Simulations of fiber flocculation: Effects of fiber properties and interfiber friction

Non-Brownian fibers commonly flocculate in flowing suspensions at relativel y low concentrations ( < 1% by weight). We have developed a particle-level simulation technique modeling fibers as chains of rods connected by hinges to probe fiber flocculation. The model incorporates fiber flexibility, irre gular fiber equilibrium shapes, and frictional fiber interactions. Model fi bers reproduce known orbits of isolated rigid and flexible fibers in shear flow. Simulation predictions of first normal stress differences in homogene ously dispersed, dilute flexible fiber suspensions agree with experimental data. Fiber features such as flexibility and irregular equilibrium shapes s trongly impact single fiber and suspension behavior. Fibers aggregate in si mulations with interfiber friction, in the absence of attractive forces bet ween fibers. Strong flocculation is observed in suspensions of stiff fibers with irregular equilibrium shapes. Flocs contain many fibers with three or more contact points, and derive cohesiveness from elastic energy held in f ibers-consistent with the elastic interlocking mechanism of flocculation. A t higher concentrations (nL(3) approximate to 100, where n is the fiber num ber density and L is the fiber length), coherent fiber networks form in sim ulations. Average numbers of contacts per fiber and contact force magnitude s in sheared and static networks are compared with existing fiber network t heory predictions. (C) 2000 The Society of Rheology. [S0148-6055(00)01404-8 ].