Date: Wed, 2 Nov 1994 03:11:24 -1000 From: vdhamer@prl.philips.nl Message-Id: <9411021311.AA16887@isthp2.prl.philips.nl> Organization: Division of Applied Sciences, Harvard University Subject: Dyneema info - 2nd edition This is an edited version of my earlier posting: I read my previous mail out over the phone to the DSM friend, and got some corrections and new info (areas are marked with a ">"). ------------------------------------------------------ I spoke to a chemical engineer from DSM in the weekend. He is an old school pal, and certainly not a marketing type. Some pieces of info I got from him on Dyneema (for the trivia fans; probably not of much practical use): *>Dyneema floats, Keflar (=Twaron=aramide) doesn't. This is relevant for salvage work because a very long cable of Keflar or steel breaks under its own weight. In principal you can use Dyneema for salvage operations at 10 km depth. * Dyneema is based on research work by a Dutch university (Groningen). The work and ensuing DSM patents are about how to make the stuff: the basic idea that long strands of polyethyleen are strong was previously known. The real problem was how to create very long chains with few defects and how to allign them in the direction of the fibre. * Spectra is from Allied Chemicals and was developed after the Dyneema patent. >Spectra is chemically and physically the same as Dyneema (although the molecular weight might differ somewhat): Allied Chemicals produces Spectra under some sort of licence agreement with DSM. * Dyneema is primarily used in anti-ballistic applications. There has been a recent major contract for the stuff for fibre-reinforced army helmets. More well-known applications are bullet-proof vests. *>A DSM brochure lists sports aplications as the second use of Dyneema and mentions sailing and kite flying. It is thus an educated guess that the kiting use of Dyneema and Spectra amounts to several percent of the total production. *>The Sailing application of Dyneema are *not* for ropes/lines: there have been one or two world-class racing boats with Dyneema sails (!). DSM used this opportunity for propmotional purposes (Whitbread race?, DSM logo on sails). *>From all this one can conclude that (assuming you can afford it) you could build a kite with Dyneema sails and Dyneema reinforced rods and fly it using Dyneema lines. I would guess that the rods would have to be developed for you and might result in a kite costing about the same as those sailboats ;-). * DSM talks about Dyneema pricing per unit of weight (yes, the stuff is expensive because it is VERY hard to make). The factory for Dyneema is located in Heerlen in Limburg, a so-called hilly part of Holland. *>Dyneema is (unlike other hi-tech fibres) not very relevant for reinforcement of vehicle tires because it "can't take the heat". At the moment only some Formula 1 cars use high-tech fibres instead of steel. *>Another property of Dyneema (which probably doesn't hurt for kiting) is that it "creeps": it sloooowly stretches under load. This is primarily due to mutual slippage of the long chains of polyethyleen. This is not the same for certain other fibres: there is nothing dipolar along the chains to help in the bonding; its only losts of weak "van der Waals" bindings. *>If you are still with me, here's the best part: my friend mentioned that Dyneema (and similar fibres) weren't very good at handling lateral strain. I asked how one is supposed to apply lateral strain to a rope. The answer was very enlightening: "that determines how well the fibre can handle knots". The tightening of a know causes lateral strain on the fibles. This is similar (but not quite as drastic) as cutting the line with a pair of scissors. It is not untypical for a knotted high-tech rope to break at, say, 100f its rated load. Note that the exact value depends on the type of fibre (and obviously the type of knot and use of sleeving). The friend said that values between 5and 25were credible based on his own measurements on Twaron/aramide (=Kevlar). *>This implies that the use of sleeving should help: it will increase the radius of the bends (and thus reduce the angle between direction of strain and the orientation of the fibres) and obviously also spreads out the pressure over a larger area (that's why people like to sit on cushions). A sleeved knot should thus do a lot better than 100f rated strength. *>When I asked "Where does a knotted line break?", I got: it should break right at the knot (in contrast to reports that lines tend to break several inches from the knot; I would suspect other sources of mechanical damage in these areas). To test line strength, you are supposed to wrap the ends of the line around a kind of solid metal cylinder (e.g. 10 cm diameter for thin lines) and to use some sort of clamping mechanism which applies pressure to a large part of the line wrapped around the cylinder. If the line breaks right at either end, you didn't do it right (or had bad luck ;-) and thus need to repeat the experiment. The line should break at the weakest spot which can be anywhere along the line. The world is actually quite simple, when you think about it... *>Dyneema fibres get some sort of chemical coating ("wax-like") to make them more manageable. This may affect the friction between intertwined kite lines. My friend mentioned you could probably make all types of coatings (including silicones), but they wouldn't be cheap if you were the only customer. For the lawyers: Dyneema is a trademark of DSM, Twaron is a trademark of AKZO-Nobel, Kevlar of Dupont and Spectra of Allied Chemical. But don't shoot me because I'me just an engineer (at least I like to think so). Peter van den Hamer vdhamer@prl.philips.nl = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 3 Nov 1994 05:20:26 -1000 From: andrewh@phoenix.harvard.edu (Andrew Hawken) Message-Id: <39av3q$mdr@beta.qmw.ac.uk> Organization: Queen Mary & Westfield College, London, UK Subject: Re: Dyneema info - 2nd edition vdhamer@prl.philips.nl wrote: :*>If you are still with me, here's the best part: my friend mentioned that : Dyneema (and similar fibres) weren't very good at handling lateral strain. : I asked how one is supposed to apply lateral strain to a rope. : The answer was very enlightening: "that determines : how well the fibre can handle knots". The tightening of a know causes lateral : strain on the fibles. This is similar (but not quite as drastic) : as cutting the line with a pair of scissors. It is not untypical for a knotted : high-tech rope to break at, say, 100f its rated load. Note that the exact Another way to put latteral strain on the Dyneema is to use it for the arch section (or indeed the v lines) in a Sputnik! I am still trying to find a combination of materials to make up the bridle which does not cut though itself, without suffering the weight/size penalty of Dacron. I may end up with Dacron yet :-( Andy -- ____________________________Andrew Hawken______________________________ "However many ways there may be of being alive, it is certain that there are vastly more ways of being dead" R Dawkins. Home : 0895 420110 QMW : 071 975 5542 AIIT : 0494 677045 Email : A.Hawken@QMW.AC.UK = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 3 Nov 1994 09:41:02 -1000 From: silntobsvr@aol.com (SilntObsvr) Message-Id: <39bece$odr@newsbf01.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Dyneema info - 2nd edition In article <9411021311.AA16887@isthp2.prl.philips.nl>, vdhamer@prl.philips.nl writes: >*>Dyneema is (unlike other hi-tech fibres) not very relevant for reinforcement > of vehicle tires because it "can't take the heat". At the moment only > some Formula 1 cars use high-tech fibres instead of steel. Ummm...just a few months ago, when I was shopping for tires for my wife's Hyundai, I almost bought a set that used Kevlar over the steel belts. I gather that the Kevlar, being wrapped over the edge of the steel, prevents or reduces belt separations if you reverse the rotation of the tires, as well as adding further stiffness and tread penetration resistance. +----------------------------------------------------------------------+ | SilntObsvr@aol.com | This .sig brought to you by the Geoworks | | Owner/Operator of | Ensemble 2.01 Text File Editor, substituting | | TableTop Publications | for features left out of the AOL newsreader. | +----------------------------------------------------------------------+ | All opinions expressed are my own, and should in no way be mistaken | | for those of the reader. | +----------------------------------------------------------------------+ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =