| The wide application of anchor rods in mines, pavements, railways and many underground constructions offers clear benefits to employees and the industry for safer working environments. However, in-service anchor rods are subjected to defects like corrosions and fracture for the harsh working environments, which may cause serious safety problems. Based on magnetostrictive effects of ferromagnetic materials, this thesis proposed a novel method for anchor rod detection applying magnetostrictive guided waves. Magnetostrictive guided wave detection is a kind of non-contact detection method which has the merit of inspecting over a long distance from a single position. This research lays the foundation for practical engineering application.The thesis focuses on guided wave propagation in free rods and in the rods embedded in concrete, as presented in the following chapters:The first chapter presents the background and key technologies of the program, bringing the latest research and developing orientation of the NDT of anchor rods.The second chapter studies the modeling of guided wave propagation in cylindrical structures, the calculation of guided waves dispersion curves in anchor rod, and then several key points of guided wave research were paid special attentions.The third chapter works on magnetostrictive guided wave detection system. The system consists three main part: the guided wave excitation unit, the guided wave detection unit, and the signal processing unit. Each unit was discussed in detail.In the fourth chapter of the thesis, guided wave propagation in a free rod was studied. Experiments were conducted to study the effects of frequency, bias magnetic field, and excitation pulse numbers in guided waves excitation and receiving. Experimental results indicated that guided wave can measure the length of the free anchor rod precisely, guided wave reflection coefficients from notches can be a potentially measurement to judge the severity of the defects.The fifth chapter focuses on guided wave propagation in embedded anchor rod. Guided wave dispersion curves in embedded rod was given for choosing the proper guided wave mode for long range inspection. Experiments was conducted to study the influence of frequency in guided wave propagation. Then man-made notches were studies, reflected signals from the notches can be recognized when the their percentage of cross-section is larger than 10%.The sixth chapter summarizes the achievements of the research, then give recommendations for further scientific research. |
PDF Full Text Request