, pp. 6-9 (Nov. 1987).

G. Barnea and C. E. Dick, "Monte Carlo Studies of X-ray Scattering in

Transmission Diagnostic Radiology," Medical Physics 13 . No. 4, pp. 490-495

(Jul/Aug 1987)

M. A. Baum, "Back to the Basics," NBS Research Reports . NBS SP 735 . pp . 5-8

(Dec. 1987).

G. Birnbaum, "NBS NDE Program," Proc . 16th Symposium on Nondestructive

Evaluation , pp. xliii-xlv (Southwest Research Institute, 1987).

G. Birnbaum, "NBS Presentation," Summary Record of the 1988 Meeting of the Ad

Hoc Working Group on Nondestructive Evaluation (NDE) . Office of Science and

Technology Policy (OSTP) /Committee on Materials (COMAT) . IDA Memorandum Report

M-474, pp . 21-37 (Institute for Defense Analyses, Alexandria, VA, July 1988).

G. V. Blessing and D. G. Eitzen, "Ultrasonic Real-Time Monitoring Device for

Part Surface Topography and Tool Condition In Situ," U.S. Patent No. 4,738,131,

7 pp. (April 19, 1988).

G. V. Blessing, D. G. Eitzen, J. F. Henning, A. V. Clark, Jr., and

R. E. Schramm, "Precision Ultrasonic Thickness Measurements of Thin Steel

Disks," Review of. Progress in Quantitative Nondestructive Evaluation 7B . pp. 1563-1572 (1988).

G. V. Blessing and M. P. Jones, "Characterization of Ceramics by Ultrasonics,"

Advanced Ceramics '87 Conference Papers (Society of Manufacturing Engineers,

1987).

T. E. Capobianco and F. R. Fickett, "A Proposed Military Standard for

Commercial Eddy Current Probes Based on Characterization of Performance,"

Proc. 35th Defense Conference on Nondestructive Testing , pp. 134-141 (Ogden

Air Logistics Center, UT, 1986).

T. E. Capobianco and D. F. Vecchia, "Coil Parameter Influence on Eddy Current

Probe Sensitivity," Review of Progress in Quantitative Nondestructive

Evaluation 7A . pp. 487-492 (1988).

D. Chandler -Horowitz and G. A. Candela, "Ellipsometric Instrumentation for

Optical Metrology in Thin Films," Proc, SEMICON/West '87 . pp . 126-132 (1987).

54
A. V. Clark, Jr., "Ultrasonic Characterization of Texture and Formability ,

MRS Bulletin XIII . No. 4, pp . 40-42 (Materials Research Society, 1988).

A. V. Clark, G. V. Blessing, R. B. Thompson, and J. F. Smith, "Ultrasonic

Methods of Texture Monitoring for Characterization of Formability of Rolled

Aluminum Sheet," Review of Progress in Quantitative Nondestructive Evaluation

7B, pp. 1365-1373 (1988)

A. V. Clark, J. C. Moulder, R. B. Mignogna, and P. P. DelSanto, "Comparison of

Several Ultrasonic Techniques for Absolute Stress Determination in the

Presence of Texture," Proc . ONR Symposium on Solid Mechanics Research for

QNDE , Evanston. IL. Sept, 18-20. 1985 . pp . 345-360 (1987).

A. V. Clark, R. C. Reno, R. B. Thompson, J. F. Smith, G. V. Blessing,

P. P. Delsanto, and R. B. Mignogna, "Texture Monitoring in Aluminum Alloys: A

Comparison of Ultrasonic and Neutron Diffraction Measurement," Ultrasonics 26 . pp. 189-197 (1988).

R. B. Clough, H. N. G. Wadley, and R. Mehrabian, "Acoustic Emission Studies of

Electron Beam Surface Modification of Aluminum," Metallurgical Transactions B

19B . pp. 493-503 (June 1988).

G. T. Davis, "Piezoelectric Polymer Transducers," Advances in Dental Research

1 , No. 1, pp . 45-40 (Oct. 1987).

