| 1. |
- Agde Tjernlund, Jessica, et al.
(författare)
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Length-scale effects on damage development in tensile loading of glass-sphere filled epoxy
- 2006
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 43:24, s. 7337-7357
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Tidskriftsartikel (refereegranskat)abstract
- Particle-reinforced polymers are widely used in load-carrying applications. The effect of particle size on damage development in the polymer is still relatively unexplored. In this study, the effect of glass-sphere size on the damage development in tensile loaded epoxy has been investigated. The diameter of the glass spheres ranged from approximately 0.5-50 mu m. The first type of damage observed was debonding at the sphere poles, which subsequently grew along the interface between the glass spheres and epoxy matrix. These cracks were observed to kink out into the matrix in the radial direction perpendicular to the applied load. The debonding stresses increased with decreasing sphere diameter, whereas the length to diameter ratio of the resulting matrix cracks increased with increasing sphere diameter. These effects could not be explained by elastic stress analysis and linear-elastic fracture mechanics. Possible explanations are that a thin interphase shell may form in the epoxy close to the glass spheres, and that there is a length-scale effect in the yield process which depends on the strain gradients. Cohesive fracture processes can contribute to the influence of sphere size on matrix-crack length. Better knowledge on these underlying size-dependent mechanisms that control damage development in polymers and polymer composites is useful in development of stronger materials. From a methodology point of view, the glass-sphere composite test can be used as an alternative technique (although still in a qualitative way) to hardness vs. indentation depth to quantify length-scale effects in inelastic deformation of polymers.
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| 2. |
- Alfredsson, Svante, et al.
(författare)
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Flexure analysis of unsymmetric orthotropic beams with an interlayer
- 2009
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 46:10, s. 2093-2110
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a layer-wise stress and deformation analysis of a three-layer beam configuration consisting of two dissimilar orthotropic adherends of different thicknesses that are joined together by a deformable interlayer of finite thickness. Analytical solutions for the case of three-point flexure loading are presented for both compressible and incompressible interlayers. Parametric analysis reveals the influences of asymmetry of moduli and adherend thicknesses, interlayer thickness, and overhang of the beams on the beam compliance. Analytical predictions of beam compliance show very good agreement with finite element results. Experimental measurements of compliance of various unsymmetric beams consisting of aluminum adherends separated by a rubber interlayer were performed in order to validate the analysis. Excellent agreement between measured and predicted compliance values was observed.
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| 3. |
- Alfthan, Johan, et al.
(författare)
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Linear constitutive model for mechano-sorptive creep in paper
- 2005
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 42:24-25, s. 6261-6276
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Tidskriftsartikel (refereegranskat)abstract
- The creep of paper is accelerated by moisture cycling. This effect is known as mechano-sorptive creep. It is assumed that this is an effect of transient stresses produced during moisture content changes in combination with non-linear creep behaviour of the fibres. The stresses produced by the moisture content changes are often much larger than the applied mechanical loads. If this is the case, the mechanical loads are only a perturbation to the internal stress state, and it will appear as if the mechano-sorptive creep is linear in stress. It is possible to take advantage of this feature. In the present report the pure moisture problem is first solved. The mechanical load is then treated as a perturbation of the solution to the moisture problem. Using this strategy, it is possible to linearize a non-linear network model for mechano-sorptive creep and to formulate a continuum model. As a result, the number of variables in the model is reduced. This is a significant improvement as it will be possible to use the linearized model to describe the material in a finite element program and solve problems with complicated geometries.
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| 4. |
- Balzani, D., et al.
(författare)
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A polyconvex framework for soft biological tissues. Adjustment to experimental data
- 2006
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 43:20, s. 6052-6070
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Tidskriftsartikel (refereegranskat)abstract
- The main goal of this contribution is to provide a simple method for constructing transversely isotropic polyconvex functions suitable for the description of biological soft tissues. The advantage of our approach is that only a few parameters are necessary to approximate a variety of stress-strain curves and to satisfy the condition of a stress-free reference configuration a priori in the framework of polyconvexity. The proposed polyconvex stored energies are embedded into the concept of structural tensors and the representation theorems for isotropic tensor functions are utilized. As an example, the medial layer of a human abdominal aorta is investigated, modeled by some of the proposed polyconvex functions and compared with experimental data. Hereby, the economic fitting to experimental data, and hence the easy handling of the functions is shown.
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| 5. |
- Barsoum, Imad, et al.
(författare)
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Rupture mechanisms in combined tension and shear - Experiments
- 2007
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 44:6, s. 1768-1786
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Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation of the rupture mechanisms in a mid-strength and a high-strength steel were conducted employing a novel test configuration. The specimen used was a double notched tube specimen loaded in combined tension and torsion at a fixed ratio. The effective plastic strain, the stress triaxiality and the Lode parameter were determined in the centre of the notch at failure. Scanning electron microscopy of the fractured surfaces revealed two distinctively different ductile rupture mechanisms depending on the stress state. At high stress triaxiality the fractured surfaces were covered with large and deep dimples, suggesting that growth and internal necking of voids being the governing rupture mechanism. At low triaxiality it was found that the fractured surfaces were covered with elongated small shear dimples, suggesting internal void shearing being the governing rupture mechanism. In the fractured surfaces of the high-strength steel, regions with quasi-cleavage were also observed. The transition from the internal necking mechanism to the internal shearing mechanism was accompanied by a significant drop in ductility.
