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Title: Computational micromechanics of matrix-inclusion composites
Language: English
Authors: Schneider, Konrad 
Issue Date: 2019
Abstract (english): This thesis is concerned with aspects of the computational retrievement of macroscopic material responses and investigations of the microscopic deformation behavior of random matrix-inclusion composites. To this end, the focus lies on the representative volume element (RVE) approach in the scope of finite element analyses and its applicability and integration into engineering practice. The artificial random generation of the microstructural geometry, in a periodic and non-periodic manner, is established by studying and enhancing existing methods such as the random sequential adsorption method or collective rearrangement methods for cubic RVEs. Based on distance computations between two inclusions, the non-overlap requirement, which is characteristic for matrix-inclusion composites, is ensured for ellipsoidal, capsular, cylindrical and convex polyhedral inclusion shapes. To comply with the state-of-the-art approach that utilizes fully periodic RVEs featuring a periodic topology, a periodic discretization and periodic boundary conditions (PBC), a new algorithm that automatically generates periodic meshes is developed. The algorithm systematically combines various meshing tools in an efficient and robust way. Special emphasis is placed on the discretization procedure to maintain a high quality mesh with as few elements as possible, thus, manageable for computer simulations applicable to high volume concentrations, high number of inclusions and complex inclusion geometries. Examples elucidate the ability of the proposed approach to efficiently generate large RVEs with a high number of anisotropic inclusions but still maintaining a high quality mesh and a low number of elements. Since the generation of such a state-of-the-art RVE can significantly reduce the overall efficiency in multiscale finite element simulations, a benchmark study that investigates possible relaxations to this cumbersome task is performed. In particular, the RVE size, periodic and non-periodic RVE topologies, different discretization variants and various types of boundary conditions that either require periodicity or do not require periodicity of the underlying discretization are benchmarked. Approximate periodic boundary conditions are discussed in detail. The benchmark study proves that a fully periodic topology and mesh discretization with periodic boundary conditions is not necessary in order to identify effective macroscopic material parameters for technologically relevant composites. Eventually, the gathered methodologies are applied to model a modern high-tech polymer nanocomposite. By utilizing a sophisticated material model for the polymeric matrix, the entropic and energetic deformation regime can be represented in a physically meaningful way. Furthermore, the explicit consideration of the matrix-inclusion interface failure via a cohesive zone model accounts for the non-negligible surface effects. Comparisons with experiments underline the predictive character of the modeling approach and allow for investigations of local deformation mechanisms.
DOI: 10.15480/882.2520
Institute: Kontinuums- und Werkstoffmechanik M-15 
Type: Dissertation
Advisor: Cyron, Christian J. 
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