1、Designation: C 1576 05Standard Test Method forDetermination of Slow Crack Growth Parameters ofAdvanced Ceramics by Constant Stress Flexural Testing(Stress Rupture) at Ambient Temperature1This standard is issued under the fixed designation C 1576; the number immediately following the designation indi
2、cates 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination
3、 of slow crackgrowth (SCG) parameters of advanced ceramics by usingconstant stress flexural testing in which time to failure offlexure test specimens is determined in four-point flexure as afunction of constant applied stress in a given environment atambient temperature. In addition, test specimen f
4、abricationmethods, test stress levels, data collection and analysis, andreporting procedures are addressed. The decrease in time tofailure with increasing applied stress in a specified environ-ment is the basis of this test method that enables the evaluationof slow crack growth parameters of a mater
5、ial. The preferredanalysis in the present method is based on a power lawrelationship between crack velocity and applied stress inten-sity; alternative analysis approaches are also discussed forsituations where the power law relationship is not applicable.NOTE 1The method in this test method is frequ
6、ently referred to asstatic fatigue or stress-rupture testing (1-3)2in which the term fatigue isused interchangeably with the term slow crack growth. To avoid possibleconfusion with the fatigue phenomenon of a material that occurs exclu-sively under cyclic loading, as defined in Terminology E 1823, t
7、his testmethod uses the term constant stress testing rather than static fatiguetesting.1.2 This test method applies primarily to monolithic ad-vanced ceramics that are macroscopically homogeneous andisotropic. This test method may also be applied to certainwhisker- or particle-reinforced ceramics as
8、 well as certaindiscontinuous fiber-reinforced composite ceramics that exhibitmacroscopically homogeneous behavior. Generally, continuousfiber ceramic composites do not exhibit macroscopically iso-tropic, homogeneous, continuous behavior, and the applicationof this test method to these materials is
9、not recommended.1.3 This test method is intended for use with various testenvironments such as air, other gaseous environments andliquids.1.4 The values stated in SI units are to be regarded as thestandard and in accordance with IEEE/ASTM SI 10 Standard.1.5 This test method may involve hazardous mat
10、erials,operations, and equipment. This standard does not purport toaddress all of the safety concerns associated with its use. It isthe responsibility of the user of this standard to establishappropriate safety and health practices and determine theapplicability of regulatory limitations prior to us
11、e.2. Referenced Documents2.1 ASTM Standards:3C 1145 Terminology of Advanced CeramicsC 1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC 1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC 1368 Test Method for Determination of
12、Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Flexural Testing at Ambient TemperatureC 1465 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Flexural Testing at Elevated TemperatureE4 Practices for Force Verification o
13、f Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE112 Test Methods for Determining Average Grain SizeE 337 Test Method for Measured Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E 399 Test Method for Plane-Strain Fracture Toughness ofMeta
14、llic MaterialsE 1823 Terminology Relating to Fatigue and Fracture Test-ingSI10-02 IEEE/ASTM SI 10 American National Standardfor Use of the International System of Units (SI): TheModern Metric System1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direc
15、t responsibility of Subcommittee C28.01 onMechanical Properties and Performance.Current edition approved June 1, 2005. Published June 20052The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.o
16、rg, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. Terminolo
17、gy3.1 Definitions: The terms described in TerminologiesC 1145, E6, and E 1823 are applicable to this test method.Specific terms relevant to this test method are as follows:3.1.1 advanced ceramic, nhighly engineered, high perfor-mance, predominately non-metallic, inorganic, ceramic mate-rial having s
18、pecific functional attributes. C 11453.1.2 constant applied stress, sFL-2, nconstant maxi-mum flexural stress applied to a specified beam test specimenby using a constant static force with a test machine or a testfixture.3.1.3 constant applied stress-time to failure diagramplotof constant applied st
