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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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- 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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| 8. |
- 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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| 9. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of the Bergström-Boyce model: Explicit expressions
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report we derive the explicit expressions associated with the calibration of the Bergström-Boyce modelof nonlinear viscoelasticity. These expressions are intended for practical use in a computational algorithm.
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| 10. |
- Johansson, Håkan, 1979, et al.
(författare)
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Parameter identification in constitutive models via optimization with a posteriori error control
- 2005
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Ingår i: International Journal for Numerical Methods in Engineering. ; 62:10, s. 1315-1340
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we outline a computational technique for the calibration of macroscopic constitutive lawswith automatic error control. In the most general situation the state variables of the constitutive law,as well as the material parameters, are spatially non-homogeneous. The experimental observations aregiven in spacetime. Based on an appropriate dual problem, we compute a posteriori the discretizationerror contributions from approximations of the parameter, state and costate fields in spacetime foran arbitrarily chosen goal-oriented error measure of engineering significance. Such a measure can beused in an adaptive strategy (not discussed in this paper) to meet a predefined error tolerance. Animportant observation is that the Jacobian matrix associated with the resulting Newton method is used(in principle) in solving the dual problem. Rather than treating the Jacobian in a monolithic fashion,we utilize a sequential solution strategy, whereby the FE-topology of the discretized state problem isused repeatedly. Moreover, the proposed solution strategy lends itself naturally to the computation offirst and second order sensitivities, which are obtained with little extra computational effort. Numericalresults are given for the prototype model of confined aquifer flow with spatially non-homogeneouspermeability. The efficiency of the optimization strategy and the effectivity of the error computationare assessed.
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