Effect of surface physical structures on interfacial shear strength of carbon fibers reinforced epoxy resin composite

The technique of quantitative characterization for the physical structure of the surface on PAN-based carbon fiber filaments was established through analyzing the cross sectional morphology which was obtained by scanning electron microscopic (SEM), followed by the image processing with Photoshop software and self-written Matlab program. The parameters such as the width, depth, and the number of surface groove structure were obtained by statistic calculation. Then the circularity, ratio of depth to width, density of groove structure along circle direction, and irregularity were also calculated to characterize the physical structure systematically. Furthermore, the groove structure of carbon fiber was regulated and controlled by adjusting the coagulation environment during the spinning process of PAN precursor, and it is found that the depth and width of groove structure on the surface of carbon fiber are decreased gradually, the shape of grooves also tends to flatten due to the decreased ratio of depth to width, the irregularity is decreased by about 7.5%, while the density of groove structure is increased by about 50 % when the temperature of coagulation bath is increased from 25 degrees C to 45 degrees C. The above carbon fibers with different surface physical structures were used as reincial shear strength (IFSS) of composites is increased with the increasing of groove size and aspect ratio, as well as the surface irregularity of carbon fibers.