1、Designation: C 1499 08Standard Test Method forMonotonic Equibiaxial Flexural Strength of AdvancedCeramics at Ambient Temperature1This standard is issued under the fixed designation C 1499; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, 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 the determination of the equibi-axial strength of advanced ceramics at ambie
3、nt temperature viaconcentric ring configurations under monotonic uniaxial load-ing. In addition, test specimen fabrication methods, testingmodes, testing rates, allowable deflection, and data collectionand reporting procedures are addressed. Two types of testspecimens are considered: machined test s
4、pecimens and as-fired test specimens exhibiting a limited degree of warpage.Strength as used in this test method refers to the maximumstrength obtained under monotonic application of load. Mono-tonic loading refers to a test conducted at a constant rate in acontinuous fashion, with no reversals from
5、 test initiation tofinal fracture.1.2 This test method is intended primarily for use withadvanced ceramics that macroscopically exhibit isotropic,homogeneous, continuous behavior. While this test method isintended for use on monolithic advanced ceramics, certainwhisker- or particle-reinforced compos
6、ite ceramics as well ascertain discontinuous fiber-reinforced composite ceramics mayalso meet these macroscopic behavior assumptions. Generally,continuous fiber ceramic composites do not macroscopicallyexhibit isotropic, homogeneous, continuous behavior, and theapplication of this test method to the
7、se materials is notrecommended.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of
8、this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 1145 Terminology of Advanced CeramicsC 1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Dis
9、tribution Parameters for AdvancedCeramicsC 1259 Test Method for Dynamic Youngs Modulus, ShearModulus, and Poissons Ratio for Advanced Ceramics byImpulse Excitation of VibrationC 1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsE4 Practices for Force Verifica
10、tion of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE83 Practice for Verification and Classification of Exten-someter SystemsE 337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)F 394 Test Method for Biaxial Fl
11、exure Strength (Modulusof Rupture) of Ceramic Substrates (Discontinued 2001)3IEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI): The Modern Metric System3. Terminology3.1 DefinitionsThe definitions of terms relating to biaxialtesting appearing in Terminology E6and Terminology
12、C 1145may apply to the terms used in this test method. Pertinentdefinitions are listed below with the appropriate source given in1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 onMechanical Properties and P
13、erformance.Current edition approved Aug. 1, 2008. Published September 2008. Originallyapproved in 2001. Last previous edition approved in 2005 as C 1499 05.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AST
14、MStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.parentheses.Additional terms used in conjunction with this testmethod are defin
15、ed in the following section.3.1.1 advanced ceramic, nhighly engineered, high perfor-mance predominately non- metallic, inorganic, ceramic mate-rial having specific functional attributes. C 11453.1.2 breaking load, F, nload at which fracture occurs.E63.1.3 equibiaxial flexural strength, F/L2, nmaximu
16、mstress that a material is capable of sustaining when subjected toflexure between two concentric rings. This mode of flexure isa cupping of the circular plate caused by loading at the innerload ring and outer support ring. The equibiaxial flexuralstrength is calculated from the maximum-load of a bia
17、xial testcarried to rupture, the original dimensions of the test specimen,and Poissons ratio.3.1.4 homogeneous, ncondition of a material in which therelevant properties (composition, structure, density, etc.) areuniform, so that any smaller sample taken from an originalbody is representative of the
18、whole. Practically, as long as thegeometrical dimensions of a sample are large with respect tothe size of the individual grains, crystals, components, pores, ormicrocracks, the sample can be considered homogeneous.3.1.5 modulus of elasticity, F/L2, nratio of stress tocorresponding strain below the p
19、roportional limit. E63.1.6 Poissons ratio, nnegative value of the ratio oftransverse strain to the corresponding axial strain resultingfrom uniformly distributed axial stress below the proportionallimit of the material.4. Significance and Use4.1 This test method may be used for material development,
