| 1. |
- Adams, Camiel, 1992, et al.
(författare)
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Efficient modelling of delamination growth using adaptive isogeometric continuum shell elements
- 2020
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 65:1, s. 99-117
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Tidskriftsartikel (refereegranskat)abstract
- The computational efficiency of CAE tools for analysing failure progression in large layered composites is key. In particular, efficient approximation and solution methods for delamination modelling are crucial to meet today’s requirements on virtual development lead times. For that purpose, we present here an adaptive continuum shell element based on the isogeometric analysis framework, suitable for the modelling of arbitrary delamination growth. To achieve an efficient procedure, we utilise that, in isogeometric analysis, the continuity of the approximation field easily can be adapted via so-called knot insertion. As a result, the current continuum shell provides a basis for an accurate but also computationally efficient prediction of delamination growth in laminated composites. Results show that the adaptive modelling framework works well and that, in comparison to a fully resolved model, the adaptive approach gives significant time savings even for simple analyses where major parts of the domain exhibit delamination growth.
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| 2. |
- Amirian, Benhour, et al.
(författare)
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Phase-field approach to evolution and interaction of twins in single crystal magnesium
- 2022
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Ingår i: Computational Mechanics. - : Springer Nature. - 0178-7675 .- 1432-0924. ; 70:4, s. 803-818
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Tidskriftsartikel (refereegranskat)abstract
- Crack initiation and propagation as well as abrupt occurrence of twinning are challenging fracture problems where the transient phase-field approach is proven to be useful. Early-stage twinning growth and interactions are in focus herein for a magnesium single crystal at the nanometer length-scale. We demonstrate a basic methodology in order to determine the mobility parameter that steers the kinetics of phase-field propagation. The concept is to use already existing molecular dynamics simulations and analytical solutions in order to set the mobility parameter correctly. In this way, we exercise the model for gaining new insights into growth of twin morphologies, temporally-evolving spatial distribution of the shear stress field in the vicinity of the nanotwin, multi-twin, and twin-defect interactions. Overall, this research addresses gaps in our fundamental understanding of twin growth, while providing motivation for future discoveries in twin evolution and their effect on next-generation material performance and design.
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| 3. |
- Bargmann, Swantje, 1980, et al.
(författare)
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An extended crystal plasticity model for latent hardening in polycrystals
- 2011
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 48:6, s. 631-645
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution, a computational approach to modeling size-dependent self- and latent hardening in polycrystals is presented. Latent hardening is the hardening of inactive slip systems due to active slip systems. We focus attention on the investigation of glide system interaction, latent hardening and excess dislocation development. In particular, latent hardening results in a transition to patchy slip as a first indication and expression of the development of dislocation microstructures. To this end, following Nye (Acta Metall 1:153-162, 1953), Kondo (in Proceedings of the second Japan national congress for applied mechanics. Science Council of Japan, Tokyo, pp. 41-47, 1953), and many others, local deformation incompatibility in the material is adopted as a measure of the density of geometrically necessary dislocations. Their development results in additional energy being stored in the material, leading to additional kinematic-like hardening effects. A large-deformation model for latent hardening is introduced. This approach is based on direct exploitation of the dissipation principle to derive all field relations and (sufficient) forms of the constitutive relations as based on the free energy density and dissipation potential. The numerical implementation is done via a dual-mixed finite element method. A numerical example for polycrystals is presented.
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| 4. |
- Berthelsen, Rolf, et al.
(författare)
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Computational homogenisation for thermoviscoplasticity : application to thermally sprayed coatings
- 2017
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 60:5, s. 739-766
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Tidskriftsartikel (refereegranskat)abstract
- Metal forming processes require wear-resistant tool surfaces in order to ensure a long life cycle of the expensive tools together with a constant high quality of the produced components. Thermal spraying is a relatively widely applied coating technique for the deposit of wear protection coatings. During these coating processes, heterogeneous coatings are deployed at high temperatures followed by quenching where residual stresses occur which strongly influence the performance of the coated tools. The objective of this article is to discuss and apply a thermo-mechanically coupled simulation framework which captures the heterogeneity of the deposited coating material. Therefore, a two-scale finite element framework for the solution of nonlinear thermo-mechanically coupled problems is elaborated and applied to the simulation of thermoviscoplastic material behaviour including nonlinear thermal softening in a geometrically linearised setting. The finite element framework and material model is demonstrated by means of numerical examples.
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| 5. |
- Bharali, Ritukesh, 1991, et al.
(författare)
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A micromorphic phase-field model for brittle and quasi-brittle fracture
- 2024
-
Ingår i: Computational Mechanics. - 1432-0924 .- 0178-7675. ; 73:3, s. 579-598
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Tidskriftsartikel (refereegranskat)abstract
- In this manuscript, a robust and variationally consistent technique is proposed for local treatment of the phase-field fracture irreversibility. This technique involves an extension of the phase-field fracture energy functional through a micromorphic approach. Consequently, the phase-field is transformed into a local variable, while a micromorphic variable regularizes the problem. The local nature of the phase-field variable enables an easier implementation of its irreversibility using a pointwise 'max' with system level precision. Unlike the popular history variable approach, which also enforces local fracture irreversibility, the micromorphic approach yields a variationally consistent framework. The efficacy of the micromorphic approach in phase-field fracture modelling is demonstrated in this work with numerical experiments on benchmark brittle and quasi-brittle fracture problems in linear elastic media. Furthermore, the extensibility of the micromorphic phase-field fracture model toward smultiphysics problems is demonstrated. To that end, a theoretical extension is carried out for modelling hydraulic fracture, and relevant numerical experiments exhibiting crack merging are presented. The source code as well as the data set accompanying this work would be made available on GitHub (https://github.com/ritukeshbharali/ falcon).
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| 6. |
- Bonnaud, Etienne L., et al.
