FINITE ELEMENT ANALYSIS OF DUCTILE FAILURE IN STRUCTURAL STEEL SUBJECTED TO MULTIAXIAL STRESS STATES AND HIGH STRAIN RATES

Notched specimens of the structural steel Weldox 460 E have been tested at high strain rates in a Split Hopkinson Tension Bar. The aim was to study the combined effects of strain rate and stress triaxiality on the strength and ductility of the material. It is further considered important to obtain experimental data that may be used in validation of constitutive relations and fracture criteria. The force and elongation of the specimens were measured continuously by strain gauges on the half-bars, while the true fracture strain was calculated based on measurements of the fracture area. Optical recordings of the notch deformation were obtained using a digital high-speed camera system. Using image processing of the digital images, it was possible to estimate the true strain versus time at the minimum cross-section in the specimen. The ductility of the material was found to depend considerably on the stress triaxiality. Non-linear finite element analyses of the notched tensile specimens at high strain rates have been carried out using LS-DYNA. A computational material model including viscoplasticity and ductile damage has been implemented in LS-DYNA and determined for Weldox 460 E steel. The aim of the numerical simulations was to assess the validity of the material model by comparison with the available experimental results.