The Research Of Digital Speckle Correlation Method

Digital speckle correlation method (DSCM) have been extensively used toaccurately determine two-dimensional in-plane displacements and strains in boththeoretic study and engineering measure .The work reported herein is concerned withthe development of new DSCM, on which a stable , high-speed and accurate DSCMdata processing system is built. A new method named Single Search of each Subset is provided, which improvesthe speed of calculation, while precision is not sacrificed. The character of thisapproach is as follows: the displacements and deformations of the central pixel of thesubset are calculated through Gradient iteration method,whose results are insertedinto elastic mechanical formulas to obtain the initial values of the displacements ofother pixels in the subset, then derivatives are calculated by the bicubic splineinterpolation as the deformation part of initial values. The displacement types in the finite element method are introduced into theiterative calculation of the DSCM. On the assumption of the continuation ofobjective's deformation, the deformation of each point is regarded as the function ofits location, and then the displacement type is designed according to the features ofthe objective's deformation. The iterative variables will change from the 2displacement variables and 3 strain variables to the several unknown coefficients . sothe displacement field can approach the real one, at the same time the method depressthe errs of displacements. The strain field if more smooth. What's more, the 6displacement types, which are classified tow groups, geometric isotropy andgeometric anisotropy. They were tested to determine the precision and the appliedrange. When the 6 displacement types are applied, the err of displacement is 0.012pixels, and the precision of the main strain in all field can reach 50-130 με , andthe precision of the shearing strain can reach 50-100 με . Finally, the partially bending displacement type is applied for study on the silverbirch batten 's crack-tip. And then the results from DSCM were compared withthe results from finite element method. It proves that the DSCM with the partially - 4 -bending displacement type is reliable on the measurement on stress and strain field...