Astm stp 1157 1992

S T P 1157 Cyclic Deformation, Fracture, and Nondestructive Evaluation of Advanced Materials M R Mitchell and Otto Buck, editors ASTM Publication Code Number (PCN) 04-011570-30 ASTM 1916 Race Street Philadelphia, PA 19103 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Library of Congress Cataloging-in-Publication Data Cyclic deformation, fracture, and nondestructive evaluation of advanced materials / M R Mitchell and Otto Buck, editors (STP ; 1157) Based on papers presented at a symposium held in San Antonio, Tex Nov 12-13, 1990 "ASTM publication code number (PCN)." Includes bibliographical references and index ISBN 0-8031-1444-3 Composite materials Fatigue Congresses Non-destructive testing Congresses I Mitchell, M R (Michael R.), 1941II Buck, Otto III Series: ASTM special technical publication ; 1157 TA418.9.C6C83 1992 620.1' 186 dc20 92-16045 CIP Copyright 1992 A M E R I C A N SOCIETY FOR TESTING AND MATERIALS, Philadelphia, PA All rights reserved This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of the publisher Photocopy Rights Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by the A M E R I C A N SOCIETY FOR TESTING AND MATERIALS for users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the base fee of $2,50 per copy, plus $0.50 per page is paid directly to CCC, 27 Congress St., Salem, MA 01970; (508) 744-3350 For those organizations that have been granted a photocopy license by CCC, a separate system of payment has been arranged The fee code for users of the Transactional Reporting Service is 0-8031-1444-3/92 $2.50 + 50 Peer Review Policy Each paper published in this volume was evaluated by three peer reviewers The authors addressed all of the reviewers' comments to the satisfaction of both the technical editor(s) and the ASTM Committee on Publications The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s), but also the work of these peer reviewers The ASTM Committee on Publications acknowledges with appreciation their dedication and contribution to time and effort on behalf of ASTM Printed in Ann Arbor, MI Aug 1992 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Foreword This publication, Cyclic Deformation, Fracture, and Nondestructive Evaluation of Advanced Materials, contains papers presented at the symposium of the same name held in San Antonio, Texas, 12-13 November 1990 The symposium was sponsored by ASTM Committee E9 on Fatigue and its Subcommittees, E9.03 on Fatigue of Advanced Materials and E9.01.07 on Research on Nondestructive Evaluation of Advanced Materials M R Mitchell, Rockwell International, and Otto Buck, Iowa State University, presided as symposium chairmen and are editors of this publication Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions auth Contents Overview Cyclic Fatigue of A i u m n i a - - c - K J L I N , T A M A Y E R , A N D D F SOCIE Fatigue C r a c k G r o w t h in Ceramics and Ceramic Matrix Composites R JOHN AND N E ASHBAUGH 28 Fatigue Test Methodology a n d Results for C e r a m i c M a t r i x Composites at R o o m and Elevated T e m p e r a t u r e s - - L M B U T K U S , L P Z A W A D A A N D G A H A R T M A N 52 Small-Crack Behavior and Safety-Critical-Design C r i t e r i a for Cyclic Fatigue in M g - P S Z C e r a m i c s - - A A STEFFEN, R H DAUSKARDT, AND R O RITCHIE Modeling C r a c k G r o w t h Resistance in Ceramics and Ceramic-Matrix C o m p o s i t e s - J LLORCA AND M ELICES 69 82 Thermomechanical Cyclic D e f o r m a t i o n of M e t a l - M a t r i x C o m p o s i t e s - M KARAYAKA AND H SEHITOGLU 101 Fatigue C h a r a c t e r i s t i c s of Heavily Cold-Roiled Cu-20Nb B s BINER AND W A S P I T Z I G Effect of Tensile M e a n Stress on Fatigue B e h a v i o r of Single-Crystal and Directionally Solidified S u p e r a l l o y s - - s KALLURI AND M A, MCGAW 121 136 Mechanical Properties of Amorphous and Roll-Drawn Polypropylene-D M C C A M M O N D , A N SINCLAIR~ A N D L A S I N C L A I R 151 T h e Influence of C o n s t i t u e n t Properties on the C o m p r e s s i o n B e h a v i o r of Laminates with D i s c o n t i n u i t i e s - - D L CRANE, W L BRADLEY, AND D L BARRON 171 Cyclic Creep Effects in Single-Overlap Bonded Joints Under Constant-Amplitude Testing R A CHERNENKOFF 190 I n t e r p r e t a t i o n of L a b o r a t o r y Test I n f o r m a t i o n for Residual S t r e n g t h a n d Life Prediction of Composite S y s t e m s - - K L REIFSNIDER 205 Crack Resistance, Fracture Toughness, and Instability in Damage-Tolerant A l u m i n u m - L i t h i u m A i l o y s - - R J H WANHILL, L SCHRA, AND W G J ' T H A R T 224 Ultrasonic Wave Technique to Assess Cyclic-Load Fatigue Damage in SiliconCarbide Whisker Reinforced 2124 Aluminum Alloy Composites J D A C H E N B A C H , M E F I N E , I KOMSKY, A N D S MCGUIRE 241 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Nondestructive Characterization for Metal-Matrix Composite Fabrication-P K L I A W , R E S H A N N O N , W G CLARK, JR., A N D W C HARR1GAN, JR 251 Nondestructive Evaluation of a Ceramic Matrix Composite Material-P P GROSSKOPF A N D J C D U K E , JR 278 Acoustic Emission Monitoring of Fatigue in Titanium Aiuminide XD Composite-E U L E E , D M G R A N A T A , A N D W R SCOTT 293 On the Flexure Test and Nondestructive Evaluation for Nicalon/CAS Ceramic Composites s s L E E , E G H E N N E K E , A N D W W S T I N C H C O M B 312 Split Spectrum Processing of Backscattered Rayleigh Wave Signals to Improve Detectability of Fatigue Microcracks M T RESCH AND P KARPUR 323 Author Index 335 Subject Index 337 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized STP1157-EB/Aug 1992 Overview The implementation and usage of tailored engineering materials in structural and engine design requires our understanding of their cyclic deformation behavior and fracture resistance With such knowledge, we can proceed to determine the mechanistics of material response to service environments and establish inspection procedures and intervals commensurate with consumer usage This particular symposium, which is the first of several planned on this topic, was outlined to encompass the cyclic deformation and fracture of advanced metallic, ceramic and polymeric monolithic, and composites, as well as methodologies for nondestructive evaluation of these same material systems Such a joint venture required the cooperation of Subcommittees E9.03 on Fatigue of Advanced Materials and E9.01.07 Research on Nondestructive Evaluation of Advanced Materials Organization of presentation first covers