Fracture mechanical behaviour of laser beam-welded AA2198 butt joints and integral structures

Abstract

Purpose – Composite materials and metallic structures already compete for the next generation of single-aisle aircraft. Despite the good mechanical properties of composite materials metallic structures offer challenging properties and high cost effectiveness via the automation in manufacturing, especially when metallic structures will be welded. In this domain, metallic aircraft structures will require weight savings of approximately 20 per cent to increase the efficiency and reduce the CO2 emission by the same amount. Laser beam welding of high-strength Al-Li alloy AA2198 represents a promising method of providing a breakthrough response to the challenges of lightweight design in aircraft applications. The key factor for the application of laser-welded AA2198 structures is the availability of reliable data for the assessment of their damage tolerance behaviour. The paper aims to discuss these issues. Design/methodology/approach – In the presented research, the mechanical properties concerning the quasi-static tensile and fracture toughness (R-curve) of laser beam-welded AA2198 butt joints are investigated. In the next step, a systematic analysis to clarify the deformation and fracture behaviour of the laser beam-welded AA2198 four-stringer panels is conducted. Findings – AA2198 offers better resistance against fracture than the well-known AA2024 alloy. It is possible to weld AA2198 with good results, and the welds also exhibit a higher fracture resistance than AA2024 base material (BM). Welded AA2198 four-stringer panels exhibit a residual strength behaviour superior to that of the flat BM panel. Originality/value – The present study is undertaken on the third-generation airframe-quality Al-Li alloy AA2198 with the main emphasis to investigate the mechanical fracture behaviour of AA2198 BMs, laser beam-welded joints and laser beam-welded integral structures. Studies investigating the damage tolerance of welded integral structures of Al-Li alloys are scarce.

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

“…For comparison, the fatigue crack surface in the AA2198 alloy of the Al–Mg–Cu–Li system had the dimpled structure 10 . Also, the dimpled structure was on the fracture surfaces of the laser welds of this alloy 37 …”

“…Enz et al 36 have studied the fatigue crack behaviour and the fracture toughness of the laser welds of the advanced PA734 alloy (the Al–Zn system). Kashaev et al 37,38 have investigated resistance to fatigue and the crack propagation in the laser welds of the 2198 Al–Cu–Li alloy. It has been found that the fatigue strength of the laser welds has been almost 25% lower (but 1.7 times higher for the T‐joint) than that of the base metal.…”