Experimental Analysis of a Model Based Crack Identification Approach for Rotating Machines

In this paper an experimental application of a crack identification methodology based on combinational resonances is proposed. The technique uses external applied diagnostic forces at combinational frequencies, together with a pseudorandom optimization code, Differential Evolution, in order to characterize the signatures of the crack in the spectral responses of the flexible rotor. A finite element model is used to obtain the dynamic responses of the rotating machine. In this system, the additional excitations are applied by means an electrodynamic shaker. The method of multiple scales is used to determine the frequency of the excitation force under which combinational resonances appear. The breathing crack is simulated according to the Mayes model, in which the crack transition from fully opened to fully closed is described by a cosine function. The additional flexibility introduced by the crack is calculated by using the linear fracture mechanics theory. The results show that the methodology is a promising tool for estimates the crack location and depth.