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Abstract. The spherical flexible joint is extensively used in engineering. It is designed to provide flexibility in rotation while bearing vertical compression load. The linear rotational stiffness of the flexible joint is formulated. The rotational stiffness of the bonded rubber layer is related to inner radius, thickness and two edge angles. FEM is used to verify the analytical solution and analyze the stiffness. The Mooney-Rivlin, Neo Hooke and Yeoh constitutive models are used in the simulation. The experiment is taken to obtain the material coefficient and validate the analytical and FEM results. The Yeoh model can reflect the deformation trend more accurately, but the error in the nearly linear district is bigger than the Mooney-Rivlin model. The Mooney-Rivlin model can fit the test result very well and the analytical solution can also be used when the rubber deformation in the flexible joint is small. The increase of Poisson's ratio of the rubber layers will enhance the vertical compression stiffness but barely have effect on the rotational stiffness.

Bridge-type flexure hinge is a classical flexure amplification mechanism. The amplification ratio and stiffness are the key parameters in an amplification mechanism. Elastic mechanics was used to analyze the input and output stiffness of bridge-type amplification mechanism in relation to the translational and rotational stiffness of the flexure pivots. The result showed that the stiffness model can explain well the outer characteristic of bridge-type flexure hinge.