Nonuniform load distribution of two-dimensional C/SiC z-pinned joints with four pins in a rectangular array prepared via chemical vapor infiltration

Abstract

The design of ceramic matrix composite (CMC) mechanical joints takes into account the pseudoplastic mechanical behavior of CMC fasteners and the effect of the nonuniform microstructure. In this study, based on the linear correlation between the shear performance of two-dimensional (2D) C/SiC rivets and the rivet porosity, special z-pinned joints with four pins in a rectangular array with different porosities were prepared via the chemical vapor infiltration online gas-phase joining method, and a method is proposed to indirectly characterize the pin load distribution by measuring the strain distribution around the holes. The results show that the nonuniform distribution of the 2D C/SiC rivet density leads to an uneven distribution of the pin loads in the z-pinned joints with four pins in a rectangular array. The bearing ratio of the transversal rivets depends on the inverse of the ratio of the compliance coefficient of the two. The longitudinal rivets are capable to transfer the load; that is, the bottom transversal joint of the rivets is loaded first, and after the load limit is reached, the top transversal joint of the rivets starts to be loaded. Matrix cracking, crack deflection, interlayer sliding, fiber shearing, and fiber pull-out control rivet shearing. The dense rivets squeeze around the holes, leading to an uneven distribution of the pin loads. Oxidation at 700 °C leads to the fibers debonding from the matrix and cracking, which promotes crack deflection, interlayer sliding, and fiber pull-out; thus, the uneven pin load distribution tends to be uniform.

Keywords

• Chemical vapor infiltration
• Two-dimensional C/SiC
• Riveting
• Pin load distribution
• Failure mechanism