1、Designation: C 1161 02c (Reapproved 2008)Standard Test Method forFlexural Strength of Advanced Ceramics at AmbientTemperature1This standard is issued under the fixed designation C 1161; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method cove
3、rs the determination of flexuralstrength of advanced ceramic materials at ambient temperature.Four-point14 point and three-point loadings with prescribedspans are the standard. Rectangular specimens of prescribedcross-section sizes are used with specified features in pre-scribed specimen-fixture com
4、binations.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 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 est
5、ablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesC 1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distrib
6、ution Parameters for AdvancedCeramicsC 1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC 1368 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Flexural Testing at Ambient TemperatureE 337 Test Method f
7、or Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)2.2 Military Standard:MIL-STD-1942 (MR) Flexural Strength of High Perfor-mance Ceramics at Ambient Temperature33. Terminology3.1 Definitions:3.1.1 complete gage section, nthe portion of the specimenbetween
8、 the two outer bearings in four-point flexure andthree-point flexure fixtures.NOTE 1In this standard, the complete four-point flexure gage sectionis twice the size of the inner gage section. Weibull statistical analysis onlyincludes portions of the specimen volume or surface which experiencetensile
9、stresses.3.1.2 flexural strengtha measure of the ultimate strengthof a specified beam in bending.3.1.3 four-point14 point flexureconfiguration of flexuralstrength testing where a specimen is symmetrically loaded attwo locations that are situated one quarter of the overall span,away from the outer tw
10、o support bearings (see Fig. 1).3.1.4 Fully-articulating fixture, na flexure fixture de-signed to be used either with flat and parallel specimens or withuneven or nonparallel specimens. The fixture allows fullindependent articulation, or pivoting, of all rollers about thespecimen long axis to match
11、the specimen surface. In addition,the upper or lower pairs are free to pivot to distribute forceevenly to the bearing cylinders on either side.NOTE 2See Annex A1 for schematic illustrations of the requiredpivoting movements.NOTE 3A three-point fixture has the inner pair of bearing cylindersreplaced
12、by a single bearing cylinder.3.1.5 inert flexural strength, na measure of the strength ofspecified beam in bending as determined in an appropriate inertcondition whereby no slow crack growth occurs.NOTE 4An inert condition may be obtained by using vacuum, lowtemperatures, very fast test rates, or an
13、y inert media.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 Jan. 1, 2008. Published January 2008. Originallyapproved in 1990. Last previous
14、 edition approved in 2002 as C 116102ce1.2For 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.3Available from Stan
15、dardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http:/www.dodssp.daps.mil.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Copyright by ASTM Intl (all rights reserved); Mon S
16、ep 15 23:15:50 EDT 2008Downloaded/printed byGuo Dehua (CNIS) pursuant to License Agreement. No further reproductions authorized.3.1.6 inherent flexural strength, nthe flexural strength of amaterial in the absence of any effect of surface grinding orother surface finishing process, or of extraneous d
17、amage thatmay be present. The measured inherent strength is in general afunction of the flexure test method, test conditions, andspecimen size.3.1.7 inner gage section, nthe portion of the specimenbetween the inner two bearings in a four-point flexure fixture.3.1.8 Semi-articulating fixture, na flex
18、ure fixture designedto be used with flat and parallel specimens. The fixture allowssome articulation, or pivoting, to ensure the top pair (or bottompair) of bearing cylinders pivot together about an axis parallelto the specimen long axis, in order to match the specimensurfaces. In addition, the uppe
19、r or lower pairs are free to pivotto distribute force evenly to the bearing cylinders on eitherside.NOTE 5See Annex A1 for schematic illustrations of the requiredpivoting movements.NOTE 6A three-point fixture has the inner pair of bearing cylindersreplaced by a single bearing cylinder.3.1.9 slow cra
