Pore Analysis of Isotropic Graphite using Image Processing of Optical Micrographs

Abstract

Parameters of strength of isotropic high-density graphite are thought to be strongly correlated to pore structure of the graphite from experimental results on fracture toughness. Until now the pore structure has not been analyzed quantitatively, and the relation between the parameters of strength and the pore structure has not been explained clearly. In the present paper, pore structure of the isotropic graphite has been analyzed by means of a polarizing microscope combined with an image analyzer. The polarizing microscope images of the isotropic graphite are digitized using an image scanner. Distribution of area size, number, circularity, and fractal dimension of cross-section of the pores are measured, and are analyzed quantitatively. When there is an increase in the number of small pores, the elastic modulus and bending strength also increase. We believe that a structure which includes many pores increases plane strain fracture toughness (KIC) and critical crack opening displacement (CODf), because crack propagation can be inhibited by the pores.