Effect of aircraft rivet installation process and production variables on residual stress, clamping force and fatigue behaviour of thin sheet riveted lap joints

Abstract

This paper presents research on the effect of riveting process parameters on residual stresses, clamping stresses and clamping force in thin sheet riveted joints, as well as the fractographic observations of riveted lap joints. The following variables were considered in the study: riveting force, sheet thickness, sheet material and rivet material, rivet hole tolerance and rivet diameter tolerance. The research was carried out for 2024-T3 aluminium alloy sheets with a thickness of 1.6 mm and 1 mm and universal head MS20470-AD (2117-T4 aluminium alloy) rivets with shank diameters of 3.96 mm and 3.18 mm. The results obtained from finite element (FE) analyses were linked with observations of the fatigue crack initiation site, crack path and fretting phenomenon in real three-row riveted lap joints. The results show that the crack initiation site depends on the zone of compressive residual hoop stress in the sheets and the clamping force. The location of the crack path can be related to the location of the largest favourable residual normal stress in the sheets (acting in the direction of the joint loading), the value of the clamping force and the range of the residual clamping stress zone. Large fretting wear regions on the contact surface of sheets for joints with more severely squeezed rivets are associated with a larger zone and a higher value of clamping stresses, which during fatigue loading through friction intensify the harmful phenomenon of fretting.