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A better understanding of the thermomechanical loading of brake discs is important for controlling material fatigue and crack propagation in the disc. In the present study, full-scale drag braking experiments were performed on brake discs made from eight different grey cast iron alloys. The well-performing materials were also tested with an alternative brake pad material. A testing procedure with repeated drag brakings was used. The disc and pad temperatures were registered by thermocouples embedded at selected locations, and the disc surface temperatures by a thermocamera. Extensive analyses of the measured temperatures were performed. The results for the thermocouples at the mid-radius of the disc and at the end of brake applications indicatd that the two sides of the disc have opposite deviations from the mean temperature. The temperature deviations are generally temporally alternating, but also stationary variations can be found. The thermocamera gives the possibility of identifying the phenomena behind the temperature variations found from the thermocouples. Banding of the disc-pads contact with alternating one band and two bands of high temperatures is observed for the studied brake discs exposed to severe braking load cases. Moreover, it was found that hot-spot patterns develop on the disc surface, which are spatially fixed during each brake application. However, they may be either slowly migrating or fixed relative to the disc during consecutive brake applications. Thermal images show that small cracks do not affect hot-spot migration as a hot spot migrates over the crack. However, at a critical length of the crack, the heat becomes localized at the crack and increases its growth, thus limiting the life of the disc. The tests indicate that a combination of hot-spot migration, alternating bands and small temperature differences over the disc are significant factors to be considered when improving the lifespan of the discs.

The eect of adding a superimposed high-frequent strain load, denoted as a high-cycle fatigue strain component, upon a strain-controlled thermomechanical fatigue test has been studied on a compacted graphite iron EN-GJV-400 for dierent thermo-mechanical fatigue cycles and high-cycle fatigue strain ranges. It is demonstrated that the successive application of an high-cycle fatigue load has a consistent eect on the fatigue life, namely the existence of a constant high-cycle fatigue strain range threshold below which the fatigue life is unaected but severely reduced when above. This eect on the fatigue life is predicted assuming that microstructurally small cracks are propagated and accelerated according to a Paris law incorporating an experimentally estimated crack opening level.