An experimental investigation of the bolt clamping force and friction effect on the fatigue behavior of aluminum alloy 2024-T3 double shear lap joint

In this article, the effect of bolt clamping force on the fatigue life of bolted double shear lap joints was investigated. To do so, fatigue tests were carried out on the bolt clamped double shear lap joint specimens made of aluminum alloy 2024-T3. These fatigue tests were conducted with applied torques of 0.25, 2 and 4 N m at different cyclic longitudinal load levels in un-lubricated and lubricated states. From these tests the stress–life (S–N) data for different clamping forces for un-lubricated and lubricated states were obtained. The results show that clamping force increases fatigue life compared to clearance fit specimens. In general, at higher tightening torque higher fatigue lives were achieved, however, below a certain load level the life improvement was discontinued because of fretting phenomenon. Also lubricating the parts of the specimens reduces the advantage of clamping force or torque tightening.

► Increasing the tightening torque or clamping force on the double shear lap joints, leads to improved fatigue life.
► In un-lubricated joints, the crack initiation locations and the fatigue damage process dependent on the tightening torque and load level.
► In un-lubricated joints, a certain lower limit for cyclic stress was found below which the fatigue life did not increase.
► Lubrication of the joints between the plates diminished the advantages gained by torque tightening and reduces the fatigue life.