--- Erik Reuter <[EMAIL PROTECTED]> wrote: > Deborah Harrell wrote: > > > Having read somewhere that "spider silk has > greater tensile strength > > than steel" .... It seems that....while still not >understood, [the structure] involves sheets of > 'stiff' alanine chains > > coupled with more flexible/elastic protein > sequences, twined together > > in different ways for different types/uses of the > silk. It is > > comparable to Kevlar (one article said 'tougher'), > but much lighter. <snip> > > So, could the structure and properties of dragline > silk be helpful in > > the design of carbon nanotubules for a space > elevator? (Of course, I'm > > guessing you wouldn't want it to be that elastic, > but the structure is intriguing...) > > I don't really know enough about practical building > considerations > to answer your question, but I think it is an > interesting subject. I > just did some reading, and I mostly found that it is > a much more > complex subject than I initially thought. Especially > when you get > away from basic materials properties and start > looking at weaves and > composite materials .... Anyway, here are > a few observations. > > Spider silk is much more rubbery than kevlar. Silk > can stretch by 30% to > 40% before it breaks. Steel can stretch, too, but > most steel structures > are designed to operate safely below the "yield > point" which is where > the steel starts to get very plastic. In the links > below, note how > steel has very low strain (little elongation) up to > a well-defined > yield-point where it starts to stretch, whereas silk > does not have a > well-defined yield point and it follows a "smoother" > elongation curve until it breaks. > http://www.umeciv.maine.edu/cie111/tension/default.htm http://www.nature.com/nature/journal/v410/n6828/box/410541a0_bx1.html <snip> > >"...Thus Kevlar is 3 times stronger but spider silk is > 5 times tougher > because it is 8 times more extendible" > > The article I posted before quotes 60 GPa as the > necessary number for > a space elevator. So spider silk by itself is much > too weak. But as a > component in a composite? Maybe it could be helpful, > I don't know.
I was thinking more of the structure, rather than the actual silk; I'm going to guess that dragline silk, being a protein polymer, would be damaged by the conditions of space/vacuum, unless it was sealed off from the outside. Researchers at MIT are working on creating artificial polymers based on what we currently understand about spider silk structure: http://www.utdallas.edu/research/friday_fyi/030425/internews.htm (second story segment of this newsletter) "...James-Korley's work focuses on the soft segment of spider silk. It has been suggested that this soft part has two different regions, one of which is slightly harder than the other because the polymer fibers are partially aligned. If this idea is correct, spider silk actually has three different phases: hard, soft and intermediate. The hard segments anchor the partially aligned regions, holding them in place in a matrix of soft material... "Pollock is studying a different structural element-the interface between the crystallites in spider silk and the soft region around them. How the interfacial material slides past the crystallites without pulling away from them may hold the key to spider silk's toughness..." > Obviously, when you are designing a structure like > this, you want to > build in a safety factor so that the worst stress > that you expect to be > applied is say, 40% lower than that which will break > the structure. With > steel, this is relatively easy to design since the > steel has a > well-defined yield point, and as long as you stay > below that, the > steel has virtually no permanent deformation, so you > can count on your > structure staying the same size and shape. But if > there is an impact, > with a short but very high stress applied, the steel > may break. > > With something like spider silk, which stretches > better, it may be > possible to handle a very short but extreme stress > better than steel > (toughness). On the other hand, it looks like a very > challenging design > problem....Would > the space elevator wiggle back and forth like an > anemone? It may be > possible to design a space elevator with a rubbery > material, but I think > it makes for a very complex design that would > require decades of study > and testing to fully understand the implications. > Here are a couple > links that only begin to get into some of the > complexities. > > http://fiberarchitects.com/reading/rebars.html > http://calcul.com/ian/thesis/node47.html <grin> Now I'm envisioning "robot spiders" that are programmed to run up and down the space elevator cable, checking for strain/weakness, and having the capability of extruding an elastic 'patch' material that will hold the cable together until more definitve repairs can be made... <serious> However, some think that actual spidersilk might make a good protective layer inside spacecraft: http://www.space.com/businesstechnology/technology/debris_protection_020710-1.html "...What that means for mission planners, Kaufmann said, is that while in tight astronaut suits BioSteel [the Nexia GM silk] wouldn't afford much protection. It might be great as a layer inside the space station walls -- it's too heat-sensitive for the exterior -- because there's enough room for a skin of it to stretch a bit on impact. However, like nanotubes, no one has produced BioSteel in sufficient quantity to seriously consider it for near-term projects...." >From a lecture by a spider specialist for NASA: http://www.gse.rutgers.edu/announce/catley.htm "...Spider silk, he told the NASA audience, has a tenacity slightly less than nylon but is twice as elastic, with a tensile strength superior to rubber or bone. "It has to be 40 miles long before it breaks under its own weight," he reports. And spiders work swiftly. Their light, translucent webs can be woven in less than half an hour in zero gravity. " "Spiders have been around for more than 350 million years and if they haven't gotten it right by now, presumably they never will," he quips. "If you really want to learn how to build an incredibly light structure that's also incredibly strong, then this is an excellent place to start the research." " As Catley discoursed on optical properties, molecular structure, adhesive features and web architecture during the three-day workshop held in Oxnard, Calif., he made it clear just how complicated it will be for scientists to synthesize spider silk. "What you guys have been asked to do in a few generations, spiders have been doing for a long, long time," Catley told the space experts..." (The rest of this article is mostly about the researcher's project to find new spiders and engage school children in the search.) So it looks like 'artificial spider silk' by itself would be too elastic for a space elevator cable, but as part of a *composite* cable it might be a safety factor...? Debbi I Still Like My 'Spider Robots In Space' Maru :) __________________________________ Do you Yahoo!? SBC Yahoo! 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