[HN Gopher] Sea snail teeth top Kevlar, titanium as strongest ma...
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Sea snail teeth top Kevlar, titanium as strongest material (2015)
Author : thunderbong
Score : 117 points
Date : 2025-05-02 16:16 UTC (4 days ago)
(HTM) web link (www.cbc.ca)
(TXT) w3m dump (www.cbc.ca)
| gweinberg wrote:
| Materials that are strong under compression aren't necessarily
| strong under tension, and vice-versa. I would think teeth (just)
| need to be really strong under compression, and spider silk
| really strong under tension.
| potato3732842 wrote:
| Strength per weight vs strength per volume are an issue as
| well.
| hwillis wrote:
| It's tensile strength, not specific strength. Strength over
| an area.
|
| There also is no such thing as strength per volume.
| e28eta wrote:
| I was curious about what they meant by strength, and the link
| at the bottom of the article says this is tensile strength. So
| the comparison to spider silk was actually appropriate.
|
| I also noticed that it's from 2015, although it was still new
| to me and interesting.
| prmph wrote:
| To be fair tensile strength is more impressive and to me is the
| only true strength. Water has great compressive strength, and
| yet is it difficult to think of it as "strong".
| sk5t wrote:
| Water being mostly incompressible is not the same as having
| high compressive strength. Liquid water makes for a poor
| tooth or structural column.
| prmph wrote:
| That's my point; think about it deeply.
| jmillikin wrote:
| You wrote "water has great compressive strength", sk5t
| directly (and correctly) refuted that claim. What is
| there to think about?
|
| Are you confusing "compressive strength" with
| compressibility?
| stormfather wrote:
| I think his point is that things very rarely experience
| purely compressive forces. Just being compressed induces
| tension in other directions, like water being squished
| out between your clapping hands. So even though water has
| great compressive strength, in practice this isn't very
| useful.
| prmph wrote:
| Exactly.
|
| Many materials would have compressive strength easily,
| just by being relatively uncompressible.
|
| But most loads have a (troublesome) tensile component.
| Fundamentally, the ability of a rigid material to resist
| deformation (in the most general sense) is what is most
| important, and that requires tensile strength.
|
| See this comment elsewhere in this sub-thread that
| explains it probably better than I did:
| https://news.ycombinator.com/item?id=43904800
| prmph wrote:
| Look up the Wikipedia definition [1] of compressive
| strength:
|
| > In mechanics, compressive strength (or compression
| strength) is the capacity of a material or structure to
| withstand loads tending to reduce size (compression). It
| is opposed to tensile strength which withstands loads
| tending to elongate, resisting tension (being pulled
| apart).
|
| Google search AI summary states:
|
| > Compressive strength is a material's capacity to resist
| forces that try to reduce its volume or cause
| deformation.
|
| To be fair, compressive strength is a complex measure.
| Compressibility is only one aspect of it. See this
| Encyclopedia Britannica article [2] about how compressive
| strength is tested.
|
| [1] https://en.wikipedia.org/wiki/Compressive_strength
|
| [2] https://www.britannica.com/technology/compressive-
| strength-t...
| brennanpeterson wrote:
| Please tell me how to make a water prism to test
| compressive strength and deformation resistance. Water is
| an incompressible fluid, that is different.
|
| These are well understood terms in the field.
| Unfortunately, this illustrates the bounds of ai in
| subfields like materials: it confuses people.
| prmph wrote:
| I'm not saying water meets the strict definition of a
| material with high compressive strength (it does meet
| some, since it resists forces that attempt to decrease
| its volume well). I am just using as an extreme example
| of the issues with the concept of compressive strength.
| thatcat wrote:
| lower the temperature
| jmillikin wrote:
| Nothing that you wrote here indicates you understand what
| is being discussed.
|
| Water has very low compressive strength, so low that it
| freely deforms under its own weight. You can observe this
| by pouring some water onto a table. This behavior is
| distinct from materials with high compressive strength,
| such as wood or steel.
