Watching this channel is making me realize that I'm a snob. I go in assuming that a couple of free-spirit climbing bums aren't going to teach me anything about stress and strain. I'm a mechanical engineer, after all. And then they teach me stuff and I feel bad for being an a***ole. I really like the work you guys are doing.
Hey man, the bigger test of character is being self aware enough to notice things like that, and even better on you for being willing to admit it and call yourself out when your initial assumptions were wrong. That counts for more than anything else in my book
I've done a course on theoretical physics last semester and we learned some things about slings/ropes and how they behave force-wise under certain setups. The biggest issue with the theoretical rope stuff is (at least in my course) that the rope is seen as one-dimensional most of the time, so it only matters how often it is wrapped around something. If the rope is a three-dimensional object, meaning that it has a mass and more importantly friction, only the friction between the rope and the surface is calculated, while the friction between overlapping parts of the rope is neglected. These are some pretty massive simplifications in comparison to real-life but obviously, theoretical physics should only give us a general of how some things behave during certain situations, and then it's up to guys like you to test it under real circumstances. Keep up the great work!
There are some good points made, that i would subscribe. Also i think the setup puts a lot of energy and thus friction into the system generating a lot of heat. It would be interesting to see, if you guys would get any different results if you would do the test way slower. See, you want to create a static situation, but static is not to be seen in contrast to a climbing situation here, but more to the internal timescales of the stretching dynamics of the rope. Maybe the setup was too dynamic for the sling itself, and it could handle more if you would increase the force with rests in between.
I don't know if you're going to take Mechanical or civil engineering, but The friction from overlapping ropes increases the amount of energy they can store, effectively making them stronger. It's the angle of the loading and rubbing of edges which are the largest causes of failure here. When it's being pulled in a simple straight line, the loading is axial and only has normal stresses, but when it is pulled at an angle, the body develops sheer stresses, which greatly increase the equivalent stress in the body. The edge rubbing both decreases the effective cross section, wears the material (I suspect this is negligible), and creates stress concentrations which can double or triple the effective stress at the bottom of the folds caused by the rubbing.
@@christophredlich1442 the heat actually occurs when the strap unloads. When it is stretched to failure it permanently deforms to be longer than the original strap. The energy stored in this deformation cannot be mechanically unloaded because the strap won't return to it's original length. This energy is dissipated as heat and vibrations and stuff.
Another important point is that this is not at all a rigorous test, they only have 2 data points for each set up, while these results are interesting you can't really make any kind of conclusive statement with out significantly more data points.
For the theoretical 4x, They still failed in tension. My take would be that the load is not evenly distributed on the 4 passes because of various mechanisms. So that would make some of them to elongate more before the same load is applied to the less stiff ones (see them as springs that are not leveled). That way you lose quite a bit of resistance because the full load is applied on one spring before the whole system can reach its capacity. It makes sense because if you could actually reach 4x, you would have 4 clean failures instead of just one. Theoretical physics can still be applied here. Just have to make the right assumptions!
Hello. I'm an Entertainment Industry rigger, turned engineer. A few thoughts on things: 1. Have a look at your industrial slings. A choke (or girth hitch), should be good for 80% of strength. That's in a straight line pull. This is on every sling I've ever used. 2. If you choke something, then fold the sling back over itself, it will continue to decrease in strength, depending on the angle. Folded all the way over, you should end up at 50% of 80%, so 40% strength.This is from when I did my IRATA level 1 (many years ago now). 3. MBS is minimum breaking strength. In order to have that as a minimum, everything should be breaking a bit above this. The weakest one made needs to break at MBS. It's a minimum. 4. That minimum might not be based on a straight line pull. The manufacture might account for things like doubling it over etc, then work backwards from there (that's a theory). 5. The one with the wraps actually opens up the other side, giving you a bit of a bridle angle. It's pretty small, but its there. Might be worth playing with the numbers to compare it that way too (I'm happy to help with that if you like) 6. The ones where it was double double folded (that's a technical term I think), you get a bit of twisting and weird compression of the fibers going on. I was still really surprised it went at 78 not 88. 7. In general, wrapping a tensioned line around something decreases the tension as it goes around. This is why winch drums need a minimum of three wraps on them. After that, there's no tension in the line. This is something I'd like to do more research on, but it's a real thing. So When you wrap the sling around the shackle pin, there is something interesting going on there in terms of directing forces inwards weirdly and if the wraps are over top of each other, then you'll be getting weird compression and heat build up. This was a great video though! I like your guys stuff. If you want to discuss any of this stuff with me, the entertainment industry is still pretty quiet, you know, with The Plague stalking the Land, so I have a bit of spare time. Leave me a replay and I'll drop you an email.
Ah clearly you know you're shit, so let me make a claim. I agree with all points except the double double. I would expect less than 88 because the way it is wrapped will never let the forces equalizer, so even if the entire sling was perfectly uniform and ready to break at 22kn, one of the 4 legs would hit 22kn while the other 3 still have strength left on the table. Basically breaking strength had all to do with neatness in the original unloaded setup. Replace the shackles with 4pulleyd and you'll see a much more repeatable number close to 88. But wrapped around a single solid shaft, it is UPTO88, often much less
@@whyiseverythingonfireagain1190 Yes absolutely right! Also consider a slight differential load on the outside edge of the double double. If you look closely the geometry makes the doubled up one load up first on the outside edges first effectively causing a greater point load on the outside edges of the straps then the inside legs.
Excellent video. I think a lot of people are missing the real gold of this episode. It's testing how to make a sling stronger... so if you're rapping off some old tat that you shouldn't be, at least we know how much (%) we can increase the strength with various configurations.
"It's not that helpful when you're trying to research something just to find your own research". Aka the terrifying moment you realise you're the subject matter expert now.. Great work as always guys!
IT guy here. I had an absolutely baffling problem with a Windows server and was searching the interwebs for a solution, and came across a forum post describing my exact symptoms, underlying cause, and easy solution. It had been posted to that forum about 9 months prior ... by me.
I don’t climb and I don’t plan on it in the future, and this entirely seems outside of content I would normally watch but I find it fascinating none the less. Thank you for the content you create!
Thank you very much. An interesting idea from Bobby to test gear multiple times with 50% load and then break it! I am stoked with 45 K subscribers. This channel is GOLD!!
I'd be really curious to see that, especially in high speed. Stretching the fibers in the rope should cool them down, but friction will of course generate heat.
I work on communication towers and these forces happen often we just get told some of this information it's nice to see it for real and a few good tips well done
I'm not a slackliner, but I find this information very useful for my job as a tower technician. We use the wrapped slings and girth hitched slings often on towers. We don't measure anything in KN, but we pull loads in the range of 1000lbs from very abused slings using those methods without problems. Keep up the great content!
I reckon if the sling is just doubled, than it self equalizes the load easily, whilst when it's wrapped around than the wrap pinches the sling and force might not be distributed evenly, resulting in lowered strength, whith one part of the sling getting more load than the other. Seeing Your test is always an improvement for my intuition. Visual thinking is king.
I think it's more about the friction between the strands as they pull, not any difference in load distribution. I don't really know the answer to this, but it seems like any tiny potential difference in equalization would be less significant than the change in friction
This was my conclusion as well. If the sling was free to slide it would distribute the load to all eight strands evenly. In reality, as soon as you put tension on, the strands are locked in place on the bar and the shortest of the strands takes a higher load. It breaks while the rest of the strands are still at partial load, so you never get full utilization out of the other strands.
Came here to say this. I think what's happening is a parallel to the test they did with the pulleys that didn't get the theoretical advantage. The friction of the looping over the shackle, and any friction between loops, causes the load to not get distributed evenly among the loops.
It's just AWESOME that you guys are out there testing this stuff, and making it accessible. Also, lost of interesting and clever insights in the comments. All of this makes us all safer out there 🤘 And that's cool.
Hey, the reason for decreased strength is due to overlapping the straps. When they are under that much tension they will lock together rather than slip past each other. That will lock the length once the load gets high enough (well below MBS). Once you do that the shortest length will see a much higher load. The best way to mitigate that problem is to use longer test pieces so you can use larger shackles. This will allow you to avoid overlapping the test pieces.
