  Elastomers that can sustain large reversible strain are essential components
for stretchable electronics. The stretchability and mechanical robustness of
unfilled elastomers can be enhanced by introducing easier-to-break cross-links,
e.g. through the multi-network structure, which also causes stress-strain
hysteresis indicating strain-induced damage. However, it remains unclear
whether cross-link breakage follows a predictable pattern that can be used to
understand the damage evolution with strain. Using coarse-grained molecular
dynamics and topology analyses of the polymer network, we find that
bond-breaking events are controlled by the evolution of the global shortest
path length between well-separated cross-links, which is both anisotropic and
hysteretic with strain. These findings establish an explicit connection between
the molecular structure and the macroscopic mechanical behavior of elastomers,
thereby providing guidelines for designing mechanically robust soft materials.
