抄録
The nondestructive testing for structures such as poles or cables has been developing. However, since current techniques are generally visual inspection or point measurement, they require an automatic and efficient system for nondestructive testing. Guided waves can spread a long distance without energy loss. That suggests a possibility of efficient nondestructive testing of large-scale structures such as pipes and wires. However, there are some problems for practical use. For instance, distinguishing contribution of a particular mode from receiver signals is incomplete, and moreover, mechanisms of guided waves in wires are further difficult because of its complex geometry. The goal of this research is to establish a flaw detection method using a particular mode of guided waves in a seven-wire strand whose each wire is further composed of nineteen-stranded fine wires known as 7×19 type wire. We first verified generation of guided waves in a rod and a wire under excitation at a specific frequency from experiments. That suggests modes of guided waves in the experimental results can be determined by the theoretical value such as the frequency, the group velocity and displacement distributions. Moreover, we applied the finite element method to analysis of wave propagation in a cylindrical center strand and in a helical peripheral strand. According to these results, for general lay angle, modal exchange of guided waves did not occur in the helical peripheral strand though it has complex geometry and the longitudinal mode of guided waves was less damped than the flexural mode of them.
