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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.

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.

>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/DuctileF...

Then the ideal armor must be sea snail teeth woven together with spider silk. This advancement could save millions in mythril and adamantine.

Finally the Druids get a viable endgame armour set!

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).

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.

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.

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.

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".

Water being mostly incompressible is not the same as having high compressive strength. Liquid water makes for a poor tooth or structural column.

That's my point; think about it deeply.

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?

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.

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

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...

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)

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

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.

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.

Very hard to force it to failure into permanent changes in shape.

so we need both to build a space elevator?

Strength per weight vs strength per volume are an issue as well.

It's tensile strength, not specific strength. Strength over an area.

There also is no such thing as strength per volume.

Doesn't surprise me in the slightest - Have you ever tried grabbing one of those things off a rock>!?

They don't hold on with their teeth, they use their foot.

Ten years ago.

Has there been any progress since then?

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

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.

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.

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

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

Apparently comparing snail shell size to airplane size will be much more common. "This one is the size of Snailbus 42".

Dentist: I already found 5 cavities.

They constantly grow new teeth so thats not a big deal.

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If you're going to post ChatGPT output then at least bother to click on the links. If people wanted ChatGPT output, especially uncurated output, then they'd just go to ChatGPT themselves.

I know you have not clicked on the links as the article that "reports tensile strengths up to ∼4.9 GPa" is just referencing the original article from 2015 to get that number.

The iron snail, Chrysomallon, inhabits undersea volcanic vents. It sticks to magnets. When probed with a diamond tip indentation test, it doesn't indent.

Wait! Are we talking about strength or hardness?

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.

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...

I believe they're comparing the tensile strength of the fibers of the tooth.

Though the pop article is light on details.