Frictional changes during repeated tightening of zinc plated threaded fasteners

Experimental and numerical analysis of clamped joints in front motorbike suspensions

“…Lubrication (A=1) always increases the preloading forces, while the tightening replicas (D=1) progressively decrease the preloading forces, mainly in case of dry surfaces, as demonstrated also in Ref. [10]. Secondly the outcomes of the present analysis have been applied to an unlubricated, spray-painted, cast aluminium wheel clamp, realized by the Paioli Meccanica S.p.A. of Bologna (IT), which produces front motorbike suspensions.…”

A contribution to the selection and calculation of screws in high duty bolted joints

“…As well highlighted for steel connections in dry conditions by Eccles et al [3], the thread coefficient of friction can increase up to the value of 0.78 and its discrepancy from the first to the tenth tightening operation is equal to 55%. Also in the case of steel-aluminium connections in dry conditions the increase of the thread coefficient of friction is demonstrated to be significant (þ50%) from the first to the sixth tightening operation (Croccolo et al [4]) up to the value of 0.39.…”

“…From the other side, in many cases, the important issue of friction is experimentally neglected and/or insufficient information is given about the actual value of the coefficients of friction. In mechanical joint values between 0.1 and 0.2 are typically chosen for all materials in contact (steel, aluminium, titanium, CFRP composite) and, furthermore, these values are often considered as constant throughout several analyses, without taking into account, as an example, (i) the evolution of the coefficient of friction from its initial value to a peak value due to the presence of wear produced by several tightening and loosening operation, as well demonstrated by some recent works (see Eccles et al [3] and Croccolo et al [4]); (ii) the effect of coatings thickness on the coefficient of friction (see Nassar et al [5]); (iii) the effect of tightening speed on the coefficient of friction (see Nassar et al [6]). …”

Experimental and numerical studies of bolted joints subjected to axial excitation

“…Accordingly, the follow-up experiments are conducted on those bolt specimens having the following condition: the preload range is between 13.5 kN and 14.5 kN when a tightening torque of 30 Nm is applied. The change of preload during repeated tightening of electro-zinc plated joints has been studied by a number of researchers [26]. To investigate the effect of the number of tightening on preload, five bolted joints are tested, and each one is loaded in 12 repeated cycles of tightening and loosening.…”