Closed cracks can cause the underestimation or overlook by conventional (linear) ultrasonic method, because the ultrasound is transmitted through closed cracks. To solve this problem, we have developed an imaging method, subharmonic phased array for crack evaluation (SPACE), based on subharomonic generation by large-amplitude short-burst-wave input and phased-array imaging algorithm with frequency filtering. Thus far, we have demonstrated in the crack depth measurement in closed fatigue cracks and stress ...
英字タイトル:
Sizing of Closed Cracks Using Subharmonic Phased Array

In this study, superconducting electromagnetic acoustic transducer (EMAT) is developed to transmit strong ultrasound, which is expected as an experimental tool for mechanism study of nonlinear ultrasound. For the purpose, EMAT experiment is carried out using uniform and strong filed generated by a superconducting magnet, and surface displacement of specimen is measured by a laser Doppler vibrometer. As the result, the linear relationship between the surface displacement and magnetic flux density was co...
英字タイトル:
Development of superconducting electromagnetic acoustic transducer system and quantitative evaluation of ultrasound transmission by numerical analysis

A new method for detection and sizing of closed crack is described which uses transient waveform of subharmonics with half input frequency i n ultrasonic nondestructive evaluation. In analogy to the resonant characteristics of vibration of bubbles in liquids, we formulate an equat ion for resonant excitation of subharmonics at partially closed cracks. The equation has been partially verified by comparison between exper imental and calculated waveforms. An apparatus for imaging closed cracks in critical com...
英字タイトル:
Nonlinear Ultrasonic Imaging Method for Closed Cracks