| 1. |
- Wysocki, Maciej, 1969, et al.
(författare)
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Anisotropic and tension-compression asymmetric model for composites consolidation
- 2010
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 41:2, s. 284-294
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Tidskriftsartikel (refereegranskat)abstract
- A constitutive model for anisotropic and tension-compression asymmetric response of a fibrous preform is developed and solved using a FE software. Applicability of the method to complex geometries is demonstrated by analysis the consolidation of an axisymmetric filament wound pressure vessel made from commingled yarns. Three different winding patterns are considered. In conclusions, the consolidation of the whole vessel, except at the opening, is prevented by the loading mode, where the pressure is applied on the interior. To succeed in manufacturing of this type of pressure vessel, use of an oversized preform that allows extension in the fibre direction is suggested.
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| 2. |
- Wysocki, Maciej, et al.
(författare)
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Two phase continuum modelling of composites consolidation
- 2009
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Ingår i: Plastics, rubber and composites. - 1465-8011 .- 1743-2898. ; 38:2-4, s. 93-97
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Tidskriftsartikel (refereegranskat)abstract
- A finite element model is developed to solve consolidation problems for composites manufacturing. The model is developed from a generic two-phase continuum theory allowing for coupling between the solid and fluid responses. The code is applied to a case study consisting of consolidation of a hat stringer to evaluate nonlinear effects.
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| 3. |
- Hård af Segerstad, Per, 1977, et al.
(författare)
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A micropolar theory for the finite elasticity of open-cell cellular solids
- 2009
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Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 465:2103, s. 843-865
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Tidskriftsartikel (refereegranskat)abstract
- A mechanistic model is presented for an open-cell cellular solid consisting of a threedimensional network of elastic struts. By considering the bending and torsion as well as stretching and buckling of the struts, we allow for length-scale effects in the macroscopic response. Constitutive equations are developed for the force and couple stress tensors, accounting for finite deformations and anisotropy. The consistent tangent stiffness operators are derived and the equations are fully implemented in a nonlinear twodimensional finite-element solution scheme for the coupled displacement/rotation problem. A boundary-value problem of a shear gap with prescribed boundary rotations is analysed, and the model is shown to predict the well-known gap size effect. The mechanistic model allows some detailed interpretation of the micropolar behaviour, such as the effects of strut slenderness, strut length and anisotropy.
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| 4. |
- Larsson, Ragnar, 1960, et al.
(författare)
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A micromechanically based model for dynamic damage evolution in unidirectional composites
- 2022
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Ingår i: International Journal of Solids and Structures. - : Elsevier Ltd. - 0020-7683 .- 1879-2146. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses the micromechanically motivated, quasistatic to dynamic, failure response of fibre reinforced unidirectional composites at finite deformation. The model draws from computational homogenization, with a subscale represented by matrix and fibre constituents. Undamaged matrix response assumes isotropic viscoelasticity–viscoplasticity, whereas the fibre is transversely isotropic hyperelastic. Major novelties involve damage degradation of the matrix response, due to shear in compression based on a rate dependent damage evolution model, and the large deformation homogenization approach. The homogenized quasi-brittle damage induced failure is described by elastically stored isochoric energy and plastic work of the undamaged polymer, driving the evolution of damage. The developed model is implemented in ABAQUS/Explicit. Finite element validation is carried out for a set of off-axis experimental compression tests in the literature. Considering the unidirectional carbon–epoxy (IM7/8552) composite at different strain rates, it appears that the homogenized damage degraded response can represent the expected ductile failure of the composite at compressive loading with different off-axes. Favourable comparisons are made for the strain and fibre rotation distribution involving localized shear and fibre kinking. © 2021 The Authors
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| 5. |
- Larsson, Ragnar, 1960, et al.
(författare)
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A micromechanically based model for strain rate effects in unidirectional composites
- 2020
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Ingår i: Mechanics of materials. - : Elsevier B.V.. - 0167-6636 .- 1872-7743. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses dynamic behaviour of fibre reinforced polymer composites in terms of a transversely isotropic viscoelastic-viscoplastic constitutive model established at the unidirectional ply level. The model captures the prelocalized response of the ply in terms of rate dependent elasticity and strength without damage. A major novelty is that the model draws from computational homogenization, with matrix and fibre materials as subscale constituents for a representative volume element of the ply. The micromechanics of the strain rate dependent polymer matrix is represented by an isotropic pressure sensitive viscoelastic-viscoplastic prototype model. For the fibre material, transverse elasticity is assumed. The constituents are homogenized via the fluctuating strain of the subscale, where a simple ansatz is applied to allow for constant stress in the plane transverse to the fibre orientation. Despite the relatively simple modelling assumptions for the constituents, the homogenized model compares favourably to experimental data for an epoxy/carbon fibre based composite, subjected to a variety of challenging uniaxial off-axis tests. The model response clearly reflects observed strain rate dependencies under both tensile and compressive loadings.
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| 6. |
- Larsson, Ragnar, 1960, et al.
(författare)
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Damage growth and strain localization in compressive loaded fiber reinforced composites
- 2018
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 127, s. 77-90
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Tidskriftsartikel (refereegranskat)abstract
- To increase the use of polymeric structural composites, a major issue is to properly account for intra-laminar failure mechanisms, such as fiber kinking which is typically induced in compression. We propose a new set of continuum damage models that are able to predict fiber kinking response under compression. A structure tensor based formulation is established at the unidirectional ply level, where the elastic material response is governed by transverse isotropy. To consider geometrical effects in conjunction with fiber kinking instability, a continuum damage formulation at finite strain is developed. The fracture area progression includes a convective and a local damage production involving a finite progression speed. In this framework, two damage evolution models are considered; one non–local model including the gradient damage effect and a local one, without the gradient enhancement. The models are implemented in a FE–code and validated for a compression loaded specimen. The models are computationally robust and can predict the localized nature of fiber kinking. A thorough sensitivity study is presented to show how the different formulations influence the predicted responses.
