Atomistic modelling of cavitation of glassy polymers

Abstract

A detailed atomistic approach has been used to investigate the molecular segment kinematics as a glassy, atactic polypropylene system was dilated by 30%. The microstructural stress-dilatation response consisted of smooth, reversible portions bounded by sudden, irreversible stress jumps, but when compared to the microstructural stress-strain curve of the shear simulation, the overall trend more closely resembled macroscopic stress-strain curves. The peak negative pressure was in the neighbourhood of 12% dilatation, with a corresponding secondary maximum in the von Mises shear stress. The peak negative pressure was relieved by a stress jump that signalled cavitation, which was most pronounced in the large system. The cavities were found to be flat and irregular; for the large system that had been dilated by 20%, the cavities extended 0.5 to 0.8 nm with a characteristic thickness of 0.080 nm, and the total cavity volume fraction was 0.02. The surface energy of the cavities was estimated to be 53.4mJm⁻², which is within 17% of the experimental value.