Emulated elasticity
Emulated elasticity is one of the most perceptible and most important properties of products of AP technology.
Contents
- 1 How to make brittle gemstones tough - basics
- 2 Advanced elasticity emulation
- 3 Emulated elasticity goes way beyond utility fog
- 4 Reversibility in structure & energy
- 5 Why gum like materials emulated by brittle materials (almost) don't break
- 6 Reversible plastic deformation
- 7 Maximizing toughness
- 8 Diffeculties in design
- 9 Rough iplementation considerations
- 10 Related
How to make brittle gemstones tough - basics
It's well known that diamondoid materials (and hard gemstones in general)
aren't good building materials as they are typically rather brittle.
But …
- this is only true for large chunks (bulk) wherein there always will be flaws at which cracks can start.
- this is not true for nanoscale pieces of gemstone (crystolecules) that can be made to have no flaws.
While flawless atomically precise structures of small macroscale quantity might be producible, given enough reliability and error correction. Ambient radiation will always destroy that flawlessness rather quickly (unless truly extraordinary measures in isolation are taken). So with radiation induced flaws a cup made out of a diamond or sapphire single crystal will break just like a glass cup if dropped onto a hard floor. With a cracks starting from these flaws.
In contrast nanoscale chunks of gemstone (crystolecules) can remain atomically precise over a very long time despite some natural radiation being present. Just as the chance of being hit is so much lower. They are and remain >10% bendable.
So how to get that 10% bendability to macroscale products? The answer is interlocking crystolecules to make mechanical metamaterials. This is the very basis for more advanced emulated elasticity.
For macroscale products one will always end up at a high probability to be hit by radiation no way around that (except truly ludacris expeiments). But by weaving many small chunks together in some way shape or form …
- Cracks are stopped at every interface between nanoscale pieces and
- cracks may not even start from flaws as load concentrations are kept away from the faults.
One gets reversible >10% stretchability of flawless diamond carried over from nanoscale to macroscopic products. One gets Gem-gum.
For this reason interlocking crystolecule metamaterials are the basis for more advanced emulated elasticity. This is just elasticity form passive meta materials tough. Just the natural superelasticity of flawless gemstones plus some vdW force trickery perhaps.
More simple metamaterials might still behave brittle beyond a certain (but huge) amount of stiff stretching. (wiki-TODO: Investigate the mechanical properties of metamaterials which use microcomponents that bind together only by Van der Waals force or bind together by simple fir tree dovetail interlocking.)
Advanced elasticity emulation
Beyond basic metamaterial elasticity it really starts to get interesting. Advanced elasticity emulating diamondoid metamaterials will allow for materials with exceptional mechanical properties.
Advanced emulated elasticity goes beyond simple metamaterial structures. It adds active elements. Sensing forces and providing active counter-forces. There may be special mechanisms between the microcomponents. Short grippers, gripping rollers, springs, encaplsulated controlled breakable bonds,... many options.
Emulated elasticity goes way beyond utility fog
The informed reader might think this is basically about utility fog. There are some huge differences though.
- Utility fog is specialized on generality rather than performance whereas
- Emulated elasticity is specialized on performance rather than generality
Emulated elasticity can be dense structures with no or almost no compute It won't need to be able to emulate low density gasses or emulate liquid flow in most cases. Emulated elasticity will often come with physically hard-coded constraints that can't be changed without disassembly & reassembly or can't be changed at all. Constraints could include e.g. certain anisotropic (direction dependent) behavior.
Reversibility in structure & energy
Elasticity (and plasticity) emulating metamaterials can be made reversible. Thwre are two aspects on reversibility
- there is structurally reversibility and
- there is energetic rversibility
The former can be FAPP 100% The latter can get quite close to 100% but this might not always be desired.
Thake the specific example of high performance crush dampers. It is possible to build metamaterials that are
- structurally reversible but not
- energetical reversible.
These crush damper metamaterials convert mechanical energy into heat very fast. Heat that is left to equilibrate with the environment (heat dissipation). This may allow simpler and higher performance designs.
Why gum like materials emulated by brittle materials (almost) don't break
It's one of the common misconceptions about APM that diamond and the like can't build flexible materials.
