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Technical Paper

Procedure Improvements for Brake Burnish and Wear Testing

The commercial vehicle industry has seen regulations create new requirements over the last few years. Reductions to stopping distance, improvements to vehicle emissions, and the overall need for lighter weight vehicles has caused the commercial vehicle industry to look for new solutions to meet these needs. One such solution is light-weight aluminum metal matrix composite (MMC) brake drums. Aluminum MMC brake drums create the opportunity to reduce weight, lower brake temperatures, improve brake life cycle, and improve brake performance. During the evaluation of these aluminum MMC components it has been seen that existing procedures do not create accurate comparisons for this new material. Current procedures were designed and implemented for cast iron braking solutions. This paper will outline two procedures; FMVSS121 dynamometer burnishing and SAE J2115 wear performance testing, that do not allow direct comparisons from brake system to brake system to be made.
Technical Paper

Light-Weight Aluminum Composite Brake Drum Damage Tolerance

The use of Aluminum Metal Matrix Composites (MMC's) is becoming a viable solution to help meet the new regulations of the medium to heavy-duty truck markets. The objective of this paper is to present both analytical and dynamometer data that demonstrate the damage tolerance of a selectively reinforced Aluminum MMC brake drum. In particular, dissimilar coefficients of thermal expansion (CTEs) between the MMC and Aluminum portion of the drum results in favorable compressive stresses in the Aluminum. This state of stress facilitates the slowing of crack growth for flaws whose depth reaches the boundary between MMC and Aluminum. This paper will present an analytical study utilizing finite-element models to predict stress levels in a drum subject to thermal and mechanical loading. Examination of the stress-fields for braking events at room temperature and elevated temperature provides evidence of the aforementioned compressive stresses in the Aluminum portion of the drum.
Technical Paper

Light-weight Aluminum Composite Fade Response and Speed Sensitivity Results

Rising fuel costs, shorter stopping distance requirements, and the growth in hybrid vehicles all lead to an increased demand in lightweight vehicle components. Changing market needs generate innovative products. One innovative product is a lightweight aluminum metal matrix composite (MMC) brake drum that is substantially lighter than the traditional cast iron product. The objective of this paper is to present the lightweight brake drum using both analytical and dynamometer data to demonstrate the effectiveness during speed sensitivity testing. Thermal analysis tools were developed to predict brake temperatures. These predictions utilize system parameters and braking event characteristics to create realistic predictions of temperature, which have been validated with dynamometer testing. This paper will also present dynamometer data that shows the effectiveness of braking events at varying brake speeds and system pressures.