Propagation characteristics of high-frequency guided waves in bolt anchorage structures

The low-attenuation characteristics of high-frequency guided waves(greater than 1 MHz) in bolt-anchored structures have a great application value in the on-site non-destructive testing of bolts. Through the analysis of the dispersion characteristics of the finite anchoring structure model in laboratory,the optimal excitation wave with the least attenuation in the anchoring structure is obtained,and verified by numerical simulation and laboratory experiments. The research results of three methods can confirm each other,and they all prove that the high-frequency guided waves can perform a non-destructive testing of finite anchorage structures,and also verify the correctness of the established anchorage structure dispersion characteristics analysis model. Then,the difference and similarity of the guided wave propagation characteristics between the low-frequency guided wave and the high-frequency guided wave in the finite and infinite anchored structures are determined by analyzing the dispersion characteristics of anchored structures with different sizes and the corresponding wave structures. The difference is that when the excitation wave is a low-frequency guided wave,there are modes with less attenuation in the finite anchor structure,but there is no similar mode in the infinite anchor structure,which shows that the propagation law of low-frequency guided waves in the finite anchored structures cannot be applied to the non-destructive testing of infinite anchored structures on site. And the similarity is that when the excitation wave is a high-frequency guided wave,there are modes in the anchor structure that are not affected by the boundary conditions, which means that the mode state can be directly applied to the non-destructive testing of on-site bolts. The different behaviors of low-frequency guided waves and high-frequency guided waves propagating in the finite bolt structures and the infinite bolt structures can be intuitively explained by the wave structure:in the schematic diagram of the displacement wave structure,the modal energy of the small relative displacement in the rod is more concentrated,the attenuation is smaller,and the propagation distance is longer. Otherwise,it is not suitable for the non-destructive testing.