Modeling and nonlinear dynamic analysis of bolt joints considering fractal surfaces

The surface morphology has an important influence on the dynamic response and bolt loosening of bolted joints. In this paper, based on the fractal contact model, an original nonlinear dynamic model of the bolted joint structure including the piecewise restoring force and dry friction is proposed to predict the normal and tangential coupling vibration and investigate the dynamic characteristics. The relative sliding behavior between bolts and connected parts is considered for avoiding the bolt loosening failure, which is rarely mentioned in previous studies. Furthermore, normal and tangential fractal contact stiffness models are experimentally validated by comparing the modal test and finite element simulation with virtual material layer. The joint interface is equalized as the equivalent layer in the FE model, and its material parameters are deduced by the measured surface profiles. Numerical simulation is employed to investigate the effects of harmonic excitation, bolt preload and fractal parameters on the dynamic characteristics. The abundant nonlinear phenomena, such as quasi-period motion, chaotic motion and jump discontinuous, are captured. The predicted nonlinear vibration response is helpful for preventing the resonance and instability of system.