Calculation of load capacity of spur and helical gears — Part 4: Calculation of tooth flank fracture load capacity

This document describes a procedure for the calculation of the tooth flank fracture load capacity of cylindrical spur and helical gears with external teeth.

It is not intended to be used as a rating method in the design and certification process of a gearbox.

The formulae specified are applicable for driving as well as for driven cylindrical gears while the tooth profiles are in accordance with the basic rack specified in ISO 53. They can also be used for teeth conjugate to other racks where the actual transverse contact ratio is less than εα = 2,5. The procedure was validated for case carburized[15] gears and the formulae of this document are only applicable to case carburized gears with specifications inside the following limits:

— Hertzian stress: 500 N/mm2 ≤ pH ≤ 3 000 N/mm2;

— Normal radius of relative curvature: 5 mm ≤ ρred ≤ 150 mm;

— Case hardening depth at 550 HV in finished condition: 0,3 mm ≤ CHD ≤ 4,5 mm.

This document is not applicable for the assessment of types of gear tooth damage other than tooth flank fracture.