dyneema, nylon and mixed slings ...
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bearbreeder wrote:But lets take a real world example You set up a rap with a sling extension ... Girth hitch that sling to yr harness and tie and overhand knot for the rap device ... A very common thing to do ... Youve now cut the strength in half of that sling with the hitch and the knot to ~6 KNPeople should be using nylon for this rather than spectra anyway for two reasons: 1 Knots reduce the strength by less in nylon than spectra 2 Unlike spectra, knots in nylon absorb energy and reduce impact force |
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bearbreeder wrote:constant flexing and knotting (which is a well known phenomenom for over a decade woth spectra/dyneema)Maybe so with knotting, but not with flex fatigue. Dyneema is virtually unaffected by flex fatigue, as is clearly indicated in the chart I just posted, and plenty of other souses easily found on Google. Do you have a source that says knotting Dyneema reduces its lifespan faster than not knotting it? |
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eli poss wrote: 2 Unlike spectra, knots in nylon absorb energy and reduce impact forceThe appears to be extrapolated from other concepts. I don't believe it is supported. Can you back it up? |
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Xam wrote: The appears to be extrapolated from other concepts. I don't believe it is supported. Can you back it up?i'm too lazy to actually pull the link but either Rigging for Rescue or DMM I believe did tests with dynamic falls on various personal tethers. in this test, nylon slings that were knotted had lower impact forces from the same fall as nylon slings that were unknotted |
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eli poss wrote: i'm too lazy to actually pull the link but either Rigging for Rescue or DMM I believe did tests with dynamic falls on various personal tethers. in this test, nylon slings that were knotted had lower impact forces from the same fall as nylon slings that were unknottedThe test is from DMM . But they show that in some cases knotted dyneema is better then knotted nylon, which is the opposite to what you claim above. See the "Equalised with Overhand Knot + Anchor Point Fail" test. They hypothesize that the low coefficient of friction of dyneema allows the knot to slip more and thus absorb more energy. In addition, in all cases, the knotted setup was better in terms of force then the unkotted sliding-x setup for both dyneema and nylon. The test is not definitive, but your claim of "Unlike spectra, knots in nylon absorb energy and reduce impact force" is not substantiated. |
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20 kN wrote: Maybe so with knotting, but not with flex fatigue. Dyneema is virtually unaffected by flex fatigue, as is clearly indicated in the chart I just posted, and plenty of other souses easily found on Google. Do you have a source that says knotting Dyneema reduces its lifespan faster than not knotting it?the DAV link indicates that flexing (knotting) affects dyneema directly ... but not nylon (and likely not mixed slings as much) Mechanical damage and signs of wear are immediate grounds to retire webbing and quickdraws. The more fibres of a sling are damaged, the greater the loss of strength. The most significant mechanical aging is caused by flexing. It can be recognized by intense 'furrification' of the material. Aramid's vulnerability for changing flexing loads was discussed early on, but has shown itself to not be relevant in real life. The number of flexes required to weaken the fibre cannot really be reached during the product's ten year life-span. More recent experiments however have shown that caution must be used with respect to the aging of narrow Dyneema slings (6 and 8 mm width). With their small diameter area, the breaking strength of those slings when they are new is just a little bit above the norm requirements of 22 kN. After three to five years of use, some of them drop down to 13-15 kN. They should be retired after no more than five years, earlier if they are heavily used. climbing anchors 2006, gaines and long the thing about slings in climbing applications is that knotting and unknotting in the real world almost always means more abrasive damage regardless - unknotting the slings pulled tight, especially if you use the "roll method", abrades the knot pretty quickly ... - the knot itself is the part most likely to stick out and rub against something over time ... if one does use a "PAS" made from a sling or rope with the knot at the mid point, one will notice that that area abrades fairly quickly - the loading of the knot in falls itself causes wear, especially with high loads ... which is why sport climbers chop their ropes after awhile so whether the wear is strictly caused by "abrasion" or "flex" from knots is a moot point ... in climbing applications they are synonymous as to UV ill post it now before i head off ... UV rays penetrate deeper in dyneema UV penetration with cord (dyneema or nylon), the nylon sheath protected the core from UV ... so there was little loss however with a cord with a dyneema (PE) sheath, or with slings ... because of the exposed surface, or in the case of the PE sheath where the UVs penetrate deeper ... they all loss stength from UV exposure ... UV exposure they tested materials left out at altitude and ground level in at 4 year intervals ... you will see that at the altitude level a nylon slings has the