Development of short surface fatigue cracks in 20Kh13 steel and VT9 alloy

Abstract

1. It has been established that in the 20Kh13 steel and VT9 alloy microcracks are initiated at very early stages of cyclic loading and grow at stress intensity factor values which are below the threshold values. After initiation the short fatigue cracks propagate at a relatively high rate; later, however, their growth rapidly decreases. Some of them become arrested, while others, of different length, depending on the yield stress in the surface layer and the crack resistance threshold, are temporarily retarded; later however, their growth increases. 2. It is shown that the physical reason for the initiation and acceleration of the growth rate of short fatigue cracks is local plastic strain formed in the weakened surface layer at stresses substantially smaller than the macroscopic yield stress. 3. The use of a two-parameter criterion, which includes the range of the nominal plastic strain in the surface volume of the metal and the stress intensity factor, makes possible a description of the process of the development of short fatigue cracks.