Methodology and features of a computational experiment to assess the resource of responsible engineering facilities

Abstract

The problem of obtaining estimates of the strength and resource characteristics of critical engineering infrastructure facilities under operational multiparametric nonstationary thermomechanical impacts is considered. The basic degradation mechanisms in structural materials (metals, alloys) under these influences are identified. The methodology of resource assessment of responsible engineering facilities  based on end-to-end modeling of the entire life cycle of the object is substantiated. End-to-end modeling forms a set of computational experiments of different levels of complexity, each of which has its own characteristic features and semantics. From the perspective of the mechanics of the degraded continuum, a mathematical model of the damaged medium has been developed, in which the processes of thermoplasticity and damage accumulation are generated by thermal fatigue. The model describes the effects of cyclic thermoplastic deformation; kinetics of damage accumulation; conditions of macroscopic destruction of the material. The model postulates the representation of the yield surface and the principle of gradiency of the velocity vector of plastic deformations at the loading point. A variant of the thermoplasticity equations describes the main effects in proportional and disproportionate modes. The thermoplasticity model is constructed as a system of “nested” models and contains the forms of equations of the theory of plastic flow under small deformations: various variants of isotropic hardening (ideally plastic material with a constant flow surface, linear isotropic hardening, variant of isotropic nonlinear hardening), various cases of kinematic hardening (linear kinematic hardening, the case of purely nonlinear kinematic hardening) and the general case of translational isotropic hardening. The kinetics of fatigue damage accumulation is described by introducing a scalar damage parameter and based on the energy principles of taking into account the main effects of the damage accumulation process for arbitrary complex loading modes. The condition of reaching the critical damage value is used as a criterion for macroscopic destruction. The relationship between the components of the model is carried out by introducing effective stresses. The paper presents a numerical analysis of the thermal fatigue life of a compact sample with stress concentrators simulating the operation of parts in the nozzle box of a steam turbine of a nuclear power plant. During the analysis, the characteristic features of thermal fatigue in the details of power equipment were studied. It is shown that the end-to-end modeling technology can be effectively used to assess the resource characteristics of power equipment parts under operational loading conditions.

Keywords

• numerical modeling
• computational experiment
• model of damaged medium
• stress-strain state
• thermocyclic fatigue
• damage
• destruction
• resource