In-field experimental stress analysis in the elastic and plastic fields on motorbike handlebar clamped joints

In a motorbike different types of shaft-hub couplings are used to join the handlebar to the suspension legs of the front wheel. Some papers were recently published with reference to the experimental determination of the starting friction coefficient of the fork-steering pin compression coupling [1], to the development of FEM assisted design strategies for the fork-pin [2], fork-leg [3] and leg-pin couplings [4]. On the other hand, another important joint, the clamping between the fork and the handlebar has been less investigated. The clamp (aluminium alloy, EN AW-6082, Fig. 1 A, B) consists of two parts, the lower one (connected to the fork by two screws), interfacing with the lower part of the handlebar, and the upper one, shaped to lodge the upper part of the handlebar. The assembly procedure consists in the insertion of the handlebar between the two clamp parts and in screw tightening, according to a particular procedure. Screws indicated as 1 and 2 are tightened first to create contact between mating surfaces of the two clamp parts, screws 3 and 4 are then applied to complete clamp closing. No information are available about stress trends during screw tightening, and about non symmetric effects in stress distribution, depending on the tightening order of screws 3 and 4. Moreover, no studies are available on the effects of yield strength overcome over a small region, and in case, on the safety of disassembling and reassembling the same clamp during maintenance procedures. Consequently, the main objects of this work were the followings: • Experimental determination of stress trends in the elastic field: discussion on non symmetric effects depending on tightening sequence. • Experimental stress analysis in the elasto-plastic field and discussion on the safety of the coupling, even in case of disassembling and reassembling of the same parts.