1、Designation: C1161 18Standard 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 revision, the year of last r
2、evision. 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 U.S. Department of Defense.1. Scope1.1 This test method covers the determinat
3、ion of flexuralstrength of advanced ceramic materials at ambient temperature.Four-point-14-point and three-point loadings with prescribedspans are the standard as shown in Fig. 1. Rectangularspecimens of prescribed cross-section sizes are used withspecified features in prescribed specimen-fixture co
4、mbinations.Test specimens may be 3 by 4 by 45 to 50 mm in size that aretested on 40-mm outer span four-point or three-point fixtures.Alternatively, test specimens and fixture spans half or twicethese sizes may be used. The method permits testing ofmachined or as-fired test specimens. Several options
5、 formachining preparation are included: application matchedmachining, customary procedure, or a specified standard pro-cedure. This method describes the apparatus, specimenrequirements, test procedure, calculations, and reporting re-quirements. The test method is applicable to monolithic orparticula
6、te- or whisker-reinforced ceramics. It may also beused for glasses. It is not applicable to continuous fiber-reinforced ceramic composites.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 t
7、o 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, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was
8、 developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Reference
9、d Documents2.1 ASTM Standards:2C1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distribution Parameters for AdvancedCeramicsC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsC1368 Test Method for Determination of Slow CrackGrowth Par
10、ameters of Advanced Ceramics by ConstantStress Rate Strength Testing at Ambient TemperatureE4 Practices for Force Verification of Testing MachinesE337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)2.2 Military Standard:3MIL-STD-1942(MR) F
11、lexural Strength of High Perfor-mance Ceramics at Ambient Temperature3. Terminology3.1 Definitions:3.1.1 complete gage section, nthe portion of the specimenbetween the two outer bearings in four-point flexure andthree-point flexure fixtures.NOTE 1In this standard, the complete four-point flexure gag
12、e sectionis twice the size of the inner gage section. Weibull statistical analysis onlyincludes portions of the specimen volume or surface which experiencetensile stresses.3.1.2 flexural strength, FL2, na measure of the ultimatestrength of a specified beam in bending.3.1.3 four-point-14-point flexur
13、e, nconfiguration of flex-ural strength testing where a specimen is symmetrically loadedat two locations that are situated one-quarter of the overall spanaway from the outer two support bearings (see Fig. 1).1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is
14、 the direct responsibility of Subcommittee C28.01 onMechanical Properties and Performance.Current edition approved Jan. 1, 2018. Published February 2018. Originallyapproved in 1990. Last previous edition approved in 2013 as C1161 13. DOI:10.1520/C1161-18.2For referenced ASTM standards, visit the AST
15、M 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 Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philade
16、lphia, PA 19111-5098, http:/www.dodssp.daps.mil.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the De
17、cision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.4 fully articulating fixture, na flexure fixture designedto be used either with flat and parallel specimens or withun
18、even or nonparallel specimens. The fixture allows fullindependent articulation, or pivoting, of all rollers about thespecimen long axis to match 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 An
19、nex A1 for schematic illustrations of the requiredpivoting movements.NOTE 3A three-point fixture has the inner pair of bearing cylindersreplaced by a single bearing cylinder.3.1.5 inert flexural strength, FL2, na measure of thestrength of specified beam in bending as determined in anappropriate iner
20、t condition whereby no slow crack growthoccurs.NOTE 4An inert condition may be obtained by using vacuum, lowtemperatures, very fast test rates, or any inert media.3.1.6 inherent flexural strength, FL2, nthe flexuralstrength of a material in the absence of any effect of surfacegrinding or other surfa
21、ce finishing process, or of extraneousdamage that may be present. The measured inherent strength isin general a function of the flexure test method, test conditions,and test specimen size.3.1.7 inner gage section, nthe portion of the specimenbetween the inner two bearings in a four-point flexure fix
22、ture.3.1.8 semi-articulating fixture, na flexure 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 matc
23、h the specimensurfaces. In addition, the upper 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 cylindersreplace
24、d by 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 ordiffusive crack growth.3.1.10 three-point flexure, nconfiguration of flexuralstrength test
25、ing where a specimen is loaded at a locationmidway 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 ceramicswho
26、se strength is 50 MPa (7 ksi) or greater.4.2 The 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 shoul