Yeah I would like to see a slightly longer one I think it would perform the same as the regular (shorter one.) I dont get why anybody expects that hitch to be half strength, its not THAT much different than a regular loop.
Also, if the issue was effectively having multiple pieces of slightly different [unloaded] lengths once everything locks, then presumably using a longer sling but keeping the shackles the same (so tending to keep the same absolute differences in lengths between pieces) and increasing the overall length between the shackles would mean the relative differences in [unloaded] lengths between the pieces would be lower, so the differences in load between pieces would also be lower.
Came here to say exactly this but vid being 2y.o I first check comments. Glad to see some people with a brain here and experience here, shows thoses guy have no clue what they are doing.
@@AlphaGamingCa I guess it depends on what a viewer thinks they were doing. They did say they were inspired by the diagram (showing what were effectively "ideal" results for the first 4 arrangements), and that diagram was using a carabiner, which would end up with straps overlapping and resulting uneven load distribution. In the real world, not many people are going to carry around huge shackles to use in setting up a belay, so wouldn't end up with an ideal setup either.
As a mechanical engineering student The number is calculated from where 50% of samples fail when their entire cross section reaches a specific principal stress, something on the order of several tens of megapascals is usually where polymers fall. Pressure is force divided by area, so the force they rate to is that tens of MPa times the cross section area when in simple axial tension. From there, usually, there is a safety factor. For human use where someone's life is on the line, it's usually 4 to 5, hence why him falling in that video was 5KN but the strap supports 22KN of axial loading. This is entirely expected. Angled loading from wrapping is not axial, it creates internal sheer and axial loading. Sheer loading causes *massive* increases in the principal stress on a body. That's the first reason why all the wrapped portions failed early. The second reason for failure was the rubbing, which creates concentrated stresses at the contact point that are higher than the axial tension. The third reason for failure I can pull off the top of my head is the strain rate, how fast it is loaded. The faster a polymer is loaded, the less stress it can handle, and if your strap is loaded faster than the manufacturing test strap, it will fail before the test strap does. Seeing as your strap failed at 29ish but was rated for 22, I suspect you were slower than the test, which makes sense because the strap is designed to resist shock loading, not gradual loading. The heat you felt in the strap actually occured once it unloaded rapidly and the energy stored in the tension of the strap was released. Because the strap is permanently longer at failure than it originally was before testing, any energy stored in the elongation cannot be mechanically returned to the strap, and so is lost as heat.
I love the destruction but honestly the thing I like the most is the confidence it gives me when I know just how much force and abuse it takes for these components to fail thank you 👌
The wrapped sling introduces an angle to the attached leads of the sling, would be interesting to divide the measured breaking strength by the angle cosines to see if the straight tensile breaking force is close to the original double looped variation
Yeah, as other people have brought up, There are basically two different factors that are not addressed in the original photo. 1. Friction is almost impossible to anticipate in situations like this. Friction between the strands and between the strands and the steel shackles, means that each strand will likely be stressed unequally (as seen many times on this and other channels, perfect equalization is a myth!). 2. There are angles on almost all of these set-ups and, while the angles are easier to account for with physics, they were clearly not accounted for in the original drawing/photo. The original sketch is basically the answer that you get in High school math when the problem says "There is zero friction in the system".
Hi guys this was very interesting to me as I'm in the rope access industry and it is great knowing that the gear we are using is more than safe enough for the jobs we do on a daily basis as long as it is being used correctly. Cheers guys🤘🤘
The one that you’re calling a “double fold” is rigged incorrectly. It is instead a double loop - a spiral, not a fold. Look at the routing arrows near the drawing. If done correctly, it does indeed hang parallel and not at 90 degrees - it also does not lay on top of itself as much as how you had it.
Was going to comment this, doing it as drawn would also avoid the folded over strand in the configuration. I'm guessing you'd still have the unequal loading between strands / self-friction that's reducing the strength, but I'd expect a few more kN strength as a minimum. Great video, though!
@@w8stral TIL that I apparently do not live in reality as proven by my use of this exact arrangement before with block and tackle to hoist significant loads.
@@diamondflaw If you are hoisting significant loads all the time, what the Hell are you doing using a paltry wrapped sling instead of a dedicated sling when there are superior methods for attaching a sling.
I have basically no interest in climbing and absolutely zero interest in physics, but this was a really fun video. Y’all seem like you have a cool channel. Thanks TH-cam recommendations
A lot of the reasons for increasing my safety rating when doing highlines is more about using the most safe anchor for a given situation and being aware of failure potential. Another thing I try to keep in control is how much stretch is in a system. Once I get my patient, the more stretch I have in a system the less comfortable the ride is for them.
Reminds me of tying up barges. About 8,500T loaded. Sometimes they'd be moving so you put a few wraps on the bollard and hang on to the end. A 3inch line would stretch down to about 2inch then you flip some slack and do it again. Once in a while I'd just toss a eye over the bollard and get out of the way. It would sound like a gun shot when it broke.
Great video I get similar results using the straight and girth hitch methods. I use lots of 6-12k straps combined with a 4k chainsaw winch, 10k pulys and 2-10k bow shackles for small scale logging. I find that the girth hitch typically exceeds the rated capacity of the strap. I typically use straight or girth hitch ties for all my strap connections with bow shackles or straight to another strap. I mat double my strap if using a 6k strap for an 8k pull. I have broken around 20 straps and mostly they brake somewhere in the middle due to weave failure or less often at the stitching. However, under tension any somewhat sharp edge that comes in contact with the strap can potentially cut it. Decent straps are Great. I have way more problems with my 1/4 inch 4400 pound test aircraft cable wearing on the cable guide and getting squished on the winch drum. I wear out and break the cable every few hours of use. Fun fact: with a starting load over 2k I just tie the leading end of the cable to a bow shackle and it holds full rated strength once the knot has pulled tite under heavy load. This saves time and doesn't leave anything sticking out to get snagged. The cable typically only breaks where it has been worn by the cable guide. Thanks again for the great video I found it applicable to my work.
I love these videos for giving me more confidence in my climbing gear. One factor that is not mentioned (that I could find) is that you would of course always have to watch for is sharp rocks that can cut those supper strong ropes and slings - like the rock, paper, scissors children's game.
Manufacturers try to do every test the same way and control every variable for certification and QC. This is completely valid for its purpose. Theory ignores the fine details and makes different predictions. Also valid and expected. Both are useful for choosing gear and deciding how to solve a particular problem in real life. Having a healthy margin of error on individual pieces of gear and also having redundancy on things like anchors covers real world variations and the fact that a lot of my gear is old and a little worn. I think all this is why climbing accidents are almost always caused by human error and not by a piece of gear failing under loads we'd expect it to hold. It says a lot about the industry that makes our gear and our culture of safety. I love this channel because you do real-world tests. Things are a little messy and imprecise. You might pull a random sling off your rack. It's much more like real life. It's interesting to see just how much forces our safety systems can really handle e . It's educational because it encourages us to stop a think about stuff we take for granted. And it's just plain fun to watch you test stuff to destruction. Thanks!
This would be fun but I would garner uneventful.... I love the beer knot. Super clean. My guess is they'll break almost identical as they essentially are the same thing. Same layers of nylon, same type of knot.... only difference I can really think of is the inner potion of webbing might get a little squeezed and Misshaped a bit due to the nature of the beer knot.
@@v0hero691 I mostly use slings for moving rocks for trail work and I like the beer knot a lot as well. They’re definitely structurally very similar but the literature online says the water knot retains around 64% of strength and the beer knot claims to retain 80%, so it would be fun see if that claim is true
Great video.. the second ‘doubled’ setup is known almost universally in pro climber (arborist/aerial rescue) as ‘basket configuration’. Best.. And the people questioning the need for anything greater than 14kn... you want to come watch an arborist negative rig some one tonne + bits of tree out of the sky sometime.. or some window cleaners rigging a huge scaffold up the side of a skyscraper.. there’s plenty of rope professionals out there besides you weekend rock guys :) [edit] I see a minute later you use the term ‘basket’ yourself, sorry :)
To be honest arborist and window cleaners are not supposed to have dynamic falls or w/e unless something go really really off. So they dont really need all those huge KN safeties. Using the "weekend rock guys" doesn't give you any credibility and the false air of self - esteem is smelling all around.
