3D-C/C-TiC-Cu carbon fiber ceramic matrix composites significantly enhance toughness and electro-thermal conductivity by incorporating high-toughness Ti-Cu alloy. Owing to their 3D braided structure and multiphase interfacial properties, the composites exhibit complex anisotropic damage evolution. To clarify damage modes and evolution under different loading directions, this study combines acoustic emission (AE) technology with three-point bending graded cyclic loading tests. Through k-medoids algorithm, four typical damage modes were identified, including interlayer peeling, interfacial debonding, matrix cracking, and fiber breakage. Results show fiber breakage dominates the entire loading process, followed by interlaminar delamination, while matrix cracking is the least frequent. Parallel to the needling direction, damage initiates earlier, develops more severely and rapidly. Conversely, perpendicular loading shows more gradual damage evolution, with late-stage rapid failure caused by concentrated fiber bundle fracture, indicates that perpendicular-needled specimens exhibit higher flexural strength and slower damage accumulation. Furthermore, the AE activity rate metric was proposed to identify load thresholds where damage significantly varies between the two stress directions, enabling a quantitative assessment of material damage anisotropy. This work provides critical theoretical and technical support for precise service load control and safe engineering applications of such composites.
Wang et al. (Thu,) studied this question.