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| 2. |
- Ristinmaa, Matti, et al.
(författare)
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Mixture theory for a thermoelasto-plastic porous solid considering fluid flow and internal mass exchange
- 2011
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225 .- 1879-2197. ; 49:11, s. 1185-1203
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Tidskriftsartikel (refereegranskat)abstract
- A thermoelastic-plastic body consisting of two phases, a solid and a fluid, each comprising two constituents is considered where one constituent in one phase is allowed to exchange mass with another constituent (of the same substance) in the other phase. A large strain setting is adopted and the formulation applies to general anisotropy and the existence of residual stresses. Generalized forms of Fourier's, Fick's and Darcy's laws are derived and also the stresses on the constituent, phase and mixture level are established; in addition, the evolution law for general plasticity is given. Finally, and in particular, a general evolution law for the rate of deformation tensor related to mass exchange is proposed and this leads to general absorption and desorption evolution laws for mass exchange between two constituents (of the same substance), one belonging to the solid phase and the other to the fluid phase. Equilibrium curves for absorption and desorption also emerge from the theory.
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| 3. |
- Fisk, Martin, 1981-, et al.
(författare)
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Coupled electromagnetic-thermal solution strategy for induction heating of ferromagnetic materials
- 2022
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Ingår i: Applied Mathematical Modelling. - : Elsevier. - 0307-904X .- 1872-8480. ; 111, s. 818-835
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Tidskriftsartikel (refereegranskat)abstract
- Induction heating is used in many industrial applications to heat electrically conductive materials. The coupled electromagnetic-thermal induction heating process is non-linear in general, and for ferromagnetic materials it becomes challenging since both the electromagnetic and the thermal responses are non-linear. As a result of the existing non-linearities, simulating the induction heating process is a challenging task. In the present work, a coupled transient electromagnetic-thermal finite element solution strategy that is appropriate for modeling induction heating of ferromagnetic materials is presented. The solution strategy is based on the isothermal staggered split approach, where the electromagnetic problem is solved for fixed temperature fields and the thermal problem for fixed heat sources obtained from the electromagnetic solution. The modeling strategy and the implementation are validated against induction heating experiments at three heating rates. The computed temperatures, that reach above the Curie temperature, agree very well with the experimental results.
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| 4. |
- Tryding, Johan, et al.
(författare)
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Delamination of cellulose-based materials during loading–unloading conditions : Interface model and experimental observations
- 2023
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- A cohesive interface model based on a master curve is proposed for the analysis of delamination in paperboard under various loading, unloading, and reloading conditions. The model is thermodynamically consistent and considers the effects of elasticity, plasticity, and damage. The proposed model is verified by comparing its predictions with experimental data obtained from multiple loading–unloading–reloading cycle experiments using a split double cantilever beam specimen. The results show that the model can predict the cyclic behavior of shear loading and provide insight into the damage evolution associated with different loading paths by analyzing the shear stress distribution in the fracture process zone. The model’s calibration process requires monotonic normal and shear loading data but only cyclic normal loading data. Additionally, the model accounts for the paperboard’s fiber–fiber friction and normal dilatation due to shear loading. In total, nine parameters are needed to calibrate the mode.
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| 5. |
- Hallberg, Håkan, et al.
(författare)
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Model Describing Material-Dependent Deformation Behavior in High-Velocity Metal Forming Processes
- 2009
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Ingår i: Journal of Engineering Mechanics - ASCE. - 1943-7889 .- 0733-9399. ; 135:4, s. 345-357
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Tidskriftsartikel (refereegranskat)abstract
- A constitutive model for rate-dependent and thermomechanically coupled plasticity at finite strains is presented. The plasticity model is based on a J(2) model and rate-dependent behavior is included by use of a Perzyna-type formulation. Adiabatic heating effects are handled in a consistent way and not, as is a common assumption, through a constant conversion of the internal work rate into rate of heating. The conversion factor is instead derived from thermodynamic considerations. The stored energy is assumed to be a function of a single internal variable which differs from the effective plastic strain. This allows a thermodynamically consistent formulation to be obtained which, as shown, can be calibrated by use of simple procedures. Choosing 100Cr6 steel in two differently heat treated conditions as prototype material, experimental tests are performed, enabling the model to be calibrated. Significant differences in deformation behavior are noted as the differently heat treated specimens are compared. In addition, the local stress-updating procedure is reduced to a single scalar equation, permitting a very efficient numerical implementation of the model. The constitutive formulation proposed was employed in an explicit finite element solver, illustrative simulations of a high-velocity metal forming process being performed to demonstrate the capabilities of the model and certain characteristic traits of the materials that were studied.
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| 6. |
- Robertsson, Kristofer, et al.
(författare)
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Efficient and accurate simulation of the packaging forming process
- 2018
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Ingår i: Packaging Technology and Science. - : Wiley. - 0894-3214. ; 31:8, s. 557-566
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Tidskriftsartikel (refereegranskat)abstract
- To allow for large-scale forming applications, such as converting paperboard into package containers, efficient and reliable numerical tools are needed. In finite element simulations of thin structures, elements including structural features are required to reduce the computational cost. Solid-shell elements based on reduced integration with hourglass stabilization is an attractive choice. One advantage of this choice is the natural inclusion of the thickness, not present in standard degenerated shells, which is especially important for many problems involving contact. Furthermore, no restrictions are imposed on the constitutive models since the solid-shell element does not require the plane stress condition to be enforced. In this work, a recently proposed efficient solid-shell element is implemented together with a state-of-the-art continuum model for paperboard. This approach is validated by comparing the obtained numerical results with experimental results for paperboard as well as with those found by using 3D continuum elements. To show the potential of this approach, a large-scale forming simulation of paperboard is used as a proof of concept.