@@ProjectMaelstrom there is some merit to that.... until you recognise that arborists are also rigging large bits of tree down to the ground (which I specifically mentioned above..). So yes, they’ll avoid shock loading their climbing system/life support at all costs.. but they’ll frequently have little to no choice on their other system which is subject to significantly greater loads than a 90kg bloke with a saw and a helmet. Also, honestly, yes rope professionals avoid shock loading their system.. but it can and does happen, and when it does it is just as catastrophic. So they DO need those huge ratings on their gear. Professional standards and insurers frequently require a 10:1 or greater ‘overengineering’ on climbing and rigging systems btw, so a system for a 100kg load (for example) may require gear rated for a minimum of a metric tonne for coverage. Be safe up there, best. PS “weekend rock guys” is not an attack at all. But these are the guys who seem to be the most insular in any discussion of this type, who don’t really perceive anybody else who may have experience in these fields. Arborists, aerial rescue, linesmen, window cleaners, even hobbyist mountaineers and cavers..they’re all well aware of rock climbing communities. But rock climbing communities are full of people who only perceive rock climbing communities, regardless wether this applies to you or not. Best.
Wow... I was really surprised with the girth hitch, especially on dyneema. Also the doubled sling was great to see. Thank you Bobby for donating the sling. Also ... maybe I have also girth hitched a bolt and hanger here and there... Sometimes you do what you have to. Wouldn't whip on a girthed hanger tho..
Hi, rope access trainer here. Most of my observations will be based around that attack vector. First observation: You don't need 14kN and if you do, your setup is busted. The european norm for industrial use anchorage (EN795) demands 12kN and tape slings fall under that norm (Type B: Mobile anchorage). Based on that, if you get 14kN out of a sling, it technically is still over-dimensioned for the purpose and A-OK. Ok, yes, in slacklines you can and will place massive loads onto your anchors, so yes, there it would be the exception on the rule. Please, go big on slacklines. What I am more referring to, is general useage (anything without an extreme angle **upwards of 150 deg where you have around 150% x load on each anchor** ), but rather in mostly vertical systems. In such a system, if you can bring 14kN together, you might want to rethink how you work/play because you are doing it wrong. That being said, the difference in time spent between doubling up, choking or double plus wrap, is neglegable, so why not go for stronger? Double and wrap is my go-to when no external factors come into play. Best of both worlds. Last thing I will point out, is that another test might be in order on the choker: A drop test where the dynamic forces of sudden implimentation of force comes into play. Example: the friction in the knot and the heat caused due to slippage. I am pretty sure that should you drop something in a choked sling, you will have a pretty different result. Not -50% (also to take into consideration is the angle of pull in comparison to the knot), but more in the area of -30%. Obviously the diameter of the core would have an effect. Last consideration is that factors such as age, wear, UV exposure and even something like having a sling lie crumpled up in the bottom of a bag, would also reduce the potencial strength.
The answer to why all straps break below their theorized (or sometimes advertised) maximum is because of heat. And heat, as we know, is the enemy of plastic, which webbing is made from. As you put energy into the webbing by means of tension, the excess gets shed out of the webbing in the form of heat, and that heat *necessarily* changes the mechanical properties of the webbing. In theory, you could achieve a higher (e.g. much closer to theorized maximum) load on the straps by 1) Stretching them much slower, 2) cooling them as you're stretching, and 3) stretching them in small, stepped intervals. Now, obviously, this isn't really a *practical* way to achieve the maximum because there's no real-world use case where loads are slow and stepped *and* the webbing is being actively cooled at the same time. But.. that's how you'd get to the listed max's. You basically have to cheat and have super granular control the conditions that the webbing is being stretched under.
The problem with knots should be on dynamic loads. When you take a fall, knot tightens up fast and heat generated that way can melt the sling, weakening its rated strength. On static loads, like in this test, that is not the case, so it is probably the reason numbers are much higher with girth hitch.
Estimatedly speaking, it would reach 88 Kn, but theory teaches us that there are factors that are not taken into account when carrying out the tests, one of those factors is the friction that the material generates with itself, I think that would be the greatest difficulty. Excellent work.
ACKCHYUALLY 2:08 the image is not "wrong", look at the arrow next to the sling: You start by clipping one "end" of the sling into the biner, then take it over the bar, and thread it through the biner a few times, and then you clip the remaining end into the biner! So the image is quite accurately drawn in my opinion:) keep up the great work!
What are we thinking about shock load compared to the steady increase of load that your system uses? Seems like the heat may have less time to dissipate and therefore be hotter with shock load? Either way I love watching stuff break so good job.
That's plausible. Another possibility is that you'd get a lot less strain (and therefore stress*dstrain = denergy), because elastic response is time-dependent. I think this is very likely in a material like nylon, because time dependent deformation mechanisms are responsible for the majority of the strain. At higher strain rates, the material wouldn't have the time to relax, meaning that energy wouldn't be released as heat. If the time span were longer, or in a less strain-rate sensitive material like steel, I think you'd be correct.
A really helpful test would be a piece of dynamic rope put directly on a hanger with an overhand knot. I see this a lot at the crags in my area when a bolt is a bit too high.
Just found the channel, great video. I have a break test suggestion, and if it's already been done please point me in a direction. Two anchors, level with each other, say a foot apart: the scenarios are A) each end of a sling attached to one anchor, so the sling + load make a "Y"; and B) the sling looped through BOTH anchors, essentially drawing a line across the top of the Y to close it. I was told this second scenario greatly increases the forces on the anchors and should never ever be used. I don't doubt it, but I'd like to see real numbers.
Have you tested how strain rate affects the strength of each configuration? Shock loading versus a slower loading would be cool to look at! Or have you looked at the “creep” or steady state strain that would occur when you keep a sling under a constant load, then test the subsequent strength? It would be interesting to know if equipment you rig slack lines with that have a lot of time under tension really shouldn’t be used for climbing.
Great video, might be a life saver one day. I think TH-cam suggested this because I watch Project Farm or Engineering Explained, as I've never been interested in climbing.
Interesting results! What is also interesting is that @09:10 upper-right side of a sling is tearing apart first (the inner side). It looks like the angles makes quite a difference, and probably its possible to achieve above 44 kN if sling would be aligned more perpendicular to the shackles.
About 11:00 minutes. Super interesting. It would be important to run the experiment with a single fiber and using calorimetry. If the single fiber heats up to the point of undergoing a phase transition, it is a common entropic-spring effect that happens to elastomers. Upon mechanical alignment, the entropy of the system decreases and heat is produced. This is easy to test with a rubber band. This can be the source of heat. But again: it would require a "clean" experiment with a single fiber and a calorimetric equipment. It can also be guesstimated by calculations, but the experiment is crucial. Super cool the heating effect you detected.
Great stuff as always! Important to point out about the girth hitch: when you tie it around something with high friction (a tree as opposed to a metal bar) then you can position the knot where you want it. Correctly done, you will get very little tension in the knot. Do it the wrong way and you probably will lose a lot of strength. Try it out!
English is not my native language, but I'll try anyway to explain a little mistake I saw in the video. Girth hitch is supposed to halve the resistance of the sling if you apply a dynamic load (like in a fall). In static force application, as you get from a testing bench, it only takes out 20% of the total MBS, what is consistent with the obtained results. I'm an instructor for lifting equipment and you can find it in the label (what we call 'form factor' compared with that of direct pull) of an EN 1492 textile lifting sling. Hope that helps. Great video by the way. Regards from Spain.
As a climber with an extensive background in occupational safety. The similarities in standards between mountaineering and OSHA is absolutely delightful. You gentlemen did an absolutely wonderful job with this demonstration. I'm actually subscribing to you guys. :)
I’m not sure that you would get the mechanical expected in the wrapped scenario as the wraps are touching and would add friction that would impact the spread of the load
I've used nylon climbing webbing in these ways to connect shackles to rope pulleys in stump pulling systems, and I found this very fascinating. The breaker machine seems to apply the load slowly. I'm eager to find out how the dyneema vs nylon girth hitch may respond with a faster loading impact, such as in a drop tower scenario.
