Totimorphic Structures for Space Applications

Background

Totimorphic structures [1], or neutral-stability structures [2], are a novel type of lattice metamaterial which takes advantage of a neutrally-stable unit cell to construct a larger lattice which is neither rigid nor freely-hinged, but has an equal stability and energy state in every possible configuration. In this mode, these structures are completely compliant to outside forces and displacements, however by removing one degree of freedom from the unit cells, the structure can be made completely rigid and vice versa. This property could allow the development of structures that can sustain radical shape transformation, and then also provide rigid load-bearing capacity through control of the unit cells. This behaviour may be very advantageous in a variety of scenarios, especially in space, where mass is at a premium and multi-functional structures with low mass are highly desireable.

Project overview

To implement this structure in a real space application, there are many challenges that must be solved; how to manufacture the unit cells, how the efficently actuate the structure between shapes, how to minimise the actuation complexity of the structure etc. The goal of this project is to develop a totimorphic toolbox that will allow dynamic, structural and control analysis of these lattices, which will be used to explore their viability for space application. A particular area of interest is the actuation of the structure between shapes, the obvious method of changing the behaviour of the unit cells from neutrally-stable to rigid is through locking and unlocking the joints between the beams and levers. In practice having active control of each joint in a structure is expensive and complex, so minimising the number of active locking mechanisms is highly desirable. However, this requires analysis to identify combinations of mechanisms that still allow for the desired shape transformation. Similar analysis has been done previously for Miura-ori sheets [3] but the massively increased degrees of freedom for the totimorphic structure make this problem much more complicated.

References

1. Gaurav Chaudhary, S Ganga Prasath, Edward Soucy, L Mahadevan. (2021). "Totimorphic assemblies from neutrally-stable units" Proceedings of the National Academy of Sciences Vol.118 Num.42. DOI: 10.1073/pnas.2107003118

2. Mark Schenk, Simon D. Guest. (2013). "On zero-stiffness" Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science. DOI: 10.1177/0954406213511903

3. Stephen grey, Fabrizio Scarpa, Mark Schenk. (2021). "Embedded Actuation for Shape-Adpative Origami" Journal of Mechanical Design. DOI: 10.1115/1.4049880

Outcome