Difference between revisions of "Emulated elasticity"

Revision as of 11:34, 4 December 2023

Not to scale! Well designed nano to micro structure can create extraordinary mechanical material properties (graphic not to scale). Stress strain behaviour to order may be possible (in bounds).

Artistic illustration. A gemstone based mechanical metamaterial. Through nano- and micro-structuring it is able to behave mechanically like rubber. Or quite behave more exotically in ways not possible by materials produced via conventional non-atomically precise production pathways that happen near thermodynamic equilibrium.

Emulated elasticity is one of the most perceptible and most important properties of products of gemstone based atomically precise technology.

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 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.

Delineation of emulated elasticity to utility fog and mechanical metamaterials

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 be 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.

Mechanical metamaterials might go beyond advanced elasticity emulation and add also feature active motions, shiftable density, and more. But the borderline is blurry and still open for refinement.

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 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.

Related

• Gem-gum
• Mechanical metamaterial

• 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:

• Superelasticity
• Lower stiffness of smaller machinery
• Same relative deflections across scales

• Chemospring
• Isotropy of materials

• Gem-gum tentacle manipulators
• Soft-core macrorobots with hard-core nanomachinery

External links

• Wikipedia: Infinitesimal strain theory (strain tensor)