Normalization of the stress concentrations at the rounded edges of a shaft-hub interference fit: extension to the case of a hollow shaft

This work addresses the issue of stress concentrations at the rounded edges of shaft hub interference fits. An infinitely long shaft, press fitted into a hollow hub with bore rounded edges is examined. Limited to interference fits involving a solid shaft, Strozzi and colleagues introduced a normalizing parameter, which accounts for the combined effects on the stress concentrations of the fillet radius, the shaft external radius and the interference level. The aim of this work is to extend the field of application of the said normalizing parameter, to the case of interference fits involving a hollow shaft. By means of finite element analysis, run-on geometries with different hub and shaft aspect ratios (ratio between internal and external diameters), charts for stress concentration factors as functions of the normalizing parameter were drawn. Appropriate functions are proposed, which allow obtaining the stress concentration factors valid for the case of hollow shaft, starting from the stress concentration factors valid for the case of solid shaft. The stress concentration factors predicted by means of this novel method are then compared with those provided by finite element analysis. Stress concentration factors in the presence of hollow shafts are demonstrated to be always higher than those evaluated for solid shafts. Finally, a numerical example illustrates the typical workflow to be followed in order to calculate the stress concentration factor for a defined joint.