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The mechanical properties of a gray cast iron disc brake rotor are directly influenced by the amount and morphology of the graphite present throughout the rotor. Two of these properties, the modulus of elasticity and the damping capacity, can have a significant effect on the propensity for the disc brake rotor to produce noise. The noise propensity of a disc brake is in a large part determined by the relationship between the rotor resonances and the resonances of the other brake components such as the pads. In this paper, we are concerned only with the effect that modulus of elasticity has on disc brake noise through its influence on rotor resonances. The amount and morphology of the graphite in gray cast iron is determined by the carbon content and silicon content of the iron. The carbon and silicon content are measured by one parameter called the carbon equivalent.

This paper illustrates the importance of road vibration in the study of disc thickness variation generation in disc brake rotors, showing that laboratory conditions must include vibration as well as realistic reproductions of speeds, pressures, and inertia, etc. Such conditions are made possible with the Bosch Road Load Dynamometer (RLD). A related paper, Road Load Dynamometer: Combining Brake Dynamometry with Multi-Axis Road Vibration, SAE 2003-01-1638, showed that the RLD could accurately and repeatedly reproduce field conditions, but did not contain disc thickness variation (DTV) generation data. This paper contrasts rotor wear data for a controlled experiment on the RLD, with and without vibrational input. In the control group, DTV generation data comparable to vehicle test results were recreated. In the experimental group, similar hardware was subjected to the same tests except for the absence of vibration input.