Multiscale Modeling of Polyamide 6 Using Molecular Dynamics and Micromechanics

Abstract

Polyamide 6 (PA6) is a semicrystalline thermoplastic used in many engineering applications due to its high strength, good chemical resistance, and excellent wear/abrasion resistance. The mechanical properties of PA6 are dependent on two forms of crystallinity (α/γ). Semicrystalline thermoplastics have a hierarchical microstructure spanning length scales, necessitating the use of a multiscale model. Molecular dynamics (MD) simulation with the reactive INTERFACE force field was used to predict the elastic moduli of amorphous PA6. Semicrystalline PA6 was modeled using a multiscale modeling approach originally developed for semicrystalline polyetheretherketone (PEEK). This approach was facilitated by the NASA Glenn Research Center’s micromechanics software MAC/GMC. The inputs to the multiscale model were the elastic moduli of amorphous PA6, as predicted via MD and calculated stiffness matrices from the literature of the PA6 α and γ crystal forms. The multiscale model output was Young’s modulus, shear modulus, and Poisson’s ratio as a function of α and γ crystallinity. The predicted values of Young’s modulus and shear modulus compared well with experiment. The multiscale model predictions showed that the mechanical properties of semicrystalline PA6 with α and γ crystal forms are similar from amorphous to 40% crystalline and diverge after this limit, with the γ PA6 predictions having higher Young’s and shear moduli and lower Poisson’s ratio. Overall, the good agreement with experiment validated the use of the multiscale model for semicrystalline PA6, proving that the multiscale model may be used for semicrystalline polymers beyond PEEK.

Multiscale Process Modeling of Semicrystalline PEEK for Tailored Thermomechanical Properties

“…The reactive interface force field (IFF-R), − a modification of the interface force field, was applied to describe the interactions between the atoms in the polymer system. The open-source large-scale atomic/molecular massively parallel simulator (LAMMPS) MD simulation software package was used for all MD simulations in this study.…”

Effects of Cross-Linking Degree and Characteristic Components on Mechanical Properties of Highly Cross-Linked Phenolic Resins: A Molecular Dynamics Simulation Study

“…After that, a nonequilibrium molecular dynamics method was used for the equilibrium cross-linked models to simulate the mechanical deformation of PF at different degrees of cross-linking. Deformations were simulated every time step amounting to 3% engineering strain over 300 ps (Δ t = 0.5 fs) in the uniaxial direction with a constant engineering strain rate of 10 –7 fs –1 , − which were carried out by NPT ensemble using the “fix deform” command in LAMMPS. In addition, the Nose–Hoover barostat was used to maintain 1 atm to enable Poisson contractions in the transverse directions, and a temperature of 300 K was specified. , The Young’s modulus ( E ) in the region of elastic deformation is calculated from eq : …”

Micromechanical Dilution of PLA/PETG–Glass/Iron Nanocomposites: A More Efficient Molecular Dynamics Approach

“…An MD simulation is only as accurate as the force field. The INTERFACE force field (IFF) and IFF reactive version (IFF-R) produce accurate predictions of thermal, mechanical, and interfacial properties of polymer composites. ,,,,,,,− …”