P. P. Delsanto, R. B. Mignogna, and A. V. Clark, Jr., "Ultrasonic Texture

Analysis for Polycrystalline Aggregates of Cubic Materials Displaying Orthotropic Symmetry," Nondestructive Characterization of Materials II . pp . 535-543

(Plenum, 1987) .

R. C. Dobbyn, M. Kuriyama, S. Takagi , and L. C. Chow, "High Resolution

Radiography: Applications to Biomedical Imaging," Proc. Sixth Southern

Biomedical Engineering Conference , pp . 194-197 (1987).

L. L. Dulcie and T. E. Capobianco, "New Standard Test Method for Eddy Current

Probes," Proc. 36th Defense Conference on Nondestructive Testing , pp . 154-160

(U.S. Army Aviation Systems Command, St. Louis, MO, 1987).

K. C. Duvall, "Development of a Standard 2.5-MeV Neutron Source," Nuclear

Instruments and Methods in Physics Research B24/25 . pp . 893-896 (1987).

C. M. Eisenhauer, R. B. Schwartz, and R. C. McCall, "Effect of Air Scatter on

Calibration of Instruments for Detecting Neutrons," Radiation Protection

Dosimetry 19 . No. 2, pp . 77-84 (1987).

D. G. Eitzen and G. V. Blessing, "Ultrasonic NDE for Surface Roughness," MRS

Bulletin XIII . No. 4, pp . 49-52 (Apr. 1988).

D. G. Eitzen and F. R. Breckenridge "Acoustic Emission Sensors and Their

Calibration," Nondestructive Testing Handbook . 2nd edition, Vol. 5,

pp. 121-134 (ASNT , 1987).

55
B. M. Fanconi, F. W. Wang, and D. L. Huns ton, "Comparisons Among Process

Monitoring Techniques," Proc . 45th SPE Annual Technical Conference and

Exhibit . pp . 1100-1102 (1987).

R. A. Forman, J. R. Hill, M. I. Bell, G. S. White, S. W. Freiman, and W. Ford,

"Strain Patterns in Gallium Arsenide Wafers: Origins and Effects," Proc. Inti.

Svmp . on Defect Recognition and Image Processing In III-V Compounds (DRIP

1987) . E. R. Weber, editor, pp . 63-71 (Elsevier, 1987).

H. Frederikse and A. Feldman, "Thermal Wave Inspection of Heat Resistant

Ceramic Coatings," Nondestructive Testing of High-Performance Ceramics , pp . 177-182 (American Ceramic Society, 1987).

J. L. Gross, F. Y. Yokel, R. N. Wright, A. H. Fanney, J. H. Smith, G. E. Hicho,

and T. R. Shives, "Investigation into the Ashland Oil Storage Tank Collapse on

January 2, 1988," NBSIR 88-3792, 204 pp . (June 1988).

G. Harman, "Acoustic Emission Test for Microelectronic Tape Automated

Bonding," Nondestructive Testing Handbook . 2nd edition, Vol. 5, pp . 361-364

(ASNT , 1987).

G. Harman, "Acoustic Emission Thermal Shock Test for Hybrid Microcircuit

Packages," Nondestructive Testing Handbook . 2nd edition, Vol. 5, pp . 365-369

(ASNT, 1987).

G. Harman, "Designing Microelectronic Welds for Acoustic Emission

Testability," Nondestructive Testing Handbook . 2nd edition, Vol. 5,

pp. 409-410 (ASNT, 1987).

A. W. Hartman, "Standards for Particle Size," Proc, International Conf. on

Liquid Borne Particle Inspection and Metrology , pp . 109-121 (1987).

P. R. Heyliger, J. C. Moulder, P. J. Shull, M. Gimple, and B. A. Auld,

"Numerical Modeling of Capacitive Array Sensors Using the Finite Element

Method," Review of Progress in Quantitative Nondestructive Evaluation 7A,

pp. 501-508 (1988).

