MOLECULAR-DYNAMICS STUDY OF COPPER WITH DEFECTS UNDER STRAIN

Mechanical properties of copper with various types of defects have bee n studied with the molecular dynamics method and the effective-medium theory potential both at room temperature and near zero temperature. T he loading has been introduced as constant rate straining and the dyna mics of the process region of fracture is purely Newtonian. With the m odel three types of defects were studied: point defects, grain boundar y, and an initial void serving as a crack seed. Feint defects were see n to decrease the system strength in terms of fracture stress, fractur e strain, and elastic modulus. Due to random microstructure, highly di sordered systems turned out to be isotropic, which on the other hand s eems to increase the elastic modulus. In the case of a grain boundary, the elastic modulus was found to be significantly less than the bulk value of the system. In addition, the critical strain for crack initia tion seems to be less at the grain boundary than in the bulk. In the c ase of an initial void, we studied stress concentration, dislocation p ropagation, and crack propagation in thin systems. The stress concentr ation was found to be in surprisingly good agreement with continuum pr edictions. Dislocation and crack were propagated with a velocity much below the speed of sound and they preferred the (110) crystal orientat ion. [S0163-1829(98)03826-0].