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 JF - Computational materials science 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 DO - 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 - JOUR A1 - Sommitsch, C. A1 - Sievert, Rainer A1 - Wlanis, T. A1 - Günther, Burkhard A1 - Wieser, V. T1 - Modelling of creep-fatigue in containers during aluminium and copper extrusion JF - Computational materials science N2 - During hot extrusion of aluminium alloys, extrusion dies experience cyclic temperature changes as well as multiaxial loadings. To improve the service life of the dies, cleaner and high hot strength materials are designed as well as an optimised process control is performed. For the improvement of the process guiding and a comparison of lifetime behaviour of different hot work tool steels, modelling and simulation are appropriate means. The extrusion process has been simulated using the FE-program Deform to find the stress and temperature history at the inner diameter of the liner, i.e. the boundary conditions for the subsequent cyclic simulation of the container during service. Inelastic constitutive equations have been implemented into Abaqus Standard to describe strain hardening and time recovery effects. They include the Norton viscoplastic flow rule, thermo-mechanical isotropic hardening and two non-linear kinematic hardening laws. A damage-rate model predicts failure and thus the lifetime of the container. The procedure for the identification of material parameters for both the constitutive and the damage model is described in detail for the hot work tool steel Böhler W400 VMR (EN 1.2343). KW - Extrusion KW - Hot work tool steels KW - Creep-fatigue KW - Lifetime KW - Damage PY - 2007 SN - 0927-0256 VL - 39 IS - 1 SP - 55 EP - 64 PB - Elsevier CY - Amsterdam AN - OPUS4-14530 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 JF - Computational materials science 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 DO - 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 - Drexler, A A1 - Konert, Florian A1 - Sobol, Oded A1 - Rhode, Michael A1 - Domitner, J A1 - Sommitsch, C A1 - Boellinghaus, Thomas T1 - Enhanced gaseous hydrogen solubility in ferritic and martensitic steels at low temperatures JF - International Journal of Hydrogen Energy N2 - Metals that are exposed to high pressure hydrogen gas may undergo detrimental failure by embrittlement. Understanding the mechanisms and driving forces of hydrogen absorption on the surface of metals is crucial for avoiding hydrogen embrittlement. In this study, the effect of stress-enhanced gaseous hydrogen uptake in bulk metals is investigated in detail. For that purpose, a generalized form of Sievert's law is derived from thermodynamic potentials considering the effect of microstructural trapping sites and multiaxial stresses. This new equation is parametrized and verified using experimental data for carbon steels, which were charged under gaseous hydrogen atmosphere at pressures up to 1000 bar. The role of microstructural trapping sites on the parameter identification is critically discussed. KW - Hydrogen KW - Thermodynamic modelling KW - Pressure-dependent solubility KW - Steel KW - Trapping PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-559307 DO - https://doi.org/10.1016/j.ijhydene.2022.09.109 SN - 0360-3199 VL - 47 IS - 93 SP - 39639 EP - 39653 PB - Elsevier Ltd. AN - OPUS4-55930 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Drexler, A.-K. A1 - Konert, Florian A1 - Nietzke, Jonathan A1 - Hodžić, E. A1 - Pastore, S. A1 - Domitner, J. A1 - Rhode, Michael A1 - Sommitsch, C. A1 - Böllinghaus, Thomas T1 - Effect of Tensile Loading and Temperature on the Hydrogen Solubility of Steels at High Gas Pressure JF - Steel Research International N2 - The hydrogen solubility in ferritic and martensitic steels is affected by hydrostatic stress, pressure, and temperature. In general, compressive stresses decrease but tensile stresses increase the hydrogen solubility. This important aspect must be considered when qualifying materials for high‐pressure hydrogen applications (e.g., for pipelines or tanks) by using autoclave systems. In this work, a pressure equivalent for compensating the effect of compressive stresses on the hydrogen solubility inside of closed autoclaves is proposed to achieve solubilities that are equivalent to those in pipelines and tanks subjected to tensile stresses. Moreover, it is shown that the temperature effect becomes critical at low temperatures (e.g., under cryogenic conditions for storing liquid hydrogen). Trapping of hydrogen in the microstructure can increase the hydrogen solubility with decreasing temperature, having a solubility minimum at about room temperature. To demonstrate this effect, the generalized law of the hydrogen solubility is parameterized for different steels using measured contents of gaseous hydrogen. The constant parameter sets are verified and critically discussed with respect to the high‐pressure hydrogen experiments. KW - Hydrogen KW - Solubility KW - Temperature KW - Tensile loading KW - Analytical calculation PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-586701 DO - https://doi.org/10.1002/srin.202300493 SN - 1611-3683 SP - 1 EP - 9 PB - Wiley AN - OPUS4-58670 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -