Fatigue Behaviour of Friction Stir Welded Steel Joints

Abstract

The development and application of friction stir welding (FSW) technology in steel structures in the shipbuilding industry provide an effective tool of achieving superior joint integrity especially where reliability and damage tolerance are of major concerns. Since the shipbuilding components are inevitably subjected to dynamic or cyclic stresses in services, the fatigue properties of the friction stir welded joints must be properly evaluated to ensure the safety and longevity. This research intends to fulfill a clear knowledge gap that exists nowadays and, as such, it is dedicated to the study of welded steel shipbuilding joints in GL-A36 steel, with 4 mm thick. The fatigue resistance of base material and four plates in as-welded condition (using several different parameters, tools and pre-welding conditions) were investigated. The joints culminate globally with defect-free welds, from which tensile, microhardness, and fatigue analyses were performed. The fatigue tests were carried out with a constant amplitude loading, a stress ratio of R=0.1 and frequency between 100 and 120 Hz. The experimental results show the quality of the welding process applied to steel GL-A36 which is reflected in the mechanical properties of joints tested.

Microstructure and fatigue properties of friction stir welded high-strength steel plates

“…A36-GL [21] and DH36 [22] steels welded by FSW reached fatigue strength values significantly above design recommendations [1,2]. A similar effect was observed for high-quality fusion welds [23,24].…”

Fatigue and bending behaviour of friction stir welded DH36 steel

“…5d) was observed and this has been found to negatively affect the fatigue performance [7,[9][10][11]. The tip of the notch has a large stress concentration factor associated with it which can initiate cracks.…”

“…The same authors [8] indicated that the weld's mechanical properties are not substantially affected by the heterogeneity of the microstructure. Fatigue performance of defect free FSW GL-AH36 shipbuilding steel was found to be similar and in some cases better than the base metal [9]. These welds were deemed to show very good mechanical properties.…”

Friction Stir Welding of Shipbuilding Steel with Primer

“…More recently, Avila et al [7], analysed the fracture toughness of API5LX80 steel in butt joints welded in two passes by FSW till -20 degrees with good results for pipeline applications, For shipbuilding applications McPerson et al [8] compared fatigue behaviour of submerged arc and friction stir weld in DH36 concluding on am improved performance of the later, Azevedo et al [9] analysed fatigue behaviour in friction stir welded 4mm thick GL-A 36 steel, while Pandley and Gupta [10] studied fatigue growth of mild steel plate welded by friction stir welding and concluded that the growth rate in the welded material is lower than in the base material. Nathan et al [11] confirmed the superior mechanical properties in naval grade high strength alloy (HSLA) when welded with FSW in comparision with arc welding as GMA and SMA.…”

“…The experimental approach consisted in performing welds in 4mm steel plates with using a welding procedure which leads to sound welds, Azevedo [12], and conduct a detailed analysis of the welds obtained, based in metallographic examination, analysis of the chemical composition of the different weld zones using EDS (energy dispersive spectroscopy) and assessment of the mechanical behaviour by microhardness, tensile and fatigue testing.…”