Dynamic modelling and vibration characteristics analysis for the bolted joint with spigot in the rotor system

Abstract

The bolted flange joints with spigot (short for bolted joints) are widely used in the rotor system of aero-engine. The current models of the bolted joint usually ignore the spigot, therefore cannot account for the effect of spigot on joint's mechanical characteristics. In this paper, a new analytical model of bolted joint is proposed to describe its nonlinearity under bending moment. The model takes into account the sticking and sliding statuses of spigot by introducing a Jenkins element, therefore is able to describe the joint's damping effectively. By performing a comparison study with the finite contact element model, the accuracy of the proposed model is validated. Meantime, the comparison study highlights the important role of spigot on the hysteresis nonlinearity of the bolted joint. After that, a dynamical model of the bolted rotor is developed, in which the proposed bolted joint model is introduced by considering the influence of rotor's whirl motion. Based on the dynamical model, the dynamic characteristics of the bolted rotor are investigated in detail. The results show that the bolted joint mainly produces stiffness loss and damping nonlinearity into the rotor system. The stiffness loss occurs in any loading conditions and leads to a decrease of the rotor's critical speed. While the damping nonlinearity is mainly excited under large unbalance, it may induce a self-excited components in rotor's response at super-critical speed. The influence of the bolted joint on rotor dynamics can be reduced by decreasing flange length, friction coefficient and interference fit of the spigot.