1.1This test method determines the open-hole (notched) tensile strength of continuous fiber-reinforced ceramic matrix composite (CMC) test specimen with a single through-hole of defined 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 continuous fiber-reinforced CMCs at ambient temperature. The OHT strength can be compared to the tensile strength of an unnotched test specimen to determine the effect of the defined open hole on the tensile strength and the notch-sensitivity of the CMC material. If a material is notch-sensitive, then the OHT strength of a material varies with the size of the through-hole. Commonly, larger holes introduce larger stress concentrations and reduce the OHT strength. 1.2This test method defines two baseline OHT test specimen geometries and a test procedure, based on Test Method C1275 (Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramic Composite) and the Test Method D5766 (Open-Hole Tensile Strength of Polymer Matrix Composite Laminates). A flat, straight-sided ceramic composite test specimen with a defined laminate fiber architecture contains a single through-hole (either 6 mm or 3 mm in diameter) centered by length and width in the defined gage section (Figure 1 - OHT Test Specimens A and B). A uniaxial, monotonic tensile test is performed along the defined test-reinforcement axis at ambient temperature, measuring the applied force versus time/displacement in accordance with Test Method C1275. Measurement of the gage length extension/strain is optional, using extensometer/displacement transducers. Bonded strain gages are optional for measuring localized strains and assessing bending strains in the gage section. 1.3 The open-hole tensile strength (SOHTx) for the defined hole diameter x (mm) is the calculated ultimate tensile strength based on the maximum applied force and the gross cross-sectional area, disregarding the presence of the hole, per common aerospace practice (See Section 4.4). The net-section tensile strength(SNSx) is also calculated as a second strength property, accounting for the effect of the hole on the cross-section area of the test specimen. 1.4This test method applies primarily to ceramic matrix composites with continuous fiber reinforcement in multiple directions. The CMC material is typically a fiber-reinforced 2-D laminated composite in which the laminate is balanced and symmetric with respect to the test direction. Composites with other types of reinforcement (1-D, 3-D, braided, unbalanced) may be tested with this method with consideration of how the different architectures may affect the notch effect of the hole on the OHT strength and the tensile stress-strain response. This test method does not directly address discontinuous fiber-reinforced, whisker-reinforced or particulate-reinforced ceramics, although the test methods detailed here may be equally applicable to these composites. 1.5This test method may be used for a wide range of CMC materials with different reinforcement fibers and ceramic matrices (oxide-oxide composites, silicon carbide (SiC) fibers in SiC matrices, carbon fibers in SiC matrices, and carbon-carbon composites) and CMCs with different reinforcement architectures. It is also applicable to CMCs with a wide range of porosities and densities. 1.6Annex A1 and Appendix X1 address how test specimens with different geometries and hole diameters may prepared and tested to determine how those changes will modify the OHT strength properties, determine the notch sensitivity, and affect the stress-strain response. 1.7The test method may be adapted for elevated temperature OHT testing by modifying the test equipment, specimens, and procedures, per Test Method C1359 and as described in Appendix X2. The test method may also be adapted for environmental testing [controlled atmosphere/humidity at moderate (30C) temperatures] of the OHT properties by the use of an environmental test chamber per Section 7.6.
Open-hole tensile tests of composites are necessary for the development, design, production, and engineering use of composite materials in structural components. Performing open-hole tests for composite materials with a baseline test specimen geometry provides valid, comparable information showing if a composite material is notch sensitive and how it will perform in an open-hole application. The polymer matrix composite (PMC) community has the ASTM Test Method D5766 which establishes a baseline PMC specimen geometry with a 6 millimeter (mm) diameter thru-hole centered in a 36 mm wide gage section. However, there is no ASTM standard test method for open-hole tensile tests of ceramic matrix composites (CMC). This standard test method establishes a baseline test specimen geometry (6 mm diameter center hole in a 36 mm wide x 60 mm long gage section) and test procedure for the open-hole tensile strength of continuous fiber-reinforced CMCs.
Keywordsceramic composite materials; open-hole tensile strength; tensile testing; stress concentration; notch strength; notch sensitivity.
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top
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