Crack detection in shafts via analysis of vibrations and orbital paths: A comparison

Shafts are often subjected to difficult operating conditions in high-performance rotating equipment such as compressors, steam and gas turbines, generators and pumps. As a result, shafts are susceptible to fatigue failures due to transverse cracks. Formation and propagation of cracks in rotors represent a fundamental problem. Vibration monitoring is one approach for detecting cracks, it is known that the presence of faults alters the vibrational characteristics of rotor dynamic systems, and therefore, those variations have often been used to detect damage in rotating machinery. Another method is observation of the rotor orbitals which vary in the presence of cracks. In this study, both vibration monitoring and orbital paths were used to detect the presence of a flaw in a shaft. The flaw considered is a straight slot, representing an open crack. Specimens of different depths were examined in order to assess the detection capability. The presence of a straight slot in the shaft was found to be detectable and the flaw size can be classified. Observation of the orbital paths created at different rotating speeds is examined for indication of flaw detection and a new approach incorporating unique condition indicators is suggested. A comparison between the two methods is presented.