NASA Technical Memorandum 87203 Nondestructive Techniques for Characterizing Mechanical Properties of Structural Materials-An Overview Alex Vary and Stanley J. Klima Lewis Research Center Cleveland, Ohio INASA-TM-87203) hCNDESTRUCTIVI TECHNIQUES N86-1S636 'OR CHARACTERIZING MECHANICAL fEGFEEIIES OF JTBUCTUEAL MATEBIALS: AN CVEBVIEK (NASA) .1 P HC A02/MF A01 CSCL 1UD Unclas G3/38 05180 Prepared for the 31st International Gas Turbine Conference sponsored by the American Society of Mechanical Engineers Dusseldorf, West Germany, June 8-12, 1986 r\i/\sA https://ntrs.nasa.gov/search.jsp?R=19860010165 2020-06-04T17:10:47+00:00Z
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NASA Technical Memorandum 87203
Nondestructive Techniques for CharacterizingMechanical Properties of StructuralMaterials-An Overview
Alex Vary and Stanley J. KlimaLewis Research CenterCleveland, Ohio
INASA-TM-87203) h C N D E S T R U C T I V I T E C H N I Q U E S N86-1S636'OR C H A R A C T E R I Z I N G M E C H A N I C A L f E G F E E I I E S OFJ T B U C T U E A L M A T E B I A L S : A N C V E B V I E K ( N A S A ).1 P HC A02/MF A01 CSCL 1UD Unclas
G3/38 05180
Prepared for the31st International Gas Turbine Conferencesponsored by the American Society of Mechanical EngineersDusseldorf, West Germany, June 8-12, 1986
NONDESTRUCTIVE TECHNIQUES FOR CHARACTERIZING MECHANICAL PROPERTIES
OF STRUCTURAL MATERIALS - AN OVERVIEW
Alex Vary and Stanley J. KHmaNational Aeronautics and Space Administration
Lewis Research CenterCleveland, Ohio 44135
SUMMARY
An overview of nondestructive evaluation (NDE) 1s presented to Indicatethe availability and application potentials of techniques for quantitativecharacterization the mechanical properties of structural materials. The pur-
• pose of this brief survey 1s to review NDE techniques that go beyond the usualemphasis on flaw detection and characterization. This survey covers currentand emerging NDE techniques that can verify and monitor entrlnslc properties(e.g., tensile, shear, and yield strengths; fracture toughness, hardness; duc-tility; elastic moduli) and underlying mlcrostructural and morphological fac-tors. Most of the techniques described are, at present, neither widely appliednor widely accepted 1n commerce and Industry because they are still emergingfrom the laboratory. The limitations of the techniques may be overcome byadvances 1n applications research and Instrumentation technology and perhapsby accommodations for their use 1n the design of structural parts.
INTRODUCTION00in
£j The usual emphasis 1n NDE 1s on detection and characterization of a varl-L^J ety of discrete hidden flaws that can Impair structural Integrity and reduce
life (I.e., cracks 1n metals, delamlnatlons 1n composites, Inclusions 1n ceram-ics, etc..). In failure prevention schemes, the specification of flaw criticallyand prediction of safe life depend on the assumption of a realistic set ofextrinsic properties. Fracture analysis models presuppose flaw development 1nmaterials with "known" moduli, ultimate strengths, fracture toughness, andfatigue and creep properties.
There are emerging NDE techniques that may be used to verify the mechani-cal properties mentioned above and also to assess their degradation 1n service.Ultimately, these techniques may be adapted for application to a variety ofmaterials and actual structural parts and help circumvent sole reliance onhandbook or representative values based on prior screening or sampling tests.A holistic approach to reliability assurance would combine nondestructivecharacterization of flaws with characterization of material environments 1nwhich the flaws reside (Ruud and Green, 1983; Buck and Wolf, 1981; Vary 1984).This approach would engender more realistic assessments of structural Integrityand service degradation by providing a better Information base for fractureanalysis and life prediction. The development and adaptation of the types oftechniques discussed 1s needed to assure structural reliability and safe ser-vice life of components made of advanced materials 1n systems that demandefficient performance under extreme operating conditions.
