Harvard SEAS has harnessed the domino effect to design new deployable systems that can expand quickly with a small push, and are stable and locked into place after deployment.
Deployable structures aren’t always reliable or autonomous. They usually require complicated locking mechanisms to hold them in place.
The Harvard SEAS team has done away with such complexities by focusing on a simple system of bistable joints linked by rigid bars.
“Today, multi-stable structures are being used in a range of applications including reconfigurable architectures, medical devices, soft robots, and deployable solar panels for aerospace,” says first author and postdoctoral fellow, Ahmad Zareei.
“Usually, to deploy these structures, you need a complicated actuation process but here, we use this simple domino effect to create a reliable deployment process.”
A domino effect – in mechanical lingo – occurs when a multi-stable building block (the domino) switches from its high-energy state (standing) to its low-energy state (laying down), in response to an external stimulus like the push of a finger.
When the first domino is toppled, it transfers its energy to its neighbor, initiating a wave that sequentially switches all building blocks from high to low energy states.
The scientists have carefully designed the connections between the system’s links to ensures that the transition waves propagate through the entire structure – transforming the initial straight configuration to a curved one.
These building blocks have proven integral while designing a deployable dome that can pop-up from flat with one small push.
“Being able to predict and program this kind of highly non-linear behavior opens up many opportunities and has the potential not only for morphing surfaces and reconfigurable devices but also for propulsion in soft robotics, mechanical logic, and controlled energy absorption,” says senior author of the study and Harvard SEAS professor, Katia Bertoldi.
Bertoldi’s lab is also working on understanding and controlling transition waves in two-dimensional mechanical metamaterials.
Her team recently demonstrated a 2D system that controls the direction, shape, and velocity of transition waves by changing the shape or stiffness of the building blocks and incorporating defects into the materials.
The scientists have so far designed materials wherein the waves moved horizontally, vertically, diagonally, circularly, and even wiggled back and forth like a snake.
Image and content: Bertoldi Lab/Havard SEAS