## 1 Introduction  
Austientic stainless steel (ASS) is widely utilised to make metro vehicle components for modern urban mobility due to its affordability, strength, corrosion resistance, and resistance spot welding (RSW) weldability [1; 2; 3; 4; 5; 6]. Due to its high thermal expansion coefficient, austenitic stainless steel (ASS) cannot be welded with traditional arc welding. Thus, the RSW technique is regarded as the best welding method for ASS metro vehicle components [7; 8]. The aerospace industry commonly uses titanium grade 2 due to its excellent properties, such as low weight, high strength, corrosion resistance, and good fatigue properties [9; 10], making it suitable for use in industrial sectors like aviation and medical sectors [11; 12]. Composites made of titanium alloy and stainless steel (SS) have potential applications in the automotive and aerospace sectors. The dissimilar metals' properties guarantee that they are lightweight and robust [13; 14; 15]. Replacing stainless steel components with titanium and titanium alloy might be a promising way to reduce aircraft weight [16]. Joining dissimilar metals like titanium and stainless steel can be used in the development of surgical instruments and implants. Also, joining dissimilar metals is promising to employ in the energy sector, such as in heat exchangers and turbine blades [17]. The thermal expansion mismatch is the main challenge to overcome when welding different metals since it has the potential to generate residual strains, cracks, and distortion [17]. Brittle intermetallic compounds (IMCs) occur at the welding contact due to metallurgical incompatibility, which further reduces the joint quality [18]. Welding processes are the most commonly used processes in engineering applications like railroads, civil construction, automobiles, aircrafts, and ships. The welding process has the ability to significantly alter the properties of the joint area compared to the parent material [19; 20]. In the context of modern manufacturing, RSW is one of the oldest and most complex processes, yet it is used in industrial sectors due to its several advantages [21; 22; 23]. Over the past century, the RSW process has advanced, and there have been significant improvements that have transformed the spot-welding process from a mere metal-interfacing or joining process into a method that is capable of penetrating electrically conductive metals and other dissimilar metals [24; 25]. Fatigue is the main challenge in resistance spot-welded joints since these joints are subjected to varying loads in the vehicle body and repeated flight cycles in the aircraft structure [26; 27]. In the heat-affected zone (HAZ), the fatigue fracture starts at the inside surface of welded sheets. Understanding the rate at which cracks propagate in the spot-welded part is crucial for assessing the RSW joints' serviceability prior to rupture [28; 29]. In order to guarantee structural durability, reliability, and safety, it is also necessary to validate the behaviour of the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) of the resistance spot-welded joints, as well as the related failure processes, when developing innovative design ideas [30]. However, there is a scarcity of published research on the fatigue behaviour of resistance spot-welded joints for similar titanium grade 2 alloy and AISI 304 stainless steel joints, as well as dissimilar joints between these particular metals. Mechanical joint characteristics are crucial for the engineering of a structural part since a detailed analysis of their behaviour is important to enhance the reliability, especially when the joint design is approached using mechanical fastening. Fatigue behaviour, in particular, contributes significantly to the structural integrity of a part because the majorpart of these joints is subjected to a fatigue process during all or most of their service life.