crack initiation and propagation in monolithic and composite ceramics principally at elevated temperatures Several interesting ramifications of phase changes occurring at high temperatures and their influence on smooth and notched fatigue behavior are examined Contributions of matrix cracking, fiber bridging and pull out, and their effects on crack propagation are explained Experimental methodologies and techniques for these "difficult to test" materials as well as short/long fatigue crack propagation threshold behavior is discussed Modeling of crack growth resistance in ceramic and ceramic matrix composites is followed by constitutive modeling of a metal matrix composite for cyclic, isothermal, and thermomechanical behavior Initiation and growth of cracks are discussed for an in situ metal matrix composite (MMC) The influence of mean stresses on the fatigue behavior of single crystal and directionally solidified (DS) alloys as well as crack resistance and toughness of light weight alloys are presented in two subsequent papers Constituent properties of a polymeric laminate with discontinuities is followed by creep effects in bonded polymer composite joints and the interpretation of test information for residual strength and life prediction of composite systems complete the cyclic deformation and fracture portion of this STP The latter presentation by K L Reifsnider of Virginia Polytectnic Institute and State University received "Best Paper" award for this symposium The final topic covered in the symposium was nondestructive evaluation (NDE) of tailored materials About fifteen years ago, N D E began to evolve from testing with improved instrumentation along with a better understanding of materials behavior NDE aims to detect and characterize flaws and microstructural changes in materials, and based on consideration of physical mechanisms controlling materials behavior in a specific application, to predict future performance and reliability of the component In the present publication, ultrasonic surface wave and acoustic emission techniques are applied to monitor cyclic fatigue damage (microcracks) in whisker reinforced metal matrix composites and homogeneous materials The so-called acousto-ultrasonic technique (a sophisticated form of the well-known "cointapping") as well as acoustic microscopy are used to determine damage due to monotonic loading of ceramic composites Finally, one paper describes the application of eddy current in combination with ultrasonic techniques for process control of metal-matrix composites, with the possibility to provide on-line, closed-loop control of the fabrication parameters The symposium chairmen affably acknowledge the authors and reviewers of manuscripts Their participation as well as that of the ASTM staff has made this publication possible It is hoped that the subject matter of this symposium will generate interest and stimulate Copyrightby 1992 by ASTM lntcrnational www.astm.org Copyright ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized EVALUATIONOF ADVANCED MATERIALS participation in the sponsoring ASTM committees We welcome your cooperation and contributions to the Second Symposium on Cyclic Deformation, Fracture, and Nondestructive Evaluation of Advanced Materials planned for November 1992, in Miami, Florida M R Mitchell Rockwell International Science Center, Thousand Oaks, CA 91360; symposium chairman and editor Otto Buck Iowa State University, Ames Laboratories, Ames, IA 50011; symposium chairman and editor Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized C.-K Jack Lin, Thomas A Mayer, ~ and Darrell F Socie t Cyclic Fatigue of Alumina REFERENCE: Lin, C.-K J., Mayer, T A., and Socie, D F., "Cyclic Fatigue of Alumina," Cyclic Deformation, Fracture, and Nondestructive Evaluation of Advanced Materials, ASTM STP 1157, M R Mitchell and O Buck, Eds., American Society for Testing and Materials, Philadelphia, 1992, pp 3-27 ABSTRACT: Mechanical behavior of polycrystalline alumina under cyclic and static tensile loading was studied Smooth cylindrical specimens of 99.8% alumina were cyclically loaded at both room temperature and 1200~ to produce stress-life curves A decrease in strength was observed with an increase in temperature Macroscopic fracture surfaces were found similar for both temperatures A fiat semicircular region that originated from the surface indicated a period of stable crack growth The size of this zone agreed with the estimates from the fracture toughness of the material and maximum load during the fatigue cycle Lifetimes of static fatigue specimens tested at 1200~ appeared to be shorter compared with cyclic fatigue tests The viscous boundary phase may be the primary contributor to the improved fatigue resistance under cyclic loading Specimens with two circumferential notches were loaded cyclically at 1200~ to simulate a component and study notch sensitivity effects A further decrease in strength was observed as a result of the stress concentration However, the alumina became increasingly less sensitive to the stress concentration factor, K,, at the lower stresses, suggesting a fatigue notch factor, KI, that is less than K, KEY WORDS: advanced materials, fatigue (materials), ceramics, cyclic fatigue, static fatigue, notch effects, high temperature Ceramic materials are rapidly being developed for an increasing number of engineering applications, for example, in advanced heat engines They offer combinations of thermal and mechanical properties that are unavailable in other materials These desirable properties such as high specific strength, high-temperature resistance, erosion-corrosion resistance, and high hardness give ceramic materials the potential for use in more efficient engines requiring higher operating temperatures Although many of the engineering ceramic components were subjected to cyclic loading at elevated temperatures for prolonged periods, the study of fatigue in ceramics is still inadequate and inconclusive, in particular at elevated temperatures In the ceramic literature, static fatigue (or stress rupture) has been used to describe the fracture of a ceramic component subjected to a constant load If the fracture occurs under cyclic loading, it is termed cyclic fatigue Polycrystalline alumina is representative of a class of modern structural ceramics Although a considerable amount of research has investigated its physical and mechanical properties [1], very little is known about its cyclic fatigue behavior at room temperature and even less information exists regarding