Research On Maximum Stress Calculation Method Of Flexure-Based Mechanisms

A compliant mechanism is a device which achieves some or all of its motion through the deflections of flexible segments. A compliant mechanism exhibits many advantages over its rigid-body counterpart, such as increased precision, decreased manufacturing, and reduced number of parts. Therefore, it attracts wide attention from both academia and industry. Because the flexure hinges are the most vulnerable parts in a flexure-based mechanism due to their smaller dimensions and stress concentration characteristics, evaluating the maximum stresses generated in them is crucial for assessing the workspace and the fatigue life of the mechanism. Therefore, we need to build a accurate modeling, predicted the maximum stress of flexure-based mechanisms by stress concentration factor and insure the fatigue life, all of these are important to design and optimize flexure hinges.Stress concentration factors characterize the stress concentrations in flexure hinges, providing an analytical and efficient way to evaluate the maximum stress. In this work, by using the non-dimensional parameter ζ=pc/t as the only fitting variable, generalized equations for both the bending and tension stress concentration factors were obtained for two generalized models, the conic model and the elliptic-arc-fillet model, through fitting the finite element results. The equations are applicable to commonly used flexure hinges including circular, elliptic, parabolic, hyperbolic, and various corner-fillet flexure hinges, with acceptable errors. The empirical equations are tractable and easy to be employed in the design and optimization of flexure-based mechanisms. The case studies of the bridge-type displacement amplifiers demonstrated the effectiveness of the generalized equations for predicting the maximum stresses in flexure-based mechanisms. Furthermore, based on the theoretical stress concentration factor, the paper makes a preliminary research on effective stress concentration factor which is more accurate to describe the stress concentration.The equations for both the bending and tension stress concentration factors were proposed in the paper for two generalized models is simple, versatile and convenient to use for design work.