Experimental and numerical study of dynamic strain ageing and its relation to ductile fracture of a C-Mn steel

Abstract : Ductile fracture of a C-Mn steel was characterized by tensile tests performed in a large temperature range (from 20 to 350 °C) on round notched and CT specimens. The experimental results revealed a sharp decrease in fracture strain and fracture toughness around 200 °C. These temperatures correspond to the domain of dynamic strain ageing (DSA). The Portevin-Le Chatelier (PLC) effect, which is the most classical manifestation of DSA, was simulated for round notched and CT specimens with a mechanical constitutive model which includes the strain ageing effect and the stiffness of the testing machine. It is shown that changes in stiffness can amplify the DSA effect. 3D-Modeling was used to correctly capture the complex space-time correlation of strain localization, particularly in side-grooved CT specimens. The results were compared to classical elastic-plastic simulations. The local approach to fracture was then applied to predict the ductile fracture of round notched specimens using the Rice and Tracey criterion. In the DSA domain, the approach used in this study predicts a decrease of the fracture strain which is less than observed experimentally.