Strength evolution of cyclic loaded LSI-based C/C-SiC composites

An experimental investigation was performed to study the influence of fatigue damage introduced by different loading cycles on the residual tensile strength (RTS) of plain-weave reinforced C_f/C-SiC composites (2D C/C-SiC). The specimens were subjected to the fatigue stress of 57 MPa for the preselected numbers of cycles as follows: 10², 10⁴ and 10⁵, respectively, before the static tensile test. The microstructures and fractured surfaces after the tensile test were examined by optical and scanning electron microscopy, respectively. The results showed that the RTS of the specimens after the preselected fatigue cycles numbers of 10², 10⁴ and 10⁵ increase to 89.8, 94.1 and 82.4 MPa, respectively, which are somewhat higher compared to the virgin samples (79.7 MPa). Additionally, we found that the linear part of the tensile stress-strain curve is independent on the fatigue cycles. Finally, the increased fatigue damage in C/C-SiC composites could determine a reduction of elastic modulus in all cases of fatigue tests.