This study uses ANSYS workbench 16.0 (modeling software) to conduct thermal structure analysis: to observe the thermal stresses and heat fluxes of brake rotors using different materials and designs. It uses this type of analysis to evaluate rotor performance under extreme braking conditions (when heat related issues are most prevalent).
Modern braking systems involve a rotor and caliper design. A rotor attached to a hub spins along with a vehicle’s wheel and a caliper applies pressure to this moving rotor (via brake pad) to slow it down. Rotor slotting and drilling are common techniques used to improve cooling and prevent heat related issues and failures. This paper’s goal is to analyze the effectiveness of these techniques and to determine the optimal materials for designing a brake rotor.
The first step was to review the issues experienced by rotors under harsh braking. These are: hot spots resulting in thermal judder (violent shaking), uneven wear along the rotor’s surface, and rotor deformation and oscillation. Lack of effective and even cooling can result in thermal buckling and warping, pad imprinting (brake pads cooling at different rates than rotors they come in contact with) and material failure. Lastly, high temperatures in a braking system can lead to friction loss (friction between pad and rotor is what slows a vehicle) and can lead to ineffective braking known as brake fade.
The next step in the study was software tests. Disc brakes were first modeled using Solidworks 2016. Next, computer programs were used to simulate hard braking and gather temperature and deformation data. The test assumed all kinetic energy was lost to the brake discs (tires not considered) and that the heat transfer was uniform. The tests performed were to simulate repeated hard braking and do not predict the longevity of the discs.
Several simulation images using color coding for temperature were presented. Slotted discs experienced redzones (peak temp) at the outer edge of the rotor. This redzone developed from the friction force applied by the brake caliper. Drilled and slotted rotors showed superior heat convection and their max temperature was lower than just slotted rotors. Stainless steel max temperature was 947.4 degrees C vs 630.18 degrees C for cast iron. Cast iron discs showed a 33% reduction in temperature and a 75% reduction in thermal deformation compared to stainless steel.
While some performance vehicles use carbon ceramic materials in their braking systems, such designs can be expensive and impractical in daily driving (brakes are grabby until they reach operating temperature). This study clearly presents that a slotted and drilled set up using cast iron is most effect in dissipating heat and in preventing deformation or other structural issues. It is important to note that no considerations were made about rotor longevity or about the effect of slotting and drilling on pad life.