Numerical Investigations of Ultrasonic Reverse Time Migration for Complex Cracks Near the Surface

Junjie Chang,Wenchao Li,Yuan Tang,Congcong Wang

doi:10.1109/access.2021.3140119

Abstract

Metal materials will produce fatigue cracks under long-term cyclic loading. It is difficult to fully image the topography of defects with the current mainstream ultrasound imaging technology. The Reverse time migration (RTM), which has extensive application in geophysical exploration, can image complex geological structures. This research introduces the RTM into the field of ultrasonic non-destructive testing. Through numerical simulation, it is concluded that the RTM based on no absorbing boundary can make the defect contour clearer, but the RTM based on the absorbing boundary can make the image contrast metric higher. In order to obtain the RTM results with high contrast metric and clear defect contours, the solution given in this study is to increase the migration aperture. Then this research discusses the influence of different cross-correlation imaging condition on the imaging quality. And compared with the prevailing total focusing methods (TFM), it shows the superiority of the RTM to the bottom opening crack (BOC) imaging. Finally, the RTM was used to complete the imaging of the curved and bifurcated cracks with complex structures. And after reducing the number of ultrasonic transducers, there are still good imaging results, which can reduce the waste of resources and energy.

Highlights

In engineering structures, metal materials under long-term cyclic loading will produce fatigue cracks, which will increase the possibility of failure of metal materials [1], [2]
The traditional ultrasonic imaging method can only obtain the image of the upper surface or the upper end of the defect
Chang et al.: Numerical Investigations of Ultrasonic Reverse time migration (RTM) for Complex Cracks Near Surface holes in the aluminium block based on the principle of the RTM, and compared it with the total focusing methods (TFM) [13]

Summary

INTRODUCTION

Metal materials under long-term cyclic loading will produce fatigue cracks, which will increase the possibility of failure of metal materials [1], [2]. J. Chang et al.: Numerical Investigations of Ultrasonic RTM for Complex Cracks Near Surface holes in the aluminium block based on the principle of the RTM, and compared it with the TFM [13]. Chang et al.: Numerical Investigations of Ultrasonic RTM for Complex Cracks Near Surface holes in the aluminium block based on the principle of the RTM, and compared it with the TFM [13] These indicate the RTM’s ability to detect internal defects, while this study is to image the BOC near the surface. Based on the RTM principle, this research perform complete imaging of curved and bifurcated BOC with complex geometries. This paper ends with a conclusion section and description of future work

PRINCIPLE THE RTM

ABSORBING BOUNDARY CONDITIONS

REVERSE TIME WAVEFIELD EXTRAPOLATION

CROSS-CORRELATION IMAGING CONDITIONS

CONCLUSION