|
| (I say "very low" instead of "zero" because surface
| tension could be considered a type of compressive
| strength at small scales, such as a single drop of water
| on a hydrophobic surface)
| prmph wrote:
| Your comments betrays a lack of comprehension and
| understanding. Please reads my comments and linked
| definitions carefully.
|
| See this comment elsewhere in this sub-thread that
| explains it probably better than I did:
| https://news.ycombinator.com/item?id=43904800
| cma wrote:
| Very hard to force it to failure into permanent changes
| in shape.
| blitzar wrote:
| It is useless until you are in a movie gun fight next to a
| pool / river. At that point jumping into the water is both
| life saving and cinematic with turbulent bullet trails
| follwing you in the water but falling just short of you.
| hwillis wrote:
| https://royalsocietypublishing.org/doi/10.1098/rsif.2014.132...
|
| > The tensile strength of discrete volumes of limpet tooth
| material measured using in situ atomic force microscopy was
| found to range from 3.0 to 6.5 GPa
|
| Also "compressive strength" is not really a thing, in that it's
| only a metric that is useful for practical applications. It's
| proportional to tensile strength, and unlike tensile strength
| it does not generalize well to things like modeling stress.
| Tensile strength is a much more fundamental quality than
| compressive strength.
|
| Strength of a material is force per area. In ideal terms it is
| measured over an infinitely short length; if you measure over a
| long distance then the sample is stretched and becomes thinner,
| changing the measurement. If you test on a shorter and shorter
| sample you get closer and closer to the ideal value.
|
| The same is not true for compressive strength tests. If you
| measure compressive strength by pressing on a very very thin
| disc of material it will just resist all force; it has
| effectively infinite strength. The actual failure mode of
| compression is always tensile strength in the radial direction,
| or buckling or something. You press the sample and it stretches
| sideways until it exceeds the sample's tensile strength in that
| direction. The shorter the sample is, the less it can expand
| radially and the stronger it appears to be. There is no "ideal"
| compressive strength, only useful test setups.
| hydrogen7800 wrote:
| >Also "compressive strength" is not really a thing.
|
| This is true, but neither is "tensile strength" really a
| thing for the same reason. A simple uni-axial tensile test is
| not really uni-axial, but a combination of orthogonal normal
| stresses that ultimately results in shear failure. I've heard
| it said that "all failure is shear failure", and I think
| that's true. When you look closely at the ductile fracture
| surface of a ruptured tensile specimen, the characteristic
| "cupping"[0] appearance consists of various surfaces at 45
| degrees from the direction of the applied load. Principle
| shear stresses are always oriented 45 degrees from the
| principle normal stresses.
|
| [0]https://upload.wikimedia.org/wikipedia/commons/1/1b/Ductil
| eF...
| hwillis wrote:
| > This is true, but neither is "tensile strength" really a
| thing for the same reason.
|
| Well, not the _same_ reason. Shear strength is in many ways
| more _important_ because failure usually propagates from an
| origin like a rip- by shearing.
|
| But fundamentally, tensile strength and shear strength are
| both much more empirical than compressive strength. Tensile
| strength can be used with ~99% accuracy on a wire that is
| microns long or miles long. If you double the relative
| width of a testing sample it will dramatically change the
| measured compressive strength even without buckling.
| throw7383753 wrote:
| You could take that further and say that shear does not
| exist. It's a construct we have created to deal with
| tension failures in other planes. Everything basically
| comes down to a truss model. The failure you idealize as a
| shear stress is really a failure of a tension element in a
| miniature truss. This is true in bolt shear, scissors, etc.
|
| This is why the code forces you to use strut and tie model
| deep concrete beams. As much as you may want to idealize a
| shear stress, really what's happening is the beam is
| arching over the span.
| hydrogen7800 wrote:
| Ha, yes! I've even heard some argue that stress isn't
| even real! Whatever "real" means. Nothing is real; it's
| models all the way down.
