Braking Pad Thermal Finite Element Analysis

Goal: Mechanical simulation of maximum frictional force to substitute conventional testing

To further ensure the safety of the braking system, it is necessary to analyze the energy loss from the brakes that will be converted into heat, which will additionally cause thermal stresses in the braking subsystem. Failure occurring within the braking subsystem could result in a failure to brake in time or structural instability, which could lead to injuries or loss of life. Physical testing of the brakes is impractical due to logistical issues such as the Hyperjackets’ capsule not being fully constructed yet, not having access to a physical testing location, and the cost of potentially destroying the capsule during the test, therefore the main objective will be performing finite element analysis to try predicting the failure of the system and avoid catastrophic failure.

Material Properties

The specific brake pads being used are the Scan-Pac Manufacturing Inc RF52 brakes[1]. RF52 is a non-asbestos organic brake pad. Organic brake pads have the benefit of being gentle on the braking system and being lower cost than other types of brakes. RF52 also has a stable coefficient of friction over a high range of temperatures. The manufacturer’s recommended maximum operating condition, as well as the expected limits, are tabulated on the left. The table shows that the maximum expected pressure is within the manufacturer’s specification, however, the maximum rubbing speed is 3 times higher than what the manufacturers recommended. Currently, the HyperJackets design is meant for one-time competitive use, so excessive wear and tear issues are potentially acceptable over the course of one usage. Based on the hand calculations, the theoretical maximum temperature is 556℃, which is above the manufacture’s recommendations as well. At excessively high temperatures, the coefficient of friction of the material can be adversely affected, which could cause issues with braking time [1].

ANSYS Finite Element Analysis

This extremely simplified model was necessary to maximize the computation capabilities of the Georgia Tech machines. Because of these computational limitations, another simplification was made to the rail to find the temperature profile. This simplification involved scaling down the length of the rail, which was causing errors, to 1 m and concurrently scaling up the total applied pressure. This manipulation would conserve the work done by the system, thereby producing accurate temperature data.

Next, the brake pads thermal and structural profiles are coupled and solved for, using a transient modeler called LS-DYNA, where the simplifications resulting from insights in the static structural model are paramount to minimizing the computation time on this more complex FEA package. LS-DYNA is an optimized general purpose finite element program that is ideal for solving non-linear systems with changing boundary conditions, or transient dynamic systems like automotive crashes. Considering this braking systems is designed to aggressively decelerate from approximately 120 m/s to standstill over the course of about 2.5 seconds or 125 m, LS-DYNA will be the most effective modeler. The element type is selected as linear quadrilaterals for their rapid solve time in a more computationally intensive ANSYS module.

This model solution is included on the left highlighting a maximum temperature of 702.32 ℃(1291°F ). The max temperature is experienced at the leading edge of the brake pad as expected, diminishing rapidly toward the aluminum topper, where on the top face, the temperature is approximately room temperature, 23.577℃. This, therefore, leads us to believe that thermal stresses do not play a significant role in the aluminum body. Lastly, The rails temperature distribution is also found but exhibits a temperature gradient that only approaches 30℃.

References

[1] Scan-Pac Mfg, “Brake Lining Material RF52”,REV.000, Dec. 95

 

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