Application Of Ultrasonic Imaging In The Large-scale Bridge Components Nondestructive Testing

Ultrasonic imaging is a kind of computer tomography. It is a modern nondestructive testing that developing rapidly. The technology is based on elements of the parameters of acoustic and structural changes has a good correlation, according to testing the time of ultrasonic through monitoring profile, and then use the appropriate algorithm inversing the distribution situation of ultrasonic velocity and amplitude of testing profile, the last under the connection of ultrasonic velocity and materials determine the defect distribution of testing profile. Because the length of ultrasonic wave is short, ultrasonic imaging technology has high resolution, and reasonable layout of measuring line density and inversion mesh can be assured that the test within the region have adequate resolution.In recent years, as the development of construction, large bridge component has used extensively, and will continue to develop in the next long-term period, so we must study new method to meet the requirements of testing. At present, we often detect internal defects of component by penetration testing. But there are some shortcomings by conventional ultrasonic method, such as defects can be only infered basis on some of testing lines, specific location and size is difficult to determined, and the accuracy is not high. It only gives some and not all sections of concrete quality. As the testing value reflects the average quality of quality, it is difficulty to quantify the extent of defects. In recent years, the researchers pay attention to the solid imaging technology, many people made some research according to using ultrasonic wave in imaging technology. They use intensive cross-ray penetrating concrete, can limit the space of defects and gain the concrete quality of entire section. It makes up for the shortcomings of the conventional method. Although ultrasound imaging technology in the detection of concrete obtains some results, but the inversion accuracy of the technology need to be further improved and the parameter selection also need to be further studied. In past years, use the method obtaining the intensive cross-ray needs far more workload and cost than conventional method because don't have the support of advanced ultrasound equipment, it didn't conduct comprehensivly in the test.The paper take the method that inspiring at one point and accepting by multi-channel at the same time, thus greatly reduce the workload and costs. It improves the volume of data and accuracy of test. The new method will play great role for promoting the tomography technology.The paper introduces the theoretical basis of elastic wave CT, that is Randon transformation and image reconstruction. Image reconstruction consists of continuous and discrete image reconstruction. Discrete image reconstruction converts into the problem of solving linear equations. Generally, the solving methods of equations adopt iterative algorithms. It concludes back projection technique ( BPT ) , algebraic reconstruction technique(ART), simultaneous iterative reconstruction technique(SIRT) and LSQR technique.The theoretical basis of ray tracing is showed, especially straight ray tracing and linear interpolation ray tracing. The ray tracing has many methods. Different algorithms has differences in applicable conditions, computational efficiency and applicable effect. We can adopt straight ray tracing method when the measured profile is uniform. Or we adopt bending ray tracing method in order to calculate head wave traveltime and path rapidly. While bending ray tracing method is realized by Fermat's principle.The paper introduces the SRS64 multi-channel ultrasonic detection system and makes a choice on geophone and source through analysis and then introduces the procedure of preprocessing.At last, the paper mainly introduces the applications of the new method in the practical engineering. It introduces the layout mode of observing system and testing line in different bridge component, such as T-beam bridges, roof, floor, web and clapboard. Then gives map of the results and certificated that it achieved good results.