| rda2 wrote:
| For those who are interested in learning more:
|
| "All failure is shear failure" - this is a simple
| explanation of Tresca's Yield Criterion. For materials with
| higher compressive than tensile strength, the equivalent is
| the Mohr-Coulomb failure criterion.
|
| https://en.wikipedia.org/wiki/Material_failure_theory
| kurthr wrote:
| For a simple example try twisting a ductile aluminum bolt
| (or clay), twisting a brittle piece of chalk (or
| concrete), or twisting a composite (twig). They all fail
| differently (and the first two at 45deg to each other.
| Mohr's circle is interesting, and fatigue failure more
| interesting still.
|
| https://youtu.be/1YTKedLQOa0?t=533
| adrian_b wrote:
| The "infinite" compressive strength for a sample that cannot
| expand laterally is only an approximation valid for small
| pressures.
|
| At high enough pressures, all materials change their
| molecular and crystalline structures into structures with
| higher densities of atoms per volume and the volume of the
| tested samples diminishes, so the samples collapse at certain
| pressure thresholds.
|
| The well known transformation of graphite into diamond is
| just an example of what happens with any substance at high
| pressures. Diamond is a more unusual example just because it
| remains stable even after the pressure that has created it is
| removed.
|
| Moreover, for non-homogeneous materials, like concrete or
| many natural rocks used in construction, which are composed
| of harder particles cemented in a weaker matrix, it is normal
| to have a tensile strength that is many times smaller than
| the compressive strength, because when subjected to tension
| the weaker matrix allows pieces to detach, but in compression
| the strength may be determined mostly by the threshold where
| the harder particles break.
|
| The snail teeth are also made of composite materials, mineral
| crystals in a protein matrix, so they are also likely to have
| different strengths depending on what kind of stresses are
| applied and in what directions.
| throwawee wrote:
| Then the ideal armor must be sea snail teeth woven together
| with spider silk. This advancement could save millions in
| mythril and adamantine.
| AndrewOMartin wrote:
| Finally the Druids get a viable endgame armour set!
| VladVladikoff wrote:
| If you're into this kind of fantasy bioengineering I highly
| recommend reading The Tainted Cup and the sequel, A Drop of
| Corruption. And if anyone has read these, please tell me
| about any other books in this similar bioengineering genre,
| or even just highly unique fantasy worlds (I'm just so sick
| of books about dragons and boring magic).
| yreg wrote:
| Tress of the Emerald Sea is set on quite a unique world.
| The planet is covered by oceans of magical "spores" which
| react violently to water.
|
| For example the spores in the Emerald Sea, where the hero
| is from, instantly grow into massive vines that destroy
| everything in their path. That makes sailing rather
| dangerous.
|
| The story is whimsical, perhaps an adult fairy tale (or
| just a fairy tale?), so I don't know if it fits your taste.
| dekhn wrote:
| A long time ago, Harry Harrison wrote a series
| (https://en.wikipedia.org/wiki/West_of_Eden) where
| dinosaurs weren't wiped out, evolving for millions of years
| before primates showed up. The dinosaurs have a genetic-
| engineering based industry.
| doorpheus wrote:
| Try the children of time it's a great scifi book about a
| spider civilization evolving with all the different tech
| they create
| georgeecollins wrote:
| I second the recommendation of Children of Time! A
| cracking fun novel that goes in some weird directions.
| Very well realized "aliens" that have their own culture
| and technology.
| foobarbecue wrote:
| You might like some of the Paolo Bacigalupi windup world
| stuff. Some great belivable ideas, some that go too far
| beyond belivability for my taste, but I enjoyed it a lot.
| The basic idea is that there's an advanced society where
| for some reason electricity & electronics tech was never
| developed, so mechanical mechanism technology progressed
| instead.
| ozim wrote:
| But how much time to grind is needed and is there close by
| spawn point for sea snails and spiders or do you have to
| first get loot from snails and then travel to farm spiders.
|
| So many questions and quests.
| lawlessone wrote:
| so we need both to build a space elevator?
| andrewinardeer wrote:
| Ten years ago.
