Effect of stitching on resin film infusion and damage tolerance of stiffened composite structure

This study investigates the effectiveness of stitching in providing an alternate method to increase the damage tolerance of composite structures. Stitching is considered as one of the most promising method to reduce manufacturing cost and provide a cost-effective method to join variety of components to form a complex composite structure. The effects of stitching on tensile and compressive properties are modeled based on a representative volume element that accounts for undulation and out-of-plane reinforcement, and a failure strength prediction based on unstitched strength is formulated using average stress distribution method. The effects of stitching on resin film infusion process are analytically investigation using finite element process simulation that accounts for capillary pressure and permeability changes. Various stitched and unstitched stiffened panels are fabricated using stitched resin film infusion (S/RFI) process. The fabricated panels are impacted using drop weight impact, and subsequent compression after impact (CAI) testing was performed to evaluate the damage tolerance of the stitched, stiffened composites panel according to SACMA recommended test method. The damages induced by impact on stitched and unstitched panels are modeled using finite element method. Results indicate enhanced resin infusion, reduction of damage size, increased compression strength and increased CAI strength, and an analytical methodology for stitched composite structure is established.