There have been many theoretical investigations for brittle fracture initiation. Among them, a theory of crack opening displacement using the model of dislocations, developed by Bilby, Cottrell, Swinden, has recently appeared before the footlight. The theory would be especially to be available even for the phenomena of the initiation of the brittle fracture initiation at considerably high stress level such as near the general yield condition.
The authors tried to extend the theory of the crack opening displacement to the problems for arbitrarily distributed stress field and to apply to analysis for “Longitudinally Welded I-Type Test” which has structural discontinuities and ununiform welding residual stresses. The calculation results are in good agreement with the experimental ones.
In connection with calculation, further, the authors examined the brittle fracture initiation in the steel plate with deep edge notches, of which tip is at the boundary of plate thickness discontinuity, and proposed by some theoretical consideration the effective crack length for brittle fracture initiation into the different thickness plate.