1、Designation: C1161 02c (Reapproved 2008)1C1161 13Standard Test Method forFlexural Strength of Advanced Ceramics at AmbientTemperature1This standard is issued under the fixed designation C1161; 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.This standard has been approved for use by agencies of the Department of Defense.1 NOTEAdded research report
3、 footnote to Sections 11.3, 11.4, and 11.5 editorially in September 2008.1. Scope1.1 This test method covers the determination of flexural strength of advanced ceramic materials at ambient temperature.Four-point14 point and three-point loadings with prescribed spans are the standard. standard as sho
4、wn in Fig. 1. Rectangularspecimens of prescribed cross-section sizes are used with specified features in prescribed specimen-fixture combinations. Testspecimens may be 3 by 4 by 45 to 50 mm in size that are tested on 40 mm outer span four-point or three-point fixtures.Alternatively, test specimens a
5、nd fixture spans half or twice these sizes may be used. The method permits testing of machined oras-fired test specimens. Several options for machining preparation are included: application matched machining, customaryprocedure, or a specified standard procedure. This method describes the apparatus,
6、 specimen requirements, test procedure,calculations, and reporting requirements. The test method is applicable to monolithic or particulate- or whisker-reinforcedceramics. It may also be used for glasses. It is not applicable to continuous fiber-reinforced ceramic composites.1.2 The values stated in
7、 SI units are to be regarded as the standard. The values given in parentheses are for information only.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and h
8、ealth practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesC1239 Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Cera
9、micsC1322 Practice for Fractography and Characterization of Fracture Origins in Advanced CeramicsC1368 Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-RateStrength Testing at Ambient TemperatureE337 Test Method for Measuring Humidity with a Psych
10、rometer (the Measurement of Wet- and Dry-Bulb Temperatures)2.2 Military Standard:MIL-STD-1942 (MR) Flexural Strength of High Performance Ceramics at Ambient Temperature33. Terminology3.1 Definitions:3.1.1 complete gage section, nthe portion of the specimen between the two outer bearings in four-poin
11、t flexure and three-pointflexure fixtures.NOTE 1In this standard, the complete four-point flexure gage section is twice the size of the inner gage section. Weibull statistical analysis onlyincludes portions of the specimen volume or surface which experience tensile stresses.1 This test method is und
12、er the jurisdiction of ASTM Committee C28 on Advanced 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 1990. Last previous edition a
13、pproved in 20022008as C116102c (2008)1. DOI: 10.1520/C1161-02CR08E01. 10.1520/C1161-132 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 Summary
14、page on the ASTM website.3 Available from Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http:/www.dodssp.daps.mil.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of wha
15、t 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 standard as published by ASTM is to be considered the
16、 official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.2 flexural strengtha measure of the ultimate strength of a specified beam in bending.3.1.3 four-point14 point flexureconfiguration of flexural strength testing whe
17、re a specimen is symmetrically loaded at twolocations that are situated one quarter of the overall span, away from the outer two support bearings (see Fig. 1).3.1.4 Fully-articulating fixture, na flexure fixture designed to be used either with flat and parallel specimens or with unevenor nonparallel
18、 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 pairs are free to pivot to distribute force evenly to the bearingcylinders on either side.NOTE 2See Annex A1 for schema
19、tic 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 strength, na measure of the strength of specified beam in bending as determined in an appropriate inertcondition whereby
20、 no slow crack growth occurs.NOTE 4An inert condition may be obtained by using vacuum, low temperatures, very fast test rates, or any inert media.3.1.6 inherent flexural strength, nthe flexural strength of a material in the absence of any effect of surface grinding or othersurface finishing process,
21、 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 Semi-articul
22、ating 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 specimen surfac
23、es. In addition, the upper or lower pairs are free to pivot to distributeforce evenly to the bearing cylinders on either side.NOTE 5See Annex A1 for schematic illustrations of the required pivoting movements.NOTE 6A three-point fixture has the inner pair of bearing cylinders replaced by a single bea
24、ring 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 flexureconfiguration of flexural strength testing where a speci
25、men is loaded at a location midway betweentwo 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 ceramics whose strength is
26、 50 MPa (7 ksi) or greater.NOTE 1Configuration:A: L = 20 mmB: L = 40 mmC: L = 80 mmFIG. 1 The Four-Point14 Point and Three-Point Fixture ConfigurationC1161 1324.2 The flexure stress is computed based on simple beam theory with assumptions that the material is isotropic andhomogeneous, the moduli of
27、elasticity in tension and compression are identical, and the material is linearly elastic. The averagegrain size should be no greater than one fiftieth of the beam thickness. The homogeneity and isotropy assumption in the standardrule out the use of this test for continuous fiber-reinforced ceramics
28、.4.3 Flexural strength of a group of test specimens is influenced by several parameters associated with the test procedure. Suchfactors include the loading rate, test environment, specimen size, specimen preparation, and test fixtures. Specimen sizes andfixtures were chosen to provide a balance betw
