Analytical Study of Bolt Looseness Effect on Nonlinear Vibration Behavior of Bolt Joints

Bolt connections often loosen under environmental loading conditions and system vibrations, which can lead to disaster risks during its operation. In this study, the behavior of nonlinear vibrations of an aluminum single-lap joint has been studied analytically and experimentally. Accordingly, considering the effects of nonlinear behavior at the bole joint, a nonlinear two-degree of freedom model for this type of connection is proposed. Then, in order to determine the unknown parameters of the proposed model, the vibrational and dynamic properties of this structure have been estimated using experimental modal analysis and model updating method. Finally, the effect of amplitude of the excitation force and the preload force of the bolts on the dynamic behavior of these systems has been studied analytically. Examination of amplitude-frequency curves shows that reducing the preload force of the bolts reduces the natural frequency and also distorts the amplitude-frequency curve to the left side, which indicates the softening nonlinear behavior of the system with decreasing applied bolt preload force. In addition, the comparison of the theoretical and experimental natural frequencies shows that the proposed model predicts the vibrational characteristics of these systems with a good accuracy and using the proposed model can study the dynamic behavior of these systems for different parameters.