its high-temperature fatigue properties Research that investigated the fatigue properties of alumina did not begin until about 1956 [2-4] Since that time, several researchers have tested alumina cyclically and the results are conflicting with regard to the causes of the observed damage Some of the work has concluded that alumina 1Graduate research assistant, graduate research assistant, and professor, respectively, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 Mr Mayer is currently at Ford Motor Co., Dearborn, MI 48121 Copyright 1992 by ASTM lntcrnational www.astm.org Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized EVALUATIONOF ADVANCED MATERIALS is not susceptible to cyclic fatigue and undergoes only static fatigue where failure or any crack growth is attributed to stress corrosion [5,6] To the contrary, much of the work done has determined that alumina does indeed exhibit a cyclic fatigue effect at room temperature [3,7-15], while still other research has observed a cyclic effect only under certain conditions [16-18] Also, certain studies have simply reported cyclic fatigue data for alumina in the form of stress-life curves [4,19-22] without determining the cause of the failures In an early study, Krohn and Hasselman [17] subjected a polycrystalline alumina'to roomtemperature four-point bend tests including static tests and cyclic tests at various frequencies and amplitudes Within the scatter of the data, no clear cyclic fatigue effects can be seen except, perhaps, at the highest frequency (40 Hz), as most of the measured cyclic data lie within the range of predicted lifetime based on static fatigue data [5,18] Therefore, it was suggested that cyclic fatigue in that alumina at room temperature was essentially a manifestation of stress corrosion [5] However, some other data indicate alumina does exhibit cyclic as well as static fatigue For example, room-temperature uniaxial tension-compression tests using another polycrystalline alumina were done by Guiu [10] He reported an apparent influence of cyclic loading on fatigue lifetime as the specimens under constant loading took "a much longer time" to fail than the cyclically loaded specimens Ewart and Suresh [11] have demonstrated cyclic fatigue crack growth at room temperature in edge-notched specimens of a commercial polycrystalline alumina The application of cyclic compressive loads to the specimen results in local tensile stresses at the notch causing crack growth Ewart and Suresh [12] conducted similar experiments in vacuo (~10 -4 Pa) to verify that this crack growth was not simply the result of stress corrosion Several researchers have also investigated cyclic fatigue of alumina without attempting to determine the cause of the damage For instance, Glenny and Taylor [19] conducted cantilever bend tests on an alumina at room temperature and 1000~ and observed increases in time to failure with decreases in stress at both temperatures Ko [20] obtained similar results using rotary bend tests on another alumina at room temperature Furthermore, Ko [21] went on to show that the fatigue strength of polycrystalline alumina increases with a decrease in average grain size Finally, Liu and Brinkman [22] have subjected specimens with an alumina content of 94% and 99.8% to cyclic uniaxial tensile loads and observed decreases in lifetimes for both materials as the applied stress increases Most of the preceding studies utilized either small bend specimens or larger plate-type specimens with large cracks in them These various bend tests have been popular in the testing of brittle materials because they are relatively simple to conduct and are easily adaptable to testing at high temperatures It must be kept in mind that ceramics are very sensitive to surface or volume flaws In bending test specimens, only a small portion of the material is under the maximum stress and the chance of encountering a critical flaw in this highly stressed region is small As a result, the strength of the material is overestimated with these specimens These types of tests may be appropriate for screening work but are not suitable for studying the mechanical behavior and extrapolating this information to structures Long crack growth behavior is studied with large plate-type specimens where the cracks are several millimetres long While such information regarding this behavior may be useful, failure of a ceramic component will most likely have occurred long before the crack reaches such lengths Thus, tension testing of ceramics is necessary for reasons including: (1) there is smaller scatter of test results due to a larger volume of material subjected to the maximum stress in a uniaxial tension test specimen compared with small bending test specimens and a higher probability of flaws existing in this larger volume; and (2) uniaxial homogeneous stress distributions are necessary for fatigue tests at high temperatures to avoid the stress redistribution effects Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authoriz RESCH AND KARPUR ON SPLIT SPECTRUM PROCESSING 325 2024-T6 Aluminum 0.0070.006(O 0.005- E o 0.004- O o 0.0030.0020.0010 i 20 40 60 80 100 Crack Depth, a 0Jm) 120 FIG Reflection coefficient, $21, as a function o f the crack depth, a, for half-penny shaped cracks at a frequency o f 4.0 MHz The normalized crack depth, Ka = 1, at a = 115 p.m under these conditions transmitting transducer This normalized quantity shall heretofore be referred to as the reflection coefficient, $21, in which the subscripts refer to the transmitting transducer as "1" and the receiving transducer as "2." Additionally, in order to compare the results of scattering experiments from similar-sized cracks performed at varying frequencies, the crack depth, a, is normalized to the wavelength of the ultrasonic waves through the wave number, K, where K = 2xr/h The normalized crack depth, Ka, is the crack depth multiplied by the wave number For surface acoustic waves produced at a frequency of MHz on metals such as aluminum and steel, the resulting wavelength is approximately mm As a point of reference, the crack depth that corresponds to a normalized crack depth of unity at this wavelength is k/27r, or approximately 150 p.m This value of normalized crack depth is important, because it defines the maximum allowable crack size that may be inferred from an ultrasonic scattering experiment at a particular acoustic wavelength (defined by the frequency), as described in the next section In order to interpret the reflected echo from surface cracks