EFFECT OF BRAKE PAD (CARBON) MATERIALS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AUTOMOBILE BRAKE DISC

Abstract

The disc brake is a wheel brake which slows rotation of the wheel by the friction caused by pushing brake pads against a brake disc with a set of callipers. In the process of braking the vehicle in motion, a thin layer of brake pad material actually transfers and sticks (adheres) on to the rotor face. In this research, the effect of brake pad materials deposits on the mechanical properties (tensile strength, hardness, impact and compressive) and Microstructural view on the automobile brake disc. Two automobile brake discs used were the old and new discs. The old brake discs used were selected locally from the automobile workshop in Ilesa while the new brake discs used were purchased from the market. The samples were ground to remove rough surfaces, these was moulded with a plastic for proper holding, the surfaces were polished, cleaned by emery paper and etched to remove dirt, the samples were dipped in 2% Nital agent for etching and finally dried by blower. The microstructure of the new grey cast iron brake disc for both Toyota and Mazda when viewed under optical microscope gave a low and soft strength of graphite flakes as the first phase, the second phase seen was the ferrite phase which surrounds the graphite flakes, they are pure iron. These phases seen under microscope were also noticed in the literature review. The microstructure of the used grey cast iron brake disc for both Toyota and Mazda when viewed under optical microscope shows a dark spot which was not seen on the new brake disc when viewed and also in literature review. This occurs as a result of carbon inclusion, which helps in pearlite formation and reduction of graphite flakes. The pearlite is the combination of ferrite and cementite and as a lamella appearance. Pearlite is a microstructural constitute with hard and high strength. In the present investigation the mechanical properties such as material hardness, tensile strength, compressive strength and impact force were measured also. The results acquired from the mechanical properties of the new grey cast iron brake disc are: Tensile strength 146.95 Mpa, which experienced elasticity between 0-20 Mpa, plasticity between 20-146.95 Mpa and failed at 76.56 Mpa at a load of 3311.58 N, Compressive strength 230.1474 Mpa, material hardness 219.8 HRV and impact force 16.0 N. The results acquired from the mechanical properties of the used grey cast iron brake disc are: Tensile strength 194.21 Mpa, which experienced elasticity between 0-10 Mpa, plasticity between 10-194.21 Mpa and failed at 114.64 Mpa at a load of 8170.85 N, Compressive strength 274.153 Mpa, material hardness 258.4 HRV and impact force 15.2 N.