Experimental investigation of the tension-torsion coupling behavior on needled unidirectional C/SiC composites

Mechanical responses and failure mechanisms of ceramic matrix composites under tension-shear loading are important for structure design. In this paper, tension-torsion coupling tests were performed to study the mechanical behaviors of the needled unidirectional C/SiC composites. The results showed that the coupled tensile load decreases the torsional stiffness and failure load. The stable stage of the torsional damage with coupled tensile load was shorter than that of pure torsion. The failure mechanisms at micro level include fiber fracture, long range fiber bundle pull-out, fiber bridging, fiber/matrix interface debonding, matrix cracking, matrix fragment desquamating and matrix peeling. The failure mechanisms at macro level include delamination, axial split and irregular fracture at the root of specimens. The extent of axial split failure and the fibers distribution of the irregular fracture under pure torsion and torsion-tension coupling load were different.