Subharmonic Wave Generation at Interfaces of a Thin Layer between Metal Blocks

Abstract

Subharmonic wave was significantly generated at interfaces of aluminum blocks and an aluminum foil subjected to a 6 MHz burst incident wave. Although the fundamental wave amplitude was linearly varied with input voltage, subharmonic wave generated at the interfaces indicated strong nonlinearity. Analyzing the relationship of the subharmonic generation, the applied contact pressure and stress of ultrasonic wave has revealed that subharmonic components can generate when the incident ultrasonic wave has sufficiently large stress to separate the contacting interfaces. At rough surfaces, subharmonic peak could not be observed because large true contact pressure prevented the interfaces from separating.

Closed-crack imaging and scattering behavior analysis using confocal subharmonic phased array

“…To this end, ultrasonic testing using reflection and scattering at a crack with an air gap has been widely used to measure cracks. [1][2][3][4][5][6][7][8] However, sometimes cracks are partially closed because of compression residual stress 9,10) or oxide film generation between crack faces. 11,12) This leads to underestimation or overlooking of cracks because ultrasound is transmitted through them.…”

Subharmonic phased array for crack evaluation using surface acoustic wave

“…Crack depth can be accurately measured using ultrasound if cracks are open, since ultrasound is scattered at the crack tip. [1][2][3][4][5][6][7][8][9] However, if cracks are closed because of compressive residual stress 10,11) and=or the oxide film generated between the crack faces, 12) ultrasound is transmitted through the closed crack. This leads to underestimation or nondetection of cracks, resulting in catastrophic accidents.…”

Defect detection and size estimation in billet from profile of time-of-flight using ultrasonic transmission method with linear scanning

“…To detect defects inside steel products, ultrasonic inspection is effective. [4][5][6][7][8] The pulse echo method, by which defects are detected using echoes is generally used in a steel production line. 9,10) Although this method is simple and fast, it is hard to detect signals from high-attenuation billets such as cast steel because an echo becomes feeble owing to its diffusion and grain boundary scattering as the distance between the transducer and the defect increases.…”