Also, I've recently read that slings labelled as Dyneema are often hybrids of dyneema and nylon, specifically if they have a combination of colored fibers and white fibers.
I think the reason why the break strength was a lower number on the wrapped configuration vs the doubled over (or basket) is because of the extra friction in the wrapped configuration limited the amount that the two sides of the sling equalized tension as it was loaded, therefore loading one side slightly more, making the combined break strength a bit lower, whereas with the basket, it was able to distribute the load to each leg more effectively, sharing the load.
It would be interesting to see things break in slow motion. Seeing the failure mechanisms and locations would help understand why it fails. And how to improve our assumptions for the theoretical models to get them closer to reality!
14:17 I feel like that tests that seemingly refute common safety recommendations (try to avoid girth hitching your slings) should be tested in ways that better represent real life usage. Here I'd really have liked to have seen the girth hitch in 2 carabiners (both ends) instead of big, rounded shackles. Really appreciate all the effort though!
As Expected: load will NOT be shared equally on parallel members. Some load will be higher, some lower. Analogous effects are Parallel Electrical circuits. Some formulas for parallel resistors, or parallel batteries, will shed light on this effect. (Also, the more members you have sharing the same load, the wider the variation from average they become. Some members will feel almost no load, others will pick-up the slack and have higher loads. There is friction in the system, and the members cannot self-adjust their length to compensate for load variations between them.) Your results agree with calculated expectations; they were just using the wrong equations for their estimates. They needed a RMS (Root Mean Squared) term. Happens all the time. ... GOOD VIDEO 👍
Dan Merrick here. One issue I've had with testing is that the shackle pins rotate pretty freely. Rubbing seems to reduce sling strength pretty significantly so I am curious if the girth hitch would perform as well if the pin didn't rotate while loading. I think the result should be close to the same but I am not certain.
Nice video! My guess is that inconsistent force across the sling (see 13:22) due to folds and bunching is reducing the strength of the "double double" sling. This may be another example of the benefits of a well-dressed anchor. I wonder if the result would be different for a longer sling...
My guess for the 4X wraps breaking early is that it’s not evenly pulling on the 4 length. Is locks itself tight, but 1 strand will inevitably be slightly tighter than the rest and will brunt more of the load.
Girth hitch: Climbing on Giant's Washbowl (Adirondaks NY) ~1980. Partner was leading, girth-hitched the eye of an in-situ piton with a 1" nylon sling (pretty standard for the time), placed a nut some feet higher, and fell from some more feet higher. Nut ripped, piton pulled, next nut down caught the fall. The shock load on the sling in the piton welded the girth hitch in to one blob of nylon in and around the eye of the piton. I think he still has that souvenir.
At 11:57 probably an heating over 300C plus for a split second from the intense compression and that is what is causing the break. What about using a wet sling? or setting up some dripping water on it to cool it? Remotely of course so it doesn't kill you LOL!
Hey, my background is engineering and from what i can see i would assume that the lower tensile strength is due to each "strand" of the sling not carrying the same load, so instead of it being each one carrying the same load and maxing out, some will carry more and and some less due to many factors, so it fails once the highest loaded section reaches its maximum load capacity
As a certified industrial rigger I have some knowledge of fabric slings and their proper usage. One of the things that caused your premature failure was whether the eye ends of the slings were vertical or at an angle. Angle loading of slings greatly reduces overall breaking strength and the steeper the angle the lower the breaking strength. If you use longer slinger to reduce the angle on the multi wrap connections it would have a direct effect on your ultimate breaking strength. The reason you encountered melting of your slings where the choke overlapped due to wrapping or doubling is the inner portion of the sling cannot move freely over the shackle due to the outer layer pinching it down as it loads. The result of this pinching is friction and subsequent chaffing between the layers and an uneven loading of the sling and pressure points within the wrap. The final variant where you have made a loop of the sling and passed through that loop will normally fail on the section where you formed the loop. When tightened, the loop is pulled until it begins to have too tight a bend radius and that causes the failure. To see what is happening and why they fail the way they do, take your footage and slow the playback speed as much as possible. With a slower playback you should be able to see where the failure starts and surmise why it fails. A very good book regarding rigging and other associated lift or retention of loads is the IPT Crane and Rigging Handbook which can be purchased on line from WWW.iptbooks.com . or email: iptpub@compusmart.ab.ca . IPT's books are also listed on Amazon.
"some" data on bend radius strength effects could be extrapolated from the gin pole diameter data in the ANSI/TIA 1019-a also in that technical they claim synthetics need a 10:1 safety factor probably for the reasons you were discovering with friction heat and cutting itself. This is probably why you dont typically if ever see synthetic ropes used in the rescue bag
Something interesting: I was retiring some rope by chopping it into sections with an axe over a stump, and the ends automatically melted/fused from the axe going through it. It doesn’t take a whole lot to melt these things.
Seeing the wrapped sling break strength was great because it's the worst case scenario for an equalised two anchor setup if made with a sling between it. if you're using one sling to two anchors and adding a cross over to attach the equalising carabineer, if one anchor fails, the carabineer slides along the loop to the end effectively creating this scenario.
The 4x twist doesn’t gain the full 4x because it only needs one link of the ‘chain’ to break to unload the whole rope. The length of rope isn’t equal in strength, as the forces even out the average force will peak above the weakest part and snap it before reaching the overall average of the 4x twist.
Great video I love to see the same for two slings on two anchors connected to one shackle for angles (distance between anchors) at work the lifting slings are marked on a label for different angles.
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Watching this channel is making me realize that I'm a snob. I go in assuming that a couple of free-spirit climbing bums aren't going to teach me anything about stress and strain. I'm a mechanical engineer, after all. And then they teach me stuff and I feel bad for being an a***ole.
I really like the work you guys are doing.
Hey man, the bigger test of character is being self aware enough to notice things like that, and even better on you for being willing to admit it and call yourself out when your initial assumptions were wrong. That counts for more than anything else in my book
ego is the enemy
Yea, crazy people experimenting, breaking and blowing stuff up is where all the engineering, physics, and chemistry equations come from.
also an ME. yes, engineers are assholes. never work with them.
@@ccolagio_ You're problem was being an ME, EE's are chill
I've done a course on theoretical physics last semester and we learned some things about slings/ropes and how they behave force-wise under certain setups. The biggest issue with the theoretical rope stuff is (at least in my course) that the rope is seen as one-dimensional most of the time, so it only matters how often it is wrapped around something. If the rope is a three-dimensional object, meaning that it has a mass and more importantly friction, only the friction between the rope and the surface is calculated, while the friction between overlapping parts of the rope is neglected. These are some pretty massive simplifications in comparison to real-life but obviously, theoretical physics should only give us a general of how some things behave during certain situations, and then it's up to guys like you to test it under real circumstances. Keep up the great work!
There are some good points made, that i would subscribe. Also i think the setup puts a lot of energy and thus friction into the system generating a lot of heat. It would be interesting to see, if you guys would get any different results if you would do the test way slower. See, you want to create a static situation, but static is not to be seen in contrast to a climbing situation here, but more to the internal timescales of the stretching dynamics of the rope. Maybe the setup was too dynamic for the sling itself, and it could handle more if you would increase the force with rests in between.
I don't know if you're going to take Mechanical or civil engineering, but
The friction from overlapping ropes increases the amount of energy they can store, effectively making them stronger.
It's the angle of the loading and rubbing of edges which are the largest causes of failure here.
When it's being pulled in a simple straight line, the loading is axial and only has normal stresses, but when it is pulled at an angle, the body develops sheer stresses, which greatly increase the equivalent stress in the body.
The edge rubbing both decreases the effective cross section, wears the material (I suspect this is negligible), and creates stress concentrations which can double or triple the effective stress at the bottom of the folds caused by the rubbing.
@@christophredlich1442 the heat actually occurs when the strap unloads. When it is stretched to failure it permanently deforms to be longer than the original strap. The energy stored in this deformation cannot be mechanically unloaded because the strap won't return to it's original length. This energy is dissipated as heat and vibrations and stuff.
