Pneumatic Optimally Tapered Inflatable Lattices with Deployable and Conformal Characteristics

Deployable and conformal structures with extreme and tunable specific stiffness are crucial for technologically demanding space applications like deployable solar panels, protective armors, conformal structures, active stiffness control, large space systems developed through in-space assembly, and space habitation. To achieve high specific stiffness pushing the limits of feasible effective elastic properties, lattice metamaterials having optimal 2- and 3-dimensional architectures have been extensively investigated in literature, wherein the primary deformation mechanism of the solid beam-like constituting elements includes bending- and stretching-dominated modes. We propose to break the traditional boundaries of specific stiffness in lattice metamaterials by exploiting fundamentally different mechanics, wherein pneumatic membrane deformation mode is exploited to derive stiffness of the lattices. A new class of optimally designed inflatable lattices is developed here, wherein the constituting beam-like elements are inflatable in nature, leading to a periodic network architecture when air pressure is applied. Such lattices possess deployability features and are conformal to a target surface while having exorbitantly high specific stiffness and being able to be stored in a minimum volume configuration. To maximize the specific stiffness and the volume of required air in a deployed state, we further introduce spatially varying tapered beam-level architectures following a bilevel design framework, wherein the expanded coupled design space of beam and unit cell geometries is exploited for pneumatically programmable elastic property modulation. Normal and shear modes of lattice stiffness are investigated through an iterative approach of the inflatable Timoshenko beam model coupled with unit cell mechanics including joint rotation of the inflatable lattices.