In this study, an attempt has been made to investigate the effect of shoulder flatness, shoulder diameter, transverse welding speed and pin profile on mechanical and microstructural properties of friction stir welded (FSWed) armor aluminium alloy AA7039 T6. In total 21 experiments were performed as per center composite design (CCD) approach of response surface methodology (RSM). The tensile tests were carried out to observe the ultimate tensile strength, yield strength and percentage elongation of the FSWed joints. The quadratic regression mathematical model was developed to establish a relation between inputs and outputs. ANOVA was used to ensure the significance of the process parameters and their interactions. Optimized combination of process parameters was determined using grey relation coupled with principal component analysis, a hybrid approach. The results reveal that the process parameters considered for study have a significant effect on the variation of the studied responses. The optimum values of shoulder diameter, shoulder flatness, pin profile and welding speed were found as 18 mm, 2 mm, square and 30 mm/min, respectively. The microstructural variation across different subzones of welded joint was examined to confirm the relation obtained between process variables and tensile properties. Fractographic examination of tensile specimens and microstructural examination of joints revealed that shoulder flatness with concavity and pin pulsating effect has helped in proper mixing of material and evenly distribution of secondary phase precipitates which has imparted good mechanical properties to the FSWed joint.

Purpose: Inverse distance weighted (IDW) functions are utilized to make models of heterogenous materials such as functionally graded materials (FGM) in computer aided design (CAD). However, the use of IDW function based FGM for stress concentration reduction is scarcely available in the literature. The present work aims to analyze and reduce the stress concentration around a circular hole in IDW function-based finite FGM panel under biaxial loading.Design/methodology/approach: Extended finite element method (XFEM) model was prepared using MATLAB to investigate the effect of geometrical and material parameters on the stress concentration factor (SCF). The obtained results of IDW FGM are compared with homogeneous material as well as two different FGMs based on the power-law function.Findings: It was observed that the IDW function based FGM is simple in material modeling, conformal with all domain boundaries and shows lower stress concentration in comparison with the homogeneous material case. While comparing IDW FGM with power-law based FGMs, it was observed that the IDW FGM has least values of stress concentration for low d/W (diameter of the hole to panel width ratio) and is comparable with power-law based FGMs for high d/W.Originality/value: It can be stated that IDW FGM is highly suitable for stress concentration reduction in finite panels with d/W = 0.5, which can further be intended for obtaining optimum hole and panel designs.