An investigation of mechanical behavior and failure mechanisms of composite T-joints with transverse stitching

A new low cost damage tolerant method of joining load-bearing composite structures using two-dimensional dry fabric preforms with transverse stitching and a novel fiber insertion process with resin transfer molding has recently been developed, however, knowledge of strength prediction and failure mechanisms is not well understood. In this investigation, fundamental knowledge of T-joint mechanical behavior was developed through detailed experimental, numerical, and post failure analyses. Experiments were conducted under flexure, tension, and shear loads and failed specimens were examined to discern failure modes. T-joint constituent elastic and strength properties were experimentally determined. Elastic properties were used as input to the finite element analysis and strength properties were used as limiting values in the T-joint failure analysis. Linear elastic, nonlinear elastic, and progressive damage finite element models were developed under each load condition. T-joint numerical models are shown to predict experimental behavior through ultimate load. Damage accumulation was characterized based on experimental, numerical, and post failure analyses. A parametric finite element analysis was conducted and design curves were derived to demonstrate the effect of varying key T-joint interface parameters on mechanical behavior under each load condition. Results of this research enable the application of T-joints with transverse stitching to future products and predictive finite element models developed herein reduce the structural testing required to validate these designs.