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At the end of the 19th century, in the wake of railway transportation and the beginning of automotive vehicle production, new technology-based materials became necessary for the manufacture of brake systems to provide safer and more effective braking of vehicles transporting heavy loads at higher speeds. These devices serve to decelerate vehicles by friction, transforming most of the kinetic energy into thermal energy, which is dissipated by the brake system during the braking process [IOMBRILLER, 2002]. Many parts contribute actively or passively to a vehicle’s satisfactory performance, but safety is closely linked to the efficiency of the brake system, which is subjected to relatively high thermal and mechanical stresses during regular braking action. Therefore, a crucial factor is the precision of the analysis and development of brake systems taking into account all the aspects involved in their thermal and dynamic behavior [MAZUR et al., 2005]. During severe deceleration by braking, the temperature of the brake system may reach up to 650oC and overheating of the brake discs may lead to serious consequences that reduce the vehicle’s safety [IOMBRILLER, 2002]. This temperature variation causes thermal shock and localized overheating points, changing the behavior of the metal involved due to metallurgical transformations, as well as crack nucleation in the disc in response to plastic flow of the surface metal and inducing stresses after cooling [MAZUR et al., 2005]. Even disregarding the presence of thermal shock, a few braking cycles with abrupt deceleration still suffice to produce small cracks in the usable part of brake discs. The study of the mechanical behavior and fracture mechanisms of these materials is essential to allow for the design and rational use of these components. Figure 1 illustrates the failure in front brake rotor in a disc submitted to penetrating liquid inspection to reveal cracks. The cyclic stresses resulting from the continuous use of vehicles can cause fatigue, propagate cracks and fracture of the brake component [IOMBRILLER, 2002]. This mechanism may cause crack nucleation and growth in the material when subjected to cyclic strain. As cyclic loading conditions in brake discs are induced mainly by temperature gradients, thus essentially strain-controlled tests were planned for this study. In this way, it

Thermomechanical and Isothermal Fatigue Behavior of Gray Cast Iron for Automotive Brake Discs