1、Designation: C1291 16Standard Test Method forElevated Temperature Tensile Creep Strain, Creep StrainRate, and Creep Time-to-Failure for Monolithic AdvancedCeramics1This standard is issued under the fixed designation C1291; the number immediately following the designation indicates the year oforigina
2、l 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 of tensilecreep strain,
3、creep strain rate, and creep time-to-failure foradvanced monolithic ceramics at elevated temperatures, typi-cally between 1073 and 2073 K. A variety of test specimengeometries are included. The creep strain at a fixed temperatureis evaluated from direct measurements of the gage lengthextension over
4、the time of the test. The minimum creep strainrate, which may be invariant with time, is evaluated as afunction of temperature and applied stress. Creep time-to-failure is also included in this test method.1.2 This test method is for use with advanced ceramics thatbehave as macroscopically isotropic
5、, homogeneous, continu-ous materials. While this test method is intended for use onmonolithic ceramics, whisker- or particle-reinforced compositeceramics as well as low-volume-fraction discontinuous fiber-reinforced composite ceramics may also meet these macro-scopic behavior assumptions. Continuous
6、 fiber-reinforced ce-ramic composites (CFCCs) do not behave as macroscopicallyisotropic, homogeneous, continuous materials, and applicationof this test method to these materials is not recommended.1.3 The values in SI units are to be regarded as the standard(see IEEE/ASTM SI 10). The values given in
7、 parentheses aremathematical conversions to inch-pound units that are pro-vided for information only and are not considered standard.1.4 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 estab
8、lish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C1145 Terminology of Advanced CeramicsC1273 Test Method for Tensile Strength of MonolithicAdvanced Ceramics at Ambient TemperaturesE4 Pract
9、ices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE83 Practice for Verification and Classification of Exten-someter SystemsE139 Test Methods for Conducting Creep, Creep-Rupture,and Stress-Rupture Tests of Metallic MaterialsE177 Practice for Use of
10、 the Terms Precision and Bias inASTM Test MethodsE220 Test Method for Calibration of Thermocouples ByComparison TechniquesE230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE639 Test Method for Measuring Total-Radiance Tempera-ture of Heated Surfaces Usi
11、ng a Radiation Pyrometer(Withdrawn 2011)3E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1012 Practice for Verification of Testing Frame and Speci-men Alignment Under Tensile and Compressive AxialForce ApplicationIEEE/ASTM SI 10 American National Stan
12、dard for Use ofthe International System of Units (SI): The Modern MetricSystem3. Terminology3.1 DefinitionsThe definitions of terms relating to creeptesting, which appear in Section E of Terminology E6 shall1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is
13、the direct responsibility of Subcommittee C28.01 onMechanical Properties and Performance.Current edition approved Sept. 1, 2016. Published October 2016. Originallyapproved in 1995. Last previous edition approved in 2010 as C1291 00a (2010).DOI: 10.1520/C1291-16.2For referenced ASTM standards, visit
14、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.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM
15、International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1apply to the terms used in this test method. For the purpose ofthis test method only, some of the more general terms are usedwith the restricted meanings given as follows.3.2 Definitions of Terms Speci
16、fic to This Standard:3.2.1 axial strain, a, L/L, naverage of the strain mea-sured on diametrically opposed sides and equally distant fromthe test specimen axis.3.2.2 bending strain, bL/L, ndifference between thestrain at the surface and the axial strain.3.2.2.1 DiscussionIn general, it varies from p
17、oint to pointaround and along the gage length of the test specimen. E10123.2.3 creep-rupture test, ntest in which progressive testspecimen deformation and the time-to-failure are measured. Ingeneral, deformation is greater than that developed during acreep test.3.2.4 creep strain, , L/L, ntime depen
18、dent strain thatoccurs after the application of force which is thereaftermaintained constant. Also known as engineering creep strain.3.2.5 creep test, ntest that has as its objective the mea-surement of creep and creep rates occurring at stresses usuallywell below those that would result in fast fra
19、cture.3.2.5.1 DiscussionSince the maximum deformation isonly a few percent, a sensitive extensometer is required.3.2.6 creep time-to-failure, tf, T, ntime required for atest specimen to fracture under constant force as a result ofcreep.3.2.6.1 DiscussionThis is also known as creep rupturetime.3.2.7
