Assesment of the texture of composite materials pyrocarbon matrix by the opical method using a graphic editor

Abstract

One of the methods for controlling the characteristics of composite materials is the formation of a pyrocarbon matrix with the required anisotropy of pyrocarbon. This work presents results assessing the texture of pyrolytic carbon matrices in composite materials using an optical method. The extinction angle —

a quantitative characteristic of texture — was determined by registering the intensity (brightness) of the quadrant of the pyrolytic carbon spherulite around the carbon fiber. The sought-after value was identified as the angle of rotation of the microscope analyser corresponding to the minimum intensity. A series of micrographs depicting the microstructure of the pyrolytic carbon spherulite, acquired at various analyser rotation angles relative to the polariser, were processed within a graphical editor. Subsequently, the mean grey-level values of selected pixels in a defined region were analysed to identify the point of minimum intensity. It was demonstrated that, with appropriate illumination levels, the spectral characteristics of the light source exert a negligible influence on the image processing and brightness measurement when using graded grey levels. Limitations associated with the geometric dimensions of the investigated pyrolytic carbon were assessed. Extinction angle determination for samples incorporating diverse pyrolytic carbon matrices (including a bilayer matrix) revealed that pyrolytic carbon produced via a temperature gradient method exhibits a highly textured structure, whereas material produced via an isothermal method displays a lower degree of texture. The extinction angles for the bilayer pyrolytic carbon matrix were found to differ between the individual layers. The findings are expected to contribute to the refinement of techniques for microstructural analysis of pyrolytic carbon.