This paper discusses research into the possibility of reducing gear tooth root stresses by adding internal stress relief features. For many years, gear designs have improved with the incremental addition of design features. Materials have improved, surfaces are selectively hardened with heat treatment and carborization, and shot peening is used to improve surface properties. All of these improvements are related to material attributes. Little has been done to change the gear geometry to improve durability and strength. Although the exterior of the gear is governed by the necessary involute profile of the teeth, nothing prevents interior changes. In this study holes were drilled along the axis of a test gear segment in an effort to provide stress relief in critical areas. A finite element model was constructed for use in a systematic test of the effect of hole size and hole placement on tooth root stress. A constant force was applied at the pitch diameter, and all results were normalized with respect to the values obtained for a solid gear. Results show that it is possible to reduce the tooth root tensile stress considerably without producing stresses in the holes greater than on an unmodified gear. These results were verified by photoelastic testing on greatly oversized plastic models. Since gear teeth fail due to fatigue over many cycles, even a slight reduction in the root tensile stress produces a great increase in fatigue life.

1.
ANSI/AGMA 2001-C95, January, 1995, “Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth.”
2.
ANSYS 5.0 Manual, Swanson Analysis Systems, 1992.
3.
Chang, S. H., Houston, R. L., and Coy, J. J., June, 1982, “A Finite Element Stress Analysis of Spur Gears Including Fillet Radii and Rim Thickness Effects,” University of Cincinnati Research Annals, College of Engineering, Number MIE 115, Vol. 82.
4.
Coy, J. J., and Hu-Chin Chao, C. December, 1981, “A Method of Selecting Grid Size to Account for Hertz Deformation in Finite Element Analysis of Spur Gears,” ASME Publication.
5.
Dally, J. W., and Riley, W. F., 1991, Experimental Stress Analysis, Third Edition, McGraw-Hill, New York.
6.
Dippery, R. E., 1990, “A Study in Stress Concentration Optimization Using Boundary Element Methods,” Ph.D. Dissertation, University of Cincinnati.
7.
Dudley, D. W., 1984, Handbook of Practical Gear Design, McGraw-Hill, New York.
8.
Kuske, A., Robertson, G., 1974, Photoelastic Stress Analysis, John Wiley & Sons, New York.
9.
Srinivasulu, B., 1992, “Spur Gears—A New Approach to Tooth Design,” American Gear Manufacturers Association, Technical Paper 92FTMS1.
10.
Von Eiff
H.
,
Hirschmann
K. H.
, and
Lechner
G.
, December,
1990
, “
Influence of Gear Tooth Geometry on Tooth Stress of External and Internal Gears
,”
ASME JOURNAL OF MECHANICAL DESIGN
, Vol.
112
, pp.
575
583
.
11.
Yang, T. Y., 1986, Finite Element Structural Analysis, Prentice-Hall, Englewood Cliffs, New Jersey.
This content is only available via PDF.
You do not currently have access to this content.