20、material comparison, quality assurance, characterization anddesign code or model verification.4.2 Engineering applications of ceramics frequently involvebiaxial tensile stresses. Generally, the resistance to equibiaxialflexure is the measure of the least flexural strength of amonolithic advanced cer
21、amic. The equibiaxial flexural strengthdistributions of ceramics are probabilistic and can be describedby a weakest link failure theory, (1, 2)4. Therefore, a sufficientnumber of test specimens at each testing condition is requiredfor statistical estimation or the equibiaxial strength.4.3 Equibiaxia
22、l strength tests provide information on thestrength and deformation of materials under multiple tensilestresses. Multiaxial stress states are required to effectivelyevaluate failure theories applicable to component design, andto efficiently sample surfaces that may exhibit anisotropic flawdistributi
23、ons. Equibiaxial tests also minimize the effects of testspecimen edge preparation as compared to uniaxial testsbecause the generated stresses are lowest at the test specimenedges.4.4 The test results of equibiaxial test specimens fabricatedto standardized dimensions from a particular material and/or
24、selected portions of a component may not totally represent thestrength properties in the entire, full-size component or itsin-service behavior in different environments.4.5 For quality control purposes, results derived from stan-dardized equibiaxial test specimens may be considered indica-tive of th
25、e response of the bulk material from which they weretaken for any given primary processing conditions and post-processing heat treatments or exposures.5. Interferences5.1 Test environment (vacuum, inert gas, ambient air, etc.)including moisture content (for example, relative humidity)may have an inf
26、luence on the measured equibiaxial strength.Testing to evaluate the maximum strength potential of amaterial can be conducted in inert environments and/or atsufficiently rapid testing rates so as to minimize any environ-mental effects. Conversely, testing can be conducted in envi-ronments, test modes
27、 and test rates representative of serviceconditions to evaluate material performance under use condi-tions.5.2 Fabrication of test specimens can introduce dimensionalvariations that may have pronounced effects on the measuredequibiaxial mechanical properties and behavior (for example,shape and level
28、 of the resulting stress-strain curve, equibiaxialstrength, failure location, etc.). Surface preparation can alsolead to the introduction of residual stresses and final machiningsteps might or might not negate machining damage introducedduring the initial machining. Therefore, as universal or stan-d
29、ardized methods of surface preparation do not exist, the testspecimen fabrication history should be reported. In addition,the nature of fabrication used for certain advanced ceramiccomponents may require testing of specimens with surfaces inthe as-fabricated condition (that is, it may not be possibl
30、e,desired or required to machine some of the test specimensurfaces directly in contact with the test fixture). For veryrough or wavy as-fabricated surfaces, perturbations in thestress state due to non-symmetric cross-sections as well asvariations in the cross-sectional dimensions may also interferew
31、ith the equibiaxial strength measurement. Finally, closegeometric tolerances, particularly in regard to flatness of testspecimen surfaces in contact with the test fixture componentsare critical requirements for successful equibiaxial tests. Insome cases it may be appropriate to use other test method
32、s (forexample, Test Method F 394).5.3 Contact and frictional stresses in equibiaxial tests canintroduce localized failure not representative of the equibiaxialstrength under ideal loading conditions. These effects mayresult in either over or under estimates of the actual strength (1,3).5.4 Fractures
33、 that consistently initiate near or just outsidethe load-ring may be due to factors such as friction or contactstresses introduced by the load fixtures, or via misalignment ofthe test specimen rings. Such fractures will normally constituteinvalid tests (see Note 14). Splitting of the test specimen a
34、longa diameter that expresses the characteristic size may resultfrom poor test specimen preparation (for example, severegrinding or very poor edge preparation), excessive tangentialstresses at the test specimen edges, or a very weak material.Such fractures will constitute invalid tests if failure oc
