A stress-based approach to analyse fretting fatigue life behaviour of electroless Ni-P coated Al 7075-T6

The purpose of this study is to examine the fretting fatigue performance of Ni-P coated (EN coated) Al 7075-T6 plates. In addition, the effect of two stress-based fretting mechanical parameters (clamping pressure and friction force) on the fretting fatigue performance is evaluated using a finite element stress analysis of the contact region. It was found that the fretting fatigue life of the EN coated specimens tested at high cycle fatigue improved significantly by up to 54±5% and 69±22% when clamped at 2 kN and 5.6 kN, respectively. The harder EN coated surface was found to reduce the contact stress due to the clamping pressure and thus assisted in improving the fretting fatigue life. The EN coated surface was also found to decrease the friction coefficient which assisted in mitigating surface wear damage, thus reducing the probability for fretting cracks to initiate. Furthermore, fractographic analyses revealed the presence of coating defects which were found to be the cause of fatigue failure at low cycle fatigue. These defects could possibly initiate fatigue cracks earlier, thus overruling the fretting phenomenon all together.