Filament wound composite pipes subject to torsion and bending loads

Abstract

Filament winding has been extensively used to fabricate fibre reinforced composite pipes. The fibres are primarily oriented in such a way to increase the structural efficiency of the pipes to withstand internal pressure, that namely load the pipes in the hoop direction. However, the various intricate pipe systems and connections will also subject these pipes to torsional and bending loads. In this study different fibre orientation lay-up sequences consisting of four E-Glass /polyester resin layers were fabricated using a standard four-axis filament winding machine and experimentally subjected to torsion and bending load tests. During the curing process the samples were also vacuum bagged to minimise the void content. The respective volume fractions are also identified through ignition loss tests. The load versus deformation and ultimate failure load were recorded. The onset of first ply failure was also identified through acoustic/vibration measurements and observable differences in load/deformation plots. Different failure modes were observed ranging from buckling failure to matrix failure. The primary failure mode for pipes subject to bending was either compressive or tensile failure at the upper or lower strands of the pipe as a result of the imposed bending stresses. On the other hand, buckling or shear failure was observed in the pipes subject to torsional loading. The best fibre orientation based on loading conditions was identified. In the case of bending, the load carrying capacity increased when fibres are oriented closer to the axial direction, however care is to be taken to ensure that the pipes do not buckle. In the case of torsional loading, pipes with fibres oriented at 45⁰ were able to sustain the highest load.