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With potential applications including adaptive airless tyres, the structure was developed by researchers at London South Bank University (LSBU), with support from materials testing firm Tinius Olsen.
The hind wings of the sun beetle (Pachnoda marginata) change shape in flight using an unusual bell-shaped structure that is compliant in one direction, but almost 10-times stiffer in the opposite direction. The researchers found that the structure is an effective one-way hinge that achieves its functionality using a single material, with no extra mass.
“Mechanical ‘hinges’ and associated asymmetric bending and twisting are widespread in insect wings and, whilst operating in flight, these hinges allow the wings to deform automatically and asymmetrically between the upstroke and downstroke. They also control the precise, complex patterns of folding and unfolding in the hind wings,” said Hamed Rajabi from LSBU.
The sun beetle hinge is a double membrane, dependent on reversible thin-plate buckling. From real-scale computational simulations and upscaled physical modelling, the researchers showed it is stiff when it is in tension and bending upwards, but flexible in compression and bending downwards.
The team replicated the structure, which they said could have applications over a “considerable” size range.
“By systematically varying its design parameters in a computational model, we showed that the properties of the double-layer membrane hinge can be tuned over a wide range. This enabled us to develop a broad design space, which we later used for model selection,” said Rajabi.
“We used selected models in three distinct applications, which proved that the double-layer hinge represents a simple yet effective design strategy for controlling the mechanical response of structures using a single material and with no extra mass.”
The researchers first created a modular design that could easily be assembled and disassembled, followed by a design for an airless tyre, which they said could have applications in a number of sectors. They also created a metamaterial with zero Poisson’s ratio, meaning it does not deform along its length when stretched.
Tinius Olsen supplied a Model 1ST Universal Testing Machine, designed for tension, compression, flexure, and shear strength testing. Equipped with a 500N loadcell, it performed the required tension and compression testing. It was also used in combination with custom set-ups developed by Rajabi and his team.
The work was published in PNAS.
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