Experimental study on failure behaviour of stiffened composite panel under combined shear and compressive loading

A bespoke test apparatus has been developed to investigate the buckling and post-buckling behaviours of a stiffened composite panel under combined shear and compression. A pair of four-bar linkage shear frames coupled with actuators have been introduced to produce the shear force along the lateral edges of the panel, enabling adaptive adjustment to the direction of shear force as the panel undergoes in-plane shear deformation. Experimental results have verified the capability of the apparatus for producing a uniform strain distribution over the area of interest for the panel and the effectiveness in independently controlling the shear and compressive loads without interference during the combined loading. The failure loads of the panel are 50% greater than the initial buckling loads in this combined loading case, showing a sufficient load carrying capability in the post-buckling regime. Results show that local buckling in skin bays is the primary buckling mode for the panel studied. The stiffeners are capable of sustaining axial compression while the skin has buckled locally. The buckling-induced waviness in skin bays produces a twist effect on the stiffeners, contributing to skin-stiffener debonding and stiffener breakage, and therefore ultimately leading to the collapse of the stiffened panel.