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 - GEN A1 - Boubidi, Pascal A1 - Sievert, Rainer ED - Fuentes, M. T1 - Analysis of low-cycle fatigue at notches in a single crystal superalloy at high temperature T2 - 13th European Conference on Fracture CY - San Sebastián, Spain DA - 2000-09-06 KW - LCF KW - Kerben KW - Einkristalle KW - Turbinenschaufeln PY - 2000 SN - 0-08-043699-4 SN - 1566-1369 N1 - Serientitel: ESIS publication – Series title: ESIS publication IS - 26 PB - Elsevier CY - Amsterdam AN - OPUS4-1074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Levkovitch, Vladislav A1 - Sievert, Rainer A1 - Svendsen, B. T1 - Application of extended crystal plasticity to the modeling of glide and kink bands and of crack opening in single crystals N2 - In this work, the influence of the development of geometrically necessary dislocations (GNDs) at a crack tip in single crystals on the hardening and crack propagation behaviour is investigated. In particular, we are interested in examining the effect of such additional hardening on the development of glide and kink bands at the crack tip as well as on the process of crack opening. To this end, following Nye and many others, local deformation incompatibility in the material is adopted as a measure of the density of GNDs. Their development results in additional energy being stored in the material, leading to additional kinematic-like hardening. A thermodynamic formulation of the model in the context of the dissipation principle facilitates the derivation of the corresponding hardening relation. Results suggest that this additional hardening retards kink-band development, but has little or no influence on glide-band development. It also influences the crack tip opening displacement (CTOD). It turns out that the simulated CTOD correlates well with experimentally determined crack-propagation rates for different crack growth direction in the crystal. KW - Thermodynamics KW - Single crystal plasticity KW - Geometrically necessary dislocations KW - Hardening KW - Glide and kink bands KW - Crack-opening displacement PY - 2005 SN - 0927-0256 VL - 32 IS - 3-4 SP - 426 EP - 434 PB - Elsevier CY - Amsterdam AN - OPUS4-7067 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Skrotzki, Birgit A1 - Brookes, Stephen-Peter A1 - Kühn, Hans-Joachim A1 - Sievert, Rainer A1 - Klingelhöffer, Hellmuth A1 - Pfetzing, J. A1 - Peter, D. A1 - Eggeler, G. ED - Khan, A.S. ED - Kabirian, F. ED - Liu, J. T1 - Axial-torsional thermo-mechanical fatigue of a near-gamma tial-alloy T2 - Plasticity '12 - 18th International symposium on plasticity and its current applications CY - San Juan, PR, USA DA - 2012-01-03 KW - TMF KW - Multiaxial fatigue KW - Titanium aluminides PY - 2012 SN - 0-9659463-0-4 SP - 187 EP - 189 PB - NEAT Press CY - Fulton, Maryland, USA AN - OPUS4-25325 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Brookes, Stephen-Peter A1 - Kühn, Hans-Joachim A1 - Skrotzki, Birgit A1 - Klingelhöffer, Hellmuth A1 - Sievert, Rainer A1 - Pfetzing, J. A1 - Eggeler, G. ED - K. Maruyama, ED - M. Niinomi, ED - S. Akiyama, ED - M. Ikeda, ED - M. Hagiwara, T1 - Axial-torsional thermo-mechanical fatigue of Ti-45 Al-5Nb-0.2B-0.2C T2 - 11th World Conference on Titianium (JIMIC 5) CY - Kyoto, Japan DA - 2007-06-03 KW - Gamma titanium aluminide KW - Thermo-mechanical fatigue KW - TMF KW - Axial-torsional loadings KW - Microstructure PY - 2007 SN - 978-4-88903-406-6 VL - 1 SP - 679 EP - 682 PB - Japan Institute of Metals CY - Kyoto AN - OPUS4-16669 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Brookes, Stephen-Peter A1 - Kühn, Hans-Joachim A1 - Skrotzki, Birgit A1 - Klingelhöffer, Hellmuth A1 - Sievert, Rainer A1 - Pfetzing, J. A1 - Peter, D. A1 - Eggeler, G. ED - Kim, Young-Won ED - David Morris, ED - Rui Yang, ED - Christoph Leyens, T1 - Axial-torsional thermo-mechanical fatigue of Ti-45 Al-5Nb-0.2B-0.2C T2 - TMS 2008 Annual Meeting & Exhibition, "Structural Aluminides for Elevated Temperatures - Gamma Titanium and Other Metallic Aluminides" CY - New Orleans, Louisiana, USA DA - 2008-03-09 KW - Titanium Aluminide KW - Thermo-mechanical Fatigue KW - Axial-torsional Loading PY - 2008 SN - 978-0-87339-7209 SP - 103 EP - 109 PB - TMS CY - Warrendale, Pa AN - OPUS4-17904 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brookes, Stephen-Peter A1 - Kühn, Hans-Joachim A1 - Skrotzki, Birgit A1 - Klingelhöffer, Hellmuth A1 - Sievert, Rainer A1 - Pfetzing, J. A1 - Peter, D. A1 - Eggeler, G. T1 - Axial-torsional thermomechanical fatigue of a near-gamma TiAl-alloy N2 - The uniaxial, torsional and axial-torsional thermomechanical fatigue (TMF) behavior of the near-γ TiAl-alloy TNB-V5 was investigated. TMF tests were performed at 400-800 °C with mechanical strain amplitudes ranging from 0.15% to 0.7%. The tests were conducted thermomechanically in-phase (IP) and out-of-phase (OP). For the same lifetimes, uniaxial