Deformation and Ductile Fracture of a Low Alloy Steel under High Strain Rate Loading

Ductile failure of metals always occurs after a specific amount of plastic deformation. Therefore, the investigation and characterization of the deformation behaviour is required to understand the damage process and to describe the failure by a suitable constitutive relation. The effects of temperature and strain rate on the mechanical properties are important for the description of the material behavior in many applications. The MTS model is used here to describe the material behavior of some low alloy steels in a wide range of temperature and strain rates. A new part of stress is added to the MTS model in order to consider the effect of the dynamic strain aging at low strain rate and high temperature. The determination of material data at high strain and high strain rate is needed to describe the real material behaviour, specially for the simulation of high deformation and fracture. A special technique is used here to stop the deformation of tension specimen at high strain rate in the necking zone to determine the true stress and true strain. Using FEM computations (LS-DYNA 3D), the stress triaxiality in the necking zone of a tensile specimen is calculated up to the crack initiation. It is shown that the strain hardening characteristics affect the development of stress triaxiality