| According to the need in evaluation of the crack in structure, the author of this paper developed a new system based of photoelastic mechanics and digital image proccessing, which is specialy used to measure the length and width of crack. In the prophase the author paticpated the mading of the hardware of the system made of optial lens , CCD, image card and computer. Then the software which composed the filtering of noise, the product of binary image, image segmentation, edge detector, and thinning is finished. Also the image element is calibrated accoring to the digital speckle correlation method (DSCM)oAnd then the length divided by the interal pixel is hunted and caculated, the width divided by subpixel is also done. Finaly many experiments are completed in the lab in diffrient conditions , which contains illuminance of crack , contrast of image , distance of shotting and focal length, to review the accuracy of the new system and to analys the rule of th effection of the accuracy .This system can non-contacting and fast measure , and the measuring accuracy satisfied the demand of engineering.It shows its dominance and characteristic when it is use to measure the crack which is in dangerous or high temperature field . It can be forecasted that this system can be made to a new equipment applied in the field of detection widespreadly, when the system is improved . |
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