ATOMISTIC MODELING OF PLASTIC-DEFORMATION OF GLASSY-POLYMERS

A detailed atomistic approach has been used to investigate the kinemat ics of plastic deformation in glassy atactic polypropylene to 20% stra in. The microstructural stress-strain behaviour was found to consist o f smooth reversible portions bounded by irreversible sharp stress drop s indicating plastic rearrangement of the structure. Averaging the str ess-strain behaviour over an ensemble of 1.815 nm microstructures show ed a yield point in the neighbourhood of 5-7% strain. The transformati on shear strain for plastic structural rearrangements was found to be broadly distributed, averaging 1.5% shear strain with a standard devia tion of 2.6% shear strain. Combining this result with the activation v olume measurements of common glassy polymers showed the size of the pl astically transforming region to have a diameter of about 10 nm, thus involving several thousand segments. The transformation shear strain w as independent of the system size. Scrutiny of the molecular segment m otions associated with plastic rearrangements showed no recurring simp le kinematical configurations and no correlation of the local atomic s train to topological features of the chain.