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

为了保证核电站等结构的安全可靠性，有必要对闭合裂纹进行非线性超声检测。亚谐波相控阵裂纹检测技术是一种实用的裂纹检测方法，但其横向分辨率不够高。在本研究中，我们开发了共焦空间与一个单一的阵列传感器，可以发送一个大振幅的聚焦波和检测散射波使用一个单一的阵列传感器。然后，我们成功地成像SCC的热影响区（HAZ）的类型304不锈钢试样，在高温加压水中形成的，并成功地可视化的高选择性的亚谐波图像中的封闭裂纹尖端，而不考虑强线性散射在晶界。我们还成功地对这些波进行了二维模拟。这一结果将大大有助于提高核电站的安全性和可靠性。

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.