The Elastic Deformation of Lubricated Carbon Fiber Bundles: Comparison of Theory and Experiments

During typical composites manufacturing processes, fibers are deformed in ways that alter their processing characteristics (e.g., permeability, stresses and resin pressure, etc.) and their resulting microstructure (fiber volume fraction, void fraction, etc.). In this paper, we review all available data for the deformation behavior of lubricated carbon fiber bundles and compared it to a recently developed 3-D theory [15]. Most of the data, which is for transverse compression, exhibits very large scatter, but can be collapsed by shifting along the fiber volume fraction axis. It is hypothesized that the shifts represent different “states” for the fiber bundle, which can be represented in the model by a single variable, the available fiber volume fraction V_a It is then shown that all available aligned carbon fiber bundle data, including bulk compression, axial extension, and coupling be havior can be fit to the modified model by only adjusting V_a In one case (the coupling be havior), the available fiber volume fraction was directly measured. Observations on how the “state” of the fiber bundle can be modified by the processing conditions are included. On the basis of this analysis, a simple, practical test to determine V_a is proposed.