Multi-fidelity Modeling of Interfacial Micromechanics for Off-Aligned Polymer/Carbon Nanotube Nanocomposites

摘要

Multi-fidelity modeling of interfacial load transfer micromechanics for off-aligned discontinuously reinforced polymer/carbon nanotube nanocomposites is conducted. The effects of off-alignment angle on nanocomposite mechanical properties, including strain energy storage and dissipation, are of primary interest. The methodology is separated into two independent modeling tracks: simplified analytical micromechanics modeling and higher-fidelity 3D finite element modeling (FEM). Both uniaxial strain and uniaxial stress external loading conditions are considered. The analytical model is based on principles from an extended Cox model for discontinuous fiber reinforcement and generalized shear-lag analysis for off-aligned discontinuous fibers; energy dissipation is based on a simple amplitude-dependent friction damper analogy. From the analytical model derivation, it is shown that nonzero and non-right off-alignment induces interfacial shear stress variations along the azimuthal direction of the inclusion. For a low loading condition, in which interfacial slip has not occurred, the FEM and analytical model predictions for interfacial shear and nano-inclusion normal stress distributions generally display good agreement. Furthermore, properly accounting for inclusion end effects associated with perfect interfacial bonding in the analytical model improves the correlation with FEM results. After verifying the interfacial shear variation predicted by the analytical model with FEM, energy dissipation calculations due to interfacial slip are conducted with the analytical model neglecting end effects. For the uniaxial strain case, the partially-embedded model predicts reduced interfacial slip damping as off-alignment increases, with initiation of slip becoming impossible at relatively high off-alignment angles. However, for the uniaxial stress case, the partially-embedded model predicts that zero interfacial slip damping occurs comparatively at more moderate off-alignment angles, with nonzero damping occurring at both lower and higher off-alignment angles. Overall, the results demonstrate that nano-inclusion alignment angle substantially affects nanocomposite stiffness and interfacial slip damping and that azimuthal variation of the interfacial shear is a critical feature of nanocomposite mechanics.