Combined ductile-brittle fracture simulation of API X80 under impact loading

This study explores finite element (FE) simulation of the combined ductile-brittle fracture behavior of API X80 steel under impact loading, incorporating the influences of strain rate and adiabatic heating. The Johnson-Cook (J-C) deformation model is employed for deformation analysis, while ductile fracture is modeled using the J-C fracture strain model, and brittle fracture is captured using a critical stress model. Temperature-dependent parameters for the J-C model were calibrated through smooth round bar (SRB) tests conducted at varying temperatures, while strain rate-dependent parameters were identified using the Charpy V-notch (CVN) impact test at room temperature (RT). Additionally, the critical stress model for brittle fracture was determined via FE simulation of CVN tests at RT. The calibrated deformation and combined fracture models were applied to simulate both CVN and drop-weight tear test (DWTT) over a temperature range of −120 °C to 0 °C. The simulations accurately captured deformation behavior, load-displacement curves, and fracture surfaces. Sensitivity analyses highlighted the roles of adiabatic heating and strain rate effects in fracture behavior.