A Novel Dynamic Characteristic for Detecting Breathing Cracks in Blades Based on Vibration Response Envelope Analysis

Fatigue cracks in blades pose a significant threat to the safe operation of rotating machinery. Currently, the application of non-contact displacement sensors in blade vibration measurements has enabled the widespread analysis of nonlinear dynamic characteristics, such as natural frequency deviations and spectral anomalies, to enhance crack fault diagnosis in rotating machinery. However, these two dynamic characteristics are not distinguishable for crack changes, especially for incipient cracks, leading to potential misdiagnosis. In this paper, a dynamic characteristic called the envelope diagram image of vibration responses (EDIVR) was extracted from blade tip displacement signals collected during acceleration–deceleration cycles for crack diagnosis. Initially, considering the breathing effect of fatigue cracks, a structural dynamics finite element model of a blade containing a breathing crack is established to calculate its dynamic response under aerodynamic force. Subsequently, the sensitivity of three characteristics (natural frequency, frequency spectrum, and EDIVR) to crack fault changes is quantitatively compared based on the simulated response signals. Experimental validation confirms the accuracy of the proposed dynamic model and the effectiveness of the proposed feature. The study shows that under identical operational conditions, blades with cracks of equivalent depth and location exhibit maximum sensitivity to crack detection when EDIVR dynamic characteristics are employed as the fault diagnostic criterion. Moreover, this characteristic is less susceptible to signal noise interference compared to other dynamic characteristics, enhancing its potential for crack diagnosis in engineering applications.