Damage characterization of composite wing subjected to impact loading - An experimental study

Damage on woven composites is a phenomenon that is difficult to characterize due to complex weave geometry. A woven composite wing structure adds to the complexity of characterizing damage through Fiber Bragg Grating (FBG) sensors. The present paper studies the FBG response and damage characterization of foam core and hollow composite wings. Plain and twill weave wings were manufactured and subjected to low energy (52.5J) and high energy (150J) impacts. Damage was assessed using FBG sensors, flash thermography, and visual inspection of the wings. Two FBG sensors were placed along the chord length and the spanwise direction at equal distances from the impact site to measure the axial strain as a function of time. The main failure modes of foam core wings were fiber breakage and foam crushing for high energy impacts, while core crushing and delamination between the core and the composite wing was found for low energy impacts. The hollow wings had a significant reduction in stiffness, resulting in a ripple effect where the wing would go into tension, then compression. This phenomenon varied depending on the location of the sensors on the wing. Although the impact zone was near the middle of the chord length of the wing, the resulting stress has caused large damage at the leading edge and significant debonding at the trailing edge of the hollow wing. An FE model was created to validate the experimental results and showed good correlation between the high stress areas in the model, the FBG response, and the damage sites on the wing.