in the classical pitch-catch configuration, two techniques have been demonstrated to be useful In the most general case, cracks are assumed to be semielliptical in shape, with maximum depth beneath the surface, a, and length along the surface, 2c The length at the surface is measured independently (usually by optical microscopy) Under these conditions, a single-valued relationship exists between the reflection coefficient of a surface acoustic wave incident on an isolated crack and the normalized crack depth, Ka [2, 9] However, for crack growth in the "small-crack" size regime, it has been observed experimentally that cracks quickly attain the half-penny shaped configuration with a = c For this simplified case, it is not necessary to independently determine crack length at the surface, and a simplified scattering model is all that is necessary to evaluate the single-valued relationship between the normalized crack depth and the reflection coefficient of the S A W [11] (see Fig 1) Certain restrictions of acoustics limit the size of maximum crack depth and minimum specimen thickness that can be utilized for a fixed value of the frequency of the ultrasonic waves For example, the boundary conditions required for propagation of a surface acoustic Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions author 326 EVALUATION OF ADVANCED MATERIALS wave on the surface of a substrate require that the thickness, t, of the substrate be at least 4h of the acoustic wave This limit is necessary so that the "tail" of the stress field of the S A W beneath the surface cannot interact with the free surface of the bottom of the finite thickness specimen If the minimum thickness requirement is not met, the wave will not propagate as a "pure" Rayleigh wave, but rather as a plate mode, resulting in considerable complication of the determination of the stress field that interacts with the crack Additionally, the existing theory for predicting ultrasonic scattering from surface cracks requires that the normalized crack depth exist within the range -< Ka -< for a single-valued relationship to exist between $2~ and Ka This limitation ensures that the entire area of the surface crack resides in the tensile portion of the longitudinal stress field of the S A W (collinear to the direction of propagation), resulting in a simplified calculation of the elastic energy associated with the crack due to the stress field of the acoustic wave using the elastostatic approximation Nonspecular Reflections from Microstructures Real engineering materials are not truly homogeneous, but contain microscopic regions that are locally anisotropic (grains) joined by planar areas that are atomically thin (grain boundaries) The orientations between adjacent grains are dissimilar enough to create a significant impedance mismatch for an ultrasonic wavefront attempting to travel across each boundary This process results in an imperfect transfer of energy in the direction of propagation, and the ultrasonic energy reflected back toward the transmitter (or the receiver) will heretofore be referred to as the microstructural backscatter A significant difference between reflections from the microstructure and cracks is that unlike the interaction of ultrasonic waves from cracks with surface roughness much smaller than a wavelength that is relatively frequency independent (specular), the microstructural backscatter is highly frequency dependent (nonspecular) For extremely small cracks with the amplitude of the reflected echo smaller than the amplitude of the microstructural backscatter, it has been HALF PENNY SHAPE (a=c) RENE i ~///////////X~ TYPE 410 SS ~ / / / / / / j ~ 2.5 C r-1 Mo ~ , / / J J Y J / / ~ 4140 QUENCHED ~ Z / Z / ' Z Z / Z / ~ ~ i i ~ i 2024-T351 AL ~ / ; Z / 2 ~ , ! i ! : 7075-T651 AL ~ / / / / / ~ ~ ) ' ~ ' ~ I" ( ( ," ,' 10 20 30 40 50 60 70 MINIMUM DETECTABLECRACK DEPTH (~m) FIG Minimum detectable crack size for a number of commercially available alloys of aluminum and steel Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized RESCH AND KARPUR ON SPLIT SPECTRUM PROCESSING 327 observed experimentally that detection of crack initiation is relatively difficult, if not impossible, due to the complex interaction of the reflected echo with returning re-radiated signals from microstructural features in the vicinity of the crack Measurements of backscattered amplitudes and the corresponding theoretically inferred crack size have been previously reported for a number of technologically important alloys [2,11] In Fig 2, the largest crack that satisfies the long wavelength approximation of the scattering theory is about 150 p.m at a frequency of MHz For most of the alloys shown, the interference pattern due to microstructural features obscures the first 50 p~m of crack growth, reducing the effective measuring range of the SAW scattering technique to the largest two thirds of its potential range Measurements of crack size between zero and approximately 50 p.m are usually not possible due to the masking effect of grain scattering As a result, there is a need for a signal processing technique that can differentiate between the coherent, frequency dependent interference noise due to grain scatter and specular, frequency independent reflection due to microcracks The split spectrum processing (SSP) is one such method that has been shown [14] to be effective in signal-to-noise ratio (SNR) enhancement applications (although in applications involving macro-anomalies, that is, when the anomalous reflector is orders-of-magnitude larger than both the wavelength and grain size) Split spectrum processing has been used in this research effort for SNR enhancement for microcracks that are orders of magnitude smaller than the reflectors involved in the previous works [14-17] Split Spectrum Processing The first mention of SSP in ultrasonic applications dates back to 1979 Newhouse et al [14], proposed a new technique of introducing frequency diversity in ultrasonic signals and images Newhouse et al showed how frequency diverse signals could be obtained in receivemode by splitting the wideband spectrum of the received signal They called their newly conceived technique the Split Spectrum Processing (SSP) Since the time of inception in the late 1970s, SSP has been internationally well researched [14-22] and successfully implemented [23-25] Although the techniques are well documented [21,22,24,26,27], a brief account is provided here for the sake of unity Implementation of the Technique Split spectrum processing