Vehicle: Bicycle: Frame
Spidergoat Bicycle Frame   (+4, -2)  [vote for, against]
Strong and lightweight alternative bike frame construction

Riffing on [UnaBubba]'s burglarious spidergoat bike protector, I figure the material might be well employed for the construction of the bikes themselves.

Spider silk is incredibly light, it also has a higher tensile strength than steel.

Spider silk is traditionally difficult to utilise, spiders being difficult beasts to farm successfully.

Recent developments in goat technology have allowed us for the very first time, to produce spider silk on an industrial scale.

Carbon fibre reinforced plastics are very strong, and light, but tend towards being brittle, and expensive.

Spider Silk Reinforced Plastics should provide great strength, at a fraction of the weight, and be less brittle than CF.

I would prefer to do without the plastic altogether, but silk has a very high tensile strength, and not a lot of oomph in other directions (much like carbon fibre) so some rigidifying material is required, and until we can replace plastic, we're stuck with it.
-- zen_tom, Feb 05 2008

(?) Spidergoat Bicycle Theft Protection Spidergoat Bicycle Theft Protection
Inspiration [zen_tom, Feb 05 2008]

Fire up the goat, it's bicycle time. http://jrp.sagepub....t/abstract/25/4/339
Reinforcing Composites Using Waste Silk Fabric [Amos Kito, Feb 05 2008, last modified Feb 07 2008]

Whatever happened to Nexia? (PDF)
"Between 1993 and 2000, Nexia raised $67 million and went public . But by 2005, the Montreal-based firm had spent most of its cash and sold part [of] its business for shares in another speculative biotech outfit." [jutta, Feb 05 2008]

Artificial Spider Silk
I've used this stuff for fishing, and I seem to recall it was touted as artificial spider silk, although I cannot now find that tout, and they may just be using the name. [DrCurry, Feb 05 2008]

CarPool - Jon Ronson
It seems that "Men that stare at goats" may have something to add. All worth watching, but specifically around 11mins on [Dub, Mar 12 2010]

Genetically Engineered Silkworms Spin Like Spiders http://news.discove...html#mkcpgn=rssnws1
[Dub, Oct 14 2010]

Bullet-proof Spider's Web http://boingboing.n...letproof-flesh.html
"By implementing this bulletproof matrix of spider silk produced by transgenic goats in human skin I want to explore the social, political..." [Dub, Aug 24 2011]

Ted Talks: Cheryl Hayashi: The Magnificence of Spider Silk
R/T:6:28 - Cheryl Hayashi studies spider silk, one of nature's most high-performance materials. Each species of spider can make up to 7 very different kinds of silk. How do they do it? Hayashi explains at the DNA level -- then shows us how this super-strong, super-flexible material can inspire. [Dub, Dec 08 2011]

Tensioned bicycle frame
[pocmloc, Dec 08 2011]

A silk bicycle, spider silk or not - I'd go for that, if you could make it work!
-- DrCurry, Feb 05 2008

So this is a suggestion for a new material for a bike frame? Not really an invention then, is it? Especially since the material is not really available and might not work.
-- baconbrain, Feb 05 2008

bb: "not really available and might not work" - and in what way precisely does that make this unsuitable for the Halfbakery?
-- DrCurry, Feb 05 2008

// Recent developments in goat technology have allowed us for the very first time, to produce spider silk on an industrial scale.

I've heard this differently. These are not recent developments (they're about ten years old); they're not producing spider silk (instead, the company has refocused on nanofibers, away from textiles); and they're definitely not producing on an industrial scale.
-- jutta, Feb 05 2008

[DrC], good point, indeed. Which is why I put "not really available and might not work" second. But I do find it odd to be posting an idea based on something that is pretty much speculative. I'll accept that if the idea is good, though.

I do object to posting an obvious material suggestion as an idea. That seems to me to be a flavor, or make X bigger, kind of thing. I'm sure that if goat silk ever gets working, folks'll be putting it into everything from helmets to kayak paddles, without hinting from the HB.

My criteria for ideas includes deciding whether a posting here on the Halfbakery is needed to accomplish the desired objective--if this idea was not posted, would goat-silk bicycle frames still be made someday? Yep, provided goat silk ever becomes useful. (I'll waive that criterion for extreme foresight or cleverness, of course.)
-- baconbrain, Feb 05 2008

I thought that "they" haven't yet figured out how to turn the spider silk protein from the goats milk into usable strands of web.

I have CF, does that mean I'm brittle?
-- BJS, Feb 05 2008

//Spider Silk Reinforced Plastics//

This is based on a huge number of spectacular misconceptions.

First misconception: spider silk has remarkably high tensile strength for its weight. Not so. It's no better than quite a lot of commercial fibres, despite the popular myth.

Second misconception: bike-frame material needs a high tensile strength. Not so. What you need is a high specific Young's modulus (high stiffness per unit mass), and a tensile strength high enough to support it. Steel cables have high tensile strength but a very very low specific modulus in bending, so a frame of steel cables would just flop about. Brick has a decent modulus but an inadequate tensile strength, so a bike made of brick would snap. See following.

Third misconception: spider silk has a high specific modulus. Not so. Spider silk has a ludicrously low modulus - it not only bends easily (because it's thin) but it also stretches very easily, like rubber.

