Heatwave distortion correction using an improved reference sample compensation method and multispectral digital image correlation.

Heatwave distortions, caused by unevenly distributed temperature and refractive index in the optical path, unavoidably occur in high-temperature digital image correlation (DIC) measurement. To eliminate these distortions, a multispectral DIC-aided reference sample compensation method is proposed. The proposed method first adheres a correcting transparent glass (decorated with fluorescent speckle patterns) onto the test specimen (sprayed with red speckle patterns). Then, by illuminating the specimen with ultraviolet- and red-light sources, the blue light excited from the correcting glass and the red light reflected from the specimen surface can be captured by a 3CCD camera, forming a color image. After separating the recorded color images into red and blue subimages, the original and the correcting displacement fields can be calculated from these two sets of subimages using the subset-based local 2D-DIC algorithm. By point-to-point subtracting the correcting displacement fields from the original ones, the heatwave distortions can be eliminated, and the corrected real displacement fields can be obtained. For validation, static heatwave experiments show the feasibility and accuracy of the proposed method in correcting heatwave distortions. A uniaxial tensile test of an aluminum specimen with a central hole was also performed, further confirming the practicality of the proposed method in correcting heatwave distortions and revealing heatwave-hidden deformation.