Crack Detection in Shaft Using Lateral and Torsional Vibration Measurements and Analyses

Abstract

In this paper experimental and numerical investigations are carried out to identify the presence of a crack in a cylindrical overhanging shaft with a propeller at the free end. In the experimental study, cracks of different depths are located at the (uncracked) maximum bending moment position. Shaft response parameters for lateral (using an accelerometer) and torsional vibrations (using shear strain gages fixed at three different locations) are obtained using the modal analysis software, LMS Test LabTM. The experimental results are used to validate the numerical results obtained using the three-dimensional isoparametric elements (element types 186 and 187) available in the ANSYS FEM program; the open crack is embedded in the shaft and the mesh generation is suitably modified to incorporate the stress intensity effects present at the crack tip. From the results it is observed that the rate of change of torsional frequencies that occur during initial crack growth can be better used to detect crack presence in rotating shafts than bending frequencies. Copyright © 2012 by ASME.