COMPUTER-SIMULATION OF STRESS-RELAXATION

Molecular dynamics simulations of stress relaxation have been performed for models of metals and polymers. The method which employs coupling between the simulation cell and an external thermal bath as well as an applied stress has been used. Two-dimensional models of the materials are defined with interactions described by the Lennard-Jones (Mie 6-12) and harmonic potentials. A special method is employed to generate chains in dense polymeric systems. Simulated stress relaxation curves are similar for metals and polymers, while there exist essential differences in the stress-strain behavior of the models. During the relaxation, trajectories of the particles in different materials display a common feature: there exist domains in which movement of the particles is highly correlated. This observation supports the cooperative theory of stress relaxation developed by one of us. The results of the simulations do not significantly depend on the number of particles in the system nor on other simulation details.