This document specifies the fundamental formulae for use in tooth bending stress calculations for involute external or internal spur and helical gears with a rim thickness s_R > 0,5 h_t for external gears and s_R > 1,75 m_n for internal gears. In service, internal gears can experience failure modes other than tooth bending fatigue, i.e. fractures starting at the root diameter and progressing radially outward. This document does not provide adequate safety against failure modes other than tooth bending fatigue. All load influences on the tooth root stress are included in so far as they are the result of loads transmitted by the gears and in so far as they can be evaluated quantitatively.

This document includes procedures based on testing and theoretical studies such as those of Hirt^[11], Strasser^[14] and Brossmann^[10]. The results are in good agreement with other methods (References [5], [6], [7] and [12]). The given formulae are valid for spur and helical gears with tooth profiles in accordance with the basic rack standardized in ISO 53. They can also be used for teeth conjugate to other basic racks if the virtual contact ratio ε_αn is less than 2,5.

The load capacity determined on the basis of permissible bending stress is termed "tooth bending strength". The results are in good agreement with other methods for the range, as indicated in the scope of ISO 6336-1.

Cross References:
ISO 4287:1997
ISO 4287:1997/Amd 1:2009
ISO 4287:1997/COR 1:1998
ISO 4288:1996
ISO 4287:1997/Cor 2:2005
ISO 6336-1
ISO 6336-5
ISO 53:1998
ISO 1122-1:1998 (R09)
VDI 2737
DIN 3990 (all parts)
ISO/TR 10064-4
VDI 2226
TGL 10545:1963
ISO 1328-1:2013
ISO 701:1998 (R08)
ISO 54:1996


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