PSI - Issue 60

Aritro Chatterjee et al. / Procedia Structural Integrity 60 (2024) 13–19 Aritro Chatterjee, Arpan Mandal, Anoj Giri / Structural Integrity Procedia 00 (2019) 000–000

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Stir Welding (FSW) is generally preferred for the joining of Aluminum alloy, due to the elimination of defects like hot cracks, porosity and the larger heat affected zone. The formation of residual stresses is a common phenomenon during the welding; however, the magnitude of residual stress depends upon the type of welding process, welding parameters and their conditions. Residual stress can have an impact on material's performance and the lifespan of a component. The residual stress measurement is very important as it has a direct impact on the reliability, usability, and safety of the components, due to this the estimation of residual stress becomes necessary. Lim et al. (2018) Knowledge of residual stress may also guide and enhance a variety of processes, including heat treatment, surface strengthening, stress reduction and even the detection of material defects Huang et al. (2013). The residual stresses in FS Welded joint were measured by blind hole drilling or XRD method Li et al. (2008), Lemmen et al. (2010). Still there are challenges in residual stress measurement by BHD method like the compatibility of strain rosette with the material, error estimation etc. So, improvision in BHD method i.e. DIC in conjunction with BHD are being explored by the researchers. Digital Image correlation is a noncontact optical method for measuring full-field displacement and strains Lemos et al. (2019). The DIC monitors subsets, which are a collection of nearby pixels that indicate a specific area of the sample. Speckle patterns which are arbitrary contrast points are made in the specimen to register and monitor each subset. Basically, DIC tracks the change in speckle pattern on the surface of the specimen to determine the change in strain in the sample. Lord et al. (2008) studied the feasibility of DIC for the residual stress measurement and investigated the surface displacement and strains in equi-biaxial stress in shot peened samples. Arabul et al. (2022) developed the low cost DIC set up for residual stress measurement set up. They validated DIC results with conventional BHD method by measuring the residual stress in four-point bending specimen. Nelson et al. (2006). investigated the residual stress in Aluminum 6061-T6 sample using 3D DIC system. The work with respect to measurement procedure and the feasibility of DIC in conjunction with BHD is still in the developing stage. As we are eliminating the physical strain rosette to virtual one, there is a scope of validation against popular residual stress measurement techniques. The aim of the work is to study the feasibility of DIC-BHD approach for the residual stress measurement. To accomplish this, the Friction Stir Welded Aluminum joints were prepared, and the residual stresses were investigated by novel DIC-BHD approach. Nomenclature ā calibration constant for isotropic stresses b̄ calibration constant for shear stresses E young’s modulus P isotropic (equi-biaxial) stress p uniform isotropic (equi-biaxial) strain Q 45° shear stress q uniform 45° shear strain U longitudinal displacement V transverse displacement σ x uniform normal x-stress σ y uniform normal y-stress ν poisson’s ratio ε x relieved strain in x-direction ε y relieved strain in y-direction 2. Experimental details The materials selected for the current study is AA 6082-T6 with dimensions of 50 mm x100 mm each having 6.35 mm thickness. The chemical composition of the base material is given in Table 1.