1、Designation: C1465 08 (Reapproved 2013)Standard Test Method forDetermination of Slow Crack Growth Parameters ofAdvanced Ceramics by Constant Stress-Rate FlexuralTesting at Elevated Temperatures1This standard is issued under the fixed designation C1465; the number immediately following the designatio
2、n indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determin
3、ation of slow crackgrowth (SCG) parameters of advanced ceramics by usingconstant stress-rate flexural testing in which flexural strength isdetermined as a function of applied stress rate in a givenenvironment at elevated temperatures. The strength degrada-tion exhibited with decreasing applied stres
4、s rate in a specifiedenvironment is the basis of this test method which enables theevaluation of slow crack growth parameters of a material.NOTE 1This test method is frequently referred to as “dynamicfatigue” testing (Refs (3-5)2in which the term “fatigue” is usedinterchangeably with the term “slow
5、crack growth.” To avoid possibleconfusion with the “fatigue” phenomenon of a material which occursexclusively under cyclic loading, as defined in Terminology E1823, thistest method uses the term “constant stress-rate testing” rather than“dynamic fatigue” testing.NOTE 2In glass and ceramics technolog
6、y, static tests of considerableduration are called “static fatigue” tests, a type of test designated asstress-rupture (Terminology E1823).1.2 This test method is intended primarily to be used fornegligible creep of test specimens, with specific limits on creepimposed in this test method.1.3 This tes
7、t method applies primarily to advanced ceramicsthat are macroscopically homogeneous and isotropic. This testmethod may also be applied to certain whisker- or particle-reinforced ceramics that exhibit macroscopically homogeneousbehavior.1.4 This test method is intended for use with various testenviro
8、nments such as air, vacuum, inert, and any other gaseousenvironments.1.5 Values expressed in this standard test are in accordancewith the International System of Units (SI) and IEEE/ASTM SI 10.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. I
9、t is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C1145 Terminology of Advanced CeramicsC1211 Test Method for Flexural Strength o
10、f AdvancedCeramics at Elevated TemperaturesC1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distribution Parameters for AdvancedCeramicsC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC1368 Test Method for Determination of Slow Cra
11、ckGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Strength Testing at Ambient TemperatureD1239 Test Method for Resistance of Plastic Films toExtraction by ChemicalsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE220 Test M
12、ethod for Calibration of Thermocouples ByComparison TechniquesE230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E616 Terminology Relating to
13、 Fracture Testing (Discontin-ued 1996) (Withdrawn 1996)4E1150 Definitions of Terms Relating to Fatigue (Withdrawn1996)41This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 onMechanical Properties and Performance
14、.Current edition approved Aug. 1, 2013. Published September 2013. Originallyapproved in 2000. Last previous edition approved in 2008 as C146508. DOI:10.1520/C1465-08R13.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, vis
15、it the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.Copyright AS
16、TM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1IEEE/ASTM SI 10 American National Standard for Use ofthe International System of Units (SI): The Modern MetricSystemE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 Defini
17、tions:3.1.1 The terms described in Terminologies C1145, E6, andE1823 are applicable to this test method. Specific termsrelevant to this test method are as follows:3.1.2 advanced ceramic, na highly engineered, high-performance, predominately, nonmetallic, inorganic, ceramicmaterial having specific fu
18、nctional attributes. (C1145)3.1.3 constant stress rate, FL2t1,na constant rate ofincrease of maximum flexural stress applied to a specifiedbeam by using either a constant load or constant displacementrate of a testing machine.3.1.4 environment, nthe aggregate of chemical speciesand energy that surro
19、unds a test specimen. (E1150)3.1.5 environmental chamber, na container surroundingthe test specimen and capable of providing controlled localenvironmental condition.3.1.6 flexural strength, fFL2,na measure of theultimate strength of a specified beam specimen in bendingdetermined at a given stress ra
