Designation: C1341 − 13Standard Test Method forFlexural Properties of Continuous Fiber-ReinforcedAdvanced Ceramic Composites1This standard is issued under the fixed designation C1341; the number immediately following the designation indicates the year oforiginal adoption or, in the case of 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. Scope*1.1 This test method covers the determination of flexuralproperties of continuous fiber-reinforced ceramic compositesin the form of rectangular bars formed directly or cut fromsheets, plates, or molded shapes. Three test geometries aredescribed as follows:1.1.1 Test Geometry I—A three-point loading system utiliz-ing center point force application on a simply supported beam.1.1.2 Test Geometry IIA—A four-point loading system uti-lizing two force application points equally spaced from theiradjacent support points with a distance between force applica-tion points of one half of the support span.1.1.3 Test Geometry IIB—A four-point loading system uti-lizing two force application points equally spaced from theiradjacent support points with a distance between force applica-tion points of one third of the support span.1.2 This test method applies primarily to all advancedceramic matrix composites with continuous fiber reinforce-ment: uni-directional (1-D), bi-directional (2-D), tri-directional(3-D), and other continuous fiber architectures. In addition, thistest method may also be used with glass (amorphous) matrixcomposites with continuous fiber reinforcement. However,flexural strength cannot be determined for those materials thatdo not break or fail by tension or compression in the outerfibers. This test method does not directly address discontinuousfiber-reinforced, whisker-reinforced, or particulate-reinforcedceramics. Those types of ceramic matrix composites are bettertested in flexure using Test Methods C1161 and C1211.1.3 Tests can be performed at ambient temperatures or atelevated temperatures. At elevated temperatures, a suitablefurnace is necessary for heating and holding the test specimensat the desired testing temperatures.1.4 This test method includes the following:SectionScope 1Referenced Documents 2Terminology 3Summary of Test Method 4Significance and Use 5Interferences 6Apparatus 7Precautionary Statement 8Test specimens 9Procedures 10Calculation of Results 11Report 12Precision and Bias 13Keywords 14ReferencesCFCC Surface Condition andFinishingAnnex A1Conditions and Issues in HotLoading of Test specimensinto FurnacesAnnex A2Toe Compensation on Stress-Strain CurvesAnnex A3Corrections for ThermalExpansion in FlexuralEquationsAnnex A4Example of Test Report Appendix X11.5 The values stated in SI units are to be regarded as thestandard in accordance with IEEE/ASTM SI 10 .1.6 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC1211 Test Method for Flexural Strength of AdvancedCeramics at Elevated TemperaturesC1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distribution Parameters for AdvancedCeramics1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.07 onCeramic Matrix Composites.Current edition approved Feb. 15, 2013. Published April 2013. Originallyapproved in 1996. Last previous edition approved in 2006 as C1341 – 06. DOI:10.1520/C1341-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.*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 States1C1292 Test Method for Shear Strength of Continuous Fiber-Reinforced Advanced Ceramics at Ambient TemperaturesD790 Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating Materi-alsD2344/D2344M Test Method for Short-Beam Strength ofPolymer Matrix Composite Materials andTheir LaminatesD3878 Terminology for Composite MaterialsD6856 Guide for Testing Fabric-Reinforced “Textile” Com-posite MaterialsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or ProcessE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE220 Test Method for Calibration of Thermocouples ByComparison TechniquesE337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodIEEE/ASTM SI 10 American National Standard for Use ofthe International System of Units (SI): The Modern MetricSystem3. Terminology3.1 Definitions:3.1.1 The definitions of terms relating to flexure testingappearing in Terminology E6 apply to the terms used in thistest method. The definitions of terms relating to advancedceramics appearing in Terminology C1145 apply to the termsused in this test method. The definitions of terms relating tofiber-reinforced composites appearing in Terminology D3878apply to the terms used in this