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| 2. |
- Abiri, Olufunminiyi
(författare)
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Simplifications of non-local damage models
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ductile fracture presents challenges with respect to material modelling and numerical simulations of localization. The strain and damage localization may be unwanted as it indicates a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying coupled plastic and fracturing/damage behaviour of the material, metal in the current context as well as the robustness of the simulation procedure. The focus of this thesis is on efficient and reliable finite element solution of the localization problem through the non-local damage model. The non-local damage model extends the standard continuum mechanics theory by using non-local continuum theory in order to achieve mesh independent results when simulating fracture or shear localization. In this work, the non-local damage model and its various simplifications are evaluated in an in-house finite element code developed using Matlab™. The accuracy, robustness, efficiency and costs of the models are investigated and also compared to a general multi-length scale finite element formulation. A numerical study versus published data is used to demonstrate the validity of the model. The explicit non-local damage variant will be implemented in a commercial finite element code for use in machining simulation
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| 3. |
- Ahadi, Aylin, et al.
(författare)
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Simulation of a Friction Stir Welding Process using FE technique
- 2006
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Ingår i: Report TVSM. - 0281-6679.
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Konferensbidrag (refereegranskat)abstract
- In this paper a three dimensional FE model of the friction stir welding (FSW) is presented and the FSW process is simulated. The model has been implemented in FE code Abaqus with user subroutines DLOAD, DFLUX and UMASFL. The material data used to describe the welded panels is from an aluminium alloy called AL-2024-T3 and the material is assumed to be isotropic with temperature dependent yield stress and elastic modulus. A nonlinear-coupled thermo-mechanical analysis was performed in order to study the temperature and stress distribution.
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| 6. |
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| 7. |
- Alexandersson, Marcus, et al.
(författare)
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Triphasic Model of Heat and Moisture Transport with Internal Mass Exchange in Paperboard
- 2016
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 112:2, s. 381-408
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Tidskriftsartikel (refereegranskat)abstract
- Mixture theory is used to derive a triphasic model to describe processes in paperboard consisting of solid fiber, bound water and gas. The gas is viewed as a miscible mix of the two constituents dry air and water vapor. The governing equations are mass conservation laws for bound water, dry air, water vapor, and mixture energy balance. Constitutive relations are found by exploiting the macroscale dissipation inequality. Resulting constitutive equations include Fickian diffusion of water vapor and dry air, Darcian flow for gas and Fourier heat conduction for the mixture. Mass exchange between bound water, and water vapor due to adsorption/desorption is driven by the difference in chemical potential. The interaction function is based on equilibrium considerations for the bound water–water vapor system. From the description of the sorption isotherm, expressions for net isosteric heat and free energy related to water–fiber interaction are derived. The resulting thermodynamically consistent model is used to simulate moisture and heat dynamics for paperboard rolls. Simulation results are presented for a paperboard roll with anisotropic material properties subjected to a change in ambient relative humidity from 50 to 80 %.
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| 8. |
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| 9. |
- Ask, Anna, et al.
(författare)
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Electromechanics of polyurethane elastomers
- 2011
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Konferensbidrag (refereegranskat)abstract
- It is well known that electroactive polymers (EAP) deform under electric fields. An advantage of EAP is that it may undergo deformations much larger than those capable by electroactive ceramics, however at comparatively low forces. As common for polymers, EAP exhibit time-dependent material behavior, i.e. an electro-viscoelastic effect. In the modeling the deformation as well as the electric potential are introduced as global degrees of freedom, the internal variables accounting for the viscous response are incorporated at the so-called constitutive level. The proposed model is calibrated against experimental data, and a simple coupled finite element example is studied to show the applicability of the finite deformation electro-viscoelastic formulation proposed.
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| 10. |
- Ask, Anna, et al.
(författare)
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Electrostriction in electro-viscoelastic polymers
- 2012
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Ingår i: Mechanics of Materials. - : Elsevier BV. - 0167-6636. ; 50, s. 9-21
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Tidskriftsartikel (refereegranskat)abstract
- Electrostrictive polyurethane (PU) elastomers belong to the class of materials commonly referred to as electroactive polymers (EAP). These materials have their use in a variety of applications, including biomimetics and microrobotics where traditional engineering components may fall short. PU is one of the materials considered for so called dielectric actuators, where the electromechanical response is generally due to Coulomb forces on the actuator electrodes, giving rise to a compressive pressure and thereby large deformations of the polymer. On the other hand, for more moderate electric fields, which may be more attractive in certain applications, a large part of the electroactive response for PU elastomers is due to inherent electrostriction. The latter phenomena is the focus of this work. As is common in elastomers, PU elastomers are viscoelastic. A coupled electro-viscoelastic phenomenological constitutive model for electrostrictive PU is proposed and fitted to experimental data available in the literature. The possibility of performing simulations of EAP is of interest as the number of applications grow. Considering this, the computational model is embedded in a coupled finite element formulation and, based on this, representative simulations of inhomogeneous boundary value problems are presented.
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