Crack Damage Detection Of Beam Structure Based On Ultrasonic Guided Wave

At present,China’s infrastructure construction has made great achievements.It is of great significance to carry out real-time and effective detection,monitoring and evaluation of the built structures and timely discover and dispose of structural diseases,which guarantees the safety of people’s lives and property.Conventional detection methods have problems of low efficiency and high cost,which gradually cannot meet the needs of the detection industry.The structural damage detection method based on ultrasonic guided wave has high efficiency,wide detection range and high sensitivity,and can better meet the actual needs.The main research work of this paper is as follows:(1)The calculation theory of equivalent crack compliance is studied.In this paper,two concepts,stress intensity factor and energy release rate,which are usually used to describe the mechanical behavior with cracks in fracture mechanics,are introduced.Taking a rectangular beam with a crack as an example,the local compliance coefficient of the beam at the crack is derived by calculating the formula of the card theorem.Considering the coupling effect of stiffness caused by crack,the local additional compliance matrix generated by crack is derived.After obtaining the local additional compliance matrix caused by crack,the crack can be equivalent to a two-node elastic joint element and its stiffness matrix is derived.(2)The propagation process of guided wave in the bar is simulated by ANSYS finite element software.The basic theory of guided wave is described,The finite element model of non-damaged bar and the finite element model of damaged bar with crack are established by Solid185 in ANSYS finite element simulation software.The modulation process of excitation signal is studied and the influence of the length and section size of the rod on the propagation of guided wave in the non-damaged steel rod and the influence of the damage depth and damage location of the rod on the propagation of guided wave in the crack damaged steel rod is discussed.(3)The establishment process of structural spectrum element model of beam with cracks is studied.The basic principle,development process and Laplace transform principle of spectral element method are described,and the feasibility,accuracy and high efficiency of spectral element method in simulating ultrasonic guided wave propagation in bar are illustrated.Based on the Love bar theory,modified Timoshenko beam theory and Saint-Venant torsion theory,a three-dimensional spectral element model of spatial bars was established.A two-node polycondensation spectrum element model with cracks was established by dynamic polycondensation method.The propagation process of guided waves in steel bars under different damage depths,different crack widths,cantilever constraints and free-free constraints is studied.The calculated results of three-dimensional spectral element model with cracks are compared with those of ANSYS solid finite element model.The results show that the spectral element method has high accuracy and is suitable for simulating wave propagation in the bar.