Fatigue properties and failure characterisation of self-piercing riveted 6111 aluminium sheet joints

Abstract

Aluminium has been long considered as an alternative material for steel in the automobile industry. However, welding of aluminium is more difficult and prone to defects compared with steel. Therefore other methods of joining aluminium sheets are being investigated. In the present investigation, the fatigue properties of self-piercing riveted joints in 6111 aluminium alloy sheets has been studied using tensile shear and coach peel type specimens. Different thickness combinations of aluminium sheet joints and different load ratio R were also investigated in the fatigue tests. Fatigue crack initiation and growth were observed and analysed. It has been found that the maximum fatigue load increases with increasing sheet thickness in both tensile shear and coach peel specimens, but this increase is smaller for high fatigue cycles. With the same maximum fatigue load, specimens under load ratio of R=0·3 have a longer fatigue life than that of specimens under R = 0·1. In most of the cases (>90%), specimens failed in the upper sheet (with the rivet head) during fatigue loading in the case of equal thickness combination and thick upper sheet combination, for both tensile shear and coach peel specimens. As for different thickness combination rivet joints, the thinner sheets are usually the places where failure occurs whichever it is the upper sheet or lower sheet in the combination.