19、ress against time to failure. Constantapplied stress and time to failure are both plotted on logarith-mic scales.3.1.4 constant applied stress-time to failure curvecurvefitted to the values of time to failure at each of several appliedstresses.NOTE 2In the ceramics literature, this is often called a
20、 static fatiguecurve.3.1.5 test environment, naggregate of chemical speciesand energy that surrounds a test specimen. E 18233.1.6 test environmental chamber, ncontainer surround-ing the test specimen that is capable of providing controlledlocal environmental condition. C 1368, C 14653.1.7 flexural s
21、trength, sfFL-2, nmeasure of the ulti-mate strength of a specified beam test specimen in flexuredetermined at a given stress rate in a particular environment.3.1.8 fracture toughness (critical stress intensity factor)KICFL-3/2, n generic term for measures of resistance toextension of a crack. E 1823
22、, E 3993.1.9 inert flexural strength FL-2, nflexural strength of aspecified beam as determined in an inert condition whereby noslow crack growth occurs.NOTE 3An inert condition may be obtained by using vacuum, lowtemperature, very fast test rate, or an inert environment such as silicone oilor high p
23、urity dry N2.3.1.10 R-curve, nplot of crack-extension resistance as afunction of stable crack extension. C 11453.1.11 run-out, ntest specimen that does not fail before aprescribed test time.3.1.12 slow crack growth (SCG), nsubcritical crackgrowth (extension) which may result from, but is not restric
24、tedto, such mechanisms as environmentally-assisted stress corro-sion or diffusive crack growth. C 1368, C 14653.1.13 slow crack growth (SCG) parametersparametersestimated as constants in the log (time to failure) versus log(constant applied stress), which represent a measure of sus-ceptibility to sl
25、ow crack growth of a material (see AppendixX1).3.1.14 stress intensity factor, KIFL-3/2, nmagnitude ofthe ideal-crack-tip stress field stress field singularity) subjectedto mode I loading in a homogeneous, linear elastic body.E 18233.1.15 time to failure, tft, ntotal elapsed time from testinitiation
26、 to test specimen failure.4. Significance and Use4.1 The service life of many structural ceramic componentsis often limited by the subcritical growth of cracks. This testmethod provides an approach for appraising the relative slowcrack growth susceptibility of ceramic materials under speci-fied envi
27、ronments at ambient temperature. Furthermore, thistest method may establish the influences of processing vari-ables and composition on slow crack growth as well as onstrength behavior of newly developed or existing materials,thus allowing tailoring and optimizing material processing forfurther modif
28、ication. In summary, this test method may be usedfor material development, quality control, characterization,design code or model verification, and limited design datageneration purposes.NOTE 4Data generated by this test method do not necessarily corre-spond to crack velocities that may be encounter
29、ed in service conditions.The use of data generated by this test method for design purposes,depending on the range and magnitude of applied stresses used, may entailextrapolation and uncertainty.4.2 This test method is related to Test Method C 1368(constant stress-rate flexural testing); however, Tes
30、t MethodC 1368 uses constant stress rates to determine correspondingflexural strengths whereas this test method employs constantstress to determine corresponding times to failure. In general,the data generated by this test method may be more represen-tative of actual service conditions as compared w
31、ith those byconstant stress-rate testing. However, in terms of test time,constant stress testing is inherently and significantly moretime-consuming than constant stress rate testing.4.3 The flexural stress computation in this test method isbased on simple elastic beam theory, with the assumptions th
32、atthe material is isotropic and homogeneous, the moduli ofelasticity in tension and compression are identical, and thematerial is linearly elastic. The grain size should be no greaterthan one-fiftieth (150) of the beam depth as measured by themean linear intercept method (Test Methods E112). In case
33、swhere the material grain size is bimodal or the grain sizedistribution is wide, the limit should apply to the larger grains.4.4 The test specimen sizes and test fixtures have beenselected in accordance with Test Methods C 1161 and C 1368,which provides a balance between practical configurations and
34、resulting errors, as discussed in Refs (4,5).4.5 The data are evaluated by regression of log appliedstress vs. log time to failure to the experimental data. Therecommendation is to determine the slow crack growth param-eters by applying the power law crack velocity function. Forderivation of this, a