Another important point is that this is not at all a rigorous test, they only have 2 data points for each set up, while these results are interesting you can't really make any kind of conclusive statement with out significantly more data points.
For the theoretical 4x, They still failed in tension. My take would be that the load is not evenly distributed on the 4 passes because of various mechanisms. So that would make some of them to elongate more before the same load is applied to the less stiff ones (see them as springs that are not leveled). That way you lose quite a bit of resistance because the full load is applied on one spring before the whole system can reach its capacity.
It makes sense because if you could actually reach 4x, you would have 4 clean failures instead of just one.
Theoretical physics can still be applied here. Just have to make the right assumptions!
Hello. I'm an Entertainment Industry rigger, turned engineer. A few thoughts on things:
1. Have a look at your industrial slings. A choke (or girth hitch), should be good for 80% of strength. That's in a straight line pull. This is on every sling I've ever used.
2. If you choke something, then fold the sling back over itself, it will continue to decrease in strength, depending on the angle. Folded all the way over, you should end up at 50% of 80%, so 40% strength.This is from when I did my IRATA level 1 (many years ago now).
3. MBS is minimum breaking strength. In order to have that as a minimum, everything should be breaking a bit above this. The weakest one made needs to break at MBS. It's a minimum.
4. That minimum might not be based on a straight line pull. The manufacture might account for things like doubling it over etc, then work backwards from there (that's a theory).
5. The one with the wraps actually opens up the other side, giving you a bit of a bridle angle. It's pretty small, but its there. Might be worth playing with the numbers to compare it that way too (I'm happy to help with that if you like)
6. The ones where it was double double folded (that's a technical term I think), you get a bit of twisting and weird compression of the fibers going on. I was still really surprised it went at 78 not 88.
7. In general, wrapping a tensioned line around something decreases the tension as it goes around. This is why winch drums need a minimum of three wraps on them. After that, there's no tension in the line. This is something I'd like to do more research on, but it's a real thing. So When you wrap the sling around the shackle pin, there is something interesting going on there in terms of directing forces inwards weirdly and if the wraps are over top of each other, then you'll be getting weird compression and heat build up.
This was a great video though! I like your guys stuff. If you want to discuss any of this stuff with me, the entertainment industry is still pretty quiet, you know, with The Plague stalking the Land, so I have a bit of spare time. Leave me a replay and I'll drop you an email.
Ah clearly you know you're shit, so let me make a claim. I agree with all points except the double double. I would expect less than 88 because the way it is wrapped will never let the forces equalizer, so even if the entire sling was perfectly uniform and ready to break at 22kn, one of the 4 legs would hit 22kn while the other 3 still have strength left on the table. Basically breaking strength had all to do with neatness in the original unloaded setup. Replace the shackles with 4pulleyd and you'll see a much more repeatable number close to 88. But wrapped around a single solid shaft, it is UPTO88, often much less
Oh and it's the same reason why the doubled up but with wraps also brakes lower
Hey brother
@@whyiseverythingonfireagain1190 Yes absolutely right! Also consider a slight differential load on the outside edge of the double double. If you look closely the geometry makes the doubled up one load up first on the outside edges first effectively causing a greater point load on the outside edges of the straps then the inside legs.
What about circumference and surface friction (polished vs galvanised), what impact does that have?
Excellent video. I think a lot of people are missing the real gold of this episode. It's testing how to make a sling stronger... so if you're rapping off some old tat that you shouldn't be, at least we know how much (%) we can increase the strength with various configurations.
"It's not that helpful when you're trying to research something just to find your own research". Aka the terrifying moment you realise you're the subject matter expert now..
Great work as always guys!
Agreed, you guys are top of the field! Thank for doing the hard work to help us make the right choices!
IT guy here. I had an absolutely baffling problem with a Windows server and was searching the interwebs for a solution, and came across a forum post describing my exact symptoms, underlying cause, and easy solution. It had been posted to that forum about 9 months prior ... by me.
I don’t climb and I don’t plan on it in the future, and this entirely seems outside of content I would normally watch but I find it fascinating none the less. Thank you for the content you create!
Thank you very much. An interesting idea from Bobby to test gear multiple times with 50% load and then break it! I am stoked with 45 K subscribers. This channel is GOLD!!
I am hoping to find someone with a cyclic loading machine that I could abuse on weekends of off days :).
Could you use a thermal camera on the slings to see the warmth build up during the strain test?
I'd be really curious to see that, especially in high speed. Stretching the fibers in the rope should cool them down, but friction will of course generate heat.
I work on communication towers and these forces happen often we just get told some of this information it's nice to see it for real and a few good tips well done
I'm not a slackliner, but I find this information very useful for my job as a tower technician. We use the wrapped slings and girth hitched slings often on towers. We don't measure anything in KN, but we pull loads in the range of 1000lbs from very abused slings using those methods without problems. Keep up the great content!
Holy mother of Tradclimbing I love your Videos! They really make my day better and are super interesting.
Its fun testing this stuff
Been watching your channel for a few months now, just donated! Really appreciate all the hard work you guys do, and the production value is insane!
I reckon if the sling is just doubled, than it self equalizes the load easily, whilst when it's wrapped around than the wrap pinches the sling and force might not be distributed evenly, resulting in lowered strength, whith one part of the sling getting more load than the other. Seeing Your test is always an improvement for my intuition. Visual thinking is king.
Yep, I was going to reply this as well.
I think it's more about the friction between the strands as they pull, not any difference in load distribution. I don't really know the answer to this, but it seems like any tiny potential difference in equalization would be less significant than the change in friction
This was my conclusion as well. If the sling was free to slide it would distribute the load to all eight strands evenly. In reality, as soon as you put tension on, the strands are locked in place on the bar and the shortest of the strands takes a higher load. It breaks while the rest of the strands are still at partial load, so you never get full utilization out of the other strands.
Came here to say this. I think what's happening is a parallel to the test they did with the pulleys that didn't get the theoretical advantage. The friction of the looping over the shackle, and any friction between loops, causes the load to not get distributed evenly among the loops.
I've watched this video like four times now. This channel is such a great reference and I hope more people support it.
"African elephant..." Showing an Asian elephant 😅
^ came here to say this
I also came here to say this!
Came here for a discussion about elephant rigging techniques.
That elephant looked very comfortable.
I imagine both elephants are similar in weight and strength?
@@Phoenixhunter157 African elephants are significantly larger, often up to 50% heavier
It's just AWESOME that you guys are out there testing this stuff, and making it accessible. Also, lost of interesting and clever insights in the comments. All of this makes us all safer out there 🤘 And that's cool.
His smile pointing out the videos was so genuine it earned a sub
18:45 OK this is what I think! You guys are just awesome! Thank you so much for everything you do! Greetings from Austria!
Hey, another Austrian
@@LZmiljoona servus
Loving these videos man. Thanks so much.
Glad you like them.
Hey, the reason for decreased strength is due to overlapping the straps. When they are under that much tension they will lock together rather than slip past each other. That will lock the length once the load gets high enough (well below MBS). Once you do that the shortest length will see a much higher load. The best way to mitigate that problem is to use longer test pieces so you can use larger shackles. This will allow you to avoid overlapping the test pieces.
Yeah I would like to see a slightly longer one I think it would perform the same as the regular (shorter one.) I dont get why anybody expects that hitch to be half strength, its not THAT much different than a regular loop.
Also, if the issue was effectively having multiple pieces of slightly different [unloaded] lengths once everything locks, then presumably using a longer sling but keeping the shackles the same (so tending to keep the same absolute differences in lengths between pieces) and increasing the overall length between the shackles would mean the relative differences in [unloaded] lengths between the pieces would be lower, so the differences in load between pieces would also be lower.
Came here to say exactly this but vid being 2y.o I first check comments.
Glad to see some people with a brain here and experience here, shows thoses guy have no clue what they are doing.
@@AlphaGamingCa I guess it depends on what a viewer thinks they were doing.
They did say they were inspired by the diagram (showing what were effectively "ideal" results for the first 4 arrangements), and that diagram was using a carabiner, which would end up with straps overlapping and resulting uneven load distribution.
