Monitoring of fatigue crack propagation of engineering structures using time reversal method

In this study, a technology based on ultrasonic guided waves for monitoring fatigue crack in metallic structures is demonstrated in which two different sensor networks including eight and six piezoceramic (PZT) transducers are employed respectively for exciting and acquiring guided wave signals. One network is arranged for detecting the location of fatigue crack; while the other one is disposed on account of fatigue crack propagation monitoring using a time reversal method. By applying cyclic fatigue load, a fatigue crack is introduced into a 5 mm-thick steel plate by four steps mounting up in a steady graded series from 7 mm to 27 mm. It is inevitable that after a succession of fatigue tests in great intensity, the PZT transducers indicate a discrepancy in the properties of signal excitation and acquisition due to mechanical impact no matter on PZTs or bonding layers. Evidently, application of a reference-free method is significant for monitoring fatigue crack by way of averting exterior adverse impact. That is the reason why the time reversal method is involved in this study. Results of the study show that the time reversal method combined with probability-based damage imaging approach according to time of flight and coefficient are suitable for estimating the presence and propagation of fatigue crack in metallic structures.