Research On Methods And Technologies Of Micro-scale Digital Image Correlation

In modern optical measurement, digital image correlation is a simple and effective method for measuring full- field displacement and strain and is widely used in experimental mechanics and other areas. It has various advantages, such as a wide scope of application, low requirements for experimental conditions, non-contact measurement and high accuracy. The ongoing development of micromachining technology promotes the development of micro materials and devices. Therefore, there is an urgent need to develop ne w methods and techniques necessary to micro-scale digital image correlation. Speckle as a sensor element of digital image correlation, which reflects deformation of the material and structure. Its quality will directly affect the accuracy of the optical measurement results, therefore the preparation of high-quality speckle plays a very important role in optical measurement. Then, microscale deformation measurement can be achieved under the microscope platform for digital image correlation method, but The work of microscope lens distortion cause image distortion problem must be studied, otherwise it will bring great error on the test results.To meet this need, the following work was carried out in this study.1)Effect of distortion for high-power microscope lens, A method of correcting lens distortion under a high-powered microscope was developed. First, a first-order distortion function and third-order distortion function were used to rectify the distorted image. A rigid-body translation experiment was conducted using micro speckle patterns and a crossed grating template. A corresponding distortion model was constructed and the distortion coefficient was determined. The results showed that after the first order correction function the error reduces 56.3%, after third-order correction of error is reduced 81.3%, the relative error is reduced by 25%. the third-order distortion function can be used to achieve effective correction of lens distortion under a high-powered microscope.2)A method of producing micro speckles based on spin coating was developed. The quality of speckle patterns was evaluated in terms of mean gray gradient and agglomeration rate in order to investigate the influences of temperature, speed of spinning, curing time, and other parameters on the speckle patterns. The optimal technological parameters for micro speckle production were derived from the results, and the prepared micro speckle films can be easily transferred and applied to work piece surface. This method can be used to produce large speckles and allows control of particle size and distribution. Besides, the method features high adaptability to different work piece surfaces, simple technology, low cost, and easy operation.3)Experimental and applied research was conducted to validate the methods and techniques for micro-scale digital image correlation. The results of the micro-scale translation experiment showed that the average measurement error was 1.5%, far below the value observed in macro speckle measurement. The elasticity mod ulus of an aluminum specimen was measured through a tensile test; the results of measurement using micro-scale digital image correlation were consistent with the data given in the specifications. Last, the method was successfully applied to the interface between an acrylic plate’s surface, which contained a micro crack, and a 600-um-thick coating to obtain the strain field around the crack tip. Succeeded in obtaining crack tip strain field within the field of less than 2mm view it can be used to characterize the mechanical properties of materials and structures.