Simulation data for engineering graphene quantum dot epoxy nanocomposites using molecular dynamics.

Graphene quantum dots (GQDs) were reported to fill the role of nanofillers that enhance composite properties. Detailed investigation of this nanofiller in composites is largely unexplored. To understand the fundamental mechanisms in play, this study uses molecular dynamics simulations to reveal the effects of GQDs on epoxy properties. Mechanical simulations were performed on three varying GQD chemistries which included a pristine GQD and 2 edge aminated GQDs with different degrees of functionalization (5.2 % and 7.6 %). These GQDs were separately inserted in a polymer matrix across five individual replicates. The nanocomposite mechanical properties were computed using uniaxial strain simulations to display the effect of embedded GQDs.

Multiscale Process Modeling of Semicrystalline PEEK for Tailored Thermomechanical Properties.

Polyether ether ketone (PEEK) is a semicrystalline thermoplastic that is used in high-performance composites for a wide range of applications. Because the crystalline phase has a higher mass density than that of the amorphous phase, the evolution of the crystalline phase during high-temperature annealing processing steps results in the formation of residual stresses and laminate deformations, which can adversely affect the composite laminate performance. Multiscale process modeling, utilizing molecular dynamics, micromechanics, and phenomenological PEEK crystal kinetic laws, is used to predict the evolution of volumetric shrinkage, elastic properties, and thermal properties, as a function of crystalline phase evolution, and thus annealing time, in the 306-328 °C temperature range. The results indicate that lower annealing temperatures in this range result in a faster evolution of thermomechanical properties and shrinkage toward the pure crystalline values. Therefore, from the perspective of composite processing, it may be more advantageous to choose the higher annealing rates in this range to slow the volumetric shrinkage and allow PEEK stress relaxation mechanisms more time to relax internal residual stresses in PEEK composite laminates and structures.

Accurate predictions of thermoset resin glass transition temperatures from all-atom molecular dynamics simulation.

To enable the design and development of the next generation of high-performance composite materials, there is a need to establish improved computational simulation protocols for accurate and efficient prediction of physical, mechanical, and thermal properties of thermoset resins. This is especially true for the prediction of glass transition temperature (Tg), as there are many discrepancies in the literature regarding simulation protocols and the use of cooling rate correction factors for predicting values using molecular dynamics (MD) simulation. The objectives of this study are to demonstrate accurate prediction the Tg with MD without the use of cooling rate correction factors and to establish the influence of simulated conformational state and heating/cooling cycles on physical, mechanical, and thermal properties predicted with MD. The experimentally-validated MD results indicate that accurate predictions of Tg, elastic modulus, strength, and coefficient of thermal expansion are highly reliant upon establishing MD models with mass densities that match experiment within 2%. The results also indicate the cooling rate correction factors, model building within different conformational states, and the choice of heating/cooling simulation runs do not provide statistically significant differences in the accurate prediction of Tg values, given the typical scatter observed in MD predictions of amorphous polymer properties.

Prediction of the Interfacial Properties of High-Performance Polymers and Flattened CNT-Reinforced Composites Using Molecular Dynamics.

The next generation of ultrahigh-strength composites for structural components of vehicles for manned missions to deep space will likely incorporate flattened carbon nanotubes (flCNTs). With a wide range of high-performance polymers to choose from as the matrix component, efficient and accurate computational modeling can be used to efficiently downselect compatible resins and provide critical physical insight into the flCNT/polymer interface. In this study, molecular dynamics simulation is used to predict the interaction energy, frictional sliding resistance, and mechanical binding of flCNT/polymer interfaces for epoxy, bismaleimide (BMI), and benzoxazine high-performance resins. The results indicate that BMI has a stronger interfacial interaction and transverse tension binding with flCNT interfaces, while benzoxazine demonstrates the strongest levels of interfacial friction resistance.