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- Johansson, Göran, 1975, et al.
(författare)
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Computational modeling of inelastic large ratcheting strains
- 2005
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Ingår i: International Journal of Plasticity. ; 21:5, s. 955-980
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Tidskriftsartikel (refereegranskat)abstract
- A framework forphenomenological hyperelasto-plasticity with initial anisotropy,kinematic hardening as well as anisotropic damage is presented inMenzel et al. (2003a).In this contribution we exploit and extend this framework toinclude several back-stresses in order to capture the ratchettingresponse of polycrystalline metals subjected to cyclic stress withnon-zero mid-value. The evolution equations for kinematichardening resemble a linear combination of the multiple-Armstrong-Frederic and the Burlet-Cailletaudmodels, which are extended to the large strain setting. Thecapability of the model to capture various phenomenologicalcharacteristics, in particular multi-axial ratchetting, isillustrated by numerical examples. Comparisons with uni-axial andbi-axial experimental ratchetting results for carbon steel aregiven. Finally, the finite element analysis of a simplifiedrailway turnout component subjected to cyclic loading ispresented.
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| 2. |
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| 3. |
- Johansson, Göran, 1975, et al.
(författare)
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Modeling of anisotropic inelasticity in pearlitic steel at large strains due to deformation induced substructure evolution
- 2005
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Ingår i: European Journal of Mechanics - A/Solids. ; 24:6, s. 899-1088
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Tidskriftsartikel (refereegranskat)abstract
- A macroscopic model for deformation induced anisotropy due to substructure evolution at large strains in pearlitic steel is proposed within a thermodynamically consistent framework. The model is motivated via experimental observations, e.g., [Ivanisenko, Y., Lojkowski, W., Valiev, R.Z., Fecht, H.-J., 2003. The mechanism of formation of nanostructure and dissolution of cementite in a pearlitic steel during high pressure. Acta Mater. 51, 55555570]. Although each pearlitic grain has a preferred direction determined by cementite lamellas, initial random orientation of the grains is interpreted as initial macroscopic isotropy. However, the oriented grains tend to align after large shear deformation. The proposed model for evolution of orientation and stiffness is inspired by recent developments in bio-mechanics, e.g., [Imatani, S., Maugin, G.A., 2002. A constitutive model for material growth and its application to three-dimensional finite element analysis. Mech. Res. Commun. 29, 477483; Menzel, A., 2004. Modelling of anisotropic growth in biological tissues. Biomech. Model. Mechanobiol. 3, 147171]. One important application is large irreversible shear deformations in the surface layer of railway track components.
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| 5. |
- Johansson, Håkan, 1979, et al.
(författare)
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Application-specific error control for parameter identification problems
- 2011
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947. ; 27:4, s. 608-618
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Tidskriftsartikel (refereegranskat)abstract
- An often occurring scenario in the mathematical modeling of physical phenomena is that of a two-step computation consisting of, first, identifying a relevant parameter set from experiments (such as material parameters) and, second, carrying out a subsequent simulation using these parameters. In order to ensure the quality of the results from the simulation, the different sources of errors, for example, from discretization and inexact solution, must be traced and properly reduced. In this paper, a previously developed method for goal-oriented a posteriori error estimation for identification problems is extended to accommodate the combined identification and subsequent simulation. © 2009 John Wiley & Sons, Ltd.
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| 6. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a class of non-linear viscoelasticity models with adaptive error control
- 2007
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 41:1, s. 107-119
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of constitutive models is considered as an optimization problem where parameter values are sought to minimize the discrepancy between measured and simulated response. Since a finite element method is used to solve an underlying state equation, discretization errors arise, which induce errors in the calibrated parameter values. In this paper, adaptive mesh refinement based on the pertinent dual solution is used in order to reduce discretization errors in the calibrated material parameters. By a sensitivity assessment, the influence from uncertainties in experimental data is estimated, which serves as a threshold under which there is no need to further reduce the discretization error. The adaptive strategy is employed to calibrate a viscoelasticity model with observed data from uniaxial compression (i.e., homogeneous stress state), where the FE-discretization in time is studied. The a posteriori error estimations show an acceptable quality in terms of effectivity measures. © 2007 Springer Verlag.
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| 7. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a class of non-linear viscoelasticity models with sensitivity assessment based on duality
- 2007
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 69:12, s. 2513-2537
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of constitutive models is based on the solution of an optimization problem, whereby the sought parameter values minimize an objective function that measures the discrepancy between experimental observations and the corresponding simulated response. By the introduction of an appropriate adjoint problem, the resulting formulation becomes well suited for a gradient-based optimization scheme. A class of viscoelastic models is studied, where a discontinuous Galerkin method is used to integrate the governing evolution equation in time. A practical solution algorithm, which utilizes the time-flow structure of the underlying evolution equation, is presented. Based on the proposed formulation it is convenient to estimate the sensitivity of the calibrated parameters with respect to measurement noise. The sensitivity is computed using a dual method, which compares favourably with the conventional primal method. The strategy is applied to a viscoelasticity model using experimental data from a uniaxial compression test. Copyright © 2006 John Wiley & Sons, Ltd.
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| 9. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a nonlinear viscoelasticity model with sensitivity assessment
- 2005
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Ingår i: Constitutive Models for Rubber IV, edited by P.-E. Austrell & L. Kari. - 0415383463 ; , s. 341-347
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Konferensbidrag (refereegranskat)abstract
- The calibration of constitutive models isbased on the solution of an optimization problem, where parameter values are sought such that optimal correspondence between measured and simulated response is achieved. The calibration problem is solved using a recently proposed strategy, which has the advantage that discretization errors induced in the simulated response, leading to errors in the optimal parameter values, isrelatively straightforward to estimate. Furthermore, it ispossible to estimate how sensitive the obtained solution is to uncertainties in the experimental data.
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