Finite element simulation method for combined Ductile-Brittle fracture of small punch test in hydrogen

Abstract

This paper presents a simulation method for combined ductile–brittle fracture of small punch (SP) test in hydrogen and application to test data of API X70 steel. For ductile fracture simulation, the multi-axial fracture strain damage model determined from un-embrittled material with the hydrogen-embrittlement constant determined from SP test in hydrogen is used. To simulate brittle fracture, the critical stress method is proposed, where the critical stress is determined using the V notch round bar tensile test in hydrogen. The determined models are applied to simulate the SP test in hydrogen showing combined ductile and brittle fracture mode. Simulation can well reproduce not only the load–displacement curve but also the circumferential ductile cracking, followed by radial brittle cracking, observed in the test.