Wear Mechanism and Debris Characterization of Commercial Brake Pad Materials under Dry Sliding

Abstract This study employed a ball-on-disc friction test to investigate the dry sliding friction and wear performance, as well as the wear debris morphology characteristics, of three types of brake pads—copper-free non-asbestos organic (Cu-free-NAO), copper-containing non-asbestos organic (Cu-full-NAO), and low-metallic (LM)—under different loads using a silicon nitride ball (Si 3 N 4 ) as the friction pair. The research results indicate that the Cu-free NAO brake pad exhibited the highest friction coefficient with relatively stable performance (mean standard deviation 0.0105), while the Cu-full NAO brake pad showed the largest friction coefficient fluctuation (mean standard deviation 0.0128). The LM brake pad demonstrated the smallest friction coefficient fluctuation (mean standard deviation 0.0064). The wear rates and debris mass of all three brake pads showed an increasing trend with rising loads. The LM brake pad exhibited the highest wear rate and debris mass, with maximum values of 17.7 × 10 −11 mm 2 N −1 and 9.4 mg, respectively, whereas the Cu-free NAO brake pad showed the lowest wear rate and debris mass, with maximum values of 13.6 × 10 −11 mm 2 N −1 and 5.76 mg. At lower loads, abrasive wear dominated the wear mechanisms of all three brake pads, accompanied by fatigue spalling. As the load increased, the wear mechanism shifted to fatigue spalling and delamination. The wear debris particles were predominantly below 10 μm in size, with smaller particles exhibiting near-spherical morphology. Larger particles consisted of plate-like friction layer fragments and irregular primary material spalling fragments.