The need for nondestructive materials characterization 1s Indicated wherelocal properties are critical or where the presence, Identity, and distributionof potentially critical flaws can only be assessed statistically. In the lat-ter case, flaws can be so microscopic, numerous, and dispersed that 1t 1sImpractical to resolve them Individually. Large populations of nonresolvableflaws may Interact with each other (e.g., surface versus volume flaws) or withrtlorphologlcal anomalies. These Interactions would be manifested as degradedbulk properties, (e.g. deficiencies 1n strength, toughness). While a structuremay be free of discrete critical flaws, 1t may still be susceptible to failurebecause of Inadequate or degraded Intrinsic mechanical properties. This canarise from faulty material processing and/or degradation under aggressive ser-vice environments. It 1s for these reasons, amplified by the examples given1n table I, that 1t 1s Important to have nondestructive methods for quantita-tively characterizing mechanical properties.
Ultimately, mechanical properties are controlled by composition, micro-structure, and morphology (R1ce, 1977). These factors also Influence variousNDE probe media, e.g., ultrasonic waves, electric currents, magnetic fields,x-rays, etc. (McMaster, 1959; Green, 1973; Vary, 1973; Anon., 1973). Modula-tions of probe media by materials give quantitative measurements that correlateto differing degrees with strength, hardness, toughness, and other properties.
Examples of current laboratory techniques with potentials for field useare reviewed 1n this paper. Host of the techniques described are, at present,neither widely applied nor widely accepted 1n commerce and Industry. Adapta-tion to practical use on actual structural parts 1s still emerging from thelaboratory 1n most Instances. Wide application of the types of NDE techniquesdescribed herein await advances 1n applications research and Instrumentationtechnology and 1n many cases will require design accommodations for theireffective use.
TECHNIQUES
General
Nondestructive materials characterization techniques may be divided Intotwo major categories. The first category pertains to NDE measurements thatcorrelate with moduli, strength, hardness, toughness, and other extrinsic pro-perties. The second category pertains to NDE measurements that correlate withmorphological and mlcrostructural factors that govern the previously mentionedproperties (e.g., grain size distribution, elastic anlsoptropy, second andtertiary phases, etc.).
An Inventory of NDE techniques that address the previously mentionedattributes of structural solids appears 1n table II. As Indicated 1n table II,directly measured quantities Include ultrasonic velocity and attenuation,electric current, magnetic flux, x-ray attenuation, and similar physical vari-ables. The essential problem 1s that of evolving practical signal Insertion/acquisition, processing, and analysis methods for relating NDE measurements toparticular extrinsic properties exhibited by a material. Table II gives exam-ples of extrinsic properties that can be directly measured by various NDE tech-niques. The following papagraphs elaborate on selected operational techniques
and methodologies 1n the principal areas of dynamic excitation, ultrasonic/acoustic, electromagnetic, penetrating and particle radiation, andphoto-optical NOE.
Dynamic Excitation
Dynamic tests are among the oldest forms of NDE. The genera Includesstriking or coin tapping and listening to the sound produced (I.e., to determ-ine 1f an object "rings true"). In modern versions of this acoustic "signatureanalysis" approach the vlbratlonal frequencies are often beyond the audiblerange and require electronic Instruments for signal acquisition and processing.These tests are nondestructive because amplitudes and mechanical strains arequite small and leave the material unaltered. They may be applied to simplelaboratory specimens and also to structural parts having complex shapes. Auto-mated acoustic signature analysis merits consideration for Inferring the Integ-rity and condition of a range of finished articles (McMaster, 1959; Vary, 1973).
