A proposed method for fatigue crack detection and monitoring using the breathing crack phenomenon and wavelet analysis

Abstract

In this paper the dynamic behavior of a fatigue cracked beam is investigated. The purpose is to reveal the nonlinear behavior of the structure with fatigue damage by using wavelet transform. A cracked cantilever beam is modeled by the finite element (FE) method using ALGOR™ software. A breathing crack is described in the FE method as a surface to surface contact of the two edges the crack during vibration. Strain time history in the area adjacent to the crack has been analyzed using data processing techniques. Nonlinear effects in signals are usually difficult to detect by conventional data processing methods such as fast Fourier transform. However wavelet transform has recently been shown to be an effective method of detecting such nonlinear effects in signals. Modulus maxima, an important property of wavelet transform, have been used as an indicator of the crack size. Numerical results obtained from the FE analysis are presented in this paper, as well as some experimental results. It is shown that detection of fatigue cracks using breathing behavior and wavelet transform can be used to develop a vibration-based crack detection technique.