Key Technologies Research On 3-D Reconstruction Of Internal Defects In Part Based On Serial ICT Slice Images

With the advancement in science and technology, there are increasing demands on quality and reliability of mechanical parts. Internal defects in mechanical part have important influence on overall quality and reliability, but they are difficult to detect directly and analyze quantificationally. Conventional practices are concentrated on 2-D images. To fulfill the needs of research on defects configuration and deformation under forces or stresses, furthermore to provide accurate and reliable theoretical basis for judgment quality and reliability of mechanical parts,3-D reconstruction of internal defect in mechanical part is systematically studied in this dissertation. ICT(Industry Computerized Tomography) is referred as the best technique in Nondestructive Testing field, so it is used to detect and obtain the slice images of internal defects in mechanical part. This dissertation focuses on the key technologies of internal defects 3-D reconstruction in mechanical part based on its ICT slice images.Firstly, characteristics of ICT slice images of internal defects in mechanical part are summarized and advantages and disadvantages of existed defects segmentation methods based on images are analyzed. Based on previous research, an adaptive morphological filtering method is presented to extract all potential internal defects in mechanical parts. In this method, simulation background image is obtained from morphological operation to original slice image, and the structure element is set as the fitting ellipse of the maximum region contour after watershed transform of original slice image. Therefore, the defects are well segmented out by subtraction operation between simulation background image and original slice image.Secondly, vectorization of defect contours data and coordinate transform between image and 3-D are studied after 3-D coordinate system is constructed. The similarities of defect contours on between different slice images belong'to one defect body are summarized. The conception of similarity measure is introduced to describe the similarity degree between two defect contours on neighboring slices, and the geometry and non-geometry information are considered to calculate the value of similarity measure. The parameters of fitting ellipse of defect contour are used to describe geometry information, and the pixel gray information internal defect contour is used to describe the non-geometry imformation. A matching algorithm of defect contours based on similarity measure is presented, and a matching strategy of two steps is used to deal with the branching of defect contours. For improving accuracy rate and reducing computational complexity of contours matching, a method of determination candidate matching region based on one order space neighborhood of contour points is presented. Adjustment criterion to distinguishing the true or false defects from all potential defects is proposed according to the results of 3-D topological reconstruction. The accuracy and reliability of presented methods are validated by experiments.Thirdly, a method of triangular mesh building is presented based on characteristics of defect contours data from serial ICT slice images. In this method, the first step is feature points detection and contour data reduction by Freeman code difference function, the second step is feature points matching based on similar theory of feature points, the third step is feature points supplement to deal with the instance of feature points with no matching relation, the last step is triangular facet construction based on a local optimal method. By this method, not only detailed characteristics of defects are kept but also data amount is reduced.Lastly, a prototype system is designed and developed based on the foregoing researches. Functions and structure of the system are designed in this prototype system, and calculation methods of some key parameters of reconstructed defects model are presented.