(författare)
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Explicit, fully implicit and forward gradient numerical integration of a hyperelasto-viscoplastic constitutive model for amorphous polymers undergoing finite deformation
- 2019
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Ingår i: Computational Mechanics. - : Springer. - 0178-7675 .- 1432-0924. ; 64:5, s. 1389-1401
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Tidskriftsartikel (refereegranskat)abstract
- Following the growing use of amorphous polymers in an expanding range of applications, interest for numerical modeling of polymer behavior has greatly increased. Together with reliable constitutive models, stable, accurate and rapid integration algorithms valid for large deformations need to be developed. Here, in the framework of hyperelasto-viscoplasticity and multiplicative split formulation, three integration algorithms (explicit, fully implicit and forward gradient) are generated for a constitutive polymer model and respective stability is investigated. The algorithms are furthermore implemented in a commercial Finite Element code and simulation of a full field tensile test is shown to capture the actual deformation behavior of polymers.
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| 7. |
- Brouzoulis, Jim, 1984, et al.
(författare)
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Strategies for planar crack propagation based on the concept of material forces
- 2011
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 47:3, s. 295-304
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a computational framework for the simulation of planar crack growth (including kinking) driven by "material forces". An evolution law for the crack tip position is formulated, which is shown to give rise to different propagation strategies when subjected to certain assumptions on regularity. Three such strategies, that previously have been proposed in the literature in principle: Explicit Proportional Extension (EPE), Implicit Proportional Extension (IPE) and Maximum Parallel Release Rate (MPRR), are outlined and assessed. Based on the results of two numerical examples, it is concluded that the presented propagation strategies produce almost identical results and are robust with respect to time discretization.
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| 8. |
- Börjesson, Elias, 1992, et al.
(författare)
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A generalised path-following solver for robust analysis of material failure
- 2022
-
Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 70:2, s. 437-450
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Tidskriftsartikel (refereegranskat)abstract
- When analysing complex structures with advanced damage or material models, it is important to use a robust solution method in order to trace the full equilibrium path. In light of this, we propose a new path-following solver based on the integral of the rate of dissipation in each material point, for solving problems exhibiting large energy dissipating mechanisms. The method is a generalisation and unification of previously proposed dissipation based path-following solvers, and makes it possible to describe a wider range of dissipation mechanisms, such as large strain plasticity. Furthermore, the proposed method makes it possible to, in a straightforward way, combine the effects from multiple dissipation mechanisms in a simulation. The capabilities of the solver are demonstrated on four numerical examples, from which it can be concluded that the proposed method is both versatile and robust, and can be used in different research domains within computational structural mechanics and material science.
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| 9. |
- Cannmo, Patrik, et al.
(författare)
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Modelling of interfacial viscoplastic slip coupled to damage in a polycrystalline microstructure
- 1997
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Ingår i: Computational Mechanics. - 0178-7675 .- 1432-0924. ; 20:1-2, s. 12-19
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Tidskriftsartikel (refereegranskat)abstract
- The mesomechanics behavior of a polycrystalline microstructure subjected to creep and constant strain rate loadings is investigated. The analysis is based on a Voronoi polygonization strategy for the generation of grains, that are bonded to each other via interfaces along the grain boundaries. A new constitutive model is proposed for the rate-dependent debonding along these interfaces, whereby damage is kinetically coupled to viscoplastic slip and dilatation. The paper may be viewed as generalizing the rate-independent model used in Cannmo et al. (1995).
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| 10. |
- Carlsson, Kristoffer, 1989, et al.
(författare)
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A comparison of the primal and semi-dual variational formats of gradient-extended crystal inelasticity
- 2017
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 60:4, s. 531-548
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we discuss issues related to the theoretical as well as the computational format of gradient-extended crystal viscoplasticity. The so-called primal format uses the displacements, the slip of each slip system and the dissipative stresses as the primary unknown fields. An alternative format is coined the semi-dual format, which in addition includes energetic microstresses among the primary unknown fields. We compare the primal and semi-dual variational formats in terms of advantages and disadvantages from modeling as well as numerical viewpoints. Finally, we perform a series of representative numerical tests to investigate the rate of convergence with finite element mesh refinement. In particular, it is shown that the commonly adopted microhard boundary condition poses a challenge in the special case that the slip direction is parallel to a grain boundary.
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| 11. |
- Dahlberg, Carl F. O., et al.
(författare)
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An improved strain gradient plasticity formulation with energetic interfaces : theory and a fully implicit finite element formulation
- 2013
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 51:5, s. 641-659
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Tidskriftsartikel (refereegranskat)abstract
- A fully implicit backward-Euler implementation of a higher order strain gradient plasticity theory is presented. A tangent operator consistent with the numerical update procedure is given. The implemented theory is a dissipative bulk formulation with energetic contribution from internal interface to model the behavior of material interfaces at small length scales. The implementation is tested by solving some examples that specifically highlight the numerics and the effect of using the energetic interfaces as higher order boundary conditions. Specifically, it is demonstrated that the energetic interface formulation is able to mimic a wide range of plastic strain conditions at internal boundaries. It is also shown that delayed micro-hard conditions may arise under certain circumstances such that an interface at first offers little constraints on plastic flow, but with increasing plastic deformation will develop and become a barrier to dislocation motion.
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| 12. |
- Draganis, Andreas, 1984, et al.
(författare)
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Finite element analysis of transient thermomechanical rolling contact using an efficient arbitrary Lagrangian-Eulerian description
- 2014
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 54:2, s. 389-405
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical and computational framework for the analysis of thermomechanically coupled transient rolling contact, based on an arbitrary Lagrangian-Eulerian (ALE) kinematical description, is developed. A finite element formulation featuring 2D cylinder-plate rolling contact is implemented. The implementation features penalty-type contact formulations for mechanical and thermal contact. It is noted that the ALE formulation allows for a simplified time description, a compact computational domain and localized mesh refinement. Numerical simulations considering stationary and transient rolling conditions are presented. Highlighted aspects include the influence of variations in thermal contact conductivity, rolling speed and external mechanical load on the contact interface heat flow. The model is shown to give predictions in qualitative agreement with results in the literature. For the velocity range studied, numerical issues such as spurious numerical dissipation/oscillations in the temperature field are noted to have a prominent influence. These phenomena are addressed using a Streamline-Upwind Petrov-Galerkin stabilization scheme together with a bubble function approach.
