Unveiling the fracture mechanism for entangled polymer melts under extensional flow with molecular dynamics simulations

Entangled polymer melts exhibit fracture behavior under strong extensional flows. The rapid deformation rate at high Weissenburg number surpasses the reciprocal relaxation time of the polymer chains leading to strongly deformed chain conformations. Consequently, stress accumulates within the melts, and ultimately results in cavitation. We conducted molecular dynamics simulations of polymer melts under extensional flow using the Kremer-Grest model incorporating a breakable bond potential. The simulation results demonstrate the possibility of cavitation without rupture of bonds and melt fracture by chain pullout, suggesting that the critical stress for fracture can be related to cavitation rather than bond ruptures. Bond scission after cavitation was observed at higher extension rates due to fracture of the entanglement network. The distribution of broken bond positions is peaked at the location of higher tension in the middle of the chains.