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. Additionally, fracture mechanics methods are utilized to calculate crack propagation for a particular event. The analytical approach for crack growth prediction utilizes the finite element models of the brake drum in combination with a detailed submodel, into which cracks were introduced at various depths. ANSYS was used to calculate stress intensity factor at each crack depth for the duty cycle under consideration, followed by a calculation of crack depth verses loading cycles. Dynamometer testing was also completed which demonstrates this damage tolerance. Dynamometer data will be presented that shows MMC's maintain performance under certain test cycles even with a crack in the aluminum MMC brake drum. In short, these simulation tools, models, and data demonstrate that aluminum MMC components can be a viable way to offer new technology solutions for the medium to heavy duty truck markets.