The microcomponents themselves are still made from brittle diamondoid material but they need much more extreme conditions to break. Beside the encapsulation of flaws that occur in a few DMEs the reason is the acceleration tolerance property of nano-scale objects (see: scaling laws)
As an analogy example consider the resilience of small glass beads or the brittle chitinous exoskeleton of bugs against crash.
Breakage by squishing is another matter but systems can be designed such that squishing reversibly compresses them down to an extremely pressure resilient compact state - think: rubber band tensegrity.
The result is that in a design that controls the breakage between microcomponents only very high static forces (not present in daily use) or very high speeds (bullet or above that is e.g. space debris) may actually irreversibly damage microcomponents mechanically.
For practical purposes common formed parts of those materials would without safety limits (strangulation risk etcetera) be near indestructible by force.
[Todo: For a better intuitive understanding work out what a micro-scale cup with the same proportions of a everyday glass-cup can tolerate in terms of acceleration and in terms of speed when crashed uncushioned against an ideal wall - what effects does the lack of crystallographic defects have and at which point is there melting/evaporation instead of breaking]
Reversible plastic deformation
Metamaterials can be made such that they emulate plastic deformation with the big advantage of being capable to return to their original shape. The behaviour is similar to nitinol memory metal alloys but the recovery of the original shape is not activated by temperature swings but by other means e.g. a digital signal or when the stress on the material almost falls to zero (that is actually an elastic material with a giant hysteresis).
Depending on the remaining stress level at which the retraction should set in either sufficient energy must be supplied from externally or recuperated from stored bending energy. The step from these metamaterials to mokels isn't far anymore. There might be a continuum in design space to those metamaterials.
Maximizing toughness
By maximizing the amount of energy that the metamaterial can absorb (force times bending length) materials with Unprecedented high toughness can be created. For maximal toughness an optimal combination of conversion to chemical energy conversion to thermal energy and maximal bending length has to be found. For almost all practical applications such extreme toughness won't be necessary.
Diffeculties in design
Emulating toughness isn't easy. Especially when it shall be almost independent of direction (isotropic).
- Atomically precise fabricated DMEs can be bent quite a bit. All crystal flaws are contained and can't propagate.
- distributed pure elastic bending
- controlled reversible breakage of encapsulated bonds
- mechanical property emulation can use up a significant part of the volume
- differences to metal dislocations - more localized - more regular - oblique non canonical axis sliding - role of vacancies
- shift beyond one µcomponent cell - deformation memorisation
- controlled breakage (e.g. hexagons from sheets & thinning limit)
- emulated sliding about arbitrary planes not coinciding with the main crystallographic planes
- limited bending cells for stretching factors (strains) >>100% and how to make an omnidirectional diamondoid metamaterial from these
[Todo: generalize away from microcomponents?]
Rough iplementation considerations
For compact elastic energy storage spiral springs have proven to be suitable. Thus they may be a suitable option to be used in elasticity emulating metamaterial microcomponents (EEMCs). It seems to make sense to map each degree freedom in the strain tensor to a separate spring in a elasticity emulating microcomponents (EEMCs). Internal nanomechanics can redirect movements such that the springs can be oriented in a compact way. Internal nanomechanical logic and amplifiers allows to program damping and other behaviour. Overall the whole stress strain behaviour should be adjustable in a wide range including memory of history (for whatever that may be needed).
Linkages to other EEMCs should be short and bulky to preserve material strength. Still even with these short linkages it seems not unreasonable to expect capabilities to emulate strains up to +-15% If the linkages hit the limits of their range of motion it would probably be best if they break in a controlled way (See: splinter prevention).
If a mechanism is included to move EEMCs hand over hand over distances greater than the size of one EEMC permanent displacements will be induced. Either this is only repairable by recomposing the microcomponents in the upper layers of a nanofactory or the material itself is capable of that (tagged microcomponents plus active sensing and actuation). In that case we already come rather close to fully fledged utility fog just that it has shorter and viewer linkages.
Related
- Chemospring
- Isotropy of materials
- Utility fog -- differences: long "legs", many "legs", lots of memory and intelligence included (extremely large quasi-plastic deformations can be made reversible. See also: "Legged mobility"
- Infinitesimal strain theory (strain tensor) - (leave to wikipedia)
base substrate properties to build upon:
Off-topic: Low spring constants at the nanoscale (as a natural result of scaling):
