What Makes Spider Webs Tough As Steel

sciencehabit writes "A new analysis reveals the intricacies of spider web design, showing how the unique properties of its silk turn webs into flexible yet strong traps. Computer simulations reveal that heavy forces spread over the entire net rather than stay local. Real spider silk can be either stretchy or stiff at different times, which produces threads that flex and then snap in just the right way to avoid wrecking nearby spokes."

Comments

Diamond

[Anonymous Coward]

I think all this research is just skirting around the "real" material engineering question: What makes diamonds the hardest metal?

Re:Diamond

[Anonymous Coward]

... the hardest metal?

/facepalm

Re:Diamond

[sadness203]

They already know that.... And there's other stuff harder than diamond too. Wurtzite boron nitride and the mineral lonsdaleite come to mind.

Re:Diamond

[Yaotzin]

I always thought Dragonforce was the hardest metal known to man.

Re:Diamond

[Anonymous Coward]

chemistry is hard

Re:Diamond

[CSMoran]

Diamonds are made of carbon and carbon is not metal under usual conditions.

FTFY

Re:Diamond

[Anonymous Coward]

Okay, okay -- if you're going to be that picky: One of the hardest metals.

Re:Diamond

[silentcoder]

http://www.diamondedgeband.com/

See, it's rock not metal :P

Re:Diamond

[silentcoder]

>Diamonds are made of carbon and carbon is not metal under usual conditions.

Metals are a specific set of elements. They have a specific set of properties caused by the way their atoms combine with themselves and each other. This allows them to form unique types of compounds we call "alloys", to be highly effective energy conductors (notably electricity and heat), and causes them to shine (yes, being shiny is an attribute of metals). Many other substances (both elements and compounds) share some of these attributes under certain conditions (for example - glass is shiny) but only metals have them all because the combination derives from the unique lattice structures that metal atoms form.

In essence metals are those elements that don't form molecules at all (at least, not the way anything else does). Metals arrange their nuclei in intricate lattices with electrons flowing through these and capable of passing from one atom to the next. All those macroscopic identifiable properties I mentioned are caused by this structure. When metals combine with each other they merge their lattices and form alloys rather than compounds. When metals combine with non-metals they form "traditional" molecular compounds (Sodium is a metal, Chlorine is not - when they combine they don't form an alloy they form salt).
Another attribute of metals is that because of their electron structure they are always reactive to acids and all acid+metal reactions have the same result. The hydrogen in the acid gets replaced with the metal, releasing the hydrogren as a gas and forming a salt.

So erm... under what possible conditions can carbon ever change it's atomic structure and chemical behavior to become a metal ? Short of nuclear transmutation - in which case the result is NOT carbon.

Please, do explain as I would love to know.

Re:Diamond

[CSMoran]

So erm... under what possible conditions can carbon ever change it's atomic structure and chemical behavior to become a metal ? Short of nuclear transmutation - in which case the result is NOT carbon. Please, do explain as I would love to know.

Sure thing.

First, let's go beyond your high-school level description of what a metal is. There is no "specific set of elements" that are metallic. Rather, a metal is something that, owing to delocalized electrons, has no band gap at the Fermi level and thus is a good conductor of electricity and heat. This can be achieved in many elements, not necessarily those that are typically thought of as metals, by using fancy conditions, such as extreme pressures and/or temperatures.

Take, for instance, this report on metallic carbon in Phys. Rev. Lett: http://prl.aps.org/abstract/PRL/v102/i5/e055703
or the infamous metallic hydrogen, http://lt26.iphy.ac.cn/abstract/pdf/B1488.pdf

Re:Diamond

[decsnake]

hmm... I'm not a chemist, but last time I checked steel (an alloy of iron and carbon) was a metal, which seems to contradict pretty much all of what you wrote.

Spiders have always fascinated me

[Tastecicles]

I've lost count of the number of times I've sat there and just watched a spider start building a web at 4am, finishing at around 10, and just marvelling at the insane complexity and beauty of the thing.

Re:Spiders have always fascinated me

[stuckinarut]

Were the spiders on drugs too?

Re:Spiders have always fascinated me

[jones_supa]

Spider using a feature of gate to build its web around

Re:I for one

[Securityemo]

You apparently can use spider silk for cloth if you really try hard enough. (Warning: NSF arachnophobes.)

Cheryl Hayashi at Ted Talk

[Anonymous Coward]

http://www.ted.com/talks/cheryl_hayashi_the_magnificence_of_spider_silk.html

Smack yourself with steel and then a spider web

[mtm_king]

I call bullshit on the heading "Spider Webs Tough As Steel". I have hit my head on spider webs and on steel. I am absolutely sure that spider webs are not anywhere near as tough as steel. Thank you, good night.

