1、Designation: C1576 05 (Reapproved 2017)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 C1576; the number immediately following the
2、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 method
3、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 a
4、ddition, 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 grow
5、th 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 method
6、 in this standard is frequently referred to as“static fatigue” or stress-rupture testing (1-3)2in which the term “fatigue”is used interchangeably with the term “slow crack growth.” To avoidpossible confusion with the “fatigue” phenomenon of a material thatoccurs exclusively under cyclic loading, as
7、defined in Terminology E1823,this test method uses the term “constant stress testing” rather than “staticfatigue” 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-
8、 or particle-reinforced ceramics as well as certaindiscontinuous fiber-reinforced composite ceramics that exhibitmacroscopically homogeneous behavior. Generally, continuousfiber ceramic composites do not exhibit macroscopicallyisotropic, homogeneous, continuous behavior, and the applica-tion of this
9、 test 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 t
10、est 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 o
11、f regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC1368 T
12、est Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Strength Testing at Ambient TemperatureC1465 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Flexural Testing at Elevated TemperaturesE4 Pr
13、actices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE112 Test Methods for Determining Average Grain SizeE337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E399 Test Method for Linear-E
14、lastic Plane-Strain FractureToughness KIcof Metallic MaterialsE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 Definitions:1This practice is under the jurisdiction of ASTM Committee C28 on AdvancedCeramics and is the direct responsibility of Subcommittee C28.01 on Mechanic
15、alProperties and Performance.Current edition approved Feb. 1, 2017. Published February 2017. Originallyapproved in 2005. Last previous edition approved in 2010 as C1576 05 (2010).DOI: 10.1520/C1576-05R17.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3F
16、or 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 the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C70
17、0, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the Wo
18、rld Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.1 The terms described in Terminology C1145, Terminol-ogy E6, and Terminology E1823 are applicable to this teststandard. Specific terms relevant to this test method are asfollows:3.1.2 advanced ceramic, na highly engineered, high
19、performance, predominately non-metallic, inorganic, ceramicmaterial having specific functional attributes. C11453.1.3 constant applied stress, FL-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
20、.4 constant applied stress-time to failure diagramaplot of constant applied stress against time to failure. Constantapplied stress and time to failure are both plotted on logarith-mic scales.3.1.5 constant applied stress-time to failurecurvea curvefitted to the values of time to failure at each of s
21、everal appliedstresses.NOTE 2In the ceramics literature, this is often called a “static fatigue”curve.3.1.6 test environment, nthe aggregate of chemical speciesand energy that surrounds a test specimen. E18233.1.7 test environmental chamber, na container surround-ing the test specimen that is capabl
22、e of providing controlledlocal environmental condition. C1368, C14653.1.8 flexural strength, fFL-2, na measure of theultimate strength of a specified beam test specimen in flexuredetermined at a given stress rate in a particular environment.3.1.9 fracture toughness, (critical stress intensity factor
23、) KICFL-3/2, na generic term for measures of resistance toextension of a crack. E1823, E3993.1.10 inert flexural 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, l
24、owtemperature, very fast test rate, or an inert environment such as silicone oilor high purity dry N2.3.1.11 R-curve, na plot of crack-extension resistance as afunction of stable crack extension. C11453.1.12 run-out, na test specimen that does not fail beforea prescribed test time.3.1.13 slow crack
25、growth (SCG), nsubcritical crackgrowth (extension) which may result from, but is not restrictedto, such mechanisms as environmentally assisted stress corro-sion or diffusive crack growth. C1368, C14653.1.14 slow crack growth (SCG) parametersthe param-eters estimated as constants in the log (time to
26、failure) versuslog (constant applied stress), which represent a measure ofsusceptibility to slow crack growth of a material (see AppendixX1).3.1.15 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 homogene
27、ous, linear elastic body.E18233.1.16 time to failure, tft, ntotal elapsed time from testinitiation 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
28、appraising the relative slowcrack growth susceptibility of ceramic materials under speci-fied environments 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
29、 or existing materials,thus allowing tailoring and optimizing material processing forfurther modification. 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 gene
30、rated by this test method do not necessarilycorrespond to crack velocities that may be encountered in serviceconditions. The use of data generated by this test method for designpurposes, depending on the range and magnitude of applied stresses used,may entail extrapolation and uncertainty.4.2 This t
31、est method is related to Test Method C1368(“constant stress-rate flexural testing”), however, C1368 usesconstant stress rates to determine corresponding flexuralstrengths whereas this test method employs constant stress todetermine corresponding times to failure. In general, the datagenerated by thi
32、s test method may be more representative ofactual service conditions as compared with those by constantstress-rate testing. However, in terms of test time, constantstress testing is inherently and significantly more time consum-ing than constant stress rate testing.4.3 The flexural stress computatio
33、n in this test method isbased on simple elastic beam theory, with the assumptions thatthe 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 be
34、am depth as measured by themean linear intercept method (Test Methods E112). In caseswhere 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 Met
35、hods C1161 and C1368,which provides a balance between practical configurations andresulting errors, as discussed in Ref (4, 5).4.5 The data are evaluated by regression of log appliedstress versus log time to failure to the experimental data. Therecommendation is to determine the slow crack growth pa
36、ram-eters by applying the power law crack velocity function. Forderivation of this, and 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 s
37、hort-term dynamic fatigue data (6) indicates that the exponen-tial forms better predict 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.C1576 05 (
38、2017)24.6 The approach used in this method assumes that thematerial displays no rising R-curve behavior, that is, noincreasing fracture resistance (or crack-extension resistance)with increasing crack length. The existence of such behaviorcannot be determined from this test method. The analysisfurthe
39、r assumes that the same flaw type controls all times-to-failure.4.7 Slow crack growth behavior 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 und
40、erstudy. Only then can data be compared from one investigationto another on a valid basis, 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.Therefor
41、e, slow crack growth that is determined from times tofailure under given constant applied 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), s
42、eeAppendix X2. Hence, a proper range and number of constantapplied stresses, in conjunction with an appropriate number oftest specimens, are required for statistical reproducibility andreliable design data generation (1-3). This standard providesguidance in this regard.4.9 The time to failure of a c
43、eramic material for a given testspecimen and test fixture configuration is dependent 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 d
44、ata to verify that the same flaw type isdominant over the entire test range Ref (14, 15), and it is to beused 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 mat
45、erial can vary strongly with the composition andtemperature of a test environment. Testing 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 tim
46、e consuming. The overall test time is considerablygreater in constant stress testing than 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
47、 chemical variables may result in inaccurate time-to-failure data, especially for materials 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
48、to deviate at a certainhigh applied stress where the crack velocity increases rapidlywith 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
49、testing (16). If the time-to-failuredata determined in this plateau region are included 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 points shall also beexcluded in estimating the SCG parameters.NOTE 6There are no simple guidelines in determining whether aplateau region is reached, however with kno
