| 1. |
- Andersson, Lars-Erik, et al.
(författare)
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Existence and uniqueness of attractors in frictional systems with uncoupled tangential displacements and normal tractions
- 2014
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 51:21-22, s. 3710-3714
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Tidskriftsartikel (refereegranskat)abstract
- We consider the class of two or three-dimensional discrete contact problems in which a set of contact nodes can make frictional contact with a corresponding set of rigid obstacles. Such a system might result from a finite element discretization of an elastic contact problem after the application of standard static reduction operations. The Coulomb friction law requires that the tractions at any point on the contact boundary must lie within or on the surface of a friction cone, but the exact position of any stuck node (i.e., a node where the tractions are strictly within the cone) depends on the initial conditions and/or the previous history of loading. If the long-term loading is periodic in time, we anticipate that the system will eventually approach a steady periodic cycle. Here we prove that if the elastic system is uncoupled, meaning that changes in slip displacements alone have no effect on the instantaneous normal contact reactions, the time-varying terms in this steady cycle are independent of initial conditions. In particular, we establish the existence of a unique permanent stick zone T comprising the set of all nodes that do not slip after some finite number of cycles. We also prove that the tractions and slip velocities at all nodes not contained in T approach unique periodic functions of time, whereas the (time-invariant) slip displacements in T may depend on initial conditions. Typical examples of uncoupled systems include those where the contact surface is a plane of symmetry, or where the contacting bodies can be approximated locally as half spaces and Dundurs mismatch parameter beta = 0. An important consequence of these results is that systems of this kind will exhibit damping characteristics that are independent of initial conditions. Also, the energy dissipated at each slipping node in the steady state is independent of initial conditions, so wear patterns and the incidence of fretting fatigue failure should also be so independent.
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| 2. |
- Bargmann, Swantje, 1980, et al.
(författare)
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Microscopic temperature field prediction during adiabatic loading using gradient extended crystal plasticity
- 2013
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 50:6, s. 899-906
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Tidskriftsartikel (refereegranskat)abstract
- The problem of interest is grain-size-dependent hardening in polycrystalline metals. We study the multiphysics problem of heat conduction coupled to gradient crystal plasticity and investigate the temperature field on the grain level for adiabatic loading. The underlying equations for the thermomechanical coupling are derived for a crystal plasticity model with gradient hardening. The influence of the temperature field on misorientation of the slip directions between adjacent grains is investigated. Additionally, the influence of the loading velocity and the size of the grain structure are examined. Numerical simulations are presented and analyzed.
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| 3. |
- Barsoum, Imad, et al.
(författare)
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Micromechanical analysis on the influence of the Lode parameter on void growth and coalescence
- 2011
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 48:6, s. 925-938
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Tidskriftsartikel (refereegranskat)abstract
- A micromechanical model consisting of a band with a square array of equally sized cells, with a spherical void located in each cell, is developed. The band is allowed a certain inclination and the periodic arrangement of the cells allow the study of a single unit cell for which fully periodic boundary conditions are applied. The model is based on the theoretical framework of plastic localization and is in essence the micromechanical model by Barsoum and Faleskog (Barsoum, I., Faleskog, J., 2007. Rupture mechanisms in combined tension and shear-micromechanics. International Journal of Solids and Structures 44(17), 5481-5498) with the extension accounting for the band orientation. The effect of band inclination is significant on the strain to localization and cannot be disregarded. The macroscopic stress state is characterized by the stress triaxiality and the Lode parameter. The model is used to investigate the influence of the stress state on void growth and coalescence. It is found that the Lode parameter exerts a strong influence on the void shape evolution and void growth rate as well as the localized deformation behavior. At high stress triaxiality level the influence of the Lode parameter is not as marked and the overall ductility is set by the stress triaxiality. For a dominating shear stress state localization into a band cannot be regarded as a void coalescence criterion predicting material failure. A coalescence criterion operative at dominating shear stress state is needed.
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| 4. |
- Borgqvist, Eric, et al.
(författare)
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Distortional hardening plasticity model for paperboard
- 2014
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 51:13, s. 2411-2423
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Tidskriftsartikel (refereegranskat)abstract
- A distortional hardening elasto-plastic model at finite strains suitable for modeling of orthotropic materials is presented. As a prototype material, paperboard is considered. An in-plane model is established. The model developed is motivated from non-proportional loading tests on paperboard where the paperboard is pre-strained in one direction and then loaded in the perpendicular direction. A softening effect is revealed in the pre-strained samples. The observed experimental findings cannot be accurately predicted by current models for paperboard. To be able to model the softening effects, a yield surface based on multiple hardening variables is introduced. It is shown that the model parameters can be obtained from simple uniaxial experiments. The model is implemented in a finite element framework which is used to illustrate the behavior of the model at some specific loading situations and is compared with strain fields obtained from Digital Image Correlation experiments.
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| 5. |
- Edvardsson, Sverker, et al.
(författare)
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On dissipative effects of paper web adhesion strength
- 2011
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 48:1, s. 24-30
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Tidskriftsartikel (refereegranskat)abstract
- This work is concerned with the adhesion strength between a paper web and a metal roll surface, which is a common situation in paper machines world-wide. It is shown that the classic expression relating the work of adhesion to the peeling angle and web tension is, in general, insufficient. An improved model is suggested to take into account the energy dissipation due to elastic-plastic deformation behavior of wet paper materials. To judge the model, an industrially relevant example of wet newsprint and a mild steel surface is studied. It is found that the agreement between theory and experimental observations is excellent. A key result is that elastic-plastic material behavior must always be included for wet paper materials in peeling processes.
