Effect of kidney-type and circular cross sections on carbon fiber surface and composite interface

A comprehensive experimental study was conducted to identify the differences of the kidney-type section carbon fibers and circular section carbon fibers in the surface characteristics of fibers and interfacial properties of composites. It was revealed that the kidney-type fibers with larger specific surface area had a better adsorption characteristic and higher surface free energy compared with the circular fibers. Mechanical tests under interfacial shear and interlaminar shear loads have shown that the kidney-type fiber/epoxy composites outperformed the circular fiber/epoxy composites by a significant margin of 23.5% and 12.7%, respectively. The matrix was engulfed by the hollowed-out area of the kidney-type fiber, which allowed the matrix to secure more bonds, resulting in the effective transfer of the load applied to the fiber-reinforced composite system. Many kidney-type fibers overlapped and embraced with each other. Thus the large contact areas between fibers became strong bonding places and interface between fibers and matrix was not damaged easily.