Fiber-fiber interaction in concentrated suspensions: Dispersed fiber bundles

A model is proposed to describe the rheology of planar randomly oriented co ncentrated fiber bundle suspensions in a shear-thinning matrix. The approac h is that, at high fiber volume fractions, the dominant interaction mechani sms are friction and lubrication at the fiber-fiber contact points. A fiber pull-out technique is used to measure the force per unit length exerted on a single fiber tow of elliptical, cross section embedded in a bulk suspens ion. By varying the tow velocity, fiber volume fraction, resin viscosity, a nd suspension structure, the factors affecting the lubrication and friction al components of the interaction forces were analyzed. The lubrication forc e is related to the flow behavior of the neat resin. The theoretical equati ons derived in this work allow for the computation of a shear viscosity of the suspension, which is in good agreement with experimental evidence. It i s shown that dispersed fiber and dispersed fiber bundle suspensions are yie ld stress fluids. (C) 1999 The Society of Rheology. [S0148-6055(99)00304-1] .