Fig.1 The dimensions of the sample and the fretting pad (a) sample;(b) fretting pad (unit: mm)
The fretting fatigue experiment was performed using a MTS809 tension-torsion combined electro-hydraulic servo fatigue testing system. The equivalent cyclic stress(σe) was 400MPa. The contact stress(P) was 50MPa, 150MPa, 250MPa respectively. The loading paths were DP and SP. Two fretting pads were symmetrically fixed to both sides of the sample by screws, and a ring-type load cell was used to clamp the fretting pad to the sample for changing and measuring the contact stress. The diagrams of fretting pad clamping device are shown in Fig. 2. Both axial and torsional directions were cyclically loaded in square waves with a stress amplitude ratio of -1. The axial and torsional frequencies were 3Hz with a phase difference of 90°. The strain change of the sample during the test was measured by the strain sensor. When the measured strain exceeded a certain set value, the experiment was automatically stopped.
In this paper, the micro-morphology, fracture morphology and wear debris composition of the fretting area were analyzed. The morphology observations were conducted by using the FEI Quanta200F scanning electron microscope (SEM) and the composition of the wear debris were detected by using the energy dispersive X-ray spectrometer (EDX).