Fatigue crack detection under the vibration condition based on ultrasonic guided waves

Ultrasonic guided wave is an encouraging tool in structural health monitoring for civil, mechanical, ship, and aerospace devices. Most of heavy devices required a long-time running during the service, and the structure of these devices is under the vibration condition due to their inherent properties and working condition. This article mainly researches fatigue crack detection in vibration condition caused by operation using ultrasonic guided waves, aiming to study the application of ultrasonic guided waves in the field of structure dynamics. The detection method based on the difference index and the sequence curve of difference index between different states of crack is proposed to detect fatigue crack in vibration condition. The experiments are carried out on the fatigue testing platform and the vibration test-bed to investigate the relationship between opening states of fatigue crack and the difference index value of ultrasonic guided waves. In order to reduce the influence of loads applied by the fatigue testing platform on ultrasonic guided waves propagation, the initial experiment is first carried out to select the range of applied loads which have minimal influence on wave propagation. The results show that loads from 0 to 24 MPa have minimal effect on ultrasonic guided waves, and the difference index values of intact beam and cracked beam are in different orders of magnitude. Therefore, the method based on difference index value and sequence of difference index is credible to detect fatigue crack for structure in vibration condition.