PSI - Issue 64

Hamid Dahaghin et al. / Procedia Structural Integrity 64 (2024) 1192–1199 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Fatigue failure is a prevalent issue in steel structures, necessitating the retrofitting of fatigue-related damages to prolong their service life (Heydarinouri et al., 2021). Rehabilitating structures is preferred over replacement, as it reduces costs, time, and CO 2 emissions, thus improving sustainability (Ghafoori, 2019). Various retrofit techniques exist, including traditional methods like using tensioned bolts (Al-Emrani, 2002) or welding steel patches (Duong et al., 2006), as well as newer approaches like carbon fiber reinforced polymers (CFRPs) (Ghafoori & Motavalli, 2015) and shape memory alloys (SMAs) (Wang et al., 2021). Additive manufacturing (AM), also known as 3D printing, enables the creation of complex geometries that enhance structure performance (Baqershahi et al., 2024; Jafarabadi et al., 2023). AM, particularly the direct energy deposition (DED) technique, is considered for repairing and strengthening steel structures due to its advantages (Rahito et al., 2019). Within DED, wire and arc additive manufacturing (WAAM) is prominent, involving layer-by-layer construction using a robotic arm to melt welding wire with an electric arc (Huang et al., 2023). WAAM offers rapid manufacturing of large metal parts, utilizing standardized industrial robots and commercial welding wire, albeit with potential drawbacks such as increased residual stresses (RS) and distortions due to elevated heating rates and uneven cooling conditions (Buchanan & Gardner, 2019; Gardner, 2023). This study utilized the WAAM technique to strengthen damaged steel plates. The WAAM process involves melting steel wire and depositing it onto the target area of a steel plate, followed by a cooling phase. Fig. 1 illustrates the strengthening of a steel plate using double-sided WAAM deposition. A finite element (FE) simulation was conducted using Abaqus software to assess the effectiveness of this technique. After determining the sample dimensions, fatigue tests were performed on reference and strengthened specimens. Finally, fractography analysis was conducted to identify the fatigue crack initiation mechanism.

Nomenclature CFRPs Carbon fiber reinforced polymers SMAs Shape memory alloys AM Additive manufacturing DED Direct energy deposition WAAM Wire arc additive manufacturing RS Residual stress FE Finite element CMT Cold metal transfer

Deposited WAAM

Side view

Top view

Steel plate with a central notch

Right view

Fig. 1. Schematic configuration of the repaired steel plate with deposited WAAM

2. Methodology A thermomechanical simulation was employed to predict RS in deposited WAAM and plate. Initially, a thermal analysis was performed to establish the temperature field, which was then used to calculate the mechanical field. The dimensions of the steel plate and the deposited WAAM used in the simulation are shown in Fig. 2. Each bead of