THE LIMITING STATE OF A STEEL STRUCTURE UNDER EXTREME THERMOMECHANICAL LOADINGS

Using numerical methods, the problem of determining the strength and limiting state of a steel shell structure under thermomechanical loading is solved. The operating stresses are determined by solving a physically nonlinear boundary value problem for a shell of revolution. The classical theory of shells, based on the Kirchhoff – Love hypotheses, and the method of integrating shell equations with discrete S.K. Godunov orthogonalization are used. By integrating a system of ordinary differential equations at each point of the shell, the meridional and circumferential stresses and the corresponding deformations are calculated. When taking into account the plastic deformation of the material, the boundary value problem becomes nonlinear. The relationship between stress and strain is linearized by the method of additional strains. A limiting state criterion for thin-walled structures is proposed. In the absence of the necessary parameters for the material of construction, interpolation and extrapolation of the experimental data based on neural networks is used. The method uses the example of a muffle, which is a revolution shell structure loaded with an internal excess pressure of a hydrogen-containing gas and a non-stationary thermal field. The muffle is designed for high-temperature annealing of the electrolytic steel, and is made of non-heat-resistant St3 steel, its mechanical properties have not been sufficiently studied at temperatures above 500 °C. However, the operating temperature of the muffle can reach more than 1000 °C. Under the influence of such a thermal load, noticeable residual deformations are formed in the muffle structure and the muffle may lose its load-bearing capacity. For thermomechanical loads, a maximum temperature of 1000 °C is determined at which the limit state occurs and the operation of the muffle is not permissible. A satisfactory agreement was obtained with the actual muffle temperature during operations of 1100 °C, at which the muffle loses its load-bearing capacity.