Slip-link simulations of long-fiber networks under uniaxial compression

Abstract

A coarse-grained molecular simulation approach originally developed for entangled polymeric liquids is extended to model the mechanical behavior of long-fiber networks. The model, based on the slip-link picture of chain entanglements, resolves the force balance at contact points and accounts for fiber slippage under these topological constraints. Two key governing equations describe the time evolution of contact-point positions and the local fiber fraction between adjacent contact points. A yield-force criterion determines whether contact points are displaced or remain pinned, as well as whether fiber slippage occurs at contact points. Uniaxial compression simulations corresponding to press molding of fiber-reinforced thermoplastics were performed for networks with varying fiber lengths and compression rates. The results were qualitatively consistent with experimental observations of long-fiber thermoplastics. The model captures physics inaccessible to the classical van Wyk theory of fiber network compression, which is quasi-static and insensitive to fiber length. This work demonstrates that the slip-link framework, already validated for polymer melts, provides a promising mesoscale simulation tool for understanding and predicting the processing behavior of non-thermal fiber networks.