The middle layer model has been used in recent years to better describe the connection behavior in composite structures. The influencing parameters including low pre-screw and high preload have the main effects on nonlinear behavior of the connection as well as the amplitude of the excitation force applied to the structure. Therefore, in this study, the effects of connection behavior on the general structure in two sections of increasing damping and reducing the stiffness of the structures that

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... lead to non-linear phenomena have been investigated. Due to the fact that in composite structure we are faced to the limitation of increasing screw preload which tend to structural damage, so the investigation on the hybrid connection (metal-composite) behavior is conducted. In this research, using the two-dimensional middle layer theory, the stiffness properties of the connection are modeled by normal stiffness and the connection damping is modeled using the structural damping in the shear direction. Nonlinear frequency response diagrams have been extracted twice for two different excitation forces and then proposed by a high-order multitasking approximation according to the response range of the nonlinear finite element model for stiffness and damping of the connection. The effect of increasing the amplitude of the excitation force and decreasing the preload of the screw on the nonlinear behavior of the component has been extracted. The results show that the limited presented novel component model has been accurately verified on the model obtained from the vibration experimental test and the reduction of nonlinear model updating based on that is represented. The comparison results show good agreement with a maximum of 1.33% error.