Effect of overload on fatigue crack retardation of aerospace Al-alloy laser welds using crack-tip plasticity analysis

Abstract

Investigations on fatigue crack growth retardation due to single tensile and periodic multiple over load in strength undermatched laser beam welded 3.2 mm thick aerospace grade aluminium alloy 2139T8 sheets are conducted. The effect of overload on the fatigue crack propagation behaviours of the homogenous base metal and welded panels (200 mm wide, centre cracked) was compared using experimental and FE analysis methods. The effective crack tip plasticity has been determined in homogeneous M(T) specimens using Irwin's method and in both homogeneous and laser welded specimen by calculating crack tip plastic strain using FE analysis for single tensile overload. The crack retardation due to the overload in welded specimens are described by the Wheeler Model. The crack tip plastic zone size in the welded specimen was determined by FE analysis using maximum plastic zone extension at the mid sheet thickness. The results show that the Wheeler Model can be implemented to the highly heterogeneous undermatched weld to describe the crack retardation in fatigue following single tensile overload. Fatigue crack growth retardation due to single overload is found to be larger than the base metal. However, after periodic multiple overload, shorter crack retardation has occurred for undermatched welds than the base metal.

Fatigue crack growth modelling based on CTOD for the 7050‐T6 alloy

“…Third, da/dN was obtained experimentally in M(T) specimens for different stress ratios. 70 3 Plane stress Daneshpour et al 71 M(T) 3.2 2139-T8 Plane stress Feng et al 72 Round CT 3.6 1070 steel Plane stress Lopez-Crespo et al 73 CT 3 316L stainless steel Zheng et al 74 CT Plane stress More plane strain Plane strain Fourth, the plastic CTOD was determined numerically using the FEM. The numerical model replicated the experimental procedure used to determine da/dN in terms of geometry, material properties and loading.…”

In Situ Experiments with Synchrotron High‐Energy X‐Rays and Neutrons

“…The occurrence of an overload (high‐low load sequence) can lead to strong fatigue crack growth retardation 7. To provide a deeper understanding of the mechanisms of retardation of the fatigue crack tip due to an overload, stress fields were determined in specimens containing a fatigue crack under external load.…”

Effect of temperature on the fracture behaviour of heat‐treated Al–Cu–Li alloy laser welds under low‐cycle fatigue loading

“…The fatigue strength of the welds was less than that of the 2024 aluminium alloy plates with holes in them. Daneshpour et al 32 have shown the effect of single and multiple tensile loads on the fatigue crack propagation in the 2139 aluminium alloy plates and their laser welds. Later, the same authors have investigated crack retardation mechanisms during the fatigue tests of the AA6056‐T6 alloy and its welds 33 .…”