Research Of Sub-pixel Displacement Measurement Methods And Experiment In Digital Speckle Correlation

Digital speckle correlation method or digital image correlation is a new photometric technology developed in 1980s. Its principal theory is that through comparing two digital speckle images of original and deformed object surface to find displacement and strain of the whole field. Through twenty years development and improvement , Digital speckle correlation method has become an important method for displacement and strain measurement in the experimental mechanics because of its superiority such as full-field analysis, non-contact measurement, simple path of rays,high measurement precision and so on.In this paper,different sub-pixel registration methods in DSCM are discussed in detail and theirs math models are established including the Gray-value Interpolation base on sub-pixel reconstruction method(GIRS), the correlation coefficient distribution based on fitting method(CCDF), the algorithm of gradient-based sub-pixel registration and the hybrid method for sub-pixel registration. This paper makes use of digital speckle image translational motion experimental simulation to discuss the precision of these sub-pixel registration methods in DSCM. The computer program about digital speckle correlation method was written by the Object Oriented programming software C++ Builder with standard C++ code and this paper also gives optimum programming mode.On the aspect of experiment, there are three mechanical application experiments to test the theory and the program. They are rigid body translational motion experiment, tensile experiment and three points bend experiment. Conclusion was obtained by comparing the theoretical value and the experimental value. In addition, this paper design the experiment of cantilevel beam vibration to research dynamic digital speckle correlation technology, use multiple images correlation calculation to gain waveform so as to other parameter such as periods and amplitude.The quality of image has an important effect on measurement precision in Digital speckle correlation method, so it is necessary to do the research for the image. The last section discusses the ideal sinusoidal images with the case of rigid body translation to prove the inherent accuracy.