Design improvement of clamped joints in front motorbike suspension based on FEM analysis

This paper aims at defining the tensile state in shaft–hub joints realized between the clamp (hub) located at the end of the suspension leg of the front motorbike suspensions and the wheel pin (shaft). The clamp under investigation has an asymmetric shape and a slot useful for the assembly operation: one or two bolts (depending on the vehicle performances) are tightened in order to generate the coupling pressure which is necessary to lock the pin. The fundamental objective of this work is to define a mathematical model to calculate the maximum stress generated on the clamp by the tightening forces. The mathematical model was defined by comparing the De Saint Venant theoretical bending stress (the maximum stress on the clamp) with several FEM results. Thus a sort of theoretical stress concentration factor was calculated in function of the dimension and of the location of the spot facings of the clamp. The new developed model is useful to optimize and to verify, in a very short time, this type of coupling without performing any complex numerical analysis. The validity of the model has been demonstrated by several FEM results and by some experimental tests carried out on a high performance vehicle.