Szary M., Filip P.

Measurements of sound generated by pair disc-pad were performed according to SAE J2521/Noise Matrix (Single-ended Inertia Dynamometer Test) in semianechoic chamber attached to full scale dynamometer. The unwanted sound characterized commonly in literature as squeaks or squeal (from 1 kHz to~17 kHz) and rattles or groan (< 1 kHz) is generated by instabilities on the contact surface between pad and disc. Those instabilities are characterized by the mechanical coupling between two deformable bodies and represented by instantaneous contact zones. Distibution of contact zones versus time and disc position is influenced by vibrations of the disc-pad pair and associated components and also becomes a source of generation of vibration/sound. Other parameters like relative velocity, contact pressure and temperature, humidity, properties of materials in contact and their composition changes significantly spectra of generated sound. The one-third-octave spectrum analyzer was used to monitor radiation of sound power. The sound spectra indicate that sudden changes in the friction are responsible for the squeaks, and the low frequecy random changes in the surface contact/friction are often described as rattles. Results shows, that most often significant amount of sound power is radiated at the begining of the breaking time. Results of the common 'stick-slip' modeling correlate closely with the experimental data.