20、ck growth (SCG), nsubcritical crack growth(extension) which may result from, but is not restricted to, suchmechanisms as environmentally-assisted stress corrosion ordiffusive crack growth.3.1.10 three-point flexureconfiguration of flexuralstrength testing where a specimen is loaded at a locationmidw
21、ay between two support bearings (see Fig. 1).4. 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 ceramicswhose strength is 50 MPa (7 ksi) or greater.4.2 Th
22、e flexure stress is computed based on simple beamtheory with assumptions that the material is isotropic andhomogeneous, the moduli of elasticity in tension and compres-sion are identical, and the material is linearly elastic. Theaverage grain size should be no greater than one fiftieth of thebeam th
23、ickness. The homogeneity and isotropy assumption inthe standard rule out the use of this test for continuousfiber-reinforced ceramics.4.3 Flexural strength of a group of test specimens isinfluenced by several parameters associated with the testprocedure. Such factors include the loading rate, test e
24、nviron-ment, specimen size, specimen preparation, and test fixtures.Specimen sizes and fixtures were chosen to provide a balancebetween practical configurations and resulting errors, as dis-cussed in MIL-STD 1942 (MR) and Refs (1) and (2).4Specificfixture and specimen configurations were designated
25、in order topermit ready comparison of data without the need for Weibull-size scaling.4.4 The flexural strength of a ceramic material is dependenton both its inherent resistance to fracture and the size andseverity of flaws. Variations in these cause a natural scatter intest results for a sample of t
26、est specimens. Fractographicanalysis of fracture surfaces, although beyond the scope of thisstandard, is highly recommended for all purposes, especially ifthe data will be used for design as discussed in MIL-STD-1942(MR) and Refs (25) and Practices C 1322 and C 1239.4.5 The three-point test configur
27、ation exposes only a verysmall portion of the specimen to the maximum stress. There-fore, three-point flexural strengths are likely to be much greaterthan four-point flexural strengths. Three-point flexure has someadvantages. It uses simpler test fixtures, it is easier to adapt tohigh temperature an
28、d fracture toughness testing, and it issometimes helpful in Weibull statistical studies. However,four-point flexure is preferred and recommended for mostcharacterization purposes.4.6 This method determines the flexural strength at ambienttemperature and environmental conditions. The flexuralstrength
29、 under ambient conditions may or may not necessarilybe the inert flexural strength.NOTE 7time dependent effects may be minimized through the use ofinert testing atmosphere such as dry nitrogen gas, oil, or vacuum.Alternatively, testing rates faster than specified in this standard may beused. Oxide c
30、eramics, glasses, and ceramics containing boundary phaseglass are susceptible to slow crack growth even at room temperature.Water, either in the form of liquid or as humidity in air, can have asignificant effect, even at the rates specified in this standard. On the otherhand, many ceramics such as b
31、oron carbide, silicon carbide, aluminumnitride and many silicon nitrides have no sensitivity to slow crack growthat room temperature and the flexural strength in laboratory ambientconditions is the inert flexural strength.5. Interferences5.1 The effects of time-dependent phenomena, such as stresscor
32、rosion or slow crack growth on strength tests conducted at4The boldface numbers in parentheses refer to the references at the end of thistest method.NOTE 1Configuration:A: L = 20 mmB: L = 40 mmC: L = 80 mmFIG. 1 The Four-Point14 Point and Three-Point FixtureConfigurationC 1161 02c (2008)2Copyright b
33、y ASTM Intl (all rights reserved); Mon Sep 15 23:15:50 EDT 2008Downloaded/printed byGuo Dehua (CNIS) pursuant to License Agreement. No further reproductions authorized.ambient temperature, can be meaningful even for the relativelyshort times involved during testing. Such influences must beconsidered
34、 if flexure tests are to be used to generate designdata. Slow crack growth can lead a rate dependency of flexuralstrength. The testing rate specifed in this standard may or maynot produce the inert flexural strength whereby negligible slowcrack growth occurs. See Test Method C 1368.5.2 Surface prepa
35、ration of test specimens can introducemachining microcracks which may have a pronounced effecton flexural strength. Machining damage imposed during speci-men preparation can be either a random interfering factor, or aninherent part of the strength characteristic to be measured.Withproper care and go
