Sharing the load: stress redistribution governs fracture of polymer double networks

TL;DR

This study uses coarse-grained simulations to reveal that in polymer double networks, inhomogeneous stress redistribution, rather than homogeneous load sharing, critically influences fracture mechanics and chain failure processes.

Contribution

It demonstrates that stress redistribution in polymer double networks is highly inhomogeneous and governs fracture behavior, contrasting with prior affine (homogeneous) models.

Findings

Inhomogeneous stress redistribution dominates fracture mechanics.

Affine models overestimate chain breakage by nearly tenfold.

Fracture occurs in two steps due to load sharing within and between networks.

Abstract

The stress response of polymer double networks depends not only on the properties of the constituent networks, but also on the interactions arising between them. Here we demonstrate, via coarse-grained simulations, that both their global stress response and their microscopic fracture mechanics are governed by load sharing through these inter-network interactions. By comparing our results with affine predictions, where stress redistribution is by definition homogeneous, we show that stress redistribution is highly inhomogeneous. In particular, the affine prediction overestimates the fraction of broken chains by almost an order of magnitude. Furthermore, homogeneous stress distribution predicts a single fracture process, while in our simulations fracture of sacrificial chains takes place in two steps governed by load sharing within a network and between networks, respectively. Our results thus provide a detailed microscopic picture of how inhomogeneous stress redistribution after rupture of chains governs the fracture of polymer double networks.