Morphing structures, which can reconfigure on demand, offer designers new routes to increase structural performance and improve efficiency. Such structures find applications across many fields such as wind-turbines, robotic end-effectors and medical devices. Morphing structures typically utilize actuators or active-smart materials to develop shape changes, but these systems often add undesirable weight penalties or mechanical complexity. To overcome these challenges, new approaches to the design of morphing systems must be explored.In most morphing systems, transformation occurs via large mechanical deformations, such as bending, stretching and twisting. However, the topology (connectivity) of the elements within the system remains constant. Here we explore the potential for new tailoring capabilities by allowing the system's topology to change by merging/splitting structural elements. This rearrangement of components offers a new approach to robustly control structural stiffness properties, enhancing the performance of morphing devices.&nbsp;Specifically, we consider a planar lattice composed of rectangular unit-cells. The walls of the unit cells, when subject to a sufficiently-large compressive load, buckle and make contact with their neighbours. This changes the effective topology to that of a kagome lattice.To characterise this system's behaviour, we perform a series of non-linear post-buckling analyses in ABAQUS. We investigate parametrically the effect of cell geometry and stiffness on the lattice’s behaviour. We observe a step-change in the shear modulus when the system’s topology changes, thus demonstrating the capability of the system to morph between distinct operating regimes. A finite element analysis of a typical lattice with this design shows an increase in shear modulus from its initial value by a factor of 15 under an effective compressive strain of 0.15. In addition, the lattice stiffness doubles due to the structure transforming from being bending-dominated topology to being stretching-dominated.&nbsp;We further investigate tuning the system's response through the use of initial geometric imperfections in the unit-cell’s shape to promote buckling in desirable directions and to tune the critical compressive load. We also explore the additional tailoring capabilities of this design by varying the aspect ratio of the rectangular unit cells.Fabrication of structures using composite materials for the proposed design can provide additional ability to tailor the response to achieve reduced weight, multi-stability and minimal actuation load.&nbsp; For example, through the use of composites with fibre pre-stress and laminate anisotropy, geometric non-linearity in structural response can be exploited to obtain desirable multistability and snap-through behavior.This proof-of-concept demonstration of topology morphing structures paves a new route for the robust control of non-linear stiffness of structures in a passive way which can serve a wide variety of applications.

Topology Morphing Lattice Structures

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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