DefinePK

Abstract

The presence of crack in a structure tends to modify its modal parameters (natural frequencies and mode shapes). The fact can be used inversely to predict the crack parameters (crack depth and its location) from measurement of the changes in the modal parameters, once a functional relationship between them has been established. The machine components like turbine blade can be treated as a cantilever beam and a shaft as a simply supported beam. Vibration analysis of cantilever beam and simply supported beam can be extended successfully to develop online crack detection methodology in turbine blades and shafts. In the present work, finite element analysis of a cantilever and simply supported beams for flexural vibrations has been considered by including two transverse open U-notches. The modal analysis has been carried out on cantilever and simply supported beams with two U-notches and observed the influence of one U-notch on the other for natural frequencies and mode shapes. This has been done by carrying out parametric studies using ANSYS software to evaluate the natural frequencies and their corresponding mode shapes for different notch parameters (depths and locations) of the cantilever and simply supported beams FEM model. Later, by using a central difference approximation, curvature mode shapes were then calculated from the displacement mode shapes. The location and depth corresponding to any peak on this curve becomes a possible notch location and depth. The identification procedure presented in this study is believed to provide a useful tool for detection of medium size crack in a cantilever and simply supported beam applications.