Failure analysis of hybrid Aluminium-to-Steel welded joints under Uniaxial/Multiaxial fatigue loading

This paper conducts a comprehensive crack path analysis of hybrid aluminium-to-steel welded joints fabricated using EWM coldArc® welding technology, focusing on uniaxial/multiaxial fatigue loading conditions. Following fatigue failure of the specimens under investigation, detailed examination of the crack initiation and propagation phases was performed, with particular attention to the crucial role of crack initiation in failure under multiaxial fatigue loading. Through crack path analysis, four primary crack initiation locations were identified across uniaxial, pure torsional, and biaxial fatigue loading scenarios, i.e., weld toe, weld start/stop position, weld itself, and the aluminium heat-affected zone (HAZ). Results indicate that the weld toe region is the predominant site of crack initiation, especially under uniaxial and biaxial constant amplitude fatigue loading. However, under specific loading conditions, crack initiation shifts towards the weld start/stop position, possibly due to localised stress concentration effects induced by weld geometry. Remarkably, cracks originating from the weld itself were relatively uncommon, underscoring the effectiveness of EWM cold arc technology in welding thin dissimilar aluminium-to-steel connections. Additionally, crack plane orientation analysis revealed shear stresses as governing crack initiation and normal stresses as controlling crack propagation. Experimental and theoretical crack plane orientations demonstrated close correlation, with crack initiation angle error mainly within ± 20 % of the maximum shear stress plane angle and crack propagation angle error mainly within ± 30 % of the maximum normal stress angle. This study offers valuable insights into the behaviour of such joints under multiaxial fatigue loading, with potential implications for enhancing their structural integrity and reliability in engineering applications.