Predicted influence of materials' thermal properties on disc brake roughness due to thermoelastic instability
Passenger car disc brakes occasionally exhibit objectionable vibration during operation. Low frequency vibration (< 100 Hz) that occurs when the brakes are applied is called brake roughness or judder and is caused by a variation in torque at the friction interface. Brale torque variation can result from disc thickness variation and/or thermal distortions. Thermal distortions or hot spots may occur during a long brake drag such as a mountain descent due to the onset of a phenomenon known as frictionally excited thermoelastic instability (TEI). Models of TEI can be used to predict the propensity of a brake system to generate torque variation or roughness during long brake drags. TEI modeling requires accurate materials properties such as Young's modulus, Poisson's ratio, specific heat, thermal diffusivity, thermal conductivity, density and thermal expansion of both the disc and the brake pad materials. The authors have measured the thermal transport properties of a series of disc materials, gray cast irons and aluminum metal matrix composites, and commercially available brake pad friction materials. For example, room temperature thermal diffusivity measured by the laser flash technique was found to vary from 0.002--0.009 cm{sup 2}/sec for friction materials, 0.15--0.21 cm{sup 2}/sec for gray cast irons, and 0.43--0.89 cm{sup 2}/sec for aluminum metal matrix composites (Al MMCs). This paper will consider the behavior of Al MMC rotors versus traditional gray cast iron rotors coupled with a non-asbestos organic brake pad. The relevant materials properties were used in a TEI analytical model of a mid-sized passenger car disc brake. The analysis shows that Al MMC rotors have a lower critical speed at which TEI is predicted to occur than gray cast iron rotors.
- Research Organization:
- Ford Research Lab., Dearborn, MI (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 20014214
- Resource Relation:
- Conference: 1999 TMS Fall Meeting, Julia R. Weertman Symposium: Advanced Materials for the 21st Century, Cincinnati, OH (US), 10/31/1999--11/04/1999; Other Information: PBD: 1999; Related Information: In: Advanced materials for the 21st century: The 1999 Julia R. Weertman symposium, by Chung, Y.W.; Dunand, D.C.; Liaw, P.K.; Olson, G.B. [eds.], 585 pages.
- Country of Publication:
- United States
- Language:
- English
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