29、een practical configurations and resulting errors, as discussed in MIL-STD 1942 (MR) and Refs (1) and (2).4 Specific fixture and specimen configurations were designated in order to permit readycomparison of data without the need for Weibull-size scaling.4.4 The flexural strength of a ceramic materia
30、l is dependent on both its inherent resistance 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 standard, is highly recommended for
31、all purposes, especially if the data will be usedfor design as discussed in MIL-STD-1942 (MR) and Refs (25) and Practices C1322 and C1239.4.5 The three-point test configuration exposes only a very small portion of the specimen to the maximum stress. Therefore,three-point flexural strengths are likel
32、y 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 fracture toughness testing, and it is sometimeshelpful in Weibull statistical studies. However, four-point flexure is preferre
33、d and recommended for most characterizationpurposes.4.6 This method determines the flexural strength at ambient temperature and environmental conditions. The flexural strengthunder ambient conditions may or may not necessarily be the inert flexural strength.NOTE 7time dependent effects may be minimi
34、zed through the use of inert testing atmosphere such as dry nitrogen gas, oil, or vacuum. Alternatively,testing rates faster than specified in this standard may be used. Oxide ceramics, glasses, and ceramics containing boundary phase glass are susceptibleto slow crack growth even at room temperature
35、. Water, either in the form of liquid or as humidity in air, can have a significant effect, even at the ratesspecified in this standard. On the other hand, many ceramics such as boron carbide, silicon carbide, aluminum nitride and many silicon nitrides have nosensitivity to slow crack growth at room
36、 temperature and the flexural strength in laboratory ambient conditions is the inert flexural strength.5. Interferences5.1 The effects of time-dependent phenomena, such as stress corrosion or slow crack growth on strength tests conducted atambient temperature, can be meaningful even for the relative
37、ly short times involved during testing. Such influences must beconsidered if flexure tests are to be used to generate design data. Slow crack growth can lead a rate dependency of flexural strength.The testing rate specifed in this standard may or may not produce the inert flexural strength whereby n
38、egligible slow crack growthoccurs. See Test Method C1368.5.2 Surface preparation of test specimens can introduce machining microcracks which may have a pronounced effect on flexuralstrength. Machining damage imposed during specimen preparation can be either a random interfering factor, or an inheren
39、t partof the strength characteristic to be measured. With proper care and good machining practice, it is possible to obtain fractures fromthe materials natural flaws. Surface preparation can also lead to residual stresses. Universal or standardized test methods of surfacepreparation do not exist. It
40、 should be understood that final machining steps may or may not negate machining damage introducedduring the early course or intermediate machining.5.3 This test method allows several options for the machining of specimens, and includes a general procedure (“Standard”procedure, 7.2.4), which is sati
41、sfactory for many (but certainly not all) ceramics. The general procedure used progressively finerlongitudinal grinding steps that are designed to minimize subsurface microcracking. Longitudinal grinding aligns the most severesubsurface microcracks parallel to the specimen tension stress axis. This
42、allows a greater opportunity to measure the inherentflexural strength or “potential strength” of the material as controlled by the materials natural flaws. In contrast, transverse grindingaligns the severest subsurface machining microcracks perpendicular to the tension stress axis and the specimen i
43、s more likely tofracture from the machining microcracks. Transverse-ground specimens in many instances may provide a more “practical strength”that is relevant to machined ceramic components whereby it may not be possible to favorably align the machining direction.Transverse-ground specimens may be t
44、ested in accordance with 7.2.2. Data from transverse-ground specimens may correlate betterwith data from biaxial disk or plate strength tests, wherein machining direction cannot be aligned.6. Apparatus6.1 LoadingSpecimens may be loaded in any suitable testing machine provided that uniform rates of d
45、irect 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 read-out of the maximum force applied to the specimen. The accuracy of the testing machine shall be in accordancewith Practices E4 but wit
46、hin 0.5 %.4 The boldface numbers in parentheses refer to the references at the end of this test method.C1161 1336.2 Four-Point FlexureFour-point14 point fixtures (Fig. 1) shall have support and loading spans as shown in Table 1.6.3 Three-Point FlexureThree-point fixtures (Fig. 1) shall have a suppor
47、t span as shown in Table 1.6.4 BearingsThree- and four-point flexure:6.4.1 Cylindrical bearing edges shall be used for the support of the test specimen and for the application of load. The cylindersshall be made of hardened steel which has a hardness no less than HRC 40 or which has a yield strength
48、 no less than 1240 MPa(;180 ksi).Alternatively, the cylinders may be made of a ceramic with an elastic modulus between 2.0 and 4.0 105 MPa (3060 106 psi) and a flexural strength no less than 275 MPa (;40 ksi). The portions of the test fixture that support the bearings mayneed to be hardened to preve
49、nt permanent deformation. The cylindrical bearing length shall be at least three times the specimenwidth. The above requirements are intended to ensure that ceramics with strengths up to 1400 MPa (;200 ksi) and elastic modulias high as 4.8 105 MPa (70 106 psi) can be tested without fixture damage. Higher strength and stiffer ceramic specimens mayrequire harder bearings.6.4.2 The bearing cylinder diameter shall be approximately 1.5 times the beam depth of the test specimen size employed. SeeTable 2.6.4.3 The bearing cylinders shall be
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