Study On Digital Speckle Correlation Method And Its Application

The Digital Speckle Correlation Method (DSCM), a non-contact full-field optical measuring technique, possesses quite a few advantages compared with other optical methods. The 2D (two-dimensional) DSCM, studying the in-plane deformation, had been well developed during the last 2 decades. Today, it is the high time that 2D DSCM be applied, as an effective tool, on the engineering and scientific investigations. Nevertheless, the 3D (three-dimensional) DSCM is far from prefect in basically experimental theory and should be further studied.This thesis firstly presents the basic principles of 2D/3D DSCM. The DSCM detects the deformation field according to the relevant statistics of the speckles, randomly distributing on the object surface, before and after the deformation. By introducing the principle of binocular stereo vision, it is possible to obtain the surface 3D-pattern and 3D-deformation of the object by applying the DSCM, which is named as 3D- DSCM.It is almost impossible to achieve enough mechanical properties, especially the Poisson's ratio, of nano-composite materials in micro-scale by traditional tensile machine. In this thesis, 2D DSCM is applied to detect the Poisson's ratios of porous silicon films and carbon nanotube composites, providing several kernel parameters for the further studies of these materials.The thesis presents a new improved 3D DSCM by combining the rough-search technique with the initializing method based on non-linear transform in 3D matching algorithm, which raises both the matching speed and accuracy of the same name points. Furthermore, by increasing the qualities of chessboard-grid targets, the vision field of binocular cameras is reduced to 15×15mm, making the deformation measurements by 3D DSCM in small vision fields possible. Based on above theoretical work, an image-processing software for 3D-pattern reconstruction and 3D-displacement measurement is developed in this thesis, which is successfully applied on the deformation measurements around the crack tips of rubber materials.