Ultrasonic phased array with surface acoustic wave for imaging cracks

Abstract

To accurately measure crack lengths, we developed a real-time surface imaging method (SAW PA) combining an ultrasonic phased array (PA) with a surface acoustic wave (SAW). SAW PA using a Rayleigh wave with a high sensitivity to surface defects was implemented for contact testing using a wedge with the third critical angle that allows the Rayleigh wave to be generated. Here, to realize high sensitivity imaging, SAW PA was optimized in terms of the wedge and the imaging area. The improved SAW PA was experimentally demonstrated using a fatigue crack specimen made of an aluminum alloy. For further verification in more realistic specimens, SAW PA was applied to stainless-steel specimens with a fatigue crack and stress corrosion cracks (SCCs). The fatigue crack was visualized with a high signal-to-noise ratio (SNR) and its length was measured with a high accuracy of better than 1 mm. The SCCs generated in the heat-affected zones (HAZs) of a weld were successfully visualized with a satisfactory SNR, although responses at coarse grains appeared throughout the imaging area. The SCC lengths were accurately measured. The imaging results also precisely showed complicated distributions of SCCs, which were in excellent agreement with the optically observed distributions.

Multi-mode 3D ultrasonic phased array imaging method using piezoelectric and laser ultrasonic system (PLUS)

“…On the other hand, the use of the different modes has been extensively examined in PA imaging with piezoelectric array transducers. 13,[43][44][45][61][62][63][64] For example, multi-mode PLUS can utilize the shear-wave incidence. By making a wedge with an angle between the first and second critical angles for the piezoelectric transmitter, only the shear wave incidence can be performed.…”

“…Moreover, a transmitter for PLUS can adopt a wedge with a third critical angle 67) to generate Rayleigh waves. This can realize a surface-acoustic-wave phased array (SAW PA), 13,62,64,68,69) which can visualize the defects in the vicinity of the surface. By inputting a shear wave with an inplane displacement, the ultra-multiple LDV scan used in PLUS allows the utilization of a mode-converted longitudinal evanescent field, 8,70) which enables super-resolution imaging of surface-subsurface micro defects.…”

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

“…However, it is impossible to suppress the dead zone perfectly. For the inspection of the subsurface region in concrete structures, a surface-acoustic-wave phased array (SAW PA) [33][34][35] seems promising. The SAW PA uses a wedge to generate a Rayleigh wave via mode conversion.…”

Numerical analysis of the phased array imaging with a stacked plate buffer

“…[1][2][3][4][5][6][7][8][9][10] Especially in nuclear power plants, accurate sizing of cracks in the heat-affected zone is of great interest because it enables accurate decision of pipe-replacement schedule, resulting in reducing radioactive waste and ensuring the integrity of the plant at the same time. [11][12][13] Imaging techniques using phased-array (PA) ultrasonic have been used for crack sizing in the heat-affected zone. The PA ultrasonics is a technique for imaging the source of ultrasonic reflections inside a material by using a large number of signals emitted and detected separately from multiple vibrating elements.…”