test method. Pertinent definitionsas listed in Test Method C1161, Test Methods D790, Termi-nology C1145, Terminology D3878, and Terminology E6 areshown in the following with the appropriate source given inbrackets. Additional terms used in conjunction with this testmethod are also defined in the following.3.1.2 advanced ceramic, n—highly engineered, high-performance, predominately nonmetallic, inorganic, ceramicmaterial having specific functional attributes. C11453.1.3 breaking force, n [F]—The force at which fractureoccurs. (In this test method, fracture consists of breakage of thetest bar into two or more pieces or a loss of at least 20 % of themaximum force carrying capacity.) E63.1.4 ceramic matrix composite, n—material consisting oftwo or more materials (insoluble in one another) in which themajor, continuous component (matrix component) is a ceramic,while the secondary component(s) (reinforcing component)may be ceramic, glass-ceramic, glass, metal, or organic innature. These components are combined on a macroscale toform a useful engineering material possessing certain proper-ties or behavior not possessed by the individual constituents.3.1.5 continuous fiber-reinforced ceramic composite(CFCC), n—ceramic matrix composite in which the reinforc-ing phase consists of a continuous fiber, continuous yarn, or awoven fabric.3.1.6 flexural strength, n [ FL−2]—measure of the ultimatestrength of a specified beam in bending. C11613.1.7 four-point-1⁄3 point flexure, n—a configuration of flex-ural strength testing where a test specimen is symmetricallyloaded at two locations that are situated one third of the overallspan away from the outer two support bearings.3.1.8 four-point-1⁄4 point flexure, n—a configuration of flex-ural strength testing where a test specimen is symmetricallyloaded at two locations that are situated one quarter of theoverall span away from the outer two support bearings. C11613.1.9 fracture strength, n [ FL−2]—the calculated flexuralstress at the breaking force.3.1.10 modulus of elasticity, n [FL−2]—the ratio of stress tocorresponding strain below the proportional limit. E63.1.11 proportional limit stress, n [FL−2]—greatest stressthat a material is capable of sustaining without any deviationfrom proportionality of stress to strain (Hooke’s law).3.1.11.1 Discussion—Many experiments have shown thatvalues observed for the proportional limit vary greatly with thesensitivity and accuracy of the testing equipment, eccentricityof force application, the scale to which the stress-straindiagram is plotted, and other factors. When determination ofproportional limit is required, the procedure and sensitivity ofthe test equipment shall be specified. E63.1.12 slow crack growth, n—subcritical crack growth (ex-tension) that may result from, but is not restricted to, suchmechanisms as environmentally assisted stress corrosion ordiffusive crack growth.3.1.13 span-to-depth ratio, n [nd]—for a particular testspecimen geometry and flexure test configuration, the ratio(L/d) of the outer support span length (L) of the flexure testspecimen to the thickness/depth (d) of test specimen (as usedand described in Test Method D790).3.1.14 three-point flexure, n—a configuration of flexuralstrength testing where a test specimen is loaded at a locationmidway between two support bearings. C11614. Summary of Test Method4.1 A bar of rectangular cross section is tested in flexure asa beam as in one of the following three geometries:4.1.1 Test Geometry I—The bar rests on two supports andforce is applied by means of a loading roller midway betweenthe supports (see Fig. 1.)4.1.2 Test Geometry IIA—The bar rests on two supports andforce is applied at two points (by means of two inner rollers),each an equal distance from the adjacent outer support point.The inner support points are situated one quarter of the overallspan away from the outer two support bearings. The distancebetween the inner rollers (that is, the load span) is one half ofthe support span (see Fig. 1).4.1.3 Test Geometry IIB—The bar rests on two supports andforce is applied at two points (by means of two loading rollers),C1341 − 132situated one third of the overall span away from the outer twosupport bearings. The distance between the inner rollers (thatis, the inner support span) is one third of the outer support span(see Fig. 1).4.2 The test specimen is deflected until rupture occurs in theouter fibers or until there is a 20 % decrease from the peakforce.4.3 The flexural properties of the test specimen (flexuralstrength and