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| 2. |
- Hård af Segerstad, P., et al.
(författare)
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A constitutive equation for open-cell cellular solids, including viscoplasticity, damage and deformation induced anisotropy
- 2008
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 24:5, s. 896-914
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Tidskriftsartikel (refereegranskat)abstract
- A thermodynamically consistent approach is developed for modelling the response of an open-cell cellular solid at finite compressive strains. The cellular solid is considered as a network of struts, where each strut connects two vertex points. A hypothesis is proposed that the vertex points move affinely in the finite strain regime, where the struts buckle plastically. The strut deformation is assumed to be 1-dimensional and depend directly on the macroscopic deformation; thus the description of the strut response requires only a scalar valued response function. Owing to this simple ansatz it is possible to include multiple nonlinear mechanisms, such as hyperelasto-viscoplasticity and damage. The macrostress is obtained by averaging over a statistical ensemble of struts. The model has been implemented in the context of finite strains and damage coupled to viscoplastic Perzyna type behaviour. All model parameters may be determined by performing tests in simple compression. The model is well capable of reproducing data from compression experiments on various open-cell aluminium foams.
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| 3. |
- Larsson, R., et al.
(författare)
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Process-modeling of composites using two-phase porous media theory
- 2004
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier BV. - 0997-7538 .- 1873-7285. ; 23:1, s. 15-36
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Tidskriftsartikel (refereegranskat)abstract
- A biphasic continuum model is proposed for the modeling of a family of forming processes for fiber composites. The processes considered involve deformation of a fiber bundle network, wetting by penetration of resin into fiber bundles, and resin flow through the fiber bundle network. The continuum model represents three (or more) actual micro constituents as two continuous phases: a solid phase being the fiber network plus any extra void within the fiber bundles and a fluid phase being the liquid matrix. The model framework thus comprises the continuum formulation of a nonlinear compressible porous solid saturated with an incompressible fluid phase. Guided by the entropy inequality, we specify constitutive relations concerning three different mechanisms pertinent to the forming process: effective stress response of the fiber bundle network, compaction of the solid phase, and Darcian interaction between the two phases. We are particularly concerned with the compaction of the fiber-bundles of the solid phase, consisting of elastic packing combined with a viscous wetting process driven by the fluid pressure. The paper is concluded with a couple of numerical examples, where the volumetric deformation-pressure response of a fluid saturated fiber bundle network at undrained conditions is considered. Both volumetric relaxation and volumetric creep tests are analyzed. In particular, the response for different loading rates is assessed. As a final example, a finite element analysis of a relaxation test for the macroscopically undrained compression of a fluid-filled fibernetwork specimen is carried out.
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| 4. |
- Wysocki, M., et al.
(författare)
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Hydrostatic consolidation of commingled fibre composites
- 2005
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 65:10, s. 1507-1519
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Tidskriftsartikel (refereegranskat)abstract
- A molten hybrid-yarn composite is modelled as a continuum. Constitutive equations governing hydrostatic consolidation are formulated, based on a two-phase continuum mechanical framework developed in a recent paper [Larsson R, Wysocki M, Toll S. Process-modelling of composites using two-phase porous media theory. European Journal of Mechanics-A 2004;23:15-36]. The fibre bundles are assumed to be completely surrounded by resin, thus subjected to hydrostatic pressure. To model the infiltration of resin into the fibre bundles, we introduce a compressible solid phase consisting of fibres plus intra-fibre void. The compression of the solid phase is caused by a combination of infiltration and elastic compression of the fibre bundles. The models are micromechanical, and all parameters have a clear physical meaning and are measurable in principle. Using parameter values out of the literature and estimated from micrographs, the number of adjustable parameters may be brought down to one: a spring constant for the fibre bundle elasticity. Consolidation experiments are performed, where a tool is closed to a prescribed compression and then held fixed, while the pressure is monitored over time. The predicted and measured pressure traces are in good agreement.
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| 5. |
- Wysocki, Maciej, et al.
(författare)
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Press forming of commingled yarn based composites : The preform contribution
- 2007
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 67:3-4, s. 515-524
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Tidskriftsartikel (refereegranskat)abstract
- The process of press forming commingled yarn composites is studied and modelled based on the theory of porous media. Two sub processes are considered: (1) the wetting and compaction of individual bundles and (2) the overall preform deformation. An experimental method is introduced, to study these two sub processes separately. The experiment suppresses the fluid pressure build-up, and thus the process of wetting and bundle compaction, by draining the resin into a porous wall. In consequence, the measured response consists only of the preform contribution. Finally, the total response is simulated and tested against independent consolidation experiments. It was demonstrated that the present approach gives better predictions compared to models based on the bundle response only.
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