Research On Concrete Damage Imaging Based On Time Reversal Theory

Since the concrete material is made of cement,sand,aggregate and other materials,it will cause defects of the type of holes due to various factors such as vibration and template in the course of the construction.During the long service period,under the influence of external load and environmental impact,the development of defects in concrete will affect the durability and reliability of the overall structure,and may even lead to serious catastrophic accidents.Among the many concrete detection methods,the ultrasonic time reversal model based on the principle of acoustic reciprocity has good adaptability to the location of internal defects of concrete structures,and the operation is simple.It can be adaptively focused in the equivalent parameter model.To Realize the positioning and imaging of damage defects.In the previous research on concrete,most of the concrete is regarded as homogeneous material,which also magnifies the error between theoretical calculation and actual engineering to some extent.In this paper,monte carlo sampling function is combined with concrete aggregate gradation.The curve is built by MATLAB to build the numerical model of aggregate,and the time reversed model(Time Reversed Model-TRM)is simulated.A method of contrast imaging based on peak time identification is proposed.At the end of the paper,the concrete test block is poured and the experiment is built.The platform verifies the simulation experiment.The experimental results show that the time reversal model can effectively identify the damage interface and complete the positioning imaging in the test of concrete test block,which has good applicability,the peak time contrast imaging method can effectively improve the accuracy of positioning imaging.The main work of this paper is as follows:(1)Based on the Monte Carlo random sampling function and the concrete aggregate grading curve,the numerical model of concrete random aggregate was established based on MATLAB programming,and the finite element software was introduced and the material definition,parameter setting,hole defect setting and mesh division were carried out;(2)The time reversal model is built,and the process is mainly divided into two steps:forward detection and time reversal imaging.The first step is forward detection.The piezoelectric transducer transmits the excitation signal and receives the response signal inside the structure to extract the preset holes.The echo signal of preset hole interface is extractedand time reversal processing is performed;the second step is loading and imaging,the imaging is loaded,and the time-reverse signal is loaded in the corresponding position in the equivalent elastic parameter model to form a time-inverted wave field,and the maximum field value image is realized.Meanthile the peak time of the model and the peak time of the preset hole position were compared,and the waveform data of the peak time is extracted and reloaded,and the peak time contrast imaging is completed;(3)Based on the finite element simulation results,the concrete test block is poured,and the experimental platform is built.The excitation signal is transmitted through the piezoelectric transducer,and the response signal inside the material is received.The echo signal of the preset hole interface is extracted from the collected response signal.The the time reversal processing is carried out and the corresponding position in the equivalent elastic parameter model is loaded to form the time reversal wave field,realize positioning imaging and complete experimental verification;(4)Based on the experimental platform,the interface between cement mortar and steel reinforcement was identified,and a preliminary exploration was conducted through finite element simulation and experiment,to verrified that the time-reversed focusing model can effectively identify the interface between cement mortar and steel bar.