Vasyl'yev O. Fracture Micromechanisms and Fracture Toughness at a Brittle-to-Ductile Transition.

The dissertation is devoted to investigation of influence of temperature on fracture micromechanisms and mechanical behavior of metallic and ceramic materials at their transition from a brittle state into a ductile one. The influences of dislocation structure, state of interphases, porosity on a change of fracture micromechanisms and toughness were analyzed. The phenomenological approaches describing the temperature influence on fracture toughness of materials under separate fracture micromechanisms were found also. For the fracture micromechanisms changing along a crack growth the criterion that unites yield strength and crack length forerunning cleavage was established. The mechanisms of cleavage with relaxation and pores nucleation in one phase materials were proposed. The effect of toughening of brittle materials by pores was found and analyzed.