| 1. |
- Harrysson, Magnus, et al.
(författare)
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Description of evolving anisotropy at large strains
- 2007
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Ingår i: Mechanics of Materials. - : Elsevier BV. - 0167-6636. ; 39:3, s. 267-282
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Tidskriftsartikel (refereegranskat)abstract
- A description of texture evolution at large strain plasticity is developed. Texture evolution is defined in terms of changes taking place in the substructure of the material. The changes in the substructure are specified by means of a tangent map defined in the same manner as for the continuum in terms of a multiplicative decomposition. It is shown that the description of the changes in the substructure can be formulated in a way completely analogous to the description of the deformation of the continuum. Within the framework of thermodynamics the evolution of the substructure, driven by its conjugated force emerging from the dissipation inequality, is studied. The performance of the model presented is studied in relation to off-axis uniaxial stress, the evolution of the substructure being compared with experimental findings. In addition, two different evolution laws for cubic material symmetry are investigated.
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| 2. |
- Kroon, Martin, et al.
(författare)
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Influence of crack deflection into the carbide/ferrite interface on cleavage fracture initiation in ferritic steels
- 2008
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 40:9, s. 695-707
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Tidskriftsartikel (refereegranskat)abstract
- n this and a companion study (Kroon, M., Faleskog, J., 2005. Micromechanics of cleavage fracture initiation in ferritic steels by carbide cracking. J. Mech. Phys. Solids 53, 171–196), the initiation of cleavage fracture in ferritic steels is studied. The initiation is modelled explicitly in the form of a microcrack, which nucleates in a brittle carbide and propagates into the surrounding ferrite. The carbide is modelled as an elastic cylinder and the ferrite as an elastic viscoplastic material. The crack growth is modelled using a cohesive surface, in which the tractions are governed by a modified exponential cohesive law. The advancing microcrack, which has nucleated in the carbide, may either continue into the ferrite or deflect into the interface between the carbide and the ferrite. Special attention is given to the influence of the mode mixity factor β, which is defined as the ratio between the shear and tensile strength of the interface between the carbide and the ferrite. Crack growth in the interface occurs in shear mode and is driven by a fibre loading mechanism. For mode mixity values β⩽0.2, the crack deflects into the interface. The results indicate that crack growth in the interface can have a profound influence on the macroscopic fracture toughness of ferritic steels.
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| 3. |
- Kulachenko, Artem, et al.
(författare)
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Basic mechanisms of fluting formation and retention in paper
- 2007
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 39:7, s. 643-663
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Tidskriftsartikel (refereegranskat)abstract
- Out-of-plane deformations of paper, such as fluting, significantly deteriorate the quality of a printed product. There are several explanations of fluting presented in the literature but there is no unanimously accepted theory regarding fluting formation and retention which is consistent with all field observations. This paper first reviews the existing theories and proposes a mechanism that might give an answer to most of the questions regarding fluting. The fluting formation has been considered as a post-buckling phenomenon which has been analysed with the help of the finite element method. Fluting retention has been modelled by introducing an ink layer over the paper surface with the ink stiffness estimated from experimental results. The impact of fast drying on fluting has been assessed numerically and experimentally. The result of the study suggests that fluting occurs due to small-scale hygro-strain variations, which in turn are caused by the moisture variations created during fast convection (through-air) drying. The result also showed that ink stiffening alone cannot explain the fluting amplitudes observed in practice, but that high drying temperatures promote inelastic (irreversible) deformations in paper and this may itself preserve fluting.
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| 4. |
- Lindgren, Lars-Erik, et al.
(författare)
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Dislocations, vacancies and solute diffusion in physical based plasticity model for AISI 316L
- 2008
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 40:11, s. 907-919
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Tidskriftsartikel (refereegranskat)abstract
- A physical based model for the evolution of flow stress of AISI 316L from room temperature up to 1300 °C, strains up to 0.6 and strain rates from 0.0005 up to 10 s-1 is developed. One set of tests have been used for model calibration and another more complex set of tests for its validation. The model is based on a coupled set of evolution equations for dislocation density and (mono) vacancy concentration. Furthermore, it includes the effect of diffusing solutes in order to describe dynamic strain ageing (DSA). The model described the overall flow stress evolution well with exception of the details of the effect of the DSA phenomenon. Its numerical solution is implemented in a format suitable for large-scale finite element simulations.
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| 5. |
- Liu, Hongyuan, et al.
(författare)
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Numerical studies on the inter-particle breakage of a confined particle assembly in rock crushing
- 2005
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 37:9, s. 935-954
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Tidskriftsartikel (refereegranskat)abstract
- Understanding rock crushing mechanisms may provide an efficient key to better fragmentation efficiency. In this paper, firstly the fracture processes of a rock specimen under uniaxial and triaxial compressions are simulated using the rock and tool interaction (R–T2D) code and compared with the results from experimental observations in literatures. It is found that, with increasing confinement, the fracture process is more progressive and the failure mechanism gradually changes from axial splitting to shear fracture. Then the inter-particle breakage process in a particle bed under confined conditions is numerically investigated from a mechanics point of view. The results show that when the particle breaks depends on the strength criterion, how it is broken depends on the stress distribution and redistribution, and where it is broken depends on the heterogeneous distribution in the particle. It is found that, irrespective of the particle shape or particle bed arrangement, the fragmentation starts from the particles which are loaded in quasi-uniaxial compression. The resulting fragmentation is usually axial splitting between the two highest stressed loading points. After that, the particles which are loaded at first in quasi-triaxial compression, because of the confinement from the neighbouring particles, the loading plate or the container wall, fail progressively. Depending on the location of the loading points, small fragments are torn off at the loading points with a large piece preserved. In the final stage, the local crushing at the highest stressed contact points becomes an important failure mechanism. Through this study, it is concluded that the R–T2D code can capture the features of the inter-particle breakage process, and a better qualitative understanding of the physics and mechanics of deformation and breakage is gained.
