Coda Wave Array Based Preliminary Experimental Study Of Stress Test In Reinforced Concrete Beam

Ultrasonic non-destructive testing technology has been used for decades in the field of civil engineering,and direct wave(head wave)is used as the research object in the most traditional acoustic detection,While for the study of the coda wave,is still less.The coda wave is the elastic wave produced by diffraction and scattering in the medium.Due to the superposition of these diffraction and multiple scattering,the propagation path of the coda wave in the medium is longer than that of the direct wave,so the time of arrival is shorter than that of direct wave.It is because the propagation path of the coda wave is longer,the wave contains rich information.At the same time,the coda wave has a very high sensitivity to the weak change of the medium,which can be detected when the concrete structure has weak change.Based on researching for foreign literature,analyzing the theory of coda wave interferometry and experimental research from the several foreign scholars,detailed described the coda wave principle and coda wave interferometry.Reference foreign scholars’ experiment device and experiment method,we do experiment,and designed different experiment schemes and experiment device with foreign.We test coda wave experiment tests stress change of reinforced concrete beam in laboratory.Detailed describes and explains the problems in the process of experiment.Then when data analysis,seeing coda wave time domain as the research object,we use MATLAB software to deal with the data,and set up a time domain method of data processing.To compare and analyse the coda wave experiment data by two methods,coda wave interferometry and amplitude information analysis.The first is coda wave interferometry,the core is correlation coefficient,the corresponding time for time delay(or before)could be calculated through the maximum correlation coefficient.Firstly a time window could be established,time delay will be got by correlation analysis in the time window,finally the speed rate is derived by time delay.Another is by amplitude information analysis,the core is the standard deviation,the difference of the amplitude of different waveforms is calculated,and the standard deviation of the difference is calculated.Comparing the results of the two types of analysis,which can test the result of the measurement,It is beneficial to the quantitative analysis and to reduce the uncertainty in measurement,which a more effective means for further research can be provided.Using a variety of processing methods to analyze these the coda wave data,more meaningful research results would be obtained,This is also beneficial to promote the study of coda wave and get new results,And it also provides a direction for other researchers.In the paper,based on the national natural science foundation program,“Coda Wave Array Based Non-Loading-Non-Unloading Type Stress Field Measurement of Concrete Structure” for the project support,is combined with research content.The result of the paper which adopted the different processing method is similar,and the results of the two methods are linear.Through coda wave interferometry to obtain thewave velocity change rate,which is same as quantifying the wave velocity change rate of the concrete structure’s stress changes by foreign scholars,the order of magnitude both are 10-3/MPa.This illustrates the diversity of the coda wave data processing technology,and is also proved that the coda wave has a high sensitivity to the weak change of the medium.