ATOMISTIC MODELING OF CAVITATION OF GLASSY-POLYMERS

A detailed atomistic approach has been used to investigate the molecul ar segment kinematics as a glassy, atactic polypropylene system was di lated 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 o f the shear simulation, the overall trend more closely resembled macro scopic stress strain curves. The peak negative pressure was in the nei ghbourhood of 12% dilatation, with a corresponding secondary maximum i n 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 exten ded 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 cavi ties was estimated to be 53-4 mJ m-2, which is within 17% of the exper imental value.