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  • 1. Eriksson, Magnus
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Somani, M.C.
    University of Oulu.
    Karjalainen, L.P.
    University of Oulu.
    Testing and evaluation of material data for analysis of forming and hardening of boron steel components2002Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 10, nr 3, s. 277-294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Finite element modelling and simulation is becoming an increasingly important tool in the development process for structural automotive components, manufactured using thermo-mechanical forming techniques. Accurate and reliable analysis of coupled thermo-mechanical processes requires efficient simulation tools as well as good quality and relevant material data, usually obtained by experimental testing of the mechanical and thermal properties. The work present in this paper concerns methods for obtaining and evaluating the mechanical properties, required for modelling the high-temperature forming of a high-strength boron-alloyed steel. The material data was obtained from high temperature compression tests and dilatometric measurements made using a Gleeble 1500 thermo-mechanical simulator. Two examples of finite element simulations using the data obtained are also presented. The first example is an isothermal finite element simulation of a thin-walled tubular beam subjected to high-temperature bending. The predicted press force showed acceptable agreement with experimental results in the initial part of the process. In the second example, a cylindrical specimen compressed during continuous cooling was simulated, and the press force and radial displacement were compared with experimental results. Again the simulations showed acceptable agreement with experimental results but indicated the need for further improvements in the simulation technology and methods used for material parameter evaluation.

  • 2.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Modelling and simulation of metal powder die pressing with use of explicit time integration1994Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 2, nr 4, s. 893-911Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pressing of hard metal components is analyzed with numerical methods. The analyzed components are selected from produced components for which the density distribution in the material after pressing has been measured. The expected results from the analyses are the density distribution and the springback after unloading and ejection of the components. The highly non-linear quasistatic problem is analyzed with the use of explicit integration of the equations of motion. A contact constraint method based on direct integration of the equations of the contact interface is used in the analyses. The contact and friction algorithms have been developed in earlier work and are further verified by analyses of a test problem that has an analytical solution. The behaviour of the powder is described by a special cap plasticity material model developed for powder applications. In one example the results obtained using the cap model are compared with results obtained with a multisurface plasticity model. The parameters of the constitutive models are fitted to triaxial experimental data through optimization methods. The presented methods are evaluated by comparing the results with experimental data from density measurements where a technique based on gamma ray absorption is used. The density distributions are qualitatively in good agreement with experimental results. The springback obtained in the simulation of unloading and ejection is in good agreement with measured values.

  • 3.
    Liu, J.
    et al.
    Nanyang Technological University.
    Edberg, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Tan, M.J.
    Nanyang Technological University.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Castagne, S.
    Nanyang Technological University.
    Jarfors, A.E.W.
    Jönköping University.
    Finite element modelling of superplastic-like forming using a dislocation density-based model for AA50832013Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 21, nr 2, s. 25006-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Superplastic-like forming is a newly improved sheet forming process that combines the mechanical pre-forming (also called hot drawing) with gas-driven blow forming (gas forming). Non-superplastic grade aluminium alloy 5083 (AA5083) was successfully formed using this process. In this paper, a physical-based material model with dislocation density and vacancy concentration as intrinsic foundations was employed. The model describes the overall flow stress evolution of AA5083 from ambient temperature up to 550 °C and strain rates from 10−4 up to 10−1 s−1. Experimental data in the form of stress–strain curves were used for the calibration of the model. The calibrated material model was implemented into simulation to model the macroscopic forming process. Hereby, finite element modelling (FEM) was used to estimate the optimum strain-rate forming path, and experiments were used to validate the model. In addition, the strain-rate controlled forming was conducted for the purpose of maintaining the gas forming with an average strain rate of 2 × 10−3 s−1. The predicted necking areas closely approximate the localized thinning observed in the part. Strain rate gradients as a result of geometric effects were considered to be the main reason accounting for thinning and plastic straining, which were demonstrated during hot drawing and gas forming by simulations.

  • 4.
    Murgau, C Charles
    et al.
    University West, Trollhättan.
    Pederson, Robert
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A model for Ti–6Al–4V microstructure evolution for arbitrary temperature changes2012Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 20, nr 5, artikel-id 055006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a microstructure model for the titanium alloy Ti–6Al–4V designed to be used in coupled thermo-metallurgical-mechanical simulations of, e.g., welding processes. The microstructure evolution is increasingly taken into consideration in analyses of manufacturing processes since it directly affects the mechanical properties. Thermally driven phase evolutions are accounted for in the model. A state variable approach is adopted to represent the microstructure with the objective to integrate the microstructure changes with a thermo-mechanical model of manufacturing process simulation such as welding. The model is calibrated using the literature data and also validated against a cyclic temperature history during multi-pass welding.

