Difference between revisions of "Emulated elasticity"
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But due to shape-memory the damage can be restored structurally. | But due to shape-memory the damage can be restored structurally. | ||
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Metamaterials can be made such that they emulate plastic deformation with the big advantage of being capable to return to their original shape. | Metamaterials can be made such that they emulate plastic deformation with the big advantage of being capable to return to their original shape. | ||
Revision as of 09:12, 5 December 2023
Emulated elasticity is one of the most perceptible and most important properties of products of gemstone based atomically precise technology.
Contents
- 1 How to make brittle gemstones tough - basics
- 2 Advanced elasticity emulation
- 3 Delineations
- 4 Reversibility in structure & energy
- 5 Maximizing toughness
- 6 Diffeculties in design
- 7 Rough implementation considerations
- 8 Why gum like materials emulated by brittle materials (almost) don't break
- 9 Related
- 10 External links
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 of mechanosynthesis). 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. Crystolecules are and remain >10% bendable. That is just because the chance of being hit is so much lower for a much smaller parts. Volume is what matters here rather than size, making the effect especially huge.
So how to get that >10% bendability preserved when going up 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. There is no way around that (except truly ludacris experiments). But by interlocking/interweaving 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 mechanical metamaterials tough. Giving just the natural superelasticity of flawless gemstones plus some vdW force soft spring trickery before that perhaps.
Simple elasticity emulating mechanical 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
Advanced emulated elasticity goes beyond simple passive 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.
Delineations
Delineation to utility fog
The informed reader might think that advanced elasticity emulation metamaterials are basically equivalent to utility fog.
There are some significant differences though.
- Utility fog is specialized on generality rather than performance whereas …
- … emulated elasticity is specialized on performance rather than generality.
Emulated elasticity can achieved by dense structures with no (or almost no) compute.
Unlike utility fog elasticity emulating mechanical metamaterials
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 of the material (or can't be changed at all).
Constraints could include e.g. certain anisotropic (direction dependent) behavior.
Delineation to mechanical metamaterials
Mechanical metamaterials go well beyond basic passive elasticity emulation.
The borderline to advanced elasticity emulation is less clear more blurry and still open for refinement.
Advanced elasticity emulation covers a good part of mechanical metamaterials.
Though maybe not all. There is also …
- locally shiftable density (not globally changeable density as mass can only me moved not changed)
- emulated plasticity (clay like formability possibly with shape memory)
- motion beyond actively resisting external forces
- influence on semi mechanical properties like emulated thermal expansion
- and perhaps more
Reversibility in structure & energy
Elasticity (and plasticity) emulating metamaterials can be made reversible.
There are two aspects on reversibility:
- structural reversibility
- energetic reversibility
The former can be FAPP 100%.
The latter can get quite close to 100% but this might not always be desired.
Take the specific example of high performance crush dampers.
It is possible to build metamaterials that are structurally reversible but not energetically 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.
E.g. for crush-collapsible zone in vehicles.
But due to shape-memory the damage can be restored structurally.
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 behavior 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 falls back almost to zero (that is actually an elastic metamaterial with a giant hysteresis area).
Depending on the remaining stress level at which the shape restoration should set in sufficient energy must be …
- either 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 mechanical 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 though.
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 implementation considerations
For compact elastic energy storage spiral springs have proven to be suitable in macroscale clocks.
Thus they may be a suitable option to be used in elasticity emulating metamaterial microcomponents (EEMCs).
For more general purpouse EEMCs it seems to make sense to map each degree freedom in the strain tensor to a separate spring.
Internal nanomechanics can redirect movements such that the springs can be oriented in a compact way.
Internal nanomechanical logic and amplifiers allow to program damping and other behavior.
Overall the whole stress strain behavior should be adjustable in a wide range.
Including eben memory of history to implement custom hysteresis behavior (for whatever that may be needed).
Unlike in utility fog linkages to other EEMCs should be short and bulky to preserve material strength.
Still even with 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 predefined way.
(See: splinter prevention).
If an overload handling mechanism is included to move EEMCs over distances greater than the size of one EEMC,
then 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 the latter case we already come rather close to fully fledged utility fog.
Just that it has shorter and viewer linkages.
Why gum like materials emulated by brittle materials (almost) don't break
(wiki-TODO: This section is somewhat redundant with the intro. Either merge or factor out to common misconceptions or both.)
It's one of the common misconceptions about gemstone based atomically precise manufacturing that diamond and gemstones can't build flexible materials.
The microcomponents themselves are still made from brittle diamondoid material but they need much more extreme conditions to break. the reasons:
- encapsulation of crystal flaws that occur in a few DMEs
- acceleration tolerance property of nano-scale objects (see: scaling laws)
As an analogy example consider the resilience of small glass beads compared to a big glass ball.
Beside breakage from high speed crashes breakage by slow speed high force squishing is another concern. Low density systems can be designed such that squishing them reversibly compresses them down to an extremely pressure resilient compact state. Think: Rubber band tensegrity.
The result of proper designs design that control 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.
Parts of common shape for practical purposes (including e.g. ropes) would be near indestructible by force. As this poses a risk (strangulation et cetera) intended breakage safety limits may often be a good idea.
(wiki-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)
Related
- 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"
base substrate properties to build upon:
External links
- Wikipedia: Infinitesimal strain theory (strain tensor)
