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

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 547; pp. 19 - 31
• Main Authors: Wang, H.D., Berdin, C., Mazière, M., Forest, S., Prioul, C., Parrot, A., Le-Delliou, P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15-06-2012; Elsevier
• Subjects: Applied sciences; Ductile fracture; Dynamic strain ageing; Elasticity. Plasticity; Engineering Sciences; Exact sciences and technology; Fractures; Local approach; Materials; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Numerical modeling; Strain localization; Numerical modeling; Ductile fracture; Strain localization; Local approach; Dynamic strain ageing; Constitutive equation; Notched test piece; Manganese steels; Tension test; Strain ageing; Fracture toughness; Compact tension test; Three dimensional model; Lueders band; Elastoplasticity; Fractography; Portevin Le Chatelier effect; Dynamic load
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2012.03.069

► Constitutive law accounting for Dynamic Strain Aging is used. ► Complex local mechanical variables variations with time due strain localization. ► Damage variable is independent on strain localizations. ► Accounting for strain aging is not sufficient to explain ductility drop in steel.
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.