SYNOPSISThe X-ray absorption coefficients of carbon fibers, different polymeric matrix materials, and composites were measured and the fiber contents in the composites were calculated from the measured absorption. In addition the fiber content determinations were performed by means of acid digestion of the polymeric matrix and weighing. Good agreement was found between the results obtained by the two different methods. The experimental error in the fiber content measurements was determined as a function of the difference in the absorption coefficient of the matrix material and the fiber.
I NTRODUCTIO NThe fiber content is one of the most important parameters in establishing the composite's strength and stiffness characteristic^.'-^ Due to different effects, like bleeding out of fibers in the case of thermosets, the fiber content cannot be completely controlled by processing. Therefore, it is important to have available nondestructive methods for the determination of the amount of fibers present in the composites.Up to now the most commonly used techniques for determining the fiber content were density measurement or acid digestion of the polymer m a t r i~.~.~ In the present paper we want to present a new method based on X-ray absorption measurement. This method is nondestructive and yields good results provided the difference between the absorption coefficients of the fiber and the matrix is sufficiently large.
PRINCIPLE OF MEASUREMENTWhen an X-ray beam passes through a sample of thickness d , the intensity I, is decreased by absorption to the intensity I given by
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