Numerical modelling of the dynamic plasticity and fracture behaviour of X70 pipeline steel

Present research aims at establishing a numerical framework that allows for a realistic description of the dynamic plasticity, damage, and fracture properties of an API-5L X70 pipeline steel. An extended version of the Modified Bai-Wierzbicki (eMBW) model is implemented in the commercial finite element code Abaqus. The eMBW model constitutes a coupled isotropic damage-plasticity law wherein the influences of plastic strain, stress state, strain rate, and temperature are accounted for in the yield function. A stress state dependent phenomenological criterion defines the initiation of damage followed by an energy-based damage propagation rule. The material model parameters are calibrated using well-designed damage experiments performed at wide ranges of quasi-static and dynamic strain rates. The experimental design consists of a variety of specimen types, namely uniaxial tension, and 2 notched tension, whose geometrical characteristics result in a wide range of stress states. The more pronounced strain hardening and improvement in fracture properties exhibited by the X70 steel at high strain rates are predicted by the proposed model. Experiments are also modelled using a coupled effect of strain rate and temperature on material plasticity replacing the multiplicative correction functions in the original formulation. Thus, a significantly better conformance between experiments and simulations is found. The material model is additionally validated using Charpy impact test