Non-Linear Characters of Stiffness of Combination Structure Based on Equivalent Model

In the case of different axial loads, a combination structure shows its non-linear axial stiffness, which is hard to calculate. To solve this problem, an equivalent model, bending beam-double springs, was proposed. The influence of bolt pre-tightening force and geometric parameters on the non-linearity of joint axial stiffness of combination structure with different material properties of gaskets was discussed. Results indicate that when aluminum alloy gasket is used, inflection point occurs in axial load-displacement curve between the stages of stress and tension. When graphite gasket is used, displacement curve demonstrates apparent non-linear stiffness in the stages of both stress and tension. Compared with the thickness of the gasket, bolt pre-tightening force, flange thickness and position of the bolt play a more significant role on axial stiffness, and the influence law is related to loading direction and material properties of gasket.