Form closure
(also called: shape locking, positive locking, positive closure, ...)
Contents
Usage against thermal Van der Waals bond breakage in the low nanoscale - hirachical locking
When the contacting area of two building blocks is made smaller then they wont stick together as strong as before. If the contacting area gets so low that the Van der Waals bonding energy falls in the range of the energy range of the thermal excitations it becomes likely that connections get knocked open just by chance.
Note that the critical surface area is rather small for room temperature and bulk (hydrogen terminated) diamond. A nice thing is that with linear rising contact area breakage probability for the VdW-bond falls exponentially thus areas that will never break are quickly reached.
Shape locking might be especially important for high temperature applications where small contact areas become insufficient to hold things together.
Hierarchical locking
To prevent building blocks from falling apart by accident one can chain shape locking together. Part A can't be removed because part B is in the way. Part B can't be removed because part C is in the way. And so on and so forth.
The last clip that does not use shape locking but energetic locking must be strong enough to reliably withstand thermal fluctuations of the operation temperature. Used can be:
- Van der Waals sticking with sufficient surface (and back-volume density)
- Clipping - a crystal deformation is needed to open the lock
(unlike macroscopic gemstones up to ~30% deformation is possible in flawless crystolecules) - Sparsely packed covalent bonds - (only reopenable in practically perfect vacuum)
- Densely packed covalent bonds - (not reopenable at all - see: atomically precise disassembly)
Examples for possible solutions of this problem (1D structure examples):
- sturdy chain that uses shape locking - leave to thingiverse
- serial hierarchical locking structure - leave to thingiverse
[todo: calculate the amount of reduction in probability of failure in chained shape locking structures depending on contact areas and temperatures]
The necessary surface area for energetic locking via VdW sticking may be includable in a distributed form along the whole length of the chain '''todo:''' investigate this.
Note that an too long chains make parallel assembly process impossible thus chains shouldn't be made longer than necessary. One can also merge the shape lock chain such that one ends up with a tree topology in the order of assembly. That way a high surface area energetic end lock may be more naturally includable. Kartesian 90° turns can be used to tie chains together. E.g. to disassemble a cube shaped assembly the disassembly must start at a corner then work down an edge proceed along a surface and finally disassemble the whole volume.
One can also include forkings in the shape lock chaining. That is at some point at least two parts need to be removed such that the held part can be removed. Then one ends up with a directed acyclic graph topology.
- Why not use clipping? Clipping may make recuperating energy in the recycling process harder.
- If an energy barrier of the lower levels is overcome first it leads to a complete destruction of the structure.
- Interfaces could be hierarchically locked with sliding planes. [Todo: add info-sketch]
Usage in bigger scales
To make assembly reversible with low energy turnover while retaining near full material strength
Usage in hierarchies
...
