Improvement of truck brake disc lifespan by material design

Premature failure by cracking is one of the major p roblems for truck brake disc lifespan. One improvement way is to evolve disc material with the aim of increasi ng their braking resistance. We chosed to modify th e graphite morphology and to study a nitrogen-enriched cast ir on with short graphite flakes and a cast iron with a microstructural gradient (small graphite flakes nea r the surface and coarse graphite flakes in the dep th) in comparison with a commercial grey cast iron. First step consisted in braking test on a lab-scale tribo meter to check their friction behavior. The test consisted i n a series of stop-braking and a series of slowdown s with heat accumulation. The results showed that the reduction of the graphite flake size does not have a signifi cant impact on friction behaviour. The second step consisted in thermal cycle testing to evaluate the thermomechan ical resistance of the new materials under cyclic loadin g. A specific test was developed, taking into accou nt the thermal stresses induced by braking. It is shown th at the cracks propagation is limited with short gra phite flakes. To develop this test to be as close as possible to real brake conditions, we based the test parameters choice on a previous coupled numerical-experimental study on full-scale braking.