Design, Fabrication, and Mechanical Properties of T-700^TM Multiaxial-Warp-Knitting-Needled-C/SiC Composite and Pin

In this paper, the 12k T-700^TM Multiaxial-Warp-Knitting-Needle (MWK-N) C/SiC composite and pin were designed and fabricated using the isothermal chemical vapor infiltration (ICVI) method. The composite's microstructure and mechanical properties were examined by subjection to tensile and interlaminar shear tests. Three types of double-shear tests were conducted for C/SiC pins, including shear loading perpendicularly, along, and at 45° off-axial to the lamination. The fracture surface of the tensile and shear failure specimens was observed under scanning electronic microscope (SEM). The relationships between the composite's microstructure, mechanical properties, and damage mechanisms were established. The composite's average tensile strength was σ_uts = 68.3 MPa and the average interlaminar shear strength was τ_u = 38.7 MPa. For MWK-N-C/SiC pins, the double-shear strength was τ_u = 76.5 MPa, 99.7 MPa, and 79.6 MPa for test types I, II, and III, respectively. Compared with MWK-C/SiC pins, the double-shear strength of MWK-N-C/SiC pins all decreased, i.e., 26.7%, 50.8%, and 8% for test types I, II, and III, respectively. The MWK-N-C/SiC composite and pins possessed high interlaminar shear strength and double-shear strength, due to the needled fiber in the thickness direction, low porosity (10-15%), and high composite density (2.0 g/cm³).