The geometry of plastic gears used today is usually based on conventional steel gears, which are bound to the restrictions of the machining production of gears. The injection molding process provides more design freedom here. In this work, simulative results in terms of tooth root stress in plastic gears with various tooth root fillet designs are shown. The simulation method is based on finite element analysis and takes into account the different fiber orientation as well as the complex material behavior of short fiber reinforced plastics.

The analysis includes fully rounded, elliptical and bionic tooth root fillets. The calculation is carried out with homogeneous material (unreinforced thermoplastics) as well as with short-fiber reinforced plastics. In addition to the tooth root stress in the initial state, results are also presented for the geometry changed by abrasive wear during operation. For the initial condition, the results of the finite-element analysis are compared with analytical calculation methods.

The study shows the potential of stress reduction by specific geometrical adjustments as well as the change of the maximum tooth root stress over the running time of plastic gears. The research results can be an aid in the design of plastic gears to achieve a higher tooth root load carrying capacity.