20、te in a particular environment.3.1.7 flexural strength-stress rate diagrama plot of flex-ural strength as a function of stress rate. Flexural strength andstress rate are both plotted on logarithmic scales.3.1.8 flexural strength-stress rate curvea curve fitted tothe values of flexural strength at ea
21、ch of several stress rates,based on the relationship between flexural strength and stressrate:log f= 1/(n + 1) log + log D (see Appendix X1)3.1.8.1 DiscussionIn the ceramics literature, this is oftencalled a “dynamic fatigue” curve.3.1.9 fracture toughness, KICFL3/2,na generic term formeasures of re
22、sistance to extension of a crack. (E616)3.1.10 inert flexural strength FL2,na measure of thestrength of a specified beam specimen in bending as deter-mined in an appropriate inert condition whereby no slow crackgrowth occurs.3.1.10.1 DiscussionAn inert condition at near room tem-perature may be obta
23、ined by using vacuum, low temperatures,very fast test rates, or any inert media. However, at elevatedtemperatures, the definition or concept of an inert condition isunclear since temperature itself acts as a degrading environ-ment. It has been shown that for some ceramics one approachto obtain an in
24、ert condition (thus, inert strength) at elevatedtemperatures is to use very fast (ultra-fast) test rates 3104MPa/s, where the time for slow crack growth would beminimized or eliminated (6) .3.1.11 slow crack growth (SCG),nsubcritical crackgrowth (extension) which may result from, but is not restrict
25、edto, such mechanisms as environmentally assisted stress corro-sion or diffusive crack growth.3.1.12 stress intensity factor, KIFL3/2,nthe magnitudeof the ideal-crack-tip stress field (stress-field singularly) sub-jected to Mode I loading in a homogeneous, linear elastic body.(E616)3.1.13 R-curve, n
26、a plot of crack-extension resistance as afunction of stable crack extension. (E616)3.2 Definitions of Terms Specific to This Standard:3.2.1 slow crack growth parameters, n and D, ntheparameters estimated as constants in the flexural strength (inmegapascals)-stress rate (in megapascals per second) eq
27、uation,which represent a measure of susceptibility to slow crackgrowth of a material (see Appendix X1). For the units of D, see9.3.1.4. Significance and Use4.1 For many structural ceramic components in service,their use is often limited by lifetimes that are controlled by aprocess of slow crack grow
28、th. This test method provides theempirical parameters for appraising the relative slow crackgrowth susceptibility of ceramic materials under specifiedenvironments at elevated temperatures. This test method issimilar to Test Method C1368 with the exception that provi-sions for testing at elevated tem
29、peratures are given.Furthermore, this test method may establish the influences ofprocessing variables and composition on slow crack growth aswell as on strength behavior of newly developed or existingmaterials, thus allowing tailoring and optimizing materialprocessing for further modification. In su
30、mmary, this testmethod may be used for material development, quality control,characterization, and limited design data generation purposes.NOTE 3Data generated by this test method do not necessarilycorrespond to crack velocities that may be encountered in serviceconditions. The use of data generated
31、 by this test method for designpurposes may entail considerable extrapolation and loss of accuracy.4.2 In this test method, the flexural stress computation isbased on simple beam theory, with the assumptions that thematerial is isotropic and homogeneous, the moduli of elasticityin tension and compre
32、ssion are identical, and the material islinearly elastic. The average grain size should be no greaterthan one fiftieth (1/50) of the beam thickness.4.3 In this test method, the test specimen sizes and testfixtures were chosen in accordance with Test Method C1211,which provides a balance between prac
33、tical configurations andresulting errors, as discussed in Refs (7, 8). Only the four-pointtest configuration is used in this test method.4.4 In this test method, the slow crack growth parameters (nand D) are determined based on the mathematical relationshipbetween flexural strength and applied stres
34、s rate, log f= 1/(n+ 1) log + log D, together with the measured experimentaldata. The basic underlying assumption on the derivation of thisrelationship is that slow crack growth is governed by anempirical power-law crack velocity, v=AKI/KICn(seeAppendix X1).NOTE 4There are various other forms of cra
