Influence of unbalance angle and eccentricity on the vibration of a cracked rotor

Many fatigue crack models in literature neglect the effects of dynamic loads such as mass unbalance. A breathing model that includes the effects of unbalance angle and eccentricity on the breathing mechanism of a fatigue crack is proposed. When the proposed model was used to simulate the vibration of a cracked rotor, it was revealed that 120–180° placement of the unbalanced mass relative to the crack direction resulted in critical speed and peak amplitude values similar to an undamaged shaft. Also, 180° placement of the unbalanced mass resulted in the diminishing of 2× and 3× frequency amplitudes for a poorly balanced rotor. However, a decently balanced rotor still revealed an appreciable 2× frequency amplitude despite 180° placement of the unbalance mass. These findings suggest that unbalance angle placement can only shroud the presence of cracks in poorly balanced rotors, therefore highlighting the importance of controlling the unbalance angle and magnitude to ensure the greatest detection of fatigue cracks