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There has been a lot of discussion recently on the topic of Dyneema and its various uses within the slackline realm. Wether it's using the fiber for the webbing you walk on, to make soft shackles for connectors, to use it as a backup on a highline, or to make adjustable length slings. There isn't much information on its' use with Slacklining and so I thought I would put together a nice guide on the fiber as well as show how to use the fiber for various things.
Dyneema is a trade name used by DSM for HMPE (High Molecular-Weight Polyethylene). It's an incredible strong fiber that is considerably stronger than steel at the same weight. Dyneema is used to make a variety of different ropes as well as webbings. It's used in many industries for different purposes. A common use that us slackliners may be familiar with is climbing slings. Often times the webbing used for climbing slings is a hybrid weave with Dyneema and Nylon. It's favored because of the extremely low weight and extremely high tensile strength.
The material specifications for Dyneema are quite impressive. To begin showcasing some of these specs, I first need to say that there are a number of different types of Dyneema, with developments constantly being made by DSM, the manufacturer of Dyneema. The most common type of Dyneema on the market for ropes and webbing is Dyneema SK75. Other varieties include SK25, SK60, SK62, SK65, SK78, SK90, and SK99. As the SK number increases, it represents a newer version of the fiber. With each new generation of Dyneema, the specs get better and better.
Some of the earlier versions of Dyneema suffer from severe creep issues. Creep is the process of plastic deformation under load. That means when you tension a piece of Dyneema, it will continue to loose tension and physically become longer over time. New versions of Dyneema have started to mitigate this issue, with the creep properties of SK-99 being substantially better than all of its predecessors. This issue only becomes a problem when using the fiber near its breaking strength or if left under substantial tensions for a long period of time.
Here is more information about creep: Understanding Creep
Dyneema is a very impressive fiber when it comes to technical specifications. It's the strongest fiber in the world by weight, has virtually no stretch, has incredible chemical resistance, excellent UV resistance, and extremely good abrasion resistance. Checkout the full spec sheet for this amazing fiber here: Dyneema (UHMWPE) Fiber Specifications
One common use for Dyneema is to make a rope from it (such as Amsteel Blue), commonly made in a 12-strand braid to make for easy splicing. The specifications of these 12-strand Dyneema ropes can vary by thousands of pounds when comparing similar sizes. The reason behind this spec difference is either the use of a newer and stronger version of Dyneema, or the process of heat-setting the rope. Dyneema is unique in the fact that it can be work-hardened by applying high tension to the rope under high heat. This aligns the chemical structure of the fibers causing the strength of the rope to increase by as much as 40%! Be aware! According to a study done by Samson Rope (the makers of Amsteel Blue), this work hardening does increase the strength, but it also decreases the cyclic lifespan of the rope by as much as 40%! That means that the work-hardened Dyneema rope will fail with 40% less load cycles (think about wind bouncing a slackline up and down, each of those would be a cycle).
Another finding of the study is that work-hardened Dyneema rope is also more susceptible to abrasion damage. The study finds that work-hardened Dyneema fails with less than half the abrasion cycles compared to non-work-hardened Dyneema.
What this study also tells us is that Dyneema, if not work-hardened by the manufacturer, will actually get STRONGER with continued use (up to a certain number of cycles)! This is a very interesting concept, especially when considering the different applications for Dyneema. If you require something with a super high strength and very low weight, it may be advantageous to use work-hardened rope. However, I would argue that the added lifespan and abrasion resistance of non heat-set rope is an attractive trait for the various uses in our application. If additional strength is needed, the ability to go up a size in your rope with not much weight gain is a huge plus.
Here is the full study: HMPE Post Production Processing (August 2013)
Dyneema rope is an incredible amazing thing. Just a 1/4" rope made from Dyneema SK75 weighs just 22 grams per meter and clocks-in at 8,600 lbf breaking strength! When looking at this size of rope, it's hard to believe these numbers. Also when feeling this type of rope, you will likely notice how slippery it is. It makes you wonder just how abrasion resistant the rope is. What happens if the rope rubs on a rock while under tension? Or how about if there is serious abrasion on it? How do we know if the rope is still safe for use?
Samson did another study where they tested the breaking strength of various damaged samples of Amsteel Blue. These samples ranged from brand new looking to completely mangled. From the 300+ samples they tested, they were able to form a sort of scale to be able to compare your line to to get an idea of what the retained breaking strength is of the potentially damaged rope. The scale is posted below.
This is an incredibly useful tool for inspecting things like soft shackles or Dyneema slings for damage. I would recommend retiring anything that is higher than a 4 on the above scale.
Here is the full article for inspection criteria for Dyneema products: Inspection Criteria for HMPE Rope
The two most commons ways for Dyneema Rope to fail is by abrasion and UV damage. Both of these failure modes provide visual queues for when they are negatively affecting the substrate. Constantly inspect your Dyneema ropes and webbings for abrasion and UV damage. Retire the rope if either of these presents a risk.
What are some of the ways we can use Dyneema in our slackline rigs? Well, for starters, soft shackles! These incredible pieces of gear are ground-breaking in the world of connectors. They are amazingly strong, extremely versatile, and you can make them yourself! I have a huge number of tests that I will be publishing about soft shackles very soon. I will also be posting a guide on how to make your own. There will be ready-made soft shackles in the BC shop and supplies to make your own as well.
Another great use for Dyneema is for what is called "Whoopie Slings". A Whoopie Sling is an adjustable length sling made from Dyneema rope. I use them for my bolt-backups on bolted highline anchors, as seen in this post: . These are easily made on your own as well. We will sell ready-made Whoopie Slings for bolt backups in the shop.
A lot of people are also using Dyneema as the primary fiber in their slackline webbings. This can be a great thing due to the extremely high tensile strength and ultra low weight of Dyneema. However, there are potential issues with the ultra low stretch of this fiber. For this reason, a webbing made from Dyneema needs to have extremely high strength since it will experience much higher shockloads in dynamic events (bouncing, leash falls, etc...). It's also best used as a very long slackline webbing. Anything below 200 feet (60m) can be potentially dangerous if setup as a highline. I would recommend a strength of at least 40 kN for any slackline webbing made from Dyneema (or any high-tech fiber for that matter).
Dyneema is an incredible fiber that has superior properties. It's use in slackline rigging is a new concept that still needs to be further explored. It's exciting to see how Dyneema can improve our highline and longline rigging in the future. The potential for weight savings is massive and the safety margin has the potential to grow to new heights.
Thanks for reading the article. Please feel free to comment below with any questions or more information.
Here are links to further studies done on Dyneema by Samson Rope:
Rope Selection Usage Retirement (May 2013)
Bending Fatigue Enhancement of Synthetic Fiber Rope (March 2006)
Residual Strength Testing on Dyneema Fiber Tug Lines (May 2002)
Tensile Behavior of Ropes Composed of Fiber Blends (July 2010)
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