Considerations of the effect of residual stresses on fatigue of welded aluminium alloy structures

A new class of large, high-speed seagoing ferry-boat is under development for service around the world. The ships, which are built entirely of aluminium-alloy plate and stiffeners, show a propensity for fatigue cracking of the welded structure. Cracks may occur in both the hulls and the superstructure early in their 20-year service life. Early appearance of fatigue cracks is shown to result from the combined stress and strain fields set up in weld zones by the static residual stresses and cyclic loads, beyond the effects of weld and detail geometry. A numerical example demonstrates that conventional methods of fatigue analysis overestimate the lifetime of the welded aluminium structure, while damage tolerance analysis based on fracture mechanics leads to improved prediction.