THEORY AND APPLICATION OF PRESTACK MIGRATION IN FLAW DETECTION OF CONCRETE STRUCTURE

An ultrasonic method based on prestack migration imaging is proposed for detecting arbitrary angle damages from one side of the structure. In this method, after the specimen is excited on the surface, the reflection waves are collected and processed with prestack migration algorithm, which yields the image with the interior damages. In the study, the factors influencing the resolution and precision of the migration sections are analyzed theoretical and experimentally. In addition, the resulted images using the present method are compared with that using the other method, showing that: compared with the horizontal stack method, the prestack migration achieves higher precision and possesses more adaptability to the inclining interface of the damages; when the migration speed is relatively larger, the detection result is deeper, and vice versa; the resolution of the migration section would be high under the following three conditions: 1) the main frequency of the filter agrees with that of the effective echo, 2) the space between transducers is no larger than one quarter of the dominating wave-length of the reflecting waves, 3) the migration speed is no lower than the physical wave speed.