1、Designation: C1211 13C1211 18Standard Test Method forFlexural Strength of Advanced Ceramics at ElevatedTemperatures1This standard is issued under the fixed designation C1211; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 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 determination of the flexural strength of advanced ceramics at elevated temperatures.2 Fou
3、r-point-14point -point and three-point loadings with prescribed spans are the standard as shown in Fig. 1. Rectangular specimens ofprescribed cross-section are used with specified features in prescribed specimen-fixture combinations. Test specimens may be 3 by4 by 45 to 50 mm in size that are tested
4、 on 40 mm 40-mm outer span four-point or three-point fixtures.Alternatively, test specimensand fixture spans half or twice these sizes may be used. The test method permits testing of machined or as-fired test specimens.Several options for machining preparation are included: application matched machi
5、ning, customary procedures, or a specifiedstandard procedure. This test method describes the apparatus, specimen requirements, test procedure, calculations, and reportingrequirements. The test method is applicable to monolithic or particulate- or whisker-reinforced ceramics. It may also be used forg
6、lasses. It is not applicable to continuous fiber-reinforced ceramic composites.1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.1 This test method is under the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is
7、 the direct responsibility of Subcommittee C28.01 on MechanicalProperties and Performance.Current edition approved Aug. 1, 2013Jan. 1, 2018. Published September 2013January 2018. Originally approved in 1992. Last previous edition approved in 20082013as C1211 02 (2008). 13. DOI: 10.1520/C1211-13.10.1
8、520/C1211-18.2 Elevated temperatures typically denote, but are not restricted to, 200 to 1600C.1600 C.NOTE 1Configuration:A: L = 20 mmB: L = 40 mmC: L = 80 mmFIG. 1 Four-Point-14 Point -Point and Three-Point Fixture ConfigurationsThis document is not an ASTM standard and is intended only to provide
9、the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the stan
10、dard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.3 This standard does not purport to address all of
11、the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was devel
12、oped in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documen
13、ts2.1 ASTM Standards:3C1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient TemperatureC1239 Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced CeramicsC1322 Practice for Fractography and Characterization of Fracture Origins in
14、 Advanced CeramicsC1341 Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic CompositesC1368 Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-RateStrength Testing at Ambient TemperatureC1465 Test Method for Determina
15、tion of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-RateFlexural Testing at Elevated TemperaturesE4 Practices for Force Verification of Testing MachinesE220 Test Method for Calibration of Thermocouples By Comparison TechniquesE230 Specification and Temperature-Electromotive
16、Force (EMF) Tables for Standardized Thermocouples3. Terminology3.1 Definitions:3.1.1 complete gage section, nthe portion of the specimen between the two outer bearings in four-point flexure and three-pointflexure fixtures.NOTE 1In this standard, the complete four-point flexure gage section is twice
17、the size of the inner gage section. Weibull statistical analyses, in thisinstance, only include portions of the specimen volume or surface which experience tensile stresses.3.1.2 flexural strengthstrength, FL2, na measure of the ultimate strength of a specified beam in bending.3.1.3 four-point-1/4fo
18、ur-point-14 point-point flexure, flexurena configuration of flexural strength testing in which aspecimen is symmetrically loaded at two locations that are situated at one-quarter of the overall span, away from the outer twosupport bearings (see Fig. 1).3.1.4 fully-articulating fully articulating fix
19、ture, na flexure fixture designed to be used either with flat and parallel specimensor with uneven or nonparallel specimens. The fixture allows full independent articulation, or pivoting, of all rollers about thespecimen long axis to match the specimen surface. In addition, the upper or lower pairs
20、are free to pivot to distribute force evenlyto the bearing cylinders on either side.NOTE 2See Annex A1 for schematic illustrations of the required pivoting movements.NOTE 3A three-point fixture has the inner pair of bearing cylinders replaced by a single bearing cylinder.3.1.5 inert flexural strengt
21、h, FL2, na measure of the strength of a specified beam specimen in bending as determined in anappropriate inert condition whereby no slow crack growth occurs.3.1.6 inherent flexural strength, FL2, nthe flexural strength of a material in the absence of any effect of surface grindingor other surface f
22、inishing process, or of extraneous damage that may be present. The measured inherent strength is in general afunction of the flexure test method, test conditions, and test specimen size.3.1.7 inner gage section, nthe portion of the specimen between the inner two bearings in a four-point flexure fixt
23、ure.3.1.8 semi-articulating fixture, na flexure fixture designed to be used with flat and parallel specimens. The fixture allows somearticulation, or pivoting, to ensure the top pair (or bottom pair) of bearing cylinders pivot together about an axis parallel to thespecimen long axis, in order to mat
24、ch the specimen surfaces. In addition, the upper or lower pairs are free to pivot to distributeforce evenly to the bearing cylinders on either side.NOTE 4See Annex A1 for schematic illustrations of the required pivoting movements.NOTE 5A three-point fixture has the inner pair of bearing cylinders re
25、placed by a single bearing cylinder.3.1.9 slow crack growth (SCG), nSubcriticalsubcritical crack growth (extension) which may result from, but is not restrictedto, such mechanisms as environmentally-assisted environmentally assisted stress corrosion or diffusive crack growth.3.1.10 three-point flexu
26、reflexure, na configuration of flexural strength testing in which a specimen is loaded at a positionmidway between two support bearings (see Fig. 1).3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standa
27、rdsvolume information, refer to the standards Document Summary page on the ASTM website.C1211 1824. Significance and Use4.1 This test method may be used for material development, quality control, characterization, and design data generationpurposes. This test method is intended to be used with ceram
