Effects of flexural fatigue cycles on the internal friction behavior of SiCnws-C/C composites

After loaded for different cycles at stress level of fatigue limit, the internal friction behavior of SiC nanowires reinforced carbon/carbon (SiCnws-C/C) composites was investigated. Experimental results indicate that the fatigue limit of SiCnws-C/C composites is 70% of the static flexural strength. Influence of temperature on internal friction is correlated with the synergistic effect of SiC nanowires, pyrolytic carbon, as well as defects induced by fatigue load. For SiCnws-C/C composites, internal friction increases with the increasing fatigue cycles. The reason is attributed to the increasing interfacial sliding and friction induced by the formation of matrix cracks, interfacial debonding and interlayer delamination. Despite the matrix internal friction decreases a bit due to the increasing Van der Waals force between carbon layers, this partial reduction is smaller compared with the increased internal friction caused by interfacial sliding. Thus, the post-fatigued SiCnws-C/C composites still exhibit increased internal friction.