Effect of porosity on the tensile strength and Micromechanisms of laminated stitched C/C-SiC composites

This study examines how pore defects affect the tensile strength of laminated stitched carbon fiber reinforced carbon and silicon carbide (C/C-SiC) composites. Using computed tomography (CT) technology, internal characteristic parameters were obtained, and a representative volume cell contains pore (RVC-CP) defects was established. The homogenization method and strength estimation technique were applied to connect material properties from the microscopic to the mesoscopic scale. Progressive damage analysis of the representative volume cell (RVC) yielded tensile strength results within 2% of the average tensile test measurements, validating finite element models for strength prediction. The study found that pores create stress concentrations, leading to the failure of transverse and longitudinal fiber bundles, as well as the matrix. Additionally, it was observed that 8.9% pore content results in a 27.2% reduction in tensile strength compared to non-porous material. Based on these findings, empirical formulas for predicting tensile strength reduction due to pores are proposed. This paper presents a mesoscale computational model with pores that enhances the efficiency and accuracy of strength design for stitched C/C-SiC materials. In engineering, the model can be combined with non-destructive testing to quickly assess local strength reduction, offering valuable insights for designing C/C-SiC materials in aircraft and high-speed trains. © 2024