Ultrasonic crack evaluation by phase coherence processing and TFM and its application to online monitoring in fatigue tests

This work proposes a new ultrasonic imaging method for crack evaluation with arrays, and investigates its application to online monitoring of crack propagation in fatigue tests. The Total Focusing Method (TFM) is used to obtain the best possible image of the crack propagation path and orientation, while Phase Coherence Imaging (PCI) is used to precisely determining its length by accurately locating the tips position. Experimental verification was performed with a 15 MHz array and a set of 4 samples tested up to different crack lengths by cyclic loading. Crack orientation and length obtained with the proposed method showed good matching with optical measurements, and sizing by tip detection with PCI was more robust than amplitude-drop sizing with TFM.