A buckling mechanics model for pattern transformation of lattice superstructures assembled by soft-hard materials integrated units

Abstract

Compression-induced sudden change of organizations and patterns in lattice structures composed of truss materials or granular colloids has been leveraged to design a broad variety of novel functional materials and structures. However, mechanics theory underlying these instabilities remains underexplored. Here, we report an instability phenomenon in lattice superstructures comprised of soft-hard materials integrated Janus structure units under an externally applied uniaxial compression in a rigid-walled constraint container and establish a constrained buckling mechanics model to describe the instability and its induced pattern transformation. Finite element analysis (FEA) shows that when these superstructures are compressed beyond a critical load, the assembly components of soft-hard materials integrated units begin to slide and rotate, leading to pattern transformation. We propose an instability mechanics framework of pattern transformation by developing a beam buckling model constrained laterally by a series of elastic springs. These spring constraints represent the contact status between adjacent soft-hard integrated units in the superstructures and are correlated with rotation of units. Theoretical predictions of both instability mode and pattern transformation agree well with FEA results. The effects of the initial orientation of individual units and assembly patterns of the superstructures are also discussed. This work provides a theoretical mechanics foundation to design superstructures with controllable pattern transformations by tailoring soft-hard materials integrated assembly components.