strain, fracture strength and strain, modulus ofelasticity, and stress-strain curves) are calculated from theforce and deflection using elastic beam equations.5. Significance and Use5.1 This test method is used for material development,quality control, and material flexural specifications. Althoughflexural test methods are commonly used to determine designstrengths of monolithic advanced ceramics, the use of flexuretest data for determining tensile or compressive properties ofCFCC materials is strongly discouraged. The nonuniformstress distributions in the flexure test specimen, the dissimilarmechanical behavior in tension and compression for CFCCs,low shear strengths of CFCCs, and anisotropy in fiber archi-tecture all lead to ambiguity in using flexure results for CFCCmaterial design data (1-4). Rather, uniaxial-forced tensile andcompressive tests are recommended for developing CFCCmaterial design data based on a uniformly stressed test condi-tion.5.2 In this test method, the flexure stress is computed fromelastic beam theory with the simplifying assumptions that thematerial is homogeneous and linearly elastic. This is valid forcomposites where the principal fiber direction is coincident/transverse with the axis of the beam. These assumptions arenecessary to calculate a flexural strength value, but limit theapplication to comparative type testing such as used formaterial development, quality control, and flexure specifica-tions. Such comparative testing requires consistent and stan-dardized test conditions, that is, test specimen geometry/thickness, strain rates, and atmospheric/test conditions.5.3 Unlike monolithic advanced ceramics which fracturecatastrophically from a single dominant flaw, CFCCs generallyexperience “graceful” fracture from a cumulative damageprocess. Therefore, the volume of material subjected to auniform flexural stress may not be as significant a factor indetermining the flexural strength of CFCCs. However, the needto test a statistically significant number of flexure test speci-mens is not eliminated. Because of the probabilistic nature ofthe strength of the brittle matrices and of the ceramic fiber inCFCCs, a sufficient number of test specimens at each testingcondition is required for statistical analysis, with guidelines forsufficient numbers provided in 9.7. Studies to determine theexact influence of test specimen volume on strength distribu-tions for CFCCs are not currently available.5.4 The four-point loading geometries (Geometries IIA andIIB) are preferred over the three-point loading geometryFIG. 1 Flexure Test Geometries and Force DiagramC1341 − 133(Geometry I). In the four-point loading geometry, a largerportion of the test specimen is subjected to the maximumtensile and compressive stresses, as compared to the three-point loading geometry. If there is a statistical/Weibull charac-ter failure in the particular composite system being tested, thesize of the maximum stress region will play a role in deter-mining the mechanical properties. The four-point geometrymay then produce more reliable statistical data.5.5 Flexure tests provide information on the strength anddeformation of materials under complex flexural stress condi-tions. In CFCCs nonlinear stress-strain behavior may developas the result of cumulative damage processes (for example,matrix cracking, matrix/fiber debonding, fiber fracture,delamination, etc.) which may be influenced by testing mode,testing rate, processing effects, or environmental influences.Some of these effects may be consequences of stress corrosionor subcritical (slow) crack growth which can be minimized bytesting at sufficiently rapid rates as outlined in 10.3 of this testmethod.5.6 Because of geometry effects, the results of flexure testsof test specimens fabricated to standardized test dimensionsfrom a particular material or selected portions of a component,or both, cannot be categorically used to define the strength anddeformation properties of the entire, full-size end product or itsin-service behavior in different environments. The effects ofsize and geometry shall be carefully considered in extrapolat-ing the test results to other configurations and performanceconditions.5.7 For quality control purposes, results from standardizedflexure test specimens may be considered indicative of theresponse of the material lot from which they were taken withthe given primary processing conditions and post-processingheat treatments.5.8 The flexure behavior and strength of a CFCC aredependent on its inherent resistance to fracture