SIMULATION OF PLASTIC-DEFORMATION IN A FLEXIBLE CHAIN GLASSY POLYMER

A short report of a new computer simulation of plastic deformation is given in a typical flexible chain glassy polymer-polypropylene. The model which makes no arbitrary assumptions about structure and modes of molecular segment relaxations is based on systematic static energy minimizations in a small periodic cell representing a typical molecular environment. The simulation shows that because of the relatively inflexible nature of backbone bonds and bond angles, permitting conformational changes only through alterations in torsional degrees of freedom, the size of a coherent plastic relaxation unit is typically 8 to 10 nm in dimensions. Careful scrutiny of conformational alterations reveals no recurring simple kinematical configurations such as dislocations, disclinations, rotons, strophons, or the like. The best emerging picture is that plastic relaxation is by the repeated nucleation of shear transformations in a very large group of segments in a very cooperative manner resulting, however, in transformation shear strains of only about 1.5%. While such transformations are dilatant in polypropylene, they are the opposite in polycarbonate which has a more structured and stiff molecule.