This Standard takes into account many modern theories and has been substantiated, in part, by laboratory testing.
This Standard is not intended as a textbook. It is written for use by those skilled in the art of shaft design and stress calculations. This Standard provides a common basis for discussion and understanding between persons involved in shaft design.
A design procedure is presented for computing the diameter of either hollow or solid rotating steel shafts under combined cyclic bending and steady torsional loading for unlimited life. The method is based on an elliptical variation of fatigue strength with increasing torque as exhibited by combined stress fatigue data.
The corrected reversed-bending fatigue limit of the shaft to be designed is used in the recommended design formula. It is calculated from the fatigue limit of the material from rotating beam specimen data, such as that listed in Appendix B. Fatigue modifying factors are cited to correct the polished, unnotched specimen data for a number of service factors. These service factors include surface condition, size, reliability, temperature, duty cycle, fatigue stress, concentration, and miscellaneous effects.
Although the present design procedure ensures that the shaft is properly sized to provide adequate service life, it is not the only shaft design consideration. A shaft must also be stiff enough to limit deflections of key power transfer elements such as gears and pulleys, and also have sufficient stiffness to minimize misalignment through bearings and seals. Furthermore, the shaft must have sufficient radial and torsional stiffness or lack of stiffness to avoid unwanted vibrations at the operating speed, These factors have not been included in this Standard,although checking them is good design practice. Calculation procedures for these factors may be found in most machine design textbooks. An example of how to calculate shaft deflection and critical speed is given in Appendix C.