1、Designation: C 1291 00a (Reapproved 2005)Standard Test Method forElevated Temperature Tensile Creep Strain, Creep StrainRate, and Creep Time-to-Failure for Advanced MonolithicCeramics1This standard is issued under the fixed designation C 1291; the number immediately following the designation indicat
2、es 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of
3、 tensilecreep strain, creep strain rate, and creep time-to-failure foradvanced monolithic ceramics at elevated temperatures, typi-cally between 1073 and 2073 K. A variety of specimengeometries are included. The creep strain at a fixed temperatureis evaluated from direct measurements of the gage leng
4、thextension over 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 macrosco
5、pically isotropic, 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 assump
6、tions. Continuous 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).1.4
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. Referenced Docu
8、ments2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE83 Practice for Verification and Classification of Exten-someter SystemE 139 Test Methods for Conducting Creep, Creep-Rupture,and Stress-Rupture Tests of Metallic
9、 MaterialsE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 220 Test Method for Calibration of Thermocouples byComparison TechniquesE 230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE 639 Test Method for Measuring Total-Radian
10、ce Tempera-ture of Heated Surfaces Using a Radiation PyrometerE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 1012 Practice for Verification of Specimen AlignmentUnder Tensile LoadingIEEE/ASTM SI 10 American National Standard for Use ofthe Internati
11、onal System of Units (SI): The Modern MetricSystem3. Terminology3.1 DefinitionsThe definitions of terms relating to creeptesting, which appear in Section E of Terminology E6shallapply to the terms used in this test method. For the purpose ofthis test method only, some of the more general terms are u
12、sedwith the restricted meanings given as follows.3.2 Definitions of Terms Specific to This Standard:3.2.1 axial strain, ea, nd, naverage of the strain mea-sured on diametrically opposed sides and equally distant fromthe specimen axis.3.2.2 bending strain, ebnd, ndifference between thestrain at the s
13、urface and the axial strain.3.2.2.1 DiscussionIn general, it varies from point to pointaround and along the gage length of the specimen. E 10123.2.3 creep-rupture test, ntest in which progressive speci-men deformation and the time-to-failure are measured. Ingeneral, deformation is greater than that
14、developed during acreep test.1This 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 June 1, 2005. Published June 2005. Originallyapproved in 1995. L
15、ast previous edition approved in 2000 as C 1291 00a.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 the standards Document Summary page onthe ASTM website.1Copyrigh
16、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4 creep strain, e, nd, ntime dependent strain thatoccurs after the application of load which is thereafter main-tained constant. Also known as engineering creep strain.3.2.5 creep test, ntes
17、t that has as its objective the mea-surement of creep and creep rates occurring at stresses usuallywell below those that would result in fast fracture.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, s, ntime
18、required for aspecimen to fracture under constant load as a result of creep.3.2.6.1 DiscussionThis is also known as creep rupturetime.3.2.7 gage length, l, m, noriginal distance betweenfiducial markers on or attached to the specimen for determiningelongation.3.2.8 maximum bending strain, ebmax, nd,
19、nlargestvalue of bending strain along the gage length. It can becalculated from measurements of strain at three circumferentialpositions at each of two different longitudinal positions.3.2.9 minimum creep strain rate, emin,s1, nminimumvalue of the strain rate prior to specimen failure as measuredfro
20、m the strain-time curve. The minimum creep strain rate maynot necessarily correspond to the steady-state creep strain rate.3.2.10 slow crack growth, n, m/s, nsubcritical crackgrowth (extension) which may result from, but is not restrictedto, such mechanisms as environmentally assisted stress corro-s
21、ion, diffusive crack growth, or other mechanisms.3.2.11 steady-state creep, ess, nd, nstage of creepwherein the creep rate is constant 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
22、.12.1 DiscussionSuch environmental effects com-monly include the action of moisture, as well as other corrosivespecies, often with a strong temperature dependence.3.2.13 tensile creep strain, et, nd, ncreep strain thatoccurs as a result of a uniaxial tensile-applied stress.4. Significance and Use4.1
23、 Creep tests measure the time-dependent deformationunder load at a given temperature, and, by implication, theload-carrying capability of the material for limited deforma-tions. Creep-rupture tests, properly interpreted, provide ameasure of the load-carrying capability of the material as afunction o
24、f time and temperature. The two tests complimenteach other in defining the load-carrying capability of a materialfor a given period of time. In selecting materials and designingparts for service at elevated temperatures, the type of test dataused will depend on the criteria for load-carrying capabil
25、itythat best defines the service usefulness of the material.4.2 This test method may be used for material development,quality assurance, characterization, and design data generation.4.3 High-strength, monolithic ceramic materials, generallycharacterized by small grain sizes (2K. It is preferable to
26、usefully sheathed thermocouples in order to minimize degrada-tion.6.5.3 Pyrometers:6.5.3.1 CalibrationThe pyrometer(s) must be calibratedin accordance with Test Method E 639.6.5.3.2 AccuracyThe measurement of temperature mustbe accurate to within 5 K. This shall include the error inherentto the pyro
