Mechanical properties of copper with various types of defects have been studied with the molecular dynamics method and the effective-medium theory potential both at room temperature and near zero temperature. The loading has been introduced as constant rate straining and the dynamics of the process region of fracture is purely Newtonian. With the model three types of defects were studied: point defects, grain boundary, and an initial void serving as a crack seed. Feint defects were seen to decrease the system strength in terms of fracture stress, fracture strain, and elastic modulus. Due to random microstructure, highly disordered systems turned out to be isotropic, which on the other hand seems 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 initiation seems to be less at the grain boundary than in the bulk. In the case of an initial void, we studied stress concentration, dislocation propagation, and crack propagation in thin systems. The stress concentration was found to be in surprisingly good agreement with continuum predictions. Dislocation and crack were propagated with a velocity much below the speed of sound and they preferred the (110) crystal orientation.