Numerical investigation of speed dependent dynamic fracture toughness of line pipe steels

Recent Drop Weight Tear Test (DWTT) showed that dynamic fracture toughness of line pipe steels depends on fracture speed. Based on a properly designed separation–traction law, standard and modified DWTT of API X80 line pipe steel are simulated by Cohesive Zone Model (CZM) based FEA (finite element analysis). The loading-displacement curve, fracture speed, and crack tip opening angle (CTOA) in FEA simulations are compared with experimental results. The agreement between the present FEA and experimental results shows that the present FEA can well describe high-speed fracture of the standard and modified DWTT of API X80 line pipe steel. The relation between CZM fracture energy, steady-state CTOA and steady-state fracture speed are investigated through two groups of FEA simulations designed for standard and modified DWTT. Our FEA results show that both CZM fracture energy and steady-state CTOA decrease with steady-state fracture speed, and two empirical relations are suggested to describe the dependence of the two toughness measures on steady-state fracture speed.