High-Selectivity Ultrasonic Imaging of Closed Cracks Using Global Preheating and Local Cooling

Abstract

High-selectivity ultrasonic imaging of closed crack is an important subject for avoiding not only underestimation but also misidentification of closed cracks. Thus far, the combination of load difference phased array (LDPA) and the crack opening method (GPLC) that combines global preheating (GP) and local cooling (LC) has been verified. Here the LDPA utilized the subtraction of the phased array (PA) images before and after the application of thermal stress induced by GPLC. However, as the cooling time increased, the change in wave velocity depending on the temperature within specimen is not negligible. This results in ghosts that degrade the selectivity of closed crack in subtracted images. In this study, on the basis of the finding that the change in crack response is faster than that in the wave velocity during GPLC, we propose a short time interval subtraction (STIS) method as an option in LDPA. This is based on the subtraction of a PA image from that obtained before a short time interval. It was experimentally verified in a closed fatigue crack specimen made of aluminum alloy.

High-resolution 3D phased-array imaging of fatigue cracks using piezoelectric and laser ultrasonic system (PLUS)

“…Since crack depth is a critical parameter for the maintenance management of aging infrastructures, the accurate measurement of crack depth has been intensively studied. [6][7][8][9][10][11][12][13][14][15][16][17] On the other hand, fracture mechanics 18) indicates that crack depth can change in the crack-length direction. 19,20) However, B-scan images obtained by a linear array transducer give a spatially-averaged crack geometry over the elevation aperture of the linear array transducer.…”

Development of Low-Frequency Phased Array for Imaging Defects in Concrete Structures

“…PAs were originally developed for medical diagnosis [7] and have also been widely adopted to visualize the internal defects of metals for industrial applications. The recent progress in PAs for the inspection of metals is noteworthy [8][9][10][11][12][13][14]. PAs typically use a linear array transducer composed of multiple rectangular piezoelectric elements that can act as both transmitters and receivers.…”

Characterization of Nonlinear Ultrasonic Diffuse Energy Imaging

“…Other techniques seek to modulate a parameter of the system and examine changes within the transmission bandwidth of the back scattered signal. These modulation parameters have included static load [9], temperature [10] and amplitude of the transmitted signal [11]. These coherent scattering techniques recover only a small proportion of the total information pertaining to elastic nonlinearity that is encoded onto the field.…”