MECHANICAL-BEHAVIOR OF + -55-DEGREES FILAMENT-WOUND GLASS-FIBRE/EPOXY-RESIN TUBES .1. MICROSTRUCTURAL ANALYSES, MECHANICAL-BEHAVIOR AND DAMAGE MECHANISMS OF COMPOSITE TUBES UNDER PURE TENSILE LOADING, PURE INTERNAL-PRESSURE, AND COMBINED LOADING/

This series of papers on +/-55 degrees filament-wound glass-fibre/epox y-resin tubes consists of three parts. In Part I, the microstructure o f the composite tube was first investigated by image processing to qua lify the microstructural defects produced during manufacturing. A seri es of mechanical tests was then carried out under various combinations of hoop and axial stresses to evaluate the tubes' mechanical behaviou r under pure axial tensile load, pure internal pressure, and under com bined loading. Observations on specimens loaded to 20-50% of the ultim ate tensile strength showed that the main damage initiation mechanisms are microcracking (matrix and transverse cracks) and delamination. De pending on the loading conditions, one of the mechanisms dominates ove r the other. The effect of microstructural defects on the damage initi ation was clearly demonstrated. In Part II, micromechanical modelling of the damage initiation will be conducted in order to determine (1) t he mechanical conditions under which different microcracking mechanism s occur and (2) the critical sigma(zz)/sigma(theta theta) ratio which corresponds to the change from one mechanism to another. Emphasis is p laced on assessing the influence of microstructural defects and the co mpetition between the different mechanisms. In Part III, a macroscopic al behaviour law for the tubing structure with and without damage will be presented, and the simulation results will be compared with experi mental ones. (C) 1997 Elsevier Science Limited.