Dynamic Modeling and Nonlinear Characteristics of a Cracked Bolt-Disk Combined Rotor System

Abstract

Different from the crack on the rotating shaft, the crack on the bolt which is a connecting part of the bolt-disc combined rotor is a kind of local defect. The local crack on the bolt under high pretension is always in open state, and it increases the overall vibration of the combined rotor significantly in practice. This paper studies the modelling of the crack on the bolt and nonlinear dynamic behaviors of the cracked bolt-disc rotor system. The circumferential bolts with a transverse open crack are treated as several bar elements under the assumption that each bolt has the same original tensile extension length. The cracked correction coefficient is introduced to describe the decreasing amount of bolt's tension due to crack. After this coefficient is obtained according to finite element method, the stiffness matrix of circumferential bolts with crack is built based on total potential energy. The dynamic model consists of a time-independent stiffness matrix for perfect bolts, a time-variant reductive stiffness and an additional moment. As a result, the crack in bolt reduces rotor's nonlinear stability and leads to greater vibration and fluctuation. In addition, crack depth has much larger influence than crack location on the dynamic behaviors.

Bolt looseness localization with connection-stiffness-varying flange

“…The failure forms include local cracks and * Author to whom any correspondence should be addressed. fatigue fractures, which are attributed to bolts being subjected to cyclic reciprocating loads at load-bearing positions of the structure over a long period [10,11]. In the early stages, these bolt failures manifest as bolt looseness.…”