Ultrasonic nondestructive inspection of solid objects

Ultrasonic testing (UT) has been used for nondestructive evaluation (NDE) of materials for more than half a century. A number of NDE techniques have been developed and specific standards have been created for the UT applications in different areas of engineering. UT has two main goals related to inspection of solid objects, firstly, detection and characterization of material discontinuities (flaws), and secondly, material characterization. This paper is focused on the selected techniques for flaw detection and imaging using bulk waves as well as guided waves. The main part of the paper contains presentation of array techniques used for the inspection of solid structures with focus on ultrasonic imaging of discontinuities. An overview of the high resolution imaging methods based on synthetic aperture concept (SAFT) is given and illustrated with experimental results. The UT review is concluded with a short presentation of recently developed methods using Lamb waves for monitoring planar structures in structural health monitoring (SHM) applications. Damage detection methods based on application of multiple transducers (2D arrays) for generating and detecting Lamb waves in metallic and composite plates are presented.