Estimation of the fiber orientation distribution of carbon fiber–reinforced plastics using small-angle X-ray scattering

The orientation of discontinuous carbon fibers (CFs) in CF-reinforced plastics (CFRPs) determines their properties, necessitating convenient evaluation methods. Herein, a fast and non-destructive method is proposed for the evaluation of the orientation distribution of CFs in CFRPs based on small-angle X-ray scattering (SAXS). The width of the equatorial streak in the SAXS pattern of (or azimuthal intensity distribution of scattering from) a CFRP depends on the orientation distribution of its CFs; a calibration curve for this relationship was derived by assuming the orientation distribution to be Gaussian. This calibration curve was used to determine the orientation distributions of CFRPs featuring CFs with different orientation distributions, which correspond well with the orientation distributions determined by X-ray computed tomography. Thus, the proposed method can be used to conveniently and quantitatively evaluate the orientation distribution of discontinuous CFs in CFRPs. Because this method is based on scattering from elongated nanovoids in CFs, it can be used to evaluate composite materials in which reinforcing fibers containing elongated scattering bodies, e.g., high-strength organic fibers containing fibrils, are preferentially oriented