This document specifies the fundamental formulae for use in the tooth root stress calculation of straight and helical (skew), Zerol and spiral bevel gears including hypoid gears, with a minimum rim thickness under the root of 3,5 m_mn. All load influences on tooth root stress are included, insofar as they are the result of load transmitted by the gearing and able to be evaluated quantitatively. Stresses, such as those caused by the shrink fitting of gear rims, which are superposed on stresses due to tooth loading, are intended to be considered in the calculation of the tooth root stress, σ_F, or the permissible tooth root stress σ_FP. This document is not applicable in the assessment of tooth flank fracture.

The formulae in this document are based on virtual cylindrical gears and restricted to bevel gears whose virtual cylindrical gears have transverse contact ratios of ε_vα < 2. The results are valid within the range of the applied factors as specified in ISO 10300-1. The bending strength formulae are applicable to fractures at the tooth fillet, but not to those on the active flank surfaces, to failures of the gear rim or of the gear blank through the web and hub.

This document does not apply to stress levels above those permitted for 10³ cycles, as stresses in that range can exceed the elastic limit of the gear tooth.

NOTE            This document is not applicable to bevel gears which have an inadequate contact pattern under load.

The user is cautioned that when the formulae are used for large average mean spiral angles (β_m1 + β_m2)/2 > 45°, for effective pressure angles α_e > 30° and/or for large facewidths b > 13 m_mn, the calculated results of this document should be confirmed by experience.