Development of automatic measuring system of ultrasonic attenuation using spectrum analysis

近年来，人们对高温植物的寿命延长有着强烈的期望，因此对高温植物的剩余寿命进行准确的评估已成为一个重要的问题。提出了一种利用超声波对高温构件的蠕变和高温疲劳老化劣化损伤进行无损评价的新技术。在以前的工作中，超声波衰减是从脉冲回波的第1和第2个峰值来评估的。然而，由于叠加噪声对衰减值的影响较大，用这种方法求得的衰减值存在一定的误差。本文提出了两种利用频谱分析提高超声衰减测量精度的新算法。一种是从原始超声包络曲线求衰减值的方法，另一种是从第一次和第二次回波计算试样的系统函数求衰减值的方法。对蒙特卡罗模拟和退化试样得到的几种超声波进行了分析，并与传统方法进行了比较。通过比较表明，所提出的方法能够比以前更准确地测量超声波衰减，并且衰减值随着剩余寿命的减小而增大。并阐明了衰减值作为蠕变和高温疲劳的无损评价参数是有效的。所开发的算法安装在由个人计算机、超声仪和数字存储示波器组成的测量系统上。此外，在系统中加入fft分析仪，大大缩短了分析时间。最后，所有的仪器和分析程序都可以完全自动化，这将使我们能够将上述超声方法应用于实际结构。

The life extension of high temperature plants is strongly expected recently, so that the accurate remaining life assessment of them has come to be an important problem. This report presents a new non-destructive evaluation technique using ultrasonic waves for the evaluation of aging deterioration damage ( caused by creep and high temperature fatigue ) of high temperature components. In previous works, ultrasonic attenuation is evaluated from the 1st and 2nd peak values of pulse-echo ultrasonic wave. However the attenuation values evaluated by this method may have some error, because those values are greatly affected by the super-imposed noise. In the present work, two new algorithms for the improvement of measuring accuracy of ultrasonic attenuation using spectrum analysis has been developed. One is the method that evaluates the attenuation values from envelope curve of original ultrasonic waves, the other is that evaluates the attenuation values by calculating the system function of specimen from the 1st and 2nd echoes. Several ultrasonic waves obtained from Monte Carlo simulation and degraded specimen are analyzed by using, both the proposed methods and the conventional method. It is shown through the comparison that the proposed methods enable us to measure ultrasonic attenuation more accurately than before, and that the attenuation values tend to increase as decreasing of the remaining life. It is also clarified that the attenuation values is effective as non- destructive evaluation parameter of creep and high temperature fatigue. The developed algorithms are installed on the measuring system which consists of a personal computer, ultrasonic apparatus, and digital storage oscilloscope. In addition the analysis time is very much shortened by incorporating FFT-analyzer in this system. Finally, all of procedures of instrumentation and analysis can be automated fully, and it will enable us to apply the above ultrasonic method to real structures.