Fatigue crack propagation into the residual stress field along and perpendicular to laser beam butt‐weld in aluminium alloy AA6056

Abstract

A B S T R A C T Laser beam butt welds in Al-alloys are very narrow and are accompanied by steep residual stress gradients. In such a case, how the initial crack orientation and the distance of the notch tip relative to the weld affect fatigue crack propagation has not been investigated. Therefore, this investigation was undertaken with two different crack orientations: along the mid-weld and perpendicular to the weld. Fatigue crack propagation 'along the midweld' was found to be faster in middle crack tension specimens than in compact tension specimens. For the crack orientation 'perpendicular to the weld', the relative distance between the notch tip and the weld was varied using compact tension specimens to generate either tensile or compressive residual stresses near the notch tip. When tensile residual stresses were generated near the notch tip, fatigue crack propagation was found to be faster than that in the base material, irrespective of the difference in the initial residual stress level and whether the crack propagated along the mid-weld or perpendicular to the weld. In contrast, when compressive weld residual stresses were generated near the notch tip, fatigue crack arrest, slow crack propagation, multiple crack branching and out of plane deviation occurred. The results are discussed by considering the superposition principle and possible practical implications are mentioned.

A modified loading method for separating the effect of residual stress on fatigue crack growth rate of welded joints

“…In these methods, FCGR data obtained by laboratory specimen tests are adopted for the life prediction of components based on the theory of linear elastic fracture mechanics (LEFM). Significant amount of research has been conducted in the past 20 years to understand the crack growth behaviours in welded joints . Some works indicate that changes in microstructure and hardness play a major role in the fusion zone or weld nugget and residual stress plays a major role outside these zones .…”

“…Significant amount of research has been conducted in the past 20 years to understand the crack growth behaviours in welded joints. [4][5][6][7][8][9][10][11][12][13] Some works indicate that changes in microstructure and hardness play a major role in the fusion zone or weld nugget and residual stress plays a major role outside these zones. 10,13 Therefore, it is a common practice that only the primary influential factor is considered in crack growth analysis of welds; e.g.…”

Simulated investigation on the deformation of double laser beam bilateral and simultaneous welding for aircraft panel

“…A comparison between the experimental and simulation results shows a good agreement. In 2012, Vaidya et al 10 studied the effect of crack orientation and the distance between the notch tip and the weld on fatigue crack propagation in a laser beam welded butt joint of the airframe Al-alloy AA6056. Fatigue crack propagation "along the midweld" was found to be faster in middle crack tension specimens than in compact tension specimens.…”

Fatigue crack growth property of laser beam welded 6156 aluminium alloy

“…As a result, much research was conducted on the fatigue property of aluminium alloy welds. Vaidya et al . investigated the fatigue crack growth (FCG) in laser beam welded aluminium alloy AA6056.…”

“…As a result, much research was conducted on the fatigue property of aluminium alloy welds. Vaidya et al 3 investigated the fatigue crack growth (FCG) in laser beam welded aluminium alloy AA6056. The result showed that FCG in weld was faster than that in the base material when residual stress near the notch tip of the specimens was tensile.…”