Crack Depth Estimation in Shaft for an Overhung Rotating Shaft System: An Experimental Investigation

This paper focuses on transverse crack detection and its depth estimation in the shaft by applying extrinsic excitation for an overhung rotating shaft system. The dynamics of overhung rotating shaft system with six different shafts having different crack depth parameters are studied experimentally and through the finite element method (FEM). Variation of natural frequencies with crack depth parameters is studied using FEM through ANSYS. The practical application of axial extrinsic excitation is employed to an overhung rotating shaft system for spectrum analysis in two mutually perpendicular directions. The comparison of spectrum for healthy and cracked overhung rotating shaft system shows the appearance of distinctive peaks for cracked rotor system along with 2X component which is major for crack detection. The appearance of peaks at the summation of extrinsic excitation frequency plus rotational frequency along with extrinsic excitation frequency and its harmonics provides an early warning of the crack in the rotor system. The amplitude of these peaks also increases with the crack depth parameter, which estimates crack depth in the shaft. The approach presented in this paper can be very well adapted for crack detection and estimate its depth in the overhung rotating shaft system during its operation.