Buckling behavior of composite laminated stiffened panels under combined shear and axial compression

Experimental results on the behavior of four torsion boxes, each comprising of two stringer stiffened cylindrical graphite-epoxy composite panels that have been subjected to torsion, axial loading and their combinations are reported. The buckling and post buckling behavior of these torsion boxes demonstrated consistent results. Prior to performing the buckling tests, the initial geometric imperfections of the boxes were scanned and recorded. The tests were complemented by finite element calculations, which were performed for each box. These detailed calculations have also assisted in identifying critical regions of the boxes and the boxes were reinforced accordingly to avoid their premature failure. The tests indicated that: the torsion carrying capacity is laminate lay-up dependent; axial compression results were in very good agreement with previous tests performed with single identical panels; and that the boxes have a very high post-buckling carrying capacity.