Dynamic-sonic vibration techniques are suitable for studyingmlcrostructure-dependent properties (Nowlch and Berry, 1973). Damping andresonant frequency measurements can be used to study phase transformations,plastic deformation, hardening, cold working, alloy composition effects, etc.(Uygur, 1980). Elastic moduli and dynamic constants of structural materialscan be assessed for predicting dynamic response. Dynamic-sonic methods havebeen used to evaluate porosity and density 1n ceramics, fiber/resin ratio 1ncomposites, bond strength 1n laminates, and grain texture 1n metals (DICarloand Malsel, 1970; Papadakls and Kovacs, 1980).
Ultrasonic/Acoustic
Well established theory and experimental demonstrations underly ultra-sonic velocity measurements of elastic constants such as longitudinal andshear moduli. Fundamental relations among elastic moduli and ultrasonic wavevelocities are given 1n table III (Schrelber, et al., 1973; Green, 1973).
Measurement of elastic moduli are fundamental to understanding and pre-dicting material behavior (e.g., bending moments, thermal expansion, strainunder load, etc.). Since they are related to Interatomic forces, elasticmoduli Indicate maximum attainable strength. In the case of brittle materials(e.g., ceramics) ultrasonic velocity measurements are preferred for measuringelastic moduli because of the minute strains usually exhibited by these mater-ials under tension or compression. Magnitudes of elastic constants correlatedirectly with strengths for some classes of brittle materials. Combined ultra-sonic longitudinal and transverse velocity measurements can form the basis forverifying the relative strengths of materials such as concrete, cast Iron, andceramics (Kraukramer, 1977).
Ultrasonic velocity measurements can form the basis for determining activeand residual stress fields 1n a range of objects from bolts to railway tracks(Heyman, 1977; Bray, 1981). The underlying phenomenon for this 1s the vari-ation of ultrasonic velocity with lattice strains (Noronha and Chapman, 1973).Ultrasonic birefringence, critical angle reflectivity, and combined ultrasonic/magnetic field measurements comprise auxiliary methods for residual stressevaluations (Namkung and Heyman, 1984).
Correlations between ultrasonic velocity and various other properties ofsolids also exist. For example, age hardening of aluminum and effects ofcarbon content 1n steels have been characterized by velocity measurements(Frlant, et al., 1981; Heyman, et al., 1983). Empirical relations have beenfound that connect density (porosity) and velocity 1n monolithic ceramics(KHma, 1984; KHma and BaakHnl, 1986). Combined velocity and attenuationmeasurements In metals correlate with mlcrostructural factors like mean grainsize, grain size distribution, and grain morphology (Vary, 1980; Generazlo,1986; Serablan, 1986).
Measurements of energy loss of ultrasonic waves Interacting with materialmlrcrostructures underly empirical correlations with mechanical properties. Afundamental equation, given 1n terms of energy Intensity I at distance dfrom a source I0 of ultrasound, 1s I = I0 exp(-a d), where a 1s thefrequency-dependent attenuation coefficient. The attenuation coefficientIncludes effects of absorption and scattering of ultrasonic waves (e.g., bygrains, second phase particles, etc. 1n polycrystalUne solids). Attenuationmeasurements are most useful when made over a broad range of frequencies. InpolycrystalUne solids the frequency dependence of the attenuation coefficientcorrelates with a variety of extrinsic properties (e.g., strength, toughness)via the attenuating effects of mlcrostructural factors on ultrasonic wavepropagation (Vary, 1980; 1984).
Theoretical dependences of attenuation coefficient on frequency are Indi-cated 1n table IV for polycrystalUne aggregates (Serablan, 1980; Vary andKautz, 1986). Functional relations between the attenuation coefficient andultrasonic frequency for the various loss mechanisms Indicated 1n table IVhave been confirmed for a range of engineering solids (Mason and McSk1mm1n,1947, 1948; Truell, et al., 1969). These relations form bases for ultrasonicevaluation, verification, and monitoring of mechanical properties governed bythe mlcrostructural factors Involved. An example concerning the use of ultra-sonic attenuation for determining fracture toughness 1s highlighted at a laterpoint 1n this paper.
