Experimental evaluation of brake pad material propensity to stick-slip and groan noise emission

Frictional and dynamic responses of brake pad materials, when sliding on brake disc counterfaces, are at the origin of noise, vibration and harshness (NVH) issues such as brake noise emissions. In more detail, groan is a low frequency noise emission often associated to the stick-slip frictional response of the brake system. The instability of such contact is the result of the coupling between the system dynamics and the frictional response of the materials in contact. In this work, an experimental approach is proposed for measuring the frictional response and the propensity to generate stick-slip of different lining materials, coming from commercial brake pads, when sliding on a worn surface of a brake disc, under the same controlled boundary conditions. The proposed methodology allowed for comparing the propensity of the tested pad materials to stick-slip vibrations, which is in agreement with feedback from automotive industry on groan emission.