Phd thesis: Experimental characterization and constitutive modeling of reinforced thermoplastic and thermosetting polymers
Most important publications (for more information please visit my google scholar profile)
- (n)-and (n+ 1)-layered composite sphere models for thermo-chemo-mechanical effective properties with Rolf Mahnken and Peter Lenz. International Journal for Multiscale Computational Engineering: Our work presents extensions of multi layered composite sphere models known from the literature to temperature- dependent elastic effects accompanied by curing. In particular volumetric effective properties are obtained by homogenization for a representative unit cell (micro-RVE) on the heterogeneous microscale for thermo- chemo-mechanical coupling with linear elasticity. To this end, analytical solutions for (n)- and (n + 1)-layered composite sphere models are derived, in addition to Voigt and Reuss bounds resulting from the assumption of a homogeneous mixture. As a further result the equivalence for the thermo-chemo-mechanical volumetric effective properties of the (n)- and the (n + 1)-layered composite sphere model is shown. In a numerical study for a (3)-phase matrix it is demonstrated that the effective elastic and thermal properties lie within the Voigt and Reuss bounds, whilst for the chemical part of the model, an analogous result is obtained for the effective strains.
- A three-scale framework for fibre-reinforced-polymer curing Part I: Microscopic modeling and mesoscopic effective properties with Rolf Mahnken. International Journal of Solids and Structures: Our work presents a three-scale model for temperature-dependent visco-elastic effects accompanied by curing, which are important phenomena in a resin transfer molding (RTM) process. In Part I, bounds for the bulk quantities of the matrix material in dependence of the degree of cure for an equally distributed, homogeneous mixture with phases resin, curing agent and solid are derived. Furthermore, effective bulk quantities are obtained by homogenization for a representative unit cell (micro-RVE) on the heterogeneous microscale, taking into account the geometrical arrangement of phases. To this end, an analytic solution is derived by extension of the composite spheres model known from the literature. For simplification, we restrict the material behavior of the micro-RVE to linear thermo-chemo-elasticity. In a study we compare different meso material properties including bounds and effective material constants. In the examples we compare the meso-micro relations for the homogeneous matrix with those derived for the heterogeneous matrix.
- A three-scale framework for fibre-reinforced-polymer curing Part II: Mesoscopic modeling and macroscopic effective properties with Rolf Mahnken. International Journal of Solids and Structures: Important phenomena in a resin transfer molding (RTM) process for polymeric materials are temperature-dependent visco-elastic effects accompanied by curing. In Part 1 we propose a three-scale model and a comparative study for different meso material properties including bounds and effective material constants. Based on those preliminaries, in this work, Part 2, we present basic relations in a thermodynamic framework for temperature-dependent visco-elastic effects accompanied by curing which is specialized to the scenario of a mechanical-thermal-chemical process. During curing and subsequent mechanical loading, the periodic mesostructure defined by a visco-elastic polymeric matrix and linear-thermo-elastic carbon fibres is taken into account as a representative unit cell (meso-RVE) subjected to thermo-mechanical loading on the mesoscale. Homogenization of the mesoscale by volume averaging is applied to obtain the effective properties for the fully cured composite on the macroscale. In the examples we use DSC-measurements for parameter identification and simulate the curing process as well as mechanical loading of the cured part with the finite-element-method.
- Experimental Investigation of PC-Films Using Optical Measurements with Ismail Caylak and Rolf Mahnken. International Polymer Processing: The alignment of polymer chains is a well known microstructural evolution effect due to straining of polymers. This has a drastic influence on the macroscopic properties of the initially isotropic material. In this work, cold forming is performed at room temperature on a tensile testing machine. Polycarbonate films are examined in two loading phases. In the first phase, the specimen is loaded to induce anisotropy, and in the second, it is re-loaded, while the material direction is varied. The investigations are supported by an optical measurement system to gain knowledge about the inhomogeneous material behavior in the initial loading phase and about the anisotropic homogeneous behavior during the re-loading phase. Two dimensional strain contours are obtained from the test data. Additionally, we propose a method for approximation of the macroscopic true stress and compare the results with a common approach based on volume consistency. In the future, the test data will set a basis for parameter identification of constitutive equations taking into account a combination of inhomogenous and homogenous material behavior, exhibiting strain induced anisotropy.
- Simulation of strain-induced anisotropy for polymers with weighting functions with Rolf Mahnken. Archive of Applied Mechanics: We investigate the role of manipulation in boundedly rational opinion dynamics. Agents are subject to persuasion bias and repeatedly communicate with their neighbors in a social network. They can exert effort to manipulate trust in the opinions of others in their favor and update their opinions about some issue of common interest by taking weighted averages of neighbors' opinions. We show that manipulation can connect a segregated society and thus lead to mutual consensus. Second, we show that manipulation fosters opinion leadership; and surprisingly agents with low trust in their own opinion might get more influential even by being manipulated. Finally, comparative simulations reveal that manipulation is beneficial to information aggregation when preferences and abilities for manipulation are homogeneous, but detrimental in case abilities are concentrated at few powerful agents.