N. N. Hsu, G. Chen, and M. Sansalone, "Characterization of a Piezoelectric

Transducer Coupled to a Solid," Proc. 1987 Ultrasonics Symposium . IEEE Cat.

#87, CH2492-7, pp . 689-692 (1987).

N. N. Hsu and D. G. Eitzen, "Point Source/Point Receiver Ultrasonic Wave Speed

Measurement," Proc, 1987 Ultrasonics International Conference , pp . 509-514

(1987) .

L. J. Inglehart, "Photothermal Characterization of Ceramics," Nondestructive

Testing of High-Performance Ceramics ." pp . 163-176 (American Ceramic Society,

1987) .

L. J. Inglehart and E. LeGal La Salle, "Thermal Wave Physics of Insulating

Materials," Review of Progress in Nondestructive Evaluation 7A . pp . 231-237

(1988).

56
A. I to and T. Kashiwagi, "Measurement Technique for Determining the

Temperature Distribution in a Transparent Solid Using Holographic

Interferometry," Applied Optics 26 . No. 5, pp . 954-958 (1 March 1987).

F. S. Jing, A. W. Hartman, and R. J. Hocken, "Noncontacting Optical Probe,"

Review of Scientific Instruments 58, No. 5, pp . 864-868 (May 1987).

M. P. Jones and G. V. Blessing, "The Dynamic Poisson's Ratio of a Ceramic

Powder During Compaction," Proc . 1987 Ultrasonics Symposium . IEEE Cat. #87,

CH2492 - 7 , pp. 587-590 (1987).

M. P. Jones and G. V. Blessing, "Ultrasonic Evaluation of Spray-Dried Ceramic

Powders During Compaction," Nondestructive Characterization of Materials II . pp. 139-147 (Plenum, 1987).

M. P. Jones and G. V. Blessing, "Ultrasonic Evaluation of Spray-Dried Ceramic

Powders During Compaction," International Advances in Nondestructive Testing

13 . W. J. McGonnagle, editor (Gordon & Breach Science Publishers, NY, 1988).

M. P. Jones and G. V. Blessing, "Ultrasonic Evaluation of Spray-Dried Alumina

Powder During and After Compaction," Nondestructive Testing of HighPerformance Ceramics . pp . 148-155 (American Ceramic Society, 1987).

A. H. Kahn and M. L. Mester, "An Eddy Current Sensor for the Measurement of

Resistivity and Temperature of Aluminum Rod during Extrusion Processing,"

Review of Progress in Quantitative Nondestructive Evaluation 7B . pp . 1599-1605

(1988)

J. Kosko, "Concrete Research at NBS : New Ways to Understand an Old Material,"

NBS Research Reports . NBS SP 733 . pp . 20-22 (Aug. 1987).

H. M. Ledbetter, R. J. Fields, and S. K. Datta, "Creep Cavities in Copper: An

Ultrasonic-Velocity and Composite-Modeling Study," Acta Metall. 35, No. 9,

pp. 2393-2398 (1987).

P. Lumbroso and C. E. Dick, "X-Ray Attenuation Properties of Radiographic

Contrast Media," Med. Phvs . 14 . No. 5, pp . 752-758 (Sept. /Oct. 1987).

M. L. Mester, A. H. Kahn, and H. N. G. Wadley, "Measuring Internal

Temperatures of Aluminum Extrusion," Proc. Fourth Inti. Aluminum Extrusion

Technology Seminar , pp . 259-265 (Chicago, IL, April 1988).

R. H. Mignogna, P. P. Delsanto, and A. V. Clark, "Energy Distribution for

SH-Waves in Slightly Anisotropic Materials," Review of Progress in

Quantitative Nondestructive Evaluation 7B . pp . 1375-1382 (1988).

R. K. Miller, D. Dornfeld, A. Hamilton, J. Mitchell, and K. Yee , "Process

Monitoring with Acoustic Emission," Nondestructive Testing Handbook . 2nd

edition, Vol. 5, pp . 467-511 (ASNT , 1987).