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| 6. |
- Barsoum, Imad, et al.
(författare)
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Rupture mechanisms in combined tension and shear - Micromechanics
- 2007
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 44:17, s. 5481-5498
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Tidskriftsartikel (refereegranskat)abstract
- A micromechanics model based on the theoretical framework of plastic localization into a band introduced by Rice is developed. The model consists of a planar band with a square array of equally sized cells, with a spherical void located in the centre of each cell. The periodic arrangement of the cells allows the study of a single unit cell for which fully periodic boundary conditions are applied. The micromechanics model is applied to analyze failure by ductile rupture in experiments on double notched tube specimens subjected to combined tension and torsion carried out by the present authors. The stress state is characterized in terms of the stress triaxiality and the Lode parameter. Two rupture mechanisms can be identified, void coalescence by internal necking at high triaxiality and void coalescence by internal shearing at low triaxiality. For the internal necking mechanism, failure is assumed to occur when the deformation localizes into a planar band and is closely associated with extensive void growth until impingement of voids. For the internal shearing mechanism, a simple criterion based on the attainment of a critical value of shear deformation is utilized. The two failure criteria capture the transition between the two rupture mechanisms successfully and are in good agreement with the experimental result.
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| 7. |
- Bjerkén, Christina, et al.
(författare)
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Growth of a short fatigue crack - A long term simulation using a dislocation technique
- 2009
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 46:5, s. 1196-1204
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the growth of a short edge crack during more than 14 000 cycles of fatigue loading is investigated in detail. An edge crack, in a semi-infinite body with no pre-existing obstacles present, is modelled in a boundary element approach by a distribution of dislocation dipoles. The fatigue cycles are fully reversed (R = -1), and the load range is well below the threshold for long fatigue cracks. The developing local plasticity consists of discrete edge dislocations that are emitted from the crack tip. The movements of discrete dislocations are restricted to slip along preferred slip planes. The present model is restricted to a 2D plane strain problem with a through-thickness crack, assuming no 3D irregularities. A remote load is applied perpendicular to the crack extension line, and the material parameters are those of a BCC crystal structure. The competition between influence of the global loading on and local shielding of the crack tip governs the crack growth. The growth rate increases in discrete steps with short periods of retardation, from approximately the size of Burgers vector, b, up to 25 b per cycle as the length of the crack is tripled. The plastic zone changes from having an elongated, slender form to include a low angle grain boundary, which, eventually, divides into two parts. The crack growth is found to change from constant acceleration to constant growth rate as the event of the low-angle grain boundary split is approached. The results are compared to long crack characteristics, for which linear elastic fracture mechanics and Paris law can be used to predict fatigue crack growth. The exponent in Paris law varies between 1 and 0 in the present study, i.e. smaller than typical values for ductile BCC materials. The ratio between static and cyclic plastic zone sizes is found to increase during crack growth, and the angle of the general plastic zone direction increases, showing a tendency towards long crack values. The characteristics of the simulated crack growth, found in the present study, are typical for below-threshold growth, with slow acceleration, constant growth rate. and, eventually, either arrest or transition to long crack growth behaviour, as reported in the literature. (c) 2008 Elsevier Ltd. All rights reserved.
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| 8. |
- Eman, Jesper, et al.
(författare)
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Spatially resolved observations of strain fields at necking and fracture of anisotropic hardened steel sheet material
- 2009
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 46:13, s. 2750-2756
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Tidskriftsartikel (refereegranskat)abstract
- In this work plastic strain localization, also referred to as necking, of press-hardened ultra-high strength steel is observed using digital speckle correlation. The region of the neck is studied during tensile tests of specimens specially designed to facilitate strain localization at an inner point of the material, thus avoiding edge effects on localization and fracture. By using measurements with a length scale small enough to properly resolve the neck, its growth and shape can be studied. Furthermore, the anisotropy of the material is investigated by examining specimens cut out at different angles to the rolling direction. It is seen that the local fracture strain of specimens cut out along the rolling direction is approximately twice as high as it is for specimens cut out perpendicular to the rolling direction.
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| 9. |
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| 10. |
- Fredriksson, Per, et al.
(författare)
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Finite element implementation and numerical issues of strain gradient plasticity with application to metal matrix composites
- 2009
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 46:22-23, s. 3977-3987
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Tidskriftsartikel (refereegranskat)abstract
- A framework of finite element equations for strain gradient plasticity is presented. The theoretical framework requires plastic strain degrees of freedom in addition to displacements and a plane strain version is implemented into a commercial finite element code. A couple of different elements of quadrilateral type are examined and a few numerical issues are addressed related to these elements as well as to strain gradient plasticity theories in general. Numerical results are presented for an idealized cell model of a metal matrix composite under shear loading. It is shown that strengthening due to fiber size is captured but strengthening due to fiber shape is not. A few modelling aspects of this problem are discussed as well. An analytic solution is also presented which illustrates similarities to other theories.
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