锚杆锚固结构中高频导波传播特性

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

锚杆锚固结构中高频导波(大于1MHz)的低衰减特性在现场锚杆无损检测中具有巨大的应用价值。通过对实验室有限锚固结构模型的频散特性分析,获得锚固结构中衰减最小的最佳激发波,并用数值模拟和室内试验进行验证,3种方法的研究结果均能够互相印证,证明高频导波能够对有限锚固结构进行无损检测,同时也验证了所建立的锚固结构频散特性分析模型的正确性。而后通过对不同尺寸锚固结构的频散特性分析和相应的波结构分析确定了低频导波和高频导波在有限与无限锚固结构中导波传播特征的差异性与相似性。差异性表现为当激发波为低频导波时,有限锚杆结构中锚固结构中存在衰减较小的模态,而无限锚杆结构中则不存在类似模态,这说明低频导波在有限锚固结构中的传播规律无法应用于现场的无限锚固结构的无损检测;相似性表现为当激发波为高频导波时,锚杆结构中存在不受边界条件影响的模态,这意味着该模态能够直接应用于现场锚杆的无损检测。低频导波和高频导波在有限锚杆结构和无限大锚杆结构中传播的不同表现,可以通过波结构进行直观解释:在位移波结构示意图中,杆内相对位移小的模态能量更集中,衰减更小,传播距离更远;反之,则不适合进行无损检测。

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.