Peculiarities of Short Fatigue Cracks Growth from a Blind Hole in Specimens Made of Steel 45. Part 1. Experimental Results

Results of in situ measurements of short fatigue cracks growth from a blind hole of diameter 0.6 and 1.6 mm in specimens from steel 45 during cyclic loading at different cycle asymmetry are presented. Studies of fatigue fracture specimens have shown that a characteristic feature of their fatigue failure is the fact that the fatigue crack, which was initiated from the surface of the hole, can originate either on the surface of the specimen or under the surface at a certain depth. Typically, one or two of these cores are at a depth of approximately 0.3–0.5 mm from the specimen surface. This agrees well with the results of finite-element elastic analysis of the stress-strain state in the vicinity of such a hole, which, in turn, show the presence of a maximum of local stresses on the surface of the hole at a depth of 0.3 mm from the surface of the specimen. The number of loading cycles during the growth of short fatigue crack up to 1.5 mm can exceed the number of cycles by the time of its initiation from the hole up to five times. The experimental results obtained will be used to check the validity of the developed model describing the kinetics of short fatigue crack growth from an obtuse stress concentrator.