【作者】 孙继华；

【导师】 李书光；

【作者基本信息】 中国石油大学 ， 无线电物理， 2008， 硕士

【摘要】 现代无损检测技术正向高精度、高准确度方向发展,传统的理论和实验方法已不能满足其发展的要求,这就使得数值模拟越来越多的应用到超声无损检测研究上来。对于检测信号,一般在时域中分析所获得的缺陷信息是有限的。随着数字信号处理技术的发展起来的频谱分析方法已广泛应用到超声无损检测中来,应用频谱分析技术可以在频域中获得缺陷的更多信息。本文应用有限元方法,建立了各向同性固体二维超声无损检测有限元模型。首先,对材料中无缺陷以及含有裂纹、方形横穿孔、圆柱形横穿孔缺陷的情况进行了模拟计算,在时域信号中可以看出各种回波和透射波幅度等特征的区别;重点对信号进行了频谱分析,计算得到了缺陷回波、底面回波以及透射波的频域特征量:峰值、峰值频率、中心频率、带宽、半高宽和缺陷谐振敏感频率等的变化;同时针对圆柱形横穿洞不同的直径,获得了其透射波各种频域特征量的变化规律曲线。其次,通过对平面和弧面凹槽的模拟计算,得到了相同深度不同宽度凹槽的底面回波幅度和频域特征量的不同,同时得到了不同宽度平底孔底面回波频域特征量的变化规律。最后,对钢中有各种金属和非金属夹杂的情况进行了模拟计算,通过时域回波信号相位的分析,验证了模拟结果与理论计算的一致;通过对回波和透射波进行频谱分析可以得到各种夹杂的不同频域特征量。上述模拟结果能很好地识别出本文所述的各种缺陷,证明了应用有限元方法和频谱分析技术建立的模拟程序的正确性,这为理论和实验研究提供了参考,为进一步深入研究超声无损检测技术提供了新思路。更多还原

【Abstract】 The modern nondestructive testing technologies (NDT) are developed towards the direction of high precision and accuracy. The numerical simulation have been more and more applied to the research of ultrasonic nondestructive testing because of the traditional theory and test method cannot meet the requirements of NDT development. It is generally believed that we can obtain limited flaw information in time domain. Hence, the spectrum analysis method which has been developed with the digital signal processing technology is used widely in NDT to obtain more features of flaws.In this paper, two-dimensional NDT models have been developed by finite element method. Firstly, the model which has three different size defects: crack, traverse square cavity and traverse cylindrical cavity is studied by simulation, we can obtain the different amplitude by the echo and transmission signal, and we can obtain the different characteristics in frequency domain, such as: peak, peak frequency, center frequency, bandwidth, half high width, quarter high width and sensitivity frequency etc; aiming at the transmission signal of traverse cylindrical cavity, variation laws of frequency characteristics can be obtained from spectrum analysis. Secondly, studying the model of planar and arc groove, we can obtain the different amplitude of the back wall echo and transmission signal, and we can obtain the characteristics in frequency domain and the sensitivity frequency; variation laws of planar groove in frequency domain can be obtained from the spectrum analysis of transmission signal also. Finally, the finite element models with metal and nonmetal inclusions are developed in steel to study the ultrasonic propagation; the results are proved to be correct and reliable by analysis of echo phase, and we can obtain the characteristics in frequency domain and the sensitivity frequency of all inclusions.The results can recognize defects and proved the correctness of finite element method and spectrum analysis technology in this paper. The simulation results may be useful to theory and test study, and offer a new idea for NDT.更多还原