Low-velocity impact response analysis of composite pressure vessel considering stiffness change due to cylinder stress

To accurately analyse the transient response and damage of pressurized vessels subjected to a drop impact or foreign object impact, we must consider the change in stiffness due to pre-stress. The pre-stress condition induces a phenomenon where thin plates with in-plane pre-stress show different stiffness during out-of-plane deflections compared to the original plate without the in-plane pre-stress. Because the cylindrical wall of a pressurized vessel is under in-plane pre-stress induced by the vessel's internal pressure, we must consider the 'change in stiffness' to accurately analyse the impact response and damage. In this study, we investigated the low-velocity impact response of a composite laminated cylinder wall of a pressure vessel with high internal pressure. The shear deformation theory of a doubly curved shell and von Karman's large deflection theory, as well as a newly proposed strain-displacement relation including initial strain terms to consider the stiffness change induced by cylinder stress due to internal pressure, were used to develop a geometrically nonlinear finite-element program. Numerical results that were calculated for the cylinder stress showed larger contact force and smaller deflection. By comparing strain values, a simple superposition of strain value calculated without considering cylinder stress and initial cylinder strain value showed 10-20% more strain than that accurately calculated with considering the stiffness change due to cylinder stress.