How Does the Character of Glassy-Polymeric Cavitation Depend on Entanglement Density and the Local Poisson Ratio?

Abstract

Using molecular dynamics simulations of two generic glassy polymers, we distinguish factors promoting cavitation that is followed by unrestrained void growth and coalescence (i.e. by crazing and brittle fracture) from “ductile” cavitation that does not lead to massive void growth. Strain-controlled deformation in a wide range of wide Poisson ratios ν reveals several features not apparent from the uniaxial-deformation or uniaxial-stress protocols employed by the vast majority of previous studies. In particular, for 0.125 ≲ ν ≲ 0.45, semiflexible, tightly entangled chains have a significantly lower void volume fraction (but far more voids) at the same strain and volumetric expansion ratio than their flexible, loosely entangled counterparts. Voids in loosely entangled glasses coalesce more often and grow faster, whereas voids in tightly (but not loosely) entangled glasses continue to nucleate well into the strain-hardening regime.