| dc.description.abstract | Networks of interconnected materials permeate throughout nature, biology, and technology due to exceptional mechanical performance. Despite the importance of failure resistance in network design and utility, no existing physical model effectively reconciles strand mechanics and connectivity to predict fracture in diverse networks that constitute polymeric, architected, and biological materials. While traditional models predict the intrinsic fracture energy – the minimum energy to propagate a crack per unit area – of a polymer network is the energy to rupture a layer of chains, they can underestimate experiments by up to two orders of magnitude. In Part I, we show that the intrinsic fracture energy of polymer-like networks stems from nonlocal energy dissipation. We then reveal a general scaling law that captures nonlocal energetic contributions and connects strand mechanics with topological connectivity to universally predict the intrinsic fracture energy of stretchable networks. We measure intrinsic fracture energy using experiments and simulations of 2D and 3D networks with various strand constitutive behaviors, defect densities, strand length distributions, lattice topologies, and length scales. Results show that local strand rupture and nonlocal energy release contribute synergistically to the measured intrinsic fracture energy in networks. These effects align such that the intrinsic fracture energy scales independent of the energy to rupture a strand; it instead depends on the strand rupture force, breaking length, and connectivity. In Part II, we present a model for real polymer fracture and design elastomers with highly regular connectivity. End-linking then deswelling star polymers produces a class of elastomers with low defects and no trapped entanglements, enabling ultrahigh straininduced crystallinity of up to 50% and stretchability that scales beyond the saturated limit. These features promote a pronounced elastocaloric cooling effect and enable reversible two-way tuning of thermal conductivity by strain or temperature modulation. The mechanical and thermal properties of these polymer networks offer promise in addressing challenges in clean energy, thermal management, and biomedicine. Our findings establish a physical basis for understanding network fracture and design principles for fabricating tough polymeric, biological, and architected materials across multiple length scales for advanced applications. | |
