What shaft cracks in the rotor system may lead to?

Shaft cracks in a rotor system may lead to destructive failure, if undetected at the right time. The transient vibrations of a rotor system with transverse breathing crack during rotor shut-down has been analyzed using Finite Element Method (FEM) for flexural vibrations. Since the vibration signals during shut-down are non-stationary, the continuous wavelet transform (CWT) has been used to extract the crack feature when the rotor is decelerating through critical speed during shut-down. A parametric study for different crack depths and locations and for different accelerations has been studied, and it is found that the CWT can be effectively used to detect the crack during the rotor shut-down.

Unbalance in the rotor-bearing system induces bending fatigue loads on the shaft, which may cause cracking of the shaft during operation. Timely detection of shaft cracks increases the reliability of the rotating machines which otherwise leads to catastrophic failures. Detection and monitoring of fatigue cracks in a rotor-bearing system using vibration response is the subject of considerable interest since the past several years.

The earlier works mainly focused on the detection of cracks through steady-state vibrations, i.e. when the rotor is operating at the constant speed. The vibration signals during machine startup or rundown are transient (frequency changes with time) in nature. Crack detection through the transient vibration analysis is equally important especially for a high-speed machine which starts and stop quite frequently such as aircraft engines.