Evaluation of crack closure stress by analyses of ultrasonic phased array images during global preheating and local cooling

Abstract

Crack closure stress (CCS) is an important parameter that affects crack propagation rate. However, the method for measuring CCS in practical fields has yet to be developed. In this study, we propose a practical method of estimating CCS. In our experiment, a closed fatigue crack was imaged by a linear phased array (PA) method during crack opening by global preheating and local cooling (GPLC). Here, we assumed that the crack appears in PA images after the thermal stress induced by GPLC exceeds CCS. Therefore, we calculated the thermal stress induced by GPLC using an analytical solution and thereby estimated CCS. Then, to validate the CCS estimation method, we simulated the PA images by a finite difference time domain (FDTD) method with a damped double node (DDN) model, where CCS was relieved by the calculated thermal stress. Consequently, the temporal variation in crack depth observed in the PA image was successfully reproduced in the simulation. Thus, the CCS estimation method was verified by comparing experimental results with analysis results.

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.…”

Dark-field ultrasonic imaging method using mode-converted longitudinal evanescent field

“…Most UT employs piezoelectric transducers. Among them, the ultrasonic phased array, using a piezoelectric array transducer, has been intensively studied for visualizing internal [8][9][10][11][12][13][14][15][16] and surface defects. [17][18][19] Additionally, various types of UT using laser scanning, have also been studied.…”

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.…”