Experimental analysis of failure modes depending on different loading conditions applied on cylindrical polyamide 66 gears

Engineering plastics are increasingly used for engineering applications, such as the automotive sector, e-mobility sector, and household appliances. The use of engineering plastics is conditioned by the lack of knowledge of their material properties, especially for gears. A selection of the materials for a given gear pair has a significant impact on the mechanical and thermal response of the whole system. In this paper, steel-Polyamide 66 gear pairs were tested under various torques to define failure life and associated failure modes of the polymer gears. Additionally, to discover new knowledge on the field of tribological contact between observed gear pairs, meshing temperatures were monitored and correlated with calculated wear coefficients of Polyamide 66 material according to technical guideline VDI2736-2. The results show that gear flank wear of PA66 HT is directly proportional to the meshing temperature and torque. Thermal melting is a characteristic failure mode of the polymer gears which are exposed to higher load levels. In the middle torques, the dominant failure mode is flank fracture known as pitch point fracture. The greater impact of the gear wear mechanism occurs at lower torques where initial crack propagation starts at the pitch point and ends in the tooth root area.