Re:Smack yourself with steel and then a spider web

[BasilBrush]

Steel is really soft. They make wool out of it.

Re:Smack yourself with steel and then a spider web

[geminidomino]

When was the last time you "hit your head" on a thread of steel 0.15mm in diameter?

Re:Smack yourself with steel and then a spider web

[mtm_king]

Good point. But back at you.... When is the last time you "hit your head" on a 1/4 inch plate of spider web.

Re:Smack yourself with steel and then a spider web

[Zinho]

You're confusing hardness, strength, and toughness; it's easy to do, considering that laymen use these terms loosely and interchangeably. The researchers in the article were almost certainly using the technical definitions, which are roughly as follows:

Hardness is a measure of how well a material resists deformation. Typical hardness tests involve things like seeing what it will scratch/what scratches it (Mohs scale) or how deeply a probe will dent it under a given load (Rockwell scale). It's used as an indication of wear resistance, and steels used for cutting tools or stamping dies often have high hardness.

Strength is a measure of how much stress (force divided by cross sectional area) is required to permanently deform (yield strength) or break (ultimate strength) a sample of the material. Strength is widely used in engineering design to make sure there is enough material (cross sectional area) to safely handle a given load (force).

Toughness is the energy required to break a sample of the material. This can be found by integrating the area under the stress/strain curve of a tensile test (work = force x distance) or measured directly with purpose-built tools (Izod or Charpy impact test).

Hardness is correlated with strength, and can be used as a non-destructive estimate of strength for finished parts. In contrast, the toughness of samples with the same strength will vary depending on the brittleness of the samples. Ductile samples will stretch a large amount (high strain) before failing and so will have higher toughness than brittle materials of equal strength which won't stretch as far (low strain) before failing.

Given those definitions it's easy to see that even if spider silk had lower strength than steel it could easily have the same or higher toughness if it can stretch far enough. Since spider silk is actually comparable in strength to premium steels and has much better elongation before failure (stretches to 4x original length) I'd expect its toughness to be much higher than steel.

Which I'd rather be smacked in the head with is an entirely different question, that has to to with suitability as a weapon. The steel bar is likely to be denser (therefore heavier) and stiffer than a same-size block of spider silk, so it would probably do more damage to my head at equal speeds. I don't know how the spider silk would do for hardness in bulk, but with better toughness it would likely take more of a beating while keeping its original shape; on the other hand a well-used steel pipe would probably work better as a threat than a new-looking spider silk baton. On the gripping hand, a blackjack made with spider silk would be pretty cool, and I definitely wouldn't want to get hit with one. Pick your poison, I guess.

Skin?

[aaronb1138]

Not to deny the amazing properties of spider silk, but the article mentions, "In fact, such self-sacrificing by a unit is highly unusual among natural materials, Buehler notes."

I find this highly inconsistent with biology in general. In the human body, one such system we call skin. As a specific example, callouses are groupings of skin cells which die and harden to protect areas of the hands and feet frequently engaged by stresses, such as shoes and using hand tools (normally skin sloughs off). Continuing just with skin, note the way that even when cleaved, skin puts significant friction against the object cleaving (watch a piercing in slow motion some time). To overcome this, physicians are taught to cut along skin grains, which also reduces scarring.

Other sacrificial organic materials, well tree bark is frequently harder than the material inside. Hair on various animals prevents predators from getting a firm grip. Salamander tails come off once a tension threshold is crossed. Cell membranes flex, usually right up to the point contents would be damaged by the intrusion anyway. Cell walls work like bricks, giving plants firm structure, and making them difficult if not impossible to slice up for electron microscopy (not sure if that barrier has been crossed). Trees and plants lose branches in the wind and tumbleweed completely detaches from its roots. Fruit has skins just strong enough to prevent spoiling several days before being eaten by animals, thus spreading seeds. Seeds and nuts have cleavage lines to make them strong, but allow the bud to break out.

There are many other examples, but functional, purpose built tissues and substances in organic materials are very common.

What Makes Spider Webs Tough As Steel

[Anonymous Coward]

Spiders.

Next!

Only on slashdot!

[mcgrew]

Will you have a serious discussion of chemistry, metalurgy, and physics in response to a joke! And maybe even learn something.

Re:Skin? Context is important.

[b4dc0d3r]

"Natural materials" and "tissues and organic materials" seem to be different things. Going by dictionary meanings might lead you in one direction, but the context of the quote suggests Ferris was not talking about "anything [natural] made of matter."

I wouldn't consider a salamander tail to be a "natural material", nor would I consider skin nor cells nor plants as a whole. You could maybe make an argument for bark and hemp fiber, but I think that still qualifies as "highly unusual among natural materials."