Influence of pressure and deflection loads on the critical behavior of flexible joints

Flexible joints are axisymmetric composite structures composed of spherical elastomeric rings alternating with reinforcement rings, an outer fixed attach ring and an inner movable attach ring. In the present work, a miniature flexible joint with silicone rubber as the elastomer was designed and tested in order to study the variation regularity of spring ratio torque with pressure and deflection loads. It was found that the spring ratio torque presents a down and up trend with the increase of pressure and vector angle. The relationship between the strain of elastomer and mechanical properties of flexible joint are obtained based on the finite element model (ANSYS) of flexible joints and constitutive model parameters of elastomeric material. Simulation results are in good agreement with the experimental data. A correspondence relationship is proved between knee points of the shear strain-modulus curve of elastomeric material and spring ratio torque-pressure (or vector angle) curve of the flexible joint. Results highlight that the above phenomenon is caused by the shear modulus of silicone rubber and relate to the value and distribution of strain. Further research found that the theory is also applicable for flexible joints with natural rubber as the elastomeric material.