Meta(llic) Clay

Abstract

Shape-morphing and shape-locking describe objects’ ability to transform their shape and stay in that state, respectively. These qualities often come into play when grabbing or supporting an object. The contact area is increased by changing the shape, after which sustaining the shape maintains the support over time. We can imagine several ways of implementing this in engineered structures. One way of implementing shape-morphing and -locking is using kinematic movement, where a structure comprises relatively rigid parts connected by joints that allow motion. This work focuses on this type and presents a framework for analyzing it.

We identified and studied the factors determining the performance of kinematic morphing and locking structures. Three distinct steps were employed that explore the envelope of possible designs by i) creating and verifying a morphing modeling approach based on multibody dynamics principles, ii) analyzing a morphing and locking structure by applying the model, designing and experimentation, and iii) analyzing the effects of design parameters on the morphing and locking qualities in the light of geometrical features such as curvature. Spanning these steps, we developed several structures and fabricated them with additive manufacturing. These structures are i) a 3D modular system that allows easy experimentation with layouts and joint types, ii) an essentially 2D system that deforms in-plane and is selectively and reversibly locked by applying magnetic fields, and iii) a 3D deforming non-assembly metallic structure that can follow single and double curvatures and is irreversibly locked as a whole by applying bone cement. To assess the performance of these structures, in addition to the presented simulation approach, we developed methods that test the physical morphing and locking qualities visually and mechanically. These methods included 3D-scanning and mechanical testing, accompanied by digital image correlation to measure full-field strain distribution.

The presented framework shows the potential of kinematic shapemorphing and -locking mechanisms to endow structures with new functionalities. Specifically, we showed that structures incorporating the mechanism can be rationally designed, manufactured, and assessed. A multibody model predicts the morphing behavior accurately. We can use such a method to design the structures for specific applications such as orthopedic implants or soft robotics. Locking the mechanism as a whole or per individual degree of freedom obstructed the morphing capability effectively, whether or not in a reversible manner. Simulations and experiments show that we can alter the transformation and load-bearing performance of the structures as desired by changing their design parameters. The matching capacities are affected by parameters like structural body shape, dimensional ratios, and the curvature of the to-be-attained shape. These principles can be further developed and tailored for specific needs in a variety of fields.