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 o f tubes. The helical winding method often produces interweaving of fibres i nside the layers. The aim of this study is to characterise the influence of the degree of this interweaving on the mechanical performance of cylindric al structures under various loadings. We present, first, the basics of the helical winding method and of a filament-winding machine designed for the s tudy. The specimens studied are glass/epoxy tubes with a [+/- 55 degrees](6 ) lay-up. All manufacturing parameters are kept constant except for the win ding pattern. Quality of the fabrication is assessed by strict monitoring o f the geometry and the microstructure of the tubes. Tests carried out on th e specimens consist in progressive repeated loadings, aimed at characterisi ng the damage behaviour under various loadings. Damage growth is shown to b e increased by the degree of interweaving of the tubes only for closed-ende d internal-pressure loading. Weeping tests under this loading show that the presence of fibre crossovers may induce premature weeping of the pipes. Th e undulation regions and the voids found near these regions possibly repres ent an initiation site for cracking, thus increasing damage growth and the possibility of leaking in high interwoven structures. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.