NASA Technical Memorandum 102491 

Recent Advances in Nondestructive 

Evaluation Made Possible by Novel 

Uses of Video Systems 

Edward R. Generazio and Don J. Roth 

Lewis Research Center 

Cleveland, Ohio

ORGLk iTAtNS

COlOR ILLUSTRATIONS 

Prepared for 

MiCon 90: Advances in Video Technology: Materials 

sponsored by the American Society for Testing and Materials 

San Francisco, California, May 23-25, 1990 

- CENT AUVANCES IN N9O-26- 

NONDESTRUCTIVE EVALUATION MADE P0STB1E BY 

NOVEL UStS OF VIDEO SYSTIMS (NASA) 20 p -

CSCI 140 Unclas 

3/38 0275344 

-
RECENT ADVANCES IN NONDESTRUCTIVE EVALUATION MADE POSSIBLE 

BY NOVEL USES OF VIDEO SYSTEMS 

Edward R. Generazio and Don J. Roth 

REFERENCE: Generazio, E. R., Roth, D. 3., "Recent Advances 

in Nondestructive Evaluation Made Possible by Novel Uses of 

Video Systems", MiCon 90: Advances in Video Technology for 

Microstructural Control, ASIM SIP 1094, George Vander 

Voort, Ed., American Society for Testing and Materials, 

Philadelphia, 1990. 

ABSTRACT: Complex materials are being developed for use in 

future advanced aerospace systems. High-temperature materials have been targeted as a major area of materials development. The development of composites consisting of ceramic 

or metallic matrix, and ceramic fibers or whiskers is currently being aggressively pursued internationally. These 

advanced materials are difficult and costly to produce; however, their low density and high operating temperature range 

are needed for the next generation of advanced aerospace 

systems. These new materials represent a challenge to the 

nondestructive evaluation community. 

Video imaging techniques not only enhance the nondestructive evaluation, but they are also required for proper 

evaluation of these advanced materials. Specific research 

examples are given, highlighting the impact that video systems have had on the nondestructive evaluation of ceramics. 

An image processing technique for computerized determination 

of grain and pore size distribution functions from microstructural images is discussed. The uses of video and computer systems for displaying, evaluating, and interpreting 

ultrasonic image data are presented. 

KEYWORDS: nondestructive evaluation, image processing, 

nondestructive testing, ceramics, silicon nitride, silicon 

carbide, ultrasonic, microstructure, grain size, porosity 

Edward R. Generazio and Don J. Roth are Research Scientists 

at NASA Lewis Research Center, Cleveland, Ohio 44135.

ORIGINAL CONTAINS 

COLOR ILLUSTRATIONS
INTRODUCTION 

Advanced high-temperature materials [l] are being developed for use 

in the next generation of aerospace systems. Recently, considerable 

attention has been given to monolithic SIC and S13N4 ceramic materials 

[2) for these high-temperature applications. Research on monolithic 

ceramics subsequently led to the current developmental research on 

advanced high-temperature composites. These composites consist of particles, whiskers, or fibers in metal or ceramic matrices. A variety of 

processing techniques are being investigated in an effort to produce 

high-temperature composites with optimized thermal and mechanical properties. Plasma spraying, reaction bonding, slurry pressing, and sintering are typical techniques used to produce high-temperature 

ceramics. These processes often result in a material that has a widely 

variable microstructure. Typical rnicrostructural variations, such as 

porosity, agglomerates, grain size, interfacial structure between 

phases, and orientation of phases and grains, all play a role in determining the material's properties. The importance and effects of these 

microstructural variations on the composite material's thermal and 

mechanical properties are being aggressively researched [1-8). 

