Open coil helical springs, in which the wire helix is wound at a pitch large enough that successive turns do not lie in a single plane, transmit an axial load as four internal force resultants — axial tension, transverse shear, torsion (twisting moment), and bending moment — resolved from the applied load and its moment through the helix angle, rather than the pure direct-shear-plus-torsion state of a closed coil spring. This belongs to the mechanics-of-materials theory of springs (a subtopic of strength of materials), and the resulting normal and shear stress components are combined via principal-stress transformation (Mohr's circle) to obtain maximum stress, while castigliano/strain-energy-style integration of the torsional and bending rotations over the wire length yields the axial deflection and angular rotation of the spring.
Open coil helical springs, in which the wire helix is wound at a pitch large enough that successive turns do not lie in a single plane, transmit an axial load as four internal force resultants — axia…