Fig. 6. 3D printed multimaterial metamaterial structures with tunable changes in stiffness.

a, 3D structure, 3 × 3 × 3 cells with constant diameter of the links and nodes, respectively. b, The links rendered in pink are soft, and the nodes rendered in violet are rigid. c, Force displacement curves for compression tests on six different specimens. The decrease in force at high displacement in the brown plot line corresponds to the collapse of the structure due to buckling. The bend in the force strain curve in the second half of the displacement graph corresponds to the rigid nodes making contact, leading to increased stiffness of the structure. The dashed lines show a prediction of how the curve would have behaved without the rigid nodes making contact. d, Still images of compression tests conducted on the material. No compression (d = 0 mm) is shown to the left; compression when the nodes are touching (d between 10 mm to 17 mm) is shown in the centre; and approximately 50% compression is shown to the right.