It is generally accepted that neither conventional x-ray radiographic nor ultrasonic evaluation is able to identify, a priori, defects that will eventually cause failure in ceramics. There are two 

problems that prevent us from obtaining this crucial information a 

priori. The first is that these ceramic materials, even the monolithic ones, are complex systems that yield x-ray and ultrasonic data 

that are difficult to interpret. For example, we found that standard 

techniques for making ultrasonic attenuation measurements for metals 

(i.e., single point measurements) were inadequate for monolithic ceramics [9,10]; therefore, imaging techniques are required. We must reevaluate and modify our NDE methods and theories and adapt them to 

these new systems. The second problem is that the complicated structure of monolithic and composite ceramics has caused the modification 

of NDE methods and theories to be slow and the interpretation of ultrasonic and radiographic data to remain ambiguous. 

In spite of these problems, NDE technologies can be expected to 

nonintrusively monitor and track processes that lead to the creation 

of critically sized pores and the matrix-second phase interface in composites. In order to assist in the development of these advanced 

ceramic materials, NDE must reposition itself with respect to the materials' development; that is, NDE must be performed during the material's processing rather than after the ceramic material has been produced. Perhaps NDE will have to be incorporated in situ and at the 

end of each processing stage. In situ NDE during developmental processing of ceramic materials is a new concept that can be carried over 

to total quality management during manufacturing. 

Imaging by video and computer systems has proven crucial to promoting NDE technology to the level where it can have an impact on the 

development of advanced high-temperature materials. These systems have 

been instrumental in guiding and expanding NDE technologies toward the 

in situ processing environment. The work presented herein gives an 

overview of two new image-intensive techniques developed specifically 

2
for assisting in producing these advanced materials: tone-pulse encoding of microstructural images, to determine microstructure size distributions; and precision acoustic imaging of porosity variations produced 

during sintering. 

MICROSTRUCTURE SIZE DISTRIBUTIONS 

Material characteristics, such as tensile strength, hardness, 

yield stress, fracture stress, impact resistance, and fracture toughness, are directly related to grain, porosity, and whisker size distributions. Thus, prediction of these properties requires detailed 

knowledge of the related size distributions. The theoretical determination of size distributions has received considerable attention 

[11). Several accepted techniques determine the mean grain or pore 

size without measuring the size distribution function. These techniques, however, are not applicable to any arbitrary system; the 

researcher must often determine which method will yield the most accurate data. The guidelines for making this decision are quite general 

and, as such, can lead to considerable error in the results [11]. 

In this section, an objective technique is described for determining the grain and pore size distribution functions from a metal lographIcally prepared sample. The resulting relationship is two-dimensional 

and yields the grain and pore size distribution functions from which 

the mean shape, size, and orientation can be obtained. 

The theory for the tone-pulse-encoding technique can be found elsewhere [12]. Briefly, a microstructural image (Fig. 1) Is digitally 

recorded into a 512 by 512 pixel array by a video camera attached to a 

computer-controlled video digitizer. This image may reveal grain and 

pore boundaries. The preferred, but not required, method is to work 

with images that reveal only one feature such as grains or, perhaps, 

pores.

r GRAIN 

/ BOUNDARY 

II 

20 PIXELS 

Fig. 1 -- Digitized image of grain 

structure.

3
A two-dimensional gradient of the image (Fig. 2) is used to enhance 

the boundaries of the feature that we are interested in. The optical 

noise in the gradient image is removed by using a two-level gray scale 

to highlight the boundaries. Next, a tone-pulse-encoded image containing the fundamental harmonics of each grain is generated. The torte 

pulse begins and ends at a grain boundary and has a width equal to the 

width of the grain. The amplitude of the tone pulse is inversely proportional to the width. A new tone pulse is started at an adjacent 

grain boundary, which generally has a different width. This is done 

digitally, starting from the center of the image and proceeding outward along the radius to the perimeter of the image. The process is 

repeated for all angles (0 to 21r rad) so that a frequency-encoded image 

appears as shown in Fig. 3.

,- ENHANCED 

/ GRAIN 

BOUNDARY 

20 PiXELS 

Fig. 2 -- Two-dimensional gradient 

of Fig. 1 exhibits enhanced grain 

boundaries. 

