Estimation of frictional damping of bolted plate structures by dynamic contact analysis

Abstract

In mechanical structures where the components are joined by bolts, the vibration damping depends mainly on energy dissipation due to friction at the contact surfaces. In this paper, we propose a method for estimating modal damping ratios of bolted structures with partial overlap region by the dynamic finite element contact analysis. First, the eigenvalue analysis considering the contact surface stiffness is performed and the natural frequencies are evaluated to determine the pressure load to be applied to the contact surface in the contact analysis. Then the transient analysis is performed with a single frequency sinusoidal forced displacement to obtain the frictional dissipated energy for each mode shape and the modal damping ratios are estimated from the dissipated energy. The validity of the proposed method is confirmed by comparing the estimated damping ratios with the experimental results. We carry out the contact analyses by varying the excitation amplitude to examine the amplitude dependence of the damping ratio and reveal the reason for its amplitude dependence based on the slip velocity and the frictional force on the contact surface. The results show that the modal damping ratios have a strong amplitude dependence. The damping ratios change drastically in the lower amplitude range while they indicate a small change in the higher amplitude range. This is because the transitions from sticking to slipping occur over the whole contact area in the lower amplitude range, as a result, the dissipated energy rapidly increases compared to the vibration energy. In contrast, the dissipated energy increases at the same rate as the vibration energy in the high amplitude range.