Mechanics of rate-dependent large strain localization in staggered hyperelastic-viscoelastic composites

Abstract Soft staggered composites are attractive for combining toughness, deformability, and structural robustness, yet their mechanics have been understood mainly from quasi-static or rate-insensitive perspectives. In many biological and bioinspired systems, however, soft constituent phases are inherently viscoelastic, so their stiffness and load-transfer behavior can vary markedly with loading rate. How such rate dependence interacts with staggered geometry to govern deformation localization and failure remains unclear. Here, we investigate the tensile mechanics of a soft staggered composite composed of viscoelastic domains embedded in a continuous hyperelastic matrix. Experiments and finite element analysis show that the mechanical response is jointly controlled by loading rate and geometric architecture. As the strain rate increases, the viscoelastic phase becomes stiffer and drives stronger redistribution of axial strain, lateral strain, and shear strain into the surrounding hyperelastic ligaments. Geometric parameters further regulate this load transfer, thereby altering stiffness and strain localization. These findings reveal a simple route to program rate-sensitive deformation through the coupling of viscoelasticity and staggered architecture, and provide guidance for designing adaptive soft composites and mechanically functional soft devices.