| Summary: | <p>A multiscale model using simulated nanoscale damage (free volume) evolution and continuum damage evolution equations (void nucleation, growth, and coalescence) for the amorphous phase of polyethylene (PE) is presented. Explicit-atom Molecular Dynamics (MD) simulations using a Modified Embedded Atom Method (MEAM) for saturated hydrocarbons are employed to study the deformation mechanisms and evolution of pores, or voids, under various applied stress states (tension, shear, compression), strain rates (1E<sup>6</sup> 1E<sup>10</sup>), and temperatures (150 350 K). The MD simulations are shown to capture the stress-strain and creep behavior in accord with the experimental behavior of PE. The progression of damage, i.e., void nucleation, growth, and coalescence, is correlated to specific regions of the deformation response and is shown to enhance the plastic flow and chain dynamics (kinks and entanglements) throughout deformation. Continuum Internal State Variable (ISV) equations for isotropic damage in polymers are calibrated to the nanoscale MD results. A new rate form for void coalescence in polymers, based on the Nearest Neighbor Distance (NND) of voids, is developed to more accurately capture the complex damage mechanisms arising from the interactions between neighboring voids, especially interactions associated with void nucleation. Through the modified nucleation, growth, and coalescence equations, the evolution of the void volume fraction (damage) is accurately captured and compares favorably to volumetric strains seen experimentally during deformation in High-Density Polyethylene.</p>
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