The paper presents the main statements of a mathematical model of fatigue damage accumulation in structural materials of reactor plant equipment and systems, which was developed on the basis of methods of damaged medium mechanics, and the results of its verification.Introduction. The structural elements of reactor plant (RP) equipment operate under complex manifold in-service conditions, which are characterized by strong multiparametric nonstationary thermomechanical and radiation actions, which lead to combined multiaxial stresses in structural elements and development of degradation processes in structural materials. As a result of such processes, nucleation and formation of macrocracks~1-2 mm in length and their propagation up to construction failure take place in structural elements of the equipment. The life of the RP equipment and systems is determined by the life of their danger zones, in which the rate of degradation processes is highest. In this case, the rate of damage accumulation in the material of these zones and their exhausted life depend largely upon the actual RP operation model (the sequence of performance of operating modes). The problem is complicated by the fact that the access to such zones of the technical means of nondestructive monitoring of the state of the material during RP operation is practically impossible. In view of this, the assessment of the degree of accumulated damage in the material of danger zones and in-service monitoring of the exhausted and remaining life of equipment and systems on the basis of mathematical modeling is a complicated scientific and technical problem.Mathematical Model of Fatigue Damage Accumulation. The proposed mathematical model of damage accumulation is based on two groups of evolution equations: of nonstationary nonisothermal elastoplastic deformation and fatigue damage accumulation [1].Below are given thermoplasticity equations, which were taken as a basis of the developed procedure and make it possible to describe effects which are essential for the development of fatigue damage processes in structural materials under quasistatic nonstationary thermomechanical loading.The relation between stresses and the elastic components of strain tensor is established on the basis of known thermoelasticity equations: s a = --3
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