is schematically represented in Fig In practice, many equally spaced Gaussian bandpass filters are used for "splitting" the spectrum The center frequencies of the first and the last filters are determined by the half-power bandwidth of the received signal The bank of filters, when applied in the frequency domain to the complex spectrum of the signal received from the test material, split the spectrum into N narrowbanded frequency spectra Each one of the N narrow-banded spectra yields one time domain signal when the inverse fast Fourier transform (FFT) is taken The resultant N time domain signals (called split time domain signals or the spectral decomposition components) are normalized, which marks the completion of the initial step in SSP and sets the stage for further analysis However, the level of success achieved during further analysis is dependent on a careful selection of the processing parameters for splitting the received spectrum into N narrow bands The processing parameters important for the success of the technique are the total number of filters to be used for spectral splitting, the frequency separation between adjacent filters, their half-power bandwidth (HPBW) and the spectral bandwidth over which Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 328 EVALUATIONOF ADVANCED MATERIALS ], i IPFI i Bank of' N' Bandpass Filters of Center freq fl _ , o ~ : Inverse Fast Fourier Transformation Process ssp I Algorithms Such as Minimization ! and/or , Polarity jThresholdin I Normalization i i ! Processof the ~ ! ! Split Time i t I Domain , ~ ! Signals ~ ! FIG Schematic of split spectrum processing the bank of filters are located A theoretical model for the selection of the processing parameters is available in the literature [20,21,26] There are two important algorithms that could be applied to the frequency diverse signals obtained by splitting the spectrum They are minimization [15] and polarity thresholding [21] Minimization and polarity thresholding algorithms are based on the physics of wavegrain interaction It is a well-known fact that grain noise or clutter at a time delay (T) is an interference pattern produced by the interaction of the ultrasonic wavelets scattered by the randomly packed, unresolvable scatterers present in the material being tested Since it is an interference pattern, the clutter is dependent on the frequency of the transmitted signal The fact that the interference pattern changes when the frequency of interrogation is changed is utilized by the algorithms of SSP The algorithms are described in the following section Minimization Algorithm The split time d o m a i n signals obtained by spectral processing are used to derive the "minimized" signal A t time delay, x, the minimum absolute amplitude of the N (the number of filters) signals is selected The algebraic sign of the selected amplitude is restored and now forms the amplitude, Y(x), of the processed (minimized) signal at time delay, x The process can be mathematically represented as, Y('r) = W,(x) (1) where IWj(~)] = minimum of [[Wi(~)] , I WN(~)I] Y(~) = minimized amplitude at T, and Wi(~) = amplitude, at T, of the ith split time domain signal The algorithm provides superior SNR enhancement because; clutter, being an interference pattern produced by unresolved scatterers, is different at different frequencies On the other Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions autho RESCH AND KARPUR ON SPLIT SPECTRUM PROCESSING 329 hand, the response produced by a flaw is relatively invariant at different frequencies (over the range of frequencies contained in a transducer) As a result, the minimization process yields small amplitudes when only grain noise is present and large, relatively invariant amplitudes when a target is present Polarity Thresholding Algorithm The polarity thresholded amplitude at a time delay, ~, is equal to the input amplitude at that time delay if all the amplitudes of the N split time domain signals are all either positive or negative and is equal to zero if there is a polarity reversal in any one or more of the amplitudes (at that time delay) of the frequency diverse signals When the polarity thresholding algorithm is used in conjunction with minimization, the spectral decomposition components (split time domain signals), obtained by splitting the spectrum of the signal and the minimized signal, are the input of the polarity thresholding algorithm The process is mathematically defined as follows Z ( t ) = Y(t), if all W~(t) < O, for i = = Y(T), if all W~(t) > O, for i = N N (2) where Y(x) is the minimized amplitude at that time delay, ~, and is defined by Eq 1, Z(~) is the output of the polarity thresholding algorithm, and W,('r), i = , , N are the split time domain signals Experimental Procedure Hourglass-shaped specimens of aluminum alloy 2024-T6 were metallographically prepared in the high stress region to minimize the effect of fabrication on surface roughness and residual stress Rayleigh waves were produced on the specimens in the following way A gated r-f signal at a frequency of 4.0 MHz and three wavelengths in duration with a peakto-peak amplitude of 20 V was input to the transmitting transducer element at a repetition rate of 50 Hz The transducer configuration used dual piezoelectric elements of PZT-5 in a single RTV 615 elastomer wedge with an angle of 23 ~ and a water soluble liquid to achieve acoustic coupling between the wedge and the substrate Transducers with this configuration had a typical two-way insertion loss of approximately - 50 dB, and a HPBW of approximately 50% about the center frequency A high-pass/low-pass filter set with cut-off frequencies of and MHz was used to reduce unwanted electrical noise in the system A 60-dB amplifier was used to amplify the signal from the receiving transducer element prior to signal acquisition using a digitizing oscilloscope Before the fatigue cycling begins, the backscattered Rayleigh wave signal from the high stress region was acquired with the digitizing oscilloscope and stored on a hard disk of a computer Signals were acquired by averaging 16 waveforms of 1001 points each at a sampling rate of 20 ns/point This results in a uniform signal length of 20 p.s duration for each scan The vertical resolution under these conditions was bit over a peak-to-peak range of 160 mV The reflected echo from a crack was positioned near the center of each acquired waveform by adjusting the time delay between the beginning of the grated r-f signal to the transmitting transducer element and