Computer-Aided Fatigue Design of Power Transmission Shafts Using Three-Dimensional Finite Shaft Element and Updated Mean Stress Diagram

A three-dimensional flexural shaft element is developed for elastic analyses of power transmission shafts and geared systems. It is used for the computer-aided fatigue design of three-dimensionally loaded power transmission shafts on many rigid or elastic bearings. Bagci’s mean stress diagram—which removes the flaw related to the load line slope of zero value in the presently used mean stress theories—is used to determine the failure value of the reduced fatigue strength of the shaft at the critical sections considered. Basic stresses are defined using maximum energy of distortion theory. An interactive computer program is prepared for fatigue design of power transmission shafts, in which some of the strength reducing factors for each notch location are determined using generalized expressions. The program initially locates the weakest section on the shaft, then it redefines the dimensions for the desired factor of safety, reliability and the fatigue life at that section. An application example is included.