Improving strength for automotive plastic gears through directional fibre reinforcement

In this paper, a new topology of reinforcing plastic gears with carbon fibres is introduced. The reinforcement is placed tangentially to the critical cross section at the tooth fillet to improve bending strength. The mechanical modelling of the fibrous reinforcement is performed using an anisotropic material stiffness matrix derived from the analysis of a representative volume element using commercial stress analysis software. Benchmarking against conventional plastic gears illustrates that the maximum fillet stress, which is responsible for tooth failure in overloading conditions is greatly reduced, therefore rendering these gears suitable for considering their use in high load applications such as in the automotive industry. Also, the effect of the thickness of the reinforcement on the maximum developed tensile stress at the root is examined. The results show significant decrease of the bending stress at the root fillet rendering this design an alternative way in reinforcing plastic gears.