“…where KIC is the fracture toughness and the shape factor ƒÕ is given by an integral equation of z as follows (14) On the other hand, the fracture strength under a gentle stress distribution can be estimated from the mean length c of surface cracks, by the following formula (15) where c can be estimated from both the strength stan dardized for a volume of 1mm3 and the stress distribution. 3.1.2 Delayed fracture strength As for the delayed fracture strength, in the case of cyclic fatigue, strength can be estimated as shown in Eq.…”