Fracture and yielding in polymers: where is fracture mechanics

By using experiments to estimate inherent fracture strength, we have started to examine fracture behavior of polymers in either plastic or elastomeric state using a bottom-up approach [1]. Contrasting the conventional interpretation of high toughness in terms of energy dissipation, we show the merit to characterize brittle fracture in terms of the widely accepted fracture mechanism that local stress exceeding inherent strength is the cause of brittle fracture. The acquired new insights enabled us to explain why toughness is material specific, determined by inherent strength and a material-characteristic length related to the natural tip blunting, in terms of the Inglis and Creager-Paris solutions. In the first half of the talk, we will describe the relationship between yielding and brittle fracture in glassy polymers. In the second half, we will describe temperature effects on tensile strength and toughness of elastomers in a new framework that recognizes the existence of the hidden (internal) clock, associated with the covalent bond dissociation kinetics, contrasting the understanding accumulated over the previous seventy year that characterized elastomeric fracture in terms of polymer viscoelasticity.

[1] Wang, S. Q. et al. Macromolecules, 57, 3875-3900 (2024).