Residual Strength Evolution of 2D C/C-SiC Composites Subjected to Tensile Fatigue Stresses

An experimental investigation was performed to study the residual tensile strength (RTS) of liquid silicon infiltration (LSI)-based plain-weave reinforced C-f/C-SiC composites (2D C/C-SiC) after different loading cycles. The specimens were previously subjected to the cyclic stress of 57 MPa for the preselected numbers of cycles (10(2), 10(4) and 10(6), respectively) before the final quasi-static tensile test. The microstructures, fractured surfaces and coefficient of thermal expansion (CTE) after the quasi-static tensile test were characterized by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and a classical mechanical push-rod dilatometer, respectively. The results showed that the RTS of the specimens after the preselected fatigue cycles numbers of 10(2),10(4) and 10(6) increase to 90.9, 94.1 and 84.5 MPa, respectively, which are somewhat higher than that of virgin samples (79.7 MPa). Additionally, the tensile stress-strain curves of the post-fatigue specimens present cycle-independence within the region of linear response. Finally, the CTE in the range of 200-1000 degrees C gradually decreased with the increasing cycles owing to higher damage induced by fatigue stress along the loading direction.