Assessments of mean grain size, morphological anomalies, anlsotroples,laminations, Inclusions, and debris 1n coarse grained, multiphase, or compositematerials can apparently be accomplished by backscatter analysis. The proce-dures Involve time domain analysis and/or frequency domain spectral analysisof backscatter echoes.
Time domain backscatter measurements have been shown to correlate quitewell with metallographlc measurements of grain size 1n steels (Goebbels, 1980).Frequency domain analysis of backscatter spectra have been used to characterizemlcrostructural variations 1n a nickel base powder metal alloy (Tlttmann,et al., 1986). Broadband spectroscopy has also been Investigated for coarsegrained and layered media (Bllgutay and San11e, 1984; Halnes, et al., 1978).Broadband spectral analysis of either backor forward-scattered signals canresult 1n spectral signatures that are peculiar to the material macroand/ormicro-structure examined. Material variations might be monitored by comparisonwith standard signatures.
Thus far, only signal analysis, as opposed to Image generation and analy-sis, methods have been discussed. Obviously, methods that produce Images ofmaterial mlcrostructures and morphological anomalies can convey essentialInformation needed to characterize a material. Photomicrographs serve this
need but are obtained only by essentially destructive methodology. Nondestruc-tive ultrasonic (and radlographlc methods, discussed later) offer a means forImaging the Internal constitution of materials. Moreover, Images produced byultrasonic waves will render additional Information that differs from thatproduced by photo-optics (e.g., metallography). Ultrasonic Imaging methodsrange from mechanical macroscans (Kraukramer, 1977; Jacobs, 1970) to acousticmicroscopy (Kessler, 1977; Rosencwalg, 1979; Lemons and Quate, 1973).
A common operational macroscannlng technique, the "Immersion scan," pro-duces a mapping of ultrasonic signal amplitude onvelodty against spatialcoordinates of the part being examined. On a smaller scale, acoustic micro-scopy produces Images of only minute portions of test specimens. In eithercase, an Image 1s rendered that shows spatial variations of elastic properties,grain structure and texture, density and porosity, and similar factors thataffect the velocity, attenuation, diffraction, refraction, etc. of ultrasound.The spatial resolution of mlcrostructural features depends on the ultrasonicfrequencies that are used.
Acoustic emission 1s a passive technique that relies on spontaneous, tran-sient, and usually Inaudible ultrasonic signals generated by rapid release ofenergy (e.g., during mechanical deformation or thermal stressing). Acousticemissions can arise when a material undergoes metallurgical transformations,dislocation movements (plastic yielding), mlcrocracklng, crack growth, etc.(Matthews, 1983).
The spontaneous stress waves that constitute acoustic emission can beanalyzed to obtain Information concerning the nature, locations, abundances,distributions, etc. of the various sources activated, as during the loading orproof testing of structures (Spanner, 1974; L1pta1, et al., 1971). Operationalmethods Include event counts, rlngdown counts, energy or amplitude distributionanalysis, and frequency spectrum analysis. The acoustic emission techniqueoffers a means for monitoring structural Integrity and dynamic response andfor Inferring the current Internal condition or state of degradation of struc-tural components.
Electromagnetic
Electromagnetic methods for material characterization are generallyrestricted to assessment of nearsurface features. Applicability 1s furtherrestricted to electrically conductive or ferromagnetic solids. Eddy-currentprobes Induce small subsurface electric currents with Intensities and depthsof penetration that depend primarily on frequency and material conductivityand permeability. Factors such as alloy composition, Impurities, and grainstructure will affect the probe reactance (L1bby, 1971; Lord, 1980). Eddy-current methods have proven viable for hardness and porosity measurements 1nmaterials ranging from grey cast Iron to carbon fiber reinforced plastics(G1za and Papadakls, 1979).