In the real world, not many people are going to carry around huge shackles to use in setting up a belay, so wouldn't end up with an ideal setup either.
Thanx guys! I spent years doing rigging with my job, variables can be a &!+
As a mechanical engineering student
The number is calculated from where 50% of samples fail when their entire cross section reaches a specific principal stress, something on the order of several tens of megapascals is usually where polymers fall. Pressure is force divided by area, so the force they rate to is that tens of MPa times the cross section area when in simple axial tension.
From there, usually, there is a safety factor. For human use where someone's life is on the line, it's usually 4 to 5, hence why him falling in that video was 5KN but the strap supports 22KN of axial loading. This is entirely expected.
Angled loading from wrapping is not axial, it creates internal sheer and axial loading. Sheer loading causes *massive* increases in the principal stress on a body. That's the first reason why all the wrapped portions failed early.
The second reason for failure was the rubbing, which creates concentrated stresses at the contact point that are higher than the axial tension.
The third reason for failure I can pull off the top of my head is the strain rate, how fast it is loaded. The faster a polymer is loaded, the less stress it can handle, and if your strap is loaded faster than the manufacturing test strap, it will fail before the test strap does. Seeing as your strap failed at 29ish but was rated for 22, I suspect you were slower than the test, which makes sense because the strap is designed to resist shock loading, not gradual loading.
The heat you felt in the strap actually occured once it unloaded rapidly and the energy stored in the tension of the strap was released. Because the strap is permanently longer at failure than it originally was before testing, any energy stored in the elongation cannot be mechanically returned to the strap, and so is lost as heat.
Thanks for those videos, please keep them coming, I'm learning something pretty much everytime.
I love the destruction but honestly the thing I like the most is the confidence it gives me when I know just how much force and abuse it takes for these components to fail thank you 👌
The wrapped sling introduces an angle to the attached leads of the sling, would be interesting to divide the measured breaking strength by the angle cosines to see if the straight tensile breaking force is close to the original double looped variation
You guys need some money for a proper high speed camera. That would really be interesting to see the breaking in even slower motion...
Or a collaboration with someone who does have one already.
Yeah, as other people have brought up, There are basically two different factors that are not addressed in the original photo.
1. Friction is almost impossible to anticipate in situations like this. Friction between the strands and between the strands and the steel shackles, means that each strand will likely be stressed unequally (as seen many times on this and other channels, perfect equalization is a myth!).
2. There are angles on almost all of these set-ups and, while the angles are easier to account for with physics, they were clearly not accounted for in the original drawing/photo.
The original sketch is basically the answer that you get in High school math when the problem says "There is zero friction in the system".
13:55 try with fixed bolt. Your setup allows bolt to spin. In real life situation if bolt won't turn freely it will break earlyer?
This is great content. As someone who really values safety I love to see these kinds of tests.
Hi guys this was very interesting to me as I'm in the rope access industry and it is great knowing that the gear we are using is more than safe enough for the jobs we do on a daily basis as long as it is being used correctly. Cheers guys🤘🤘
The one that you’re calling a “double fold” is rigged incorrectly. It is instead a double loop - a spiral, not a fold. Look at the routing arrows near the drawing. If done correctly, it does indeed hang parallel and not at 90 degrees - it also does not lay on top of itself as much as how you had it.
Was going to comment this, doing it as drawn would also avoid the folded over strand in the configuration. I'm guessing you'd still have the unequal loading between strands / self-friction that's reducing the strength, but I'd expect a few more kN strength as a minimum.
Great video, though!
While that is true, that is not how in Reality, one actually is able to USE said sling alignment.
@@w8stral TIL that I apparently do not live in reality as proven by my use of this exact arrangement before with block and tackle to hoist significant loads.
@@diamondflaw If you are hoisting significant loads all the time, what the Hell are you doing using a paltry wrapped sling instead of a dedicated sling when there are superior methods for attaching a sling.
@@w8stral "all the time" was nowhere in my comment. Niether was any claim that it was the best, or even a smart solution. Just that it works.
I am so glad that the girth hitch holds up with nylon. I use them all the time for belaying anchors and such!
Thanks!
Thank you Jeff for the $toke!
I love Bobby's child like enthusiasm you guys rock from the highline stoke here in new Zealand
you have built an incredible channel and your tests are excellent. keep it up, and thankyou for sharing!
Have you done "closet storage" webbing strength testing? Basically How much weakening occurs, with age, but out of the light and no usage?
I have basically no interest in climbing and absolutely zero interest in physics, but this was a really fun video. Y’all seem like you have a cool channel. Thanks TH-cam recommendations
A lot of the reasons for increasing my safety rating when doing highlines is more about using the most safe anchor for a given situation and being aware of failure potential. Another thing I try to keep in control is how much stretch is in a system. Once I get my patient, the more stretch I have in a system the less comfortable the ride is for them.
Reminds me of tying up barges. About 8,500T loaded. Sometimes they'd be moving so you put a few wraps on the bollard and hang on to the end. A 3inch line would stretch down to about 2inch then you flip some slack and do it again. Once in a while I'd just toss a eye over the bollard and get out of the way. It would sound like a gun shot when it broke.
Great video I get similar results using the straight and girth hitch methods.
I use lots of 6-12k straps combined with a 4k chainsaw winch, 10k pulys and 2-10k bow shackles for small scale logging.
I find that the girth hitch typically exceeds the rated capacity of the strap. I typically use straight or girth hitch ties for all my strap connections with bow shackles or straight to another strap. I mat double my strap if using a 6k strap for an 8k pull.
I have broken around 20 straps and mostly they brake somewhere in the middle due to weave failure or less often at the stitching. However, under tension any somewhat sharp edge that comes in contact with the strap can potentially cut it.
Decent straps are Great. I have way more problems with my 1/4 inch 4400 pound test aircraft cable wearing on the cable guide and getting squished on the winch drum. I wear out and break the cable every few hours of use.
Fun fact: with a starting load over 2k I just tie the leading end of the cable to a bow shackle and it holds full rated strength once the knot has pulled tite under heavy load. This saves time and doesn't leave anything sticking out to get snagged. The cable typically only breaks where it has been worn by the cable guide.
Thanks again for the great video I found it applicable to my work.
I love these videos for giving me more confidence in my climbing gear. One factor that is not mentioned (that I could find) is that you would of course always have to watch for is sharp rocks that can cut those supper strong ropes and slings - like the rock, paper, scissors children's game.
That's why you keep rope and gear log sheets.
Manufacturers try to do every test the same way and control every variable for certification and QC. This is completely valid for its purpose. Theory ignores the fine details and makes different predictions. Also valid and expected. Both are useful for choosing gear and deciding how to solve a particular problem in real life. Having a healthy margin of error on individual pieces of gear and also having redundancy on things like anchors covers real world variations and the fact that a lot of my gear is old and a little worn. I think all this is why climbing accidents are almost always caused by human error and not by a piece of gear failing under loads we'd expect it to hold. It says a lot about the industry that makes our gear and our culture of safety.
I love this channel because you do real-world tests. Things are a little messy and imprecise. You might pull a random sling off your rack. It's much more like real life. It's interesting to see just how much forces our safety systems can really handle e . It's educational because it encourages us to stop a think about stuff we take for granted. And it's just plain fun to watch you test stuff to destruction. Thanks!
It would be cool to see a strength comparison of the water knot vs the beer knot for slings made from tubular nylon webbing
This would be fun but I would garner uneventful.... I love the beer knot. Super clean. My guess is they'll break almost identical as they essentially are the same thing. Same layers of nylon, same type of knot.... only difference I can really think of is the inner potion of webbing might get a little squeezed and Misshaped a bit due to the nature of the beer knot.
I plan on doing lots of knots when drop tower comes so we can compare dynamic loads and slow pull
@@v0hero691 I mostly use slings for moving rocks for trail work and I like the beer knot a lot as well. They’re definitely structurally very similar but the literature online says the water knot retains around 64% of strength and the beer knot claims to retain 80%, so it would be fun see if that claim is true
Great video.. the second ‘doubled’ setup is known almost universally in pro climber (arborist/aerial rescue) as ‘basket configuration’. Best..
