Fatigue characteristics of joints with holes cold-expanded in a multi-layer stack

Abstract Circular holes are major sources of fatigue crack initiation in aircraft structures. A widely used commercial process to improve the fatigue performance of such design features involves the passage of an oversize mandrel through a hole containing a disposable split sleeve. Fatigue tests were made to evaluate the behaviour of thick aluminium alloy specimens and simple joints with holes cold-expanded either as a single thickness of material or as part of a stack-up between aluminium or steel side plates. Out-of-plane deformations adjacent to the hole which were induced by cold expansion were also measured.