There are a number of approaches reported in the literature for modelling cracks in shafts. Although two and three dimensional finite element models may be used, the most popular approaches are based on beam models. This paper considers a number of different approaches to modelling cracks in shafts of rotating machines. Of particular concern is the modelling of breathing cracks, which open and close due to the selfweight of the rotor, producing a parametric excitation. In the simplest model the shaft stiffness is bilinear, depending on whether the crack is open or closed. More complicated functions that relate the shaft stiffness to angular position have been proposed, and two possibilities will be considered. This paper will demonstrate the influence of the crack model on the response of a Jeffcott rotor, using the harmonic balance approach.
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Penny et al. (2003) studied this question.