What type of spring is most susceptible to fatigue failure?

Leaf springs are most susceptible to fatigue failure compared to coil springs or torsion bars. Leaf springs are typically made up of multiple layers of steel strips (leaves) stacked on top of each other. These leaves are held together by clips or a center bolt. Due to the constant flexing and friction between the leaves, stress concentrations can develop at the leaf ends and around the center bolt hole. These stress concentrations make leaf springs more prone to fatigue cracking and eventual failure. Coil springs, being a single continuous piece of metal, distribute stress more evenly and are less susceptible to fatigue failure. Torsion bars, which rely on twisting force rather than bending, also tend to have better fatigue resistance than leaf springs. The multi-leaf construction of leaf springs, while providing high load-carrying capacity, inherently makes them more vulnerable to fatigue-related issues, especially in heavy-duty applications or vehicles subjected to frequent load variations and rough road conditions.