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| 7. |
- Larsson, Ragnar, 1960, et al.
(författare)
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Free surface flow and preform deformation in composites manufacturing based on porous media theory
- 2012
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier BV. - 0997-7538 .- 1873-7285. ; 31:1, s. 12-jan
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Tidskriftsartikel (refereegranskat)abstract
- In the present contribution an infusion simulation tool is developed, applicable to a quite wide range of composites manufacturing technologies. The paper focusses on isothermal, infusion like manufacturing processes involving highly deformable preforms and a free surface resin flow. There are two major issues addressed at the modelling of the infusion processes: The first one is the highly deformable preform and its shape due to the interaction between external pressure loading and the intrinsic fluid pressure. The second issue concerns the migrating free surface due to resin infiltration into the fibrous preform. To resolve these both issues simultaneously, a compressible two-phase porous media formulation is put forward involving an additional liquid mass balance relationship as compared to the standard compressible porous media formulation. As a result a governing equation for saturation degree evolution is established, which is used to monitor the free surface problem directly in terms of the compressible continuum formulation traversing into incompressibility with increasing partial saturation degree. A staggered finite element based solution procedure is advocated for the total solution advancement, involving, on the one hand, the saturation dependent porous media formulation, and, on the other hand, the computation of the saturation degree. The proposed formulation has been implemented and numerical results are provided, showing the convergence of the staggered approach, and the assessment of the proposed approach against a 1D analytical model. In addition, the infusion of a "hat" beam is considered. © 2011 Elsevier Masson SAS. All rights reserved.
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| 8. |
- Larsson, Ragnar, 1960, et al.
(författare)
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Modelling of kink-band growth based on the geometrically non-linear theory
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - 9783000533877
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We propose a new and computationally ecient continuum damage based model, able to predict fibre /matrix shear failure under longitudinal compression for a UD ply. A structure tensor based continuum damage formulation is placed in context with the UD ply, where the elastic material response is governed by transverse isotropy. To represent the proper energy dissipation, an elastic damage model is formulated in the invariants of fibre/matrix shear and fibre compression, including failure initiation and progressive damage modeling. We are guided by the anisotropic elastic model to define four strain invariants, representing key features of the UD-ply microstructure. The damage model is applied to a Non-Crimp Fabric (NCF) composite and compared to a state of the art model based on kinking theory [6]. Instead of invoking the geometric instability into the material model, a key feature is to consider the geometrical fibre kinking instability on the macro-level based on a finite strain formulation
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| 9. |
- RAZANICA, SENAD, 1988, et al.
(författare)
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Validation of the ductile fracture modeling of CGI at quasi-static loading conditions
- 2021
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Ingår i: International journal of damage mechanics. - : SAGE Publications Ltd. - 1056-7895 .- 1530-7921. ; 30:9, s. 1400-1422
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Tidskriftsartikel (refereegranskat)abstract
- Fracture modeling and experimental validation of Compacted Graphite Iron (CGI) specimens loaded under quasi-static conditions at room temperature are considered. Continuum damage mechanics coupled to plasticity is adopted to describe the evolution of damage. The damage production is based on a recently developed rate dependent damage evolution law, where the damage–plasticity coupling is modeled based on a damage driving energy that involves both stored energy and plasticity contributions. To describe ductile fracture accounting for stress triaxiality on the damage initiation, the inelastic contribution to the damage driving energy is controlled by the Johnson-Cook failure criterion. Three different damage models are defined based on elastic/inelastic damage driving energies. The damage models are validated against experiments on a set of notched specimens made of CGI with different notch geometries, where the global force-displacement curves and corresponding strain fields are obtained using digital image correlation technology. It is shown from the testing and the simulations that plastic strains generally need to be accounted for in order to properly describe the different failure processes of the CGI specimens. In addition, the ductile damage model is shown to more accurately predict the experimental force-displacement response as compared to the more simplistic stress drop, element deletion technique.
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| 10. |
- Samadikhah, Kaveh, 1982, et al.
(författare)
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Continuum-molecular modelling of graphene
- 2012
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 53:1, s. 37-43
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Tidskriftsartikel (refereegranskat)abstract
- membranes using a hierarchical modeling strategy to bridge the scales required to describe and understand the material. Quantum Mechanical (QM) and optimized Molecular Mechanical (MM) models are used to describe details on the nanoscale, while a multiscale continuum mechanical method is used to model the graphene response at the device or micrometer scale. The complete method is obtained on the basis of the Cauchy Born Rule (CBR), where the continuum model is coupled to the atomic field via the CBR and a local discrete fluctuation field. The MM method, often used to model carbon structures, involves the Tersoff--Brenner (TB) potential; however, when applying this potential to graphene with standard parameters one obtains material stress behavior much weaker than experiments. On the other hand, the more fundamental Hartree Fock and Density Functional Theory (DFT) methods are computationally too expensive and very limited in terms of their applicability to model the geometric scale at the device level. In this contribution a simple calibration of some of the TB parameters is proposed in order to reproduce the results obtained from QM calculations. Subsequently, the fine-tuned TB--potential is used for the multiscale modeling of a nano indentation sample, where experimental data are available. Effects of the mechanical response due the calibration are demonstrated.
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