JOHN W. EVERT | Mechanical Engineering Technology
Analysis
Assumptions
Vehicle Mass: 2900 lbs / 1315 kg
Diameter of Wheel/Tire: 28 in / 0.71 m
Diameter of Brake Disc: 11.75 in / 0.30 m
Velocity at Brake Zone Entry: 100 mph / 44.7 m/s
Velocity at Brake Zone Exit: 50 mph / 22.4 m/s
Braking time: 3 sec
Initial Calculations
Deceleration Rate: -7.4 m/s^2
Total Torque on Rotors: 3.47 kN*m
Assume 75% front /25% rear brake bias
1.30 kN*m per front rotor
0.43 kN*m per rear rotor
Max Rotation: 4000 RPM with Safety Factor 2.5
Analysis of Stresses
The countersunk 10-24 hardened machine screw mounting the faces to the rotor body was found to have sufficient strength to withstand the predetermined braking event.
The manufacturing standard of using 5/16 coarse thread cap screws as the fasteners between the rotor body and the hub was determined as well and deemed acceptable.
The calculated direct shear values of 13.5 MPa and 46MPa recpectively give safety factors of 40 and 12 respectively. Therefore substandard hardware and otherwise abuse is acceptable given this track specifically.
Thermal Analysis
The braking system exists to convert the car’s momentum into thermal energy by pressing a brake pad into the rotating rotor surface creating a moment about the brake rotor. After finding the total amount of kinetic energy, 123 kilo-Watts per front rotor, in each braking event, a theoretical temperature rise of 180°C and 233°C , ΔT= 53°C was calculated.
Solidworks FEA Thermal Analysis predicted 325°C rise from ambient.for the vented iron rotor and 382°C for the fabricated rotor, ΔT= 57°C
