Research on shear buckling behaviour of friction stir welding 6061-T6 aluminium alloy H-section beams

This study systematically investigated the shear buckling behaviour of the friction stir welding (FSW) 6061-T6 aluminium alloy H-section beams through experimental and numerical analysis methods. FSW is a solid-state joining process that exhibits superior retention of joint strength and markedly lower sensitivity to welding-induced defects in comparison to conventional fusion welding techniques. On the basis of experimental tests on six FSW 6061-T6 aluminium alloy H-section beams, the material properties, initial geometric imperfections, FSW-induced residual stresses, failure modes and load-deflection curves were reported. Finite element (FE) models were validated against experimental results to assess their predictive accuracy in failure modes and shear buckling resistances. A parametric analysis involving 708 FE models was subsequently conducted to expand the database. The results indicate that FE models incorporating FSW-induced strength reduction and residual stresses effectively enhanced the predictive accuracy and consistency of shear buckling resistances of specimens. The number/width of welds and residual stresses exhibited minimal influence on shear buckling performance, while the installation of rigid end posts could enhance the anchorage restraint on web tension field development, thereby improving the shear buckling capacity of beams. Initial geometric imperfections had a certain weakening effect on the ultimate bearing capacity of the beam, while the influence of their amplitude was limited. The experimental and FE results for FSW 6061-T6 aluminium alloy H-section beams were compared against current design requirements stipulated in Chinese, European, and American codes. The comparison results indicate that when the normalized width-to-thickness ratios of the web fell within the ranges of 0.5–1.0 and 0.6–1.2, the design resistance predictions of the Chinese and American codes were unsafe, and all predicted results were overall conservative by 24.0–34.5%, also with greater dispersion. Modifications were proposed based on Chinese and European codes, achieving a 6–18% improvement in prediction accuracy and reduced dispersion compared to current standards.