1、Designation: C1368 10 (Reapproved 2017)Standard Test Method forDetermination of Slow Crack Growth Parameters ofAdvanced Ceramics by Constant Stress-Rate StrengthTesting at Ambient Temperature1This standard is issued under the fixed designation C1368; the number immediately following the designation
2、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. Scope*1.1 This test method covers the determina
3、tion of slow crackgrowth (SCG) parameters of advanced ceramics by usingconstant stress-rate rectangular beam flexural testing, or ring-on-ring biaxial disk flexural testing, or direct tensile strength,in which strength is determined as a function of applied stressrate in a given environment at ambie
4、nt temperature. Thestrength degradation exhibited with decreasing applied stressrate in a specified environment is the basis of this test methodwhich enables the evaluation of slow crack growth parametersof a material.NOTE 1This test method is frequently referred to as “dynamicfatigue” testing (1-3)
5、2in which the term “fatigue” is used interchangeablywith the term “slow crack growth.” To avoid possible confusion with the“fatigue” phenomenon of a material which occurs exclusively under cyclicloading, as defined in Terminology E1823, this test method uses the term“constant stress-rate testing” ra
6、ther than “dynamic fatigue” testing.NOTE 2In glass and ceramics technology, static tests of considerableduration are called “static fatigue” tests, a type of test designated asstress-rupture (See Terminology E1823).1.2 Values expressed in this test method are in accordancewith the International Syst
7、em of Units (SI) and IEEE/ASTM SI10.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limi
8、tations prior to use.2. Referenced Documents2.1 ASTM Standards:3C1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distribution Parameters for AdvancedCerami
9、csC1273 Test Method for Tensile Strength of MonolithicAdvanced Ceramics at Ambient TemperaturesC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC1499 Test Method for Monotonic Equibiaxial FlexuralStrength of Advanced Ceramics at Ambient TemperatureE4 Practi
10、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)E1823 Terminology Relating to Fatigue and Fracture TestingIEEE/ASTM SI 10 American Na
11、tional Standard for Use ofthe International System of Units (SI): The Modern MetricSystem3. Terminology3.1 Definitions: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,
12、na highly engineered, high-performance, predominately nonmetallic, inorganic, ceramicmaterial having specific functional attributes. (C1145)1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 onMechanical Prope
13、rties and Performance.Current edition approved Feb. 1, 2017. Published February 2017. Originallyapproved in 1997. Last previous edition approved in 2010 as C1368 10. DOI:10.1520/C1368-10R17.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For reference
14、d 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.*A Summary of Changes section appears at the end of this standardCopyright
15、ASTM International, 100 Barr Harbor Drive, PO Box C700, 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 S
16、tandards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.3 constant stress rate, na constant rate of maximumstress applied to a specified beam by using either a constantloading or constant displacement rate of a testing machine.3.1.
17、4 environment, nthe aggregate of chemical speciesand energy that surrounds a test specimen. (E1823)3.1.5 environmental chamber, nthe container of bulk vol-ume surrounding a test specimen. (E1823)3.1.6 equibiaxial flexural strength F/L2, nthe maximumstress that a material is capable of sustaining whe
18、n subjected toflexure between two concentric rings.3.1.6.1 DiscussionThis mode of flexure is a cupping ofthe circular plate caused by loading at the inner load ring andouter support ring. The equibiaxial flexural strength is calcu-lated from the maximum-load of a biaxial test carried torupture, the
19、original dimensions of the test specimen, andPoissons ratio. (C1499)3.1.7 flexural strength, f,na measure of the strength of aspecified beam specimen in bending determined at a givenstress rate in a particular environment.3.1.8 fracture toughness, na generic term for measures ofresistance to extensi
20、on of a crack. (E1823)3.1.9 inert strength, na measure of the strength of aspecified strength test specimen as determined in an appropri-ate inert condition whereby no slow crack growth occurs.3.1.9.1 DiscussionAn inert condition may be obtained byusing vacuum, low temperatures, very fast test rates
21、, or anyinert mediums.3.1.10 slow crack 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.3.1.11 strength-stress rate curve, na curve fitted to thevalues of streng
22、th at each of several stress rates, based on therelationship between strength and stress rate: log f= 1/(n +1)log + log D. (See Appendix X1.)3.1.11.1 DiscussionIn the ceramics literature, this is oftencalled a dynamic fatigue curve.3.1.12 strength-stress rate diagram, na plot of strengthagainst stre
23、ss rate. Both strength and stress rate are plotted onlog-log scales.3.1.13 stress intensity factor, KI,nthe magnitude of theideal-crack-tip stress field (stress-field singularity) subjected tomode I loading in a homogeneous, linear elastic body. (E1823)3.1.14 tensile strength F/L2, nSuthe maximum te
24、nsilestress which a material is capable of sustaining.3.1.14.1 DiscussionTensile strength is calculated from themaximum force during a tension test carried to rupture and theoriginal cross-sectional area of the specimen. (C1273)3.2 Definitions of Terms Specific to This Standard:3.2.1 slow crack grow
25、th parameters, n and D, ntheparameters estimated as constants in the flexural strength-stressrate equation, which represent the degree of slow crack growthsusceptibility of a material. (See Appendix X1.)4. Significance and Use4.1 For many structural ceramic components in service,their use is often l
26、imited by lifetimes that are controlled by aprocess of SCG. This test method provides the empiricalparameters for appraising the relative SCG susceptibility ofceramic materials under specified environments. Furthermore,this test method may establish the influences of processingvariables and composit
27、ion on SCG as well as on strengthbehavior of newly developed or existing materials, thus allow-ing tailoring and optimizing material processing for furthermodification. In summary, this test method may be used formaterial development, quality control, characterization, andlimited design data generat