|
| Has there been any progress since then?
| Ancalagon wrote:
| A startup has since been founded to commercially farm limpet
| teeth for use in aircraft.
|
| First viable airplane shell is anticipated to hit the market in
| 2250.
|
| /s
| yetihehe wrote:
| Apparently comparing snail shell size to airplane size will
| be much more common. "This one is the size of Snailbus 42".
| blitzar wrote:
| They pivoted to Ai back in '24.
| 0x38B wrote:
| From a 2022 study in Nature (1) where researchers grew limpet
| teeth:
|
| "The proof-of-concept presented in this study can be scaled up
| using made-to-measure chitin sheets and synthetic substitutes
| for limpet cell-conditioned media. Given that chitin is
| currently a waste by-product of the fishing industry44, our
| approach would allow its repurposing into a novel composite
| material that could substitute for many existing synthetic
| materials that are manufactured in a polluting or unsustainable
| manner, and could help solve environmental challenges such as
| the ocean plastics crisis. Furthermore, as chitin is itself
| biodegradable, this bioinspired composite meets the key modern
| engineering challenge of sustainability. In short, this new
| material has the potential to be manufactured and disposed of
| without generating harmful waste products."
|
| 1: https://www.nature.com/articles/s41467-022-31139-0
| GrantMoyer wrote:
| The Nature article's motivation seems not very well thought
| out to me, considering the fishing industry is among the most
| unsustainsbly and polluting industries on earth. It's even an
| especially large source of ocean plastics.
| gibspaulding wrote:
| Positing that your research could contribute to
| sustainability/DEI/etc. is sort of the researchers
| equivalent of describing the pile of if statements in your
| software product as AI. Meaningless but largely harmless
| box checking to make sure that someone who might give you
| money doesn't decline to give you money because someone
| else did a better job of looking trendy. That's not to say
| the research isn't useful; you've just finished reading the
| interesting part of the abstract. If this were a resume,
| this would be the obligatory "proficient in Microsoft
| Office" item.
| lazide wrote:
| Used to be, anyway. Now it's a sure fire way to not get
| any gov't funding in the US anyway. It's going to be
| interesting to see how it all shakes out.
| gibspaulding wrote:
| Yeah, I wasn't going to get into the current politics
| around it but that's actually what made me think of this.
|
| https://www.astralcodexten.com/p/only-about-40-of-the-
| cruz-w...
| zardo wrote:
| You list a tenous military application instead.
| lm28469 wrote:
| It's coming right after the new batteries that last 100x longer
| that we discovered in 1999, and the full self driving teslas
| coming in 2014
| coolThingsFirst wrote:
| Dentist: I already found 5 cavities.
| s0rce wrote:
| They constantly grow new teeth so thats not a big deal.
| AdrianB1 wrote:
| The comparison with kevlar and titanium is weird, as they don't
| compete in the same category of strength and they are not the
| strongest in their categories. "I heard kevlar is used in flak
| vests, so it must be strong" is not a scientific argument.
| theultdev wrote:
| I believe they're comparing the tensile strength of the fibers
| of the tooth.
|
| Though the pop article is light on details.
| hwillis wrote:
| Kevlar is an appropriate comparison- it has one of the highest
| tensile strengths known. It is not just lightweight and tough,
| it is also extremely strong in absolute terms. The strongest
| kevlar is somewhere between as strong as this material and half
| as strong.
|
| Titanium is a pretty bad comparison. Its 10-20x weaker, and is
| also weaker than fiberglass, nylon, most steels, sapphire, many
| other types of metals and fibers...
| CRANQonX wrote:
| Doesn't surprise me in the slightest - Have you ever tried
| grabbing one of those things off a rock>!?
| s0rce wrote:
| They don't hold on with their teeth, they use their foot.
| CGMthrowaway wrote:
| The strength quality of the mineral in question, goethite, is
| only good at nano scale (400-800nm). If the mineral fibers get
| bigger they are not as strong. Thus presents one of the
| challenges in replicating this for human use
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