Magnetic field methods generally depend on flux leakage or eruptions ofexternally Induced fields. Passive probes are used to sense variations 1nnatural magnetic domains to measure ferroalloylng content, distribution, andanlsotroples. Degrees of aging and case hardening have been measured bymagnetic field probes (McMaster, 1959). Potentials exist for magnetic flux
leakage methods for measurements of mlcrostructural gradients, plastic damage,and stress fields (Oobmann and Holler, 1980; Davis, 1974).
Penetrating and Particle Radiation
Radiography and radlometry cover a wide range of operational techniquesthat are suitable to differing degrees for materials characterization. Pene-trating radiation Involving x-rays and gamma rays and penetrating particleradiation. Involving neutrons can be used to cast Images of grain structure,density variations, porosity, and contamination (Bryant and Mclntlre, 1985;Berger, 1965).
Images with high spatial resolution can be achieved with projection micro-radiography (BaakHnl and Roth, 1985) while high sensitivity can be achievedwith radlometry. The latter 1s a nonlmaglng, metrologlcal method useful forquantifying degrees of porosity and density gradients (Halmshaw, 1968; 1982).
Radiation scattering analysis methods may provide means for characterizinggrain structure and other morphological factors associated with thermal andmechanical processing effects (e.g., plastic deformation, precipitates, Inclu-sions, porosity, creep, etc.) 1n engineering solids (Walther and Plzzl, 1980;Berk, 1966). Small angle neutron scattering 1s a method similar to x-rayscattering for characterizing mlcrostructure. The method 1s a potentialanalytical tool for assessing thermal treatments; mlcrovold populations; anddegradation due to fatigue, creep, deformation, and Irradiation (01en, 1983).
X-ray diffraction measurement 1s used routinely for determining residualstress although the method 1s Ineffective at depths greater than about 20 A(Bryant and Mclntlre, 1983). Nevertheless, x-ray diffraction Instrumentationhas been deployed 1n Industrial environments for assessing residual stressesand characterizing damage 1n polycrystalUne materials subjected to mechanicalprocessing (I.e., cold working, etc.) (Ruud, 1983).
Photo-Optical
Laser holography 1s predominant among techniques for materials charac-terlzatlan by visible light optics. Holographic methods can be used to Imagemlcrostraln deformations. When used 1n conjunction with mild thermal ormechanical stressing holography can reveal material anomalies and morphologicalvariations through their effect on local strain patterns (Collier, et al.,1971; Ennos, 1970).
Moire and holographic Interferometry are currently laboratory techniquesthat are largely unexplored regarding their potentials for field applicationsfor materials characterization and degradation assessment (Slgler and Haworth,1981; Post, 1980). These techniques have been shown applicable to the studyof early stages 1n fatigue damage and to assess variations 1n elastic proper-ties of metals and composites (Govada, et al., 1985; Duke, et al., 1983).
EXAMPLE
Ultrasonic waves are probably the most Important probe media for assessingmechanical properties. A strong case can be stated for expecting ultrasonicvelocity and attenuation measurements to correlate with mechanical propertiesthat are governed by material mlcrostructures (Vary, 1980, 1984). Indeed, theultrasonic waves Interact with and are modified by mlcrostructural featuresthat govern extrinsic properties such as yield strength, hardness, ductility,and toughness (R1ce, 1977; Vary, 1986).
Fracture toughness 1s a material property that 1s determined by factorslike mean grain size, grain Interface characteristics, grain aspect ratios,second phase constituents, precipitates, etc. The fracture toughness of amaterial 1s a measure of Its resistance to catastrophic fracture when minorcracks are activated by stress.
Correlations between ultrasonic measurements, fracture toughness, and alsoyield strength have been demonstrated. Moreover, a theoretical basis for pre-dicting the empirical correlations has been developed (Vary, 1978, 1979).Results are shown 1n figures 1 and 2 for two maraglng steels and a titaniumalloy. In these metals the correlations appeared to be Influenced by grainsize and morphology. The "characteristic length" factor 1n figure 1 (comprisedof the ratio of plane strain fracture toughness and yield strength) 1s a mea-sure of toughness. This characteristic length (mlcrocrack blunting zone)apparently depends on the ultrasonic attenuation properties of a material.At least 1n the case of the metals studied thus far, 1t appears that toughnessIncreases when more ultrasonic stress wave energy can be retained and absorbed1n localized plastic deformation zones (via dislocation movements) (Vary andHull, 1982).
