Research on Response of Ultrasonics to Closed Cracks and Nondestructive Evaluation

1.为了建立一种高精度、高速的裂缝回波幅度自动二维扫描采样方法，以水和超声设备为介质进行超声波传播和波形数据采集。数据安装在采样速度快的数字示波器中。将闭合裂纹的理论方程简化后，导出了一个评价方程。通过对一个简化评价方程的反问题进行分析，给出了裂纹长度和裂纹闭合相对不敏感性的计算机评价方法和程序。为了开发一种改进的检测和信号处理方案，为了获得更好的超声特征响应，对单探头超声技术进行了一项关于光束角的新实验研究。在正常入射超声自动采样系统的基础上，开发了一种适用于斜角度裂纹回波数据的高灵敏度自动采样系统。实验研究了超声入射光束的斜角与波的反射和模式转换的关系。证明了斜角度超声无损评价的可能性。利用斜入射超声对两个极窄宽度、0.1 mm宽、深度分别为1和3mm的模拟小裂纹进行了评价。该方法可用于小裂纹的评定。

1.In order to establish a high accuracy and high speed sampling method by using an automatic two dimensional scanning for an amplitude of echo from crack, water and an ultrasonic equipment were used as medium for ultrasonic wave propagation and sampling of wave date. The data was installed in a digital oscilloscope which has a high sampling speed.2.An evaluation equation which was simplified from a theoretical equation of a closed crack was derived. The evaluation method and a program of a computer to get a length of crack and a relative insensitivity of crack closure was shown by analyzing an inverse problem using the simplified evaluation equation.3.In a quest to develop an improved detection and signal processing scheme, a new experimental study of a single probe ultrasonic technique concerning a beam angle has been conducted in an attempt to achieve better characteristic response of ultrasonics.4.A high sensitive and automatic sampling system applied for crack echo data with oblique angle was developed from the automatic system using normal incident ultrasonics.5.The relation between the oblique angle of ultrasonic incident beam and the reflection of the wave and also mode conversion were examined experimentally. The possibility of a nondestructive evaluation by ultrasonics with oblique angle was shown.6.Two simulated small cracks extremely narrow width, 0.1 mm-wide slit, having depths of 1 and 3mm, wer evaluated by using oblique incident ultrasonics. The method can be applied for an evaluation of small cracks.