Mechanics of Biologically Inspired Structures and Flexible Mechanical Metamaterials

Abstract

In this dissertation, I focus on exploring biologically inspired structures and the mechanics of flexible porous metamaterials by utilizing both experimental and computational methods. For the biologically inspired structures portion of this dissertation, namely chapters 2 and 3, I focus on the architectural details of the glassy skeletal system from the hexactinellid sponge, Euplectella aspergillum. In chapter 2, I show that this sponge's meso-scale skeletal system, consisting of a square-grid-like lattice architecture overlaid with a double set of crossed diagonal bracings, exhibits the highest buckling resistance for a given amount of material when compared to related lattice structures. These findings are further confirmed thorough an evolutionary optimization algorithm, through which I demonstrate that the sponge-inspired lattice geometry occurs near the design space's optimum material distribution. At another level of structural hierarchy, in chapter 3 I show that its complex maze-like organization of helical ridges that surround its main skeletal tube, not only provide additional mechanical reinforcement, but perhaps more significantly, deliver a critical hydrodynamic benefit by effectively suppressing von Karman vortex shedding and reducing fluctuations in lift forcing over a wide range of biologically relevant flow regimes. By comparing the disordered sponge ridge geometry to other more symmetrical strake-based vortex suppression systems commonly employed in engineering contexts ranging from antennas to underwater gas and oil pipelines, I find that the unique maze-like ridge organization of the sponge can completely suppress vortex shedding rather than delaying the shedding to a more downstream location. These findings highlight the sponge ridge design's potential benefit in engineering applications. Lastly, in chapter 4, I utilize similar experimental and computational methods to study the response of porous mechanical metamaterials with well-defined periodicity for their ability to exhibit complex behavior as a result of their non-linear deformation. Although it is well known that buckling-induced planar transformations occur in 2D porous metamaterials, here I explore the emergence of 3D morphologies triggered by mechanical instabilities in an elastomeric block with tilted cylindrical holes. I demonstrate that the 3D deformation of these structures can be leveraged to tune surface properties including friction and light reflection, thus providing a new experimental platform for investigating deformation-dependent dynamics for tribological and optical applications.