Modeling of evolving anisotropy at finite elasto-plastic strain

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

Evolution of Anisotropy in Continua Exposed to Large Strains

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

Spatial representation of evolving anisotropy at large strains

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

Utveckling av ett användbart Människa-Maskin-Gränssnitt

When developing a Human-Machine-Interface (HMI) it is important to make sure that it is easy to learn and use, to have high usability. If it does not, the operator of the machine suffers unnecessarily and it also becomes harder to sell for the producer of the machine. The effectiveness and efficiency of the machine drops down when it is hard to operate. To make it easier for future developers to reach a high usability factor when developing a HMI, this thesis aimed to find a carefully prepared process to follow when doing so. The result was a process that was tested out with a HMI prototype for waterjet cutting machines. This prototype was then tested in different use cases by both experienced operators as well as beginners. The testing produced positive feedback on the prototype, proving that the process that had been followed was being successful.När man utvecklar ett Människa-Maskin-Gränssnitt (HMI) så är det viktigt att se till att det är lätt att lära sig och använda, att det har hög användbarhet. Ifall den inte har det så försämrar det operatörers situation i onödan och gör det svårare för producenter att sälja produkten. Produktionseffektiviteten minskar ifall maskinen är svår att hantera. För att göra det lättare för framtida utvecklare att nå en hög användbarhet när de utvecklar ett HMI så siktade detta examensarbete på att hitta en genomtänkt process att följa vid ett sådant tillfälle. Resultatet blev en process som testades via en HMI prototyp för vattenskärnings maskiner. Denna prototyp blev sedan testad i olika användarfall av både erfarna operatörer och nybörjare. Testerna visade sig ge positiv återkoppling, vilket bevisade att processen som följts upp till den punkten fungerade

Two different approaches to model evolving directional properties at finite deformations

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

Utveckling av ett användbart Människa-Maskin-Gränssnitt

When developing a Human-Machine-Interface (HMI) it is important to make sure that it is easy to learn and use, to have high usability. If it does not, the operator of the machine suffers unnecessarily and it also becomes harder to sell for the producer of the machine. The effectiveness and efficiency of the machine drops down when it is hard to operate. To make it easier for future developers to reach a high usability factor when developing a HMI, this thesis aimed to find a carefully prepared process to follow when doing so. The result was a process that was tested out with a HMI prototype for waterjet cutting machines. This prototype was then tested in different use cases by both experienced operators as well as beginners. The testing produced positive feedback on the prototype, proving that the process that had been followed was being successful.När man utvecklar ett Människa-Maskin-Gränssnitt (HMI) så är det viktigt att se till att det är lätt att lära sig och använda, att det har hög användbarhet. Ifall den inte har det så försämrar det operatörers situation i onödan och gör det svårare för producenter att sälja produkten. Produktionseffektiviteten minskar ifall maskinen är svår att hantera. För att göra det lättare för framtida utvecklare att nå en hög användbarhet när de utvecklar ett HMI så siktade detta examensarbete på att hitta en genomtänkt process att följa vid ett sådant tillfälle. Resultatet blev en process som testades via en HMI prototyp för vattenskärnings maskiner. Denna prototyp blev sedan testad i olika användarfall av både erfarna operatörer och nybörjare. Testerna visade sig ge positiv återkoppling, vilket bevisade att processen som följts upp till den punkten fungerade

Description of evolving anisotropy at large strains

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