The influence of winding patterns on the damage behaviour of filament-wound pipes

Filament winding is one of the most common techniques for the manufacture of tubes. The helical winding method often produces interweaving of fibres inside the layers. The aim of this study is to characterise the influence of the degree of this interweaving on the mechanical performance of cylindrical structures under various loadings. We present, first, the basics of the helical winding method and of a filament-winding machine designed for the study. The specimens studied are glass/epoxy tubes with a [±55°] 6 lay-up. All manufacturing parameters are kept constant except for the winding pattern. Quality of the fabrication is assessed by strict monitoring of the geometry and the microstructure of the tubes. Tests carried out on the specimens consist in progressive repeated loadings, aimed at characterising the damage behaviour under various loadings. Damage growth is shown to be increased by the degree of interweaving of the tubes only for closed-ended internal-pressure loading. Weeping tests under this loading show that the presence of fibre crossovers may induce premature weeping of the pipes. The undulation regions and the voids found near these regions possibly represent an initiation site for cracking, thus increasing damage growth and the possibility of leaking in high interwoven structures.