Interaction between plasticity and damage in the behaviour of [+φ, -φ]n fibre reinforced composite pipes in biaxial loading (internal pressure and tension)

In this paper, we propose a new model which describes the behaviour of [ + phi, - phi](n) composite laminates. Tests were performed on glass-epoxy pipes subjected to biaxial tensile and internal pressure loading. Experiments showed that [ + 55, - 55](n) pipes exhibit varying types of damaged elastoplastic behaviour depending on the stress ratio sigma(zz)/sigma(theta theta) (axial stress/hoop stress). A plastic model is based on the definition of a yield criterion and an associated flow rule. Damaging occurs when transverse microcracks appear in the layer. A micromechanical model defines the anisotropy of the damage. Interaction between plasticity and damage was of major importance in the definition of damage kinetics. This effect was observed on proportional loadings as well as on sequential tests: a preliminary loading in pure internal pressure (sigma(zz) = 0) induced large plastic phenomena which blocked crack propagation in additional internal pressure with closed ends effect (IPCEF) tests (R = sigma(zz)/sigma(theta theta) = 1/2), even though IPCEF caused considerable damage on an unloaded specimen. (C) 1998 Elsevier Science Ltd. All rights reserved.