Evaluation of Thermoplastic Stiffened Panels for Application to Rotorcraft Airframes

An experimental evaluation of thermoplastic skin-stiffener structure was conducted by evaluating the shear strength, impact resistance, and damage tolerance of stiffened panels with thin-gage skins. Seventeen 23.5" x 23.5" three-stiffener test panels were manufactured with five skin configurations: 0.020", 0.030", and 0.040" thick IM7/APC-2 and 0.030" and 0.040" thick AS4/APC-2. In low-velocity impact trials, the IM7/APC-2 panels showed much higher impact resistance than the AS4/APC-2 panels, and both thermoplastic configurations showed higher impact resistance than AS4/3501-6 graphite/epoxy panels tested previously. In picture-frame shear tests, the undamaged thermoplastic shear panels suffered buckling-induced stiffener debonding but had failure loads above AS4/3501-6 panels with the same skin thickness. Residual panel strength after impact varied considerably due to variation in the damage states, but all failure loads were equal to or higher than those of the AS4/3501-6 panels. In tests of both undamaged and impacted panels, the failure stresses of the IM7/APC-2 and AS4/APC-2 panels were similar.