Numerical simulation of high frequency guided wave testing for anchor bolt defects

Previous research has confirmed that only high-frequency guided waves larger than 1 MHz have the minimum attenuation detection mode for anchor bolt widely used in underground projects. However, due to the complexity of numerical simulation of high-frequency guided waves, the research results are concentrated on experimental testing, which makes the research on propagation characteristics of high-frequency guided waves very limited. In order to explore the propagation of high-frequency guided wave and apply it to the on-site inspection of anchorage quality, the numerical model of anchor bolt is established by using ANSYS/LS–DYNA finite element software through parameter optimization. By analyzing the influence of different anchor thickness on the wave shape, the minimum outer diameter that can replace the field infinite anchor thickness model with the numerical simulation finite size model is obtained; In theory, the guided wave mainly propagates forward along the interior of the steel rod, and the bolt radial reflects the waveguide structure shape. Therefore, the bolt radial grid is set the densest, and the anchor body radial grid and the bar axial grid are set relatively sparse, in order to minimize the number of elements; In view of the different dispersion characteristics of guided waves with different head wave widths, the propagation process of guided waves in non-defective and defective bolts was studied, and the optimal head wave width was 0.04 ms; Based on the above three optimized parameters, the numerical models of the complete anchor bolt and the anchor bolt with defects are established respectively. The numerical simulation results are highly consistent with the laboratory test results in the literature, which proves that the numerical model established is correct and effective, and truly realizes the accurate simulation of high-frequency guided waves in the propagation application of the anchor bolt under the limited computing resources. On this basis, the anchor bolt model with different defect characteristics is built, and the defect location and depth are studied. The results show that the high frequency guided wave with specific frequency can accurately locate the steel rod defects, and the defect area can be roughly determined according to the ratio of defect echo amplitude to bottom echo amplitude.