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  • 5.
    Nilsson, Annika
    et al.
    Swerea MEFOS AB.
    Legge, David
    Luleå tekniska universitet.
    Process development of aluminium ironing using finite element analysis1999Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 7, nr 6, s. 1005-1011Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the use of finite-element simulation of an aluminum ironing process is presented. In this process friction, clearance distance between punch and die and punch radius must all be taken into consideration when designing products and processes. In practice, it is difficult to analyze individual parameters separately, but with computer simulation it is easy to see the effects of changing one specific parameter on the outcome of the process. This work has demonstrated the use of computational support in product development to gain an understanding of the effects of process and geometric parameters. The most important results were confirmation of the sensitivity of the process to clearance distance between punch and die and, also, frictional conditions, as well as the relative insensitivity of the process to change in punch nose radius

  • 6.
    Svoboda, Ales
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Wedberg, Dan
    Lindgren, Lars-Erik
    Simulation of metal cutting using a physically based plasticity model2010Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 18, nr 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metal cutting is one of the most common metal shaping processes. Specified geometrical and surface properties are obtained by break-up of the material removed by the cutting edge into a chip. The chip formation is associated with a large strain, high strain rate and a locally high temperature due to adiabatic heating which make the modelling of cutting processes difficult. This study compares a physically based plasticity model and the Johnson-Cook model. The latter is commonly used for high strain rate applications. Both material models are implemented into the finite element software MSC.Marc and compared with cutting experiments. The deformation behaviour of SANMAC 316L stainless steel during an orthogonal cutting process is studied.

  • 7.
    Wedberg, Dan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Svoboda, Ales
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling high strain rate phenomena in metal cutting simulation2012Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 20, nr 8, s. 85006-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chip formation in metal cutting is associated with large strains and high strain rates, concentrated locally to deformation zones in front of the tool and beneath the cutting edge. Furthermore, dissipative plastic work and friction work generate high local temperatures. These phenomena together with numerical complications make modelling of metal cutting difficult. Material models, which are crucial in metal cutting simulations, are usually calibrated based on data from material testing. Nevertheless, the magnitude of strains and strain rates involved in metal cutting are several orders higher than those generated from conventional material testing. A highly desirable feature is therefore a material model that can be extrapolated outside the calibration range. In this study, two variants of a flow stress model based on dislocation density and vacancy concentration are used to simulate orthogonal metal cutting of AISI 316L stainless steel. It is found that the addition of phonon drag improves the results somewhat but the addition of this phenomenon still does not make it possible to extrapolate the constitutive model reliably outside its calibration range.

  • 8.
    Wikander, Lars
    et al.
    Luleå tekniska universitet.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Näsström, Mats
    Webster, Peter
    Finite element simulation and measurement of welding residual stresses1994Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 2, nr 4, s. 845-864Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Residual strains and stresses in a hollow steel beam that had been welded to a D-shaped cross-section have been simulated by plane deformation finite element models and compared with experimental measurements obtained using the neutron diffraction strain-scanning technique. Neutron strain scanning, in contrast to other experimental techniques, is capable of measuring, accurately, non-destructively and in detail, the internal strain state at selected locations and directions within a component. This makes it a preferred method for validating model calculations of strain and stress distributions in components. In the finite element simulations a plane deformation model incorporating temperature-dependent material properties was adopted. With the assumptions for material properties that were made, the plane deformation model predicts the overall bending of the beam and the overall residual strains and stresses reasonably well. Locally, in the weld metal the predicted residual strains and stresses depend very much on the values of the thermal strain, which in one simulation include volume changes due to solid-state phase transformations. In the other simulation presented here the volume changes due to solid-state phase transformations were not accounted for.

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  • 9. Åkerström, Paul
    et al.
    Bergman, Greger
    SSAB HardTech.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical implementation of a constitutive model for simulation of hot stamping2007Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 15, nr 2, s. 105-119Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to increase the accuracy of numerical simulations of the hot stamping process, an accurate and robust constitutive model is crucial. During the process, a hot blank is inserted into a tool where it is continuously formed and cooled. For the steel grades often used for this purpose, the initially austenitized blank will decompose into different product phases depending on the cooling and mechanical history. As a consequence, the phase proportions change will affect both the thermal and mechanical properties of the continuously formed and cooled blank. A thermo-elastic-plastic constitutive model based on the von Mises yield criterion with associated plastic flow is implemented into the LS-Dyna finite element code. Models accounting for the austenite decomposition and transformation induced plasticity are included in the constitutive model. The implemented model results are compared with experimental dilatation results with and without externally applied forces. Further, the calculated isothermal mechanical response during the formation of a new phase is compared with the corresponding experimental response for two different temperatures.

  • 10. Åkerström, Paul
    et al.
    Wikman, Bengt
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Material parameter estimation for boron steel from simultaneous cooling and compression experiments2005Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 13, nr 8, s. 1291-1308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to increase the accuracy of numerical simulations of the hot stamping process, reliable material data is crucial. Traditionally, the material is characterized by several isothermal compression or tension tests performed at elevated temperatures and different strain rates. The drawback of the traditional methods is the appearance of unwanted phases for some test temperatures and durations. Such an approach is also both time consuming and expensive. In the present work an alternative approach is proposed, which reduces unwanted phase changes and the number of experiments. The isothermal mechanical response is established through inverse modelling of simultaneous cooling and compression experiments. The estimated material parameters are validated by comparison with data from a separate forming experiment. The computed global response is shown to be in good agreement with the experiments.

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    FULLTEXT01
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