Microstructure and deformation micromechanisms of concentrated fiber bundle suspensions: An analysis combining x-ray microtomography and pull-out tests

The non-Newtonian rheology of concentrated fiber suspensions, such as short fiber reinforced polymer composites during their processing, depends on both the microstructure of their fibrous network and the deformation micromechanisms arising at fiber-fiber contacts. In this work, these two aspects are investigated using model concentrated fiber suspensions made up of short glass fiber bundles impregnated in a transparent polymer. For that purpose, multiresolution x-ray microtomography was used to analyze the fibrous microstructures, showing that the studied suspensions exhibit a planar fiber orientation with fairly straight fiber bundles, the connectivity of which can be modeled by the geometrical statistical tube model. Besides, bundle-bundle contact forces together with the interaction between the bundles and the suspending fluid are analyzed by using pull-out experiments. These tests allow the influence of the pull-out velocity, the confining stress and the volume fraction of fiber bundles on the pull-out force to be quantified. Combined with the microstructure analysis, such results are then used to propose a bundle-bundle contact model which can be implemented into multiscale rheological models dedicated to concentrated fiber suspensions. (C) 2012 The Society of Rheology. [http://dx.doi.org/10.1122/1.3698185]