Shear behaviors and failure mechanisms of 2D C/SiC pins prepared by chemical vapor infiltration

Connecting and fastening large-scale all-C/SiC airfoils to the fuselage of hypersonic vehicle requires C/SiC fasteners of high-performances under the re-entry environment. In this paper, 2D C/SiC pins prepared by chemical vapor infiltration (CVI) were sheared off to demonstrate their strength sensitivity to the nonuniform microstructures, such as porosity and ply orientation. Results showed that their average shear strengths increase linearly from 85.8 to 134.8 MPa as their average total porosity decreases from 23.2% to 14.5%. The shear strengths of 2D C/SiC pins are almost the same as the in-plane shear strengths of 2D C/SiC composites, under the condition that both have identical total porosity. In contrast, the variances of the pin shear strength are much higher than the in-plane shear strength, which is mainly ascribe to the effects of the loading angle between the shear plane and the ply orientation. The porosity of the 2D C/SiC pin is the main microstructural factor influencing the pin shear strength. Matrix shear cracking, debonding between matrix and fibers, crack deflection along fibers and interlayer sliding are the main shear failure mechanisms. Due to the secondary bending deformation, the interlayer sliding and the corresponding fiber pull-out mechanisms dominate the final ductile fracture behavior.