David Balloy

Braking performance and influence of microstructure of advanced cast irons for heavy goods vehicle brake discs

It is well known that truck brakes dissipate several megajoules of energy every few seconds, which leads to high thermal stresses in the rubbing parts. Therefore, premature failure by cracking of truck brake discs is a matter of major concern. Improving the design and material of brake discs may enhance braking performance. This study focuses on the latter aspect and was carried out with the aim of developing new material solutions for increasing disc lifespan. To do so, braking experiments were conducted on a specially designed braking tribometer. The brake pads that were used were made from a commercial brake lining material. Two advanced cast irons with different graphite morphology were studied in comparison with the lamellar grey cast iron commonly used for brake disc. To verify the friction and thermal behaviour of the two cast irons, braking tests were carried out as a series of stop-brakings with increasing dissipated power and energy and as a series of slowdowns to achieve heat accumulation effects. Thermal phenomena were studied through bulk temperature measurements and infrared monitoring of the disc surface. Friction behaviour, braking performance and variations in thermal loading were analysed in relation to the level of energy dissipation. The two advanced cast irons and lamellar cast iron had equivalent braking performance and stored similar amounts of heat, according to their thermophysical properties. Observations of the rubbing surfaces indicated damage mechanisms affected by the graphite morphology. Less plastic deformation on the surface was observed with an interdendritic graphite.

Determination of the Microstructural Creep Properties of Cast Iron Connector at High Temperatures for the Prediction of the Thermo-Mechanical Behavior of Anodic Assemblies

The prediction of the air gap at the cast iron to carbon interface in the anodic assemblies as well as its closing and pressure build-up during the operation remain a complex task. It is therefore very difficult to predict the electrical performance of anodic assemblies. This main difficulty comes from the evolution of the thermophysical and thermo-mechanical properties of the microstructure mapping during these stages. To overcome this difficulty, a natural approach is to characterize this mapping of microstructures.