Modelling Orthotropic Plasticity in Thermoplastic Composite Pipes

Abstract Thermoplastic composite pipes (TCPs) leverage the highperformance benefits of fibre-reinforced composites with a thermoplastic matrix system, making large-scale manufacturing a cost-effective endeavour. Carbon fibres reinforced with a thermoplastic matrix produce a material exhibiting highly ductile behaviour that is orthotropic in nature, meaning their elasticity and plasticity differ significantly with respect to the fibre direction. To fully harness these benefits, a comprehensive understanding of the non-linear behaviour of TCPs under diverse operational conditions is crucial. This work addresses this need by presenting a material modelling approach for orthotropic plasticity in TCPs, capturing the complex elasto-plastic responses characteristic of fibre-reinforced thermoplastic laminated composites. A bespoke three-dimensional (3D) elasto-plastic orthotropic user material was developed for implementation in the ANSYS finite element framework. The material model was calibrated against experimental data from flat coupon specimens to define the underlying properties of the ply material used in the TCPs. Validation of the model was performed using full-scale pipe simulations under diverse loading conditions, pipe geometries, and laminate stacking sequences. The results demonstrated an excellent ability to predict the non-linear behaviour of TCPs, including the onset and progression of small-scale matrix cracking.