TY - JOUR A1 - Sievert, Rainer T1 - A geometrically nonlinear elasto-viscoplasticity theory of second grade N2 - A general concept for the consideration of the influence of strain gradients on elasto-viscoplastic material behaviour at finite deformation is presented that does not need to account for an additional flow rule for the plastic strain gradient. The balance of momentum including the representation of the stresses, the power of work at contact for the formulation of boundary conditions as well as the nonlocal form of the total power of deformation are derived via the dissipation inequality for the investigated nonpolar continuum model of second grade. In addition to the gradient of the elastic strain tensor, energy storage with gradients of different internal variables is considered: gradient of (i) the plastic strain Tensor itself, (ii) an internal strain tensor induced by viscoplastic straining, by which energy due to hardening is stored also with ist gradient, and (iii) scalar internal variables like the accumulated viscoplastic strain or an internal time variable of damage. Finally, for the simulation of the damage behaviour during a strain hold-time period at a crack tip the responses of a ratedependent and a quasi-rate-independent gradient-enhanced damage model are compared in finite element studies. KW - Viscoplasticity KW - Plasticity KW - Strain-gradient KW - Finite deformation PY - 2011 UR - http://www.uni-magdeburg.de/ifme/zeitschrift_tm/2011_Heft2/01_Sievert.pdf SN - 0232-3869 VL - 31 IS - 2 SP - 83 EP - 111 PB - Institut für Mechanik CY - Magdeburg AN - OPUS4-24166 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sommitsch, C. A1 - Sievert, Rainer A1 - Wlanis, T. A1 - Redl, C. T1 - Lifetime evaluation of two different hot work tool steels in aluminium extrusion N2 - During aluminium extrusion, the die experience cyclic thermo-mechanical loads that can lead to materials degradation and failure. For a process optimization and a comparison of different hot work tool steels, the finite element method is an appropriate means. Local inelastic strains result from the interaction of the applied temperature and stress loading and can be computed by suitable inelastic constitutive equations. Stress amplitudes and dwell times during extrusion result in creep-fatigue damage. A lifetime consumption model sums increments of a damage variable over time and defines materials failure as the accumulation of the resulting damage variable to a critical value. The procedure for the identification of the material parameters for both the constitutive and the damage model is described in detail, including the material parameters for the description of time-effects, and applied to the hot work tool steel Böhler W300 ISOBLOC (EN 1.2343). The lifetime consumption for two different hot work tool steels is compared on the basis of an example in aluminium extrusion. KW - Extrusion KW - Creep KW - Fatigue KW - Viscoplasticity KW - Aging KW - Failure PY - 2008 U6 - https://doi.org/10.1016/j.commatsci.2007.07.054 SN - 0927-0256 VL - 43 IS - 1 SP - 82 EP - 91 PB - Elsevier CY - Amsterdam AN - OPUS4-17585 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Levkovitch, Vladislav A1 - Sievert, Rainer A1 - Svendsen, B. ED - Portella, Pedro Dolabella T1 - Simulation of Low Cycle Fatigue Failure of FCC Single Crystals T2 - 5th International Conference on Low Cycle Fatigue (LCF-5) CY - Berlin, Germany DA - 2003-09-09 KW - Single crystal KW - Viscoplasticity KW - Simulation KW - Fatigue KW - Lifetime KW - Crack propagation KW - Blunting and resharpening KW - Laird KW - Striations KW - Re-meshing PY - 2003 VL - 5 SP - 415 EP - 420 PB - DVM, Deutscher Verband für Materialforschung und -prüfung CY - Berlin AN - OPUS4-3819 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -