Exploring the Ability of a Coarse-grained Potential to Describe the Stress-strain Response of Glassy Polystyrene

Report No. ARL-TR-6222
Authors: Thomas W. Rosch, John K. Brennan, Sergey Izvekov, and Jan W. Andzelm
Date/Pages: October 2012; 36 pages
Abstract: Molecular dynamics simulations were performed to calculate the stress-strain behavior of a coarse-grained (CG) potential corresponding to polystyrene. The force-matching (FM) technique was used to calculate the nonbonded interactions at a CG resolution of one CG site per monomer. The Inverse Boltzmann Inversion (IBI) method was used to parameterize the bonded and bond angle bending interactions. The CG model exhibited a significantly lower modulus compared to the atomistic model at low temperature and high strain rate. Addition of friction through use of the constant-temperature dissipative particle dynamics (DPD) method improved the modulus, yet was not transferrable to higher temperatures and lower strain-rates. An increase of attraction between CG beads by direct manipulation of the nonbonded potential also improved the stress response. Two parameterization protocols that shifted the force to more attractive values were explored. One corresponded to a uniform shift and the other shifted the force in a more localized region. The uniformly shifted potential greatly affected the structure of the equilibrium model as compared to the locally shifted potential, yet was more transferrable to different temperatures and strain-rates.
Distribution: Approved for public release
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Last Update / Reviewed: October 1, 2012