Parametric study of laser scanner for breathing cracked rotor damage identification

Abstract

Frequency Response Function (FRF) based damage detection method is utilized in this paper to identify the breathing cracks on a rotordynamic system in both frequency and time domain. The cracks are considered to be breathing during rotation due to the effect of gravity or imbalance mass. Zero-SIF (Stress Intensity Factor) method is employed to determine the crack closure line of open crack area. It is found that the stiffness reduction induced by a breathing crack is a function of both crack phase and rotation angle. The dynamical model of system is built based on the Lagrange principle and the assumed mode method while the crack model for periodically time-varying systems is based on the fracture mechanics. The steady-state equation of system is constructed via harmonic balance with a laser scanner as output sensor. The laser scanner enables the sufficient outputs from a single sensor by varying the scanning frequency or scanning function. Assuming a cosine function to approximate the nonlinear breathing behavior of cracks, the linear damage identification algorithms are established via Least Square and Newton Raphson methods. Finally, the dynamic response of a rotor system with nonlinear breathing cracks is simulated in time domain and the breathing cracks are successfully identified by developed damage detection algorithm.