Mechanical behavior of LSI based C/C-SiC composites subjected to flexural loadings

In general, flexural loads result in more complicated and uneven stress distributions in specimens, compared to axial loading. This study reports the influence of flexural fatigue loads including different stress levels and cycles on the mechanical behavior of a 3D C/C-SiC composite. The cyclic tensile loads in the lower part of the specimens result in strength enhancement after short fatigue duration with the expense of decreased flexural modulus due to the fatigue damage such as cracking and interfacial degradation. Whereas the upper part of the post-fatigue specimens, which is almost free of fatigue damage under compressive stress, can still properly deflect the cracks and result in quasi-plastic failures like virgin specimens. Most notably, specimens will suffer strength decline rapidly, after 50,000 cycles with maximum stress of 95 MPa for instance, because of considerable stress concentrations and wear of fibers at 90° fiber bundles in the lower part.