Evaluation of the Nonuniformity of Acoustic and Elastic Properties of Compression Coil Springs

The paper is devoted to the investigation of the acoustic and elastic properties of automotive and railway springs manufactured by cold coiling and high-temperature machining, respectively. The mirror-shadow multiple reflection method, based on measuring the velocities of longitudinal and transverse waves propagating along the rod diameter of the spring, is used to evaluate the nonuniformity of acoustic properties. Specially designed pass-through electromagnetic–acoustic transducers of transverse waves of axial polarization and transducers of longitudinal waves on the basis of flexible piezoelectric film of polyvinylidene fluoride provide multiple reflection of volume waves along the cross section of the coiled coil of the spring. The elasticity, shear moduli, and Poisson’s ratio are calculated based on the results of wave velocity measurements. It was established that the nonuniformity of acoustic and elastic properties along the length of the bar differs for automotive and railway springs. A linear variation of acoustic and elastic properties along the length of the coiled wire was observed in the railway spring (from one end to the other), caused by the technology of high-temperature mechanical processing. In the barrel-shaped automotive spring, a nonlinear variation occurs along the length of the coiled wire, correlating with the coil diameter and the formation of residual stresses.