the beginning of data acquisition from the receiving element A typical value of this delay time was 15 p~s At 2000 cycle intervals of applied fluctuating stress (maximum stress equal to 275 MPa with a stress ratio of 0.1), the digitizing and storing process was repeated This procedure continued until the initiation and growth of at least one crack was obvious in the high stress region Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions autho 330 EVALUATIONOF ADVANCED MATERIALS I m.!i l b c , , f i i i i FIG Unprocessed Rayleigh wave backscatter at (a) 80 000 cycles, (b) 70 000 cycles, and (c) 56 000 cycles Split spectrum processed signal at (d) 80 000 cycles, (e) 70 000 cycles, and (f) 56 000 cycles The presence of the crack is determined not only because the reflection from the crack begins to emerge from the surrounding grain noise, but also because the reflection from the crack completely disappears when the tensile load on the specimen is released thereby closing the crack At the termination of the fatigue cycling process (when the presence of the crack is obvious), all the acquired waveforms are processed for the evidence of earliest possible detection of reflections from surface microcracks The SSP algorithm used for this application is as shown in Eq Fifteen Gaussian-shaped filters having an HPBW of 0.082 MHz were used to split the spectrum of the received signals The filters were separated from one another by 0.049 MHz and were placed over a range of 3.71 to 4.39 MHz Experimental Results Figure 4a shows the Rayleigh wave backscattering signal at the termination point of fatigue cycling for a typical specimen after 80 000 applied cycles Figures 4b and c are a few of the acquired signals during the fatigue-cycling process (at 70 000 and 56 000 cycles, respectively) Figures 4d through f are the results of applying split spectrum processing to the signals shown in Figs 4a through c The processed signals show the presence of the microcrack without ambiguity because of the absence of the interfering grain clutter Figure shows the normalized peak-to-peak amplitudes of the crack reflection for the signals obtained in Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized RESCH AND KARPUR ON SPLIT SPECTRUM PROCESSING 331 ? a=113pm~ < -, 0.6 i i 0.4 i i a=20 pm """1"'"""-'-" "- ~ o.2 ii i z Ol 55 6'5 75 85 Number of FatigueCycles (thousands) FIG Peak-to-peak crack reflection amplitude after split spectrum processing of raw backscattered signals acquired during the crack initiation experiment as a function of the number of fatigue cycles Values are normalized to the maximum processed reflection amplitude at 80 000 cycles steps of 000 fatigue cycles until the crack reflection amplitude is completely lost (56 000 cycles) The peak-to-peak amplitude of the SSP signals is normalized to the maximum crack amplitude obtained at 80 000 cycles to simplify the determination of crack size as described in the next section Discussion Figure shows the crack size inferred from the acoustic theory as a function of the number of fatigue cycles The crack size is determined in the following way Once the existence of a crack is determined from the presence of an ultrasonic echo, the high stress region of the specimen is carefully surveyed using a reflected light microscope at a magnification of 200 diameters The crack length at the surface (in this case 226 p~m) is used to determine the actual crack depth assuming a half-penny shape This assumption has been proven to be valid in a number of earlier investigations [3, 9,11] The relationship between the reflection coefficient, $21, and crack depth, a, is calculated at the particular frequency used to generate the ultrasonic signals The value of the reflection coefficient at the optically verified maximum crack depth is then used to normalize the magnitude of the reflection coefficient at all crack sizes from zero up to the maximum size Finally, the crack depth at each of the normalized SSP amplitudes shown in Fig is obtained This procedure eliminates the need for detailed calibration measurements of the ultrasonic measuring system such as; transducer insertion loss, amplifier gain, attenuation of the Rayleigh waves due to grain scattering, and an experimentally determined near-field correction factor [2,9] The data in Fig indicate that the crack growth rate was not uniform over the interval measured In fact, several intervals are evident over which no measurable change in the SSP crack reflection amplitude was noted This is in good agreement with earlier measurements of small crack growth behavior in aluminum and steel alloys [2,3,9-11] The earliest detection of the crack was at 58 000 cycles when the crack was only 20 p.m Additionally, in contrast to Fig 5, where the crack reflection amplitude at 56 000 is represented as having zero amplitude, no crack size is plotted prior to 58 000 cycles This is intended to infer that Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions auth 332 EVALUATION OF ADVANCED MATERIALS i20 lOO ~" £ o 80 60 o 40 2O ~ 55 f 65 75 85 Number of Fatigue Cycles (thousands) FIG Crack depth, a, inferred from the processed amplitude of the crack as a function of the number of fatigue cycles for crack sizes smaller than 20 ~m, the crack reflection amplitude is simply not resolvable relative to the amplitude of the nonspecular backscatter from the microstructure In fact, SSP signals obtained prior to 56 000 cycles were observed to contain occasional false indications that disappeared with increased number of fatigue cycles, as a consequence of the reflector being of similar size as the surrounding grains Only after 58 000 cycles did the SSP algorithm consistently indicate the presence of a growing microcrack Clearly, another technique such as acetate replication performed in conjunction with the previously described ultrasonic replication technique would be beneficial in measuring the number of cycles required to produce cracks in the 20-p~m size range Conclusions Split spectrum processing has been shown here to have the potential to be an effective tool for the enhancement of SNR when the reflector of interest is many times smaller than the wavelength of the interrogating ultrasound Microcracks as small as 113 Ixm have been detected without processing and 20 pLm with processing There is still a long way to go because it is necessary to develop a theoretical basis for selection of processing parameters when the reflector is in the small reflector regime The long-range objective is to be able