A prototype disk brake for a bicycle was designed and consists of a pair of pads (area 5 cm x 1 cm) pressed against opposing faces of the steel disk. The pads are aligned with the longer dimension tangent to the direction of rotation and centers of the pad are at a distance of 10 cm from the center of the disk. To validate the durability of their design the students will test the brake on a rotating machine to simulate in-service wear. The disk rotates at a constant speed and the brakes are applied for 10 seconds every minutes, with each pad applying a normal load of 1 kN.

Determine the rotation speed (in RPM) if the test is to simulate braking a bicycle traveling at a speed of 20 km/hour. The wheel diameter (including the tire) is 70 cm. When the brakes are applied, the machine records a torque increase of 30 Nm. Find the friction force that is being applied to each pad and estimate the friction coefficient. Estimate the thickness of material removed per hour of testing, if the Archard wear constant for the materials is ka = 2x10^-8 MPa^-1. If the pads are 3 mm thick how long will they last before thye are completely worn off? What other factors influence the wear ratein service?