Dynamics of a helical spring involving intermittent frictional contact with an oscillating barrier

This study concerns the transverse and longitudinal dynamics of helical springs. When a string is wrapped in helix to form a helical spring, its bulk longitudinal stiffness reduces. This leads to complicated dynamics of the spring in both transverse and longitudinal directions especially when it involves frictional contacts against a barrier. To simulate such dynamics, experiments and numerical simulations were conducted focusing on the intermittent contact between the helical spring and an oscillating barrier. First, to investigate the effects of longitudinal stiffness on the dynamics of the spring, vibration tests were conducted using the helical spring and a piano string with higher longitudinal stiffness. Vibration of the spring showed slower attenuation and involved more frequency components than the piano string. Next, numerical simulations were conducted with intermittent contact and friction between the spring and the barrier along with the deformation of the spring in the longitudinal direction. The computed vibration in the longitudinal direction with friction resulted in also slower attenuation and more frequency components than those of the case without friction. These results indicate that by conducting simulations with longitudinal deformation and friction, the vibration of a helical spring contacting with the barrier can be simulated with high accuracy.