L. Mordfin, "International Standards for Nondestructive Testing," J. Research

NBS 92., No. 6, pp . 387-390 (Nov. -Dec. 1987).

57
L. Mordfin, editor, Mechanical Relaxation of Residual Stresses . ASTM STP 993,

122 pp. (1988) .

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

with a SQUID-Based Eddy Current Probe," J . Research NBS 92, No. 1, pp . 27-33

(Jan. -Feb. 1987).

J. C. Moulder, N. Nakagawa, and P. J. Shull, "Progress in Uniform Field Eddy

Current Methods," Review of Progress in Quantitative Nondestructive Evaluation

7A, pp. 147-155 (1988).

M. Nashman and K. J. Chaconas , "The NBS Vision System in the AMRF," J . Research

NBS 93 . No. 4, pp . 539-544 (July-Aug. 1988).

S. J. Norton, "Mossbauer Imaging," J . Research NBS 92 . No. 5, pp . 325-334

(Sept . -Oct . 1987) .

R. C. Placious and T. A. Siewert, "Real-Time Radiology Standards: Results of

Workshop," Materials Evaluation 45, pp . 1270-1271 (Nov. 1987).

R. S. Polvani, A. W. Ruff, Jr., and E. P. Whitenton, "A Dynamic

Microindentation Apparatus for Materials Characterization," J. Testing and

Evaluation 16 . No. 1, pp . 12-16 (ASTM, Jan. 1988).

R. C. Reno, R. J. Fields, and A. V. Clark, "Crystallographic Texture in Rolled

Aluminum Plates: Neutron Pole Figure Measurements," Review of Progress in

Quantitative Nondestructive Evaluation 7_B, pp . 1439-1445 (1988).

R. Rensberger, "Process Sensor Measures Internal Temperatures in Extruded

Aluminum," NBS Research Reports . NBS SP 735 . p. 25 (Dec. 1987).

M. Sansalone and N. J. Carino, "Transient Impact Response of Thick Circular

Plates," J. Research NBS 92 . No. 6, pp . 355-367 (Nov. -Dec. 1987).

M. Sansalone and N. J. Carino, "Transient Impact Response of Thick Circular

Plates," J . Research NBS 92 . No. 6, pp . 369-381 (Nov. -Dec. 1987).

M. Sansalone, N. J. Carino, and N. N. Hsu, "Transient Stress Wave Interaction

with Planar Flaws," Building Research and Practice 16 . No. 1, pp . 18-24

(1988)

T. Sato, 0. Ikeda, T. Hatsuzawa, and M. Linzer, "Real-Time Evaluation of Wear

Particles Using Electromagnetic Forced Rotation and Laser Scattering," Wear

115 . No. 3, pp. 273-284 (1987).

R. E. Schramm, A. V. Clark, Jr., D. V. Mitrakovic, and P. J. Shull, "Flaw

Detection in Railroad Wheels Using Rayleigh-Wave EMATs , " Review of Progress in

Quantitative Nondestructive Evaluation 7B . pp . 1661-1668 (1988).

58
P. J. Shull, J. C. Moulder, P. R. Heyliger, M. Gimple, and B. A. Auld,

"Applications of Capacitive Array Sensors to Nondestructive Evaluation,"

Review of Progress in Quantitative Nondestructive Evaluation 7A . pp. 517-523

(1988) .

T. A. Siewert, "Standards for Real-Time Radiography - National Bureau of

Standards , " Paper S ummaries. Real-Time Imaging III Topical Conference , pp. 21-24 (ASrr ~ul^ * Q 88)

J. A. Simmons, E. Drescher-Krasicka , H N. C. rTadley, M. Rosen, and T. M. Hsieh,

"Ultrasonic Methods for Characterizing the In_ rface in Composites," Review of

Progress in Quantitative Nondestructive Evaluation 7B . pp . 893-901 (1988).

