Development of quantitative low frequency ultrasonic testing and its application to nondestructive evaluation of concrete structures

本研究的目标是在10 kHz至100 kHz范围内开展低频超声定量检测，主要内容有：1.低频超声法的基本性质；2.低频超声法的数值方法；3.混凝土结构的应用。低频超声法的基本特性：我们对有关超声换能器的文献进行了综述，发现关于产生低频超声波的换能器的研究工作很少。研究还发现，用于混凝土超声无损检测的商用换能器并不是在基于波动理论的最佳条件下设计的。研究了激光测振仪在混凝土无损检测中的适用性。低频超声波检测的数值方法：将低频超声波方法应用于大型基础设施。因此，在超声检测的数值模拟中，需要进行大规模的计算。为此，我们发展了2.5维边界元方法和快速多极边界元方法，这两种方法对于大规模波浪分析都是有效的。在混凝土结构中的应用：将低频超声波检测应用于材料界面脱粘的评价和PC灌浆的评价。在界面脱粘的评价中，利用泄漏表面波的L扫描方法被证明是一种比传统的C扫描方法更好的方法。在PC灌浆评价中，利用小波变换对冲击回波法得到的波形进行了分析，并进行了理论和实验对比。

The objective of this research is the development of quantitative low frequency ultrasonic testing in the range of several 10kHz to 100kHz, in which major topics are 1. fundamental properties of low frequency ultrasonic method, 2. numerical method for low frequency ultrasonic wave method and 3. application to concrete structures.1. Fundamental properties of low frequency ultrasonic method :Our review of papers related to ultrasonic transducers showed that there are few works on transducers producing low frequency ultrasonic waves. It was also found that commercial transducers for ultrasonic nondestructive testing of concrete are not designed under the optimum condition based on the wave theory. Applicability of laser vibrometer to nondestructive testing for concrete was investigated.2. Numerical method for low frequency ultrasonic testing:A low frequency ultrasonic wave method is applied to large-scale infrastructures. In numerical simulation of the ultrasonic testing, therefore, large-scale calculation is required. To this end, we developed a 2.5-D boundary element method and a fast multipole boundary element method, both of which are effective for large-scale wave analyzes.3. Application to concrete structures :Low frequency ultrasonic testing was applied to the evaluation of debonding on material interface and the evaluation of PC grouting. In the evaluation of interface debonding, an L-scan method with use of leaky surface waves was demonstrated as a better method than a conventional C-scan method. In the PC grout evaluation, the wavelet transform was used for the wave analysis obtained by impact-echo method and comparison between theory and experiment was carried out.