Mechanical behaviour of +/-55 degrees filament-wound glass-fibre/epoxy-resin tubes .2. Micromechanical model of damage initiation and the competition between different mechanisms

This series of papers on +/-55 degrees filament-wound glass-fibre/epoxy-resin tubes consists of three parts. lit the present paper (Part II), micromechanical modelling of the damage initiation is conducted in order to determine (I) the mechanical conditions under which different microcracking mechanisms occur and (2) the critical sigma(zz)/sigma(theta theta) ratios which correspond to the change from interfacial failure to microcracking at porosity. Emphasis is placed on assessing the influence of microstructural defects and the competition between the different mechanisms. The general tendency of damage-envelope prediction by means of micromechanical modelling fits the microscopy observations quite well. The sensitivity of local criteria is also discussed. The correction of the local stress field has been improved by introducing a local stress concentration factor in a mean field theory model (Mori-Tanaka theory). In Part I, the microstructural analyses, mechanical behaviour and damage initiation mechanisms were presented. In Part III, the macroscopic behaviour of the tubing structure with and without damage will be presented The simulation results will be compared with experimental ones. (C) 1997 Elsevier Science Limited.