Research On Evaluation Method For Fatigue Life Of Flexure Hinges

Compliant mechanism is a new mechanism using the elastic deformations of compliant components to realize transfers and conversions of the movement, force, and energy.Compliant mechanism can reduce the number of components, assemblage and friction and improve the accuracy. In Micro-Electro-Mechanical Systems and bionics, it has very high value. Static theory is enough for those compliant mechanisms which are used for just one time. However, periodic load is required in most compliant mechanisms. Alternation stress of flexible member which produces fatigue failure can be caused by periodic load. And fatigue failure would occur when the alternating stress is far lower than the yield strength. Flexible hinge is the weakest part of compliant mechanism. Therefore, it becomes more and more important to take analysis for flexure hinge and predict the fatigue life of the compliant mechanism.The circular flexure hinge is studied in this paper. The S-N curves of the circular flexure hinge are obtained through nominal stress approach and the finite element analysis method. Empirical equations for fatigue life and analysis of parameters effects are also studied. It is concluded that surface factor and dimension parameters such as curvature radius and the minimum thickness have great effect on the fatigue life. Meanwhile, the effect of eccentricity on the conic flexure hinges is also studied. Thus proper dimension parameters and processing methods should be chosen according to life requirement.A method for predicting the fatigue life of conic flexure hinges is proposed based on nominal stress approach and generalized equations of stress concentration factors for conic flexure hinges. The case studies demonstrated the effectiveness of the method for predicting the fatigue life of conic flexure hinges.This paper provides a support for the design of flexure hinge. The fatigue life of the conic flexure hinges can be calculated in preliminary design of the flexure hinges through this method to avoid unreasonable parameters.