The Three-dimensional Reconstruction Of Defects Based On Full Matrix Capture

With the development of ultrasonic nondestructive evaluation technology, the requirement for high quality images of defects and user-friendly imaging methods has become higher and higher. In general, the phased array works by synthesizing ultrasound waves dynamically and as a result, the advantage of phased array, the rich data collected by all the single phased array elements, has not been exploited to the full to form focused images of the defects. Meanwhile, we usually need to move the phased array probe by hands or robots so that the information of defects in the entire area can be obtained and the results are not always easy to be visualized.Taking the advantage that the phased array has many elements into consideration, full matrix capture technology has been utilized to get the full matrix data of all the elements with a matrix phased array probe in order to solve the problems mentioned above. In this way, in only one single acquisition, all the A-scan signals received by all the elements were obtained and formed a matrix. Then the full matrix data corresponding to every line of elements was extracted from the matrix with a developed algorithm. Then total focusing method was developed in order to form focused B-scan images with the extracted data. Compared with conventional B-scan images, the eight images obtained by TFM were of high SNR and were with high resolving power for defects. Three-dimensional visual reconstruction was conducted with the TFM images obtained based on theory of isosurface. The three-dimensional images of the artificial defects were obtained and the information of artificial defects including the distribution, locations and sizes of defects inside the workpieces can be seen directly from the three-dimensional images obtained.A wedge was designed by the calculation in order to lead the longitudinal ultrasound beams to the intended area so that the TFM 3-D reconstruction method can be used to form images of defects in welds with irregular protrusions. In this way, the disadvantage of poor adaptability of vertical incident method to welds can be eliminated and the images obtained were of good signal-to-ratio. Experiment was conducted on practical stainless steel with the designed wedge. The results showed that the artificial defect with a diameter of 2mm and depth of 15 mm below the surface in the weld can be imaged with the TFM 3D method. The artificial defect can be seen directly from the 3D image created.