The Use of Multi-Mode TFM to Measure the Depth of Small Surface-Break Cracks in Welds

摘要

In this paper, small crack (depth = 1 mm) initiated from top surface of welds are imaged and characterized using ultrasonic array. The conventional Total Focusing Method (TFM), which allows the array to be focused at every point in the target region in both transmission and reception, is a post-processing imaging algorithm of ultrasonic array data. The TFM can be also implemented combining a variety of propagation modes and several types of waves, involving longitudinal waves and shear waves. Due to the small cracks near the top surface where the array located, no reflection from crack faces or root and tip indications are observed in the image formed using conventional TFM imaging algorithm, which includes only direct ray paths between the array and image points. For this case, it is challenge to size the small cracks initiated from top surface. This paper presents three modes of wave propagation for the TFM imaging to inspect and measure the depth of the small cracks with greater reliability than conventional TFM imaging.