Experimental investigation on edge impact damage and Compression-After-Impact (CAI) behavior of stiffened composite panels

The purpose of this paper was to investigate the effect of low velocity edge impact damage on the damage tolerance of wing relevant composite panels stiffened with both T-shaped and I-shaped stiffeners under uniaxial compression load. Six stiffened composite panel configurations, including four specimens for each configuration, were manufactured and tested. Before Compression-After-Impact (CAI) tests, the key dimensions of specimens were measured and a vertical drop-weight testing device was used to impact on critical locations such as the skin and the free edge of a stiffener. Different damage types and shapes were discovered from different locations of impact after careful inspection by visual and ultrasonic C-scan. The experimental results reveal the compression failure mechanism that local buckling, subsequent damage propagation and final fracture of the edge impacted stiffener are triggers of the final failure of a stiffened composite panel, which as well determine the ultimate load carrying capacity. In addition, under identical edge impact levels, the damage tolerance behavior of T-stiffened composite panel is distinctly superior to that of I-stiffened composite panel, which results in more cautious design regarding edge impact damage tolerance of the panel stiffened with I-stiffeners.