Fig. 3 -- Tone-pulse-encoded image.
Fig. 4 -- Density of length components 

as a function of reciprocal vector s. 

The density of length components Fm(s,)Is (Fig. 4) is obtained

by multiplying the two-dimensional Fourier transform, IF(s,)I Of 

the tone-pulse-encoded image by the magnitude s of the radial vector. 

Here 0 is the polar angle and s is the reciprocal vector of the 

spatial vector r'. By replacing s with hr 1 in F(s,)Is, we 

obtain the density of length components P(r' ,) as a function of 

length r' as shown in Fig. 5. The mean grain length D() along any 

direction is obtained from P(r ,c) and is given by 

E,jP(r',O)jr 

- D( ) (1) 

r IP(r ,)I 

Equation 1 yields the mean grain shape from which the orientation can 

be obtained.

20 PIXELS -1 

P(r14) jRAIN 

r 

10 PIXELS 

Fig. 5 -- Density of length components 

as a function of length.
The tone-pulse-encoding technique can be modified for determining 

porosity (Fig. 6) size distributions. The area that is tone-pulse 

encoded between the pores is masked out so that only the pores are 

tone-pulse encoded. Subsequent processing yields the porosity size 

distribution function.

ii 20 PIXELS 

20 PIXELS "-I k 

oi At JMEAN PORE] 

Fig. 6 -- Photomicrograph of pores, density 

of length components, and mean pore. Image 

of pores is enhanced by clipping data above a 

predetermined level to a constant value.
PRECISION ACOUSTIC IMAGING 

Ultrasonic imaging can be done by several techniques. The most 

common is that used by commercially available ultrasonic immersion 

C-scanning systems. An ultrasonic wave of known amplitude A 0 is 

transmitted through a sample as shown in Fig. 7. The final amplitude 

Af or C-scan image is a representation of relative attenuation or 

energy lost by the ultrasonic wave during Its trip from the transmitter to receiver. Unfortunately, C-scan images are not representations 

of the energy lost by the ultrasonic wave solely because of the internal structure of the sample. The ultrasonic reflection coefficients 

at the water-to-sample interfaces, which are generally assumed to be 

constant, are actually large and varying. These reflection coefficients must be Included in the analysis to determine the actual energy 

loss, or attenuation, due to the inner structure of the sample, and 

they must be used in determining the accuracy of the acoustic Image as 

well as the accuracy of the imaging technique. For this reason, the 

equations for determining the uncertainty in the measurement of ultrasonic attenuation are highlighted in this work. 

First consider the immersion scanning method. To obtain the 

reflection coefficient at the back surface, a modified two-transducer 

arrangement must be used (Fig. 8), where the transducers are both 

transmitters and receivers. The uncertainty a. in the attenuation 

measurement for this immersion arrangement is given by 

a S 1

(i - R)[(l + R) + 4R] 

(a"-)(N) = 22 22 

(1 - Rf) (i - Rb)

1/2 

+ (i - R)[(l + R) + 4R] + 2(1 - R)(l - 2ax

(2) 

(1— R)(i - R) (i - R)(l - R)] 

where S/N is the signal-to-noise ratio of the input ultrasonic pulse, 

is the measured attenuation, and Rf and Rb are the reflection 

coefficient magnitudes on the front and back surfaces of the sample, 

respectively, and x is the sample thickness. 

An alternative technique to immersion scanning is contact scanning. 

The experimental arrangement for this technique, which uses a single 

transducer to make precise and accurate attenuation measurements, is 

shown in Fig. 9. An ultrasonic wave is introduced into the sample via 

the buffer rod-couplant-sample (BCS) interface. The ultrasonic wave 

subsequently echoes within the sample. By measuring both the reflection coefficient [13) Rf at the BCS interface, and the appropriate 

echoes, the ultrasonic attenuation can be determined. The uncertainty 

In the attenuation measurement for this contact arrangement is given by 

7
\

11/2 

a ( \

21 (3) 

1 1 R + e4]e4

4 42 1 

+ I 

N _2xx[/

(i - R)

R RbRf

RR + j 

Note that the sample need not be air backed. That is, IRbI may be 

less than one.