J. A. Simmons, C. D. Turner, and H. N. G. Wadley, "Vector Calibration of

Ultrasonic and Acoustic Emission Transducers," J. Acoust. Soc . Am. 82 . No. 4,

pp. 1122-1130 (Oct. 1987)

H. N. G. Wadley, "Interfaces: The Next NDE Challenge," Review of Progress in

Quantitative Nondestructive Evaluation 7B, pp . 881-892 (1988).

H. N. G. Wadley, A. H. Kahn, Y. Gefen, and M. Mester, "Eddy Current

Measurement of Density During Hot Isostatic Pressing," Review of Progress in

Quantitative Nondestructive Evaluation 7B . pp . 1589-1598 (1988).

H. N. G. Wadley and J. A. Simmons, "Microscopic Origins of Acoustic Emission,"

Nondestructive Testing Handbook . 2nd edition, Vol. 5, Section 3, pp . 63-90

(ASNT , 1987).

H. N. G. Wadley, J. A. Simmons, R. B. Clough, F. Biancaniello

,

E. Drescher-Krasicka, M. Rosen, T. Hsieh, and K. Hirshman, "Composite

Materials Interface Characterization, First Progress Report to SDIO,"

NBSIR 87-3630 (1988)

F. W. Wang, A. J. Bur, R. E. Lowry, and B. M. Fanconi, "Fluorescence

Monitoring of Polymer Processing," Polymer Materials Science and Engineering

59 (1988)

F. W. Wang and E. S. Wu, "Cure Monitoring of Epoxy Resins by Fluorescence

Recovery After Photobleaching , " Polymer Communications 28 . pp. 73-75

(Mar. 1987).

M. B. Weppner and M. Young, "Image Processing for Optical Engineering

Applications," NBSIR 87-3065, 105 pp . (Apr. 1987).

G. S. White, C. Nguyen, and B. Rawal, "Young's Modulus and Thermal Diffusivity

Measurements of Barium Titanate Based Dielectric Ceramics," Nonde s true t ive

Testing of High-Performance Ceramics , pp . 371-379 (American Ceramic Society,

1987) .

H. T. Yolken, "Intelligent Processing of Materials," MRS Bulletin XIII . No. 4,

p. 7 (Materials Research Society, Apr. 1988).

59
H. T. Yolken, editor, "Nondestructive Evaluation, Technical Activities, 1987,"

NBSIR 87-3611, 83 pp. (Oct. 1987).

J. H. Zimmerman, "Recommended Technical Specifications for Procurement of

Commercially Available Systems for the Inspection Workstation," NBSIR 88-3379,

32 pp. (1988).

4. AWARDS AND APPOINTMENTS

Department of Commerce Silver Medal

The Silver Medal Award is bestowed for "meritorious contributions of

exceptional value to the Department." Recipients during FY 1988 included

Nicholas J. Carino of the Center for Building Technology. Dr. Carino, who led

the development of the impact-echo technique for detecting flaws in concrete

structures, was recognized for his outstanding leadership in directing the

successful investigation of the structural integrity of the U.S. embassy

building in Moscow. Carino was also elected to the title of Fellow of the

American Concrete Institute in recognition of his work on nondestructive

testing of concrete and his important contributions to several of the

Institute's technical committees.

Also honored with a Silver Medal Award was Charles R. Tilford of the Center

for Basic Standards. A principal investigator in the NDE Program's leak

testing project, Dr. Tilford was cited for his leadership role in developing

improved pressure measurement standards. His pioneering development of

ultrasonic manometry is the basis of new standards and instrumentation that

have become widely used in industry.

Department of Commerce Bronze Medal

The Bronze Medal Award for Superior Federal Service is the highest honorary

recognition available for NIST presentation. One of this year's recipients

was A. Van Clark. Jr

. of the Fracture and Deformation Division, who was

honored for his leadership and contributions in NDE of materials and components. Dr. Clark developed a strong group effort in NDE with emphasis on measurements indicative of structural integrity and reliability, which provide

the nation with improved means of assessing the safety of buildings, bridges,

and industrial facilities.

