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August 16, 2013

MIT 3D Interlock Variants and Closer to Utility Fog

MIt Gershenfeld created a new 3D interlock structure — which is made from tiny, identical, interlocking parts — to chainmail. The parts, based on a novel geometry that Cheung developed with Gershenfeld, form a structure that is 10 times stiffer for a given weight than existing ultralight materials. But this new structure can also be disassembled and reassembled easily — such as to repair damage, or to recycle the parts into a different configuration.

There are different variations of the structure which spring to mind -

1. For Tall Buildings and Bridges

Larger pieces to the length of 1 meter or 2 meters may be better suited to some construction applications. These larger structure might not have the ultralight benefits but could be superior in strength for making tall buildings. The construction approach would as a baseline not require welding. Also, modifications could be made to have either locking pins or a locking cover over the joints to reinforce or hold them in.


In the lab, a sample of the cellular composite material is prepared for testing of its strength properties. Photo courtesy of Kenneth Cheung



2. Towards Utility Fog

Thanks to one of my readers for pointing out the similarities to Josh Halls Utility Fog concept.

A. The 3D Interlocks can be made of different materials (not just composites). Utility fog was designed with crystalline material.

B. Utility fog was designed at a smaller scale of 100 micron cells with a 10 micron body. 3D Interlocks can be scaled to smaller sizes

C. Utility fog has telescoping arms. 3D interlocks could be designed with active parts.

Active, polymorphic material ("Utility Fog") can be designed as a conglomeration of 100-micron robotic cells ("foglets"). Such robots could be built with the techniques of molecular nanotechnology (see Drexler, "Nanosystems", Wiley, 1992). Using designs from that source, controllers with processing capabilities of 1000 MIPS per cubic micron, and electric motors with power densities of one milliwatt per cubic micron are assumed.

Each Foglet has twelve arms, arranged as the faces of a dodecahedron. The central body of the foglet is roughly spherical, 10 microns in diameter. The arms are 5 microns in diameter and 50 microns long. A convex hull of the foglet approximates a 100-micron sphere. Each Foglet will weigh about 20 micrograms and contain about 5 quadrillion atoms. Its mechanical motions will have a precision of about a micron.



The arms telescope rather than having joints. The arms swivel on a universal joint at the base, and the gripper at the end can rotate about the arm's axis. The gripper is a hexagonal structure with three fingers, mounted on alternating faces of the hexagon. Two Foglets "grasp hands" in an interleaved six-finger grip. Since the fingers are designed to match the end of the other arm, this provides a relatively rigid connection; forces are only transmitted axially through the grip. When at rest, foglets form a lattice whose structure is that of a face-centered cubic crystal (i.e. an octet truss).

For a mass of Utility Fog to flow from one shape to another, or to exert dynamic forces (as in manipulating objects), a laminar flow field for the deformation is calculated. The foglets in each lamina remain attached to each other, but "walk" hand over hand across the adjacent layers. Although each layer can only move at a speed differential of 5 m/s with its neighbor, the cumulative shear rate in a reasonable thickness of Fog is considerable, up to 500 m/s per centimeter of thickness.

The atomically-precise crystals of the foglets' structural members will have a tensile strength of at least 100,000 psi. As an open lattice, the foglets occupy only about 3% of the volume they encompass. When locked in place, the Fog has a more or less anisotropic tensile strength of 1000 psi. In motion, this is reduced to about 500 if measured perpendicular to the shear plane. As a bulk material it has a density of 0.2 g/cc.



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