,.- SAMPLE 

A0 AF 

TRANSMITTER RECEIVER 

1120 I I 1120 

Fig. 7 -- Standard immersion ultrasonic C-scanning arrangement. 

.- SAMPLE 

If 

TRANSMITTER/ TRANSMITTER/ 

RECEIVER RECEIVER 

H20 1120 

Fig. 8 -- Modified immersion ultrasonic scanning arrangement 

needed for determining reflection coefficients at front and 

back surfaces.

8
u-I 

LO 

-J 

C 

/ 

PIEZOELECTRIC 

CRYSTAL -/ TO PULSERRECEIVER

BACK SURFACE 

FRONT

SURFACE—'

B

AX 

6LYCERIN 

COUP LANT 

TIME 

Fig. 9. - Configuration for contact ultrasonic measurements. 

Equations 2 and 3 are shown graphically in Fig. 10. The 

experimental configuration having the lowest uncertainty values 

obtained from Eqs. (2) and (3) Is shown. The solid line in the figure 

can be used to make a decision about which technique should be applied 

for a particular experimental sample. Above the solid line a precision 

contact pulse-echo measurement is preferred. Below the solid line an 

immersion through transmission yields the least uncertainty in the 

attenuation measurement. 

Immersion ultrasonic systems generally have similar reflection coefficients for Rf and Rb. The uncertainty is symmetric with respect 

to the Rf = Rb axis for imrnersionmeasurements. The long-dashed 

line in Fig. 10 indicates the path used to determine the uncertainty. 

Many solid materials will fit on this curve between 0.84 and 0.97. 

Figure 11 shows the uncertainty for Ni, Pb, Al, PMMA, PMC, A102, W, 

Si3N4, and SIC for both immersion (Rf = Rb) and contact ultrasonic 

methods. When evaluating Ni, SiC, S13N4, A102, and N, the contact 

pulse-echo method yields the least uncertain and the most accurate 

attenuation measurement. For example, if we consider using the immersion scanning technique with a tungsten sample, the reflection coefficients are R b = Rf = 0.97, so we obtain & = 4.52. Here we assume 

that 2ax = 1 and a = 1 for comparison, and ' = 1og[/a(S/N)]. The 

same sample in a contact scanning system will have Rf = 0.74 and 

Rb = 1.0, to yield & = 3.14. Therefore, for tungsten, contact scanfling will yield a more accurate result.
1.0

- 2.75 K 0' 3.25 a' =LOG ( (--)) a = 1. 2a x = 1 

/ 3.25K a' 

I 

1.0 

Fig. 10 -- Uncertainty in the attenuation as a function of 

front and back surface reflection coefficients for both immersion and contact ultrasonic scanning. Above the solid line the 

contact scanning method is more accurate. The long-dashed line 

indicates the uncertainty for the immersion arrangement where 

the sample has identical reflection coefficients on both 

sides. Here, 2cx = 1, = 1, and o = log[c/a.(S/N)]. 

A precision acoustic scanning system (PASS) is shown in Fig. 12. 

A detailed description of the operation and use of the PASS is given 

elsewhere [9-10, 13-141. Briefly, an ultrasonic wave transmitterreceiver (transducer) is scanned over the surface of the sample. 

