Transverse Stitched T-Joints in Bending with PR520 Resin: Initial Results

An experimental investigation was undertaken to evaluate the bending strength of transversely stitched T-joints using fiber insertion as the primary load transfer mechanism and using resin transfer molding with PR520 toughened epoxy resin. Tests were conducted to determine the ultimate bending strength of two joint configurations and fractographic examination was performed to determine joint failure mechanisms. This study shows that increasing the web thickness and the subsequent number of rows of stitching has the effect of increasing the initial and maximum bending strength of the T-joint design. As indicated by the fractographic examination, initial joint failure occurs by matrix cracking initiating at the resin rich corner fillet and propagates inward toward the transverse stitching; and ultimate joint failure occurs by fiber breakage and/or fiber pullout.