Quantitative Detection of Low Energy Impact Damage in a Sandwich Composite UAV Wing

This work describes damage detection efforts applied to a foam core composite wing following a series of low energy impacts in adjacent locations. The wing is a sandwich composite, composed of 4 layers of woven carbon fiber fabric surrounding a short aluminum core in the center (where it’s connected to the fuselage) and a foam core for the outer portions of the wing. The wing measures 1320 mm. × 152.4 mm. × 13.4 mm and has an airfoil cross-section. Thirteen impacts (6 – 8 J deposited energy) were applied at adjacent locations approximately 1/3 of the way out from the center. Following one or two impacts, the wing was tested using static tip deflection and dynamic vibrational excitation. Static and dynamic strains were measured using 8 fiber Bragg grating (FBG) sensors. Dynamic acceleration was also monitored using 3 conventional accelerometers. Dynamic excitation included the output of a Lorenz oscillator (0 – ∼150 Hz), simulated gust loading (0 – 150 Hz), and Gaussian white noise (0 – 1500 Hz). The analysis is a quantitative assessment of response nonlinearity based on the assumption that the undamaged wing behaves linearly and that the damage introduces nonlinearity into the vibrational response.