The use of plastic gears in drives is growingrapidly, especially in the module size range 0.5to 1.5 mm and at maximum load cycles duringthe product life of 105 to 106. A key factor forreliability is the tooth root strength of the gears.Although injection moulding, which is thecommon production method for plastic gears,allows a high degree of freedom in designingthe tooth root geometry, plastic gears areusually fully rounded with a constant radius,similar to the production of conventional steelgears. The calculation method according to VDI2736 also assumes such a tooth root shape.However, the special properties of the materialplastic (non-linear modulus of elasticity,transient behaviour) with its high strain ratesare not taken into account. To obtainmeaningful results for an optimal tooth rootrounding, the exact understanding of thedamage criterion of plastics or plastic groupshas to be researched. The focus here is onPOM and PA66. With this knowledge, it ispossible to design plastic gears in an optimumway concerning their load and the speed of theforce impact. In the further course of the project,various tooth root geometries on plastic gearswill be tested theoretically and experimentallyand potentials for increasing the load-bearingcapacity will be derived.Essentially, the material/failure behaviour ofplastic gears is to be investigated in thisresearch project, the tooth root geometry isoptimised from this and thus impulses for thefurther development of VDI 2736 in thestandards committee has to be made.