Design Of Nondestructive Testing System For Bolt Based On Magnetostrictive Mechanism

Bolt is widely used in railway,mine,and other underground engineering support and slope nursing.Bolt has improved the level of safety technology.However,in real life,due to the influence of human destruction and natural conditions,bolt will have many defects,such as rust and fracture.Those defects will cause safety hazards.This paper based on the magnetostrictive effect of anchor bolt was designed using magnetostrictive guided wave nondestructive testing technology experiment and analysis of bolt quality through the experimental data,the test results for the practical application of magnetostrictive guided wave in bolt detection provides the basis for.The specific contents of this study are as follows:(1)The principle of magnetostriction;the basic concept of ultrasonic and ultrasonic guided waves;the multimodal characteristics of the guided wave and the dispersion of the guided wave are introduced in this content.Also,the concept of group velocity and phase velocity of guided waves is mentioned.In the paper it is focus on the longitudinal guided waves excited by bolts.Then the dispersion curves of ultrasonic guided waves in free anchors are plotted using MATLAB programming.(2)A collection system which including electromagnetic ultrasonic excitation unit and electromagnetic ultrasonic receiving unit is designed in this paper.This system can be used to solve the problem that the signal to noise ratio of ultrasonic guided wave is low and to figure out it is difficult to collect.The excitation unit modules use different area model.It includes signal selection,power amplifier,impedance matching design and magnetostrictive transducer excitation.Those is analyzed by excitation unit.The defects of weak signal and noise guided wave signals can be covered by receiving unit.The receiving unit including the receiving unit through the design of magnetostrictive transducer excitation receiver,preamplifier module,band-pass filter module,three stage amplifier module,the design of the interface between the acquisition card and the LabVIEW upper compute.(3)Because there are still many noises in the collected signals,the Hilbert transform method of variational mode decomposition(VMD)is adopted in this paper.The length and the error analysis of the free segment and the anchoring section of the bolt are measured and analyzed,and the defect location of the defective anchor is carried out.Compared with the traditional wavelet transform and the empirical mode decomposition(EMD)analysis,it is concluded that the VMD-Hilbert method is more accurate and suitable for nondestructive testing of bolt which makes up the shortcomings of the large noise of the guided wave signal and the weak signal acquisition.