An atomistic study of damage and localized anisotropic mechanical property evolution in thermoset polymers

All-atom molecular dynamics (MD) simulations are used to explore damage initiation and the local anisotropic evolution of mechanical properties in thermoset polymers under uniaxial tension with an emphasis on changes in stiffness through a series of tensile loading, unloading, and reloading experiments. By comparing the results for classical and bond order potentials, bond breakage is found to play a minimal role in damage initiation due to the highly localized plastic deformation mechanisms. The void fraction is quantified, revealing sudden initiation points and consistent growth rates, which are correlated to averaged changes in stiffness, and the state of deformation. The efficacy of incorporating MD damage data into multiscale models is evaluated considering the sensitivity of results to topological variation. In addition, the results are compared for various reference frames, demonstrating the need for fully Eulerian stress–strain pairs to isolate material behavior from the geometric changes associated with large molecular strains.