Effect of stable-structural 3D woven preform on tensile and flexural properties of carbon fiber/epoxy composites

The geometry of yarns effect the structural stability of 3D woven preform, which influence the mechanical properties of carbon fiber/epoxy composites. To investigate the effect of stable-structural preform on the elastic properties of 3D woven composites, the factors that caused the unstable structure of preform were discussed, and comparative study was conducted. The geometric models of yarn cross-section and preform were established to discuss the stability. The results showed that increasing the opening angle of warp yarns and the elongation of yarn outer contour can improve the stability of preform. The tensile and bending tests of 3DLAC and 3DBAC with stable and unstable structural preform were conducted. The results showed that the tensile and flexural elastic moduli were inversely proportional to the curvature of load-bearing yarns, and the elastic modulus of composites with stable-structural preform can increase by 9%–13%. The redistribution of internal stress in composites was macroscopically manifested as stable changes in experimental process. 3D woven composites with stable-structural preform showed the regular fracture cross-section, and fiber fracture and interface adhesion effect were the main failure mode in tensile tests, and fiber fracture on the compression surface and matrix cracking were the main failure modes in bending tests.