After collection and subsequent Fourier analysis of the appropriate 

waveforms, an accurate determination of velocity and attenuation can 

be made. This is done at different positions on the sample, in an 

organized array. The resultant data yield velocity and attenuation 

maps that are displayed on a video system. 

iLiJ
o PMMA 

? PMC 

o Al 

Pb 

sic 

O A102 

o N 

V W 

o Si3N4 

CONTACT METHOD (R b = 1) 

8

- - - MINIMUM UNCERTAINTLY WITH CONTACT METHOD 

IMMERSION METHOD (R R 

0 .2 .4 .6 .8 1.0

REFLECTION COEFFICIENT I Rs 

Fig. 11 -- Uncertainty comparison for several materials. For 

A102, Ni, W, SIC, and S13N4, the uncertainty is lower with a 

contact scanning method. Curves are generated from Eqs. 2 and 

3. Here, 2xx = 1, 1, and & = log [aaIa(S/N)]. 

A typical data set, from which approximately 25 images can be 

obtained, will contain about 2000 waveforms, 2000 Fourier spectra, and 

40 000 attenuation and velocity values. The original acquired data 

uses about 20 Mbyte of computer memory storage, whereas the reduced 

data set containing the attenuation [13], velocity [10], and reflection coefficient [13] images occupies about 5 Mbyte. 

Evaluating an image often requires examination of both the raw and 

reduced data for a particular point in the image. A data retrieval 

program provides the necessary interface to allow immediate retrieval 

of data, which are displayed in a video image overlay. For example, 

the data for one point (determined by the cursor location) in an ultra -

sonic image of velocity (Fig. 13) are displayed in an overlay as shown 

in Fig. 14. This display contains waveforms and their Fourier spectra, 

reflection and attenuation coefficients (which may be used to determine 

accuracy), phase velocity as a function of frequency, and group velocity (determined by cross correlation). We need to examine all of these 

data for irregularities when evaluating a particular point on the 

ultrasonic image. For example, if a quantitative measure of the difference in density between two points is needed, it can be determined 

from the group velocity at these points on the appropriate overlays. 

Also, the frequency dependence that attenuation exhibits has been 

related to the subsurface pore or flaw sizes [15], the state of the 

recrystallization in metals (16), and the mean grain size [17]. Easy 

access to this type of information is made possible by the use of a 

video system. 

10
0-

Su

,Z-AXIS 

X-Y-Z POSITIONING

TABLE 

WAVEFORM DIGITIZER 

TIME BASE

VOLTAGE BASE 

PRESSURE SENSOR

VOLTMETER 

TIME DELAY 

ULTRASONIC

PULSER-RECEIVER 

TO GPLB - 

CPU

PRESSURE 

GAUGE SUPPORT--,,

,- PRESSURE GAUGE 

TRANSDUCER-' 

SAMPLE J----VIBRATOR 

HOLDER

SAMPLE 

Fig. 12. - Precision acoustic scanning system (PASS). 

12
_1.13 

OR!GINAL PAGE

COLOR PHOTOGRAPH

VELOCITY. 

CM/MSEC 

--1.15 

Fig. 13 -- Ultrasonic image of SIC produced by the PASS. Cursor 

indicates the physical point on the sample that needs to be 

evaluated. Area shown is 2 cm x 2 cm.

ORIGINAL PAGE Is 

OF POOR QUALITY 

13
Fig. 14 -- Pop-up screen revealing data that are obtained for 

cursor position shown in Fig. 13. This screen contains all 

required data and analysis for proper evaluation of the ceramic 

at this cursor position. 

Video and computer systems have also played a crucial role in the 

interpretation of ultrasonic data. In the past, only a few measurements would have been taken at a small number of positions In order to 

ultrasonically, nondestructively evaluate a material. The data 

obtained from these measurements would have been averaged, and the 

standard deviation determined. These two values, the average and the 

standard deviation, would then be used to classify the sample. However, these two values may not be sufficient for giving a full understanding of the internal structure of the material. For example, from 

nine measurements we can calculate the average ultrasonic attenuation 

and its standard deviation at 100 MHz in a ceramic sample as 1.1 and 

0.3 Np/cm, respectively. But this information does not describe the 

cloudlike attenuation structure [10] revealed in the pass-obtained 

video image of that sample (Fig. 15). Another example of video 

imagings impact on the interpretation of ultrasonic data is shown in 

Figs. 16 and 17. Previously, ultrasonic attenuation in ceramics was 

believed to be due to diffractive scattering from individual grain and 

pore boundaries; therefore, an increase in the number or size of pores 

yielded an increase in the attenuation. These figures dramatically 

show that the high ultrasonic attenuation observed is due to diffractive scattering at regions exhibiting large velocity (density) gradients [9], not increased porosity.

