Fatigue Crack Detection in Steel Plates Using Guided Waves and an Energy-Based Imaging Approach

Abstract

The increasing use of ultrasonic guided waves (GWs) has been shown to have great potential for the detection of fatigue cracks and non-fatigue type damages in metallic structures. This paper reports on a study demonstrating an energy-based damage imaging approach in which signal characteristics identified through relative time differences by fatigue crack (RTD/f) through different sensor paths are used to estimate the location of fatigue crack in steel plates based on GWs generated by an active piezoceramic transducer (PZT) network. The propagation of GWs in the original 10 mm-thick plate was complicated due to its thick geometry, wave dispersion, boundary reflection and the existing boundary notch used to initiate the fatigue crack, resulting in diverse forms of interference with fatigue crack identification. Hence, RTD/fs were extracted from the wave energy spectrum with the aid of a wavelet transform (WT) and a correlation function. The series of tests carried out in this study include a fatigue test in which a fatigue crack was introduced to the steel plate, in addition to subsequent tensile and compressive tests designed to investigate the effect of loading on wave signals. Simultaneously, the proposed method was verified by finite element analysis and good agreement was obtained between the numerical and experimental results using the developed fatigue crack model. The results show that fatigue cracks can scatter GWs via discontinuous contact between crack surfaces under cyclic fatigue loadings, thus demonstrating the effectiveness of the proposed method for the real-time monitoring of fatigue cracks in metallic structures.