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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.
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