Fatigue Crack Growth in Aluminum Lithium Riveted Lap Joints

Abstract

Fatigue crack initiation sites and the subsequent fatigue crack growth rate in riveted lap joints made of 2198-T8 Al-Li alloy were investigated through fractographic examinations. Two crack initiation sites were identified: 1) near the rivet holes and 2) at multiple sites along the faying surface. Fatigue crack tunneling was developed during the fatigue crack progression in all specimens, yielding final ductile fracture during the catastrophic fracture of the specimens. The fracture surface morphology exhibited shallow fatigue striations. The second phase constituents did not affect the fracture surface morphology. Multiple micro cracks and long interlaminar cracks occurred. Stereo (3-D) fracture surface morphologies indicate a meandering fracture surface, with local fatigue crack progressing along multiple directions and at different rates. Average crack growth rate (da/dN) along the width, thickness of the specimens and the feather lines were recorded, showing the effect of grain direction, alloying, and stress level on the fatigue crack growth behavior. The number of cycles to failure was also affected by the grain direction.