Fatigue limit prediction of a compression fork-pin coupling of a front motorbike suspension under fully reversed bendino load

The fork-pin compression coupling of the front suspension of a motorbike is very important for the reliability and the safety of the vehicle. The failure of this component is very dangerous because it would make the vehicle unmanageable, and it could cause severe injuries to the driver. Therefore, the designer’s aim is to assure its reliability keeping at the same time the production costs low. One of the most important causes of failure is due to fatigue under fully reversed bending load. In this work, fatigue behaviour of fork-pin couplings, produced by the Paioli Meccanica S.p.a. of Bologna, is analysed, and the results of the tests carried out on an ad-hoc testing system are summarised. The Sines’ method for multiaxial fatigue is applied to predict fatigue life and to estimate the stress concentration factor (Kf) of the coupling.