全长黏结型锚杆高频超声导波检测应用研究

APPLICATION OF HIGH FREQUENCY ULTRASONIC GUIDED WAVES TO INSPECTION OF FULL-LENGTH-BONDING BOLT

分析高频纵向轴对称超声导波在全长黏结型锚杆中传播的特性。在不同频率范围内,锚杆中同一模态的衰减特性及速度差别较大。理论上,在1 MHz以上,高阶纵向轴对称模态在特定频率下的轴向位移集中于杆中心,衰减最小,且能量速度最大,可用于全长黏结型锚杆的质量检测。同时建立实验系统,在1.13～2.85 MHz频率范围内对直径φ22 mm、长度1 m的埋于水泥中的无缺陷锚杆进行了频率扫描,并根据实验结果做出第一次端面回波速度和幅值随频率变化曲线,分别与理论能量速度频散曲线和衰减频散曲线相吻合,并且对埋于水泥中带单缺陷锚杆进行导波检测。研究结果表明导波可用于锚杆长度检测及缺陷定位。最后,将此规律应用于在直径为φ18 mm,长度为2 m的锚杆工程现场检测,检测结果较为理想,验证高频超声导波可以应用于全长黏结型锚杆的无损检测。

Propagation characteristics of high frequency longitudinal axisymmetric modes in full-length-bonding bolt are studied.For the same mode in bolt,its attenuation and velocity vary greatly with frequency range.In theory,there is high order longitudinal mode above 1 MHz whose axial displacement concentrates in the middle of bolt.Its attenuation is the smallest,and its energy velocity is the fastest in all modes at the special high frequency.This indicates that the high order low loss longitudinal mode can be used to inspect full-length-bonding bolt.At the same time,the experiments about diameter 22 mm,1m length bolt without defect embedded in grout detected using ultrasonic guided wave are carried out.The scope of inspection frequency is between 1.13 MHz and 2.85 MHz.The velocity and amplitude curves of first end reflection with frequency are made.The experiment curves are consistent with those dispersion curves of theory.Besides,the experiment that the bolt with one defect embedded in grout detected by guided waves also is carried out.This indicates that ultrasonic guided waves can be used to inspect the length of bolt and confirm the location of defect.Finally,site inspection for diameter 18 mm,2 m length bolt is performed.The inspection results show that the guided waves technology is available for the nondestructive testing of full-length-bonding bolts.