Sub-surface damage investigation by high frequency ultrasonic echography on 100Cr6 bearing steel

This paper presents an original ultrasonic technique devoted to the early detection of sub-surface fatigue cracks in 100Cr6 bearing steels. Echographic experiments were carried out during interrupted rolling contact fatigue tests. Crack initiation and crack propagation stages were both investigated. Quantitative measurements of sub-surface crack position, depth and angle with respect to the bearing surface are presented. Experimental results are analysed and discussed in relation to rolling contact fatigue theories. Contrary to what is generally accepted the presented results show that the crack propagation stage could represent an important part of bearing life.