35、curredfrom the edge.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.C14990825.5 Deflections greater than one-quarter of the test specimenthickness can result in nonlinear behavior and stresses notaccounted for by simple plate theory.5.6 Warpage of the
36、test specimen can result in nonuniformloading and contact stresses that result in incorrect estimates ofthe test specimens actual equibiaxial strength. The test speci-men shall meet the flatness requirements (see 8.2 and 8.3)orbespecifically noted as warped and considered as a censored test.6. Appar
37、atus6.1 Testing MachinesMachines used for equibiaxial test-ing shall conform to the requirements of Practices E4. Theload cells used in determining equibiaxial strength shall beaccurate within 61 % at any load within the selected loadrange of the testing machine as defined in Practice E4. Checkthat
38、the expected breaking load for the desired test specimengeometry and test material is within the capacity of the testmachine and load cell. Advanced ceramic equibiaxial testspecimens require greater loads to fracture than those usuallyencountered in uniaxial flexure of test specimens with similarcro
39、ss sectional dimensions.6.2 Loading Fixtures for Concentric Ring TestingAnassembly drawing of a fixture and a test specimen is shown inFig. 1, and the geometries of the load and support rings aregiven in Fig. 2.6.2.1 Loading Rods and PlatensSurfaces of the supportplaten shall be flat and parallel to
40、 0.05 mm. The face of the loadrod in contact with the support platen shall be flat to 0.025 mm.In addition, the two loading rods shall be parallel to 0.05 mmper 25 mm length and concentric to 0.25 mm when installed inthe test machine.6.2.2 Loading Fixture and Ring GeometryIdeally, thebases of the lo
41、ad and support fixtures should have the sameouter diameter as the test specimen for ease of alignment.Parallelism and flatness of faces as well as concentricity of theload and support rings shall be as given in Fig. 2. The ratio ofthe load ring diameter, DL, to that of the support ring, DS, shallbe
42、0.2#DL/DS#0.5. For test materials exhibiting low elasticmodulus (E 1 GPa) it isrecommended that the ratio of the load ring diameter to that ofthe support ring be DL/DS= 0.2. The sizes of the load andsupport rings depend on the dimensions and the properties ofthe ceramic material to be tested. The ri
43、ngs are sized to thethickness, diameter, strength, and elastic modulus of theceramic test specimens (see Section 8). For test specimensmade from typical substrates (h 0.5 mm), a support ringdiameter as small as 12 mm may be required. For testspecimens to be used for model verification, it is recomme
44、ndedthat the test specimen support diameter be at least 35 mm. Thetip radius, r, of the cross sections of the load and support ringsshould be h/2 # r # 3h/2.6.2.3 Load and Support Ring MaterialsFor machined testspecimens (see Section 8) the load and support fixtures shall bemade of hardened steel of
45、 HRC 40. For as-fabricated testspecimens, the load/support rings shall be made of steel oracetyl polymer.6.2.4 Compliant Layer and Friction EliminationThebrittle nature of advanced ceramics and the sensitivity tomisalignment, contact stresses and friction may require acompliant interface between the
46、 load/support rings and the testspecimen, especially if the test specimen is not flat. Line orpoint contact stresses and frictional stresses can lead to crackinitiation and fracture of the test specimen at stresses other thanthe actual equibiaxial strength.6.2.4.1 Machined Test SpecimensFor test spe
47、cimens ma-chined according to the tolerance in Fig. 3, a compliant layer isnot necessary. However, friction needs to be eliminated. Placea sheet of carbon foil (0.13 mm thick) or Teflon tape (0.07mm thick) between the compressive and tensile surfaces of thetest specimen and the load and support ring
48、s.NOTE 1Thicker layers of carbon foil or Teflon tape may be used,particularly for very strong plates. However, excessively thick layers willredistribute the contact region and may affect results. The thicknesseslisted above have been used successfully. Guidance regarding the use ofthick layers canno
49、t be given currently; some judgement may be required.Alternatively, an appropriate lubricant (anti-seizing com-pound or Teflon oil) may be used to minimize friction. Thelubricant should be placed only on the load and support ringsso that effects of the test environment are not significantlyaltered. To aid fractographic examination, place a single stripof adhesive tape with a width of DLor greater on thecompressive face of the test specimen. Do not use multiplestrips of tape, or a strip of tape with width less than DL, as thismay result in nonuniform loa