20、gage length, l, L, noriginal distance betweenfiducial markers on or attached to the test specimen fordetermining elongation.3.2.8 maximum bending strain, bmax, L/L, nlargestvalue of bending strain along the gage length. It can becalculated from measurements of strain at three circumferentialposition
21、s at each of two different longitudinal positions.3.2.9 minimum creep strain rate, min,T1, nminimumvalue of the strain rate prior to test specimen failure asmeasured from the strain-time curve. The minimum creepstrain rate may not necessarily correspond to the steady-statecreep strain rate.3.2.10 sl
22、ow crack growth, , L/T, nsubcritical crackgrowth (extension) which may result from, but is not restrictedto, such mechanisms as environmentally assisted stresscorrosion, diffusive crack growth, or other mechanisms. C11453.2.11 steady-state creep, ss, L/L, nstage of creepwherein the creep rate is con
23、stant with time.3.2.11.1 DiscussionAlso known as secondary creep.3.2.12 stress corrosion, nenvironmentally induced degra-dation that initiates from the exposed surface.3.2.12.1 DiscussionSuch environmental effects com-monly include the action of moisture, as well as other corrosivespecies, often wit
24、h a strong temperature dependence.3.2.13 tensile creep strain, t, L/L, ncreep strain thatoccurs as a result of a uniaxial tensile-applied stress.4. Significance and Use4.1 Creep tests measure the time-dependent deformationunder force at a given temperature, and, by implication, theforce-carrying cap
25、ability of the material for limited deforma-tions. Creep-rupture tests, properly interpreted, provide ameasure of the force-carrying capability of the material as afunction of time and temperature. The two tests complementeach other in defining the force-carrying capability of amaterial for a given
26、period of time. In selecting materials anddesigning parts for service at elevated temperatures, the type oftest data used will depend on the criteria for force-carryingcapability that best defines the service usefulness of thematerial.4.2 This test method may be used for material development,quality
27、 assurance, characterization, and design data generation.4.3 High-strength, monolithic ceramic materials, generallycharacterized by small grain sizes (2K. It is preferable to usefully sheathed thermocouples in order to minimize degrada-tion.6.5.3 Pyrometers:6.5.3.1 CalibrationThe pyrometer(s) shall
28、be calibrated inaccordance with Test Method E639.6.5.3.2 AccuracyThe measurement of temperature shallbe accurate to within 5 K. This shall include the error inherentto the pyrometer and any error in the measuring instruments.6,76.6 Extensometers:6.6.1 The strain measuring equipment shall be capable
29、ofbeing used at elevated temperatures. The sensitivity andaccuracy of the strain-measuring equipment shall be suitable todefine the creep characteristics with the precision required forthe application of the data.6.6.2 CalibrationExtensometers shall be calibrated in ac-cordance with Practice E83.6.6
30、.3 AccuracyExtensometers with accuracies equivalentto the B-1 classification of extensometer systems specified inPractice E83 are suitable for use in high-temperature testing ofceramics. Results of analytical and empirical evaluations atelevated temperatures show that mechanical extensometers(16) ca
31、n meet these requirements. Optical extensometers usingflags have gage length uncertainties that will generally preventthem from achieving class B-1 accuracy (17). Empiricalevaluations at elevated temperature (18) show that theseextensometers can yield highly repeatable creep data, however.6.7 Timing
32、 ApparatusFor creep rupture tests, a timingapparatus capable of measuring the elapsed time betweencomplete application of the force and the time at which fractureof the test specimen occurs to within 1 % of the elapsed timeshall be employed.7. Test Specimens and Sample7.1 Test Specimen Size:7.1.1 De
33、scriptionThe size and shape of test specimensshall be based on the requirements necessary to obtain repre-sentative samples of the material being investigated as dis-cussed in Test Method C1273. The test specimen geometryshall be such that there is no more than a 5 % elastic stressconcentration at t
34、he ends of the gage section. Typical shapesinclude square or rectangular cross-section dogbones andcylindrical button-head geometries, and are shown in Appen-dix X1. It is recommended, in accordance with Test MethodsE139 and in the absence of additional information to thecontrary, that the grip sect
35、ion be at least four times larger thanthe larger dimension of either width or thickness of the gagesection.7.1.2 DimensionsSuggested dimensions for tensile creeptest specimens that have been successfully used in previousinvestigations are given in Appendix X1. Cross-sectionaltolerances are 0.05 mm.