IP tests required the highest strain amplitudes, while OP test conditions were most damaging and needed the lowest strain amplitudes. The Mises equivalent mechanical strain amplitudes of pure torsional tests were found in between uniaxial in-phase and out-of-phase tests for the same lifetimes. The non-proportional multiaxial out-of-phase test showed a lower lifetime at the same equivalent mechanical strain amplitude compared to the other types of tests. The microstructure has been characterized applying electron microscopy and microstructural parameters such as fraction of twinned grains, grain size, lamellar distance and dislocation density have been quantified. KW - Gamma titanium aluminide KW - TNB-V5 KW - Thermomechanical fatigue (TMF) KW - Axial-torsional loading KW - Microstructure PY - 2010 U6 - https://doi.org/10.1016/j.msea.2010.03.073 SN - 0921-5093 SN - 1873-4936 VL - 527 IS - 16-17 SP - 3829 EP - 3839 PB - Elsevier CY - Amsterdam AN - OPUS4-21289 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krumphals, F. A1 - Wlanis, T. A1 - Sievert, Rainer A1 - Wieser, V. A1 - Sommitsch, C. T1 - Damage analysis of extrusion tools made from the austenitic hot work tool steel Böhler W750 N2 - During hot extrusion of copper alloys, extrusion tools have to withstand cyclic thermal and mechanical loads. To enhance the service life of the tools, materials with high temperature strength are designed as well as an optimised process control is performed. To characterise the tool damage evolution during service and to improve process guiding, modelling and simulation are appropriate means. The extrusion process of copper billets at three different temperatures was simulated by an FE-program to obtain the temporal boundary conditions, i.e. stress and temperature distributions at the interface billet-liner. Those boundary conditions were used to simulate the elastic–viscoplastic behaviour of the tool steel Böhler W750 in service by means of Abaqus Standard™ v.6.8-3 software in conjunction with Z-Mat package. A lifetime rule was added in order to compute the lifetime consumption and the cycles to failure. KW - Hot work tool steel KW - Damage evolution KW - Lifetime prediction KW - Copper extrusion PY - 2011 U6 - https://doi.org/10.1016/j.commatsci.2010.04.022 SN - 0927-0256 VL - 50 IS - 4 SP - 1250 EP - 1255 PB - Elsevier CY - Amsterdam AN - OPUS4-23215 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Forest, Samuel A1 - Sievert, Rainer T1 - Elastoviscoplastic constitutive frameworks for generalized continua N2 - A unifying thermomechanical constitutive framework for generalized continua including additional degrees of freedom or/and the second gradient of displacement is presented. Based on the analysis of the dissipation, state laws, flow rules and evolution equations are proposed for Cosserat, strain gradient and micromorphic continua. The case of the gradient of internal variable approach is also incorporated by regarding the nonlocal internal variable as an actual additional degree of freedom. The consistency of the continuum thermodynamical framework is ensured by the introduction of a viscoplastic pseudo–potential of dissipation, thus extending the classical class of so–called standard material models to generalized continua. Variants of the higher order and higher grade theories are also reported based on the explicit introduction of the plastic strain tensor as additional degree of freedom. Within this new class of models, called here gradient of strain models, one recognizes the fact that, in a second grade theory for instance, the plastic part of the strain gradient can be identified with the gradient of plastic strain. Simple examples dealing with bending and shearing of Cosserat or second grade media are given to illustrate two types of extensions of classical J 2-plasticity : single-criterion and multi-mechanism generalized elastoplasticity. Finally, formulations at finite deformation of the proposed models are provided focusing on proper decompositions of Cosserat curvature, strain gradient and gradient of micromorphic deformation into elastic and viscoplastic parts. PY - 2003 U6 - https://doi.org/10.1007/s00707-002-0975-0 SN - 0001-5970 SN - 1619-6937 VL - 160 SP - 71 EP - 111 PB - Springer CY - Wien AN - OPUS4-1924 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Boubidi, Pascal A1 - Sievert, Rainer ED - Biallas, G. T1 - Experimental and Numerical Investigations of Macro-Crack Initiation under Low-Cycle Fatigue Loading at Notches in a Single Crystal Superalloy at High Temperature T2 - CAMP 2002 CY - Bad Lippspringe, Germany DA - 2002-04-03 KW - Single crystal KW - Notched specimens KW - Cracks KW - Lifetime KW - Turbine blades PY - 2002 SN - 3-00-009254-4 SP - 127 EP - 141 PB - Inst. für Prozess- und Werkstofftechnik CY - Paderborn AN - OPUS4-1436 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -