Diaphragm stress analysis and fatigue strength evaluation of the flex-spline, a very thin-walled spur gear used in the strain wave gearing

This paper deals with diaphragm stress analysis and fatigue strength calculation problems of the flex-spline, a thin-walled spur gear used in the strain wave gearing (SWG). Firstly, a mechanics model and theoretical method used for contact analysis of SWG are presented in this paper. Then finite element method (FEM) software is self-developed through very long time efforts in order to realize the contact analysis and stress calculations of SWG. With the developed FEM software, bending and shear stresses of the diaphragm of the flex-spline are analyzed successfully. Secondly, in order to confirm the FEM software, an experimental method and device are presented in this paper. A three-directional, strain gauge is stuck on a straight surface of the tapered diaphragm of the flex-spline next to the corner of the diaphragm with the boss. Diaphragm strains are measured under the conditions of zero and 110 Nm torques respectively and the measured stresses are compared with the calculated ones with the developed FEM software under the same conditions. It is found that the two results are in agreement with each other well. This means that the presented mechanics model and theoretical method are correct and effective. Finally, a method used to evaluate fatigue failure strength of the diaphragm is suggested based on the findings in this paper.