36、Parallelism tolerances on the faces ofthe test specimen are 0.03 mm. Various radii of curvature maybe used to adjust the gage section or change the mountingconfiguration. Although these radii are expected to be larger,resulting in a smaller stress concentration, wherever possible,resort shall be mad
37、e to a finite element analysis to determinethe locations and intensities of stress concentrations in the newgeometry.7.2 Test Specimen PreparationDepending on the intendedapplication of the data, use one of the following test specimenpreparation procedures:7.2.1 Application-matched MachiningThe test
38、 specimenshall have the same surface preparation as that specified for acomponent. Unless the process is proprietary, the report shallbe specified about the stages of material removal, wheel grits,wheel bonding, and the amount of material removed per pass.7.2.2 Customary ProcedureIn instances where
39、a custom-ary machining procedure has been developed that is completelysatisfactory for a class of materials (that is, it induces nounwanted surface damage or residual stresses), then thisprocedure shall be used. It shall be fully specified in the report.7.2.3 Standard ProcedureIn instances where 7.2
40、.1 or7.2.2 are not appropriate, then 7.2.3 will apply. This procedurewill serve as the minimum requirements, but a more stringentprocedure may be necessary.7.2.3.1 Grinding ProcessAll grinding using diamond-gritwheels shall be done with an ample supply of appropriatefiltered coolant to keep workpiec
41、e and wheel constantlyflooded and particles flushed. Grinding shall be done in at leasttwo stages, ranging from coarse to fine rates of materialremoval. All machining shall be done in the surface grindingmode, and be parallel to the test specimen long axis (severaltest specimens are shown in the app
42、endix). Do not useBlanchard or rotary grinding.7.2.3.2 Material Removal RateThe material removal rateshall not exceed 0.03 mm (0.001 in.) per pass to the last 0.066Resolutions shall not be confused with accuracy. Beware of instruments thatreadout to 1C (resolution), but have an accuracy of only 10 K
43、 or12 % of full scale(12 %of1200Kis6K).7Temperature measuring instruments typically approximate the temperature-EMF tables, but with a few degrees of error.C1291 165mm (0.002 in.) per face. Final and intermediate finishing shallbe performed with a resinoid-bonded diamond grit wheel thatis between 32
44、0 and 600 grit. No less than 0.06 mm per faceshall be removed during the final finishing phase, and at a rateof not more than 0.002 mm (0.0001 in.) per pass. Removeapproximately equal stock from opposite faces.7.2.3.3 PrecautionMaterials with low fracture toughnessand a high susceptibility to grindi
45、ng damage may require finergrinding wheels at very low removal rates.7.2.3.4 ChamfersChamfers on the edges of the gagesection are preferred in order to minimize premature failuresdue to stress concentrations or slow crack growth. The use ofchamfers and their geometry shall be clearly indicated in th
46、etest report (see 10.1.1).7.2.4 Button-Head Test Specimen-Specific ProcedureBecause of the axial symmetry of the button-head tensile testspecimen, fabrication of the test specimens is generally con-ducted on a lathe-type apparatus. The bulk of the material isremoved in a circumferential grinding ope
47、ration with a final,longitudinal grinding operation performed in the gage sectionto ensure that any residual grinding marks are parallel to theapplied stress. Beyond the guidelines stated here, more specificdetails of recommended fabrication methods for cylindricaltensile test specimens can be found
48、 elsewhere (4).7.2.4.1 Computer Numerical Control (CNC) PrecautionGenerally CNC fabrication methods are necessary to obtainconsistent test specimens with the proper dimensions withinthe required tolerances. A necessary condition for this consis-tency is the complete fabrication of the test specimen
49、withoutremoving it from the grinding apparatus, thereby avoidingbuilding unacceptable tolerances into the finished test speci-men.7.2.4.2 Grinding WheelsFormed, resinoid-bonded,diamond-impregnated wheels (minimum 320 grit in a resinoidbond) are necessary to fabricate critical shapes (for example,button-head radius) and to minimize grinding vibrations andsubsurface damage in the test material. The formed, resin-bonded wheels require periodic dressing and shaping (truing),which can be done dynamically, to maintain th
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