Doyar I. Generalized stochastic model of structural materials failure in creep taking into account damageability and strengthening

The object of investigation is the phenomenon of structural materials failure in creep operating at elevated temperatures and loads. The subject of the study is a generalized stochastic model of structural materials failure in creep operating at elevated temperatures and loads. The purpose of the study is to construct a stochastic model of structural materials failure in creep operating at elevated temperatures and loads, which allows, at specified stress and temperature values, to determine the probabilistic distribution of time to failure of the material, and also extrapolate the long-term strength of structural materials to a service life several orders of magnitude longer than the duration of experiments. Research methods: calculations were performed on the basis of optimization methods, the apparatus of probability theory and mathematical statistics. The reliability and validity of the research results is ensured by the correct mathematical formulation of the problem, the use of modern means of calculation. The obtained results - developed a stochastic model of structural materials failure in creep taking into account damageability and strengthening of the material, expands the scope of this model in comparison with the known linear models of damage accumulation. For the first time a mixed criterion of failure is considered, which is a combination of parametric and deformation criteria and takes into account both the effect of the damaging parameter and the effect of creep deformation on the time to failure of the material. A technique for the identification of creep constants of a material is proposed, based on the processing of a family of experimental creep curves. For the first time a stochastic method of basic diagrams is developed for extrapolating the long-term strength of structural materials to a service life several orders of magnitude longer than the duration of experiments. The results obtained in the thesis are introduced into the calculation practice of Yuzhnoye State Design Office (Dnipro) and into the educational process at the Mechanics and Mathematics Faculty of Oles Honchar Dnipro National University.