35、nd for alternative crack velocity functions,see Appendix X1.NOTE 5A variety of crack velocity functions exist in the literature. Acomparison of the functions for the prediction of long-term static fatiguedata from short-term dynamic fatigue data (6) indicates that the exponen-tial forms better predi
36、ct the data than the power-law form. Further, theexponential form has a theoretical basis (7-10); however, the power lawform is simpler mathematically. Both have been shown to fit short-termtest data well.4.6 The approach used in this test method assumes that thematerial displays no rising R-curve b
37、ehavior, that is, noincreasing fracture resistance (or crack-extension resistance)C1576052with increasing crack length. The existence of such behaviorcannot be determined from this test method. The analysisfurther assumes that the same flaw type controls all times-to-failure.4.7 Slow crack growth be
38、havior of ceramic materials canvary as a function of mechanical, material, thermal, andenvironmental variables. Therefore, it is essential that testresults accurately reflect the effects of specific variables understudy. Only then can data be compared from one investigationto another on a valid basi
39、s, or serve as a valid basis forcharacterizing materials and assessing structural behavior.4.8 Like strength, time to failure of advanced ceramicssubjected to slow crack growth is probabilistic in nature.Therefore, slow crack growth that is determined from times tofailure under given constant applie
40、d stresses is also a probabi-listic phenomenon. The scatter in time to failure in constantstress testing is much greater than the scatter in strength inconstant stress-rate (or any strength) testing (1, 11-13) (seeAppendix X2). Hence, a proper range and number of constantapplied stresses, in conjunc
41、tion with an appropriate number oftest specimens, are required for statistical reproducibility andreliable design data generation (1-3). This test method providesguidance in this regard.4.9 The time to failure of a ceramic material for a given testspecimen and test fixture configuration is dependent
42、 on itsinherent resistance to fracture, the presence of flaws, appliedstress, and environmental effects. Fractographic analysis toverify the failure mechanisms has proven to be a valuable toolin the analysis of SCG data to verify that the same flaw type isdominant over the entire test range (14, 15)
43、, and it is to be usedin this test method (see Practice C 1322).5. Interferences5.1 Slow crack growth may be the product of both mechani-cal and chemical driving forces. The chemical driving force fora given material can vary strongly with the composition andtemperature of a test environment. Testin
44、g is conducted inenvironments representative of service conditions so as toevaluate material performance under use conditions. Note thatslow crack growth testing, particularly constant stress testing,is very time-consuming. The overall test time is considerablygreater in constant stress testing than
45、 in constant stress-ratetesting. Because of this longer test time, the chemical variablesof the test environment must be prevented from changingsignificantly throughout all test times. Inadequate control ofthese chemical variables may result in inaccurate time-to-failure data, especially for materia
46、ls that are more sensitive tothe test environment.5.2 Depending on the degree of SCG susceptibility of amaterial, the linear relationship between log (constant appliedstress) and log (time to failure) may start to deviate at a certainhigh applied stress where the crack velocity increases rapidlywith
47、 a subsequently short test duration, that is, the appliedstress approaches the strength, (see Fig. 1). This is analogous tothe occurrence of a strength plateau observed at higher testrates in constant stress-rate testing (16). If the time-to-failuredata determined in this plateau region are included
48、 in theanalysis, a misleading estimate of the SCG parameters will beobtained (17). Therefore, the strength data in the plateau shallbe excluded as data points in estimating the SCG parameters ofthe material. Similarly, a plateau can also exist at the fatiguelimit end of the curve, and these data poi
49、nts shall also beexcluded in estimating the SCG parameters.NOTE 6There are no simple guidelines in determining whether aplateau region is reached; however, with knowledge of the inert strengthand the fracture toughness of the test material, the slow crack growth rate applied stress intensity (v-K) curve may be determined. Evaluating thiswill help determine where the experimental conditions fall.5.3 When testing a material exhibiting a high SCG resis-tance (typically SCG parameter n 70), an unrealistically largenumber of test specimens may be required i
