Copper and other heavy metals are used to generate friction in vehicle brake and clutch systems to slow down wheels or transmit torques. Frictional material formulations are complex material systems that also include various ingredients for wear resistance, thermal stability, and mechanical strength. Existing laws and regulations require phase out of copper and other heavy metals in brake pads to reduce contact of metal particulates from brake wear with storm water and discharge into nearby waterways, to limit adverse effects on aquatic life. Substitutions for metals have been suggested to include graphite, carbon fibers, nanotubes, and ceramics; however, their introduction can lead to operational safety issues, primarily through loss of friction due to thermal-mechanical instabilities. This Grant Opportunities for Academic Liaison with Industry (GOALI) Program award will support an investigation of these instabilities in brake pad component materials. The project will deliver an engineering analysis tool facilitating manufacturers a cost-effective way to meet laws or ideally exceed future regulations. The development of non-toxic frictional material alternatives will allow U.S. manufacturers to gain global market share by offering safe and high-performance brake and clutch products. Other industries using friction materials include aerospace, oil and gas, mining, and defense. In addition, this project will support the development of graduate and undergraduate courses and offer research and internship opportunities for historically underrepresented undergraduate and high school students.
In this project, computational models accounting for fundamental material characteristics and processing conditions will predict the performance of engineered frictional materials related to thermal-mechanical instabilities (TMI). The TMI phenomenon is a structural instability induced by the interaction between thermal expansion, dynamics, and mechanical stresses under high-speed contact. The onset of TMI can lead to cracks, material damage, vibration, noise, and mechanical failure; therefore, an investigation of TMI in the next generation of metal-free frictional materials systems is imperative. This work will improve fundamental understanding of compression and packing effects on the anisotropic properties of frictional materials. In this project's approach, a multiscale model of heterogeneous materials will incorporate the effects of composition and morphology of particulate or fibrous ingredients on the effective mechanical properties. The predicted properties will evaluate susceptibility of specific material compositions to TMI. Reduced-order models will be developed to combine the effects of elasticity, dynamics, contact mechanics, and thermal buckling. The research will be primarily computational, where the industry collaborators will validate key results through materials characterization and experimental measurements of critical braking speed and temperature.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