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| 13. |
- Eberlein, R., et al.
(författare)
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Multi-segment FEA of the human lumbar spine including the heterogeneity of the annulus fibrosus
- 2004
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 34:2, s. 147-163
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Tidskriftsartikel (refereegranskat)abstract
- This study pursues the numerical validation of human lumbar spine segments. By means of the finite element (FE) method, computational analyses are carried out of various load cases. In particular Flexion-Extension, Lateral Bending and Axial Torque are considered. By means of a literature review the underlying constitutive data is verified. In this context, the heterogeneity of the annulus fibrosus, the transversely isotropic stress response of the spinal ligaments and aspects of the FE discretization are particularly emphasized. The numerical results show good agreement with experimental investigations for Extension and Axial Torque for a FE model that accounts for intact human lumbar spine response. In Flexion and Lateral Bending, however, the results of the intact FE-model do not properly account for the experimental data. A good correlation for these load cases can be found by taking disc degeneration into account in the FE-model. This fact shows that tissue degeneration plays a key role in the current validation process and must be accounted for if the lumbar spine specimen is employed for spinal implant evaluation. A degenerated FE-model that represents the stage of degeneration of the specimen and fits the experimental data for all load cases could not be found in this study and warrants further work in this area.
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| 14. |
- Ekre, Fredrik, 1992, et al.
(författare)
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Combining spectral and POD modes to improve error estimation of numerical model reduction for porous media
- 2022
-
Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 69:3, s. 767-786
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Tidskriftsartikel (refereegranskat)abstract
- Numerical model reduction (NMR) is used to solve the microscale problem that arises from computational homogenization of a model problem of porous media with displacement and pressure as unknown fields. The reduction technique and an associated error estimator for the NMR error have been presented in prior work, where both spectral decomposition (SD) and proper orthogonal decomposition (POD) were used to construct the reduced basis. It was shown that the POD basis performs better w.r.t. minimizing the residual, but the SD basis has some advantageous properties for the estimator. Since it is the estimated error that will govern the error control, the most efficient procedure is the one that results in the lowest error bound. The main contribution of this paper is further development of the previous work with a proposed combined basis constructed using both SD and POD modes together with an adaptive mode selection strategy. The performance of the combined basis is compared to (i) the pure SD basis and (ii) the pure POD basis via numerical examples. The examples show that it is possible to find a combination of SD/POD modes which is improved, i.e. it yields a smaller estimate, compared to the cases of pure SD or pure POD.
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| 15. |
- Eriksson, Anders, 1953-, et al.
(författare)
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Computational stability investigations for a highly symmetric system : the pressurized spherical membrane
- 2020
-
Ingår i: Computational Mechanics. - : Springer. - 0178-7675 .- 1432-0924. ; 66:2, s. 405-430
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Tidskriftsartikel (refereegranskat)abstract
- Thin membranes are notoriously sensitive to instabilities under mechanical loading, and need sophisticated analysis methods. Although analytical results are available for several special cases and assumptions, numerical approaches are normally needed for general descriptions of non-linear response and stability. The paper uses the case of a thin spherical hyper-elastic membrane subjected to internal gas over-pressure to investigate how stability conclusions are affected by chosen material models and kinematic discretizations. For spherical symmetry, group representation theory leads to linearized modes on the uniformly stretched sphere, with eigenvalues obtained from the mechanics of a thin membrane. A complete three-dimensional geometric description allows non-axisymmetric shear modes of the sphere, and such instabilities are shown to exist. When the symmetry of the continuous sphere is broken by discretized models, group representation theory gives predictions on the effects on the critical states. Numerical simulations of the pressurized sphere show and verify stability conclusions for sets of meshing strategies and hyper-elastic models.
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| 16. |
- Eriksson, Anders, 1953-, et al.
(författare)
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Constrained stability of conservative static equilibrium
- 2019
-
Ingår i: Computational Mechanics. - : SPRINGER. - 0178-7675 .- 1432-0924. ; 64:4, s. 1199-1219
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Tidskriftsartikel (refereegranskat)abstract
- Modelling of static structural stability problems is considered. Focus is set on problems where passive physical constraints affect the response to applied forces, and where more than one free parameter describes the setting. The existence of vibration frequencies at equilibrium states is investigated, as an indication of stability. The relevant Jacobian matrix is developed, with an emphasis on the necessity to formulate the constraint equations from an energy form in a conservative problem. The corresponding mass matrix is introduced, with zero mass contribution from constraint equations. Three different forms of the relevant Jacobians are considered, and alternative methods for the eigenvalue extraction given. Stability is discussed in a context of generalized equilibrium problems, where auxiliary parameters and equations can be included in a continuation setting. Examples show the formulation, implementation and interpretation of stability.
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| 17. |
- Eriksson, Anders, et al.
(författare)
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Symmetry aspects in stability investigations for thin membranes
- 2016
-
Ingår i: Computational Mechanics. - : Springer. - 0178-7675 .- 1432-0924. ; 58:5, s. 747-767
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Tidskriftsartikel (refereegranskat)abstract
- Modelling of structural instability problems is considered for thin square membranes subjected to hydrostatic pressure, with a focus on the effects from symmetry conditions considered or neglected in the model. An analysis is performed through group-theoretical concepts of the symmetry aspects present in a flat membrane with one-sided pressure loading. The response of the membrane is described by its inherent differential eigensolutions, which are shown to be of five different types with respect to symmetry. A discussion is given on how boundary conditions must be introduced in order to catch all types of eigensolutions when modelling only a subdomain of the whole. Lacking symmetry in a FEM model of the whole domain is seen as a perturbation to the problem, and is shown to affect the calculated instability response, hiding or modifying instability modes. Numerical simulations verify and illustrate the analytical results, and further show the convergence with mesh fineness of different aspects of instability results.
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| 18. |
- Floros, Dimosthenis, 1982, et al.
