Effects of material failure on buckling behaviour of medium-thick GFRP cylindrical shells for submarine applications

The paper is concerned with the interaction of buckling and material failure in composite cylindrical shells subject to external pressure. A methodology for the numerical prediction of the strength of composite shells is discussed and an application is presented. The results of an experimental and numerical research on a composite shell structure, intended as a model for an under-water vehicle for service in deep-sea environment, are recalled. It is showed how a reasonable prediction of the buckling pressure can be obtained only including the effects of the geometric imperfections. The validated finite element model is then adopted for a parametric study on the influence of the thickness variation on the failure behaviour of cylinders. A well-known failure criteria for composite laminates (Tsai-Wu) is introduced in the model to study the interaction between buckling and material failure in composite cylinders subject to hydrostatic pressure. The values of the pressure obtained with linear buckling, first-ply and progressive failure analysis with or without geometric effects are discussed for a specific composite cylinder.