Nanoscale mechanisms of crack-tip evolution in glassy polymers: hybrid particle-continuum simulations.

Understanding nanoscale crack mechanisms in polymers is important for predicting their macroscopic properties. However, high localized stress near the crack tip introduces nonlinear and time-dependent effects that complicate fracture behavior. Our hybrid particle-continuum approach provides a promising solution by integrating multiple resolutions to overcome the limitations of traditional fracture theories and experimental methods. We model the crack tip by particles using coarse-grained molecular dynamics simulation and treat the rest as a continuum, enabling accurate representation of polymer behavior and realistic boundary conditions similar to laboratory fracture tests. Two distinct loading conditions, plane stress and plane strain, are applied to a center-cracked specimen. Our results demonstrate unique crack growth patterns: under plane stress, we observe crack tip blunting accompanied by a high plastic deformation zone. Under plane strain, cleavage occurs alongside crazing. Furthermore, we identify the specific stress states that initiate and drive crack growth and shape at the particle level for each loading scenario.