An analysis of crack identification in the shaft of sugarcane cutter system

【Objective】To get identification information of crack on the shaft from vibration characteristics of the system under the condition of various nonlinear factors.【Method】 The cutter was simplified to a vertical over-hung rotor-bearing system, and the slant crack was set near the junction between the shaft and the disk, taking into consideration two nonlinear factors. The slant crack and the nonlinear cutting force, three degrees of freedom dynamic equations of the system were founded. Based on this model, a stiffness calculation model of opening slant crack was chosen. The dynamic characteristics of the slant cracked cutter were investigated by numerical simulation.【Result and conclusion】 The results showed that when Ω=500 r·min^-1 system was only under the condition of nonlinear cutting force without crack, working frequency and combined frequencies appeared in frequency responses of transverse vibration. In the same working condition, when the system was under the condition of both crack and nonlinear cutting force, the system had working frequency, combined frequencies and also a newly added second harmonic frequency which were frequency responses. In addition, with the increase of the crack depth, the amplitude of the second harmonic frequency was also increasing. Therefore, the identification signal of crack can be attained from two nonlinear factors. Besides, in torsional vibration, working frequency newly appeared because of the crack.