Moghbelli, Ehsan (2007-08). Insights in fundamental scratch behavior of polymeric materials. Master's Thesis.
This work is mainly focused upon the analytical examination of the physical and mechanical response of plastics undergoing an induced scratch deformation caused by a semi-spherical scratch tip under a linearly increasing normal load. Evaluation of the scratch deformations in this study was based upon visual and optical observations and upon observations of failure and fracture mechanisms as well as Electron Microscopy examinations. In the first section of this study an effort was made to correlate the scratch resistance observed in Polypropylene (PP) thin sheets with material properties, such as molecular weight and surface crystallinity. In the second section of this work the scratch behavior of epoxy nanocomposites was examined and a conclusion was made based upon the effects of the addition of nano-additives with various natures into the epoxy matrix. Furthermore, a region of the scratch path prior to the onset of scratch visibility known as the mar region, which was an obscure area of deformation on a microscopic scale, was thoroughly investigated for the epoxy systems and various conclusions were made based upon those results. Finally, based on these findings and previous studies, it was shown that failure and fracture mechanisms of polymeric materials under scratch deformations are dependent on the type and physical nature of the material, whereas brittle and ductile materials show various behaviors under the specified conditions. Based on the failure mechanism which the material exhibits subsequent to the scratch deformation process and the physical and mechanical characteristics of the material, several factors were shown to effect the materials ability to scratch resistance.