Instability of imperfect composite cylindrical shells under combined loading

A numerical study using the non-linear finite element analysis has been carried out to investigate the response of composite cylindrical shells subject to combined loading. The interaction buckling curves of perfect composite cylinders subject to different combinations of axial compression, torsion, bending and lateral pressure are obtained. The postbuckling analysis of composite cylinders with geometric imperfections of eigenmode-shape is carried out to study the effect of imperfection amplitude on the critical buckling load. The initial buckling load of composite shells is substantially reduced by the existence of imperfections. Here it is shown that the effects of imperfections are more apparent when the composite cylindrical shells are subject to combined loadings. The results show that the buckling and non-linear response of geometrically imperfect shell structures subjected to complex loading conditions may not be characterized correctly by an elastic linear bifurcation buckling analysis.