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In automotive disk brake systems, frictional heat is not uniformly distributed due to various reasons such as thermal expansion and imperfections in geometry. It is well known that thermoelastic distortion due to frictional heating affects the contact pressure distribution and can lead to thermoelastic instability or TEI, where the contact load is concentrated in one or more small regions on the brake disk surface. These regions then reach very high temperatures and the passage of these hot spots moving under the brake pads can cause low frequency vibration called brake judder. Disk thickness variation (DTV) will further promote the localized contact. Nonuniform contact can also be generated by disk lateral runout (LRO). This study investigated the effects of various contact conditions on the heating patterns and judder characteristics of a disk brake by using a state of the art infrared camera technology and vibration measurements.

Thermal diffusivity and thermal conductivity of grey cast iron have been measured as a function of graphite flake morphology, chemical composition and position in a finished brake rotor. Cast iron samples used for this investigation were cut from “step block” castings designed to produce iron with different graphite flake morphologies resulting from different cooling rates. Samples were also machined from prototype alloys and from production brake rotors representing a variation in foundry practice. Thermal diffusivity was measured at room and elevated temperatures via the flash technique. Heat capacity of selected samples was measured with differential scanning calorimetry, and these results were used to calculate the thermal conductivity. Microstructure of the various cast iron samples was quantified by standard metallography and image analysis techniques, and the chemical compositions were determined by optical emission spectroscopy.