And the people questioning the need for anything greater than 14kn... you want to come watch an arborist negative rig some one tonne + bits of tree out of the sky sometime.. or some window cleaners rigging a huge scaffold up the side of a skyscraper.. there’s plenty of rope professionals out there besides you weekend rock guys :)
[edit] I see a minute later you use the term ‘basket’ yourself, sorry :)
To be honest arborist and window cleaners are not supposed to have dynamic falls or w/e unless something go really really off. So they dont really need all those huge KN safeties. Using the "weekend rock guys" doesn't give you any credibility and the false air of self - esteem is smelling all around.
@@ProjectMaelstrom there is some merit to that.... until you recognise that arborists are also rigging large bits of tree down to the ground (which I specifically mentioned above..). So yes, they’ll avoid shock loading their climbing system/life support at all costs.. but they’ll frequently have little to no choice on their other system which is subject to significantly greater loads than a 90kg bloke with a saw and a helmet.
Also, honestly, yes rope professionals avoid shock loading their system.. but it can and does happen, and when it does it is just as catastrophic. So they DO need those huge ratings on their gear. Professional standards and insurers frequently require a 10:1 or greater ‘overengineering’ on climbing and rigging systems btw, so a system for a 100kg load (for example) may require gear rated for a minimum of a metric tonne for coverage.
Be safe up there, best.
PS “weekend rock guys” is not an attack at all. But these are the guys who seem to be the most insular in any discussion of this type, who don’t really perceive anybody else who may have experience in these fields. Arborists, aerial rescue, linesmen, window cleaners, even hobbyist mountaineers and cavers..they’re all well aware of rock climbing communities. But rock climbing communities are full of people who only perceive rock climbing communities, regardless wether this applies to you or not. Best.
Wow... I was really surprised with the girth hitch, especially on dyneema. Also the doubled sling was great to see. Thank you Bobby for donating the sling.
Also ... maybe I have also girth hitched a bolt and hanger here and there... Sometimes you do what you have to. Wouldn't whip on a girthed hanger tho..
Hi, rope access trainer here. Most of my observations will be based around that attack vector.
First observation: You don't need 14kN and if you do, your setup is busted. The european norm for industrial use anchorage (EN795) demands 12kN and tape slings fall under that norm (Type B: Mobile anchorage). Based on that, if you get 14kN out of a sling, it technically is still over-dimensioned for the purpose and A-OK.
Ok, yes, in slacklines you can and will place massive loads onto your anchors, so yes, there it would be the exception on the rule. Please, go big on slacklines.
What I am more referring to, is general useage (anything without an extreme angle **upwards of 150 deg where you have around 150% x load on each anchor** ), but rather in mostly vertical systems. In such a system, if you can bring 14kN together, you might want to rethink how you work/play because you are doing it wrong.
That being said, the difference in time spent between doubling up, choking or double plus wrap, is neglegable, so why not go for stronger? Double and wrap is my go-to when no external factors come into play. Best of both worlds.
Last thing I will point out, is that another test might be in order on the choker: A drop test where the dynamic forces of sudden implimentation of force comes into play. Example: the friction in the knot and the heat caused due to slippage.
I am pretty sure that should you drop something in a choked sling, you will have a pretty different result. Not -50% (also to take into consideration is the angle of pull in comparison to the knot), but more in the area of -30%.
Obviously the diameter of the core would have an effect.
Last consideration is that factors such as age, wear, UV exposure and even something like having a sling lie crumpled up in the bottom of a bag, would also reduce the potencial strength.
Next video: "Should we be using shackles instead of carabiners when climbing? The SCIENCE carabiner companies don't want you to see"
The answer to why all straps break below their theorized (or sometimes advertised) maximum is because of heat. And heat, as we know, is the enemy of plastic, which webbing is made from. As you put energy into the webbing by means of tension, the excess gets shed out of the webbing in the form of heat, and that heat *necessarily* changes the mechanical properties of the webbing. In theory, you could achieve a higher (e.g. much closer to theorized maximum) load on the straps by 1) Stretching them much slower, 2) cooling them as you're stretching, and 3) stretching them in small, stepped intervals. Now, obviously, this isn't really a *practical* way to achieve the maximum because there's no real-world use case where loads are slow and stepped *and* the webbing is being actively cooled at the same time. But.. that's how you'd get to the listed max's. You basically have to cheat and have super granular control the conditions that the webbing is being stretched under.
Thanks guys, i used the informstion you brought here in a high-rise rope access safety meeting after a sling incident report, playin your video.
The problem with knots should be on dynamic loads. When you take a fall, knot tightens up fast and heat generated that way can melt the sling, weakening its rated strength.
On static loads, like in this test, that is not the case, so it is probably the reason numbers are much higher with girth hitch.
Would be cool to see you guys drop weights also using the different hitches both in dynaema and nylon
That has been done elsewhere previously
Dmm
@@bobbypatton4903 perhaps, but I reckon this channel could do it better and add more realistic variables
@@zanestathakis30 no, not really. The manufacturer does a fantastic job of it.
@@bobbypatton4903 I’d like to check that out, do you have the link or know what titles I can search under?
Estimatedly speaking, it would reach 88 Kn, but theory teaches us that there are factors that are not taken into account when carrying out the tests, one of those factors is the friction that the material generates with itself, I think that would be the greatest difficulty. Excellent work.
ACKCHYUALLY 2:08 the image is not "wrong", look at the arrow next to the sling: You start by clipping one "end" of the sling into the biner, then take it over the bar, and thread it through the biner a few times, and then you clip the remaining end into the biner! So the image is quite accurately drawn in my opinion:) keep up the great work!
I agree, i feel like they need to retest that one because they broke it configured differently to the image!
Yessssssss. As an engineer I’m always curious how stuff works in the real world
I love Bobby's delivery!
What are we thinking about shock load compared to the steady increase of load that your system uses?
Seems like the heat may have less time to dissipate and therefore be hotter with shock load?
Either way I love watching stuff break so good job.
That's plausible. Another possibility is that you'd get a lot less strain (and therefore stress*dstrain = denergy), because elastic response is time-dependent. I think this is very likely in a material like nylon, because time dependent deformation mechanisms are responsible for the majority of the strain. At higher strain rates, the material wouldn't have the time to relax, meaning that energy wouldn't be released as heat.
If the time span were longer, or in a less strain-rate sensitive material like steel, I think you'd be correct.
I love your channel, I wish you guys were around when I started climbing, it would have made some of my heady leads less heady!
A really helpful test would be a piece of dynamic rope put directly on a hanger with an overhand knot. I see this a lot at the crags in my area when a bolt is a bit too high.
Just found the channel, great video. I have a break test suggestion, and if it's already been done please point me in a direction. Two anchors, level with each other, say a foot apart: the scenarios are A) each end of a sling attached to one anchor, so the sling + load make a "Y"; and B) the sling looped through BOTH anchors, essentially drawing a line across the top of the Y to close it. I was told this second scenario greatly increases the forces on the anchors and should never ever be used. I don't doubt it, but I'd like to see real numbers.
Have you tested how strain rate affects the strength of each configuration? Shock loading versus a slower loading would be cool to look at! Or have you looked at the “creep” or steady state strain that would occur when you keep a sling under a constant load, then test the subsequent strength? It would be interesting to know if equipment you rig slack lines with that have a lot of time under tension really shouldn’t be used for climbing.
Great video, might be a life saver one day.
I think TH-cam suggested this because I watch Project Farm or Engineering Explained, as I've never been interested in climbing.
Interesting results!
What is also interesting is that @09:10 upper-right side of a sling is tearing apart first (the inner side).
It looks like the angles makes quite a difference, and probably its possible to achieve above 44 kN if sling would be aligned more perpendicular to the shackles.
Thank you for reassuring me that I can trust my life to the slings.
About 11:00 minutes.
Super interesting.
It would be important to run the experiment with a single fiber and using calorimetry. If the single fiber heats up to the point of undergoing a phase transition, it is a common entropic-spring effect that happens to elastomers. Upon mechanical alignment, the entropy of the system decreases and heat is produced. This is easy to test with a rubber band.
This can be the source of heat. But again: it would require a "clean" experiment with a single fiber and a calorimetric equipment. It can also be guesstimated by calculations, but the experiment is crucial. Super cool the heating effect you detected.
