Notes on the modeling of preform compaction .2. Effect of sizing on bundle level micromechanics

Composite materials processed through the general class of Liquid Composite Molding schemes must essentially go through a two step process-fiber preforming, followed by resin infusion. Although the preform itself gives the basic skeleton of the structure, the compaction stage results in significant changes to the microstructure, resulting in flattening of weft yarn bundles and simultaneous reorientation and rearrangement of those in the warp direction. The movement also results in nesting and inter-layer packing resulting from significant inter-bundle movement. Sizings are generically used to assist in wet-out and to reduce fiber damage during preforming and compaction. However, they also absorb volume in a dry preform, and indicate response similar to a two-phase system consisting of a softer concentric shell surrounding a stiffer fiber, thereby causing changes in response of the preform and composite. In this paper we focus on the effect of sizing on behavior at the bundle level, accounting for compaction effects including those under shear deformation.