Toshihiro Tsuji

Evaluation of nanoscale cracks by low-pass filter effect in nonlinear ultrasound

Cracks in solids can be detected by ultrasound if they are opened. However, it is not easy when they are closed, or with only nanoscale opening. It is the fundamental problem in ultrasonic NDE. Harmonics (2f, 3f,) is a good candidate, but it has a problem since it is generated also by transducers and liquid media (water), and it disturbs the measurement. So, we propose that subharmonics (f/2) and DC effect, which are regarded as low pass effect, is the best approach. Through theoretical and experimental investigations, we found that subharmonics is useful to detect closed fatigue cracks in aluminum, not easy to detect by conventional methods. Since it was successfully analyzed by approximate and detailed theories, it will be possible to estimate the size and property of closed crack planes by fitting measured waveforms to theories.

Multi-mode nonlinear ultrasonic phased array for closed crack imaging

Crack closure is one of the serious issues in ultrasonic testing that may cause underestimation or misdetection. Nonlinear ultrasonics is a primary means to solve this problem. Recently, several techniques using ultrasonic phased arrays to measure elastic nonlinearity, referred to commonly as nonlinear ultrasonic phased array imaging, have been proposed and have had their efficacy demonstrated in closed-crack specimens. Note that most of them use nonlinearly scattered longitudinal waves. On the other hand, nonlinear scattering at closed cracks can generate not only longitudinal waves but also mode-converted shear waves, which may have different characteristics from longitudinal one. Here we propose to use both longitudinal and mode-converted shear waves in nonlinear ultrasonic phased array imaging, which is called multi-mode nonlinear ultrasonic phased array imaging. We examined the nonlinear scattering in numerical simulation. Subsequently, it was also experimentally demonstrated.Crack closure is one of the serious issues in ultrasonic testing that may cause underestimation or misdetection. Nonlinear ultrasonics is a primary means to solve this problem. Recently, several techniques using ultrasonic phased arrays to measure elastic nonlinearity, referred to commonly as nonlinear ultrasonic phased array imaging, have been proposed and have had their efficacy demonstrated in closed-crack specimens. Note that most of them use nonlinearly scattered longitudinal waves. On the other hand, nonlinear scattering at closed cracks can generate not only longitudinal waves but also mode-converted shear waves, which may have different characteristics from longitudinal one. Here we propose to use both longitudinal and mode-converted shear waves in nonlinear ultrasonic phased array imaging, which is called multi-mode nonlinear ultrasonic phased array imaging. We examined the nonlinear scattering in numerical simulation. Subsequently, it was also experimentally demonstrated.