14
1-0 

ORIGINAL PAGE

COLOR PHOTOGRAPH

ATTENUATION,

Np/CM 

_2.5 

1

Fig. 15 -- Pass-produced ultrasonic attenuation image of SIC. 

Video image reveals the cloudlike porosity structure within the 

sample. Disk has a diameter of 4 cm.

ORIGINAL PAGE Is 

OF POOR QUALITY 

15
ORIGINAL PAGE 

COLOR PHOTOGRAptVELOCITY, 

CM/IJSEC 

- - 1.114 

Fig. 16 -- Pass-produced ultrasonic velocity image of SIC. 

Video Image reveals a pear-shaped pattern in porosity structure. There is a sharp boundary between high and low density 

regions. Area shown is 2 cm x 2 cm.

- 1.09 

- 1.04 

- .99 

ORIGINAL PAGE Is 

16

OF POOR QUALITY
I Z 14M 

g

JOr

ATTENUATION,

NP/CM 

I' 

-2 

-1 

-0 

ORIGINAL PAGE

COLOR PHOTOGRAPH

Fig. 17 -- PASS-produced ultrasonic attenuation image of sample 

region in Fig. 16. Video image reveals high attenuation 

at sharp high-to-low density boundaries. Area shown Is 

2 cm x 2 cm. 

SUMMARY 

In summary, advances in the nondestructive evaluation of materials' 

microstructure have been made possible by incorporating video systems 

into the material evaluation process. A video image processing technique for computerized determination of pore and grain size distributions has been described. The impact of the use of video systems on 

the display, evaluation, and interpretation of ultrasonic data for 

advanced ceramics has been highlighted. 

17 ORIGINAL PAGE IS 

OF POOR QUALITY
REFERENCES 

El] HITEMP Review 1989: Advanced High Temperature Engine Materials 

Technology Program, NASA CP-10039, National Aeronautics and Space 

Administration, Washington, D.C., 1989. 

[21 Structural Ceramics, NASA CP-2427, National Aeronautics and Space 

Administration, Washington, D.C., 1986. 

[3] Grell, P., Petzow, G., and Tanaka, H., Ceramics International, 

Vol. 13, No. 1, 1987, pp. 19-25. 

[4] Nickel, K.G., Hoffmann, M.J., Greil, P., and Petzow, G., 

Advanced Ceramic Materials, Vol. 3, No. 6, Nov. 1988, 

pp. 557-562. 

[5] Freedmann, M.R., Kiser, J.D., and Sanders, W.A., "A Sintering 

Model for SiC/Si3N4 Composites," NASA TM-101336, National Aeronautics and Space Administration, Washington, D.C., 1988. 

[6] Wei, G.C. and Becher, P.F., American Ceramic Society Bulletin, 

Vol. 64, No. 2, Feb. 1985, pp. 298-304. 

[7] Kobayashi, S., Karidori, T. and Wada, S., Journal of the Ceramic 

Society of Japan (Yogyo Kyokaishi), Vol. 94, No. 8, 1986, 

pp. 903-905. 

[8] Ishigaki , H., Nagata, R., Iwasa, M., Tamari , N., and Kondo, I., 

Journal of Tribology, Vol. 110, No. 3, July 1988, pp. 434-438. 

[9] Generazio, E.R., Roth, D.J., and Stang, D.B., Journal of the 

American Ceramic Society, Communications, Vol. 72, No. 7, 

July 1989, pp. 1282-1285. 

