Adaptive stiffness in lattice structures through passive topology morphing

Structures with adaptive stiffness characteristics present an opportunity to meet competing design requirements. One approach to achieve this stiffness adaptivity is through topology reconfiguration. Here, the potential of using passive topology changes to achieve desired adaptivity is explored in three lattice structure designs. The first investigation involves a planar sinusoidal lattice with rectangle-like unit cells. Under sufficient compression, the cell walls bend and contact neighbouring cells. This self-contact establishes new load paths, thus resulting in kagome-like unit cells that exhibit an approximate four-fold increase in compressive and shear stiffness. The role of key geometric and stiffness parameters in critical regions of the design space is explored through a parametric study. Second investigation explores the bilinear elastic behaviour in cylindrical sinusoidal lattices. The topology transformation leads to an approximately four-fold in-crease in stiffness under compression. The lattice exhibits negative Poisson’s ratio with a step-change from ≈ −0.66 to ≈ −0.23 prior to and during contact formation, respectively. After contact formation, it displays a nonlinear Poisson’s ratio behaviour. A comparison with planar lattices reveals that cylindrical lattices exhibit bilinear behaviour for a wider range of geometric parameters. The third lattice utilizes simultaneous tensile buckling of unit cells to induce topology change. Under tension, the lattice transitions from a rectangle-like to a triangle-/pentagon-like unit cells with a seven-fold increase in stiffness. The initial and the new topologies are dominated by membrane effects. During the transformation phase, negative stiffness accounts for approximately 82% of the total elastic deformation. Experimental observations of prototypes, either 3D-printed or fabricated, show excellent correlation with finite element analysis. The analytical results provide valuable insights into the observed behaviours. The non-linear responses demonstrated by these proposed concepts may offer designers a new approach to tailor elastic characteristics