TIGHTENING TESTS AND FRICTION COEFFICIENTS DEFINITION IN THE STEERING SHAFT OF FRONT MOTORBIKE SUSPENSION

The aim of this work is to define the maximum stress generated by the coupling of axial symmetric and continuous shafts press-fitted into axial symmetric hubs. The theoretical stresses given by the well-known formulas of the thick-walled cylinders theory are constant on the whole coupling surface, but if the shaft extends beyond the hub there is a stress concentration factor on the boundary zone. This occurrence is confirmed by finite element analyses performed by the authors on several different shaft hub couplings. The analyzed couplings have the shaft extended beyond the hub, the shafts press-fitted into the hubs and both shafts and hubs loaded by an external and by an internal pressure. The stress concentration factors have been calculated in this work and their expressions have been derived as a function of some tensile and geometrical parameters. By combining the thick-walled cylinders theory with the proposed formulas it is possible to evaluate the maximum stress located at the end of the hub without performing any numerical investigations.