Coarse-Grained Model And Mechanical Properties Of Crosslinked Epoxy Resins And Their Composites

Molecular dynamics simulation is an effective tool for studying new material properties and design.But the performance analysis based on fully atomistic model for some new materials is often limited by computational resources,especially for new composite materials involved with variety of atoms and complex configurations.Therefore,a cross-scale coarse-grained(CG)modeling technique provides a new solution for molecular dynamics simulations.For the aim of analyzing the mechanical property of carbon nanotube(CNT)/resin composites,a CG modeling method for crosslinked epoxy resin and its composites is proposed based on the CG molecular dynamics simulations which eliminates the uncontrollable factors in the experiment and the limitations of the fully atomistic simulation.The mechanical properties of CNT/resin composites are investigated by the CG molecular dynamics simulations.Firstly,the CG model capable of simultaneously predicting the morphological characteristics and mechanical properties of epoxy resin is constructed with the modified traditional CG method based on morphological matching.For the structural morphology matching,the optimization results from Iterative Boltzmann Inversion(IBI)are adopted to make sure that the distributions of the CG model can be consistent with the fully atomistic distributions.For mechanical properties matching,the phenomenon that the CG system obtained from the traditional IBI method doesn't match with the fully atomistic system due to the softening effect is solved by adjusting the intermolecular binding energy intensity and the intramolecular structural stiffness.Moreover,the CG interface parameters between CNT and resin are drivied by fitting the interface energy of their composite system.The mechanical properties of the constructed CG composite model can accurately match with the fully atomistic system.In addition,in order to make the CG force field have better portability,all the CG potentials are fitted with function expressions.Secondly,the mechanical properties of CNT/epoxy composites are investigated with the established CG model.The effects of morphology,mass fraction and orientation of theCNT on the mechanical properties of the composites are systematically studied.The results reveal that: 1)increasing the length or mass fraction of CNT can enhance the mechanical properties of the composites and the enhancement mainly occurres in the axial direction of CNT;2)compositing resin with the jointed 3D CNT structure,not only the problem of CNT aggregation is solved,but also the reinforcement is further enhanced due to the interlock effect between the 3D structure with the resin matrix;3)filling the epoxy resin into the CNT foam can greatly improve its original poor elastic modulus.