27、meter and any error in the measuring instruments.5,66.6 Extensometers:6.6.1 The strain measuring equipment must be capable ofbeing used at elevated temperatures. The sensitivity andaccuracy of the strain-measuring equipment must be suitable todefine the creep characteristics with the precision requi
28、red forthe application of the data.6.6.2 CalibrationExtensometers must be calibrated inaccordance with Practice E83.6.6.3 AccuracyExtensometers with accuracies equivalentto the B-1 classification of extensometer systems specified inPractice E83are suitable for use in high-temperature testing ofceram
29、ics. Results of analytical and empirical evaluations atelevated temperatures show that mechanical extensometers(16) can meet these requirements. Optical extensometers usingflags have gage length uncertainties that will generally preventthem from achieving class B-1 accuracy (17). Empiricalevaluation
30、s at elevated temperature (18) show that theseextensometers can yield highly repeatable creep data, however.6.7 Timing ApparatusFor creep rupture tests, a timingapparatus capable of measuring the elapsed time betweencomplete application of the load and the time at which fractureof the specimen occur
31、s to within 1 % of the elapsed time shallbe employed.7. Test Specimens and Sample7.1 Specimen Size:7.1.1 DescriptionThe size and shape of test specimensmust be based on the requirements necessary to obtain repre-sentative samples of the material being investigated. Thespecimen geometry shall be such
32、 that there is no more than a5 % elastic stress concentration at the ends of the gage section.Typical shapes include square or rectangular cross-sectiondogbones and cylindrical button-head geometries, and areshown inAppendix X1. It is recommended, in accordance withTest Methods E 139 and in the abse
33、nce of additional informa-tion to the contrary, that the grip section be at least four timeslarger than the larger dimension of either width or thickness ofthe gage section.7.1.2 DimensionsSuggested dimensions for tensile creepspecimens that have been successfully used in previous inves-tigations ar
34、e given in Appendix X1. Cross-sectional tolerancesare 0.05 mm. Parallelism tolerances on the faces of thespecimen are 0.03 mm. Various radii of curvature may be usedto adjust the gage section or change the mounting configura-tion.Although these radii are expected to be larger, resulting ina smaller
35、stress concentration, wherever possible, resort shouldbe made to a finite element analysis to determine the locationsand intensities of stress concentrations in the new geometry.7.2 Specimen PreparationDepending on the intended ap-plication of the data, use one of the following specimenpreparation p
36、rocedures:7.2.1 Application-matched Machining The specimenmust have the same surface preparation as that specified for acomponent. Unless the process is proprietary, the report mustbe specified about the stages of material removal, wheel grits,wheel bonding, and the amount of material removed per pa
37、ss.7.2.2 Customary ProcedureIn instances where 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
38、.7.2.3 Standard ProcedureIn instances where 7.2.1 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 must be done with an ample supply o
39、f appropriatefiltered coolant to keep workpiece and wheel constantlyflooded and particles flushed. Grinding must be done in at leasttwo stages, ranging from coarse to fine rates of materialremoval. All machining must be done in the surface grindingmode, and be parallel to the specimen long axis (sev
40、eralspecimens are shown in the appendix). Do not use Blanchardor rotary grinding.7.2.3.2 Material Removal RateThe material removal ratemust not exceed 0.03 mm (0.001 in.) per pass to the last 0.06mm (0.002 in.) per face. Final and intermediate finishing mustbe performed with a resinoid-bonded diamon
41、d grit wheel thatis between 320 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
42、 high susceptibility to grinding 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 mu
43、st be clearly indicated in thetest report (see 10.1.1).7.2.4 Button-head Specimen-Specific ProcedureBecauseof the axial symmetry of the button-head tensile specimen,fabrication of the specimens is generally conducted on alathe-type apparatus. The bulk of the material is removed in acircumferential g
44、rinding operation with a final, longitudinalgrinding operation performed in the gage section to ensure thatany residual grinding marks are parallel to the applied stress.Beyond the guidelines stated here, more specific details ofrecommended fabrication methods for cylindrical tensile speci-mens can
45、be found elsewhere (4).7.2.4.1 Computer Numerical Control (CNC) PrecautionGenerally CNC fabrication methods are necessary to obtainconsistent specimens with the proper dimensions within therequired tolerances. A necessary condition for this consistencyis the complete fabrication of the specimen with
46、out removingC 1291 00a (2005)5it from the grinding apparatus, thereby avoiding buildingunacceptable tolerances into the finished specimen.7.2.4.2 Grinding WheelsFormed, resinoid-bonded,diamond-impregnated wheels (minimum 320 grit in a resinoidbond) are necessary to fabricate critical shapes (for exa
47、mple,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 the cutting anddimensional integrity.7.2.4.3 Subsurface DamageThe most ser
48、ious concern isnot necessarily the surface finish (on the order of Ra= 0.2 to 0.4m) which is the result of the final machining steps. Instead,the subsurface damage is critically important although thisdamage is not readily observed or measured, and therefore,must be inferred as the result of the gri
49、nding history. Moredetails of this aspect have been discussed in Ref. (4). In allcases, the final grinding operation (“spark out”) performed inthe gage section must be along the longitudinal axis of thespecimen to ensure that any residual grinding marks areparallel to the applied stress.7.2.5 Handling PrecautionsCare must be exercised instoring and handling of specimens to avoid the introduction ofrandom and severe flaws, such as might occur if the specimenswere allowed to impact or scratch each other. Specimensshould be
