Experimental and numerical study of butt welded joints made of high strength steel

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Welded joints are wildly used in the construction sector for fabrication of steel and aluminium structures. A welded joint is traditionally divided into three regions: The Base Material (BM), the Heat-Affected Zone (HAZ), and the Weld Material (WM). The mechanical behaviour of each region varies depending on properties of BM, FM and welding parameters. In general, HAZ has a lower material strength compared to BM and WM. The material strength difference is even more significant if BM is made of High Strength Steel (HSS) and welded by using undermatching electrodes. Therefore, it is essential to obtain the constitutive model of HAZ to accurately predict the behaviour (strength, stiffness, and ductility) of the HSS welded joint. In this paper, milled coupon specimens with a transverse butt weld in the middle are used for obtaining the original stress-strain relationship of HAZ and WM based on Digital Image Correlation (DIC) measurements. The original and the modified HAZ constitutive model are validated against the milled and unmilled coupon specimens by Finite Element Analysis (FEA). Comparing the FEA and experimental results, it can be concluded that the modified HAZ constitutive model is successfully validated. Finally, the tensile behaviour of the butt-welded square hollow section is investigated through FEA. It is found that the peak deformation would be significantly overestimated if the modified HAZ constitutive model is not used.