(författare)
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On configurational forces for gradient-enhanced inelasticity
- 2018
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 61:4, s. 409-432
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we discuss how configurational forces can be computed in an efficient and robust manner when a constitutive continuum model of gradient-enhanced viscoplasticity is adopted, whereby a suitably tailored mixed variational formulation in terms of displacements and micro-stresses is used. It is demonstrated that such a formulation produces sufficient regularity to overcome numerical diffi- culties that are notorious for a local constitutive model. In particular, no nodal smoothing of the internal variable fields is required. Moreover, the pathological mesh sensitivity that has been reported in the literature for a standard local model is no longer present. Numerical results in terms of config- urational forces are shown for (1) a smooth interface and (2) a discrete edge crack. The corresponding configurational forces are computed for different values of the intrinsic length parameter. It is concluded that the convergence of the com- puted configurational forces with mesh refinement depends strongly on this parameter value. Moreover, the convergence behavior for the limit situation of rate-independent plasticity is unaffected by the relaxation time parameter
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| 19. |
- Gasser, T. Christian, et al.
(författare)
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A rate-independent elastoplastic constitutive model for biological fiber-reinforced composites at finite strains : continuum basis, algorithmic formulation and finite element implementation
- 2002
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 29:05-apr, s. 340-360
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a rate-independent elastoplastic constitutive model for (nearly) incompressible biological fiber-reinforced composite materials. The constitutive framework, based on multisurface plasticity, is suitable for describing the mechanical behavior of biological fiber-reinforced composites in finite elastic and plastic strain domains. A key point of the constitutive model is the use of slip systems, which determine the strongly anisotropic elastic and plastic behavior of biological fiber-reinforced composites. The multiplicative decomposition of the deformation gradient into elastic and plastic parts allows the introduction of an anisotropic Helmholtz free-energy function for determining the anisotropic response. We use the unconditionally stable backward-Euler method to integrate the flow rule and employ the commonly used elastic predictor/plastic corrector concept to update the plastic variables. This choice is expressed as an Eulerian vector update the Newton's type, which leads to a numerically stable and efficient material model. By means of a representative numerical simulations the performance of the proposed constitutive framework is investigated in detail.
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| 20. |
- Gasser, T. Christian, et al.
(författare)
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Finite element modeling of balloon angioplasty by considering overstretch of remnant non-diseased tissues in lesions
- 2007
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 40:1, s. 47-60
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Tidskriftsartikel (refereegranskat)abstract
- The paper deals with the modeling of balloon angioplasty by considering the balloon-induced overstretch of remnant non-diseased tissues in atherosclerotic arteries. A stenotic artery is modeled as a heterogenous structure composed of adventitia, media and a model plaque, and residual stresses are considered. The constitutive models are able to capture the anisotropic elastic tissue response in addition to the inelastic phenomena associated with tissue stretches beyond the physiological domain. The inelastic model describes the experimentally-observed changes of the wall during balloon inflation, i.e. non-recoverable deformation, and tissue weakening. The contact of the artery with a balloon catheter is simulated by a point-to-surface strategy. The states of deformations and stresses within the artery before, during and after balloon inflation are computed, compared and discussed. The 3D stress states at physiological loading conditions before and after balloon inflation differ significantly, and even compressive normal stresses may occur in the media after dilation.
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| 21. |
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| 22. |
- Guhr, Fabian, et al.
(författare)
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Computational shape optimisation for a gradient-enhanced continuum damage model
- 2020
-
Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 65:4, s. 1105-1124
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Tidskriftsartikel (refereegranskat)abstract
- An isotropic gradient-enhanced damage model is applied to shape optimisation in order to establish a computational optimal design framework in view of optimal damage distributions. The model is derived from a free Helmholtz energy density enriched by the damage gradient contribution. The Karush–Kuhn–Tucker conditions are solved on a global finite element level by means of a Fischer–Burmeister function. This approach eliminates the necessity of introducing a local variable, leaving only the global set of equations to be iteratively solved. The necessary steps for the numerical implementation in the sense of the finite element method are established. The underlying theory as well as the algorithmic treatment of shape optimisation are derived in the context of a variational framework. Based on a particular finite deformation constitutive model, representative numerical examples are discussed with a focus on and application to damage optimised designs.
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| 23. |
- Gunnars, Jens, et al.
(författare)
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On crack path stability in a layered material
- 1997
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 19:6, s. 545-552
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Tidskriftsartikel (refereegranskat)abstract
- Crack paths in an elastic layer on top of a substrate are considered. Crack growth is initiated from an edge crack in the layer. The plane of the initially straight crack forms an angle to the free surface. The load consists of a pair of forces applied at the crack mouth and parallel to the interface. Crack paths are calculated using a boundary element method. Crack growth is assumed to proceed along a path for which the mode II stress intensity factor vanishes. The inclination and the length of the initial crack are varied. The effect of two different substrates on the crack path evolution is demonstrated. A crack path initially leading perpendicularly to the interface is shown to be directionally unstable for a rigid substrate. Irrespective of its initial angle, the crack does not reach the interface, but reaches the free surface if the layer is infinitely long. At finite layer length the crack reaches the upper free surface if the initial crack inclination to the surface is small enough. For an inextendable flexible substrate, on the other hand, the crack reaches the interface if its initial inclination is large enough. For the flexible substrate an unstable path parallel with the sides of an infinitely long layer is identified. The results are compared with experimental results and discussed in view of characterization of directionally unstable crack paths. The energy release rate for an inclined edge crack is determined analytically
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| 24. |
- Görtz, Morgan, 1994, et al.
(författare)
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Iterative method for large-scale Timoshenko beam models assessed on commercial-grade paperboard
- 2024
-
Ingår i: Computational Mechanics. - 1432-0924 .- 0178-7675. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale structural simulations based on micro-mechanical models of paper products require extensive numerical resources and time. In such models, the fibrous material is often represented by connected beams. Whereas previous micro-mechanical simulations have been restricted to smaller sample problems, large-scale micro-mechanical models are considered here. These large-scale simulations are possible on a non-specialized desktop computer with 128GB of RAM using an iterative method developed for network models and based on domain decomposition. Moreover, this method is parallelizable and is also well-suited for computational clusters. In this work, the proposed memory-efficient iterative method is numerically validated for linear systems resulting from large networks of Timoshenko beams. Tensile stiffness and out-of-plane bending stiffness are simulated and validated for various commercial-grade three-ply paperboards consisting of layers composed of two different types of paper fibers. The results of these simulations show that a linear network model produces results consistent with theory and published experimental data
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| 25. |
- Hansbo, Peter, et al.
