Author(s)

M. Alfano & L. Pagnotta

Abstract

Cracks occurring in structural elements of machines cause a local reduction in the stiffness and consequently lead to a change in the modal parameters, such as the resonant frequencies. The measurement of the degree of variation in resonant frequencies can provide a suitable tool for identifying the location and the extension of damage. For this reason the variation of the natural frequencies in the cracked elements has been the subject of many investigations. In the present paper, the dynamic behaviour of free thin isotropic square plates, with a trough crack emanating from one edge, were investigated by means of an extensive series of finite element analysis carried out by a commercial code. The variations of both the natural frequencies and the modal shapes have been pointed out in terms of a dimensionless frequency factor depending on the length of the crack and on Poisson’s ratio. Numerical results have been verified by experimental measurement. Keywords: FEM, cracked plates, modal analysis. 1 Introduction Cracks occurring in structural elements of machines cause a local reduction in the stiffness and consequently lead to a change in the modal parameters (e.g., natural frequencies). The degree of change depends on the location, the nature and the extension of the damage. Frequency measurement can be cheaply carried out from the measured time response of a dynamically excited structure, therefore a frequency based approach could be a simple and economic mean to evaluate the structural damage [1-3]. For this reason the free vibration of cracked elements has been a subject of many investigations. Several papers deal with the flexural vibration of clamped and simply supported plates. Byrne [4] has

Keywords

FEM, cracked plates, modal analysis.