The Effect of Friction Radius Variation on the Friction-Induced Vibration and Noise

In mechanical equipment friction pairs, there are instances of varying friction radius (e.g., brake pads in trains), but the impact of variation in friction radius on friction-induced vibration noise (FIVN) has not yet been clearly understood and has drawn little attention. To address this, a series of tests under different friction radii were carried out using a CETR friction and wear tester, and a finite element model(FEM) based on the main structure of the tester was established to carry out complex modal and transient dynamic simulations. Furthermore, a two-degree-of-freedom (2-DOF) numerical model was proposed to analyze the stability and dynamic characteristics of the ball-disc friction system. Based on the FIVN simulation tests, finite element simulations, and numerical analysis results, the impact of variations in the friction radius on FIVN was discussed. The results indicate that the friction radius is a crucial factor impacting the intensity and evolution of FIVN. Under the experimental parameters employed in this study, the intensity of FIVN increases with the enlargement of the friction radius. Correspondingly, an increase in friction radius significantly increases the friction disc’s wear. The scratches’ width, depth, and wear volume increase. In the friction process, the increase in friction radius leads to an increase in the wear amount of the friction disk, which also results in a significant accumulation of wear debris actively engaging in the frictional process at the interface. Therefore, the degradation of the friction surface becomes increasingly severe and exhibits complex tribological behaviors. The increase in friction radius facilitates modal coupling phenomena in friction systems, inducing high-intensity unstable vibrations within this system. Furthermore, with a larger friction radius, the structure of the friction system is more prone to deform. As the friction ball moves more significantly along with the friction disk, the concentration of contact stress at the interface intensifies notably in the region adjacent to the cutting-in end, accompanied by an increase in the numerical value of the contact stress. In scenarios with a large friction radius, the concentration of contact stress on surfaces is the primary reason for the greater width, depth, and wear volume of the scratches on the friction disc. The 2-DOF numerical model of the ball-disc friction system we established effectively helped us discuss the impact of the friction radius and coefficient of friction (COF) on system stability. It is found that under a large friction radius and COF, the system exhibits modal coupling phenomena, with a state of vibrational instability. The intensity of friction-induced vibration (FIV) also increases with the friction radius. In conclusion, this study finds that the friction radius is a key factor affecting FIVN, and appropriate measures should be taken to improve the tribological behavior of the interface to suppress FIVN when encountered a large friction radius.