Prediction Method for the Surface Damage in Splined Couplings

The primary purpose of my PhD thesis was to develop design criteria and to verify procedures about fretting wear, that are applicable to crowned spline couplings of a power transmission system of the aeroengines. Fretting is a very complex phenomenon being influenced by many factors, the most important being the presence or absence of lubrication, the load distribution (contact pressure) and the sliding between the bodies. Therefore, the study of fretting needs a deep knowledge of these three main aspects. The first aspect of the problem was based on models and experimental tests considering specify specimens (crowned spline couplings) and imposed movements, so as to uniquely identify the working conditions (load and sliding), in order to facilitate the comparison between the experimental tests and the analytical models. The analytical models have been validated with numerical simulations and by comparison with experimental data, that have been obtained by means of a dedicated test bench that has been designed and built. Thanks to the test rig was possible to determinate the real contact pressure of two engaging teeth; in fact, it is one of the most important parameters affecting the fretting phenomenon, but it is very difficult to evaluate in a quantitative way, especially when considering components with complex geometries. The second phase of this thesis was the development of a predictive model for crowned splined couplings. This model is based on the Ruiz first parameter. The aim of my thesis is to demonstrate how this parameter may be correctly applied to a complex component as the crowned spline coupling, taking into account experimental and FEM validations.