to detect the initiation and growth of a microcrack while the specimen is being fatigue cycled rather than processing of the stored signals as is being done now Acknowledgment This work was supported by the U.S Air Force Office of Scientific Research (AFOSR) Contract No F33615-89-C-5612 and F49620-88-C-0053 and performed at the University of Nebraska-Lincoln in the Department of Engineering Mechanics, Lincoln, Nebraska, and at the Materials Laboratory, Wright Research and Development Center, Wright-Patterson Air Force Base, Ohio Special thanks are due to Universal Energy Systems, Inc for contributing to this research effort through the AFOSR Summer Faculty Research Program Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authori RESCH AND KARPUR ON SPLIT SPECTRUM PROCESSING 333 References [1] Leis, B N., Hopper, A T., Ahmad, J., Broek, D., and Kanninen, M F., Engineering Fracture Mechanics, Vol 23, 1986, pp 893-898 [2] Resch, M T., Nelson, D V., Yuce, H H., and Ramusat, G F., Journal of Nondestructive Evaluation, Vol 5, No 1, 1985, pp 1-7 [3] Yuce, H H., Nelson, D V., and Resch, M T in Review of Progress in Quantitative NDE, D O Thompson and E E Chimenti, Eds., Plenum Press, New York, Vol 4A, 1985, pp 103113 [4] Klima, S J., Lesco, D J., and Freche, J C., Experimental Mechanics, 1966, pp 154-161 [5] Buck, O., Ho, C L., Marcus, H L., and Thompson, R B in Stress Analysis and Growth of Cracks, STP 513, American Society for Testing and Materials, Philadelphia, 1972, pp 280-291 [6] Teller, C M., Barton, J R., Matzkanin, G A., Kusenberger, F E., and Beissner, R E., Journal of Engineering Materials and Technology, Vol 102, 1980, pp 50-55 [7] Morris, W L., Buck, O., and Inman, R V., Journal of Applied Physics, Vol 50, No 11, 1979, pp 6737-6741 [8] Thompson, R B., Buck, O., and Thompson, D O., Journal of the Acoustic Society of America, Vol 59, 1976, p 1087 [9] Resch, M T., Nelson, D V., Yuce, H H., and London, B D in Basic Questions in Fatigue: Volume I, ASTM STP 924, J T Fong and R J Fields, Eds., American Society for Testing and Materials, Philadelphia, 1988, pp 323-336 [10] London, B., Nelson, D V., and Shyne, J C., Metallurgical Transactions A, Vol 20A, 1989, pp 1257-1265 [11] Yuce, H H., "The Use of a Surface Acoustic Wave Technique to Study the Growth Behavior of Small Cracks in a High Strength Steel Alloy," Ph.D thesis, Stanford University, Stanford, CA, University Microfilms, Ann Arbor, 1987 [12] Kino, G S., Journal of Applied Physics, Vol 49, No 6, 1978, p 3190 [13] Auld, B A., Wave Motion, Vol 1, No 1, 1979, pp 3-10 [14] Newhouse, V L., Furgason, E S., Bilgutay, N M., and Saniie, J., Proceedings, Ultrasonic International Symposium, Butterworth Scientific, Guildford, U.K., 1979, pp 152-156 [15] Bilgutay, N M., "Split-spectrum Processing for Flaw-to-Grain Echo Enhancement in Ultrasonic Detection," Ph.D thesis, Purdue University, Lafayette, IN, 1981 [16] Brase, J., McKinney, R., Blaedel, K., Oppenheimer, J., Wang, S., and Simmons, J., Materials Evaluation, Vol 42, 1984, pp 1619-1625 [17] Baligand, B., Grozellier, M., and Romy, D., Materials Evaluation, Vol 44, 1986, pp 5771-5781 [18] Bencharit, "Spectral and Spatial Processing Techniques for Ultrasonic Imaging Techniques," Master's thesis, Drexel University, Philadelphia, 1987 [19] Li, Y., "Two Signal Processing Techniques for the Enhancement of the Flaw-to-Grain Echo Ratio," Master's thesis (in Chinese), Academia Sinica, China, 1985 [20] Karpur, P., Shankar, P M., Rose, J L., and Newhouse, V L., Ultrasonics, Vol 25, 1987, pp 204-208 [21] Karpur, P., "Split Spectrum Processing: Process Modeling and the Evaluation of Polarity Thresholding Algorithm for Material Noise Reduction in Ultrasonic NDE," Ph.D thesis, Drexel University, Philadelphia, 1987 [22] Shankar, P M., Karpur, P., Newhouse, V L., and Rose, J L., IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol 36, No 1, 1988, pp 114-122 [23] Silk, M G., Non-destructive Testing, Proceedings, Fourth European Conference, J M Farley and R W Nichols, Eds., Vol 1, 1987, pp 1647-1660 [24] Rose, J L., Karpur, P., and Newhouse, V L., Materials Evaluation, Vol 46, 1988, pp 114-122 [25] Takahashi, M., Komura, I., and Mozumi, T., Proceedings, Generator Retaining-Ring Workshop, L D Nottingham, Ed., Electric Power Research Institute (EPRI) Nondestructive Evaluation Center, Charlotte, NC, EPRI EL-5825, 1988, pp 4.1-4.14 [26] Karpur, P., Shankar, P M., Rose, J L., and Newhouse, V L., Ultrasonics, Vol 26, 1988, pp 204-209 [27] Karpur, P., Journal of Non-Destructive Evaluation, Indian Society for Non-Destructive Testing, Vol 10, No 1, 1990, pp 19-28 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized STP1157-EB/Aug 1992 Author Index A Karpur, P., 323 Komsky, I., 241 Achenbach, J D., 241 Ashbaugh, N E., 28 B Barron, D L., 171 Biner, S B., 121 Bradley, W L., 171 Butkus, L M., 52 L Lee, E U., 293 Lee, S S., 312 Liaw, P K., 251 Lin, C.-K J., Llorca, J., 82 M C Chernenkoff, R A., 190 Clark, W G., Jr., 251 Crane, D L., 171 McCammond, D., 151 McGaw, M A., 136 McGuire, S., 241 Mayer, T A., D R Dauskardt, R H., 69 Duke, J C., Jr., 278 Reifsnider, K L., 205 Resch, M T., 323 Ritchie, R O., 69 E S Elices, M., 82 F Fine, M E., 241 G Granata, D M., 293 Grosskopf, P P., 278 Schra, L., 224 Scott, W R., 293 Sehitoglu, H., 101 Shannon, R E., 251 Sinclair, A N., 151 Sinclair, L A., 151 Socie, D F., Spitzig, W A., 121 Steffen, A A., 69 Stinchcomb, W W., 312 H T Harrigan, W C., Jr., 251 Hartman, G A., 52 Henneke, E G., 312 't Hart, W G J., 224 W J WanhiU, R J H., 224 John, R., 28 Z K Kalluri, S., 136 Karayaka, M., 101 Copyright9 1992by ASTM lntcrnational Zawada, L P., 52 335 www.astm.org Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized STP1157-EB/Aug 1992 Subject Index A Acoustic emission, 293 Acousto-ultrasonics, 278 Adhesives, 190, 193 Advanced materials alumina, 3, 82 aluminum alloy composites, 241 aluminum-lithium alloys, 224, 226 ceramic matrix composites, 28, 52, 82 nondestructive testing, 278 cold rolled Cu-20Nb, 121 composite systems, 205 fabrication, 251 graphite fiber reinforced composites, 171, 180 metal matrix composites, 101 aluminum, 251 fabrication, 264, 271,274 metal to metal adhesive joints, 190 Mg-PSZ ceramics, 69 Nicalon/CAS ceramic composites, 312 nondestructive evaluation, 251,278 polypropylene, 151 superalloys, 136, 139 titanium aluminide XD composite, 293 zirconia, 69 Aerospace applications, 28 Aircraft turbine blade materials, 137 Alloy chemistry, 251,264, 271,274 Alumina crack growth resistance, 82 cyclic fatigue, fatigue crack growth, 28 