Multi-parameter ultrasonic computerized tomography.

摘要

Computerized tomography (CT) is a nondestructive technique which reconstructs the interior image of structures from externally accessible measurements. Although tomography has been principally applied in the medical area, it has been given attention by scientists and engineers recently as a promising method for the analysis of nondestructive test data. Specially, the ultrasonic tomographic imaging plays an important role in ultrasonic testing as it provides the capability for full field 3D imaging, enhanced ability to detect flaws and measure local material properties. In this study, residual stresses in conjunction with locally varying material thickness and density of a plate are investigated using ultrasonic computerized tomography. This is thought to be representative of corrosion. Straight ray paths are assumed here.;In conventional reconstruction algorithms, only a single parameter such as velocity, density, or amplitude is usually considered for reconstruction. In many cases, however, that is not enough to get a complete understanding of the material. We need multiple parameters to obtain the full information for a material. For example, two material constant parameters (;It is not a new skill to use ultrasonic testing to measure the thickness of a material from the accessible side of a structure. The existing method of pulse-echo C-scan images can show a two-dimensional display, but each measurement shows only the state of a corresponding single testing point. In this study, ultrasonic Lamb waves are applied to the tomographic technique to get the whole distribution thickness in a plate. A modified version of the algebraic reconstruction technique (ART), a kind of finite-series expansion method, is used for Lamb wave tomography.