## 1 Introduction
[PERSON] [23] examined hybrid finite element analysis--a life assessment method in which strain-based fatigue calculations were performed after FE simulations of a welded components. [PERSON] et al. [24] carried out analysis of the fatigue life of spot-welded joints using linear elastic fracture mechanics, and two identical materials were shown to have a longer life than two dissimilar sheet metals with differing expansion coefficients. [PERSON] et al. [25] analyzed weld failure for tensile-shear and coach-peel samples. Their study [25] used rigid spiders for modeling the weld nugget and FEM simulations carried out to determine the nodal forces and moments on a spot weld, which were then used for fatigue life calculations. [PERSON] et al. [26] presented a correlation study for the results of point-weld fatigue life analyses with the test data generated by Auto/Steel partnership. [PERSON] et al. [27] performed analyses to assess the spot-weld life with a custom post-processor and they reported experimental data verification. [PERSON] et al. [28] carried out fatigue life estimation of point-welded structures using their custom tool named as 'Expert System for Fatigue Design'. A study by [PERSON] et al. [29] examined the fatigue behavior of spot-welded joints in ferrite-martensite steel and hybrid steels. Several welding parameters were tested by authors [29], including welding time, electric current intensity, and compressive force. According to the results, electric current intensity significantly affected the fatigue life of the joints and the adhesive used in hybrid joints contributed to the increase in fatigue strength. An experimental study in [30] examined the fatigue behavior of spot-welded sheet metals. In a study by [PERSON] and [PERSON] [30], modified tensile shear (MTS) samples were subjected to fatigue life tests with varying electrode forces. The results of the research revealed that the fatigue life and failure modes were influenced by the spot-generating schemes and electrode force effects. Through optical micrograph analysis, it was observed that fatigue failure was predominantly due to through-thickness cracking. In optical micrograph analysis, through-thickness cracking was detected to be the primary cause of fatigue failure. [PERSON] and [PERSON] [31] carried out analysis for the fatigue behavior of friction stir spot welding (FSSW) in lap-shear samples of Al 6061-T6 alloy. The study identified shear fractures at elevated load levels and transverse crack growth at low load magnitudes as two fatigue failure modes. Using tensile-shear and cross-tension samples, [PERSON] et al. [32] performed microstructural characterization, microhardness testing, and tensile and fatigue tests on spot-weldeded Q&P980 steel. Fatigue cracks were observed to initiate at the interface between the sheets, with fatigue failure modes varying between fracture along the circumference or width direction for tensile-shear test components and pullout or fracture along the width direction for cross-tension samples. [PERSON] and [PERSON] [33] investigated fatigue properties and failure characterization of high-strength spot-welded steels, including DP600 GI, TRIP600-bare, and HSLA340Y GI. DP600 GI exhibited the highest microhardness, followed by TRIP600-bare and HSLA340Y GI, and both DP600 GI and HSLA340Y GI experienced softening during high-load and low-cycle fatigue tests, with HSLA showing more prominent softening behavior. Fatigue properties for welded composites were evaluated by [PERSON] et al. [34] and [PERSON] et al. [35], where experimental results were presented for nylon 6 and nylon 66 reinforced with glass fibers. A few numerical studies were carried out to understand the underpinning deformation mechanisms of the spot-welded structures. [PERSON] et al. [36] introduced an integrated search system that evaluates the tensile strength and fatigue behavior of spot-welded joints using ultrasonic testing (UT) and machine-learning approaches.