1984 Volume 1984 Issue 29 Pages 38-47
One of the factors decreasing a fatigue life of leaf springs is fretting fatigue caused by contact between leafs and cyclic bending stress.
In the present study, the conventional fretting fatigue test of small spring steel specimens with the bridges of the same material and also with spacer material (Delrin) has been made by using a general fatigue test machine. The results are as follows:
(1) The plain fatigue limit and the fretting fatigue limit of SUP 9 steel are respectively 620Mpa and 320Mpa; the fretting remarkably decreases a fatigue limit and a fatigue life.
(2) The propagation process of fretting fatigue cracks is characterized by the debrislike crack which initiates and propagates under an influence of large plastic deformation, by the first stage crack which is greatly affected by stress concentration by the contact by the intermediate stage crack corresponding to a transition stage between the first stage crack and the second stage crack with a weakened stress concentration, and by the second stage crack which comes out of a stress concentration area.
(3) In the case of the bridge material is identical with the spring material, the friction coefficient increases with a relative slip amplitude and tends to saturate at the value of 0.6.
(4) Use of Delrin as a spacer between bridge and specimen remarkably improves the fretting fatigue life. Consequently, the life approximately equals the plain fatigue life.
