The competition between buckling and stress failure of degraded composite cylindrical shell under combined axial compression and external pressure loads

When thin-walled composite cylindrical shells are subjected to combined loads, not only will they buckle, but they could fail under overstressing. Buckling-failure and stress-failure are two types of failure that compete mutually, and if one of them occurs, the structure loses its ability to carry the load. However, there is a lack of study, and very little attention was paid to the competitive-failure of the composite cylindrical shells under combined loads. To bridge this research gap, a competitive failure analysis framework of degraded composite cylindrical shells exposed to combined axial compression and external pressure loads was developed, considering the nonlinear buckling-failure interacting curve approach for buckling-failure analysis and the Tsai-Wu failure criterion for stress-failure analysis. The material degradation model was adopted to modify the properties of the failed ply based on two degrading philosophies. The proposed framework agrees well with the published results. Extensive parametric studies are accomplished and presented to detect the failure mode of composites. For material parametric study, the variation of material properties does not significantly affect the shape of the normalized buckling-failure interacting curve, while it appreciably affects the behavior of the stress-failure interacting curve. Moreover, it is found that as the proportions of the longitudinal compressive strength to longitudinal modulus and transverse tensile strength to transverse modulus of composite materials increase, the tendency for buckling-failure increases; otherwise, stress-failure happens. For a geometric parametric study, decreasing the radius-to-thickness ratio leads to an increase in the shape of the buckling-failure interacting curve and the possibility of stress-failure.