Fresh considerations regarding time-dependent elastomeric fracture

Abstract

The fracture behavior of polymers in elastomeric state exhibits rich characteristics. Stretch rate and temperature can independently, as well as in combination, influence how such polymeric networks resist crack initiation and propagation. The strong rate and temperature dependencies of tensile strength and toughness in absence of high viscoelasticity, previously shown to occur in Rubber Chem&Tech 96, 530, 2023 and plausibly in J. Polym. Sci. 18, 189, 1955 and 32, 99, 1958 are also observed in rate-sensitive elastomers. This work aims to propose, at a conceptual level, a general understanding of elastomeric fracture by addressing the considerable confusion surrounding the relationship between crack growth rate (v_c) and Griffth-Irwin's energy release rate (G_c) in different elastomeric systems. Our fracture tests demonstrate that (a) crack propagation velocity v_c varies with the applied loading level produced by either stepwise or continuous stretching, (b) emergent entanglement effectively modifies network structure and the relationship between v_c and G_c, and (c) temperature T affects v_c at a given load. We conclude that the magnitude of imposed strain, from which G_c may be evaluated, prescribes the level of bond tension in load-bearing network strands and dictates bond dissociation kinetics. Consequently, crack growth rate depends explicitly on loading level (e.g., G_c) and temperature. In the relationship between v_c and G_c, v_c is the effect and G_c is the cause, contrary to the previous viewpoint.