TY - CONF A1 - Keller, Christian A1 - Herbrich, Uwe T1 - Plastic Instability of Rate-Dependent Materials - A Theoretical Approach in Comparison to FE-Analyses - T2 - 11th European LS-DYNA Conference (Proceedings) N2 - The condition for plastic instability is a material characteristic and defines the onset of necking in tensile tests. In large deformation problems of ductile materials it is fundamental to determine the strain at which necking starts as well as the post-necking behaviour in the instability region properly. For verification purposes of material models, usually results of numerical analyses are compared to experimental outcomes. For tensile tests with ductile materials under dynamic loading, it is challenging to obtain comparable experimental and numerical results in terms of the onset of necking and the post-critical deformation behaviour. This paper focuses on the derivation of a theoretical criterion describing the plastic instability in rate-dependent materials based on the time variation of the strain gradient in a tensile specimen under isothermal conditions. We examine the influence of various constitutive equations on the theoretical stability condition predicted by different multiplicative as well as additive approaches. For multiplicative relations, the results indicate that the onset of necking is, in principle, independent of the strain rate, whereas for the considered additive relation, the dynamic necking strain must decrease with increasing strain rate. In conclusion, the theoretical stability condition is related to results from finite element simulations of dynamic tensile tests with various loading rates. It is shown that the simulated and the theoretical predicted onset of plastic instability agree reasonably. T2 - 11th European LS-DYNA Conference CY - Salzburg, Austria DA - 09.05.2017 KW - FEM KW - Plastic Instability KW - Dynamic Tensile Test PY - 2017 UR - http://www.dynalook.com/11th-european-ls-dyna-conference/crash-metal-failure/plastic-instability-of-rate-dependent-materials-a-theoretical-approach-in-comparison-to-fe-analyses SP - 1 EP - 10 AN - OPUS4-40660 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -