Modeling nonlinear viscoelastic responses of flexible composites for soft robotics applications

This study examines the deformation of soft composites comprising stiff elastic unidirectional fibers and soft matrix, such as silicone elastomer, rubber and PDMS (Sylgard 184) with potential applications for soft robots. In some soft robotic applications, precise controls of shape reconfigurations are necessary. To design soft robots with high precision motions, it requires a detailed understanding of material responses. In this study, we formulate a constitutive model for the nonlinear viscoelastic response for soft isotropic materials, which is used for the soft matrix in the composites. We examine mechanical deformations of soft composite laminas with two different matrices i.e., Ecoflex 00-30 and PDMS (Sylgard 184), which differ significantly in their extensibility, and different fiber orientations. The initial fiber orientation and matrix extensibility govern the shape reconfigurations of the laminas. The viscoelastic response of the soft matrix causes continuous shape reconfigurations associated with the creep behaviors, which influence the final shapes of the lamina. We also present the design and analyses of soft composite structural components, incorporating the nonlinear viscoelastic responses of the matrix.