Multiaxial fatigue assessment of friction stir welded tubular joints of Al 6082-T6

Abstract

ReuseThis article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can't change the article in any way or use it commercially. More information and the full terms of the licence here: https://creativecommons.org/licenses/ AbstractThe present paper addresses the problem of designing aluminium friction stir (FS) welded joints against multiaxial fatigue. After developing a bespoke FS welding technology suitable for joining aluminium tubes, some one hundred welded tubular specimens of Al 6082-T6 were tested under pure axial, pure torsional and biaxial tension-torsion loading.The influence was explored of two independent variables, namely the proportional or nonproportional nature of the biaxial loading and the effect of axial and torsional non-zero mean stresses. The experimental results were re-analysed using the Modified Wöhler Curve Method (MWCM), with this bi-parametrical critical plane approach being applied in terms of nominal stresses, notch stresses, and also the Point Method. The validation exercise carried out using these experimental data demonstrated that the MWCM is applicable to prediction of the fatigue lives for these FS welded joints, with its use resulting in life estimates that fall within the uniaxial and torsional calibration scatter bands. The approach proposed in the present paper offers, for the first time, a complete solution to the problem of designing tubular FS welded joints against multiaxial fatigue loading.

Friction stir welds in aluminium: Design S‐N curves from statistical analysis of literature data

“…The data from tests at R = −1 (categories C1 and C1H) show that the reference stress range Δ σ A,97.7% is almost halved for tubes compared with flat plate specimens, from 123 MPa (C1) to 56 MPa (C1H). This marked decrease in strength is primarily attributed to the notch effect caused by the slight undercut at the edge of the weld zone arising from the tool shoulder . An average notch root radius of about 0.5 mm was measured by Susmel et al, on both the advancing and the retreating side of the weld, which led to a local stress concentration factor of 2.4 in axial loading and 1.7 in torsion.…”

Fatigue of Friction Stir Welded Aluminum Alloy Joints: A Review

“…Aluminum alloy is widely used in aerospace, automotive and marine industries. [6] According to relevant data [7,8] fatigue failure of parts accounts for 50 to 90% of all failures in manufactured parts in general. The FSW method improved the fatigue performance by~2.4 times in comparison with the single riveting method commonly used in aerospace, and reduced the overlap area in the double riveting method, while ensuring the fatigue strength and mechanical properties.…”

Cyclic lateral behavior of friction stir spot welds of AA2219 aluminum alloy: impact of inherent flow defects

“…About 50-90 % of structural and mechanical assembly's in-service failures have been attributed to fatigue failures [12]. Welds or joints are often predominantly sensitive to fatigue loads due to their inherent residual stress level [13], microstructural variations, and the presence of inclusions and blowholes (micro or coarse pores).…”