MOLECULAR-DYNAMICS SIMULATIONS OF STRESS-RELAXATION IN METALS AND POLYMERS

Molecular-dynamics simulations of stress relaxation have been performe d for models of metals and polymers. A method that employs coupling be tween the simulation cell and an applied stress as well as an external thermal bath has been used. Two-dimensional models of the materials a re defined with interactions described by the Lennard-Jones (Mie 6-12) and harmonic potentials. A special method is employed to generate cha ins in dense polymeric systems. In agreement with experiments, simulat ed stress-relaxation curves are similar for metals and polymers. At th e same time, there exists an essential difference in the stress-strain behavior of the two kinds of simulated materials. During the relaxati on, trajectories of the particles in different materials display a com mon feature: There exist domains in which movement of the particles is highly correlated. Thus, the simulation results support the cooperati ve theory of stress relaxation.