28、ics whose flexural strength is ; 50 MPa (; 7 ;50 MPa (;7 ksi)or greater.4.2 The flexure stress is computed based on simple beam theory, with assumptions that the material is isotropic andhomogeneous, the moduli of elasticity in tension and compression are identical, and the material is linearly elas
29、tic. The averagegrain size should be no greater than 150 of the beam thickness. The homogeneity and isotropy assumptions in the test method ruleout the use of it for continuous fiber-reinforced composites for which Test Method C1341 is more appropriate.4.3 The flexural strength of a group of test sp
30、ecimens is influenced by several parameters associated with the test procedure.Such factors include the testing rate, test environment, specimen size, specimen preparation, and test fixtures. Specimen and fixturesizes were chosen to provide a balance between the practical configurations and resultin
31、g errors as discussed in Test MethodC1161, and Refs (1-3).4 Specific fixture and specimen configurations were designated in order to permit the ready comparison ofdata without the need for Weibull size scaling.4.4 The flexural strength of a ceramic material is dependent on both its inherent resistan
32、ce to fracture and the size and severityof flaws. Variations in these cause a natural scatter in test results for a sample of test specimens. Fractographic analysis of fracturesurfaces, although beyond the scope of this test method, is highly recommended for all purposes, especially if the data will
33、 be usedfor design as discussed in Ref (4) and Practices C1322 and C1239.4.5 This method determines the flexural strength at elevated temperature and ambient environmental conditions at a nominal,moderately fast testing rate. The flexural strength under these conditions may or may not necessarily be
34、 the inert flexural strength.Flexure strength at elevated temperature may be strongly dependent on testing rate, a consequence of creep, stress corrosion, orslow crack growth. If the purpose of the test is to measure the inert flexural strength, then extra precautions are required and fastertesting
35、rates may be necessary.NOTE 6Many ceramics are susceptible to either environmentally-assisted environmentally assisted slow crack growth or thermally activated slowcrack growth. Oxide ceramics, glasses, glass ceramics, and ceramics containing boundary phase glass are particularly susceptible to slow
36、 crack growth.Time dependent Time-dependent effects that are caused by environmental factors (for example, water as humidity in air) may be minimized through theuse of inert testing atmosphere such as dry nitrogen gas or vacuum. Alternatively, testing rates faster than specified in this standard may
37、 be used if thegoal is to measure the inert strength. Thermally activated slow crack growth may occur at elevated temperature even in inert atmospheres. Testing ratesfaster than specified in this standard should be used if the goal is to measure the inert flexural strength. On the other hand, many c
38、eramics such as boroncarbide, silicon carbide, aluminum nitride, and many silicon nitrides have no sensitivity to slow crack growth at room or moderately elevated temperaturesand for such materials, the flexural strength measured under in laboratory ambient conditions at the nominal testing rate is
39、the inert flexural strength.4.6 The three-point test configuration exposes only a very small portion of the specimen to the maximum stress. Therefore,three-point flexural strengths are likely to be much greater than four-point flexural strengths. Three-point flexure has someadvantages. It uses simpl
40、er test fixtures, it is easier to adapt to high temperature, and it is sometimes helpful in Weibull statisticalstudies. However, four-point flexure is preferred and recommended for most characterization purposes.4.7 The three-point test configuration exposes only a very small portion of the specimen
41、 to the maximum stress. Therefore,three-point flexural strengths are likely to be much greater than four-point flexural strengths. Three-point flexure has someadvantages. It uses simpler test fixtures, it is easier to adapt to high temperature, and it is sometimes helpful in Weibull statisticalstudi
42、es. However, four-point flexure is preferred and recommended for most characterization purposes.5. Interferences5.1 Time-dependent phenomena, such as stress corrosion and slow crack growth, can interfere with determination of the flexuralstrength at room and elevated temperatures. Creep phenomena al
43、so become significant at elevated temperatures. Creep deformationcan cause stress relaxation in a flexure specimen during a strength test, thereby causing the elastic formulation that is used tocompute the strength to be in error.5.2 Surface preparation of the test specimens can introduce machining
44、damage such as microcracks that may have a pronouncedeffect on flexural strength. Machining damage imposed during specimen preparation can be either a random interfering factor oran inherent part of the strength characteristic to be measured. With proper care and good machining practice, it is possi
45、ble to obtainfractures from the materials natural flaws. Surface preparation can also lead to residual stresses. Universal or standardized testmethods of surface preparation do not exist. It should be understood that final machining steps may or may not negate machiningdamage introduced during the e
46、arly coarse or intermediate machining.5.3 Slow crack growth can lead to a rate dependency of flexural strength. The testing rate specified in this standard may or maynot produce the inert flexural strength whereby negligible slow crack growth occurs. See Test MethodMethods C1368, and C1465,and Ref (
47、5) for more information about possible rate dependencies of flexural strength and methodologies for quantifying the ratesensitivity4 The boldface numbers in parentheses refer to the list of references at the end of the text.C1211 1836. Apparatus6.1 LoadingSpecimens may be force in any suitable testi
48、ng machine provided that uniform rates of direct loading can bemaintained. The force measuring system shall be free of initial lag at the loading rates used and shall be equipped with a meansfor retaining readout of the maximum force as well as a force-time or force-deflection record. The accuracy o
49、f the testing machineshall be in accordance with Practices E4.56.2 Four-Point Flexure Four-PoinFour-Point-14-Point Fixtures 14 Point Fixtures (Fig. 1), having support spans as given inTable 1.6.3 Three-Point Flexure Three-Point Fixtures (Fig. 1), having a support span as given in Table 1.6.4 Bearings, three-Three- and four-point flexure.6.4.1 Cylindrical bearings shall be used for support of the test specimen and for load application. The cylinders may be madeof a ceramic with an elastic modulus between 200 and 400 GPa (30 to 60 106 ps
