UC San Diego

Composite structures have been increasingly employed in the aerospace industry, particularly in commercial aircraft due to their high stiffness and strength and low density. Carbon Fiber Reinforced Polymers (CFRPs) are brittle materials, and are hence prone to leaving little residual deformation due to lack of plasticity and may fail catastrophically. This is a concerningcharacteristic especially for High Energy Wide Area Blunt Impact (HEWABI), which can cause significant internal damage without external visibility. Experiments were performed on a 6-stringer curved panel with co-cured skin, bolted shear tie and C-frame representative of commercial composite aircraft, with loading next to passenger floor beam. The first damage observed was on the shear tie radius, and other damage modes include skin-stringer delamination, fractured C-frame, cut stringer cap and more shear tie cracks. The experimental data were compared to Finite Element Analyses (FEA), which were able to predict the first shear tie crack, stringers contact to shear tie/C-frame and damage to stringer cap. However, the exact timing of the damages was not captured. Additional fastener modeling, which affects the stiffness of the FEA, was introduced. Following the experiments, Non-Destructive Evaluation (NDE) of 2-stringer with co-cured skin curved panel using Mahalanobis Square Distance for outlier analysis was able to detect damage on stringer heel.