(författare)
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A posteriori error estimates for continuous/discontinuous Galerkin approximations of the Kirchhoff-Love buckling problem
- 2015
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Ingår i: Computational Mechanics. - : Springer Berlin/Heidelberg. - 0178-7675 .- 1432-0924. ; 56:5, s. 815-827
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Tidskriftsartikel (refereegranskat)abstract
- Second order buckling theory involves a one-way coupled coupled problem where the stress tensor from a plane stress problem appears in an eigenvalue problem for the fourth order Kirchhoff plate. In this paper we present an a posteriori error estimate for the critical buckling load and mode corresponding to the smallest eigenvalue and associated eigenvector. A particular feature of the analysis is that we take the effect of approximate computation of the stress tensor and also provide an error indicator for the plane stress problem. The Kirchhoff plate is discretized using a continuous/discontinuous finite element method based on standard continuous piecewise polynomial finite element spaces. The same finite element spaces can be used to solve the plane stress problem.
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| 26. |
- Hansbo, Peter, 1959-, et al.
(författare)
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Continuous/discontinuous finite element modelling of Kirchhoff plate structures in R3 using tangential differential calculus
- 2017
-
Ingår i: Computational Mechanics. - : Springer. - 0178-7675 .- 1432-0924. ; 60:4, s. 693-702
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Tidskriftsartikel (refereegranskat)abstract
- We employ surface differential calculus to derive models for Kirchhoff plates including in-plane membrane deformations. We also extend our formulation to structures of plates. For solving the resulting set of partial differential equations, we employ a finite element method based on elements that are continuous for the displacements and discontinuous for the rotations, using (Formula presented.)-elements for the discretisation of the plate as well as for the membrane deformations. Key to the formulation of the method is a convenient definition of jumps and averages of forms that are d-linear in terms of the element edge normals.
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| 27. |
- Hansbo, Peter, et al.
(författare)
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Nitsche's method for coupling non-matching meshes in fluid-structure vibration problems
- 2003
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 32:1-2, s. 134-139
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Tidskriftsartikel (refereegranskat)abstract
- Nitsche's method [11] is a classical method for imposing essential boundary conditions weakly. Unlike the penalty method, it is consistent with the original differential equation. The strong point of Nitsche's method is that it retains the convergence rate of the underlying finite element method, whereas the standard penalty method either requires a "very large" penalty parameter, destroying the condition number of the resulting matrix problem, or, in case the condition number is to be retained, is limited to first order energy-norm accuracy. In this paper, we give a formulation of Nitsche's method suitable for the problem of fluid-structure interaction. Numerical examples are given.
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| 28. |
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| 29. |
- Hansbo, Peter, et al.
(författare)
-
The nonconforming linear strain tetrahedron for a large deformation elasticity problem
- 2016
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Ingår i: Computational Mechanics. - : Springer. - 0178-7675 .- 1432-0924. ; 58:6, s. 929-935
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate the performance of the nonconforming linear strain tetrahedron element introduced by Hansbo (Comput Methods Appl Mech Eng 200(9–12):1311–1316, 2011; J Numer Methods Eng 91(10):1105–1114, 2012). This approximation uses midpoints of edges on tetrahedra in three dimensions with either point continuity or mean continuity along edges of the tetrahedra. Since it contains (rotated) bilinear terms it performs substantially better than the standard constant strain element in bending. It also allows for under-integration in the form of one point Gauss integration of volumetric terms in near incompressible situations. We combine under-integration of the volumetric terms with houglass stabilization for the isochoric terms.
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| 30. |
- Hansbo, Peter, et al.
(författare)
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Variational formulation of curved beams in global coordinates
- 2014
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 53:4, s. 611-623
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we derive a variational formulation for the static analysis of a linear curved beam natively expressed in global Cartesian coordinates. Using an implicit description of the beam midline during derivation we eliminate the need for local coordinates. The only geometrical information appearing in the final expressions for the governing equations is the tangential direction. As a consequence, zero or discontinuous curvature, for example at inflection points, pose no difficulty in this formulation. Kinematic assumptions encompassing both Timoshenko and Euler-Bernoulli beam theories are considered. With the exception of truly three-dimensional formulations, models for curved beams found in the literature are typically derived in the local Frenet frame. We implement finite element methods with global degrees of freedom and discuss curvature coupling effects and locking. Numerical comparisons with classical solutions for straight and curved cantilever beams under tip load are given, as well as numerical examples illustrating curvature coupling effects.
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| 31. |
- Hoffman, Johan
(författare)
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Simulation of turbulent flow past bluff bodies on coarse meshes using General Galerkin methods : drag crisis and turbulent Euler solutions
- 2006
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 38:05-apr, s. 390-402
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Tidskriftsartikel (refereegranskat)abstract
- In recent years adaptive stabilized finite element methods, here referred to as General Galerkin (G2) methods, have been developed as a general methodology for the computation of mean value output in turbulent flow. In earlier work, in the setting of bluff body flow, the use of no slip boundary conditions has been shown to accurately capture the separation from a laminar boundary layer, in a number of benchmark problems. In this paper we extend the G2 method to problems with turbulent boundary layers, by including a simple wall-model in the form of a friction boundary condition, to account for the skin friction of the unresolved turbulent boundary layer. In particular, we use G2 to simulate drag crisis for a circular cylinder, by adjusting the friction parameter to match experimental results. By letting the Reynolds number go to infinity and the skin friction go to zero, we get a G2 method for the Euler equations with slip boundary conditions, which we here refer to as an EG2 method. The only parameter in the EG2 method is the discretization parameter, and we present computational results indicating that EG2 may be used to model very high Reynolds numbers flow, such as geophysical flow.
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| 32. |
- Holmström, Andreas, 1978, et al.
