Emulated elasticity
Bulk diamond, mossianite (=silicon carbide) or similar diamondoid materials are not good building materials when used in large chunks 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 which use microcomponents that bind together only by Van der Waals force or by interlocking share this brittleness (but for a different reason?).
More advanced diamondoid metamaterials with mechanisms between the microcomponents (short grippers / gripping rollers / ... ?) that in some way compensate displacement though will allow materials with exceptional mechanoical properties.
Why gum like materials emulated by brittle materials (almost) don't break
It's one of the common misconceptions about APM that diamond 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 reason is the acceleration tolerance property of nanoscale objects (see: scaling laws)
As an analogy example consider the resilience of small galss beads or the brittle chitinous exoskeleton of bugs against crash. Squishing is another matter but systems can be designed such that squishing revesibly 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 irreversible damage microcomponents mechanically. For practical purpouses 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 microscale cup with the same proportions of a everyday glasscup can tolerate in terms of acceleration and in terms of speed when crashed uncusioned against an ideal wall - what effects does the lack of crystallographic defects have and at which point is there melting/evaporation instead of breaking]
Emulated elasticity is one of the most perceptible properties of AP technology products
Diffeculties
Emulating toughness isn't easy. Especially when it shall be almost independent of direction (anisotropic).
- 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
[Todo: generalize away from microcomponents?]
