On elastic wave propagation in helical springs

The existing simple analysis for the propagation of extensional waves in helical springs of small helix angle is extended to include the effect of coupling between extension and rotation when the helix angle is not small. The wire cross-section may be of any doubly symmetrical shape and therefore covers rectangular as well as circular sections. It is shown that there are two velocities of propagation measured along the helix, one corresponding to torsion without bending and the other to bending without torsion in the wire. Both velocities are found to be quite independent of the helix angle. It is shown how the analysis may be applied to problems of shock transmission and of surging. By means of a detailed investigation of the wave propagation phenomena for a helical wire, the circumstances in which the simple analysis can be expected to be accurate are established.