Deformation and Ductile Failure of a Low Alloyed Steel under High Strain Rate Loading

It is well known that ductile failure of metal is occurring after a certain amount of plastic deformation. Therefore, knowledge about the deformation behavior of materials is required to understand damage processes and to describe the failure behavior using suitable constitutive equations. Thereby, the influence of temperature and strain rate has to be known for an accurate constitutive description of the mechanical behavior of metals. Within this study, the MTS (Mechanical Threshold Stress) model is used for the description of the material behavior of low alloyed steels in a wide range of temperatures and strain rates. In addition, the model is extended using a new mathematical part to describe the effect of dynamic strain aging at low strain rates and high temperatures. To describe the real material behavior, material data at high strains, high strain rates, and high temperatures are required, especially if the deformation and failure process is going to be simulated numerically. A new testing technique is used to perform stopped high rate tensile tests during necking process. Hence, the true stress and true strain behavior of the materials can be determined directly from high rate experiments and enhance the quality and accuracy of the parameter identification process for constitutive equations. By finite element calculations using LS-DYNA 3D, the tensile deformation of a specimen is simulated until crack initiation including necking and the stress triaxiality in the necking zone of a tensile specimen is evaluated. It is shown that the strain hardening characteristic of a material affects the development of stress triaxiality.

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