lowest loss followed by a nylon cord ... the dyneema and mixed slings lost close to half their strength in that time however at ground level, all slings loss half their strength, while the cord loss ~30% ... note that a thicker cord/rope with a thicker sheath may fare better ... UV loss real lfe the losses were higher at ground level despite the lower UV there due to higher temps, humidity and pollution in short ... in the long run ALL slings will much of their strength when exposed for years ... cord/rope fares much better as the sheath protects the core note that for personal purposes, unless you are leaving yr gear out in the sun every day on the wall for years this is irrelevant ... a normal climber wont see those kind if UV losses with the reasonable retirement timeframe ... flexing and abrasion damage will cause retirement WAY before it matters for fixed gear and tat however ... ;) |
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The DAV report is inconclusive to put it kindly. Every lab test I've seen for Dyneema has shown its biggest weakness is melting point; Dyneema has a low melting point almost half that of Nylon. |
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Ray Pinpillage wrote:The DAV report is inconclusive to put it kindly. Every lab test I've seen for Dyneema has shown its biggest weakness is melting point; Dyneema has a low melting point almost half that of Nylon.well ray to put it kindly .... you dont have a single shred of evidence about dyneema in climbing applications, not bullet proof vests heres what the journal of mountain risk management says about dyneema and the melting point Es gibt oberflächliche Verbrennungen, ähnlich wie am Seilmantel, wenn man seinen Partner zu schnell ablässt. Dieselben leichten Verbrennungen wird es aber auch bei Polyamid-Schlingen geben. Dass eine Bandschlinge in dieser Situation durchbrennt, ist nicht möglich. Wie bei der HMS läuft ja immer ein neues Stück Material aufeinander. Es kommt also nicht zu dem Phänomen, wie wenn man den katastrophalen Fehler begeht und ein Seil durch eine Schlinge fädelt und seinen Partner (dann bald Expartner) darüber ablässt. Wie sich Polyamid und Dyneema in dieser Situation verhalten, habe ich gemeinsam mit dem Kaderkurs der Schweizer Bergführer ausprobiert. Die These lautete: Dyneema-Schlingen sind dünner (geringerer Materialquerschnitt) und haben einen niedrigeren Schmelzpunkt als Polyamid. Dafür ist ihre Oberfläche glatter als die von Polyamid, somit entsteht weniger Reibung, weniger Hitze gleicht sich das aus? Ein Freiwilliger wurde schnell bestimmt und beugte sich dem Gruppendruck (der abgelassene Kollege wurde natürlich hintersichert). Der ganze Versuch wurde später standardisiert (konstante Ablassgeschwindigkeit) an der Kletteranlage von Flo Hellberg wiederholt. Das Ergebnis: Polyamid und Polyethylen schenken sich da nix. Die Merkmale (dünner, dafür glatter) heben sich gegenseitig auf. Eine 16-mm-PA-Schlinge brannte nach ca. 4,8 Metern durch, die 8-mm-PE-Schlinge nach 4,2 Metern. Das Argument, die dünnen Dyneema-Schlingen sind am Stand zu gefährlich, weil sie durchgebrannt werden könnten, schlägt also nicht. Im Übrigen wurden die Schlingen im Wortsinn nicht primär durchgebrannt, sondern mehr durch die Kombination Hitze und rauer Seilmantel durchgescheuert. Die Aramid-Reepschnur konnte in diesem Versuchsaufbau übrigens gar nicht zerstört werden. basically they did a test and found that ... The characteristics (thinner, for smoother) cancel each other. A 16-mm-PA Sling burned through after about 4.8 meters, the 8-mm-PE loop by 4.2 meters. The argument that the thin Dyneema slings are too dangerous at the booth because they could be blown, so we are proposing. Moreover, the loops were not primarily in the literal sense "Blown", but more by the combination of heat and rough rope sheath worn. The Aramid Cord could not be destroyed in this experimental setup the way become. so the difference is marginal ... and to be blunt ... its irrelevant unless you are using dyneema slings as friction knots heres one of our ole gnarly MPers who sent his used mammut dyneema slings for testing ... http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2148297 I had a half dozen Mammut skinny slings tested each year for three years of solid use - my [averaged] results were very different and very consistent. End of first year 18k End of second year 14k End of third year 11k Will be testing them again this year... Love them, but given I've been working on a route with very sharp rock of late I've switched to somewhat more substantial Yates 11mm Dyneema slings. These are definitely consumable items which should definitely be replaced every 2-3 years of moderate-to-hard use. A lot of these are likely to eventually fail on folks if folks can't acknowledge they don't last like fat slings. Sorry - there is no free lunch. Make soft goods dramatically lighter and they simply won't last as long. Me? I'm still waiting for my synthetic, biotech goat's-milk-raised, spider silk slings and ropes. the degredation of dyneema with repeated abrasion and knotting has been known for over a decade surely u didnt miss the boat on that one? ;) |
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Xam wrote:But they show that in some cases knotted dyneema is better then knotted nylon, which is the opposite to what you claim above. See the "Equalised with Overhand Knot + Anchor Point Fail" test.that's a completely different topic and is irrelavent. that is talking about how you construct an anchor. I, on the other hand, was referring to using a knotted sling as a cow's tail. for a knotted sling used as a cow's tail, nylon is obviously the better choice and my statement holds true. |
