When analyzing the structural integrity of a material or structural part, the mechanics of continuous media is traditionally used with the concept of the homogeneity and isotropy of material properties; with this approach, the fracture criteria are related to the integral characteristics of the material and are described by the invariants of the stress tensor. However, this approach does not consider the physical aspects of the occurrence of local areas of plastic deformation, which ultimately means the impossibility of predicting the fracture, and, consequently, the resource of the structure. This is especially evident in the conditions of cyclic loading, when the material can fail at stresses well below the traditional «fatigue limit». In the current work, an approach is proposed that allows to save traditional methods of design and resource forecasting by expanding the scale of modeling. The paper introduces the concept of inherent stress concentration in any structurally heterogeneous medium as its inherent attribute. A universal algorithm for determining this characteristic is presented.

It is known that most structural materials are polycrystals. Under any loading, the structural features of the polycrystal may lead to the appearance and accumulation of microplastic deformation due to stress concentrations. This statement is part of a multiscale approach to describing the fracture process. The present development of computer engineering allows modeling of complex non-homogeneous objects, such as polycrystal. In this paper, a numerical model is developed for analyzing of the polycrystal stress state under mechanical loading. It is shown that inherent stress concentration takes place. The localization and statistical estimation of inherent stress concentration is made on the example of α-Fe polycrystal.