A Gurson-Tvergaard based model to simulate the fracture of aged duplex stainless steels

Abstract

A B S T R A C T In order to use duplex stainless steels for components designed to withstand temperatures up to 475 ° C, the knowledge of the effect of ageing on the fracture mechanisms is required. For the unaged steel, the ductile fracture takes place due to the nucleation of microvoids initiated on precipitates and inclusions present in the austenitic phase. However, the ageing of the material leads to a global loss of ductility. The ferrite phase embrittlement causes it to break by cleavage at lower levels of plastic strain. These changes, both in mechanical properties and in fracture micromechanisms, can be simulated by means of variation in the parameters that govern the constitutive equation of the material. The local approach model developed by Gurson-Tvergaard has been used to simulate, by FE analysis, the elasto-plastic behaviour and the fracture of these materials at various stages of ageing at 400 °C. An extensive experimental program has been undertaken in order to obtain the Gurson-Tvergaard model parameters needed for numerical simulations, which considers the. effect of ageing conditions (time and temperature), the ferrite content of the steel that causes the global embrittlement and the geometry of the component from the stress triaxiality by using axisymmetric notched specimens. The numerical model developed allows predictions to be made for the damage constitutive parameters for duplex steels subjected to any ageing conditions and, as a consequence, can be directly used for designing components.