(författare)
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Space-time finite elements for a simplified thermo-metallurgical problem relevant to casting
- 2007
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 40:2, s. 341-353
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Tidskriftsartikel (refereegranskat)abstract
- The non-linear thermo-metallurgical problem, relevant for the cooling of a molten metal including the macro-segregation that occurs during the cooling process, is studied here. Due to the strong non-linearities involved in phase transformations, it is necessary to use a fine resolution in space-time in a finite element approximation in order to meet accuracy requirements. We derive space-time FE-methods based on the discontinuous and continuous Galerkin method in time for the energy equation. This formulation integrates the stored energy exactly for a given heat flux. When macro-segregation is incorporated into the model, the problem can be formulated in such a way that the phase-transition drives a flow of species. In addition, diffusion is possible throughout the domain. The model can be further rewritten using a potential approach. By this approach for modelling macro-segregation, we are able to obtain discretizations that guarantee that the balance equations are satisfied, and it is possible to solve the phase-transition problem either as a field problem or as a local problem (defined by a local evolution rule). © Springer Verlag 2007.
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| 33. |
- Issa, Sally, et al.
(författare)
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Diagonally implicit Runge–Kutta (DIRK) integration applied to finite strain crystal plasticity modeling
- 2018
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 62:6, s. 1429-1441
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Tidskriftsartikel (refereegranskat)abstract
- Diagonally implicit Runge–Kutta methods (DIRK) are evaluated and compared to standard solution procedures for finite strain crystal plasticity boundary value problems. The structure of the DIRK implementation is similar to that of a conventional implicit backward Euler scheme. It is shown that only very small modifications are required in order to transform the numerical scheme from one into the other. This similarity permits efficient adaption of the integration procedure to a particular problem. To enforce plastic incompressibility, different projection techniques are evaluated. Rate dependent crystal plasticity, using a single crystal is simulated under various load cases as well as a larger polycrystalline sample. It is shown that the two-stage DIRK scheme combined with a step size control and a time continuous projection technique for the update of the plastic deformation gradient is in general more accurate than the implicit backward Euler and an update based on exponential mapping.
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| 34. |
- 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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| 35. |
- Jänicke, Ralf, 1980, et al.
(författare)
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A poro-viscoelastic substitute model of fine-scale poroelasticity obtained from homogenization and numerical model reduction
- 2020
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 65:4, s. 1063-1083
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Tidskriftsartikel (refereegranskat)abstract
- Numerical model reduction is exploited for computational homogenization of the model problem of a poroelastic medium under transient conditions. It is assumed that the displacement and pore pressure fields possess macro-scale and sub-scale (fluctuation) parts. A linearly independent reduced basis is constructed for the sub-scale pressure field using POD. The corresponding reduced basis for the displacement field is constructed in the spirit of the NTFA strategy. Evolution equations that define an apparent poro-viscoelastic macro-scale model are obtained from the continuity equation pertinent to the RVE. The present model represents an extension of models available in literature in the sense that the pressure gradient is allowed to have a non-zero macro-scale component in the nested FE2 setting. The numerical results show excellent agreement between the results from numerical model reduction and direct numerical simulation. It was also shown that even 3D RVEs give tractable solution times for full-fledged FE2 computations.
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| 36. |
- Jänicke, Ralf, 1980, et al.
(författare)
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Identification of viscoelastic properties from numerical model reduction of pressure diffusion in fluid-saturated porous rock with fractures
- 2019
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 63:1, s. 49-67
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the computational homogenization and numerical model reduction of deformation driven pressure diffusion in fractured porous rock. Exposed to seismic waves, the heterogeneity of the material leads to local fluid pressure gradients which are equilibrated via pressure diffusion. However, a macroscopic observer is not able to measure the diffusion process directly but senses the intrinsic attenuation of an apparently monophasic viscoelastic solid. The aim of this paper is to establish a reliable, yet numerically efficient, computational homogenization method to identify the viscoelastic properties of the macroscopic substitute model. Inspired by the Nonuniform Transformation Field Analysis, we incorporate a Numerical Model Reduction procedure. The proposed method is validated for several scenarios ranging from pressure diffusion in an unfractured poroelastic matrix, via localized pressure diffusion in interconnected fractures embedded in an impermeable matrix, to the fully coupled pressure diffusion both in fractures and the embedding poroelastic matrix.
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| 37. |
- Kaiser, T., et al.
(författare)
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Fundamentals of electro-mechanically coupled cohesive zone formulations for electrical conductors
- 2021
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 68:1, s. 51-67
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the influence of (micro-)cracks on the effective electrical properties of material systems and components, this contribution deals with fundamental developments on electro-mechanically coupled cohesive zone formulations for electrical conductors. For the quasi-stationary problems considered, Maxwell’s equations of electromagnetism reduce to the continuity equation for the electric current and to Faraday’s law of induction, for which non-standard jump conditions at the interface are derived. In addition, electrical interface contributions to the balance equation of energy are discussed and the restrictions posed by the dissipation inequality are studied. Together with well-established cohesive zone formulations for purely mechanical problems, the present developments provide the basis to study the influence of mechanically-induced interface damage processes on effective electrical properties of conductors. This is further illustrated by a study of representative boundary value problems based on a multi-field finite element implementation.
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| 38. |
- Kaliappan, Jayabal, et al.
(författare)
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Micromechanical modelling of switching phenomena in polycrystalline piezoceramics: application of a polygonal finite element approach
- 2011
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 48:4, s. 421-435
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Tidskriftsartikel (refereegranskat)abstract
- A micromechanically motivated model is proposed to capture nonlinear effects and switching phenomena present in ferroelectric polycrystalline materials. The changing remnant state of the ferroelectric crystal is accounted for by means of so-called back fields-such as back stresses-to resist or assist further switching processes in the crystal depending on the local loading history. To model intergranular effects present in ferroelectric polycrystals, the computational model elaborated is embedded into a mixed polygonal finite element approach, whereby an individual ferroelectric grain is represented by one single irregular polygonal finite element. This computationally efficient coupled simulation framework is shown to reproduce the specific characteristics of the responses of ferroelectric polycrystals under complex electromechanical loading conditions in good agreement with experimental observations.
