[HN Gopher] Knots smaller than human hair make materials unusual...
___________________________________________________________________
Knots smaller than human hair make materials unusually tough
Author : gmays
Score : 116 points
Date : 2023-03-11 14:20 UTC (2 days ago)
(HTM) web link (www.caltech.edu)
(TXT) w3m dump (www.caltech.edu)
| thriftwy wrote:
| I wonder if it is possible to drive multiple carbon nanotubes
| through C60 buckyballs to create a fabric which has tensile
| strength of C-C binding.
| siliconunit wrote:
| Interesting behaviour, usually any normal rope knot makes the
| rope weaker at the point of maximum curvature/choking etc. Would
| be enlightening to get a comparison why the different behaviours,
| just a scale/friction non linearities?
| mihaaly wrote:
| They claim the structure is tougher (absorbs more energy) not
| stronger (maximum force before breaks). As far as I see they
| say nothing about if it is stronger or weaker than straight
| lines. Likely because it is weaker due to the curvatures
| leading to stress peaks in the material before the ultimate
| force of two straight filaments was reached. They should have
| presented the force-displacement diagram too which is essential
| data (maybe the original article has it). I'd be curious seeing
| the force-displacement diagram of the two illustrated
| experiment compared to the diagram of two straight fibres
| tested.
|
| Also I guess the toughness is just a relative matter to the
| dimensions of the structure but since uses much more material
| than two straigh fibres it is less tough by weight (due to the
| decreased strength). If the same amount of material was
| connecting the top and bottom with straight lines then that
| would lead to the toughest situation of all (absorbing the most
| energy). Again, guessing.
|
| In the video the woven material may have tighter threads with
| stronger friction or more uneven friction distribution leading
| to reaching the yield limit of the filaments quicker. The woven
| with some 'lubrication' should have had similar properties
| assuming the same amount (length or weight) of material
| included. I'd also be curious then about the reproducibility of
| the results on the same kind of structure. Like if making the
| same knotted pattern would lead to the same results or slight
| deviation of geometry was affecting the end results
| significantly.
| cwillu wrote:
| It looks like the loop of the knot permits slack which in turn
| causes stress on the fiber to be taken up by straining
| neighbouring weaves, rather than causing the stressed fiber to
| immediately strain to its failure point.
| lapinot wrote:
| Not sure "knot" is the best wording. This looks like knitting. It
| is well known that knitted material is very strong and very
| flexible (much more elastic than weaving). And that all of
| knitting/weaving/braiding already enable to improve properties
| from initial material. Not so sure how the scale is relevant. I
| guess the contribution from the paper is that this is in the
| context of 3d printing.
| A_D_E_P_T wrote:
| > The knots were not tied but rather manufactured in a knotted
| state by using advanced high-resolution 3D lithography capable of
| producing structures in the nanoscale.
|
| This would be difficult to scale. And it's possible, even likely,
| that it can't be applied to existing strong fibers, which are
| drawn at very low diameters. The paper does its best to bury the
| lede, but the polymer they were using was acrylic-based, and
| likely very weak in comparison with, e.g., Dyneema or aramid
| fibers.
|
| There are quite a lot of papers which examine the mechanical
| properties of nano-lattice and nano-architected materials, made
| with lithographic techniques, but I think that the commercial
| viability of these materials is effectively zero. And, in many
| cases, as here, it's not clear that they'd be superior to the
| standard high-strength materials that are already so ubiquitous.
| nick123567 wrote:
| Why would lithography not scale? We've got plenty of mass
| production lithography with microchips.
| thfuran wrote:
| Older processes are cheaper, but 5nm node costs something
| like $25,000 per square foot (with around 0.1 defects per
| square cm, which may result in waste) and doesn't do pieces
| larger than about 1 foot. That's pretty bad as far as
| textiles go.
| akiselev wrote:
| Economically mass producing microchips is only possible
| because they are 100s of square millimeters in size and very
| valuable per square mm. Any bigger than that and error rates
| in the fab process start to destroy the yield.
|
| These fibers are used in much bigger applications like body
| armor or mechanical composite parts where the surface area is
| on the order of square meters, not millimeters.
