Characterization of mar/scratch resistance of polymeric coatings: Part II

This two-part article (Part I was published on pages 54-60 in the March 2006 issue of JCT COATINGSTECH) briefly reviews the development of mar/scratch characterization techniques, and focuses on single-probe tests with nano instruments which have been widely used recently. Quantitative measurements of micro mar resistance (MMR), different responses of the coatings to the marring stress (i.e., elastic response, plastic deformation, and abrasive wear), and critical forces for rough trough, cracking, delamination, and chipping are described, as are some complementary test methods. Statistical investigation of damage on samples used in real environments, combined with laboratory mar/scratch tests on these samples, could determine the force distribution curve in the lab which is approximately equivalent to the field conditions. The curve is useful for development of new coatings, and it can predict the weights of different damage modes that are likely to occur at the surface of the coatings in the field. The weights, combined with the quantification of the damage levels of different modes, allow calculation of a quantitative index to characterize the mar/scratch resistance of a coating in a specific environment comprehensively To better understand the mar/scratch resistance behavior of tested materials, a detailed stress-strain study is needed, utilizing theoretical analysis and finite element modeling to complement the experimental measurements described here as an integrated approach.