LIMITATIONS
The purpose of the previous example 1s to Illustrate the viability ofultrasonics for nondestructive characterization of an Important mechanicalproperty. The example presages potential advantages to be gained by Its use1n materials research and testing and adaptations to actual parts. However,like many of the previously discussed NDE methods, ultrasonics for laboratorycharacterization of mechanical properties and subsequent technology for fieldapplications 1s essentially 1s undeveloped.
Even 1n a laboratory environment materials characterization NDE techniques(as 1n the case of the previous example) can usually be accomplished only understrict constraints. Satisfactory signal Insertion and acquisition, accuratemeasurements, and valid analysis and Interpretations require sample preparationand specific constraints on size, shape, surface finish, etc. The complexityof preparation and Incurred expense may be less than for destructive test sam-ples for similar purposes. By adapting probes and Instrumentation to them,objects for NDE may be simpler, smaller, or may just consist of selectedregions of actual parts.
Table V lists general requirements for good signal processing and accuratemeasurements by most of the NDE techniques described herein. Design accommo-dations or adaptations for NDE probes and probe media may be necessary tooptimize technique sensitivity and precision 1n applications to actual parts.
Sophisticated NDE techniques may be useless 1f reasonable provisions for theiruse are not Included 1n the design of critical structural components.
CONCLUSION
The techniques reviewed herein suggest possibilities for the nondestruc-tive evaluation of a wide range of mechanical properties and underlying micro-structural factors. Most are advanced techniques that require development forcomplementing conventional NDE for flaw detection and characterization. Apartfrom this, the techniques reviewed present possibilities for verification ofmechanical properties and assessment of service degradation of critical struc-tures. Development and adaptation of the techniques discussed 1s needed toassure structural reliability and safe service life of components made ofadvanced materials 1n systems that demand efficient performance under extremeoperating conditions.
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Serablan, S., "Ultrasonic Material Property Determinations," AnalyticalUltrasonics 1n Materials Research and Testing. NASA CP-2383, 1986, pp. 219-232.
Slgler, D.R. and Haworth, W.L., "Early Detection of Metal Fatigue by OpticalCorrelation," Nondestructive Evaluation: Mlcrostructural Characterization andReliability Strategies. The Metallurgical Society of AIME, Warrendale, PA,1981, pp. 367-386.
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Stlnchcomb, W.W., Mechanics of Nondestructive Testing, Plenum Press, New York,1980.
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12
Vary, A., Analytical Ultrasonics 1n Materials Research and Testing. NASACP-2383, 1986.
Vary, A. and Kautz, H.E., "Transfer Function Concept for UltrasonicCharacterization of Material Hlcrostructures," Analytical Ultrasonics 1nMaterials Research and Testing. NASA CP-2383, 1986, pp. 257-298.
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Walther, H. and P1zz1, P., "Small Angle Neutron Scattering for NondestructiveTesting," Research Techniques 1n Nondestructive Testing, Vol. IV, AcademicPress, London, 1980, pp. 341-391.
Werthelm, G.K., Mossbauer Effect - Principles and Applications. AcademicPress, New York, 1964.
t is longitudinal velocity, vt istransverse velocity, p is density,other quantities are defined interms of longitudinal modulus Land snear (transverse) modulus G.
TABLE IV. - THEORETICAL ULTRASONIC ATTENUATION
COEFFICIENTS FOR LINEAR ELASTIC
POLYCRYSTALLINE SOLIDS
Wavelengthrange
Independent
x > D
x < D
x « D
Attenuationmechanism
True absorption
Rayleigh scattering
Phase scattering
Diffusion scattering
Attenuation* coefficient
°a = Caf
or = CrD3f4
ap = CpDf2
ad = Cd/D
D is "nominal" grain size, x is wavelength, fis frequency, a is attenuation coefficient,and tne C's are experimental constants.
