ASTM_C_1869_-_18.pdf

Designation:C186918Standard Test Method forOpen-Hole Tensile Strength of Fiber-Reinforced AdvancedCeramic Composites1This standard is issued under the fixed designation C1869;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.Scope1.1 This test method determines the open-hole(notched)tensile strength of continuous fiber-reinforced ceramic matrixcomposite(CMC)test specimens with a single through-hole ofdefined diameter(either 6 mm or 3 mm).The open-hole tensile(OHT)test method determines the effect of the single through-hole on the tensile strength and stress response of continuousfiber-reinforced CMCs at ambient temperature.The OHTstrength can be compared to the tensile strength of an un-notched test specimen to determine the effect of the definedopen hole on the tensile strength and the notch sensitivity of theCMC material.If a material is notch sensitive,then the OHTstrength of a material varies with the size of the through-hole.Commonly,larger holes introduce larger stress concentrationsand reduce the OHT strength.1.2 This test method defines two baseline OHT test speci-men geometries and a test procedure,based on Test MethodsC1275 and D5766/D5766M.A flat,straight-sided ceramiccomposite test specimen with a defined laminate fiber archi-tecture contains a single through-hole(either 6 mm or 3 mm indiameter),centered by length and width in the defined gagesection(Fig.1).Auniaxial,monotonic tensile test is performedalong the defined test reinforcement axis at ambienttemperature,measuring the applied force versus time/displacement in accordance with Test Method C1275.Mea-surement of the gage length extension/strain is optional,usingextensometer/displacement transducers.Bonded strain gagesare optional for measuring localized strains and assessingbending strains in the gage section.1.3 The open-hole tensile strength(SOHTx)for the definedhole diameter x(mm)is the calculated ultimate tensile strengthbased on the maximum applied force and the gross cross-sectional area,disregarding the presence of the hole,percommon aerospace practice(see 4.4).The net section tensilestrength(SNSx)is also calculated as a second strength property,accounting for the effect of the hole on the cross-sectional areaof the test specimen.1.4 This test method applies primarily to ceramic matrixcomposites with continuous fiber reinforcement in multipledirections.The CMC material is typically a fiber-reinforced,2D,laminated composite in which the laminate is balanced andsymmetric with respect to the test direction.Composites withother types of reinforcement(1D,3D,braided,unbalanced)may be tested with this method,with consideration of how thedifferent architectures may affect the notch effect of the hole onthe OHT strength and the tensile stress-strain response.Thistest method does not directly address discontinuous fiber-reinforced,whisker-reinforced,or particulate-reinforcedceramics,although the test methods detailed here may beequally applicable to these composites.1.5 This test method may be used for a wide range of CMCmaterials with different reinforcement fibers and ceramicmatrices(oxide-oxide composites,silicon carbide(SiC)fibersin SiC matrices,carbon fibers in SiC matrices,and carbon-carbon composites)and CMCs with different reinforcementarchitectures.It is also applicable to CMCs with a wide rangeof porosities and densities.1.6 AnnexA1 and Appendix X1 address how test specimenswith different geometries and hole diameters may be preparedand tested to determine how those changes will modify theOHT strength properties,determine the notch sensitivity,andaffect the stress-strain response.1.7 The test method may be adapted for elevated tempera-ture OHT testing by modifying the test equipment,specimens,and procedures per Test Method C1359 and as described inAppendix X2.The test method may also be adapted forenvironmental testing(controlled atmosphere/humidity atmoderate(20 D)No specified toleranceLgage=gage section length$60 mm(10 D)Tolerance=2 mmLgrip=grip section length$30 mm(50%of Lgage)No specified toleranceh=recommended specimen thickness2 mm#h#10 mm,3 mm nominalNo specified tolerance for as-fabricated specimensParallel and flat by 2%for face-machined specimensC1869 185 reported only when appropriate failure at the center hole isobserved,in accordance with 9.11 and 12.5.6.7 System AlignmentExcessive bending stresses in thetest specimen will cause premature failure and a misleading orfalse positive result.Bending may occur as a result of mis-aligned grips or from specimens themselves(if improperlyinstalled in the grips or from out-of-tolerance dimensions).Ifthere is any doubt as to the alignment of the load train and thetest specimen in a given test machine,then the alignment shallbe checked and ad