Abstract
Different post-weld treatment methods are used to strengthen welded joints that are subjected to cyclic loading. Combining High-Frequency Mechanical Impact (HFMI) treatment with Tungsten Inert Gas (TIG) remelting is rather a new concept. In this paper, the fatigue lives of welded transverse attachments treated by HFMI-treatment, TIG-remelting, or the combination of both are estimated using fatigue damage modelling and finite element deletion. The change in local topography and residual stresses due to treatment are evaluated numerically and incorporated in the analysis. The local hardness is measured by a Vickers tester and incorporated by increasing the elemental ultimate strength. The analysis demonstrates the superiority of the combined treatment because of the introduced compressive residual stress and the improvement in topography. The analysis also shows that the damage is less distributed after the combined treatment than both individual treatments. Besides, the capability of the TIG-HFMI combination in treating existing welded structures with remaining embedded fatigue crack is proven. Besides, available fatigue test results on combined TIG-HFMI treatment shows that this combination gives always longer fatigue life than the characteristic fatigue lives of the treated details by any of the treatment methods. However, many aspects such as TIG arc and HFMI indenter positioning, and indentation and fusion depth should be taken into consideration when the combined treatment is to be applied to existing structures.
Highlights
Fatigue appears as one of the most challenging issues for designers and structural engineers dealing with welded steel structures
The proposed model takes into account several factors which can affect the degree of fatigue life improvements such as residual stress and its relaxation
The model takes into account the change in material proprieties due to welding (i.e. Tungsten Inert Gas (TIG)-remelting) or cold working (i.e. High-Frequency Mechanical Impact (HFMI)-treatment) by incorporating the hardness measurements to evaluate the local yield and ultimate strength σu,L and σy,L
Summary
Fatigue appears as one of the most challenging issues for designers and structural engineers dealing with welded steel structures. The local methods are branched into two families depending on their main in fluence: methods that change the stress distribution near the toe to create beneficial compression field like High-Frequency Mechanical Impact treatment (HFMI treatment), or methods to improve the weld toe topography to decrease the stress concentration factor such as Tungsten Gas remelting (TIG). TIG-remelting sometimes causes softening in the heat-affected zone after remelting [3], and it can even introduce detrimental tensile residual stress [4] It can induce undercuts at the position of the newly formed well toe [5,6]. It increases the hardness of the weld toe in case that TIG-remelting causes softening beforehand
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