Structural elements for nanofactories

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Shape-lock-chain-core-reinforcement

Problem

A main goal for structural elements is to make them from reusable standard pieces. The smaller and the less complex the standard pieces are the more reusable they become.

The problem with just holding a lot of small pieces together merely by Van der Waals Force is that one may loose structural stiffness (TODO: to check quantitatively) and one introduces lots of potential failure points where at elevated temperatures the especially severe thermal vibration can break things up. Clipping connections (not "noisily" connected to save energy) may be a bit sturdier but also increase complexity and size of the parts and thus potentially make them less reusable.

Solution

The solution is to use shape locking as the means for connection. The resulting structures assembled by pure shape locking usually have low stiffness though. It turns out that it is possible to stiffen big assemblies made out of lots of small simple standard parts that are shape locked together by applying the principle of concrete reinforcement.
By ...

  • threading a (indirectly) shape locked chain through a stack of small profile segments
  • preventing the chain from sliding in the stack of profile segments by widening the chains starting point and
  • pulling the chain where it comes out the stack of profile segments thereby pushing back on the stack of profile segments

... one can stiffen a long rod-like structural element with arbitrary profile shape. A profile segment can be as simple as a tube but also have more intricate shape like e.g. a guide-rail. Stacks of wider profile segments can be tensioned by multiple chains - three will often make sense since three points define a plane - four make sense for cartesian symmetry. Special profile segments can be slid on e.g. thinner spacer segments or segments that add connection points for hinges.

To tension a profile stack one could use a wide variety of spanner designs. One possibility would be a simple screw driven by a worm-gear for high mechanical gain. The worm gear needs to be strongly spring locked. In this special design the chain should be non-circular such that it can locally take on the torsional load introduced by the screw.

When shape-lock-chain-core-reinforcement is used a lot of small passivated crystolecules can be made reusable. (See: Recycling)


Shape locking and spanning drive chains is an other issue (machine element).

Trussworks & space frames

Structures that have no degrees of freedom even when all vertices do not take any momenta are of special interest. In this group falls the set of deltahedra (all faces are equilateral triangles). They can be intuitively explored by the usage of the popular geomag construction toy.

Vertices surrounded by six coplanar equilateral triangles have a different weaker character than other vertices (TODO: check if those are soft modes)

The tetrahedron is the most simple deltahedron. Note that:

  • Tetrahedra alone cant be stacked to build up linear non wavy trussworks.
  • Tetraherda cannot be used to fill space. This is what happens if you try: (link to wikimedia commons image)

In both cases octahedra need to be added.

Tensegrity

Non-redundant tensegrity base units are single point failure - if one element breaks the whole structure collapses. To avoid this redundant elements can be added. Bigger tensegrity structures can consist out of many independent base units. For stiff structures so called "soft modes" need to be avoided.

There are hollow spiral n-gonal prismatic structures that may be suitable as frames.

Related

external links

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