EFFECT OF SLIP AMPLITUDE ON FRETTING FATIGUE

The effect of slip amplitude on the fretting fatigue behaviour of several alloy steels was investigated. Fretting fatigue experiments were conducted on flat fretting junctions under axial tension at a stress ratio of 0.1, with fretting surfaces of the same material. At a normal pressure of 24.5 MPa, the fretting fatigue lives of 2Cr13 and 35CrMo (quenched, tempered for 2 h and air cooled) show a minimum value at a slip amplitude of about 20-mu-m. At a normal pressure of 49 MPa, the fretting fatigue lives of 35CrMo (quenched, tempered for 2 h and air cooled) steel decrease with increasing slip amplitude. In the range of elastic slip, the variations of tangential stress and alternating stress are in phase, i.e. the fretted area experiences proportional loading. In the range of macro-slip, the variations of tangential stress and alternating stress are out of phase owing to the occurrence of stick-slip movement, so the fretted area experiences non-proportional loading. When the normal pressure is 49 MPa, the fretted areas show ripple features at slip amplitudes of 10-mu-m. With increasing slip amplitude, the depth of wear scars increases and wear damage becomes more severe. At slip amplitudes of above 45-mu-m, adhesive transfer occurs between the fretting-damaged surfaces of 2Cr13 specimens, while abrasive ploughing takes place between the fretting-damaged surfaces of 35CrMo and 60Si2Mn specimens.