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- Harrysson, Magnus, et al.
(author)
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Spatial representation of evolving anisotropy at large strains
- 2007
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In: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 44:10, s. 3514-3532
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Journal article (peer-reviewed)abstract
- A phenomenological model for evolving anisotropy at large strains is presented. The model is formulated using spatial quantities and the anisotropic properties of the material is modeled by including structural variables. Evolution of anisotropy is accounted for by introducing substructural deformation gradients which are linear maps similar to the usual deformation gradient. The evolution of the substructural deformation gradients is governed by the substructural plastic velocity gradients in a manner similar to that for the continuum. Certain topics related to the numerical implementation are discussed and a simple integration scheme for the local constitutive equations is developed. To demonstrate the capabilities of the model it is implemented into a finite element code. Two numerical examples are considered: deformation of uniform plate with circular hole and the drawing of a cup. In the two examples it is assumed that initial cubic material symmetry applies to both the elastic and plastic behavior. To be specific, a polyconvex Helmholtz free energy function together with a yield function of quadratic type is adopted.
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- Harrysson, Lars, et al.
(author)
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Student Centred Learning in a Flexible Blended Mode Environment
- 2009
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Conference paper (peer-reviewed)abstract
- The Faculty of Sciences at Lund University has developed online courses to enhance physical as well as virtual exchange and promote joint delivery of courses among partner universities. The purpose is to increase the flexibility of studies within joint programmes. As part of the development of a blended mode course we have included an online research tool, “Global Research Gateway”.
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| 6. |
- Harrysson, Magnus, et al.
(author)
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Description of evolving anisotropy at large strains
- 2007
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In: Mechanics of Materials. - : Elsevier BV. - 0167-6636. ; 39:3, s. 267-282
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Journal article (peer-reviewed)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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| 7. |
- Harrysson, Magnus
(author)
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Evolution of Anisotropy in Continua Exposed to Large Strains
- 2008
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with the modeling of anisotropic materials at finite deformations. The major emphasis is the development of constitutive models able to account for the evolving directionally dependent properties of these materials. In addition, the numerical implementation of the models developed is addressed. In particular, the following topics are considered. To model finite elasto-plastic deformations use is made of the multiplicative split of the deformation gradient in which an intermediate configuration is introduced. Issues related to this intermediate configuration when considering an anisotropic setting are investigated and discussed. A spatial description of elasto-plastic anisotropic material is developed. The capabilities of the model are investigated where an example involving the drawing process of a cup is considered. Different approaches for the modeling of evolving anisotropic material behavior have been reported in the literature. Two of these approaches are investigated and compared, both analytical results and numerical examples being considered. Soft biological tissues, such as blood vessels and skin show anisotropic material behavior. An orientation distribution-based formulation is developed where the anisotropy is accounted for by the non-uniform orientation distribution of the collagen fibers. The evolution of anisotropic properties in soft biological tissue is also considered by introduction of an evolution law for the direction of the collagen fibers. Glassy polymers consist of individual polymer chains in which the orientation of the chains affects the anisotropic behavior of the material. An elastoviscoplastic material model which accounts for the orientation distribution of the polymer chains is proposed. The orientational averaging process involved is calculated by numerical integration over the unit sphere.
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| 8. |
- Harrysson, Magnus, et al.
(author)
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Framework for deformation induced anisotropy in glassy
- 2010
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In: Acta Mechanica. - : Springer Science and Business Media LLC. - 0001-5970 .- 1619-6937. ; 211, s. 195-213
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Journal article (peer-reviewed)abstract
- In this paper a constitutive model for glassy polymers is developed. Glassy polymers consist of a number of polymer chains that at a microscopic level form a network. If the distribution of the polymer chains shows some preferred direction, the mechanical response at a global macroscopic level will be anisotropic. To incorporate the orientational distribution of the polymer chains, a homogenization procedure involving a chain orientation distribution function was undertaken. When polymers are exposed to external loading, the chains at the microscopic level orient in a certain manner, leading to an evolution of the macroscopic anisotropic properties. This phenomenon was modeled by use of evolution equations for the chains at a microscopic level and are then—by using the orientation distribution function—transformed to the macroscopic level. The theories involved are developed in a large strain setting in which a multiplicative split of the deformation gradient for the elastic-viscoplastic response is adopted. Various numerical experiments were conducted to evaluate the model that was developed.
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- Harrysson, Magnus
(author)
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Modeling of evolving anisotropy at finite elasto-plastic strain
- 2006
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Licentiate thesis (other academic/artistic)abstract
- Simulation tools are used to a wide extent in the product development process today, both to obtain better products and to reduce the development time required. Anisotropic materials are utilized in many engineering applications. Material models for materials of these types are needed in order to obtain accurate results from the simulations undertaken. In the thesis, a constitutive framework for anisotropic materials at finite elasto-plastic strains is presented. The general framework used for the modeling of anisotropic materials is discussed in Paper A. Here the kinematics of anisotropic materials being analyzed with the aim of developing a general description. Thermodynamical considerations are taken into account to assure that the dissipation inequality is not violated. Some simple numerical examples are also studied. In Paper B the proposed model is investigated further and a formulation based on a spatial setting is developed. Here the numerical formulation is discussed and the model is implemented into the commercial finite element code ABAQUS. Two numerical examples are investigated to explore the capabilities of the model. One involving the deformation of a plate with a hole and the other the drawing process of a cup.
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| 10. |
- Harrysson, Magnus, et al.
(author)
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Two different approaches to model evolving directional properties at finite deformations
- 2008
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In: Acta Mechanica. - : Springer Science and Business Media LLC. - 0001-5970 .- 1619-6937. ; 199:1-4, s. 97-116
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Journal article (peer-reviewed)abstract
- Two different approaches to modeling evolving anisotropic material behavior are investigated. The first approach models the evolution of the directionally dependent properties of the material in terms of evolution laws for the director vectors. In the second approach the evolution law for the plastic velocity gradient is enhanced by additional terms. It is shown that both approaches lead to an evolution of the substructure that guides the directionally dependent properties of the material. The two approaches are analyzed within a thermodynamic setting and the restrictions imposed by the second law of thermodynamics are investigated. The two approaches are also compared from a kinematic point of view and equivalence between the two approaches is shown for some specific conditions. To further compare the approaches in the case in which equivalence cannot be found, two different evolution laws are considered, one for the substructure and the other for the plastic velocity gradient. These are compared for a loading that corresponds to a plane strain volume preserving deformation as well as simple shear. Here the Kirchhoff stress and the evolution of the director vectors are studied during the deformation process.
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