The present research aims to increase the safety of braking cars by increasing friction coefficient between foot and braking pad. The effect of scratching the rubber pads, to increase their deformation on friction coefficient, was investigated. Four different shapes of rubber braking pads were tested. Friction tests were carried out at normal load ranging from 50 – 250 N. Tests were carried out at dry, water wetted and oil lubricated surfaces. Measurement of friction coefficient is, therefore, of critical importance in assessing the proper friction properties of brake pedal pads and their suitability to be used in application to enhance the safety of the vehicle.
The experimental observations showed that, at dry sliding of bare foot against the tested pads, the friction increase was due to the extra deformation exerted by the pad, where the tread shape allowed for that deformation. The inclined trend of friction coefficient with increasing load is not desirable in braking pad. In the presence of water wetting the tested pads the transverse treads in the pad surface allowed the water to escape easily out of the contact area, while longitudinal treads restored considerable amount of water formed as a layer on the sliding surface. Besides, drastic decrease in friction coefficient was observed in the presence of oil on pad surface. Friction coefficient displayed by the dry sliding of rubber footwear against the tested pads gave lower values of friction than that displayed by bare foot. In the presence of water on the sliding surface, the friction values were much higher than that observed for bare foot. When oil lubricated the sliding surface, rubber footwear gave lower friction coefficient than bare foot at low loads. Finally, scratched test pads experienced relatively higher friction than smooth pads. It seems that the scratches allowed the water and oil to go out the contact surface and increased the rubber/rubber fraction area.