Three Dimensional Characterization of Defects by Ultrasonic Time-Of-Flight Diffraction (TOFD) Technique

摘要

Time-of-Flight Diffraction technique (ToFD) is one of the advanced ultrasonic testing methods. It is based on the measurement of time-of-flight of ultrasonic waves and not their amplitudes and because of that, it is more precise in measuring the location and size of defects. The test is usually carried out by a pair of longitudinal angle-beam transducers in pitch-catch mode. Despite the many benefits of ToFD, it suffers from a number of shortcomings. One limitation is that the current ToFD technique is considered as a two dimensional method which can only evaluate the defects in the cross-sectional plane of the specimen. The goal of this paper is to propose a technique for measuring the location of a defect in the three dimensional space. To this purpose, instead of using a pair of transducers, a combination of one single transmitting transducer and multiple receiving transducers, arranged in linear or curved patterns, is considered. Using the data collected by these transducers, the 3D location of the defect can then be found by solving a nonlinear error minimization problem. This method is tested on a specimen with artificially implanted defects and the three dimensional location of the defect is found with very good accuracy.