Numerical and experimental investigation on tensile fatigue performance of reinforced thermoplastic pipes

Abstract

With the rapid development of offshore drilling for harvesting oil and gas from the deep sea, the fatigue performance of offshore risers is increasingly demanding. This study investigated the tensile fatigue performance of reinforced thermoplastic pipes (RTPs). The theory of three-dimensional (3D) anisotropic elastic mechanics was combined with a strain potential-energy density function to construct the 3D constitutive relation of RTPs. The stiffness degradation law of RTPs was predicted by introducing a modified 3D Hashin failure criterion and the residual stiffness model. A user-defined material (UMAT) subroutine was developed to evaluate the progressive fatigue failure process of RTPs. A uniaxial tensile fatigue experiment of RTPs was designed to validate the numerical model's correctness. The analysis examined the damage failure modes of RTPs under cyclic loading conditions and revealed the stiffness degradation mechanism. Results suggested that the matrix fatigue damage of the reinforced layer of RTPs is the primary cause of the rapid stiffness degradation, which was observed to be faster with increasing cyclic load stress levels.