## 1 Introduction
[54; 55] to examine the effect of cyclic loading strategies on fracture behaviour. [PERSON] et al. [56] used post-failure tension-to-failure tests and constant-amplitude low-cycle fatigue tests to demonstrate that the austenite/martensite transformation caused by cyclic plastic strain was the primary cause of the changes in stainless steel's strength, ductility, and strain-hardening ability under cyclic loading. In order to calibrate the parameters of the Chaboche constitutive model, [PERSON] et al. [57] performed ultra-low-cycle fatigue and low-cycle fatigue experiments on carbon steel and austenitic stainless steel. Research by [PERSON] et al. [58] examined the effects of the strain range on the parameters of the Chaboche constitutive model, which they calibrated, and examined the effects of the BM, weld seam, and HAZ on round bars (both smooth and notched) made of S22053 duplex stainless steel. The fatigue life of AISI 304 welded T-joints is greater than that of non-welded samples, as pointed out by [PERSON] et al. [59]. [PERSON] et al. [60] introduced the concept of progressive damage in welded structures, revealing how interfacial crack propagation can significantly affect fatigue behaviour. Their work suggests that the integration of adhesive bonding can enhance the fatigue strength, a concept that could be pivotal when applied to titanium spot-welded joints, where stress concentrations are critical. By utilising the post-weld heat treatment (PWHT) method on a titanium/304 stainless steel dissimilar joint with a copper interlayer, [PERSON] et al. [61] observed an increase in the average tensile strength of the welded sample, from 330 MPa in the welded state to 352 MPa after the PWHT process, as well as an improvement in fracture elongation of 7.4-times. Despite the fact that titanium/304 SS welded joints with copper as the transition layer may achieve a tensile strength of 326 MPa through laser welding, this value is still lower than the 400 MPa of the BM. Furthermore, the welded joint exhibits a negligible elongation of about 0.3% [62]. The main causes of this are the volume loss that occurs during solidification and the creation of brittle IMCs during welding. Together, they harm the microstructure of the weld by keeping tensile stress in the welding zone (WZ). Additionally, there has been a marked shift in the weld metal's hardness in both the transverse and root directions, as well as in the dendritic core and inter-dendrite regions' composition gradients [63]. Because of their hard brittleness, IMCs are prone to dislocation accumulation, stress concentration during deformation, and ultimately brittle fracture [64]. This leads to a welded joint that is not very stable. [PERSON] et al. [65] analysed the mechanical behaviour of AISI 1005-RSW joints. [PERSON] [66] developed a rivet die for extruding AA 5052 into pre-cut AISI 1006. According to the above studies, weld defects can be generated, hence, the welding assembly often has less structural integrity compared to the joined materials. An increase in demand for very lightweight vehicles and structures, especially for use in the aircraft and automotive industries, has led to the growing application of advanced welding techniques and joining methods for high-strength, lightweight materials. Currently, knowledge of the fatigue behaviour of similar resistance-spot welded joints in AISI 304 austenitic stainless steel with equal and unequal sheet thicknesses is limited. Furthermore, a review of the literature reveals that no article has yet examined the fatigue behaviour of equal and unequal sheet thicknesses for similar titanium RSW joints or the dissimilar joints between titanium grade 2 alloy and AISI 304 austenitic stainless steel. Therefore, the aim of this project is to provide data about the fatigue life of similar and dissimilar resistance spot welded joints of titanium grade 2 and AISI 304 austenitic stainless steel, which may be used for future studies and applications.