带阻尼多层杆构件超声导波传播特性分析

Analysis of ultrasonic guided wave propagation characteristics of damped multilayer rod

应用半解析有限元法求解导波在带阻尼多层杆构件中的相速度、群速度、衰减情况和波结构等频散特性。采用有限元数值模拟的方法对带有包覆层(芯层采用直径φ=28mm的28#热轧带肋钢筋,包覆层为φ_(inner)=28mm,φ_(outer)=160mm标号为C50的混凝土)和不带有包覆层(芯层采用φ=28mm的28#热轧带肋钢筋)的两类锚杆进行三维建模,并分析了不同加载方式下导波的激励特性。结果表明:锚杆中低频频段的导波模态数量较少,衰减较小,但频散较强,信噪比较低;高频频段中存在的导波模态众多,且衰减较快。与无包覆层锚杆相比,灌浆锚杆在同样的频带范围内导波的模态数量更多更复杂,衰减明显增大。在低频时灌浆锚杆的纵向模态位移分布在全截面,高频时集中在锚杆中心部位。采用导波对杆构件进行长度检测时,对于无包覆层锚杆优选端面与侧面组合加载方式下64kHz时的L(0,1)模态,而对于灌浆锚杆优选端面梳状阵列加载方式下2250kHz时的L(0,22)模态。

The semi-analytical finite element method is used to solve the dispersion characteristics of the phase velocity,group velocity,attenuation and wave structure of the guided wave in the damped multi-layer bar member.The method of finite element numerical simulation is used for the cladding(28#hot-rolled ribbed steel bar withφ=28 mm,the cladding isφ_(inner)=28 mm,φ_(outer)=160 mm concrete with C50)and without Two types of anchors with a coating layer(φ=28 mm 28#hot rolled ribbed steel bars)are modeled in three dimensions,and the guided wave excitation characteristics under different loading methods are analyzed.Results show that the number of guided wave modes in the low frequency band of the anchor rod is small and the attenuation is small,but at the same time,the frequency dispersion is strong and the signal noise is relatively low.There are many guided wave modes in the high frequency band and the attenuation is fast.Compared with uncoated anchors,grouting anchors have more and more complex wave-guided modes in the same frequency range,and the attenuation is significantly increased.At low frequencies,the longitudinal modal displacement of the grouting anchor is distributed over the entire section,and at high frequencies it is concentrated in the center of the anchor.When using guided waves to detect the length of the rod member,the 64 kHz L(0,1)mode under the combined loading mode of the end face and the side is preferred for the uncoated anchor rod,and the comb mode array end mode for the grouting anchor rod is the 2250 kHz L(0,22)mode.