1、Designation: C1211 02 (Reapproved 2008)C1211 13Standard 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
2、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 determination of the flexural strength of advanced ceramics at elevated
3、temperatures.2 Four-point-14point and three-point loadings with prescribed spans are the standard. 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
4、 size that are tested on 40 mm outer span four-point or three-point fixtures. Alternatively, test specimens andfixture spans half or twice these sizes may be used. The test method permits testing of machined or as-fired test specimens. Severaloptions for machining preparation are included: applicati
5、on matched machining, customary procedures, or a specified standardprocedure. 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 a
6、lso be used forglasses. 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
7、 Ceramics and is the direct responsibility of Subcommittee C28.01 on MechanicalProperties and Performance.Current edition approved Jan. 1, 2008Aug. 1, 2013. Published January 2008September 2013. Originally approved in 1992. Last previous edition approved in 19982008as C1211-98a. -02 (2008). DOI: 10.
8、1520/C1211-02R08.10.1520/C1211-13.2 Elevated temperatures typically denote, but are not restricted to 200 to 1600C.NOTE 1Configuration:A: L = 20 mmB: L = 40 mmC: L = 80 mmFIG. 1 Four-Point-14 Point and Three-Point Fixture ConfigurationsThis document is not an ASTM standard and is intended only to pr
9、ovide 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 th
10、e standard 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 a
11、ll of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C1161 Test Method for
12、 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 Advanced CeramicsC1341 Test Method for Fle
13、xural 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 Determination of Slow Crack Growth Parameters of Adv
14、anced 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 Force (EMF) Tables for Standardized Thermoc
15、ouples2.2 Military Standard:MIL-STD 1942(A) Flexural Strength of High Performance Ceramics at Ambient Temperature43. 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
16、 standard, the complete four-point flexure gage section is twice 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 strengtha measure of the ultimate strength of a
17、 specified beam in bending.3.1.3 four-point-1/4 point flexurea configuration of flexural strength testing in which a specimen is symmetrically loaded attwo locations that are situated at one-quarter of the overall span, away from the outer two support bearings (see Fig. 1).3.1.4 fully-articulating f
18、ixture, na flexure fixture designed to be used either with flat and parallel specimens or with unevenor nonparallel specimens. The fixture allows full independent articulation, or pivoting, of all rollers about the specimen long axisto match the specimen surface. In addition, the upper or lower pair
19、s are free to pivot to distribute force evenly to the bearingcylinders on either side.NOTE 2See Annex A2A1 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 str
20、ength, 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, nthe flexural strength of a material in the absence of any effect of surface grinding or othersurface finishi
21、ng process, or of extraneous damage that may be present. The measured inherent strength is in general a functionof the flexure test method, test conditions, and specimen size.3.1.7 inner gage section, nthe portion of the specimen between the inner two bearings in a four-point flexure fixture.3.1.8 s
22、emi-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 match the spec
23、imen 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 A2A1 for schematic illustrations of the required pivoting movements.NOTE 5A three-point fixture has the inner pair of bearing cylinders replaced by
24、 a single bearing cylinder.3.1.9 slow crack growth (SCG), nSubcritical crack growth (extension) which may result from, but is not restricted to, suchmechanisms as environmentally-assisted stress corrosion or diffusive crack growth.3.1.10 three-point flexurea configuration of flexural strength testin
25、g in which a specimen is loaded at a position midwaybetween 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 Standardsvolume information, refer to the standards Document
26、Summary page on the ASTM website.C1211 1324. 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 ceramics whose flexural strength is ; 50 MPa (; 7 ksi) or gr
27、eater.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 elastic. The averagegrain size should be no greater than 150 of the be
28、am 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 specimens is influenced by several parameters associated with the te
29、st 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 resulting errors as discussed in MIL-STD 1942(A),Test Method C1161, and Re
30、fs (1-3).4 Specific fixture and specimen configurations were designated in order to permit the readycomparison of data without the need for Weibull size scaling.4.4 The flexural strength of a ceramic material is dependent on both its inherent resistance to fracture and the size and severityof flaws.
31、 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 be usedfor design as discussed in MIL STD 1942 (
32、A) and 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 the inert flexural strength
33、.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 rates may be necessary.NOTE
34、6Many ceramics are susceptible to either environmentally-assisted slow crack growth or thermally activated slow crack growth. Oxideceramics, glasses, glass ceramics, and ceramics containing boundary phase glass are particularly susceptible to slow crack growth. Time dependent effectsthat are caused
35、by environmental factors (e.g. water as humidity in air) may be minimized through the use of inert testing atmosphere such as dry nitrogengas or vacuum.Alternatively, testing rates faster than specified in this standard may be used if the goal is to measure the inert strength.Thermally activatedslow
36、 crack growth may occur at elevated temperature even in inert atmospheres. Testing rates faster than specified in this standard should be used if thegoal is to measure the inert flexural strength. On the other hand, many ceramics such as boron carbide, silicon carbide, aluminum nitride and many sili
37、connitrides have no sensitivity to slow crack growth at room or moderately elevated temperatures and for such materials, the flexural strength measured underin laboratory ambient conditions at the nominal testing rate is the inert flexural strength.4.6 The three-point test configuration exposes only
38、 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 simpler test fixtures, it is easier to adapt to high temperature, and it is sometime
39、s 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 to the maximum stress. Therefore,three-point flexural strengths are likely to
40、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 statisticalstudies. However, four-point flexure is preferred and recommended for most character
41、ization 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 also become significant at elevated temperatures. Creep deformationcan cause stre
42、ss 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 damage such as microcracks that may have a pronouncedeffect on flexural strengt
43、h. 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 possible to obtainfractures from the materials natural flaws. Surface preparation ca
44、n 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 early coarse or intermediate machining.5.3 Slow crack growth can lead to a rate
45、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 Method C1368, C1465, and Ref (5)for more information about possible rate dependencies of flexural strength and methodol
46、ogies for quantifying the rate sensitivity4 The boldface numbers in parentheses refer to the list of references at the end of the text.C1211 1336. Apparatus6.1 LoadingSpecimens may be force in any suitable testing machine provided that uniform rates of direct loading can bemaintained. The force meas
47、uring 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 of the testing machineshall be in accordance with Practices E4.56.2 Four-Point Flexure Fou
48、r-Poin14 Point Fixtures (Fig. 1), having support spans as given in Table 1.6.3 Three-Point Flexure Three-Point Fixtures (Fig. 1), having a support span as given in Table 1.6.4 Bearings, three- and four-point flexure.6.4.1 Cylindrical bearings shall be used for support of the test specimen and for lo
49、ad application. The cylinders may be madeof a ceramic with an elastic modulus between 200 and 400 GPa (30 to 60 106 psi) and a flexural strength no less than 275 MPa(40 ksi). The loading cylinders must remain elastic (and have no plastic deformation) over the load and temperature ranges used,and they must not react chemically with or contaminate the test specimen. The test fixture shall also be made of a ceramic thatis resistant to permanent deformation.6.4.2 The bearing cylinder diameter shall be approximately 1.5 times the beam depth of the test speci