ISHM Technical Achievement Award

The International Society of Hybrid Microelectronics selected Stanley Ruthberg

as one of three recipients of its Technical Achievement Award for 1987. A

group leader in the Center for Electronics and Electrical Engineering at the

time of his death late in 1986, Ruthberg pioneered the leak testing activities

in the NDE Program. The award recognized his long-term and diverse contributions to the technical community, particularly in the area of leak testing of

hermetic microelectronic packages.

60
Special Award for Excellence in Technology Transfer

The Federal Laboratory Consortium for Technology Transfer selected

Melvin Linzer of the Metallurgy Division and David S. Kupperman of Argonne

National Laboratory to receive one of its special awards. The joint award

commends the excellent cooperative effort by NIST, the American Iron and Steel

Institute, and Magnaflux Corporation to implement an ultrasonic sensor

technology for detecting flaws in hot metal.

AEWG Fellow

Nelson N. Hsu of the Center for Manufacturing Engineering was elected a Fellow

of the Acoustic Emission Working Group. Dr. Hsu was cited for his outstanding

professional distinction and continued significant contributions to the AEWG

and to the advancement of acoustic emission technology.

ASTM E-7 Certificate of Appreciation

ASTM Committee E-7 on Nondestructive Testing established a certificate of

appreciation in 1987 to recognize individuals for outstanding contributions to

the work of the Committee. Of twenty-eight certificates awarded to date, five

have gone to NIST staff: Julius Cohen . Donald G. Eitzen . George W. Free . Barbara Howell , and Leonard Mordfin .

NIST Safety Award

The NIST Safety Award for Superior Accomplishment recognizes unusually

significant contributions to the NIST Occupational Safety and Health program

activities. The award is presented to individuals and to organizational

units. The Office of Nondestructive Evaluation was honored with an

organizational award in recognition of an eight-year unblemished safety

record.

Community Service Awards

Twenty- seven federal employees of four agencies were honored with desk- top

plaques for their involvement in a Boulder, Colorado outreach effort called

CARE, for Career Awareness and Resource Education, coordinated by NIST. CARE

is aimed at getting students interested in pursuing studies leading to careers

in science and technology by providing the students with opportunities to meet

and talk with people who work in those areas. Among those honored were

Tom Capobianco and Fred Fickett of the Center for Electronics and Electrical

Engineering, and Ray Schramm and Peter Shull of the Fracture and Deformation

Division, all of whom participate in the NDE Program.

Gerald V. Blessing . Center for Manufacturing Engineering, was elected

Technical Vice Chairman for the 1989 International Ultrasonics Symposium of

the Institute of Electrical and Electronic Engineers.

Donald G, Eitzen . Center for Manufacturing Engineering, was appointed Chairman

of the ASTM/NIST/ASNT symposium on NDE standards, tentatively scheduled for

the fall of 1989.

61
David S. Lashmore . Metallurgy Division, was elected Chairman of the

Electrodeposition Division of the Electrochemical Society.

.

.

pH
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NISTIR 88-3839

2. Performing Organ. Report No 3. Publication Date

OCTOBER 1988

4. TITLE AND SUBTITLE

Nondestructive Evaluation -- Technical Activities - 1988

5. AUTHOR(S)

H. Thomas Yolken, editor

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

National Institute of Standards and Technology

7. Contract/Grant No.

8. Type of Report & Period Covered

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899 Annual, FY1938

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

SAME

10. SUPPLEMENTARY NOTES

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

11. ABSTRACT (A 200-word or less factual summary of most si gnificant in formation . If document includes a significant

bi bl iography or literature survey, mention it here)

A review of the Nondestructive Evaluation Program at NIST for fiscal year 1988 is

presented in this annual report.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

acoustic^ emission; composite materials; eddy currents; materials processing; metal

forming; nondestructive evaluation; powders ceramic and metal; radiography; sensors;

standards; thermal testing; ultrasonics

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

IX 1 Unl i mi ted

| | For Official Distribution. Do Not Release to NTIS 73

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