Difference between revisions of "Emulated elasticity"

Revision as of 07:33, 13 June 2015

Diamondoid materials are not good building materials when used in large chunks (bulk) since they're rather brittle. A diamond cup will break just like a glass cup if dropped on hard floor. A crack can start at a radiation induced flaw. Simple metamaterials might share this brittleness (but for a different reason?).
[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]. More advanced diamondoid metamaterials with mechanisms between the microcomponents (short grippers / gripping rollers / springs / encaplsulated controlled breakable bonds ... ?) that in some way compensate displacement will allow materials with exceptional mechanical properties though.

Emulated elasticity is one of the most perceptible and most important properties of products of AP technology.

Elasticity (and plasticity) emulating metamaterials can be made 100% structurally and additionally for a good deal energetically reversible. It is possible to build structural but not energetical reversible metamaterials that convert mechanical energy into heat that is left to equilibrate with the environment (heat dissipation). This may allow simpler 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 vew 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?]

Related

• Isotropy of materials