A study of friction, wear and particulate emissions during the bedding stage of a Cu-free friction material

In this study, the tribological behaviour and airborne particulate emissions during a bedding procedure for a Cu-free friction material for brake applications were investigated. Different tribological stages were identified. During the first stage, called run-in, friction coefficient, system wear, and emissions increased. At the end of the first stage, the friction coefficient reached a stable value. On the other hand, wear continued to increase, albeit at an increasingly lower rate, and the emissions of airborne particles started decreasing. Subsequently, also system wear and the emission of airborne particles reached a steady-state stage. The obtained results were explained considering the evolution of the characteristics of the friction layer that forms on the friction material during braking. •Friction coefficient stabilizes after 150 brake stops.•System wear and PM emissions stabilize after 350 brake stops.•During the transition stage the PM emission decreases with the brake stops.•The observed behaviour depends on the characteristics of the friction layer.