Aluminum alloy composites chemical characteristics, 271,274 cyclic load fatigue damage, 241 fabrication, 251 instability, 224, 241 SiCp, 264, 271 ASTM STANDARDS C 158-84, 278 D 790-86, 278 E 561-86, 225 E 605-80, E 616-82, 29 Automated crack size measurement, 323 Automated testing technique, 323 B Billets, 251 Bonded joints, 190 Bridging, 83 Brittle matrix, 28 C CDS (See Characteristic damage states) Ceramic materials and matrix composites alumina, composites, 28, 52, 69 desirable properties for engineering applications, Mg-PSZ ceramics, 69 Ceramic matrix composites (CMC), 28, 52 nondestructive testing, 278, 285 Nicalon/CAS, 312 Ceramics alumina, 3, 82 crack behavior, 69 fatigue crack growth, 28 and matrix composites, 82 Characteristic damage states (CDS), 206 CMC (See Ceramic matrix composites) Composite laminates, 205 Composite materials aluminum alloy composites, 241 ceramic matrix composites, 82, 278,285, 312 cold-rolled Cu-20Nb, 121 laminates, 205 metal matrix composites, 101 Compounds, 251 Compression behavior, 171 Constant amplitude testing, 190 Crack branching in alumina, 82 Crack closure, 121 Crack growth alumina, 4, 28 ceramic matrix composites, 28 cold-rolled Cu-20Nb, 121 detectability, 323 Mg-PSZ ceramics, 69 resistance, 82 titanium aluminides, 293 zirconia, 69 337 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 338 EVALUATION OF ADVANCED MATERIALS Crack initiation detection, 323 Crack resistance, 224, 236-238 Creep, 205 Creep rate, 190, 202 Creep rupture, 205 Creep tests, 151, 180 Cyclic creep, 180, 202 Cyclic deformation, 101 Cyclic fatigue alumina, Mg-PSZ ceramics, 69 zirconia, 69 I) Damage development, 206 Damage tolerance, 28, 52, 224 Deformation, 101 Degradation, 69 Density, 251 Design criteria for cyclic fatigue in Mg-PSZ ceramics, 69 Detectability of fatigue microcracks, 323 Directionally solidified superalloys, 136 E Eddy current, 251,274 Elastic wave, 293 Elevated temperature (See also Temperature, ceramic testing), 28, 52 Environmental effects, 190 Exothermic dispersion (XD) composite, 293 Extrusion, 251 F Fabrication, nondestructive evaluation, metal-matrix composite, 251 Failure, 172 Fatigue behavior, 190 Fatigue crack growth, testing at elevated temperatures, 28 Fatigue damage, 241 Fatigue crack initiation, 121 Fatigue (materials) adhesive bonded joints, 190, 202 alumina, 3, 82 aluminum alloy composites, 241 aluminum-lithium alloys, 224 ceramic matrix composites, 28, 52, 82 nondestructiver testing, 278 cold rolled Cu-20Nb, 121 composite systems, 205 graphite fiber reinforced composites, 171, 180 metal-matrix composites, 101 Mg-PSZ ceramics, 69 nicalon/CAS ceramic composites, 312 nondestructive evaluation, 251,278 superalloys, 136, 139 titanium aluminides, 293 zirconia, 69 Fatigue microcracks, initiation and behavior, 323 Fatigue resistance, Fatigue testing, 122 Fiber bridging, 28 Fiber microbuckling, 171 Fiber pullout, 28 Fiber reinforced ceramics, 82 Fiber reinforced polymeric composites, 171 Finite element analysis, 121 Flexure tests, 312 Fractography, 224, 228, 293 Fracture (materials) alumina, aluminum-lithium alloys, 224-227 ceramics, 28, 82 Mg-PSZ ceramics, 69 zirconia, 69 Fracture toughness, 171,224-227,230,233 Fracture under cyclic loading (See Cyclic fatigue) G Graphite composites, 171 Gripping system testing method, 54 It High temperature, 3, 82 Impact, 171 Interface, 171 Intermetallics, 251 L Laboratory test information, interpretation, 205 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized INDEXES Life prediction, 136, 205 Lifetime, fatigue stress/life testing, 69 Linear superposition model, 251 Loading, 102 Long crack, 69 339 O Open hole/notch properties, 171 Oriented polypropylene, 151, 164-166 Orthotropic materials, 151 Overlap joint, 190 M Manufacturing, metal matrix composites, 251 Material processing, 251 Material testing, 173-174, 180 Matrix, 251,293 Matrix cracking, 52 Mechanical degradation, under cyclic loading, 69 Mechanical properties ceramics and composites, 82 polypropylene, 151,164-166 Mechanical testing, 52 Metal-matrix composites cyclic deformation, 101, 107-108 nondestructive evaluation, 251 chemical characteristics, 271,274 SiCp, 264, 271 Methodology, 52 Mg-PSZ ceramics crack behavior, 69 design criteria for cyclic fatigue, 69 heat treatment and tensile properties, 72 Microcracks, rayleigh wave signals for detection, 323 Microcracking, 28, 82, 241 Microstructure, 251,293 Minimum detectable crack size, 323 Mix ratio, 251 Mixtures, 251 Modulus measurement, 151 N Nicalon/CAS ceramic composites, 312 Nondestructive evaluation ceramic matrix composite, 251,278, 312 load, 285 Nicalon/CAS ceramic composites, 312 Rayleigh wave signals, 323 Nondestructive testing, 313, 323 Notch effects, Particle size, 251 Performance simulation, 205 Piezoelectric sensor, 293 Plastic deformation, 293 Plastic wake, 121 Polycrystalline alloys, 136 Polycrystalline alumina, Polycrystalline plasticity, 103 Polymeric composites, 171 Powder metallurgy, 251 Powders, 251 Q Quality control, 312 R Rayleigh wave, 323 Reinforced ceramics, 82-84 Reinforcement, 293 Residual strength, 205 Resistivity, 251,274 Resonance tests, 151 Roll drawn polypropylene, 151, 164-166 Shear, 171 Silicon carbide fabrication, 251 Silicon carbide whiskers, 241 Single crystal superalloys, 136 Small crack, 69 Split spectrum processing, 323 Static creep, 190 Static fatigue, Strength decrease with temperature increase, nicalon/CAS ceramic composites, 312 Stress intensity factor, 293 Stress rupture (See Static fatigue) Stress-strain behavior, 101, 137, 206 Structural adhesives, 190, 193 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 340 EVALUATIONOF ADVANCED MATERIALS Superalloys, 136, 139 Surface acoustic wave, 323 Transformation toughening, 69 Turbine blade materials in aircraft, 137 Turbomachinery, 137 T Temperature (See also Elevated temperature) humidity exposure, bonded joints, 190 testing ceramic materials, 52 Tensile mean stress, 137, 140, 142 Tension testing, ceramics, Tests and testing (See also Mechanical testing) brittle materials, 28 fatigue stress/life, 69 nondestructive evaluation, 279 Thermomechanical behavior, 101 Titanium aluminides, 293 Toughness ceramic matrix composites, 82-84 graphite fiber reinforced composites, 171, 180 U Ultrasonic scattering, 323 Ultrasonic time-of-flight, 151 Ultrasonic wave technique, 241 Ultrasonics, 251 V Viscoelasticity, 151 Z Zirconia, crack behavior, 69 Copyright by ASTM Int'l (all rights reserved); Wed Dec 23 19:00:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized ISBN - - 4 -