# Torsional Fatigue Performance of a Spot-Welded Structure: An XFEM Analysis
## 4 Conclusions  
The number of spot weld twins, the spot-welding diameter, and the load ratio were among the important parameters that were investigated in this computational analysis to determine the fatigue failure of the spot-welded box subjected to torsional loading. The XFEM modeling technique was employed to model the propagation of cracks. Using the experimental findings from the literature, the model was verified. Deductions were made as follows:  
Figure 6: The depiction of the cracks that spread around the spot weld at the bottom adherends’ overlapping surface for different diameters of spot weld twins at \(N=N_{f}\).  
Figure 7: The depiction of the cracks that spread around the spot weld at the bottom adherends’ overlapping surface for different load ratios at \(N=N_{f}\).  
* The cracks began to spread throughout the structure's width from the spot-welding locations of the overlapping surfaces of the box. After a significant number of torsion cycles, these cracks spread to the adherends' opposing surfaces.
* The mesh size was found to affect the crack initiation sites significantly, especially the one in the thickness direction. When a rather coarse mesh was employed, the cracks did not start near the spot-welding locations but in other incorrect locations.
* When the total number of spot weld twins is even or odd, respectively, the central two or three spot weld twins accommodate the fatigue failure for the studied torsional fatigue loading. When this number was increased from 8 to 11, the \(N_{f}\) increased 7.5 times.
* When the diameter of all the spot welds was raised by 44%, the average crack propagation rate dropped by more than seven times. Also, less area around the spot welds was exposed to the fatigue failure.
* The failure cycle of the box under torsional loading is influenced by the load ratio; nevertheless, the size of the failed region of the structure remains unaffected.
* It is possible to accomplish the infinite fatigue life of the box subjected to torsional motion by adjusting the parameters studied here.  
This study's conclusions provide valuable information for improving the manufacturing and design of spot-welded joints in structures, including the aeronautical ones. Also, this research advances the longevity, structural integrity, and dependability of components, ultimately supporting the overall safety and performance of systems by deepening our understanding of fatigue performance.  
Conceptualization, M.D.; Methodology, M.D. and E.T.D.; Validation, M.D.; Formal analysis, M.D.; Investigation, M.D.; Writing--original draft, M.D.; Writing--review & editing, E.T.D. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding. The APC was funded by the American University of the Middle East, Kuwait.  
Not applicable  
The raw data supporting the conclusions of this article will be made available by the corresponding authors on request.  
Author [PERSON] was employed by the company Engine and Control Limited Company. The remaining authors declare that the re-search was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.