[10] Generazio, E.R., Roth D.J., and Baaklini, G.Y., Materials 

Evaluation, Vol. 46, No. 10, Sept. 1988, pp. 1338-1343. 

[11] Quantitative Microscopy, R.T. DeHoff and F.N. Rhines, eds., 

McGraw-Hill Book Co., NY, 1968. 

[12] Generazio, E.R., Materials Evaluation, Vol. 46, No. 4, 

March 1988, pp. 528-534. 

[13] Generazio, E.R., Materials Evaluation, Vol. 43, No. 8, 

July 1985, pp. 995-1004. 

[14] Generazio, E.R., Stang, 0.8., and Roth, D.J., in The Sixteenth Annual Review of Progress in Quantitative Nondestructive 

Evaluation, Vol. 9, D.O. Thompson and D.E. Chimenti , Eds. 

Plenum Press, NY, 1990. 

[15] Truell, R., Elbaum, C., and Chick, 8.8., Ultrasonic Methods in 

Solid State Physics, Academic Press, NY, 1969. 

[16] Generazio, E.R., Materials Evaluation, Vol. 46, No. 9, 

Aug. 1988, pp. 1198-1203. 

[17] Generazio, E.R. , Materials Evaluation, Vol. 44, No. 2, 

Feb. 1986, pp. 198-202, 208.

18
NASA 

National Aeronautics and Report Documentation Page 

Space Administration 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

NASA TM-102491 

4. Title and Subtitle 5. Report Date 

Recent Advances in Nondestructive Evaluation Made Possible by Novel 

Uses of Video Systems

6. Performing Organization Code 

7. Author(s) 8. Performing Organization Report No. 

Edward R. Generazio and Don J. Roth E-5283 

10. Work Unit No. 

510-01-lA 

9. Performing Organization Name and Address

11. Contract or Grant No. 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135-3191

13. Type of Report and Period Covered 

12. Sponsoring Agency Name and Address Technical Memorandum 

National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, D.C. 20546-0001 

15. Supplementary Notes 

Prepared for MiCon 90: Advances in Video Technology: Materials Science Applications sponsored by the 

American Society for Testing and Materials, San Francisco, California, May 23-25, 1990. Invited paper. 

16. Abstract 

Complex materials are being developed for use in future advanced aerospace systems. High-temperature materials 

have been targeted as a major area of materials development. The development of composites consisting of 

ceramic matrix and ceramic fibers or whiskers is currently being aggressively pursued internationally. These new 

advanced materials are difficult and costly to produce; however, their low density and high operating temperature 

range are needed for the next generation of advanced aerospace systems. These new materials represent a 

challenge to the nondestructive evaluation community. Video imaging techniques not only enhance the 

nondestructive evaluation, but they are also required for proper evaluation of these advanced materials. Specific 

research examples are given, highlighting the impact that video systems have had on the nondestructive evaluation 

of ceramics. An image processing technique for computerized determination of grain and pore size distribution 

functions from microstructural images is discussed. The uses of video and computer systems for displaying, 

evaluating, and interpreting ultrasonic image data are presented. 

17. Key Words (Suggested by Author(s)) 18. Distribution Statement 

Nondestructive evaluation; Image processing; Nondestructive Unclassified - Unlimited 

testing; Ceramics; Silicon nitride; Silicon carbide; Subject Category 38 

Ultrasonic; Microstructure; Grain size; Porosity 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of pages 22. Price 

Unclassified Unclassified 21 A03

NASA ti)KM 1525 OCT 86 *For sale by the National Technical Information Service, Springfield, Virginia 22161 
FOURTH CLASS MAIL I II V I 

ADDRESS CORRECTION REQUESTED W 

Postage and Fees Pad 

National Aeronautics and 

Space Admnatratun 

NASA 45 

National Aeronautics and 

Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135 

Official Business 

Penalty for Private Use $300

NASA