Crack simulations in shaft-hub-blade system using modal analysis

Abstract

Mostly turbo machines encounter failures like cracks, unbalance, mechanical looseness, misalignment, etc. as they are subjected to fatigue loads. Any of these failure conditions lead to change in the dynamic behavior of these machines. The shaft assembled with hub and blades is considered as the turbo machine rotor for which vibrations response is analyzed. This work includes modal analysis of shaft-hub-blade system with crack developed either in the shaft or in the blade. Analysis was carried out using ANSYS software to evaluate natural frequencies and mode shapes for the healthy and cracked conditions of the system. From the analysis, it was observed that the presence of crack in any component of the system has appreciable effect on the natural frequencies of the system. But the decrease in the natural frequencies of the system is more for the crack located in the shaft compared to that of crack present in the blade. So it is evident that the vibration response of the individual components of the shaft-hub-blade system needs to be measured to identify the actual cracked component.