Curved-fiber pull-out model for nanocomposites. Part 1: Bonded stage formulation

This is the first part of two papers in which an analytical curved-fiber pull-out model for nanocomposites is proposed. In nanotube-reinforced polymer composites, nanotubes are typically curved and entangled, a reinforcement morphology that will greatly impact the thermomechanical properties of the material. As the first step to explicitly take into account nanotube curvature and study its effect on nanocomposite mechanical properties, we develop a pull-out model in which the fiber has constant curvature. The model includes the entire pull-out process, namely the bonded, debonding, and sliding stages. In this first paper we formulate the bonded stage based on classic shear lag model assumptions and develop a 3D finite element model to verify assumptions. The results from a parametric study indicate that fibers with more curvature and longer embedded length need higher debond initiation force. The finite element results and analytical results show agreement both qualitatively and quantitatively.