THEORETICAL INVESTIGATION INTO THE EFFECT OF THE WINDING ANGLE OF THE FIBERS ON THE STRENGTH OF FILAMENT WOUND GRP PIPES SUBJECTED TO COMBINED EXTERNAL-PRESSURE AND AXIAL-COMPRESSION

Finite element analysis has been carried on composite pipes of length-to-internal diameter ratio of 5 and internal diameter-to-thickness ratio of 20 to assess their strength when subjected to a combination of external pressure and axial compression. The effect of the winding angle of the fibre reinforcements on the buckling and first-ply failure loads of the pipes have been examined. It is shown that the optimum winding angle of the fibres varies according to the ratio of hoop-to-axial membrane stresses in the pipes. In the case of hydrostatic external pressure loading of the pipes, the optimum angle is close to 80-degrees instead of 55-degrees reported elsewhere for internal pressure loading.