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| 39. |
- Kroon, Martin
(författare)
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Dynamic steady-state analysis of crack propagation in rubber-like solids using an extended finite element method
- 2012
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 49:1, s. 73-86
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of plane stress and steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to examine the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The computational framework builds upon a previous work by the present author (Kroon in Int J Fract 169:49-60, 2011). The model was fully able to predict experimental results in terms of the local surface energy at the crack tip and the total energy release rate at different crack speeds. The predicted distributions of stress and dissipation around the propagating crack tip are presented. The predicted crack tip profiles also agree qualitatively with experimental findings.
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| 40. |
- Kroon, Martin, et al.
(författare)
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Numerical implementation of a J(2)- and J(3)-dependent plasticity model based on a spectral decomposition of the stress deviator
- 2013
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 52:5, s. 1059-1070
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Tidskriftsartikel (refereegranskat)abstract
- A new plasticity model with a yield criterion that depends on the second and third invariants of the stress deviator is proposed. The model is intended to bridge the gap between von Mises' and Tresca's yield criteria. An associative flow rule is employed. The proposed model contains one new non-dimensional key material parameter, that quantifies the relative difference in yield strength between uniaxial tension and pure shear. The yield surface is smooth and convex. Material strain hardening can be ascertained by a standard uniaxial tensile test, whereas the new material parameter can be determined by a test in pure shear. A fully implicit backward Euler method is developed and presented for the integration of stresses with a tangent operator consistent with the stress updating scheme. The stress updating method utilizes a spectral decomposition of the deviatoric stress tensor, which leads to a stable and robust updating scheme for a yield surface that exhibits strong and rapidly changing curvature in the synoptic plane. The proposed constitutive theory is implemented in a finite element program, and the influence of the new material parameter is demonstrated in two numerical examples.
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| 41. |
- Larsson, Fredrik, 1975, et al.
(författare)
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RVE computations with error control and adaptivity: the power of duality
- 2007
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 39:5, s. 647-661
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Tidskriftsartikel (refereegranskat)abstract
- The goal of computational homogenization is to obtain the macro-scale response, normally in terms of macro-scale stress for given macro-scale deformation, via RVE-computations. In this paper we investigate, in a systematic manner, the effects of Dirichlet and Neumann boundary conditions on the RVE. Adaptive computations are carried out with respect to, in particular, control of the error in the macro-scale stress tensor. This requires the corresponding dual solutions. As a new result, it is shown how the same dual solutions can be conveniently used in computing the algorithmic tangent stiffness tensor, thereby demonstrating the "power of duality". © Springer Verlag 2007.
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| 42. |
- Le, Thanh Nam, et al.
(författare)
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Efficient formulation for dynamics of corotational 2D beams
- 2011
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 48:2, s. 153-161
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Tidskriftsartikel (refereegranskat)abstract
- The corotational method is an attractive approach to derive non-linear finite beam elements. In a number of papers, this method was employed to investigate the non-linear dynamic analysis of 2D beams. However, most of the approaches found in the literature adopted either a lumped mass matrix or linear local interpolations to derive the inertia terms (which gives the classical linear and constant Timoshenko mass matrix), although local cubic interpolations were used to derive the elastic force vector and the tangent stiffness matrix. In this paper, a new corotational formulation for dynamic nonlinear analysis is presented. Cubic interpolations are used to derive both the inertia and elastic terms. Numerical examples show that the proposed approach is more efficient than using lumped or Timoshenko mass matrices.
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| 43. |
- Marklund, P.-O., et al.
(författare)
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Optimization of airbag inflation parameters for the minimization of out of position occupant injury
- 2003
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 31:6, s. 496-504
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Tidskriftsartikel (refereegranskat)abstract
- In this paper optimization techniques together with coupled fluid-structure analysis are used to provide a better understanding of the interaction between the airbag inflation process and an Out Of Position occupant. We provide a concept for, and exemplify how these techniques can be applied to optimize the airbag inflator characteristics in order to minimize occupant injury. For a simplified, but realistic, problem we show that the head acceleration can be reduced by approximately 65% by optimizing the inlet characteristics.
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| 44. |
- Marklund, Per-Olof, et al.
(författare)
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Simulation of airbag inflation processes using a coupled fluid structure approach
- 2002
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 29:4-5, s. 289-297
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores simulation techniques for airbag inflation problems using a coupled fluid structure approach. It is to be seen as an initial study on the phenomena occurring in an airbag during a so called out of position occupant impact. The problem studied in this paper is an airbag which is set to impact a head form. The head form is positioned at a very short distance from the airbag. A multi material arbitrary Lagrangian Eulerian technique in the explicit finite element code LS-DYNA is used for the fluid and it is coupled to the structure using a penalty based fluid structure contact algorithm. The results for the head form acceleration and velocity show a good agreement to experimentally obtained values. At the early stages of the inflation process a high pressure zone is found to develop between the gas inlet and the head form. Consequently the pressure difference between the inlet and the high pressure zone is too low for an a priori assumption of sonic flow at the inlet, which is a common requirement in the control volume models used in the industry today.
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| 45. |
- Memarnahavandi, Arash, 1983, et al.
(författare)
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A goal-oriented adaptive procedure for the quasi-continuum method with cluster approximation
- 2015
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 55:4, s. 617-642
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Tidskriftsartikel (refereegranskat)abstract
- We present a strategy for adaptive error control for the quasi-continuum (QC) method applied to molecular statics problems. The QC-method is introduced in two steps: Firstly, introducing QC-interpolation while accounting for the exact summation of all the bond-energies, we compute goal-oriented error estimators in a straight-forward fashion based on the pertinent adjoint (dual) problem. Secondly, for large QC-elements the bond energy and its derivatives are typically computed using an appropriate discrete quadrature using cluster approximations, which introduces a model error. The combined error is estimated approximately based on the same dual problem in conjunction with a hierarchical strategy for approximating the residual. As a model problem, we carry out atomistic-to-continuum homogenization of a graphene monolayer, where the Carbon-Carbon energy bonds are modeled via the Tersoff-Brenner potential, which involves next-nearest neighbor couplings. In particular, we are interested in computing the representative response for an imperfect lattice. Within the goal-oriented framework it becomes natural to choose the macro-scale (continuum) stress as the "quantity of interest". Two different formulations are adopted: The Basic formulation and the Global formulation. The presented numerical investigation shows the accuracy and robustness of the proposed error estimator and the pertinent adaptive algorithm.
