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plotting true stress-strain diagrams makes it possible to determine true stresses

near concentrators in structural elements under complex loading. The use of these

diagrams in engineering calculations and computer modelling using the FEM

significantly increases their accuracy. Modelling of the damage accumulation

was carried out using the energy criterion. The damage parameter is introduced

as the ratio of the elastoplastic strain energy of the local volume to its critical

value. The elastoplastic strain energy of the local volume of the structural element

is calculated using FEM. The critical value of the elastoplastic strain (fracture)

energy is taken as a characteristic of the resistance to fracture of the material under

the given conditions of load, temperature, and working environment. It is

determined experimentally as the area under the "true stress - true strain" curve,

where the true strains in the local volume are calculated on the basis of

displacement data in two directions on the basis of 0.5 mm using the ODIC

methid. The value of the true stresses in the area of maximum strain is determined

by taking into account the change in the cross-sectional area due to the change in

the diameter of the sample during its deformation by uniaxial tension. The fracture

energy and damage parameter for the modified Bridgman sample made of steel

22K under different load regimes were determined theoretically and

experimentally.

The research methodology and the mathematical apparatus used in the

study are substantiated. To solve the formulated scientific problems, the methods

of the mechanics of a deformable solid were used, primarily the theory of

elastoplasticity and continuum damage mechanics. Numerical studies were

carried out using the finite element method in the environment of the ANSYS

2022R1 software complex, in which three-dimensional computer models were

created.

All the theoretical developments of the thesis are brought to a specific

engineering methodology for predicting the safe operation of elements of thermal

power equipment, taking into account the action of the operating environment.