Contact and Bending Stresses

To calculate the contact and bending stresses acting between the teeth of a pair of gears meshing under load, it is necessary to include in the stress formulas a number of factors that account for the geometry of the teeth, the physical properties of the materials used, and the nature of the specific application.

AGMA 908-B89 Information Sheet ^[2] gives equations for calculating the pitting resistance geometry factor, I, for external and internal spur and helical gears; and the bending strength geometry factor, J, for external spur and helical gears that are generated by rack-type tools (hobs, rack cutters, or generating grinding wheels) or pinion-type tools (shaper cutters). The document includes 66 tables of geometry factors, I and J, for a range of typical gear sets and tooth forms of 14 -, 20-, and 25-deg pressure angles and 0-, 10-, 15-, 20-, 25-, and 30-deg helix angles.

The Information sheet was prepared to assist designers making preliminary design studies and to present data useful to those without access to computer programs. Not all tooth forms, pressure angles, and pinion and gear modifications are covered. Neither are these data applicable to all gear designs; however, the data should be helpful to the majority of gear designers. Data from this Information Sheet are used with the rating procedures described in AGMA 2001-B88, Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth,...