1、Designation: C1869 18Standard 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 y
2、ear 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 matr
3、ixcomposite (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 OHT
4、strength 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 throu
5、gh-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 def
6、ined 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 for
7、ce 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-ho
8、le 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 a
9、lso 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-reinf
10、orced,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 o
11、f 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 me
12、thod 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
13、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, andaffe
14、ct 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/h
15、umidity 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 thickness 2 mm # h # 10 mm, 3 mm nominalNo specified tolerance for as-fabricated specimensParallel
16、 and flat by 2 % for face-machined specimensC1869 185reported 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. Bendin
17、g 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 adjuste
18、d as discussed in 7.3.6.8 OtherAdditional sources of potential interference anddata scatter (including slow crack growth, test environmenteffects, surface preparation, out-of-gage fracture, etc.) in test-ing of ceramic composite materials are described in Section 5of Test Method C1275.7. Apparatus7.
19、1 The test apparatus (Fig. 3) shall be in accordance withthe following sections of Test Method C1275 and cited ASTMmechanical testing references.7.2 Testing MachineThe testing machine applies and mea-sures the force on the test specimen in a controlled manner. Atesting machine commonly consists of a
20、 test frame, forcetransducers, and the actuator/drive mechanism. The test ma-chine and its components shall conform to the requirements of6.1 of Test Method C1275 and Practices E4.7.2.1 Gripping DevicesGripping devices are used totransmit the measured force to the test specimens and to keepthe speci
21、men properly aligned in the load train. Face-grippingdevices are commonly used for the flat, straight-sided testspecimens defined in this test method. Gripping devices areclassed as those employing active or passive grip interfaces.Gripping devices shall meet the requirements specified in 6.2of Test
22、 Method C1275.7.2.2 Load Train CouplersVarious types of load traincouplers are used to attach the gripping devices to the testingmachine. The load train couplers, in conjunction with the typeof gripping device, play major roles in the alignment of theload train and thus reducing bending imposed in t
23、he specimen.Load train couplers are generally classified as fixed andnonfixed. Load train couplers shall meet the requirementsspecified in 6.3 of Test Method C1275.7.2.3 Strain MeasurementGage section strain is not arequired or typical measurement in the open-hole tensile test,because of the nonunif
24、orm strain in the region of the through-hole. Optional strain measurement by extensometer, bondedstrain gages, and digital image correlation (DIC) are discussedin Appendix X3.7.3 Allowable Bending (Test Methods C1275 and D3039/D3039M and Practice E1012)The recommended maximumallowable percent bendin
25、g for alignment specimens in the loadtrain is five percent (5 %) at the onset of the cumulativefracture process (for example, matrix cracking stress).However, it should be noted that unless each individualspecimen is properly strain gaged and percent bending moni-tored until the onset of the cumulat
26、ive fracture process, therewill be no record of percent bending at the onset of fracture foreach specimen. Therefore, the load train alignment should beverified with an alignment specimen using the proceduresdetailed in 6.5 and Appendix X1 of Test Method C1275, 7.2.5TABLE 2 Dimensions and Tolerances
27、 for OHT Test Specimen BTest SpecimenB3-mmholein10-mmwidegage sectionShape and orientation: Flat bar with constant rectangular cross section with a through-hole centered in the gage section. Long tensile test axis is oriented to thedesignated reinforcement axis (for example, 0, 90, 45).Dimensional F
28、eature Dimensions Tolerance, Position, and AlignmentD = hole diameter 3.0 mm, w/D ratio = 3.33Tolerance = 0.1 mm for circularityCentered in the gage section (0.5 mm for width and 2 mm for length)w = gage section width 10 mm Uniform and parallel to 0.2 mm, 2 %L = minimum specimen length $60 mm (20 D)
29、 No specified toleranceLgage= gage section length $30 mm (10 D) Tolerance = 2 mmLgrip= grip section length $15 mm (50 % of Lgage) No specified toleranceh = recommended specimen thickness 2 mm # h # 10 mm, 3 mm nominalNo specified tolerance for as-fabricated specimensParallel and flat by 2 % for face
30、-machined specimensFIG. 3 Tensile Test Apparatus SchematicC1869 186of Test Method D3039/D3039M,orAppendix X4 of this testmethod such that percent bending with the alignment specimendoes not exceed five percent (5 %) at a mean strain equal toeither one-half the anticipated strain at the onset of thec
31、umulative fracture process (for example, matrix crackingstress), or a strain of 0.0005 (that is, 500 microstrain),whichever is greater. Note that percent bending in mounted testspecimens may be greater than 5 %, due to variations in thedimensions, flatness, and twist of individual test specimens. If
