Switchable stiffness morphing aerostructures based on granular jamming

Abstract

One of the persistent challenges facing the development of morphing aerostructures is the need to have material and structural solutions which provide a compromise between the competing design drivers of low actuation energy and high stiffness under external loads. This work proposes a solution to this challenge in the form of a novel switchable stiffness structural concept based on the principle of granular jamming. In this article, the concept of using granular jamming for controlling stiffness is first introduced. Four-point bending tests are used to obtain the flexural rigidity and bending stiffness of three different granular materials under different levels of applied vacuum loading. Nonlinear finite element analysis simulations using experimentally derived nonlinear material properties show good agreement with experiment. A specific application of this concept is then proposed based on the Fish Bone Active Camber morphing airfoil. A unit cell of this concept is built, tested and analysed, followed by the first prototype of a complete switchable stiffness Fish Bone Active Camber morphing airfoil, which is experimentally shown to be able to achieve an increase in stiffness of up to 300% due to granular jamming.

An analytical model for granular jamming beams with applications in morphing aerostructures

“…As load is increased further still, there will be a progressive movement of this splitting point inwards through the thickness, and an increasing portion of the span of the beam will become ineffective. This leads to a progressive reduction in the effective second moment of area of the beam, which induces a softening response, as shown experimentally in previous work by these authors [15].…”

“…This basic principle can create a significant change in the resulting stiffness of a morphing structure such as the FishBAC. Initial prototypes of this concept showed that the granular jamming media allows for real-time control of the bending stiffness of the FishBAC [15]. It is also capable of switching the stiffness to withstand the aerodynamic loads without requiring power from the actuator.…”

“…For example, it is possible to provide a zero-energy consumption, if the actuator is switch off during holding position because the shape is maintained due to granular jamming. The combination of these two concepts (FishBAC and granular jamming) shows the development of a new morphing concept known as Switchable stiffness FishBAC (SwitchBAC) [15], and is shown schematically in Fig. 3.…”

“…The stress-strain curves are used on a non-linear FEA model based on Von-Mises plasticity to obtain the flexural stiffness. The previous approach is a useful approach to predict the variation of stiffness of granular jamming beams in a simplified way, and within the constraints of Euler-Bernoulli beam bending assumptions [15]. However; a more generally applicable modelling of the complex, non-linear micro-mechanical response of granular jamming bending structures is needed, which motivates the combined experimental and analytical approach pursued here.…”

Mechanics of randomly packed filaments—The “bird nest” as meta-material

“…Much work has focused on the drivers, implications, and characteristics of the jamming transition in grains. Manipulation of the transition, back and forth between fluid-like and solid-like properties via external confinement has presented a basis of actuation in soft robotics 16,74,75 and deformable aerostructures 76 . Architects and artists have recently demonstrated the elegance and practical versatility that comes with embracing disorder and self-assembly instead of prescriptive control to build reconfigurable structures of emergent stability.…”