## 3 Results and Discussion
### Fatigue Results
This imbalance happens during spot welding procedures because of the varied material qualities, particularly the electrical resistance. An unequal distribution of heat prevents a perfectly symmetrical nugget from forming between the sheets. Antisymmetric nugget production reduces the fatigue strength of the unequal welded sheet combination. The S-N curves of the welded joint of AISI 304 for different cases are shown in Figure 14. It is noteworthy that as the applied stress decreased, the fatigue life of cases D, G, and H increased. However, as observed in the RSW joints of titanium alloy, the fatigue life of equal sheet thickness is greater than that of unequal sheet thicknesses. With an amplitude stress of 265 MPa, which is 0.5% of UTS for case D, the maximum fatigue life of 4.56 \(\times\) 10\({}^{6}\) cycles for case D (1-1 mm) was achieved. However, when 477 MPa (0.9% of UTS) was used as the applied stress, the fatigue life for that welded case decreased to 1.19 \(\times\) 10\({}^{6}\) cycles. Case G (0.5-0.5 mm) had a lower fatigue life than case D (1-1 mm), according to the results of the comparison of the two cases' fatigue lives. The case G fatigue life was found to be 3.35 \(\times\) 10\({}^{6}\) cycles at an applied stress of 258 MPa, which is 0.5% of UTS as shown in Figure 14, while the case G fatigue life was 6.45 \(\times\) 10\({}^{5}\) cycles at an applied stress of 464.4 MPa, which is 0.9% of UTS. There was a significant reduction in the fatigue life at different stress ratios, as shown by the fatigue findings for case H (1-0.5 mm) in Figure 14. At a loading stress of 184 MPa, which is 0.5% of UTS, the maximum fatigue life for the RSW joint of AISI 304 stainless steel is 7.39 \(\times\) 10\({}^{5}\) cycles. However, when the loading stress is increased to 331.2 MPa, which is 0.9% of UTS, the fatigue life is reduced to 2.41 \(\times\) 10\({}^{4}\) cycles, which is regarded as the lowest fatigue life. This is due to the reason that was previously stated concerning the variation in the fatigue life between titanium sheets of equal and unequal thicknesses. Figure 14: S-N curves of the different cases of austenitic stainless steel 304 resistance spot-welded joints. The fatigue behaviour of resistance spot-welded (RSW) joints between stainless steel 304 and titanium grade 2 alloy poses considerable difficulties due to the different physical, chemical, and mechanical properties of the two metals. Hence, this is the first study to perform an analysis of the fatigue behaviour of a dissimilar RSW joint between these metals. Figure 15 shows the fatigue life of four different resistance spot welded joint cases. The fatigue life of dissimilar joints, as seen in Figure 15, increased with a reduction in the loading stress, matching the pattern observed in the similar welded joints of titanium and stainless steel depicted in Figures 13 and 14. For case E (1-1 mm), the maximum fatigue life of dissimilar joints was explored at an applied stress of 57.5 MPa, which is 0.5% of UTS, and was found to be 3.7 \(\times\) 10\({}^{5}\) cycles, as demonstrated in Figure 15. In contrast, applying a loading stress of 103.5 MPa (0.9% of UTS) to that scenario causes the fatigue life to drop to its minimum of 1.69 \(\times\) 10\({}^{4}\) cycles. The results showed that case I (0.5-0.5 mm) had the highest number of fatigue cycles before failure at 6.1 \(\times\) 10\({}^{5}\) cycles, with a stress amplitude of 78 MPa (0.5% of UTS), as can be seen in Figure 15. On the contrary, a stress of 140.4 MPa (0.9% of UTS) produced the situation with the shortest fatigue life of 6.07 \(\times\) 10\({}^{4}\) cycles. Based on the findings, the highest fatigue life of 6.47 \(\times\) 10\({}^{5}\) cycles was observed with an applied stress of 92 MPa (0.5% of UTS) in case J, which is welded utilising an unequal thickness combination of 1 mm Ti and 0.5 mm St. However, when subjected to a loading stress of 165.6 MPa (0.9% of UTS), the fatigue life drops to 6.46 \(\times\) 10\({}^{4}\) cycles for this case.