Ultrasonic Inspection Of Grouted Splice Sleeves Based On Reverse Time Migration Imaging Method

Precast concrete structure is widely used in the construction field in recent years because of its advantages of environmental protection,reliable quality and convenient construction.As the most important connection mode of assembled structure,grouting sleeve connection is used for connection of prefabricated members.Sleeve grouting plays an important role in structural stability and seismic resistance,and is an important guarantee for structural stability and integrity.At present,however,the detection method for the quality of sleeve grouting is difficult to meet the requirements of resolution and field application.In this paper,an ultrasonic phased array imaging detection method based on inverse time migration algorithm is proposed to solve the grouting defects of sleeve joint members.By arranging ultrasonic phased array on the surface of the block to be tested,the elastic wave signal is excited and the full-matrix echo signal is received by the data acquisition device.By using the inverse time migration imaging algorithm to carry out migration imaging processing on the collected full-matrix data,the highresolution reconstruction image of the grouting layer inside the sleeve of assembled sleeve structure was obtained,and the visual detection of the grouting defects of the sleeve was realized.Firstly,in view of the complex structure of assembled sleeve,the optimal design of ultrasonic phased array parameters was studied,and the most suitable ultrasonic phased array parameters were obtained through simulation experiments.The parameter design of phased array mainly includes determining the center frequency of phased array and the array layout.By using the offset evaluation index of the contrast measurement,the inverse time migration imaging images at different frequencies were evaluated to obtain the best center frequency.In the same way,the optimal layout of phased array is obtained,that is,the number and spacing of elements are determined.Then a numerical experiment is carried out to verify the effectiveness of the proposed algorithm.In this study,three random medium models of assembled concrete sleeve grouting are established,which are three-fourths grouting model,all-grouting model and no-grouting model respectively.The experimental results are compared with the popular full-focus algorithm in phased array field.In order to further verify the effectiveness of the proposed algorithm and the feasibility of practical engineering application,the fifth chapter carries out laboratory experiments.The interior model contains two sleeves,one of which is grouting compactness and the other has certain grouting defects.The full matrix data of the two sleeves were collected by professional experimental instruments.The full focus imaging algorithm and inverse time migration imaging algorithm were used to compare the images.Finally,it can be concluded that the most suitable ultrasonic phased array for the detection of assembled sleeve grouting defects has a center frequency of 500 k Hz,a number of array elements of 24,and a spacing of 6 mm.Compared with the full-focus algorithm,the imaging results of numerical experiments show higher imaging resolution and precision,and the grouting defects inside the sleeve can be well recognized.The results of laboratory experiments show that the reflection intensity of the grouting non-compacting sleeve is 9 d B higher than that of the grouting compacting sleeve.The results show that the method is suitable for the inspection of the defects of the precast sleeve grouting.