A gray change detection method has been proposed to monitor damage in materials. The normalized parameter C has been defined by the displacement and the gray level value, which can reflect the gray change of each pixel point in the region of interest of the image. A zero deformation experiment has been done to discuss the feature of gray change caused by many factors except the damage. The results show that local expanded regions with concentrations of C can be considered as the damage regions. The uniaxial tensile experiments for an artificial rock specimen and a polycarbonate specimen have been done to verify the performance of the proposed method. The results show that the proposed method is effective for monitoring surface cracks in rocks and the shear band in polymers. This work provides a useful method for damage monitoring in materials. (C) 2015 Optical Society of America
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