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| 6. |
- Faleskog, Jonas, et al.
(författare)
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Tension-torsion fracture experiments-Part I : Experiments and a procedure to evaluate the equivalent plastic strain
- 2013
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 50:25-26, s. 4241-4257
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Tidskriftsartikel (refereegranskat)abstract
- Ductile failure experiments on a double notched tube (DNT) specimen subjected to a combination of ten-sue load and torque that was applied at a fixed ratio is presented. The experimental results extend those in Barsoum and Faleskog (2007a) down to zero stress triaxiality. A new and robust evaluation procedure for such tests is proposed, and a simple relation for the equivalent plastic strain at failure for combined normal and shear deformation, respectively, is developed. Tests were carried out on the medium strength medium hardening steel Weldox 420, and the high strength low hardening steel Weldox 960. The experimental results unanimously show that ductile failure not only depends on stress triaxiality, but is also strongly affected by the type of deviatoric stress state that prevails, which can be quantified by a stress invariant that discriminates between axisymmetric stressing and shear dominated stressing, e.g., the Lode parameter. Additional experiments on round notch bar (RNB) specimens are recapitulated in order to give a comprehensive account on how ductile failure depends on stress triaxiality, ranging from zero to more than 1.6, and the type of stress state for the two materials tested. This provides an extensive experimental data base that will be used to explore an extension of the Gurson model that incorporates damage development in shear presented in Xue et al.
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| 7. |
- Golub, Mikhail, 1982, et al.
(författare)
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Wave propagation of functionally graded layers treated by recursion relations and effective boundary conditions
- 2013
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 50:5, s. 766-772
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Tidskriftsartikel (refereegranskat)abstract
- Wave propagation through a layer of a material that is inhomogeneous in the thickness direction, typically a functionally graded material (FGM), is investigated. The material parameters and the displacement components are expanded in power series in the thickness coordinate, leading to recursion relations among the displacement expansion functions. These can be used directly in a numerical scheme as a means to get good field representations when applying boundary conditions, and this can be done even if the layer is not thin. This gives a schema that is much more efficient than the approach of subdividing the layer into many sublayers with constant material properties. For thin layers for which the material parameters do not depend on the layer thickness the recursion relations can be used to eliminate all but the lowest order expansion functions. Employing the boundary conditions this leads to a set of effective boundary conditions relating the displacements and stresses on the two sides of the layer, thus completely replacing the layer by these effective boundary conditions. Numerical examples illustrate the convergence properties of the scheme for FG layers and the influence of different variations of the material parameters in the FG layer.
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| 8. |
- Grassl, Peter, 1974, et al.
(författare)
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CDPM2: A damage-plasticity approach to modelling the failure of concrete
- 2013
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 50:24, s. 3805-3816
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Tidskriftsartikel (refereegranskat)abstract
- A constitutive model based on the combination of damage mechanics and plasticity is developed to analyse the failure of concrete structures. The aim is to obtain a model, which describes the important characteristics of the failure process of concrete subjected to multiaxial loading. This is achieved by combining an effective stress based plasticity model with a damage model based on plastic and elastic strain measures. The model response in tension, uni-, bi- and triaxial compression is compared to experimental results. The model describes well the increase in strength and displacement capacity for increasing confinement levels. Furthermore, the model is applied to the structural analyses of tensile and compressive failure.
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| 9. |
- Hallberg, Håkan, et al.
(författare)
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Thermo-mechanically coupled model of diffusionless phase transformation in austenitic steel
- 2010
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 47:11-12, s. 1580-1591
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedA constitutive model of thermo-mechanically coupled finite strain plasticity considering martensitic phase transformation is presented. The model is formulated within a thermodynamic framework, giving a physically sound format where the thermodynamic mechanical and chemical forces that drive the phase transformation are conveniently identifiable. The phase fraction is treated through an internal variable approach and the first law of thermodynamics allows a consistent treatment of the internal heat generation due to dissipation of inelastic work. The model is calibrated against experimental data on a Ni-Cr steel of AISi304-type, allowing illustrative simulations to be performed. It becomes clear that the thermal effects considered in the present formulation have a significant impact on the material behavior. This is seen, not least, in the effects found on forming limit diagrams, also considered in the present paper.
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| 10. |
- Hallbäck, Nils, et al.
(författare)
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Development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half-plane
- 2014
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 51, s. 2878-2892
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Tidskriftsartikel (refereegranskat)abstract
- A distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half plane has been developed. The dipole density distribution is represented with a weighted Jacobi polynomial expansion where the weight function captures the asymptotic behaviour at each end of the crack. To allow for opening and sliding at crack kinking and branching the dipole density representation contains conditional extra terms which fulfil the asymptotic behaviour at each endpoint. Several test cases involving straight, kinked and branched cracks have been analysed, and the results suggest that the accuracy of the method is within 1% provided that Jacobi polynomial expansions up to at least the sixth order are used. Adopting even higher order Jacobi polynomials yields improved accuracy. The method is compared to a simplified procedure suggested in the literature where stress singularities associated with corners at kinking or branching are neglected in the representation for the dipole density distribution. The comparison suggests that both procedures work, but that the current procedure is superior, in as much as the same accuracy is reached using substantially lower order polynomial expansions.
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