Output-Only Method for Defect Identification in the Internal Edge of the Plates with a Circular Hole Using Guided Ultrasonic Waves and Discrete Wavelet Transform

This article proposed a baseline-free method for damage localization in plates with a circular hole. Damages are defined as cracks at the internal edge of the hole with different lengths and angles. Guided ultrasonic waves (GUWs) are used to excite the plate and receive feedback with a pitch-catch active sensing configuration. The numerical simulations conducted in ABAQUS and GUWs are generated by simulating circular piezoelectric transducers located at the top surface of the plate. In this study, transducers are located on the plate in such a way that similar paths are made for waves traveling from actuators to sensors. In these similar paths, the sensor spacing of transmitter–receiver paths should be equal. Then, the first wave packet of response signals acquired by sensors is processed by discrete wavelet transform to extract actionable damage-sensitive features. The features obtained for similar paths are compared to calculate damage indexes which are used to locate damage. The numerical results reveal that the proposed method can precisely identify the location of cracks in a holed plate, only by measuring the wavelet energy of approximate coefficients at the first and second levels of wavelet decomposition. For paths in a group of similar paths, the material and geometrical properties of the structure, the actuator–sensor distance between similar paths and the sensitivity of the probing devices must be the same. In the process of sensor installation, the lengths of the paths in a group may not be equal to each other. In this paper, the effects of small differences between the measurement paths, which are supposed to be essentially the same, on the accuracy of damage detection results are investigated.