@phdthesis{,
    author = {Michaloudis, Georgios},
    title = {Numerical Modeling of Embedded Interfaces based on Frictional Contact Formulations with a Covariant Description},
    editor = {},
    booktitle = {},
    series = {},
    journal = {},
    address = {},
    publisher = {},
    edition = {},
    year = {2019},
    isbn = {},
    volume = {},
    number =  {},
    pages = {},
    url = {},
    doi = {},
    keywords = {Interfaces; Frictional Contact; Covariant description; High dynamic loading; Masonry walls; Numerical modeling},
    abstract = {This thesis addresses the behavior of interfaces between contacting bodies and provides strategies for their incorporation into numerical models within the finite element method. In a first step a typical example from civil engineering involving interfaces, the unreinforced masonry wall, will be studied. Extreme loading resulting from explosions has been chosen as external loading conditions and specific simulation strategies in order to capture the formation of damage are proposed. The proposed models cover the formulation of an appropriate material law and of the equation of state based on experimental data, as well as modeling strategies with an eye on the specific characteristics of the behavior of the interfaces and of the entire wall under extreme loading conditions. In a second step the focus lies on the development of a complete three dimensional frictional contact formulation for the modeling of interaction phenomena which occur on the interface of contact surfaces. A fully covariant approach is employed for the description of the contact conditions. A Surface-to-Surface algorithm based on a penalty regularization is implemented. Tools from differential geometry are employed in order to describe the geometry of the surfaces in an exact manner. A thermodynamic framework for dissipative processes  is formed for the definition of appropriate material laws, which are then incorporated into the contact formulation. The proposed material model is based on experimental results and is derived as a simple elastoplastic associative constitutive law with softening. The validation of the developed formulations is performed based on the experiments. A return mapping scheme is applied for the definition of the stick-slip transition and for the computation of the correct tangential traction. This traction is then used in the consistent linearization which results in a symmetric stiffness matrix not only for sticking but also for sliding, since the non-associative nature of the Coulomb friction law is abandoned. By adopting the fully covariant description, which is applied by introducing appropriate local coordinate systems, the stiffness matrix has a clear form allowing simplifications. This formulation results in an interface finite element, which consists of 8 nodes in the case of linear or of 18 nodes in the case of quadratic finite element approximations. The thesis closes with the generalization of the contact formulation for arbitrary anisotropic surfaces. The case of anisotropy resulting from inherent structural characteristics of the interface is thoroughly discussed. It is shown that by taking advantage of a fully covariant description suitable constitutive laws can be introduced straightforwardly. This issue is of great importance when experimental results are available.},
    note = {},
    
    school = {Universität der Bundeswehr München},
    
}