Strength prediction of partially aligned discontinuous fiber-reinforced composites

An experimental and theoretical approach has been described for the determination of the strength of partially aligned discontinuous fiber-reinforced composites. The fiber alignment information was obtained as a Gaussian or normal distribution function by using an x-ray-diffraction technique. The distribution function was then used in the composite strength equation to calculate the theoretical strength. This approach was applied to a composite of vapor grown carbon fiber (VGCF) in a polypropylene matrix, and the experimental and theoretical results were compared. As expected, the composite strength increased with increase in fiber volume fraction and the degree of fiber alignment. It was also observed that the composite strength was sensitive to variation in fiber length when the average fiber length was less than the critical fiber length. At higher fiber volume fractions the composite strength was much lower than predicted by theory. This is most likely due to incomplete wetting and infiltration of the VGCF.