Study on propagation characteristics of ultrasonic guided wave and detection of the defect in resin bolts

Abstract

The nondestructive testing of the bolt anchoring quality based on ultrasonic guided wave technology is significant to ensure project security. In this paper, an improved Legendre polynomial method (ILPM) is presented to study the longitudinal axisymmetric guided waves in a full-length bonding resin bolt which is a typical bilayer structure. The ILPM employs analytical integral calculation instead of numerical integral in the traditional Legendre polynomial method (TLPM), leading to superior computational efficiency. The effectiveness of the ILPM is validated, and the convergence and computational efficiency are also discussed. The attenuation and group velocity curves of guided waves are solved for the resin bolt. Through the theoretical analysis of dispersion characteristics, the optimal excitation frequencies for experimental detection can be found. Meanwhile, the guided wave detection system of a resin bolt is established to verify the theoretical results. Based on the Self-Sending and Self-Receiving experiment, the resin bolts with different anchoring defects (debonding length and incision size) are studied. The influences of L-mode defect detection ability and defect size parameters on the amplitude of the guided wave signal are analyzed. The experimental results show that L-mode can be used to detect the defects in the bolt, and the defect size can be characterized by the defect echo amplitude.