Prediction of fretting wear in spline couplings

The original contribution of this work is modeling of fretting wear in aero-engine spline couplings widely used in aero-industry to transfer power and torque. Their safe operation is very critical with respect to flight safety. They consist of two components namely hub and shaft. As they are of light weight, usually it is difficult to realize a perfect alignment. To allow for misalignment, their teeth are designed to be of crowned shape. The crowing allows a degree of misalignment without concentration of stresses which is otherwise inevitable if a misalignment is introduced in case of straight teeth. However, crowing results in another problem of fretting wear and fretting fatigue owing to kinematic constraints imposed as a result of misalignment. The focus of this work is development of mathematical models for prediction of fretting wear and not fretting fatigue. The spline couplings under consideration are industrial scale and made up of nitrogen hardened 42CrMo4. The aero industry requires a reliable method to model and predict fretting wear to be able to optimize the design of spline coupling and reduce the maintenance costs. Wear tests on crowned spline couplings on a dedicated test bench have been conducted and analyzed. Empirical, artificial neural network based and analytical models have been de- veloped to analyse, predict and formulate fretting wear in spline couplings. The empirical and artificial neural netwrok based models are specific to the given case of spline couplings and tribological conditions. However, the analytical model developed has been found to be quite general. Incremental fretting wear formulation both in terms of wear volume and wear depth has been realized. Some novel findings regarding effect of roughness parameters in conjunction with applied torque and misalignment angles with respect to fretting wear are also reported. It has been observed that the evolution of wear depth accelerates with increased applied torque or misalignment angle. Changes in roughness parameters are also found to be increasing with torque and misalignment angle in most of the cases. Preliminary tests for frequency effects on fretting wear have also been conducted.