Contact instability identification by phase shift on C/C friction materials

Carbon-carbon (C/C) composite material is currently among the most promising engineering materials for friction applications, where excellent tribological properties, lightweight and good thermal stability are needed. As a result, the industrial demand for C/C composite leads to the need to characterize in detail the frictional and vibrational response of such material, when adopted for high performance braking applications. In this context, the present work shows an experimental and numerical characterization of unstable friction-induced vibrations caused by frictional contact between C/C specimens. The results provide information on the C/C material behavior at high-temperature conditions as well as additional tools to distinguish the occurrence of different vibrational phenomena. The phase shift between vibrational signals has been correlated to different kind of contact instabilities (either mode coupling or negative friction-velocity slope), that can arise and bring to high amplitude oscillations and noise emission. Such correlation has been observed experimentally and reproduced numerically.