TABLE V. - TYPICAL CONSTRAINTS FOR ASSURING
SENSITIVE AND PRECISE QUANTITATIVE
NONDESTRUCTIVE MATERIAL
CHARACTERIZATION
Recommended constraints Ambiguities eliminated
Clean, smooth surfacesFlat, parallel surfaces, orGeometrically simple shapesAccessibility of key areasMinimum thickness, lengthPrecise pnysical dimensionsLarge part-to-probe areaAosence of overt flaws and
gross nonuniformities
Poor probe couplingSignal path uncertainties
Signal in/output relationsExcess attenuation lossesVariable miscalculationsEdge and sidewall effectsSpurious, false signals
O 200-GRADE MARAGING STEELD 250-GRADE MARAGING STEELO TITANIUM (8Mo-8V-2Fe-3AI)
6|
(O
f-^»
a£oou_
O
<:
.1
oCO
.011 10 20
"CHARACTERISTIC LENGTH",(Kj c /0y) , mm
Figure 1. - Correlation of ultrasonicattenuation factor and fracturetoughness "characteristic length"factor for three polycrystallinemetals. Kjc is plane strain fracturetoughness, <iy is yield strength,v^ is longitudinal velocity, m is thefrequency exponent in a=cfm, wherea is attenuation coefficient, f isultrasonic frequency, and p is dct/dfevaluated at a critical wave-lengthrelated to the mean gram boundaryspacing 6 (from Vary 1979, p. 573).
(Ua.
oLUDiI—ooO
Ti-8Mo-8V-2Fe-3AI200 GRADE MARAGING STEEL
1600 —
1400 —
1200 —
1000-40 -20 0 20 40
ULTRASONIC FACTOR, axlO3, MS/cm
Figure 2. - Correlation of yield strengthOy with the ultrasonic factor a for twopolycrystalline metals. Factor a equals+10~3Kjc + plf where KIc is planestrain fracture toughness and Pj isda/df evaluated at a=l (from Vary 1979,p. 574).
1 Report No
NASA TM-872032 Government Accession No 3 Recipient's Catalog No
4 Title and Subtitle
Nondestructive Techniques for CharacterizingMechanical Properties of StructuralMaterials - An Overview
5 Report Date
December 1985
6 Performing Organization Code
506-53-1A
7 Author(s)
Alex Vary and Stanley J. KHma
8 Performing Organization Report No
E-2858
10 Work Unit No
9 Performing Organization Name and Address
National Aeronautics and Space AdministrationLewis Research CenterCleveland, Ohio 44135
11 Contract or Grant No
12 Sponsoring Agency Name and Address
National Aeronautics and Space AdministrationWashington, D.C. 20546
13 Type of Report and Period Covered
Technical Memorandum
14 Sponsoring Agency Code
15 Supplementary Notes
Prepared for the 31st International Gas Turbine Conference, sponsored by theAmerican Society of Mechanical Engineers, Dusseldorf, West Germany, June 8-12,1986.
16 Abstract
An overview of nondestructive evaluation (NDE) 1s presented to Indicate theavailability and application potentials of techniques for quantitative charac-terization the mechanical properties of structural materials. The purpose ofthis brief survey 1s to review NDE techniques that go beyond the usual emphasison flaw detection and characterization. This survey covers current and emergingNDE techniques that can verify and monitor entrlnslc properties (e.g., tensile,shear, and yield strengths; fracture toughness, hardness; ductility; elasticmoduli) and underlying mlcrostructural and morphological factors. Most of thetechniques described are, at present, neither widely applied nor widely accepted1n commerce and Industry because they are still emerging from the laboratory.The limitations of the techniques may be overcome by advances 1n applicationsresearch and Instrumentation technology and perhaps by accommodations for theiruse 1n the design of structural parts.
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