1、Designation: C 1576 05 (Reapproved 2010)Standard 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 th
2、e designation 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 standard test metho
3、d covers the determination ofslow crack growth (SCG) parameters of advanced ceramics byusing constant 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
4、 addition, test specimen fabricationmethods, 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 gr
5、owth parameters of a material. 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 test meth
6、od in this standard is frequently referred to as“static fatigue” or stress-rupture testing (Refs (1-3) in which the term“fatigue” is used interchangeably with the term “slow crack growth.” Toavoid possible confusion with the “fatigue” phenomenon of a material thatoccurs exclusively under cyclic load
7、ing, as defined in E1823, this testmethod uses the term “ constant stress testing” rather than “static fatigue”testing.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
8、 particle-reinforced ceramics as 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 te
9、st method to these materials is 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
10、method may involve hazardous materials,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 re
11、gulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC1368 Test
12、Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Flexural Testing at Ambient TemperatureC1465 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Flexural Testing at Elevated TemperaturesE4 Practi
13、ces for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic Mat
14、erialsE1823 Terminology Relating to Fatigue and Fracture Test-ing1This practice is under the jurisdiction of ASTM Committee C28 on AdvancedCeramics and is the direct responsibility of Subcommittee C28.01 on MechanicalProperties and Performance.Current edition approved June 1, 2010. Published Novembe
15、r 2010. Originallyapproved in 2005. Last previous edition approved in 2005 as C1576 - 05. DOI:10.1520/C1576-05R10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to th
16、e standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E112 Test Methods for Determining Average Grain Size3. Terminology3.1 Definitions: The terms described in Terminology C1145,Terminol
17、ogy E6, and Terminology E1823 are applicable to thistest standard. Specific terms relevant to this test method are asfollows:3.1.1 advanced ceramic, na highly engineered, high per-formance, predominately non-metallic, inorganic, ceramic ma-terial having specific functional attributes. (C1145)3.1.2 c
18、onstant applied stress, sFL-2, na constant 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 diagramaplot of constant applied stress against time to failure. Constantap
19、plied stress and time to failure are both plotted on logarith-mic scales.3.1.4 constant applied stress-time to failure curveacurve fitted to the values of time to failure at each of severalapplied stresses.NOTE 2In the ceramics literature, this is often called a “static fatigue”curve.3.1.5 test envi
20、ronment, nthe aggregate of chemical spe-cies and energy that surrounds a test specimen (E1823).3.1.6 test environmental chamber, na container surround-ing the test specimen that is capable of providing controlledlocal environmental condition (C1368, C1465).3.1.7 flexural strength, sfFL-2, na measure
21、 of theultimate 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, na generic term for measures of resistance toextension of a crack (E1823, E399).3.1.9 inert flexur
22、al strength FL-2, nthe flexural strengthof a specified beam as determined in an inert conditionwhereby no slow 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 purity dry N2.3.1.10 R
23、-curve, na plot of crack-extension resistance as afunction of stable crack extension (C1145).3.1.11 run-out, na test specimen that does not fail beforea prescribed test time.3.1.12 slow crack growth (SCG), nsubcritical crackgrowth (extension) which may result from, but is not restrictedto, such mech
24、anisms as environmentally-assisted stress corro-sion or diffusive crack growth (C1368, C1465).3.1.13 slow crack growth (SCG) parametersthe param-eters estimated as constants in the log (time to failure) versuslog (constant applied stress), which represent a measure ofsusceptibility to slow crack gro
25、wth of a material (seeAppendixX1).3.1.14 stress intensity factor, KIFL-3/2, nthe magnitudeof the ideal-crack-tip stress field stress field singularity) sub-jected to mode I loading in a homogeneous, linear elastic body.(E1823)3.1.15 time to failure, tft, ntotal elapsed time from testinitiation to te
26、st 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 environmen
27、ts 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 modificatio
28、n. 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 encountered in
29、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 C1368(“constant stress-rate flexural testing”), however, C1368 us
30、esconstant stress rates to determine corresponding flexuralstrengths whereas this test method employs constant stress todetermine corresponding times to failure. In general, the datagenerated by this test method may be more representative ofactual service conditions as compared with those by constan
31、tstress-rate testing. However, in terms of test time, constantstress testing is inherently and significantly more time- con-suming than constant stress rate testing.4.3 The flexural stress computation in this test method isbased on simple elastic beam theory, with the assumptions thatthe material is
32、 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 (1/50) of the beam depth as measured by themean linear intercept method (E112). In cases where thematerial grain siz
33、e is bimodal or the grain size distribution iswide, the limit should apply to the larger grains.4.4 The test specimen sizes and test fixtures have beenselected in accordance with Test Methods C1161 and C1368,which provides a balance between practical configurations andresulting errors, as discussed
34、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, and for alternative crack veloc
35、ity 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 predict the data than the power-law f
36、orm. 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.C 1576 05 (2010)24.6 The approach used in this method assumes that thematerial displays no rising R-curve behavior, that is, noin
37、creasing fracture resistance (or crack-extension resistance)with 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 behavior of ceramic materials ca
38、nvary 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 basis, or serve as a valid basis f
39、orcharacterizing 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 applied stresses is also a probabi-l
40、istic 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 (Refs. (1, 11-13),see Appendix X2. Hence, a proper range and number ofconstant applied stresses, in conjunction with an appropriate
41、number of test specimens, are required for statistical reproduc-ibility and reliable design data generation (Ref. (1-3). Thisstandard provides guidance in this regard.4.9 The time to failure of a ceramic material for a given testspecimen and test fixture configuration is dependent on itsinherent res
42、istance 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 (Refs. 14 and 15), and it i
43、sto be used in this standard (refer to Practice C1322).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. Testing is cond
44、ucted 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 in const
45、ant 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 materials that a
46、re 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 a subseq
47、uently short test duration, i.e., the applied stressapproaches the strength, see Fig. 1. This is analogous to theoccurrence of a strength plateau observed at higher test rates inconstant stress-rate testing (Ref. 16). If the time-to-failure datadetermined in this plateau region are included in the a
48、nalysis,a misleading estimate of the SCG parameters will be obtained(Ref.17). Therefore, the strength data in the plateau shall beexcluded 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 points s
49、hall 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 requi
