Tensile properties for 2.5 dimensional C/SiC composites fabricated by chemical vapor infiltration

Multi-layer 2.5 dimensional carbon fiber reinforced silicon carbide (2.5D C/SiC) ceramic matrix composites with through-thickness reinforcements were fabricated by the isothermal low-pressure chemical vapor infiltration (ILCVI) process; thereby it is possible to manufacture the thermostructural components with one closed end. After the ILCVI densification, the resulting composites have an open porosity of 16.5%-18% and a bulk density of 1.95-2.1 g/cm³, respectively. Tensile tests for monotonic loading parallel to the warp and weft directions were carried out at room temperature. The results show that the tensile stress-strain curves of 2.5 D C/SiC composite in both loading directions exhibit largely nonlinear behavior. The composites studied have higher in-plane tensile properties, with the tensile strength of 326 MPa in the warp direction and of 145 MPa in the weft direction, and the failure strain of 0.697% in the warp direction and of 0.705% in the weft direction. Observation of scanning electron microscope photographs reveal that the failure of the composites exhibits multiple yarn fracture, and the fracture of yarns demonstrates multi-step fiber fracture and extensive fiber pullout.