Composites airframe panel design for post-buckling – An experimental investigation

Abstract

Three series of airframe composite panels with T-stiffener, I-stiffener and J-stiffener are designed and optimized to have the same local skin buckling load and weight. All the panels are designed to undergo local skin buckling between Design Limit Load (DLL) and Design Ultimate Load (DUL), approximately at 120% of DLL to utilize the reserve strength in structures. Additionally, identical panels are designed and fabricated from each series to study the effect of various extrinsic parameters such as disbond, delamination, impact damage and repeated loading to identify the best performing series for post-buckling design. All the panels are tested under compression to demonstrate no onset of damage before DUL. The influence of defects such as disbond, delamination and impact damage on the post-buckling behavior is also demonstrated. One pristine panel of each series is repeatedly loaded 1000 times beyond buckling to determine the onset of damage if any. The panels with I-stiffener and J-stiffener found to be the potential design choices for post-buckling design philosophy due to the high margin between skin buckling and collapse load even in the presence of damage. The results from this study would help in moving closer to the post-buckled composite design philosophy for airframe structure.