Selivonchyk T. Acoustik emission estimation of hydrogen-corrosive cracking of steels

The thesis for the Candidate's Degree in Technical Sciences on speciality 01.02.04 - Mechanics of Deformable Solids. - Lutsk State Technical University, Lutsk; Karpenko Physico-Mechanical Institute National Academy of Sciences of Ukraine, Lviv, 2007. The thesis is dedicated to development of theoretical and experimental grounds for estimation of hydrogen-corrosive fracture of structural steels operating under action of corresponding environment and simultaneous mechanical loading. The object of investigation is the processes of formation and development of micro- and macrocracks in structural steels caused by specified physical and chemical factors as well as the elastic dynamic fields, which appear in this case in a solid. For effective detection of these processes, scientifically validated bases of acoustic emission diagnostics of crack-like defects from fracture mechanics viewpoint are developed in the thesis. They are grounded on an acoustic emission model for estimation of formation and subcritical growth of corrosive and hydrogen induced cracks in metallic bodies, which is based on physical and chemical processes occurring in a metal (including a crack tip) during the electrolytic hydrogen transfer or hydrogenation from a gas phase and takes into account a dominant action of hydrogen embrittlement mechanism. It is shown that the early stages of formation and development of crack-like defects of corrosive-hydrogen origination are accompanied by the discrete signals of acoustic emission allowing determining effectively the change in mechanisms of hydrogen or corrosive cracking of steels, a degree of their bulk damaging. Keywords: crack, hydrogen-corrosive cracking, acoustic emission, thresh-old value of stress intensity factor, heat cycling, bulk damaging.