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| 6. |
- Salomonsson, Kent
(författare)
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Mixed mode modeling of a thin adhesive layer using a meso-mechanical model
- 2008
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Ingår i: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 40:8, s. 665-672
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Tidskriftsartikel (refereegranskat)abstract
- A representative volume element is modeled using the finite element method. It is used to analyze mixed mode behavior of a thin adhesive layer. Two sources of dissipation is modeled; plasticity and decohesion. Macroscopic traction–separation laws are extracted from the simulations. The results indicate that a boundary of mode mix exists between a region where major plastic dissipation is present and a region where it is not. Without major plastic dissipation, the fracture energy is low and essentially governed by the cohesive properties. This is the case in peel dominated loading cases. In shear dominated loading cases plastic dissipation gives a substantial contribution to the fracture energy. The results show that pure shear loading gives the largest fracture energy.
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| 7. |
- Salomonsson, Kent, et al.
(författare)
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Modeling and parameter calibration of an adhesive layer at the meso level
- 2008
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Ingår i: Mechanics of materials. - : Elsevier ltd.. - 0167-6636 .- 1872-7743. ; 40:1-2, s. 48-65
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Tidskriftsartikel (refereegranskat)abstract
- A mesomechanical finite element model of a thin adhesive layer is developed. The model is calibrated to previously performed experiments. In these, the adhesive layer is loaded in monotonically increasing peel or shear. An in situ SEM study is also performed and used to guide the modeling and calibration. The purpose of the mesomechanical finite element model is to facilitate the development of constitutive laws for adhesive layers. The modeling is based on Xu and Needleman’s method where all continuum finite elements are surrounded by interface elements that allow for the development of micro cracks. Thus, this enables the modeling of the entire process of degradation and fracture of the adhesive layer. A genetic algorithm is developed for the calibration. The simulations show good agreement with the experiments.
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| 8. |
- Singh, Chandra Veer, et al.
(författare)
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A synergistic damage mechanics approach for composite laminates with matrix cracks in multiple orientations
- 2009
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 41:8, s. 954-968
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Tidskriftsartikel (refereegranskat)abstract
- This paper treats the problem of elastic response of composite laminates containing matrix cracks in plies of multiple orientations. The approach taken has been described as synergistic damage mechanics (SDM) and has been previously illustrated for [0 m / ± θ n / 0 m / 2] s laminates with cracks of equal density in + θ and - θ plies [Singh, C.V., Talreja, R., 2008. Int. J. Solids Struct. 45(16), 4574-4589]. The current work extends the approach to [0 m / ± θ n / 90 r] s and [0 m / 90 r / ± θ n] s laminates with cracks additionally in the 90°-plies. The interaction between the ± θ-cracks and the 90°-cracks is analyzed in terms of the crack surface displacements using a three-dimensional finite element (FE) model and found to be significant only for crack orientations close to 90°. The stiffness degradation of the laminate with all cracking modes simultaneously present is formulated by continuum damage mechanics using a second order tensor characterization of damage. The elastic moduli changes predicted by the SDM procedure are validated by independent three-dimensional FE calculations. For a particular case of quasi-isotropic [0 / 90 / ∓ 45] s laminate, the elastic moduli predictions are evaluated against experimental data. Finally, a parametric study is performed to examine the effects of ply thickness changes on stiffness properties.
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| 9. |
- Sorensen, Bent F., et al.
(författare)
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Micromechanical model of cross-over fibre bridging - Prediction of mixed mode bridging laws
- 2008
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 40:4-5, s. 220-234
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Tidskriftsartikel (refereegranskat)abstract
- The fracture resistance of fibre composites can be greatly enhanced by crack bridging. In situ observations of mixed mode crack growth in a unidirectional carbon-fibre/epoxy composite reveal crack bridging by single fibres and by beam-like ligaments consisting of several fibres. Based on the observed bridging mechanism, a micromechanical model is developed for the prediction of macroscopic mixed mode bridging laws (stress-opening laws). The model predicts a high normal stress for very small openings, decreasing rapidly with increasing normal and tangential crack opening displacements. In contrast, the shear stress increases rapidly, approaching a constant value with increasing normal and tangential openings. The solutions for the bridging laws and the resulting toughening due to the bridging stresses are obtained in closed analytical form.
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| 10. |
- Unosson, Mattias, et al.
(författare)
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Failure modelling in finite element analyses : Random material imperfections
- 2005
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Ingår i: Mechanics of Materials. - : Elsevier BV. - 0167-6636. ; 37:12, s. 1175-1179
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Tidskriftsartikel (refereegranskat)abstract
- A phenomenological failure model has been developed where the material is assumed to contain initial material imperfections that influence the material strength only through the largest imperfection. The imperfections are randomly distributed and characterized by material imperfection density functions. In a first approach one type of imperfection is assumed with an exponential imperfection density function. The model parameters are optimized, using results from a deterministic finite element analysis, to match a target function representing the probability of failure in a tensile test. The developed model manages to reproduce this data well.
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