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| 46. |
- Miller, Christopher, et al.
(författare)
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Simulation of fracture in vascular tissue : coupling a continuum damage formulation with an embedded representation of fracture
- 2024
-
Ingår i: Computational Mechanics. - : Springer Nature. - 0178-7675 .- 1432-0924. ; 73:6, s. 1421-1438
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Tidskriftsartikel (refereegranskat)abstract
- The fracture of vascular tissue, and load-bearing soft tissue in general, is relevant to various biomechanical and clinical applications, from the study of traumatic injury and disease to the design of medical devices and the optimisation of patient treatment outcomes. The fundamental mechanisms associated with the inception and development of damage, leading to tissue failure, have yet to be wholly understood. We present the novel coupling of a microstructurally motivated continuum damage model that incorporates the time-dependent interfibrillar failure of the collagenous matrix with an embedded phenomenological representation of the fracture surface. Tissue separation is therefore accounted for through the integration of the cohesive crack concept within the partition of unity finite element method. A transversely isotropic cohesive potential per unit undeformed area is introduced that comprises a rate-dependent evolution of damage and accounts for mixed-mode failure. Importantly, a novel crack initialisation procedure is detailed that identifies the occurrence of localised deformation in the continuum material and the orientation of the inserted discontinuity. Proof of principle is demonstrated by the application of the computational framework to two representative numerical simulations, illustrating the robustness and versatility of the formulation.
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| 47. |
- Monge, Azahar, et al.
(författare)
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On the convergence rate of the Dirichlet-Neumann iteration for unsteady thermal fluid structure interaction
- 2018
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 62:3, s. 525-541
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Tidskriftsartikel (refereegranskat)abstract
- We consider the Dirichlet-Neumann iteration for partitioned simulation of thermal fluid-structure interaction, also called conjugate heat transfer. We analyze its convergence rate for two coupled fully discretized 1D linear heat equations with jumps in the material coefficients across these. These are discretized using implicit Euler in time, a finite element method on one domain, a finite volume method on the other one and variable aspect ratio. We provide an exact formula for the spectral radius of the iteration matrix. This shows that for large time steps, the convergence rate is the aspect ratio times the quotient of heat conductivities and that decreasing the time step will improve the convergence rate. Numerical results confirmthe analysis and show that the 1D formula is a good estimator in 2D and even for nonlinear thermal FSI applications.
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| 48. |
- Nilenius, Filip, 1982, et al.
(författare)
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Computational homogenization of diffusion in three-phase mesoscale concrete
- 2014
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 54:2, s. 461-472
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Tidskriftsartikel (refereegranskat)abstract
- A three dimensional (3D) mesoscale model of concrete is presented and employed for computational homogenization in the context of mass diffusion. The mesoscale constituents of cement paste, aggregates and Interfacial Transition Zone (ITZ) are contained within a Statistical Volume Element (SVE) on which homogenization is carried out. The model implementation accounts for ITZ anisotropy thereby the diffusivity tensor depends on the normal of the aggregate surface. The homogenized response is compared between 3D and 2D SVEs to study the influence of the third spatial dimension, and for varying mesoscale compositions to study the influence of aggregate content on concrete diffusivity. The computational results show that the effective diffusivity of 3D SVEs is about 40% greater than 2D SVEs when ITZ is excluded for the SVE, and 17% when ITZ is included. The results are in agreement with the upper Hashin-Shtrikman bound when ITZ is excluded, and close the Taylor assumption when ITZ is included.
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| 49. |
- Nilenius, Filip, 1982, et al.
(författare)
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Mesoscale modelling of crack-induced diffusivity in concrete
- 2015
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 55:2, s. 359-370
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Tidskriftsartikel (refereegranskat)abstract
- Cracks have large impact on the diffusivity of concrete since they provide low-resistance pathways for moisture and chloride ions to migrate through the material. In this work, crack-induced diffusivity in concrete is modelled on the heterogeneous mesoscale and computationally homogenized to obtain macroscale diffusivity properties. Computations are carried out using the finite element method (FEM) on three-dimensional Statistical Volume Elements (SVEs) comprising the mesoscale constituents in terms of cement paste, aggregates and the Interfacial Transition Zone (ITZ). The SVEs are subjected to uni-axial tension loading and cracks are simulated by use of an isotropic damage model. In a damaged finite element, the crack plane is assumed to be perpendicular to the largest principle strain, and diffusivity properties are assigned to the element only in the in-plane direction of the crack by anisotropic constitutive modelling.The numerical results show that the macroscale diffusivity of concrete can be correlated to the applied mechanical straining of the SVE and that the macroscale diffusivity increases mainly in the transversal direction relative to the axis of imposed mechanical straining.
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| 50. |
- Noll, Isabelle, et al.
(författare)
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A computational phase transformation model for selective laser melting processes
- 2020
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 0178-7675 .- 1432-0924. ; 66:6, s. 1321-1342
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting (SLM) has gained large interest due to advanced manufacturing possibilities. However, the growing potential also necessitates reliable predictions of structures in particular regarding their long-term behaviour. The constitutive and structural response is thereby challenging to reproduce, due to the complex material behaviour. This motivates the aims of this contribution: To establish a material model that accounts for the behaviour of the different phases occurring during SLM but that still allows the use of (basic) process simulations. In particular, the present modelling framework explicitly takes into account the mass fractions of the different phases, their mass densities, and specific inelastic strain contributions. The thermomechanically fully coupled framework is implemented into the software Abaqus. The numerical examples emphasise the capabilities of the framework to predict, e.g., the residual stresses occurring in the final part. Furthermore, a postprocessing of averaged inelastic strains is presented yielding a micromechanics-based motivation for inherent strains.
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