| AlotOfReading wrote:
| Modern panel fabs use fine masking over like 10sq. meters
| with precision on the same order of this (~dozens of
| micrometers), and people have successfully shown
| lithography over similar panel sizes by separate exposures.
| HPsquared wrote:
| The feature size is a LOT bigger than microchips though:
|
| "Each knot is around 70 micrometers in height and width,
| and each fiber has a radius of around 1.7 micrometers"
|
| That is, cheaper lithography methods could presumably be
| used.
| bigfatfrock wrote:
| I'm shocked daily by HN comment depth, what a breadth of
| experience people have. Thanks for the insight.
| nh23423fefe wrote:
| This place is all culture. People are smart and varied
| everywhere. But here we try to enforce a culture is that
| assigns low status to low effort trash. It doesn't always
| work. But that's the expectation, I don't think anything else
| could work. Comments should be for the community not to
| spread low information barnacles on every piece of original
| thought.
| ant6n wrote:
| This place also suffers from the Dunning-Kruger-Effekt.
| FieryTransition wrote:
| I guess you could argue, that most places suffer from
| that, as everyone has a boundary, at which they don't
| understand things. But the effect itself, is probably
| more relevant in an organization, as it was used to
| describe management.
| daniel_reetz wrote:
| I want to offer a tempered view. The comment does seem deep
| and it probably is. But I work in physical prototyping - new
| products, new technologies. I do the "design and manufacture
| from real materials in the real world" part. I own a few
| hundred thousand dollars in advanced machinery and make parts
| for FAANGs and tiny research startups. I'm a named inventor
| on something like 16 patents. And yet daily, I read
| confident, well worded answers here -- about my domain --
| which reflect views completely divorced from reality, or in
| living in some strange parallel reality.
|
| Personally, I try to recognize this as an opportunity for me
| to be humble (as I never know who may read my comments from a
| higher place of skill and domain knowledge), and also to take
| what is posted here with a grain of salt.
| dahfizz wrote:
| I don't see a reason why the lithography method is necessary
| here. One could design a manufacturing process which ties the
| knots mechanically, just like woven fabrics.
|
| Caltech probably already has the lithography equipment and
| expertise on hand, so they did it that way. They aren't trying
| to do their research in a manufacturing-friendly way, just the
| way that is easiest for them.
| A_D_E_P_T wrote:
| Possibly lithography was used to avoid stress concentrations
| and kinking, which can potentially be troublesome in
| mechanically-tied knots. (Presumably, especially at that
| scale.)
|
| With respect to knotted and woven fabrics, there's quite a
| lot of interesting research in "3D-woven" fabrics for high-
| impact applications like body armor. 3D fabrics are pinned by
| fibers running through the weave top-to-bottom (Z axis) and
| are effectively macroscopically knotted. They're also
| commercially available:
|
| https://compositeenvisions.com/product/fiberglass-e-
| glass-3d...
|
| Interesting stuff, but still very niche and not always
| clearly superior to plain woven composite materials.
| Scene_Cast2 wrote:
| IIRC with 3D weaves, the ratio of strands to empty space
| (that would get filled with epoxy in typical rigid part
| applications) is significantly lower.
| blacksmith_tb wrote:
| That seems likely, though it does still seem like their results
| might fall into the "things behave differently at micro-scale
| and macro-scale" category. Normally we'd expect the (macro)
| knots we're familiar with to weaken -not strengthen - the cord
| or rope they're tied in (how much varies quite a bit with which
| knot we're talking about, but I don't know of any that don't
| have at least some negative impact). The little video almost
| implies the effect is similar to stretch, that the tangled
| version can't tighten up (with friction presumably absorbing
| some energy) like the knotted one does.
| Gravityloss wrote:
| Anybody who's worked with cables or ropes knows they
| spontaneously form knots quite easily. Would it be possible to
| utilize this property in manufacturing?
|
| Shake a bunch of dry fibers before applying the matrix? Are
| they too stiff?
| mjhay wrote:
| You're more-or-less describing nonwoven fabrics, which are
| used in a huge variety of applications. There's different
| fabrication methods, but they are typically not as strong as
| standard weaves since the patterning can't really be
| controlled.
