ABSTRACT
The phased array ultrasonic nondestructive testing has played an important role since the 2000s. In a phased array setup, the ultrasonic transducer consists of small piezoelectric elements. Electronic manipulation enables to excite the elements and receive waves by the elements independently. By controlling the delay times between the elements in a transducer, incident waves of various angles of refraction, focal points can be produced. The concept of two dimensional phased array has already been introduced. However, it is still difficult to apply in practice. In comparison with the linear array transducer, larger number of elements to be manipulated is required. In addition, the size of individual element becomes smaller for the smooth wave front. On the other hand, small size causes to the deterioration of sensitivity. Fatigue cracking in the orthotropic steel deck system is a serious problem. This study focuses on closed type of longitudinal rib, because the limited accessibility from the outside of the rib makes it very difficult to inspect. As the fundamental investigation, two dimensional phased array ultrasonic testing system was applied to slit specimens modeling the two types of deck and bead propagating cracks, respectively. Synthetic aperture focusing technique was employed for the image reconstruction. The phased array system showed good accuracy of crack detection of which length is longer than 2 mm. In addition, the system showed higher accuracy for the estimation of crack length along the weld line.
