YIELDING OF A MODEL GLASSY POLYCARBONATE UNDER TENSION - A MOLECULAR MECHANICS SIMULATION

Yielding of a model glassy polycarbonate under tension was studied usi ng the molecular mechanics method. The model structures were stretched by changing the cell dimensions consistent with the applied strain an d the assumed Poisson ratio. After the deformation, the model structur es were optimized. The resultant stress-strain curves clearly indicate the yielding of the model polymer near 13% strain. The nonbonded van der Waals interactions represent the dominant contribution to the over all strain energy. The yield stress and yield strain obtained from the simulation compare favorably with the experimental data if the latter are extrapolated to 0 K. To further examine the yielding phenomenon, the same deformation scheme and an affine model were applied to a mode l atomic glass. The results support the idea that the nature of yieldi ng is the inflection exhibited on the Lennard-Jones potential represen ting the van der Waals interactions. The structural changes of the mod el polymer were studied through analyses of the Voronoi volume distrib ution of atoms, the segmental orientation, and the overall chain defor mation and orientation. Voids were developed during the deformation.