Characterization of microvoids in carbon fibers by absolute small-angle x-ray measurements on a fiber bundle

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Abstract
A method has been developed to characterize the voids in a fibrous material by using the small‐angle x‐ray scattering from a unidirectionally aligned fiber bundle, and the parameters evaluating the sizes, volume fraction, and number of the voids have been deduced. The distribution of cross‐section size of voids has also been considered in relation to the size parameters deduced. The method developed has been applied to a commercial carbon fiber. The values of the size parameters of the carbon fiber, evaluated experimentally by the method developed here, are in good agreement with those calculated by assuming that the distribution of the cross‐section size of voids obeys a Maxwellian distribution. A convenient method for determining the primary beam power by comparing the observed and theoretically calculated scattering intensities of air has also been developed in order to measure the scattering intensity of a specimen in absolute units.