Eliminating brake noise is a classic challenge in the automotive industry. Brake discs develop large and sustained friction-induced oscillations, simply referred to as brake squeal.
Two common theories describe brake-squeal phenomena:
Stick-Slip Theory -- The self-excited vibration of a brake system that occurs when the static coefficient of friction is greater than the sliding friction coefficient. Variable friction forces introduce energy into the system, which is not properly dissipated during the squealing event, resulting in large vibrations.
Mode-Coupling Theory -- When two similar characteristic modes couple with each other, instability is introduced to the braking system. This instability is caused primarily by improperly selected geometric parameters.
Both theories attribute brake squeal to variable friction forces at the disc-pad interface.
Brake noise is generally categorized as follows:
Low-frequency noise -- An example of a low-frequency noise is the "groaning" noise which occurs in the frequency range between 100 and 1000 Hz. Any noise having a frequency above 1000 Hz is considered a squeal.
Low-frequency squeal -- A result of mode coupling occurring between the out-of-plane modes of the rotor and the bending modes of the brake pad.
High-frequency squeal -- A result of mode coupling occurring between the in-plane modes of the rotor.
Low- and high-frequency squealing can be determined via complex eigensolvers. The presence of unstable modes suggests that the geometry parameters and material properties of the braking system should be modified.
For more information, see Brake-Squeal (Prestressed Modal) Analysis in the Structural Analysis Guide.