Fourth misconception: a spider-silk reinforced material would be a world- beater. Very, very not so. Suppose you reinforce a typical engineering plastic or resin with spiders silk. What sort of plastic will you go for. A fairly stiff one like fibreglass resin? Bad idea. As soon as it goes into bending, the spider silk will just stretch (by up to about 50%) with very little effort. All the load will be taken by the resin, which will snap. You might get some increase in the work of fracture overall, but the material will basically crumble around the spider silk. How about a less stiff plastic, like Delrin? Fine, but now the spider silk does no work whatsoever. When the Delrin gets into bending, the spider silk again just stretches; it's like trying to stiffen a lead pipe by filling it with rubber.

Basically, spider silk is not actually that amazing as a fibre. And, as a reinforcing material for anything rigid, it is spectacularly useless.

[-] for not thinking it through at all.
-- MaxwellBuchanan, Feb 05 2008

Hmmm, misconceptions accepted - I remember reading a William Gibson book set in San Fransisco, where the lead character rode a bike made of glass fibre wrapped around cardboard tubes.

It is an interesting conundrum, coming up with a method for using a fibre with a high tensile strength (albeit one that stretches) for something that requires a certain degree of rigidity - a composite material relying on plastic as the medium might not be ideal (is the brittleness of caron fibre-composites due to the plastic, or the carbon fibre?)And yes, perhaps goat-silk production isn't quite into industrial levels (anyone heard of industrial goat-production?) but it is (probably) better than yields from spider-farms.
-- zen_tom, Feb 05 2008

//It is an interesting conundrum, coming up with a method for using a fibre with a high tensile strength (albeit one that stretches) for something that requires a certain degree of rigidity//

The basic problem is this. Spider silk has a reasonably good tensile strength. However, its low modulus means that it only expoits that strength at very high amounts of stretch. Take a piece of thin string and a rubber band; both will have roughly similar tensile strengths (eg, they can both support say 30lb before breaking). But you have to stretch the rubber to twice its original length before it can manifest that strength. Likewise with spider silk. I really can't see any way of using it to make or contribute to a rigid structure.

The brittleness of carbon fibre composite has several causes. One is the fact that both the fibres and the matrix are brittle (ie, have a low work of fracture), but then so do both components of fibreglass. The other problem is that carbon fibre composite attains high stiffness by having a high density of the very stiff fibres bonded very securely to the matrix. Because of this, stresses at the tip of a crack are transmitted easily from the matrix to the fibres. This means that a crack can just run across the whole structure as if it were a continuum.

In contrast, fibreglass is tough because the bond between the fibres and the matrix is very weak. Whenever a crack encounters a glass fibre, it is much easier for it to spread along the interface than to cross the fibre, so the crack gets diverted and dissipated. That's why fibreglass goes white when damaged: the energy of the impact has gone into opening thousands of little gaps between the fibres and the matrix, and these gaps scatter the light.
-- MaxwellBuchanan, Feb 05 2008

// I really can't see any way of using it to make or contribute to a rigid structure.//

Just exploring the concept - but what if the silk were stretched prior to its inclusion into the supporting medium? I'm imagining winding taught silk around a subframe, hundreds and thousands of times around - prior or at the same time as a coating of hardening material is applied. It would have to be wound non linearly, so that each strand ran both around, and along the overall frame - the issue being that no matter how strong the stuff is under tensile strain, compressive forces would be wholly born by the hardening material.

Which comes back to the question - how do you build a frame like that using only a material that functions under tension i.e. would it be possible to build a bike frame that might function, stress-wise in an analogous way as a suspension bridge?
-- zen_tom, Feb 06 2008

[zen] you might try looking up "tensegrity". But no, you can't make a bike frame out of only tension elements. The basic function of a standard frame is to hold a big weight (one's body) up above two supports (the wheel hubs). The "above" part of that requires some compression somewhere.

You might be able to make a damn big wheel, using goat silk for the spokes, and make a goat-silk hammock to suspend yourself under the hub. That'd have only the rim and the hub made of compression material. Of course, a giant inflated tire could be made without a rigid rim . . . which leads to the generic answer to your question: inflatables.

A balloon has only tension in its solid materials. The compression is supplied by the air inside. So make an inflatable bike out of spidergoat, and there you are.
-- baconbrain, Feb 06 2008

"This 'ol gal's as sure footed as a mountain goat"
-- marklar, Feb 06 2008

//but what if the silk were stretched prior to its inclusion// I think another problem with silk is that it 'creeps' under tension, rather like wood, so your pre-stressing would eventually be dissipated.
-- MaxwellBuchanan, Feb 06 2008

//So make an inflatable bike out of spidergoat, and there you are.// Genius solution! I hereby incorporate this into the idea.
-- zen_tom, Feb 06 2008

{Wonders if there's a suitable catalyst that can added to goat's milk, to extract the fat and calcium, and form silk-like protein molecules. Sips another mouthful of milk and dribbles...}
-- Dub, Feb 08 2008

I suspect that pre-stressing the tensile fibres (if it could be done precisely and optimally) would be a good thing, by analogy with pre-stressed steel in concrete.

As well as creep (mentioned by [MB]), I suspect that the low modulus would still be a problem; the moduli of the matrix and the fibre need to be well matched for the fibre to do its job properly, regardless of the initial stress.
-- spidermother, Dec 08 2011

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