Finite-element Analysis of Composite Pressure Vessels with Progressive Degradation

Abstract

A degradation model incorporated into the finite-element analysis of the pressure vessel, based on a progressive failure criterion, has been discussed. A stiffness reduction scheme for the failed laminas has been implemented using package ANSYS along with a reduction in the strength of the composite (on its undegraded strength after a substantial degradation of its constituents). The degradation model used for analysis is sensitive to the mesh and the load step size. Computational efficiency (CPU time) of the finite-element model is very important in the degradation study, and accordingly, equilibrium is not re-established in the nonlinear solution procedure implemented in ANSYS (single-frame restart analysis). This is offset using a small load step size for the degradation studies of the pressure vessel. The model is qualified by a comparison with deformation measurements obtained from hydrostatic tests. The experimental deformations have an excellent match with the degraded model in comparison to the undegraded model. The redistribution of stresses in the composite constituents as a result of degradation, has been demonstrated. The burst in the pressure vessel is indicated by unusually large displacement and infeasible stress profile in consequence to a substantial degradation in the fibre material of the composite.