|
| https://en.wikipedia.org/wiki/Nonwoven_fabric
| hannasanarion wrote:
| I believe nano-scale polymer materials composed of randomly
| formed knots are normally just called "plastic".
| bookofjoe wrote:
| https://news.ycombinator.com/item?id=35094074
| dukeofdoom wrote:
| So if you tie a knot on a rope, and pull on both ends to breaking
| point. Is the claim that the rope would not break at the knot.
| Not sure how true that is.
| regularfry wrote:
| No, that is not the claim.
| Out_of_Characte wrote:
| The rope would be a series of knots. Kind of like comparing the
| tensile strength of a scarf to synthetic wool strings (since
| regular wool is always knotted anyway.)
| nick123567 wrote:
| The title calling this a "material" is disingenuous. One would
| assume that they somehow tested a "bulk" material coupon even if
| just a few mm^2. But the image in the article shows them testing
| a single knot.
| nick123567 wrote:
| In the paper, shows a test of eight knots (two sets of four in
| series)
| BiteCode_dev wrote:
| Maybe the pressure the knots hold is enough to maintain rows of
| sections of the material in close enough range for the casimir
| effect to apply, making making some part of it flexible (the
| material) and some part of it super resistant (the quantum
| fluctuation zone) which ends up giving this property.
| t344344 wrote:
| Way too big for quantum stuff, it is just plain friction.
| BiteCode_dev wrote:
| Most probably, but throwing geckos at knots is more fun.
| bglazer wrote:
| The adhesion of the gecko's foot is caused by van der waals
| forces, not the Casimir effect, just fyi
| BiteCode_dev wrote:
| Thank you for correcting me.
| bqmjjx0kac wrote:
| It won't pass the IRB if you describe it like that.
| itronitron wrote:
| Is anyone able to reach this site? the server seems to be down
| boomboomsubban wrote:
| Works fine for me, but here https://archive.is/mwRR1
| harperlee wrote:
| Coincidentally I was looking into simulating rope and knots for a
| side project, and I don't know how to really research this other
| than googling, does someone interested in these kinds of things
| know? I'd like to simulate friction and tensile strenghs, and
| other mechanical deformations (pulls, obviously).
| bg46z wrote:
| You could probably look at protein folding libraries like
| pymol. Although not exactly the same, it's generally close
| enough to ropes and it has enough knobs where you should be
| able to run the simulations you want
| gilleain wrote:
| Hmmm. PyMol is molecular viewer, which has a python scripting
| interface to various libraries ... but is not a folding
| library I would say.
|
| There is some research into the topology of DNA (especially
| circular DNA, like plasmids which is a knot) that considers
| things like writhe and twist. Not sure it would adapt too
| well to macroscopic systems though.
|
| There is also the excellent KnotPlot for actually drawing the
| knots. I bought a licence once on a whim, but rarely use it
| :)
| AlotOfReading wrote:
| In general, the interesting properties of real ropes are not
| well-modeled by simulation. Dirt, abrasion, water, stress
| concentrations, and other real factors will dramatically impact
| the results you get out in the real world. That's why these
| things are experimentally verified and ropes used in safety-
| critical applications (are supposed to) have huge safety
| margins, regular monitoring, and ideally regular replacement.
| Use the manufacturer numbers for real ropes.
|
| But if you just want to simulate ropes, there's a few models
| out there from academics going "let's try and model this
| difficult system more accurately". Take a look at stuff like
| imc-der [0] and ridgerunner [1].
|
| [0] https://github.com/QuantuMope/imc-der
|
| [1] https://jasoncantarella.com/wordpress/software/ridgerunner/
| GistNoesis wrote:
| Maybe you can look into (extended) position based dynamics
| https://positionbaseddynamics.readthedocs.io/en/latest/about...
| for ropes.
|
| If knots are what's interest you more, then maybe you can have
| a look at the self-collision avoidance of "Repulsive Curves"
| http://www.cs.cmu.edu/~kmcrane/Projects/RepulsiveCurves/
| eimrine wrote:
| I know from fishing that if you have a spontaneous tie/knot on
| your 0,2mm line than it is dead but 0.4mm is almost always able
| to be unknot.
___________________________________________________________________
(page generated 2023-03-13 23:01 UTC)