Anisotropic behavior of the nanoindentation of single carbon fibers

The mechanical behavior of carbon fibers determines the applications of carbon fiber reinforced composites in automotive and aerospace. The indentation behavior of single carbon fibers has been investigated in the indentation load range of 0.5 mN to 2.5 mN on two different cross-sections; one is a longitudinal section with the surface normal perpendicular to the fiber axis and the other is a transverse section with the surface normal parallel to the fiber axis. The indentation results reveal the anisotropic characteristics of the mechanical behavior of the carbon fibers. The contact modulus of the transverse section of the carbon fibers is about twice of that of the longitudinal section of the carbon fibers, while the indentation hardness of the transverse section of the carbon fibers is slightly larger than that of the longitudinal section. The plastic energy dissipated in the nanoindentation for both of the sections increases with the increase of the indentation load and is a power function of the indentation load with a power index of about 1.9.