Studies On Theory And Application Of Digital Speckle Correlation Method

Digital speckle correlation method (DSCM) is a photo-mechanical method for deformation inspection. DSCM is suitable to be developed to a practical engineering testing method, because it takes many advantages, such as the good compatibility for hostile measurement environments (white light illumination and unnecessary of vibration isolation), simplicity on experiment preparation, large scale for measured specimen, full-field and non-contact measurement, and so on. Unfortunately, there are still some shortages exist on the theories and the applications of DSCM. For example, the theory system of DSCM is not so strictly complete. This results in the many difficulties on development of new DSCM algorithms. On the other hand, research works concentrating on the application of DSCM to complicated engineering structure and to in-situ field measurement are very few, therefore, there are quite a few problems to be solved when considering of the practical using of DSCM. In this dissertation, the theory of motion estimation, theory of element displacement interpolation mode and theory of smooth spline fitting are introduced in DSCM, the theory system of DSCM is constructed, and the algorithms for displacement and strain calculation are improved. The DSCM is then used in complicated engineering structure and in-situ field measurement, and some inspection experimental works are performed.The theoretical research of DSCM is performed in this dissertation, the key results of this part of works are: (1) the theory system of DSCM are constructed based on the Motion Estimation (ME) technique in video compression theory. It is pointed out that the understanding and development of DSCM should follows the following 5 aspects, displacement representation mode, objective function, search method, sub-pixel registration method and strain calculation method. (2) The NDR-DSCM algorithm is developed based on a new displacement representation mode, node-based displacement representation mode. (3) A new strain calculation method is developed based on smooth spline fitting theory. (4) Considering of the problem of heterogeneous deformation field measurement in complicate engineering inspection, and the problems of non-uniform illumination, varying pixel size and large translation of measured speckle images in-situ inspection, the specific algorithms are developed to improve the resolution and accuracy of DSCM. Works above improved the theory of DSCM and preceded the necessary preparation for practical using of DSCM.The other part of work in this dissertation is the application of DSCM to complicated engineering structure and in-situ inspection. The key results of this part of work includes: (1) a wall-type foundation model experiments are performed using DSCM. The stable shearing stress distribution regularity is obtained from the experiment and the influencing factors for shearing stress distribution are analyzed. (2) The in-situ inspection of the key area deformation of a large scale assembly steel bridge is performed. The stress concentration around a rivet of the bridge is obtained. Studies above show the feasibility and advantages of DSCM in engineering measurement.