Large deformations of soft metamaterials fabricated by 3D printing

The aim of this paper is to explore large-deformation responses of hyper-elastic porous metamaterials made by three-dimensional (3D) printing technology. They are designed as a repeating arrangement of unit-cells in parallelogram and hexagonal shapes. Fused deposition modeling is implemented to fabricate metamaterial structures from soft poly-lactic acid. 3D printed metamaterials are tested under in-plane tension-compression in axial and transverse directions. Experiments reveal that unit-cell shape, direction, type and magnitude of mechanical loading have significant effects on metamaterial anisotropic response and its instability characteristics. To replicate experimental observations, a finite element solution is developed adopting the hyper-elastic Mooney-Rivlin constitutive equations and non-linear Green-Lagrange strains. Iterative Newton-Raphson approach is implemented to solve governing equations with material-geometric non-linearities. The accuracy of the computational tool is verified by capturing main features observed in the experiments. It is found that modeling of hyper-elasticity and large strain is essential to accurately predict non-linear responses of the 3D printed soft metamaterials. Due to the absence of similar results in the specialized literature, this paper is likely to advance the state of the art of metamaterial printing, and provide pertinent results that are instrumental in the design of hyper-elastic metamaterial structures and infill patterns for printing purpose.