35、ck velocity laws whichare usually more complex or less convenient mathematically, or both, butmay be physically more realistic (9) . The mathematical analysis in thistest method does not cover such alternative crack velocity formulations.C1465 08 (2013)24.5 In this test method, the mathematical rela
36、tionship be-tween flexural strength and stress rate was derived based on theassumption that the slow crack growth parameter is at least n 5 (3, 10). Therefore, if a material exhibits a very highsusceptibility to slow crack growth, that is, n 1000MPa/s) may remain unchanged so that a plateau is obser
37、ved inthe plot of strength versus stress rate, see Fig. 1a (6).Ifthestrength data determined in this plateau region are included inthe analysis, a misleading estimate of the SCG parameters willbe obtained. Therefore, the strength data in the plateau shall beexcluded as data points in estimating the
38、SCG parameters ofthe material. This test method addresses this issue by recom-mending that the highest stress rate be 1000 MPa/s.5.4 A considerable strength degradation may be observed atlower stress rates and higher temperatures for some materials.In these cases, excessive creep damage in the form
39、of creepcavities, micro- or macro-cracks, or both, develop in the tensilesurface (12-15). This results in a nonlinearity in the relation-ship between log (flexural strength) and log (applied stressrate), see Fig. 1b. It has been reported that the strengthdegradation with respect to the expected norm
40、al strength (atPoint N in Fig. 1b) ranged from 15 to 50 % (12-14). If thesedata points are used in the analysis, then an underestimate ofthe SCG parameters will be obtained. Hence, the strength dataexhibiting such a significant strength degradation occurring atlower stress rates shall be excluded as
41、 data points in obtainingthe SCG parameters of the material.5.5 Contrary to the case of significant strength degradation,an appreciable strength increase may occur for some ceramicsat lower stress rates (see Fig. 1c), due to crack healing or cracktip blunting which dominates slow crack growth (12, 1
42、6).Ithasbeen reported that the strength increase with respect to theexpected normal strength (at point N in Fig. 1c) ranged from 15to 60 % (12, 16). Since the phenomenon results in a deviationfrom the linear relationship between log (flexural strength) andlog (applied stress rate), an overestimate o
43、f SCG parametersmay be obtained if such strength data are included in theanalysis.Therefore, any data exhibiting a significant or obviousincrease in strength at lower stress rates shall be excluded asdata points in estimating the SCG parameters of the material.NOTE 6It has been shown that some prelo
44、ading (up to 80 % offracture load) prior to testing may be used to minimize or eliminate thestrength-increase phenomenon by minimizing or eliminating a chance forcrack healing (or blunting) through shortening test time, as verified onsome advanced ceramics such as alumina and silicon nitride (12, 17
45、).Ingeneral, preloading may be effective to reduce overall creep deformationof test specimens due to reduced test time. Refer to 8.10 for moreinformation regarding preloading and its application.C1465 08 (2013)35.6 Surface preparation of test specimens can introducefabrication flaws that may have pr
46、onounced effects on flexuralstrength. Machining damage imposed during specimen prepa-ration can be either a random interfering factor, or an inherentpart of the strength characteristics to be measured. Surfacepreparation can also lead to residual stress. Universal orstandardized test methods of surf
47、ace preparation do not exist. Itshould be understood that the final machining steps may ormay not negate machining damage introduced during the earlycoarse or intermediate machining steps. In some cases, speci-mens need to be tested in the as-processed condition tosimulate a specific service conditi
48、on. Therefore, specimenfabrication history may play an important role in strengthbehavior, which consequently may affect the values of the SCGparameters to be determined.6. Apparatus6.1 Test MachineTest machines used for this test methodshall conform to the requirements of Practices E4. Testspecimen
49、s may be loaded in any suitable test machine providedthat uniform test rates, either using load-control ordisplacement-control mode, can be maintained. The loads usedin determining flexural strength shall be accurate within61.0 % at any load within the selected test rate and load rangeof the test machine as defined in Practices E4. The test machineshall have a minimum capability of applying at least four testrates with at least three orders of magnitude, ranging from 101to 102N/s for load-control mode, and from 107to 10