Great stuff as always! Important to point out about the girth hitch: when you tie it around something with high friction (a tree as opposed to a metal bar) then you can position the knot where you want it. Correctly done, you will get very little tension in the knot. Do it the wrong way and you probably will lose a lot of strength. Try it out!
English is not my native language, but I'll try anyway to explain a little mistake I saw in the video.
Girth hitch is supposed to halve the resistance of the sling if you apply a dynamic load (like in a fall). In static force application, as you get from a testing bench, it only takes out 20% of the total MBS, what is consistent with the obtained results.
I'm an instructor for lifting equipment and you can find it in the label (what we call 'form factor' compared with that of direct pull) of an EN 1492 textile lifting sling.
Hope that helps. Great video by the way. Regards from Spain.
As a climber with an extensive background in occupational safety. The similarities in standards between mountaineering and OSHA is absolutely delightful.
You gentlemen did an absolutely wonderful job with this demonstration. I'm actually subscribing to you guys. :)
I’m not sure that you would get the mechanical expected in the wrapped scenario as the wraps are touching and would add friction that would impact the spread of the load
I've used nylon climbing webbing in these ways to connect shackles to rope pulleys in stump pulling systems, and I found this very fascinating. The breaker machine seems to apply the load slowly. I'm eager to find out how the dyneema vs nylon girth hitch may respond with a faster loading impact, such as in a drop tower scenario.
Also, I've recently read that slings labelled as Dyneema are often hybrids of dyneema and nylon, specifically if they have a combination of colored fibers and white fibers.
This was super cool. Just recently bought two of the yellow black diamond slings which I double up and use to extend my device when abseiling.
Great video anf very informative. Love the Monty Python reference, Get well Bobby
Great work. The twist and the friction wrapped around itself.
I think the reason why the break strength was a lower number on the wrapped configuration vs the doubled over (or basket) is because of the extra friction in the wrapped configuration limited the amount that the two sides of the sling equalized tension as it was loaded, therefore loading one side slightly more, making the combined break strength a bit lower, whereas with the basket, it was able to distribute the load to each leg more effectively, sharing the load.
Thanks for your work guys. And... I love that Bobby Tshirt !!! Good health to him !
It would be interesting to see things break in slow motion. Seeing the failure mechanisms and locations would help understand why it fails.
And how to improve our assumptions for the theoretical models to get them closer to reality!
Love having Bobby in the videos
Great video! First time viewer, subscribed. 😀
Welcome aboard!
14:17 I feel like that tests that seemingly refute common safety recommendations (try to avoid girth hitching your slings) should be tested in ways that better represent real life usage. Here I'd really have liked to have seen the girth hitch in 2 carabiners (both ends) instead of big, rounded shackles.
Really appreciate all the effort though!
But that goes beneath minimum Bend Radius of the sling.
And why use a chocke, when you have a carabiner?
You can just open that up.
As Expected:
load will NOT be shared equally on parallel members. Some load will be higher, some lower. Analogous effects are Parallel Electrical circuits. Some formulas for parallel resistors, or parallel batteries, will shed light on this effect.
(Also, the more members you have sharing the same load, the wider the variation from average they become. Some members will feel almost no load, others will pick-up the slack and have higher loads. There is friction in the system, and the members cannot self-adjust their length to compensate for load variations between them.)
Your results agree with calculated expectations; they were just using the wrong equations for their estimates. They needed a RMS (Root Mean Squared) term. Happens all the time.
... GOOD VIDEO 👍
Dan Merrick here. One issue I've had with testing is that the shackle pins rotate pretty freely. Rubbing seems to reduce sling strength pretty significantly so I am curious if the girth hitch would perform as well if the pin didn't rotate while loading. I think the result should be close to the same but I am not certain.
Could you do that girth hitch test again with a steel oval carabiner?
Nice video! My guess is that inconsistent force across the sling (see 13:22) due to folds and bunching is reducing the strength of the "double double" sling. This may be another example of the benefits of a well-dressed anchor. I wonder if the result would be different for a longer sling...
My guess for the 4X wraps breaking early is that it’s not evenly pulling on the 4 length. Is locks itself tight, but 1 strand will inevitably be slightly tighter than the rest and will brunt more of the load.
Girth hitch: Climbing on Giant's Washbowl (Adirondaks NY) ~1980. Partner was leading, girth-hitched the eye of an in-situ piton with a 1" nylon sling (pretty standard for the time), placed a nut some feet higher, and fell from some more feet higher.
Nut ripped, piton pulled, next nut down caught the fall. The shock load on the sling in the piton welded the girth hitch in to one blob of nylon in and around the eye of the piton.
I think he still has that souvenir.
At 11:57 probably an heating over 300C plus for a split second from the intense compression and that is what is causing the break. What about using a wet sling? or setting up some dripping water on it to cool it? Remotely of course so it doesn't kill you LOL!
Hey, my background is engineering and from what i can see i would assume that the lower tensile strength is due to each "strand" of the sling not carrying the same load, so instead of it being each one carrying the same load and maxing out, some will carry more and and some less due to many factors, so it fails once the highest loaded section reaches its maximum load capacity
Thank you guys so much for what you doing.
As a certified industrial rigger I have some knowledge of fabric slings and their proper usage. One of the things that caused your premature failure was whether the eye ends of the slings were vertical or at an angle. Angle loading of slings greatly reduces overall breaking strength and the steeper the angle the lower the breaking strength. If you use longer slinger to reduce the angle on the multi wrap connections it would have a direct effect on your ultimate breaking strength. The reason you encountered melting of your slings where the choke overlapped due to wrapping or doubling is the inner portion of the sling cannot move freely over the shackle due to the outer layer pinching it down as it loads. The result of this pinching is friction and subsequent chaffing between the layers and an uneven loading of the sling and pressure points within the wrap. The final variant where you have made a loop of the sling and passed through that loop will normally fail on the section where you formed the loop. When tightened, the loop is pulled until it begins to have too tight a bend radius and that causes the failure.
To see what is happening and why they fail the way they do, take your footage and slow the playback speed as much as possible. With a slower playback you should be able to see where the failure starts and surmise why it fails. A very good book regarding rigging and other associated lift or retention of loads is the IPT Crane and Rigging Handbook which can be purchased on line from WWW.iptbooks.com . or email: iptpub@compusmart.ab.ca . IPT's books are also listed on Amazon.
Dynamic ropes are also absorbing quite much of energy. If you fall into a static rope (which hurts) you will see more kN on the gauge.
"some" data on bend radius strength effects could be extrapolated from the gin pole diameter data in the ANSI/TIA 1019-a also in that technical they claim synthetics need a 10:1 safety factor probably for the reasons you were discovering with friction heat and cutting itself. This is probably why you dont typically if ever see synthetic ropes used in the rescue bag
Something interesting: I was retiring some rope by chopping it into sections with an axe over a stump, and the ends automatically melted/fused from the axe going through it. It doesn’t take a whole lot to melt these things.
Interesting. Never thought of rapid effects of a sharp versus a dull axe, and melting its way through (or not)! Wow.
Got a bowline vs figure 8 break test ?
I am one of the subscribed! Love this channel! :)
Wow, this intro where a man jumping from the mountain is very cool!
Seeing the wrapped sling break strength was great because it's the worst case scenario for an equalised two anchor setup if made with a sling between it. if you're using one sling to two anchors and adding a cross over to attach the equalising carabineer, if one anchor fails, the carabineer slides along the loop to the end effectively creating this scenario.
The 4x twist doesn’t gain the full 4x because it only needs one link of the ‘chain’ to break to unload the whole rope.
The length of rope isn’t equal in strength, as the forces even out the average force will peak above the weakest part and snap it before reaching the overall average of the 4x twist.
Great video I love to see the same for two slings on two anchors connected to one shackle for angles (distance between anchors) at work the lifting slings are marked on a label for different angles.
Seems like PT Barnum marching 21 elephants across the brooklyn bridge to prove its strength wasn't actually that silly
All of these test results are awesome. One crucial point is that the human body will disintegrate at any thing greater than 10Kn.