Stankevych O. Methodological backgrounds of identification of materials fracture types by the energy parameters of acoustic emission

The dissertation is devoted to the scientific and technical problem which consists in the development on the basis of theoretical and experimental studies the methodological backgrounds of solids fracture diagnostics and estimation of the structural materials state using energy parameters of acoustic emission of elastic wave. A general analytical solution of the problem of elastic waves propagation initiated by the displacement of the opposite surfaces of the penny-shaped cracks relative to their center in a three-layer composite structure is constructed using the boundary integral equations method. The problem for three typical partial cases of multilayered composites (“layer+halfspace with crack”, “layer+layer with crack”, “layer+layer+halfspace with crack”) was solved numerically. The displacement fields on the surface of multilayered composites depend on the elastic characteristics and geometric dimensions of their components, the frequency of displacement of the crack surfaces, the distance from the observation point to the fracture epicenter and the depth of the crack in the composite. A new energy criterion for quantitative estimation of the materials macrofracture types based on the energy parameter of WT of AE signals has been constructed. Based on the new criterion the applied method of identification of fracture types of aluminum, aluminum alloys and their welded joints has been developed. Based on the research results it was shown that the identification of the fracture types using the energy parameters of the WT of the AE signals makes it possible to correctly determine the start of the low-temperature creep cracks. A new method for the identification of the fracture mechanisms of fiber composite materials based on the energy parameters of continuous and discrete WT has been developed. An express method of qualitative ranking of dental polymers and prosthetic constructions based on the parameters of their brittleness using of the energy criterion of continuous WT has been created. The method of estimation of the state of local hydrogen degradation of materials using energy and frequency parameters of WT of MAE signals has been created. The analysis of local features of continuous WT of MAE signals made it possible to obtain information about the processes of restructuring of the domain structure during the ferromagnetic magnetization and to diagnose the state of hydrogen degradation of materials that contacts for a long period of time with the hydrogen-containing environment.