36、od machining practice, it is possible toobtain fractures from the materials natural flaws. Surfacepreparation can also lead to residual stresses. Universal orstandardized test methods of surface preparation do not exist. Itshould be understood that final machining steps may or maynot negate machinin
37、g damage introduced during the earlycourse or intermediate machining.5.3 This test method allows several options for the machin-ing of specimens, and includes a general procedure (“Stan-dard” procedure, 7.2.4), which is satisfactory for many (butcertainly not all) ceramics. The general procedure use
38、d pro-gressively finer longitudinal grinding steps that are designed tominimize subsurface microcracking. Longitudinal grindingaligns the most severe subsurface microcracks parallel to thespecimen tension stress axis. This allows a greater opportunityto measure the inherent flexural strength or “pot
39、ential strength”of the material as controlled by the materials natural flaws. Incontrast, transverse grinding aligns the severest subsurfacemachining microcracks perpendicular to the tension stress axisand the specimen is more likely to fracture from the machiningmicrocracks. Transverse-ground speci
40、mens in many instancesmay provide a more “practical strength” that is relevant tomachined ceramic components whereby it may not be possibleto favorably align the machining direction. Transverse-groundspecimens may be tested in accordance with 7.2.2. Data fromtransverse-ground specimens may correlate
41、 better with datafrom biaxial disk or plate strength tests, wherein machiningdirection cannot be aligned.6. Apparatus6.1 LoadingSpecimens may be loaded in any suitabletesting machine provided that uniform rates of direct loadingcan be maintained. The force-measuring system shall be free ofinitial la
42、g at the loading rates used and shall be equipped witha means for retaining read-out of the maximum force applied tothe specimen. The accuracy of the testing machine shall be inaccordance with Practices E4but within 0.5 %.6.2 Four-Point FlexureFour-point14 point fixtures (Fig.1) shall have support a
43、nd loading spans as shown in Table 1.6.3 Three-Point FlexureThree-point fixtures (Fig. 1) shallhave a support span as shown in Table 1.6.4 BearingsThree- and four-point flexure:6.4.1 Cylindrical bearing edges shall be used for the supportof the test specimen and for the application of load. Thecylin
44、ders shall be made of hardened steel which has a hardnessno less than HRC 40 or which has a yield strength no less than1240 MPa (;180 ksi). Alternatively, the cylinders may bemade of a ceramic with an elastic modulus between 2.0 and 4.03 105MPa (3060 3 106psi) and a flexural strength no lessthan 275
45、 MPa (;40 ksi). The portions of the test fixture thatsupport the bearings may need to be hardened to preventpermanent deformation. The cylindrical bearing length shall beat least three times the specimen width. The above require-ments are intended to ensure that ceramics with strengths up to1400 MPa
46、 (;200 ksi) and elastic moduli as high as 4.8 3 105MPa (70 3 106psi) can be tested without fixture damage.Higher strength and stiffer ceramic specimens may requireharder bearings.6.4.2 The bearing cylinder diameter shall be approximately1.5 times the beam depth of the test specimen size employed.See
47、 Table 2.6.4.3 The bearing cylinders shall be carefully positionedsuch that the spans are accurate within 60.10 mm. The loadapplication bearing for the three-point configurations shall bepositioned midway between the support bearing within 60.10mm. The load application (inner) bearings for the four-
48、pointconfigurations shall be centered with respect to the support(outer) bearings within 60.10 mm.6.4.4 The bearing cylinders shall be free to rotate in order torelieve frictional constraints (with the exception of the middle-load bearing in three-point flexure which need not rotate). Thiscan be acc
49、omplished by mounting the cylinders in needlebearing assemblies, or more simply by mounting the cylindersas shown in Fig. 2 and Fig. 3. Annex A1 illustrates the actionrequired of the bearing cylinders. Note that the outer-supportbearings roll outward and the inner-loading bearings rollinward.6.5 SemiarticulatingFour-Point FixtureSpecimens pre-pared in accordance with the parallelism requirements of 7.1may be tested in a semiarticulating fixture as illustrated in Fig.2 and in Fig. A1.1a. All four bearings shall be free to roll. Thetwo inner beari
