Study on rotational fretting wear under a ball-on-concave contact configuration

A new rotational fretting wear test rig was improved to simulate the different contact configurations of ball-on-concave (BOC) and ball-on-flat (BOF). The rotational fretting tests of one medium carbon steel (LZ50 steel) concave specimen with curvature radius of 25 mm against AISI 52100 bearing-steel ball with radius of 20 mm had been carried out under varied normal loads (Fn) from 6.425 N to 50 N and angular displacement amplitudes (θ) from 0.125° to 1.5°. In order to understand the mechanisms of rotational fretting under different contact configurations, the tests under the same maximum contact stress and normal load had been done, respectively. Under the same test conditions, the contact stiffness, friction coefficient and friction dissipation energy, wear scar size for the two contact configurations had been discussed in detail. The experimental results showed that the fretting running behaviors of the BOC contact were quite different from that of the BOF contact due to the different contact stiffness and debris behaviors. However, for both the contact configurations the same wear mechanisms had been observed in the partial slip regime and slip regime, respectively. The damage of the BOC contact was slighter than that of the BOF contact under the same normal load, while a contrary result under the same contact stress.