An imaging technique using rotational polarization microscopy for the microstructure analysis of carbon/carbon composites

A novel image analysis technique was proposed for microstructure investigation of carbon/carbon (C/C) composites. The rotational polarization microscopy was developed to meet the special imaging requirements. The samples of C/C composites were observed in reflection polarized light microscope, where the analyzer was rotated instead of the stage, and the polarizer was taken out. The bireflectance of like-graphite negative uniaxial crystal was analyzed. It was the theoretic foundation of image collection and data processing. The analyzer was rotated through 36 × 10° intervals without any movement of the specimen. The polished cross-section of C/C composites took micrographs at each analyzer orientation. All image data collected from the same field of view were processed by image registration and image fusion. The synthesized images were obtained by calculating the maximum and minimum gray values and their differences at each point of the million pixels at 18 orientations of the analyzer. They are unique and quite reliable to be applied to analyze the microstructure of C/C composites. Subsequently, image segmentation was performed, and the feature parameters of each component were calculated. Good agreement was found between the results from image analysis and experimental data.