1、Designation: C1834 16Standard Test Method forDetermination of Slow Crack Growth Parameters ofAdvanced Ceramics by Constant Stress Flexural Testing(Stress Rupture) at Elevated Temperatures1This standard is issued under the fixed designation C1834; 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination
3、of the slowcrack growth (SCG) parameters of advanced ceramics in agiven test environment at elevated temperatures in which thetime-to-failure of four-point-14 point flexural test specimens(see Fig. 1) is determined as a function of different levels ofconstant applied stress. This SCG constant stress
4、 test procedureis also called a slow crack growth (SCG) stress rupture test.The test method addresses the test equipment, test specimenfabrication, test stress levels and experimental procedures, datacollection and analysis, and reporting requirements.1.2 In this test method the decrease in time-to-
5、failure withincreasing levels of applied stress in specified test conditionsand temperatures is measured and used to analyze the slowcrack growth parameters of the ceramic. The preferred analysismethod is based on a power law relationship between crackvelocity and applied stress intensity; alternati
6、ve analysis ap-proaches are also discussed for situations where the power lawrelationship is not applicable.NOTE 1This test method is historically referred to in earlier technicalliterature as static fatigue testing (Refs 1-3)2in which the term fatigue isused interchangeably with the term slow crack
7、 growth. To avoid possibleconfusion with the fatigue phenomenon of a material that occurs exclu-sively under cyclic stress loading, as defined in E1823, this test methoduses the term constant stress testing rather than static fatigue testing.1.3 This test method uses a 4-point-14 point flexural test
8、mode and applies primarily to monolithic advanced ceramicsthat are macroscopically homogeneous and isotropic. This testmethod may also be applied to certain whisker- or particle-reinforced ceramics as well as certain discontinuous fiber-reinforced composite ceramics that exhibit macroscopicallyhomog
9、eneous behavior. Generally, continuous fiber ceramiccomposites do not exhibit macroscopically isotropic,homogeneous, elastic continuous behavior, and the applicationof this test method to these materials is not recommended.1.4 This test method is intended for use at elevated tem-peratures with vario
10、us test environments such as air, vacuum,inert gas, and steam. This test method is similar to Test MethodC1576 with the addition of provisions for testing at elevatedtemperatures to establish the effects of those temperatures onslow crack growth. The elevated temperature testing provisionsare derive
11、d from Test Methods C1211 and C1465.1.5 Creep deformation at elevated temperatures can occur insome ceramics as a competitive mechanism with slow crackgrowth. Those creep effects may interact and interfere with theslow crack growth effects (see 5.5). This test method isintended to be used primarily
12、for ceramic test specimens withnegligible creep. This test method imposes specific upper-bound limits on measured maximum creep strain at fracture orrun-out (no more than 0.1 %, in accordance with 5.5).1.6 The values stated in SI units are to be regarded as thestandard and in accordance with IEEE/AS
13、TM SI 10.1.7 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 limitations prior to use.2. Ref
14、erenced Documents2.1 ASTM Standards:3C1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC1211 Test Method for Flexural Strength of AdvancedCeramics at Elevated TemperaturesC1239 Practice for Reporting Uniaxial Strength Data andEsti
15、mating Weibull Distribution Parameters for AdvancedCeramics1This 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.Current edition approved Feb. 1, 2016. Published April 2016
16、. DOI: 10.1520/C1834-16.2The 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.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer
17、 to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1C1291 Test Method for Elevated Temperature Tensile CreepStrain, Creep Strain Rate, and Creep Time-to-Failure forAdvanced Monoli
18、thic CeramicsC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC1368 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Strength Testing at Ambient TemperatureC1465 Test Method for Determination of Slow C
19、rackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Flexural Testing at Elevated TemperaturesC1576 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress Flexural Testing (Stress Rupture) at Ambient Tem-peratureE4 Practices for Force Verific
20、ation of Testing MachinesE112 Test Methods for Determining Average Grain SizeE220 Test Method for Calibration of Thermocouples ByComparison TechniquesE230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE337 Test Method for Measuring Humidity with a Psy-ch
21、rometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE1823 Terminology Relating to Fatigue and Fracture TestingIEEE/ASTM SI 10 American National Standard for Use ofthe International System of Units (SI)
22、: The Modern MetricSystem3. Terminology3.1 Definitions:3.1.1 The terms described in Terminology C1145 and Ter-minology E1823 are applicable to this test method. Specificterms relevant to this test method are as follows:3.1.2 advanced ceramic, na highly engineered, highperformance, predominately non-
23、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 and a testfixture. C15763.1.4 constant applied stre
24、ss versus time-to-failure diagram,na plot of constant applied stress against time-to-failure forexperimental test data. (See Fig. 2)3.1.4.1 DiscussionConstant applied stress and time-to-failure are both plotted on logarithmic scales. Data may beorganized and plotted by experimental test temperature.
