Study On The Key Technology Of Corrosion Testing For Automobile Engine Cylinder Cavity Using Ultrasonic Phased Array

The automotive remanufacturing movement can effectively avoid theenvironment pollution and resource wastes caused by the great number of scrappedautomobiles and engines. Among all the problems in conducting the automotiveremanufacturing movement, the inspection of engine cylinder cavity corrosion defectsis the key and difficult one. In the field of nondestructive testing, the ultrasonicphased array inspection technology has gradually become the research hotspot for itsfast detecting, flexible beam, high sensitivity and operational safety. This thesisapplies the ultrasonic phased array inspection technology to the testing of enginecylinder cavity corrosion defects, and then studies several key techniques in thetesting process.Firstly, in consideration of the own characteristics of the engine cylinders, thisthesis designs the scheme about the ultrasonic phased array inspection applying to theengine cylinder cavity. Aiming at validating the scheme, we conduct thecorresponding acoustic field simulation, i.e., simulating and analyzing the acousticfield of linear phased array ultrasonic transducer under the condition of the concavecylindrical interface on the engine cylinder. Based on the expanded multi-Gaussianbeam model and ray acoustics theory, we deduce the expression of the radiationacoustic field of a linear phased array ultrasonic transducer in the engine cylinder, andthen simulate the radiation acoustic field in the engine cylinder, validate the feasibilityof the scheme, and analyze the relationship between the focusing quality and thedifferent element lengths and inner diameters, by the results of which, we optimize thephased array ultrasonic transducer.Secondly, this thesis proposes the new method which can quantitatively analyzethe defects, and then sets up the defects signal acquisition system based on the phasedarray ultrasonic transducer, furthermore, samples the A-scan signal of the corrosionpit defects with different diameters and taper angles. The characteristic of waveletpacket energy spectrum, the fractal feature, the peak characteristic in time domain,and some routine signal characteristic of the echo signals from defects are extractedaccording to ultrasonic signal characteristics. These extracted features construct thefeature vector of the echo signal. Aiming at solving the identification problem of the corrosion pit signal feature, we construct three types of artificial neural networks: BP,RBF, GRNN, all these can work well to get satisfactory results, specially, the RBFcan produce more accurate results than the other two, besides, it works moreefficiently and is more suitable for the identification process. Moreover, we use thegenetic algorithm to facilitate the feature optimization, which further improves theidentification accuracy and efficiency.Thirdly, we propose the defects labeling and positioning method which is basedon the image processing technology including image enhancement, image segmentand centroid extraction, and implements the automotive labeling and accuratepositioning of defects. Then, we propose the correction algorithm which transformsthe plane image back to the real cylindrical appearance, and improves the degree ofvisualization. At last, we design and manufacture the device for engine cylinder cavitytesting, and demonstrate the practical experiment of testing the real engine cylindercavity.Finally, in order to develop new detecting system which has stronger applicability,we propose the frame of the hardware system. In view of the problem of highsampling rate and large amount of data brought by the characteristic that sampling inall the channels in the imaging process, we conduct the research that applies theCompressive Sensing theory to the corrosion inspection of engine cylinder. We applythe Compressive sensing theory to the single element echo signal, make use of threedeterministic sparse transformations including discrete Fourier transformation,discrete cosine and wavelet, and then utilize relatively less sampling points toreconstruct the high resolution signal; by analyzing and comparing the sparse rate, wefind that the coefficients that acquired by decomposing the bior3.7wavelet to thefourth layer are of better sparse rate and less reconstruction error. According to theimaging method of Phased Array Ultrasonic Transducer, we obtain the B-scan imageof the corrosion pit defects under compressed sensing, which has better imagingresolution. For the significance, we say that it proposes new thinking and lays thefoundation for reducing the complexity of engine cylinder cavity testing system andthe high demand of hardware.