Witold Brostow
Departments of Materials Science and Physics, University of North Texas, Denton, TX 76203-5308, USA

Josef Kubát
Department of Polymeric Materials, Chalmers University of Technology, S-412 96 Gothenburg, Sweden

ABSTRACT

Simulations were performed using the method of molecular dynamics for lattices with defects generated by three different procedures. Curves of relaxation of stress ð vs logarithmic time t were obtained. In agreement with experimental results, the simulated curves exhibit three regions: initial, nearly horizontal, starting at ð₀; central, descending approximately linearly; and final, corresponding to the internal stress ð_i as defined by Li. The existence of the central linear part has been predicted by a cooperative theory. In agreement with the theory, the slope of the simulated central part is proportional to the initial effective stress ð₀* = ð₀ - ð_i. The central part extends over approximately one decade of log₁₀ t for ideal lattices but over several decades for lattices with defects. High values of the imposed strain correspond to low internal stresses ð_i, and vice versa. Stress relaxation is mainly due to deformations that occur in the vicinity of the defects, hence the process is related to the defect concentration and the amount of free volume v^f. Collective response of atoms in groups is observed. The origin of the defects does not seem to influence the relaxation.

**Phys. Rev. B 1993, 47, 7659.