25、 Alsocalled an SCG stress rupture diagram. (See Fig. 2) C15763.1.5 constant applied stress versus time-to-failure curve,na curve fitted to the values of time-to-failure at each ofseveral applied stresses. (See Fig. 2)FIG. 1 Four-point-14 Point Flexural Test SchematicFIG. 2 Examples of Applied Stress
26、 versus Time-to-Failure Diagrams NC132 Silicon Nitride at 1100C in Air (Ref 28) and NCX34 SiliconNitride at 1200C and 1300C in Air (Ref 29)C1834 1623.1.5.1 DiscussionIn the historical ceramics literature, theconstant applied stress versus time-to-failure curve is oftencalled a static fatigue curve.
27、A more accurate descriptive nameis a slow crack growth (SCG) stress rupture curve. C15763.1.6 crack-extension resistance, KRFL-3/2, GRFL-1orJRFL-1, na measure of the resistance of a material to crackextension expressed in terms of the stress-intensity factor, K;crack-extension force, G; or values of
28、 J derived using theJ-integral concept. E18233.1.6.1 DiscussionThe J-integral concept in this E1823definition is a metal fracture concept and is not applicable tobrittle ceramics.3.1.7 creep strain, nthe time-dependent strain that occursafter the application of a force which is thereafter maintained
29、constant. C12913.1.8 dead weight test machine, na mechanical testingmachine which uses a load frame, lever-arms, and an adjust-able weight train (with calibrated dead weights) to apply aconstant known force to the test specimen over an extendedperiod of time.3.1.9 flexural strength, fFL-2, na measur
30、e of theultimate strength of a specified beam test specimen in flexuredetermined at a given stress in a particular environment. C15763.1.10 fracture toughness, na generic term for measuresof resistance to extension of a crack. E399, E18233.1.11 inert flexural strength FL-2, nthe flexural strengthof
31、a specified beam as determined in an inert test conditionwhereby no slow crack growth occurs.3.1.11.1 DiscussionAn inert condition may be obtained bytesting at a low temperature, at a very fast test rate, or in aninert test environment such as vacuum, silicone oil, high puritydry N2, or liquid nitro
32、gen. C14653.1.12 plane-strain fracture toughness, (critical stress inten-sity factor) KICFL-3/2, nthe crack extension resistanceunder conditions of crack-tip plane strain in Mode I for slowrates of loading under predominantly linear-elastic conditionsand negligible plastic-zone adjustment. E18233.1.
