Mechanics of unusual soft network materials with rotatable structural nodes

Soft network materials consisting of filamentary horseshoe microstructures represent a class of architected materials of practical interest in flexible, bio-integrated electronics, because they can be tailored to reproduce accurately nonlinear stress-strain responses of biological tissues. The previous studies of these bio-inspired soft network materials focused mostly on the intriguing mechanical responses (e.g., J-shaped stress-strain curves and negative Poisson's ratios) before their fracture, and paid little attention on their utmost strength and stretchability. The development of soft network materials that can offer both a high stretchability (e.g., > 100%) and a relatively high strength (e.g., > 50 MPa) remains challenging. This paper presents the design, mechanics modeling and experimental measurement of a novel type of soft network materials that introduce rotatable structural lattice nodes (either with ring or disk shapes) to offer an enhanced deformability. Based on the analyses of the periodic building-block structure, we develop a nonlinear mechanics model of unusual soft network materials made of elastic constituent materials. Validated by finite element analyses (FEA) and experiments, this theoretical model can well predict the J-shaped stress-strain curves and deformed configurations of unusual soft network materials with a variety of geometric parameters. The results based on the developed model provide insights into the underlying relationship between nonlinear mechanical properties and key geometric parameters. For unusual soft network materials made of metals, an Ashby plot in terms of the strength and the stretchability is presented, highlighting the advantages of developed network materials over the existing network materials and typical soft materials. Moreover, computational models based on representative unit cells with periodic boundary conditions allow precise predictions of the utmost strength and stretchability, which can thereby serve as a reliable design tool. Due to the combined mechanical attributes of high stretchability, relatively high strength, and negative Poisson's ratio, the proposed unusual soft network materials can be used in various device systems of bio-integrated electronics.

Automated summary

Soft network materials with filamentary horseshoe microstructures are of practical interest in flexible, bio-integrated electronics due to their ability to accurately reproduce nonlinear stress-strain responses of biological tissues. Previous studies mainly focused on mechanical responses before fracture, while neglecting utmost strength and stretchability. This paper presents a novel type of soft network materials with rotatable lattice nodes to enhance deformability.