In situ investigation of failure in 3D braided SiCf/SiC composites under flexural loading

The mechanical failure of three-dimensional (3D) 4-step braided SiCf/SiC composites, processed by precursor infiltration pyrolysis, has been studied under flexural loading to investigate the condition at failure. The investigation integrated the advantages of continuous data acquisition by optical imaging and 3D reconstruction of internal structure in X-CT imaging, for in situ investigation of microstructure-related failure mechanisms. Optical imaging with digital image correlation acquired the surface displacements. X-ray computed tomographs, obtained in situ, were analysed by digital volume correlation to measure the 3D displacement fields. Image subtraction, informed by the 3D displacements, was used to detect and visualize crack development. Curvature measurement, via the displacement fields, monitored the change in effective flexural modulus. The observed failure modes included matrix cracking, inter- and intra-bundle debonding and fibre breakage. Tensile cracks were arrested by the heterogeneous microstructure, and the ultimate failure under flexural loading was due to multiple cracking in compression.

Automated summary

The mechanical failure of 3D 4-step braided SiCf/SiC composites processed by precursor infiltration pyrolysis was studied under flexural loading to investigate the conditions at failure. Optical imaging and X-CT imaging were utilized for in situ investigation of microstructure-related failure mechanisms. The observed failure modes included matrix cracking, inter- and intra-bundle debonding, and fiber breakage. Multiple cracking in compression was found to be the ultimate failure mode.