Digital Image Correlation with a Prism Camera and Its Application in Complex Deformation Measurement.

Given the low accuracy of the traditional digital image correlation (DIC) method in complex deformation measurement, a color DIC method is proposed using a prism camera. Compared to the Bayer camera, the Prism camera can capture color images with three channels of real information. In this paper, a prism camera is used to collect color images. Relying on the rich information of three channels, the classic gray image matching algorithm is improved based on the color speckle image. Considering the change of light intensity of three channels before and after deformation, the matching algorithm merging subsets on three channels of a color image is deduced, including integer-pixel matching, sub-pixel matching, and initial value estimation of light intensity. The advantage of this method in measuring nonlinear deformation is verified by numerical simulation. Finally, it is applied to the cylinder compression experiment. This method can also be combined with stereo vision to measure complex shapes by projecting color speckle patterns.

Fringe direction weighted autofocusing algorithm for gear tooth flank form deviation measurement based on an interferogram.

When measuring the form deviation of the gear tooth flank with laser interferometry, due to the limitation of the depth of field of the lens, focused and defocused regions exist in the interferogram simultaneously. The introduced errors that were generated by these defocused regions decrease the measurement accuracy. Therefore, the evaluation of definition for interferograms is necessary for image processing. However, the gradient of gray, which performs by fringes, makes it difficult for traditional algorithms to evaluate its definition. This paper proposes a method based on nonsubsampled contourlet transformation (NSCT) combined with fringe direction as weighting coefficients to solve the problem. First, the information about the directions of these fringes in interferograms was evaluated. Then, the NSCT method was applied to interferograms so that several sub-images in different scales and directions can be achieved. Based on these sub-images and directions information, an improved function for definition evaluation was conducted. Lastly, a series of simulations and experiments was carried out to verify its feasibility and accuracy.

Measurement of deformation and strain field of cantilever beam under forced vibration.

Based on digital image correlation and binocular stereo vision, a method is proposed for measuring full field deformation and strain of cantilever beam under forced vibration. First, in the actual measurement, the traditional correlation function with linear model may not be reliable to describe the deformation and light intensity change of subset. Therefore, the radial basis function is introduced into the correlation function to specify the weight of each pixel in the subset, which improves the reliability of the correlation matching. Second, the rigid motion of the excitation source is monitored by sticking a marker at the fixed end. By measuring the position of the marker in the process of vibration, the motion direction of the excitation source can be obtained and then define the new Z-axis along the motion direction. After transformation of the coordinate system, the pure deformation at any position of the beam surface is equal to the displacement at that point minus the displacement of the excitation source. Finally, the deformation and maximum principal strain field of cantilever beam under sinusoidal excitation at different frequencies is compared and analyzed. The method can provide a reference for the deformation measurement under forced vibration.