We have developed a particle-level, dynamic simulation technique to probe the structural behavior of non-Brownian fiber suspensions in simple shear flow. The model incorporates a variety of realistic features including fiber flexibility, irregular equilibrium fiber shapes, and fiber interactions. Simulated suspensions exhibit heterogeneous structures, or flocculation, when the model fibers are flexible, have deformed equilibrium shapes, and interact through static friction forces, even in the absence of attractive forces between fibers. The addition of kinetic friction and weak attractive forces has little effect on flocculation behavior, while anisotropic fiber bending tends to shift the onset of flocculation to larger coefficients of friction. (C) 2003 Elsevier Ltd. All rights reserved.