In spline couplings, torque is theoretically transmitted by all teeth, supporting the same loading level. In practice, due to manufacturing and mounting errors, not all teeth transmit the same amount of torque and as a result an overloading condition may occur. In traditional design practice, this uneven load sharing between teeth is often neglected or taken into account by means of a simplified approach. In this article, a theoretical method, non-finite element method based, is developed in order to determine both exact number of engaging teeth and shared forces in involute spline couplings with parallel offset errors. The described process consists of an iterative procedure, in which algorithm is divided into three main modules: the first one aims to calculate geometrical parameters, the second one analytically determines both deformation and stiffness of teeth and the third one calculates the actual number of engaging teeth and the shared load. The algorithm has been benchmarked against finite element method results, showing a very good agreement.

This paper presents a novel spline couplings test rig. Its peculiarity is to allow angular misalignments between hub and shaft in order to investigate the behavior of spline couplings in real working conditions, in particular, to investigate fretting wear phenomena. A preliminary experimental activity has been carried out showing a correct behavior of the test rig from all points of view. A preliminary approximated estimation of the test articles fretting wear has been obtained by means of two experimental parameters: R_a roughness and the amount of angular rotation clearance. An estimation of the Ruiz parameter has also been obtained.

Spline couplings used in aerospace applications, supporting very high specific power, need an accurate design in order to reduce the weight and to avoid failure mechanisms as fretting fatigue. One of the influence parameters of this kind of phenomena is the pressure distribution on the teeth surface. In this article, the pressure distribution on spline coupling teeth has been investigated by means of analytical approaches and experimental techniques. In particular, the contact pressure distribution between the teeth in axial direction, obtained by means of analytical models available in literature, has been compared with both experimental data and finite element method models. The experimental pressure distribution has been obtained thanks to a special film, capable of changing colour intensity with the pressure variation, and a dedicated software relating the colour intensity to the pressure level. A dedicated workbench has been set-up and a special spline shaft has been created in order to well fit the pressure measurements.