Design of a Test System for Quantitative Rating of Squeak Propensity of Material Pairs

The main difficulty in measuring squeak propensity of a materials pair is stemming from the fact that squeak is a noise resulting from a self-excited vibratory sliding motion. For example, a test system that simply employs a relative sliding motion between two surfaces measures a sound of two materials rubbing against each other, not necessarily a squeak sound. A solution to this problem is to design a test system that always induces a self-excited vibration instability. The system we developed utilizes a sprag-slip mechanism to induce vibration instability to test a pair of test materials for a wide range of operating parameters. The system also well represents the type of motion that induces squeak sounds in actual engineering systems, a vibratory motion combined with a sliding motion of large average velocity. Another difficulty is identification and quantitative rating of the squeak noise, which is handled by adopting an automatic squeak detection and rating algorithm that the authors developed in the past. Finite element method (FEM) simulation results show that material properties determine the amplitude of limit cycles resulting from self-excited vibrations, which explains why some unstable motions make squeak and some do not.