High resolution imaging of stress corrosion cracking by a confocal subharmonic ultrasonic phased array

为了保证核电站等结构物的安全可靠，有必要对闭合裂纹进行非线性超声检测。亚谐相控阵用于裂纹检测是一种实用的成像方法，但横向分辨率不高。在这项研究中，我们开发了具有单阵换能器的共焦空间，它可以传输大幅度的聚焦波，并利用单阵传感器检测散射波。然后，我们成功地在高温加压水中形成的304不锈钢试件的热影响区(HAZ)中成像了SCC，并成功地在亚谐图像中高选择性地显示了闭合的裂纹尖端，而不考虑晶界的强线性散射。我们还成功地对这些海浪进行了二维模拟。这一结果将对提高核电站的安全性和可靠性做出重大贡献。

To ensure the safety and reliability of structures such as nuclear power plants, it is necessary to detect closed crack by nonlinear ultrasound. Though the novel imaging method, subharmonic phased array for crack evaluation (SPACE)is a practical solution, the lateral resolution was not high enough. In this research, we developed confocal SPACE with a single array transducer which can transmit a large amplitude focused wave and detect scattered wave using a single array sensor. We then succeeded to image an SCC in a heat affected zone (HAZ)of type 304 stainless steel specimen, formed in high temperature pressurized water, and succeeded in visualizing the closed crack tip in subharmonic image with high selectivity, irrespective of strong linear scattering at grain boundary. We also succeeded in 2D simulation of these waves. This result will significantly contribute to improve the safety and reliability of nuclear power plants.