28、ion purposes. The conventionalanalysis of constant stress-rate testing is based on a number ofcritical assumptions, the most important of which are listed inthe next paragraphs.4.2 The flexural stress computation for the rectangular beamtest specimens or the equibiaxial disk flexure test specimens i
29、sbased on simple beam theory, with the assumptions that thematerial is isotropic and homogeneous, the moduli of elasticityin tension and compression are identical, and the material islinearly elastic. The average grain size should be no greaterthan one-fiftieth of the beam thickness.4.3 The test spe
30、cimen sizes and fixtures for rectangularbeam test specimens should be in accordance with Test MethodC1161, which provides a balance between practical configura-tions and resulting errors, as discussed in Refs (4, 5). Onlyfour-point test configuration is allowed in this test method forrectangular bea
31、m specimens. Three-point test configurationsare not permitted. The test specimen sizes and fixtures for disktest specimens tested in ring-on-ring flexure should be chosenin accordance with Test Method C1499. The test specimens fordirect tension strength testing should be chosen in accordancewith Tes
32、t Method C1273.4.4 The SCG parameters (n and D) are determined by fittingthe measured experimental data to a mathematical relationshipbetween strength and applied stress rate, log f= 1/(n+1) log + log D. The basic underlying assumption on the derivation ofthis relationship is that SCG is governed by
33、 an empiricalpower-law crack velocity, v=AKI/KICn(see Appendix X1).NOTE 3There are various other forms of crack velocity laws whichare usually more complex or less convenient mathematically, or both, butmay be physically more realistic (6). It is generally accepted that actualdata cannot reliably di
34、stinguish between the various formulations.Therefore, the mathematical analysis in this test method does not coversuch alternative crack velocity formulations.4.5 The mathematical relationship between strength andstress rate was derived based on the assumption that the slowcrack growth parameter is
35、at least n 5 (1, 7, 8). Therefore, ifa material exhibits a very high susceptibility to SCG, that is, n2000 MPa/s) mayremain unchanged so that a plateau is observed in the plot ofstrength-versus-stress rate (7). If the strength data determinedin this plateau region are included in the analysis, a mis
36、leadingestimate of the SCG parameters will be obtained. Therefore,the strength data in the plateau shall be excluded as data pointsin estimating the SCG parameters of the material. This testmethod addresses for this factor by recommending that thehighest stress rate be 2000 MPa/s.NOTE 5The strength
37、plateau of a material can be checked bymeasuring an inert strength in an appropriate inert medium.NOTE 6When testing in environments with less than 100 % concen-tration of the corrosive medium (for example, air), the use of stress ratesgreater than 1 MPa/s can result in significant errors in the slo
38、w crackgrowth parameters due to averaging of the regions of the slow crackgrowth curve (9). Such errors can be avoided by testing in 100%concentration of the corrosive medium (for example, in water instead ofhumid air). For the case of 100 % concentration of the corrosive medium,stress rates as larg
39、e as 2000 MPa/s may be acceptable.5.3 Surface preparation of test specimens can introducefabrication flaws which may have pronounced effects on SCGbehavior. Machining damage imposed during specimen prepa-ration can be either a random interfering factor or an inherentpart of the strength characterist
40、ics to be measured. Surfacepreparation can also lead to residual stress. Universal orstandardized test methods of surface 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
41、steps. In some cases, speci-mens need to be tested in the as-processed condition tosimulate a specific service condition. Therefore, specimenfabrication history may play an important role in slow crackgrowth as well as in strength behavior.6. Apparatus6.1 Testing MachineTesting machines used for thi
42、s testmethod shall conform to the requirements of Practices E4.Specimens may be loaded in any suitable testing machineprovided that uniform test rates, either using load-controlled ordisplacement-controlled mode, can be maintained. The loadsused in determining strength shall be accurate within 61.0
43、%at any load within the selected load rate and load range of thetesting machine as defined in Practices E4. The testing 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-controlled mode and from 107t
44、o 104m/sfor displacement-controlled mode.6.2 Test Fixtures, Four-Point Rectangular Beam FlexureThe configurations and mechanical properties of test fixturesshould be in accordance with Test Method C1161. The mate-rials from which the test fixtures including bearing cylindersare fabricated shall be e
45、ffectively inert to the test environmentso that they do not react with or contaminate the environment.NOTE 7For testing in water, for example, it is recommended that theC1368 10 (2017)3test fixture be fabricated from stainless steel which is effectively inert towater. The bearing cylinders may be ma
46、chined from hardenable stainlesssteel (for example, 440C grade) or a ceramic material such as siliconnitride, silicon carbide, or alumina.6.2.1 Four-Point FlexureThe four-point14-point fixtureconfiguration as described in 6.2 of Test Method C1161 shallbe used in this test method. Three-point flexure
47、 is not permit-ted. The test fixtures shall be stiffer than the specimen, so thatmost of the crosshead or actuator travel is imposed onto thespecimen.6.3 Test Fixtures, Equibiaxial Disk Flexural StrengthTheconfigurations and mechanical properties of test fixtures shouldbe in accordance with Test Met
48、hod C1499. The materials fromwhich the test fixtures including bearing cylinders are fabri-cated shall be effectively inert to the test environment so thatthey do not react with or contaminate the environment. SeeNote 7. The test fixtures shall be stiffer than the specimen, sothat most of the crossh
49、ead or actuator travel is imposed ontothe specimen.6.4 Test Fixtures, Tensile StrengthThe configurations andmechanical properties of test fixtures should be in accordancewith Test Method C1273. The materials from which the testfixtures including bearing cylinders are fabricated shall beeffectively inert to the test environment so that they do notreact with or contaminate the environment. See Note 7. Thetest fixtures shall be stiffer than the specimen, so that most ofthe crosshead or actuator travel is imposed onto the specimen
