A new open/close crack model is proposed assuming that the crack opens or closes depending upon the direction of the shaft displacement perpendicular to the crack. A theoretical and experimental analysis of the vibrations of a simple rotor model with a transverse crack is then presented and the conditions for the crack to always open or close are derived. The nonlinear differential equation for this model is also numerically solved by using the 4-th order Runge-Kutta method, then the harmonic components are analyzed with the unbalance varied in phase and magaitude. Experimental results show that the proposed open/close crack model fairly well simulates the real situations.
The experimental and simulation results show that the 1X, 2X and 3X harmonic vibration components of the cracked simple rotor are important in identifying the presence of the crack and, in particular, 1X harmonic component is very sensitive to the phase between the unbalance and crack.
