Residual Stresses in Grey Cast Iron Brake Rotors

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    William T. Donlon, Gregory M.Vyletel and James W. Fash, Ford Motor Co.
    Camden Hubbard, Steve Spooner and Andrew Payzant, ORNL
Background

Ford Motor Company has used the neutron diffraction facilities of the HTML User Center to investigate the effects of a heat treatment intended to reduce residual stresses in disc brake rotors. Residual stresses are believed to increase the rate of deformation of the rotors during overheating caused by severe braking conditions. This deformation results in non-parallel surfaces on the disc brake rotor, which generate objectionable vibrations during braking ("brake judder"). Brake judder is currently solved by replacing a customers brake rotors or remachining the rotors to bring them within design tolerances. Minimizing brake judder in Ford products without sacrificing vehicle handling and at a reasonable cost is a major effort within the Ford Research and Ford Advanced Engineering Centers. To accomplish this goal the Ford engineers must know the magnitude and variations of the residual stresses due to the casting operations. Using the unique neutron diffraction facilities at HTML, Ford researchers were able to quantitatively map out the residual stress distributions in two production discs and compare these results to a "stress-relieved" disc.


Radial strains measured in the inboard disc before and after heat treatment, showing the reduction in strain.


Results from these neutron diffraction experiments suggested that residual stresses were reduced by factors of 5 to 10 by stress relief heat treatment. In a follow-up study, one of the previously characterized "production" brake disc was re-examined following a stress-relieving heat treatment at Ford. The nondestructive neutron diffraction strain mapping provided a quantitative measure of the reductions in residual microstrain, allowing quantitative evaluation of the effectiveness of the thermal treatment.

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  • These results were presented at the ASM 2nd International Conference on Quenching & Control of Distortion, November 1996.

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Acknowledgments

URL: http://www.html.ornl.gov/rsuc/rotor.html