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| 7. |
- Askfelt, Henrik, et al.
(författare)
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Transient transport of heat, mass, and momentum in paperboard including dynamic phase change of water
- 2016
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225. ; 109, s. 1339-1351
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Tidskriftsartikel (refereegranskat)abstract
- A theory to describe deforming moist paperboard in environments where both temperature and pressure change significantly during a short period of time is presented. Paperboard is viewed as an orthotropic triphasic porous medium consisting of fibers, bound water and moist air. Furthermore, the moist air is considered as a mixture of two miscible gases, namely dry air and water vapor. A two–scale hybrid mixture theory is adopted in a large strain setting and balances of mass, linear momentum, and energy are presented on the macroscale. Constitutive relations are derived on the macroscale through exploitation of the dissipation inequality. Mass exchange between bound water and water vapor is included as a dynamic process. Mass transportation processes include chemical potential driven diffusion and nonlinear seepage flow. The elasto–plastic stress–strain response of the fiber network is described by assuming a multiplicative split of the deformation gradient associated with the motion of the fiber network. The dynamics related to the mass exchange between bound water and water vapor is illustrated by changes of pressure, relative humidity, moisture ratio, and rate of evaporation during rapid heating of a moist paperboard.
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| 8. |
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| 9. |
- Grassi, Lorenzo, et al.
(författare)
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Prediction of femoral strength using 3D finite element models reconstructed from DXA images: validation against experiments
- 2017
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Ingår i: Biomechanics and Modeling in Mechanobiology. - : Springer Science and Business Media LLC. - 1617-7940 .- 1617-7959. ; 16:3, s. 989-1000
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Tidskriftsartikel (refereegranskat)abstract
- Computed tomography (CT)-based finite element (FE) models may improve the current osteoporosis diagnostics and prediction of fracture risk by providing an estimate for femoral strength. However, the need for a CT scan, as opposed to the conventional use of dual-energy X-ray absorptiometry (DXA) for osteoporosis diagnostics, is considered a major obstacle. The 3D shape and bone mineral density (BMD) distribution of a femur can be reconstructed using a statistical shape and appearance model (SSAM) and the DXA image of the femur. Then, the reconstructed shape and BMD could be used to build FE models to predict bone strength. Since high accuracy is needed in all steps of the analysis, this study aimed at evaluating the ability of a 3D FE model built from one 2D DXA image to predict the strains and fracture load of human femora. Three cadaver femora were retrieved, for which experimental measurements from ex vivo mechanical tests were available. FE models were built using the SSAM-based reconstructions: using only the SSAM-reconstructed shape, only the SSAM-reconstructed BMD distribution, and the full SSAM-based reconstruction (including both shape and BMD distribution). When compared with experimental data, the SSAM-based models predicted accurately principal strains (coefficient of determination >0.83, normalized root-mean-square error <16%) and femoral strength (standard error of the estimate 1215 N). These results were only slightly inferior to those obtained with CT-based FE models, but with the considerable advantage of the models being built from DXA images. In summary, the results support the feasibility of SSAM-based models as a practical tool to introduce FE-based bone strength estimation in the current fracture risk diagnostics.
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| 10. |
- Ottosen, Niels Saabye, et al.
(författare)
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Framework for non-coherent interface models at finite displacement jumps and finite strains
- 2016
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Ingår i: Journal of the Mechanics and Physics of Solids. - : Elsevier BV. - 0022-5096. ; 90, s. 124-141
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with a novel constitutive framework suitable for non-coherent interfaces, such as cracks, undergoing large deformations in a geometrically exact setting. For this type of interface, the displacement field shows a jump across the interface. Within the engineering community, so-called cohesive zone models are frequently applied in order to describe non-coherent interfaces. However, for existing models to comply with the restrictions imposed by (a) thermodynamical consistency (e.g., the second law of thermodynamics), (b) balance equations (in particular, balance of angular momentum) and (c) material frame indifference, these models are essentially fiber models, i.e. models where the traction vector is collinear with the displacement jump. This constraints the ability to model shear and, in addition, anisotropic effects are excluded. A novel, extended constitutive framework which is consistent with the above mentioned fundamental physical principles is elaborated in this paper. In addition to the classical tractions associated with a cohesive zone model, the main idea is to consider additional tractions related to membrane-like forces and out-of-plane shear forces acting within the interface. For zero displacement jump, i.e. coherent interfaces, this framework degenerates to existing formulations presented in the literature. For hyperelasticity, the Helmholtz energy of the proposed novel framework depends on the displacement jump as well as on the tangent vectors of the interface with respect to the current configuration - or equivalently - the Helmholtz energy depends on the displacement jump and the surface deformation gradient. It turns out that by defining the Helmholtz energy in terms of the invariants of these variables, all above-mentioned fundamental physical principles are automatically fulfilled. Extensions of the novel framework necessary for material degradation (damage) and plasticity are also covered.
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