High speed deformation measurement using digital speckle correlation method

This article discusses an advanced deformation method based on digital speckle correlation method, which is substantially more robust and has greater dynamic range than other full-field imaging technologies such as ESPI and moiré. The system tracks the stochastic pattern applied to the measurement surface with sub-pixel accuracy. The object under test is viewed by a pair of high resolution, digital CCD cameras. Two cameras having been mounted the locations and attitudes were calibrated prior to measurement by combining nonlinear optimization with accurate calibration points. The calibration points were formed by an infrared LED, which moved with 3-D coordinate measurement machine. By using bilinear interpolation square-gray weighted centroid location algorithm, the imaging centers of the calibration points can be accurate. The speckle images of the same measured zone from different directions for the specimen are recorded by two cameras before and after deformation. Then the deformation displacement and strain of the specimen is calculated by these images using digital speckle correlation method and geometrical relation of stereography. The performance was demonstrated with real translation test.