Effect of Laminate Fibre Orientation on Thermoplastic Composite Pipe Buckling and Material Failure under Thermomechanical Loading

Thermoplastic composite pipes (TCPs) are attractive deepwater alternatives to steel due to their high specific strength and corrosion resistance but face multiple failure modes because of their anisotropic structure and the expected harsh combined loading. This study examined how laminate ply orientation and stacking order influenced buckling capacity, strength, and failure mode transitions in a TCP under combined bending, axial compression, internal/external pressure, and through-thickness thermal gradients. A 3D thermally coupled finite element model was developed for linear buckling and failure analysis, utilising temperature-dependent properties, the Tsai-Hill and Hashin criteria for the laminate, and the von Mises criterion for isotropic liners across an internal surface temperature range of 4–120 °C, considering both single-angle and double-double (DD) laminates. The critical buckling load decreased with increasing thermal gradient, exhibiting laminate-dependent decay slopes. At low temperatures, failure alternated between buckling and material failure, while at high temperatures, inner liner yield predominated. Double-double laminates with TCPs that mix low and high-angle plies delivered the best overall performance, balancing low-temperature buckling resistance with elevated-temperature material strength. These results inform temperature-resilient TCP laminate designs. • Buckling and material failure of thermoplastic composite pipes subjected to combined mechanical and thermal loads is considered. • The coupling between mechanical loads and thermal stresses increases failure risk. • Increasing internal pipe surface temperatures reduces both buckling and material failure resistance. • The critical buckling load decreased with increasing thermal gradient, exhibiting laminate-dependent decay slopes. • At low temperatures, failure alternated between buckling and material failure, while at high temperatures, inner liner yield predominated. • Double-double laminates with TCPs that mix low and high-angle plies delivered the best overall performance, balancing low-temperature buckling resistance with elevated-temperature material strength.