## Helical Springs

When close-coiled helical spring, composed of a wire of round rod of diameter *d* wound into a helix of mean radius *R* with *n* number of turns, is subjected to an axial load *P* produces the following stresses and elongation:

The maximum shearing stress is the sum of the direct shearing stress τ_{1} = *P*/*A* and the torsional shearing stress τ_{2} = *Tr*/*J*, with *T* = *PR*.