27、d be no greater than one-fiftieth of thebeam thickness. 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
28、. Such factors include the loading rate, testenvironment, specimen size, specimen preparation, and testfixtures. Specimen sizes and fixtures were chosen to provide abalance between practical configurations and resulting errors,as discussed in MIL-STD-1942(MR) and Refs (1, 2).4Specificfixture and spe
29、cimen configurations were designated 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 sca
30、tter intest results for a sample of test 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 (2-5) and Practices C1322 and C12
31、39.4.5 The three-point test configuration exposes only a verysmall portion of the specimen to the maximum stress.Therefore, three-point flexural strengths are likely to be muchgreater than four-point flexural strengths. Three-point flexurehas some advantages. It uses simpler test fixtures, it is eas
32、ier toadapt to high temperature and fracture toughness testing, and itis sometimes helpful in Weibull statistical studies. However,4The 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-Point-
33、14-Point and Three-Point Fixture Configura-tionC1161 182four-point flexure is preferred and recommended for mostcharacterization purposes.4.6 This method determines the flexural strength at ambienttemperature and environmental conditions. The flexuralstrength under ambient conditions may or may not
34、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 ceramics, glasses, and ceramics containing
35、 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 boron carbide, silicon carbide, aluminumni
36、tride, 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 stresscorrosion or slow crack growth on strength
37、tests conducted atambient temperature, can be meaningful even for the relativelyshort times involved during testing. Such influences must beconsidered if flexure tests are to be used to generate designdata. Slow crack growth can lead a rate dependency of flexuralstrength. The testing rate specified
38、in this standard may or maynot produce the inert flexural strength whereby negligible slowcrack growth occurs. See Test Method C1368.5.2 Surface preparation of test specimens can introducemachining microcracks which may have a pronounced effecton flexural strength. Machining damage imposed during sp
39、eci-men preparation can be either a random interfering factor, or aninherent part of the strength characteristic to be measured.Withproper care and good machining practice, it is possible toobtain fractures from the materials natural flaws. Surfacepreparation can also lead to residual stresses. Univ
40、ersal orstandardized test methods of surface preparation do not exist. Itshould be understood that final machining steps may or maynot negate machining damage introduced during the earlycourse or intermediate machining.5.3 This test method allows several options for the machin-ing of specimens, and
41、includes a general procedure (“Stan-dard” procedure, 7.2.4), which is satisfactory for many (butcertainly not all) ceramics. The general procedure used pro-gressively finer longitudinal grinding steps that are designed tominimize subsurface microcracking. Longitudinal grindingaligns the most severe
42、subsurface microcracks parallel to thespecimen tension stress axis. This allows a greater opportunityto measure the inherent flexural strength or “potential strength”of the material as controlled by the materials natural flaws. Incontrast, transverse grinding aligns the severest subsurfacemachining
43、microcracks perpendicular to the tension stress axisand the specimen is more likely to fracture from the machiningmicrocracks. Transverse-ground specimens in many instancesmay provide a more “practical strength” that is relevant tomachined ceramic components whereby it may not be possibleto favorabl
44、y align the machining direction. Transverse-groundspecimens may be tested in accordance with 7.2.2. Data fromtransverse-ground specimens may correlate better with datafrom biaxial disk or plate strength tests, wherein machiningdirection cannot be aligned.6. Apparatus6.1 LoadingSpecimens may be loade
45、d in any suitabletesting machine provided that uniform rates of direct loadingcan be maintained. The force measuring system shall be free ofinitial lag 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
46、testing machine shall be inaccordance with Practices E4 but within 0.5 %.6.2 Four-Point FlexureFour-point-14-point fixtures (Fig.1) shall have support and 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 BearingsT
47、hree- 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. Thecylinders 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). Alternat
48、ively, the cylinders may bemade of a ceramic with an elastic modulus between 2.0 and 4.0105MPa (30 to 60 106psi) and a flexural strength no lessthan 275 MPa (;40 ksi). The portions of the test fixture thatsupport the bearings may need to be hardened to preventpermanent deformation. The cylindrical b
49、earing length shall beat least three times the specimen width. The above require-ments are intended to ensure that ceramics with strengths up to1400 MPa (;200 ksi) and elastic moduli as high as 4.8 105MPa (70 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 Table 2.6.4.3 The bearing cylinders shall be carefully positionedsuch that the spans are accura
