Modelling viscoelastic behaviour of carbón nanotube-reinforced thermo-plastics

Abstract

Carbon nanotubes (CNTs), since their discovery by Lijima (S. Lijima, Nature, 354:56-58 (1991)), are considered a new generation of reinforcement. Their "nano" size structure makes them potentially free of defects, which provides them with excellent physical properties. There are two main nanotube types: single wall nanotubes (SWCNTs), which are made of a single wall tube; and multiwall nanotubes (MWCNTs), which consist in several concentric walls, one inside the other. A key factor for the reinforcement efficiency in a composite it is the interface bonding between the CNTs and the matrix. This work presents a new constitutive model to predict the mechanical performance of composites made of a thermo-plastic matrix reinforced with CNTs. The model takes into account explicitly the mechanical contribution of the interface between the matrix and the CNTs (F. Otero et. al., Comp Structures, 94:2920-2930 (2012)). The constitutive model is based in the mixing theory, which obtains the composite performance from the response of each constituent component, each one simulated with its own constitutive law. The model has been implemented into an in-house FEM code: PLCd. As an application example, this code is used to predict the mechanical properties of a straight beam with different material configurations. In this case, a viscoelastic constitutive model is proposed for the polymeric matrix. The viscous response within the elastic range of the materials is studied. This response shows a high capacity of energy dissipation in composites reinforced with MWCNTs.