Modal analysis of a rotor with a cracked shaft

Abstract

Modal analysis of a flexible, non-rotating rotor with a crack in a shaft is presented. The Jeffcott model of the rotor consists of the massless shaft and a disk concentrating the mass of the full system. The model includes ball bearings supporting the shaft and the model of the transverse shaft crack located near the disk. Simulation results present changes in natural frequencies of the system with the changing angular position of the rotor. Those changes are observed as doubled natural frequency peaks in the rotor’s frequency responses. They appear only for the cracked rotor and can be explained by shaft stiffness changes due to the opening and closing of crack faces under gravity. The results of the conducted numerical analyzes demonstrate that these doubled frequency peaks can be used for early shaft crack detection.