Torsion springs: Torsion springs are variant springs, from single torsion springs to double torsion springs, special-shaped torsion springs, and even the deformation of various torsion bars, which can be shaped according to design.
When the spring is twisted, the material is in a stretched or sheared state. For example, the torsion calculation mentioned above, so this twistable angle limit is caused by the failure of the material. When the material is plastically deformed, it cannot be restored to its original state. Therefore, it comes down to the tensile strength and shear strength of the material. Of course, the Von Mises stress calculated by the fourth strength theory is the strength that the material can withstand. Combined with the length of the spring, the allowable torsion angle can be calculated.