Jiang, Han (2009-08). Experimental and Numerical Study of Polymer Scratch Behavior. Doctoral Dissertation.
As part of a larger effort to understand the fundamental knowledge of polymer scratch behavior, this dissertation is focused on both experimental study and numerical analysis of scratch deformation of a broad range of polymers, with an emphasis on the mechanical understanding of how the scratch-induced damage is formed. An instrumented progressive load scratch method recommended by ASTM/ISO standards was adopted for the experimental work. The commercial finite element (FE) method package ABAQUS was employed as a numerical simulation tool to describe the stress-strain fields, and it analyzes the deformation mechanisms during the scratch process. A thorough parametric study has been performed to assess the influence of material parameters and surface properties, such as Young's modulus, yield strength, and friction coefficient, on the polymer scratch behavior. Upon investigation of the scratch behaviors of a broad range of polymer materials, various kinds of scratch damage features are identified and correlated with the mechanical characteristics of the polymers. A generalized scratch damage mechanism map for polymers is presented. Correlation between different material types and scratch damage mechanisms is made. It is found that both the material characteristics and the stress state exerted on the scratched surface are responsible for the observed scratch damage mechanisms. The phenomenological deduction of the scratch damage process based on the stick-slip mechanism is established. A more realistic material law for the scratch analysis is also provided. To evaluate the polymer resistance against scratch visibility quantitatively, an entirely new automated on-set scratch visibility determination methodology is developed based on typical visual characteristics of human eyes. Its application on the evaluation of mar and abrasion of polymer is also explored. This new methodology can quantify polymer scratch resistance consistently and reliably regardless of the sample surface characteristics and color.