| Popis: |
This study aims to relate the intrinsic mechanical response of particle-filled polymer glasses to their response in sliding friction. A previous study showed that the frictional properties of unfilled polycarbonate are quantitatively captured by finite element simulations when using a proper constitutive model, i.e. a model that captures the polymers intrinsic mechanical response quantitatively, and a rate-independent friction (stick-slip) model. Single-asperity scratch tests were successfully modeled over a range of scratch velocities and for different indenter-tip geometries. In this thesis we extend these pioneering results to the class of practically more relevant and interesting particle-filled (thermoplastic and thermoset) polymer systems. To that end, hard- and soft-particle filled polycarbonate and epoxy systems are investigated. Starting with polycarbonate (that is over the years fully characterized) as matrix material, hard inorganic (TiO2) and soft rubber (MBS) filled model systems are designed and produced. Their intrinsic response is measured in lubricated uniaxial compression tests. To reveal local events at the interparticle level, three-dimensional representative volume elements (3D-RVEs) are constructed to model the complex microstructure of these systems. Finite element simulations of these 3D-RVEs show that the intrinsic response is captured well but, moreover, they provide insight in the critical local events that lead to global failure. The simulations provide the (homogenized) material parameters that macroscopically describe these particle-filled systems, and that are used in the simulations of their scratch response in sliding friction tests. It is confirmed that by combining a proper constitutive framework with the most simple, rate-independent, friction model, all experiments are appropriately described quantitatively by the numerical simulations. Furthermore, the onset of failure during scratching becomes accessible. The local (homogenized) strains resulting from the scratch simulations can be translated to simulations on the RVE-level that reveal the extent of critical events at the interparticle level. After the successful modeling of filled thermoplastic systems, the focus is next on thermosets. Epoxy-based composites are investigated, designed and produced, since thismatrix is more relevant for coating applications. The intrinsic mechanical response ofthe matrix material, a standard epoxy, is characterized and the material parameters usedin the constitutive model are determined. The model systems filled with either softpolysiloxane rubber particles or hard TiO2 particles are created and tested. It is shownthat the complete methodology as derived and described for polycarbonate is also validfor these thermoset systems. The thesis ends with an onset of designing smart materials, inspired by our findingsfrom the simulations on the microstructures and the scratch tests. |
