2019 年 2019 巻 64 号 p. 39-44
When the crack length is larger than a certain size, the maximum stress intensity factor (K max) is used to explain the occurrence condition of brittle crack, and the limit condition of hydrogen assisted and stress corrosion crack propagation. Also, the fatigue crack can be explained by the stress intensity factor range (ΔK ). However, since the stress intensity factor deals with only linear elastic body, it is necessary for nonlinear range of crack tip to be small enough. It is known that in the case where this condition is not satisfied, the proposition shall be called the micro crack problem, and it is known that the crack size is smaller than the threshold value of the long crack. The purpose of this study is to unify the micro-cracking problems of various fracture modes. The crack length which is dependent on the threshold value can be explained by one concept considering the fact that the nonlinear region size of the crack tip is constant regardless of the crack length. In this paper, unified equation for micro crack problem to four kinds of cracks was proposed.