33、13 R-curve, na plot of crack-extension resistance as afunction of stable crack extension. C1145Also defined as a K-R curve. E18233.1.14 run-out, na test specimen that does not fail beforea prescribed test time limit. C15763.1.15 slow crack growth (SCG), nsubcritical crackgrowth (extension) which may
34、 result from, but is not restrictedto, such mechanisms as environmentally-assisted stress corro-sion or diffusive crack growth. C1368, C1465, C15763.1.16 slow crack growth (SCG) parameters, nthe param-eters estimated as constants in the log (time-to-failure) versuslog (constant applied stress), whic
35、h represent a measure of thesusceptibility to slow crack growth of a material (see AppendixX1). C14653.1.17 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.E18233.1.18 te
36、st environment, nthe aggregate of chemical spe-cies and energy that surrounds a test specimen. E18233.1.19 test environmental chamber, na container sur-rounding the test specimen that is capable of providing acontrolled local environmental condition. C1368, C14653.1.20 time-to-failure, tft, ntotal e
37、lapsed time from testinitiation to test specimen failure/rupture for a defined testcondition.4. Significance and Use4.1 The service life of many structural ceramic componentsis often limited by the subcritical growth of cracks over time,under stress at a defined temperature, and in a defined chemica
38、lenvironment (Refs 1-3). When one or more cracks grow to acritical size, brittle catastrophic failure may occur in thecomponent. Slow crack growth in ceramics is commonlyaccelerated at elevated temperatures. This test method providesa procedure for measuring the long term load-carrying abilityand ap
39、praising the relative slow crack growth susceptibility ofceramic materials at elevated temperatures as a function oftime, temperature, and environment. This test method is basedon Test Method C1576 with the addition of provisions forelevated temperature testing.4.2 This test method is also used to d
40、etermine the influencesof processing variables and composition on slow crack growthat elevated temperatures, as well as on strength behavior ofnewly developed or existing materials, thus allowing tailoringand optimizing material processing for further modification.4.3 This test method may be used fo
41、r material development,quality control, characterization, design code or modelverification, time-to-failure, and limited design data generationpurposes.NOTE 2Data generated by this test method do not necessarilycorrespond to crack velocities that may be encountered in serviceconditions. The use of d
42、ata generated by this test method for designpurposes, depending on the range and magnitude of applied stresses used,may entail extrapolation and uncertainty.4.4 This test method and Test Method C1576 are similar andrelated to Test Methods C1368 and C1465; however, C1368and C1465 use constant stress-
43、rates (linearly increasing stressover time) to determine corresponding flexural strengths,whereas this test method and C1576 employ a constant stress(fixed stress levels over time) to determine correspondingtimes-to-failure. In general, the data generated by this testmethod may be more representativ
44、e of actual service condi-tions as compared with data from constant stress-rate testing.However, in terms of test time, constant stress testing isinherently and significantly more time consuming than con-stant stress-rate testing.4.5 The flexural stress computation in this test method isbased on sim
45、ple elastic beam theory, with the followingassumptions: the material is isotropic and homogeneous; themoduli of elasticity in tension and compression are identical;and the material is linearly elastic. These assumptions arebased on small grain size in the ceramic specimens. The grainsize should be n
46、o greater than150 of the beam depth asmeasured by the mean linear intercept method (E112). In casesC1834 163where the material grain size is bimodal or the grain sizedistribution is wide, the limit should apply to the larger grains.4.6 The test specimen sizes and test fixtures have beenselected in a
47、ccordance with Test Method C1211 which pro-vides a balance between practical configurations and resultingerrors, as discussed in Refs 4 and 5. Test Method C1211 alsospecifies fixture material requirements for elevated test tem-perature stability and functionality.4.7 The SCG data are evaluated by re
48、gression of logapplied-stress vs. log time-to-failure to the experimental data.The recommendation is to determine the slow crack growthparameters by applying the power law crack velocity function.For derivation of this, and for alternative crack velocityfunctions, see Appendix X1.NOTE 3A variety of
49、crack velocity functions exist in the literature. Acomparison of the functions for the prediction of long-term constant stress(static fatigue) data from short-term constant stress rate (dynamic fatigue)data (Ref 6) indicates that the exponential forms better predict the datathan the power-law form. Further, the exponential form has a theoreticalbasis (Refs 7-10); however, the power law form is simpler mathematically.Both forms have been shown to fit short-term test data well.4.8 The approach used in this test method assumes that