32、test specimens are measured for percent bending, the recom-mended limit for percent bending in test specimens is 300 C) testing with theaddition/modification of the test apparatus, test specimens, testprocedures, and calculations as described in Appendix X2 andreferenced in Test Method C1359.8. Haza
33、rds8.1 During the conduct of this test method, the possibility offlying fragments of broken test material is high. The brittlenature of advanced ceramics and the release of strain energycontribute to the potential release of uncontrolled fragmentsupon fracture. Means for containment and retention of
34、 thesefragments for later fractographic reconstruction and analysis ishighly recommended. (Plastic shields can be used to encirclethe test fixture and specimen and to capture specimen frag-ments.)8.2 Exposed fibers at the edges of CMC test specimenspresent a hazard due to the sharpness and brittlene
35、ss of theceramic fiber.All those required to handle these materials shallbe well informed of such conditions and the proper handlingtechniques.9. Test Specimens and Sampling9.1 GeneralTwo specific OHT test specimen geometriesare defined for general use within the CMC community. Thesetwo geometries d
36、etermine the effect of two typical holediameters (6 mm and 3 mm) on the strength of a CMCspecimen. However, if testing objectives, material limitations,component size requirements, or test data comparability re-quire a different tensile specimen geometry, other tensilespecimen geometries with modifi
37、cations may be used for OHTtesting. Annex A1 describes how different Test Method C1275test specimen geometries may be modified for OHT testing fordifferent testing objectives.9.2 Baseline Test Specimen GeometryTwo baseline testspecimen geometries are defined: Test Specimen A and TestSpecimen B. Both
38、 test specimens are flat, straight-sided testspecimens with a through-hole in the center of the gagesection. Nominal thickness shall be 3 mm, with a typical rangeof 2 to 10 mm, inclusive. Test Specimen A uses a 6-mmdiameter through-hole in the center of a 36-mm wide gagesection. Test Specimen B uses
39、 a 3-mm diameter through-holein the center of a 10-mm wide gage section. The two testspecimens are illustrated by the schematic in Fig. 4 anddescribed in Tables 1 and 2. The long axis of the test specimenis oriented to the designated reinforcement axis (for example,0, 90, 645). The grip sections of
40、the test specimen areclamped into the upper and lower grip devices.9.2.1 A w/D ratio of 6 for Test Specimen A and a w/D ratioof 3 for Test Specimen B are typically sufficient to minimizestress-strain interactions between the center hole and thespecimen edges. Test specimens with lower and higher w/D
41、ratios can be tested to determine the interactions between theC1869 187edge and hole stress-strain fields as a function of specimenwidth and hole diameter. (See Appendix X1.)9.2.2 The gage section shall be long enough to provide asignificant amount of material under stress and to produce auniform st
42、rain field in the specimen outside of the influence ofthe center hole. Typically, the gage section length (Lgage)isgreater than ten times the hole diameter (D)(Lgage/ D10).9.2.3 The specimen length shall be long enough to minimizebending stresses caused by minor grip eccentricities. The gripsections
43、 shall be long enough for adequate grip surface thatwill prevent slippage in the grips or crushing in the gripsections. Typically, each grip length section is 50 % of thegage length for a grip length of 30 mm and 15 mm for the twotest specimen geometries. Different ceramic composite mate-rials with
44、different fiber architectures, porosities, and tensileand shear strengths may require longer gage, grip, and speci-men lengths to promote failure through the center hole and toprevent invalid, out-of-gage failures.9.2.4 Reinforcement ArchitectureThe CMC test speci-mens typically have multidirectiona
45、l fiber orientations (fibersare oriented in a minimum of two directions producing a 2- or3-dimensional reinforcement structure) and a balanced,symmetric, and laminated reinforcement architecture.9.2.5 Test specimens with 1D uniaxial reinforcement, 3Dwoven or braided reinforcement, unbalanced, nonsym
46、metricalarchitectures, or combinations thereof, may be tested withappropriate consideration of how those different architectureswill affect the open-hole tensile strength. Any significantvariation in the reinforcement architecture of the test materialshall be clearly noted and described in the test
47、report.9.2.6 Any variation in specimen hole diameter or position orgage section width or length, or combinations thereof, fromthat specified for Test Specimens A and B, shall be clearlynoted in the report.9.3 Specimen Fabrication and MarkingTest specimensshall be cut to align the long axis of the te
48、st specimen with thedesired test reinforcement axis (for example, the 0, 90, or645 direction with reference to the principal structural axis).9.3.1 Specimen MachiningParagraph 8.2 of Test MethodC1275 specifies four different ceramic composite machiningprotocols: as-fabricated, application-matched ma
49、chining, cus-tomary practices, and standard procedures. Depending uponthe intended application of the tensile strength data, use one ofthe defined Test Method C1275 machining procedures. Themachining procedure must avoid notches, undercuts, rough oruneven surfaces, edge damage, or delaminations and producemachined surfaces that are flat and parallel within the specifiedtolerances. Record and report the machining procedure insufficient detail to allow replication. Regardless of the prepa-ration procedure used, sufficient details regarding