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bearbreeder wrote: the degredation of dyneema with repeated abrasion and knotting has been known for over a decade surely u didnt miss the boat on that one? ;)That is a different subject. Dyneema applications are rarely the same size as Nylon so naturally they will have different wear characteristics. I'd still like to see a study supporting your assertion that time is a factor reducing the strength of Dyneema. |
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Ray Pinpillage wrote: That is a different subject. Dyneema applications are rarely the same size as Nylon so naturally they will have different wear characteristics. I'd still like to see a study supporting your assertion that time is a factor reducing the strength of Dyneema.Please provide an exact quote ray? Please note that my first 2 posts were simply summary points of the information in the DAV article for lazy bums such as yourself who cant be bothered to read the actual thing ... But rather argue online about bulletproof vests And the "10 years" (or less) timeframe is generally many manufacturers (Petzl for example) recommendations for soft goods Which in the absense of data on climbing gear one should probably follow Or are you tellig folks to use their dyneema slings beyond 10 years without any real tests by respected orgs to back it up? That wouldnt be very wise would it now from mammut on one hand its hilarious that you go off and claim that BD, DMM, petzl dont publish dyneema strength loss and assume there is none then you go off an claim one should ignore the manufacturers retirement recommendations of those very same companies Ever notice that BD, DMM, Petzl, WC, Etc pull test everything and do environmental studies on gear available on the market? Ever notice how there is an absence of available data for Dyneema strength loss? There's not an actual absence of testing, Dyneema is used in bulletproof vests and accelerated environmental studies have been performed as I posted. (your statement) ;) |
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eli poss wrote: that's a completely different topic and is irrelavent. that is talking about how you construct an anchor. I, on the other hand, was referring to using a knotted sling as a cow's tail. for a knotted sling used as a cow's tail, nylon is obviously the better choice and my statement holds true.I don't disagree with your statement about the application. I agree with you. I disagree that you have any evidence to support the following statement that you made, which I think is mistaken: eli poss wrote: Unlike spectra, knots in nylon absorb energy and reduce impact forceI think it is pretty clear that knots in both nylon and spectra will absorb energy upon tightening under force and will, in a limited way, reduce impact. The DMM test shows that quite clearly regardless of the application of the knotted sling. But this is really a subtle point having to do with the difference between material modulus in tension and in flexure or torsion and not suitable for internet discussion. And ultimately, I think your overall statement is valid and perhaps I should have left well enough alone. |
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Xam wrote:I disagree that you have any evidence to support the following statement that you made, which I think is mistakenDMM test results I could be wrong in my interpretation but to me this says that knots in nylon slings absorb energy because the impact force for the same fall is lower in a sling that has been knotted. In knotted dyneema there is also a lower impact force, but that is because the sling broke under the load. This is an assumption, however, so I could be wrong. On the other hand, nylon stretches, absorbing energy, while dyneema (for all intents and purposes) does not stretch. This, along with the above data, is this basis for my claim that knotted dyneema doesn't lower impact force. |
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eli poss wrote: I could be wrong in my interpretation but to me this says that knots in nylon slings absorb energy because the impact force for the same fall is lower in a sling that has been knotted. In knotted dyneema there is also a lower impact force, but that is because the sling broke under the load. This is an assumption, however, so I could be wrong. On the other hand, nylon stretches, absorbing energy, while dyneema (for all intents and purposes) does not stretch. This, along with the above data, is this basis for my claim that knotted dyneema doesn't lower impact force.You cannot compare knotted to unknotted ultimate forces in dyneema in this test when there is never a knotted and unknotted system of the same type that did not fail in which to compare. So you cannot say anything about dyneema knot energy 'absorption' or compare nylon to dyneema knot energy 'absorption'. Dyneema does not stretch (much). It does bend. It does twist. All of these mechanical modes 'absorb' energy. These modes occur in knots. Consider the other test in which similar systems can be compared directly both knotted and unknotted without breaking and you should be able to convince yourself the knots will absorb energy in both dyneema and nylon systems. But yes, nylon is better for the application you stated. |
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