Fracture mechanics analyses of fretting fatigue cracks considering propagation directions

In previous papers we presented estimation methods of fretting fatigue limits using fracture mechanics. Characteristics of fretting fatigue cracks were analyzed using stress intensity factors at the tip of cracks growing from the contact edges. Fretting fatigue limits were estimated by comparing the operating stress intensity factor ranges with the threshold stress intensity factor range of the material. In these previous analyses the directions of fretting cracks are restricted normal to the contact surface. But in the actual fretting fatigue cracks propagate inclined directions. This inclination will relate to the distribution of stress ranges. So in this paper the distributions of stress ranges are analyzed, and then the loci which pass maximum stress range points are plotted. These maximum stress range loci coincided well with the experimental results of fretting crack pass geometry. Finally the stress intensity factor range of these inclined cracks are analyzed and found that the stress intensity factor range of these inclined cracks are about 20% higher than that of normal cracks especially in small crack region less than 0.5mm. From these results we can confirm that the fretting fatigue strength can be estimated accurately by considering the inclination of the cracks.