Molecular dynamics simulation based size and rate dependent constitutive model of polystyrene thin films

Abstract

Rate and size-dependent properties dominate the mechanical behavior of polymeric thin films used in a variety of applications related to generation, transmission and storage of energy. In this paper, molecular dynamics (MD) simulations of polystyrene thin films are used to develop a size and rate dependent finite deformation elastic–plastic constitutive relations. Different modes of deformation are considered in the MD model, and results of simulations are homogenized to yield parametric representations of the constitutive model. The hyperelastic behavior is represented by a modified Ogden type model for films of different thicknesses at different strain rates. The MD simulations suggesting a rate-dependent yield strength is developed for a perfect plasticity model with mitigated size effects. The softer material properties of thin films are found to be the consequence of a large surface layer, which has a low density with high local chain mobility.