Nonlinear Dynamic Analysis for a Jeffcott Rotor Considering Varying Connection Stiffness of Bolted Joint

Bolted joints have been widely used in rotor assemblies of aircraft engines. A typical bolt joint is composed of two metal parts connected mechanically with pre-tensioned bolts. During operations, the bolting pretensions can vary with the changing contacting relationship between the parts, which makes the connection stiffness of the joint nonlinear on the macroscopic scale. The fundamental problems of the dynamical analysis for bolted joints are (1) to identify the transition of the change of the connection stiffness and properly model the overall connection stiffness and (2) to investigate the influence of such variable stiffness on the rotor vibration. In this paper, an analytical model is proposed considering the effect of bolted joints. The bolt of the joint is simplified as a two-node spring-like connection element considering different axial tension and compression stiffness, non-uniform preload of bolts and the contact interface friction described based on Coulomb friction. The dynamic equations of the rotor system are established based on the lumped mass modeling and the proposed connection element, and numerically solved through the Runge-Kutta method. The results indicate that the rotor system exhibits a variety of states, such as period-1 motion, multi-period motion, quasi-periodic motion and chaotic motion. The effects of friction coefficient and preload of the bolts on the nonlinear dynamic behaviors of the bolted rotor system are demonstrated in detail.