scope:

n this paper, the method to calculate the risk of tooth flank fracture, which is defined in the current draft of ISO DTS 19042-1, is investigated and discussed. Part of this investigation is a sensitivity analysis with respect to the main gear parameters. Therefore, parameters including pressure angle, helix angle, normal module, hardness depth, tip relief, and crowning were systematically varied and the respective safety factor against tooth flank fracture was calculated.

With this method, it can be shown that the risk of tooth flank fracture and the risk of pitting might have opposite trends. It is also shown that a tip relief on spur gears typically has no effect or might even increase the risk of tooth flank fracture. On helical gears, the situation is more complex. For lead modifications, a certain beneficial effect is seen by compensating misalignments of the flanks; however, if the modification chosen is too large, it will increase the risk of tooth flank fracture.

In the first part of the paper, some formulas of the draft are discussed. There, it is shown that the definition of the material factor and the calculation of the course of the hardness into the depth of the material could be improved.