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- Heintz, Per, 1975, et al.
(författare)
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Adaptive strategies and error control for computing material forces in fracture mechanics
- 2004
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 60:7, s. 1287-1299
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Tidskriftsartikel (refereegranskat)abstract
- The concept of material forces pertains to a variation of the inverse motion map while the placement field is kept fixed. From the weak formulation of the self-equilibrating Eshelby (material) stress tensor it turns out that the classical J-integral formulations in fracture mechanics are just special cases due to the choice of particular weight functions. In this contribution, we discuss a posteriori error control of the material forces as part of an adaptive strategy to reduce the discretization error to an acceptable level. The data of the dual problem involves the quite non-conventional tangent stiffness of the (material) Eshelby stress tensor with respect to a variation of the (physical) strain field. The suggested strategy is applied to the common fracture mechanics problem of a single-edged crack, whereby different strategies for computing the J-integral are compared. We also consider the case in which the crack edges are not parallel, i.e. a notch.
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| 3. |
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| 4. |
- Fagman, Henrik, 1975, et al.
(författare)
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Nuclear accumulation of full-length and truncated adenomatous polyposis coli protein in tumor cells depends on proliferation.
- 2003
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Ingår i: Oncogene. - : Springer Science and Business Media LLC. - 0950-9232 .- 1476-5594. ; 22:38, s. 6013-22
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Tidskriftsartikel (refereegranskat)abstract
- The adenomatous polyposis coli (APC) tumor suppressor is a nucleocytoplasmic protein. The nuclear accumulation of APC was recently found to vary depending on cell density, suggesting that putative APC function(s) in the nucleus is controlled by the establishment of cell contacts. We report here that the density-dependent redistribution of APC between nucleus and cytoplasm prevails in 6/6 thyroid and colorectal carcinoma cell lines. Moreover, mutated APC lacking known nuclear localization sequences had the similar distribution pattern as the full-length protein. APC invariably accumulated in the nuclei of Ki-67 expressing cells, but was largely cytoplasmic when cell cycle exit was induced by serum starvation or at high cell density. APC colocalized with beta-catenin in the nucleus only in one cell line (SW480). Also, APC maintained a predominantly nuclear position in early confluent states when cytoplasmic beta-catenin was recruited to newly formed adherens-like junctions. The results indicate that nuclear targeting of APC is driven by cell cycle entry rather than altered cell-cell contact. The ability of C-terminally truncated APC to accumulate in the nucleus suggests that nuclear import signals other than NLS1(APC) and NLS2(APC) are functionally important. Residual function(s) of N-terminal APC fragments in tumor cells carrying APC mutations might be beneficial to tumor growth and survival.
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| 5. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a Nonlinear Elastic Composite with Goal-Oriented Error Control Using a Sub-Scale Modeling Approach
- 2004
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Ingår i: Proc. of Second International Conference on Multiscale Materials Modeling, MMM-2, October 11-15, 2004. ; 1:1, s. 466-468
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A recently proposed technique for the calibration of constitutive models is based on the optimization problem expressed such that the state equation is incorporated via an additional costate field. A distinct advantage is that error control is formally straightforward. This technique is applied to calibration of a nonlinear elastic composite using a meso-macro-transition approach, whereby the RVE is analyzed using (in this case) Dirichlet boundary conditions. The numerical results show the effectivity of the error prediction.
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| 8. |
- Larsson, Fredrik, 1975, et al.
(författare)
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Computation of goal-oriented error measures in space-time finite elements for viscoplasticity
- 2001
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Ingår i: Trends in Computational Structural Mechanics. - 8489925771 ; , s. 499-510
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Konferensbidrag (refereegranskat)abstract
- We establish goal oriented residual-based a posteriori error estimates for problems in viscoplasticity. The error estimates can be used to control the spatial meshsize as well as the time step size. To this end, we use standard finite elements in space and the discontinuous Galerkin method in time.
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| 9. |
- Larsson, Fredrik, 1975, et al.
(författare)
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Error controlled meso-macro-scale material modeling and computation
- 2004
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Ingår i: 4th European Congress on Computational Methods in Applied Sciences and Engineering. - 9513918696 ; 2
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Konferensbidrag (refereegranskat)abstract
- In constitutive modeling, a key issue is to choose thecomplexity of a model such that model and discretization errors are properly balanced. In other words, there is no point in choosing a complex, and computationally demanding, constitutive model if the solution of the structural problem has low quality. In this paper, we consider combined material model and FE-mesh adaptivity in the context of Computational Meso-Macro-scale Modeling (CMM). The macro-scale model is then replaced by the homogenized response of a Representative Volume Element (RVE). Inpractice, the RVE is analyzed as a ''small-scale'' finite element problem, which is solved for each (Gauss)point in the domain. The high cost of this strategy clearly motivates the use of adaptive techniques based on a posteriori error estimates for the combined model and discretization error. The suggested adaptive procedureis applied to a particle/matrix composite with hyperelasticconstituents.
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| 10. |
- Larsson, Fredrik, 1975
(författare)
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Goal-Oriented Adaptive Finite Element Analysis in Computational Material Mechanics
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is concerned with error control in computational material mechanics. A posteriori error estimation and adaptivity for finite element discretizations is investigated. Based on the technique of solving a dual problem, it is possible to control the accuracy of arbitrary quantities. Strategies for goal-oriented error estimation and adaptivity, with respect to user-defined error measures, are presented. Application is made to problems of elasticity, thermoelasticity and viscoplasticity, where special attention is made to the rate independent limit case of plasticity. A quite general framework for a posteriori error estimation is proposed for problems where the (dissipative) material behavior is modeled using internal variables. In particular, it is investigated how the accuracy of the error estimate is affected by different approaches for solving the dual problem. Methods for computing the dual solution in space, time, and coupled space-time domains are presented. Moreover, adaptive strategies based on these estimators are proposed for spatial and temporal problems.
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