Loaded Behaviour of Gear Made of Fibre Reinforced PA6
Résumé
This paper presents an original method for computing the loaded mechanical behaviour of fibre reinforced polymer gears. Polymer gears replace metal ones in many motion and light power transmission applications. They present several advantages: they can be used without lubricant, meshing is quieter, resistance to corrosion is better, weight is reduced...Although thermoplastic gears are unsuitable for application transmitting high torque, and an addition of fibres can significantly increase their performance. The mechanical behaviour of polymer materials is very complex because it depends on time, history of displacement, temperature and, for several polymers, on humidity. Moreover, fibres make the material anisotropic. The particular case of polyamide 6 + 30% glass fibres is studied in this paper. The first part of the paper deals with moulded gear specificity. The moulded gear geometry and fibre orientation studies are based on moulding simulation and experimental investigations. A mould was developed to have a better understanding. Based on those observations and with the help of mechanical characterisation, a behaviour model was created, based on a generalized Kelvin-Voigt law. This model was defined to compute the displacement of the polymer material. It can take into account a wide relaxation time spectrum of the polyamide 6, as well as room temperature and humidity influences. In a second time, the viscoelastic model is integrated in quasi-static load sharing computation developed by the LaMCoS laboratory. The load sharing is obtained with the displacement compatibility relation in a large meshing over the entire surface of the tooth. This relation integrates the viscoelastic displacement and the geometrical influence coefficients. These coefficients allow the integration of both the bulk and contact deformations. The surface and bulk temperature increasing, due to the friction, is also taken into the load sharing computation. The method permits to obtain results such as the load sharing, the loaded transmission error, the instantaneous meshing stiffness and the root tooth stresses at different temperature, humidity and rotation speeds.