The proposed model uses modern concepts of mechanics as well as solid-state physics and metal physics to consider the behaviours of single- and polycrystalline states of metal materials in the conditions of uniform compression, when there are two types of model stress concentrators: subtraction and interstitial ones, which are analogous to the majority of the stress risers appeared in the real products. The features of the stress concentrators’ behaviours and the changing sequences of their quantity and power are demonstrated depending on their stability in the spheroidal samples. The differences in the stress increase and relaxation at the tips, which regulate the activity of the known relaxation mechanisms, are pointed out. For both the single- and polycrystalline states, the existence of critical points on the pressure axis, which limit the collective activity of vacancy and dislocation mechanisms of plastic relaxation and transition to the accumulation of only interstitial point defects with the increasing pressure, is predicted. These interstitial defects facilitate a considerable increase of potential energy of atoms in the conditions of elastic decrease of the crystal lattice parameter. The growth is accelerated near the stable stress concentrators. Priorities and peculiarities of participation of the stress concentrators in the formation of the hydrodynamic state of materials are considered. The model allows explaining majority of the experimental results related to mechanical behaviour of materials after the uniform compression. It also predicts the probability of formation of new structural states in the conditions of the rapidly decreased pressure from the certain critical value.