In situ experimental study on damage evolution of the needled Carbon/Carbon composites under different loading types by high-resolution X-ray computed tomography

Abstract

The damage evolution of the needled Carbon/Carbon (C/C) composites has a complex dependence on the load types and microstructures. In order to reveal this mechanism, this paper analyzed the initiation, coalescence and propagation of cracks in the needled C/C composites under three loading types of compression, in-plane shear and interlaminar shear by in-situ X-ray computed tomography and gray threshold segmentation methods. The growth sequence of cracks under different loads is clarified. The results show that the original defects form a network of crack nucleation inside the material. The cracks evolve from the original holes and propagate to the adjacent area through assimilation. In addition, the damage evolution changes significantly with the loading type. Compression failure is a quasi-brittle failure caused by the breakage and defects expansion of the nonwoven cloth in the needled areas, and it exhibits macroscopic delamination and out-of-plane shear. Under the in-plane shear, the cracks nucleate in the needled holes and propagate longitudinally along the 90° (loading direction) fibers. The cracks evolve independently in different layers, and 0° fibers bridge cracks. The material exhibits characteristics of progressive damage and ductile failure. As for the shear load in the interlaminar direction, the transfer yarns in the thickness direction provide beneficial lateral constraints to resist interlaminar debonding.