Finite Element Simulation on Small Punch Test for an Evaluation of J-integral for TRIP Steel

Abstract

The small punch test (SPT) has been recently successfully developed for the purpose of evaluating the fracture toughness in not only brittle but also ductile materials. It is considered that fracture toughness of materials can be estimated by means of the SPT based on the measurement of equivalent fracture strain in the SPT and its correlation with fracture toughness. Moreover, fracture toughness of TRIP (transformation-induced plasticity) steel was evaluated by J-integral by using pre-cracked specimen under three-point bending test in the past study. However, the value of J-integral is determined at a limited range of deformation rate in three-point bending test. Thus, fracture toughness of TRIP steel needs to be evaluated by means of the SPT, especially at a relatively high deformation rate. Additionally, since the effect of strain-induced martensitic transformation during plastic deformation of TRIP steel coupled with a high increase of temperature is quite complicated, a computational work is indispensable. In this study, finite element simulations are performed for the SPT at various deflection rates and different sizes of specimen and puncher by an application of damage model for type-304 austenitic stainless steel, a kind of TRIP steel. The rate-sensitivity of fracture-mechanical characteristics is examined for different sizes of specimen and puncher. Furthermore, a relationship between equivalent fracture strain in the SPT and J-integral obtained from three-point bending test is challenged to be correlated.