Non-affine dissipation in polymer fracture

Viscoelasticity is a universal property in most soft solids. Specifically, for the fracture of polymeric materials, viscoelasticity has often been regarded as a major mechanism of toughening, and the excess fracture energy beyond the intrinsic value correlated to the stress-strain hysteresis, which is commonly used to characterize viscoelasticity in the framework of continuum mechanics. Through systematically planned experiments, the current study shows that a noticeable package of energy dissipation exists besides that associated with the hysteretic deformation. This package of energy is attributed to the highly non-affine deformation near the crack tip - the rearrangement and mutual sliding of the neighboring chains caused by the rupture of a polymer chain, which are insignificant in samples under homogeneous deformation. Various means of inter-chain-friction reduction, e.g., by applying lateral stretches, diluting the chains with solvent, or subject the material to dynamic or static fatigue, can mitigate the effect of non-affine dissipation, and bring the fracture energy down to the intrinsic threshold. In contrast, by making an elastomer more elastic, e.g., by training through cyclic loading, the non-affine dissipation remains effective, and the limiting fracture energy is significantly higher than the threshold even when the hysteresis is negligible. The identification of the non-affine-dissipation mechanism paves the way to the development of new soft materials with both excellent elasticity and significant fracture toughness.& COPY; 2023 Elsevier Ltd. All rights reserved.