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slacklinejoe
May 11, 2008, 2:46 AM
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I just got back from conducting my first slackline load testing experiement. I'm hoping to make these a lot more comprehensive than anything else out there. That won't take much since nearly no real tests have been done and any that have been done have no published data. Right now I'm looking for proposed scenarios to test as well as suggestions on improving my testing procedure.
Here's the data with objective and subjective write up.
Slackline Load Test #1
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majid_sabet
May 11, 2008, 7:35 AM
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slacklinejoe wrote: I just got back from conducting my first slackline load testing experiement. I'm hoping to make these a lot more comprehensive than anything else out there. That won't take much since nearly no real tests have been done and any that have been done have no published data. Right now I'm looking for proposed scenarios to test as well as suggestions on improving my testing procedure. Here's the data with objective and subjective write up. Slackline Load Test #1
Good work Joe, but what is going on with # 5?
Why there is 10% diff on that one while the other ones are very similar to each other?
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slacklinejoe
May 11, 2008, 4:06 PM
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Majid,
Did you read through my notes on what I decided to call pre-load decay? That's my suspect.
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majid_sabet
May 11, 2008, 4:16 PM
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slacklinejoe wrote: Majid, Did you read through my notes on what I decided to call pre-load decay? That's my suspect.
Joe
let's say we leave the system under primary tension ( no weight in the middle) for some time and then take the reading. How much of a difference do you think we may see?
I mean from an hour to like six hours taking measurement every 1/2 hour.
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slacklinejoe
May 11, 2008, 4:26 PM
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The elasticity of webbing is a most peculiar thing. I've done just that before I had the load tester and it had lost most of it's tension in that time. When re-tensioned back to where I wanted it, it still slowly loosened up even more.
I do want to point out that it may not be ideal to make the webbing enter into a static condition. It might make testing easier but it will skew the numbers significantly from what normal slacklining will produce. In the mean time, I'd rather adjust for pre-load decay during testing and have numbers people can use. If anything else, the system acts as I giant load limiter, which is actually good for safety.
To give you an example, I set up the line at 650lbs. I watched it drop down to 580 during a break. I reset it at 650 and watch it drop slowly. I leaned against the line, let up, and looked at the scale - down to 590. I kept re-tensioning it in between each measurement but all in all after over an hour at the same tensiong (after spending 2 hours stretching out at lower tensions) it was still stretching.
The odd part is to my feet, this was inpercievable until it lost closer to 100 lbs of lost pre-load. In parts I think I perceived that I was getting used to the higher tensions when in fact the tensions had finally dropped closer to what I'm used to.
(This post was edited by slacklinejoe on May 11, 2008, 4:37 PM)
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AeroXan
May 11, 2008, 9:24 PM
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i wonder if you're observing creep. or maybe slipping in the tightening system. i imagine something like webbing would suffer from creep pretty noticeably. especially because of the weaving pattern tightening up.
also, i was wondering how bad a slackline failure would be. do you think the tension is high enough that the flying line could cause dismemberment? I've heard of this kind of thing with other ropes and steel cable.
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slacklinejoe
May 11, 2008, 11:25 PM
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Zero creep is possible in the tensioning system we use, that's why I picked it for this test instead of pulleys. No knots are used at any point in the system, nor any hardware that would allow slippage beyond the initial setting of the webbing. I was able to make marks on the line to verify this anyway.
Dismemberment? I don't know about that but I have heard where a carabiner broke an ankle. Keep in mind that I tested tensions far beyond normal slacklines would be exposed to, and peak load was still 25% of the webbings rated strength (it actually breaks higher than that).
The webbing itself doesn't carry the same momentum as cable and when we tested breaking it under simulated loads the result was generally unimpressive. Adding hardware into the equation obviously changes this fact, but safe rigging should be observed regardless.
(This post was edited by slacklinejoe on May 11, 2008, 11:26 PM)
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jt512
Jun 20, 2009, 11:41 PM
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slacklinejoe wrote: I just got back from conducting my first slackline load testing experiement. I'm hoping to make these a lot more comprehensive than anything else out there. That won't take much since nearly no real tests have been done and any that have been done have no published data. Right now I'm looking for proposed scenarios to test as well as suggestions on improving my testing procedure. Here's the data with objective and subjective write up. Slackline Load Test #1
The slope of that "predicted" curve looks pretty screwy. I'd venture a guess that either your model is wrong, or that you applied it incorrectly. Also, your description of your testing methodology is lacking important details.
Jay
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slacklinejoe
Jun 21, 2009, 4:14 AM
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jt512 wrote: I'd venture a guess that either your model is wrong, or that you applied it incorrectly. Also, your description of your testing methodology is lacking important details. Jay
slacklinejoe wrote: Right now I'm looking for proposed scenarios to test as well as suggestions on improving my testing procedure. |
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jt512
Jun 21, 2009, 9:16 PM
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slacklinejoe wrote: jt512 wrote: I'd venture a guess that either your model is wrong, or that you applied it incorrectly. Also, your description of your testing methodology is lacking important details. Jay slacklinejoe wrote: Right now I'm looking for proposed scenarios to test as well as suggestions on improving my testing procedure.
It's hard to critique your methodology when you haven't described it. Or did I miss it?
Jay
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slacklinejoe
Jun 22, 2009, 12:41 AM
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I listed what I listed. If you click enough links, you'll find the calculation models involved (even cited). This isn't a lab study, this is me setting up a slackline where I commonly slack and taking the time for dynometer readings. Find me anything better that's public information, or create your own and then your free to bitch about my methodology.
As duley noted in the tests, it enough data to be a useful start for future testing, but that's all it was intended to be - an absolute first step in understanding both the loads and elastic forces involved in slackline systems. Hence the request for recommendations on future testing prodcedures which would extend the knowledge and understandings of slackline systems.
But hey, you tell me what you are looking for to help with your slackline specific testing procedures or your understanding of the slackline specific content covered and I'll see what I can do to help you comprehend... no promises though, I haven't had luck teaching my dog geometry.
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jt512
Jun 22, 2009, 1:32 AM
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slacklinejoe wrote: I listed what I listed. If you click enough links, you'll find the calculation models involved (even cited). This isn't a lab study, this is me setting up a slackline where I commonly slack and taking the time for dynometer readings. Find me anything better that's public information, or create your own and then your free to bitch about my methodology.
I'm not "bitching" about anything. I couldn't give a flying fuck about slackline tension. I was attempting to provide constructive criticism, since you apparently care about slackline tension. I won't make the mistake of trying to be helpful to you in the future.
And if you don't want your testing subjected to criticism don't post your tests in The Lab.
Jay
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sixleggedinsect
Jun 28, 2009, 5:02 AM
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slacklinejoe wrote: Right now I'm looking for proposed scenarios to test as well as suggestions on improving my testing procedure.
im guessing you are doing this for your own line production, so a lot of the oddball scenarios id enjoy seeing numbers from are probably not interesting to you.
that said, im no slackliner, but i am curious about the forces seen in dynamic falls onto the slackline, as in when folks are walking high lines with a harness and tether and dont catch the line on the way down. id imagine this might be particularly high due to more fall energy and im guessing these long lines need a lot of pretension just to get things going.
id also be curious if you could make a field-quantifying mech for guessing line tension. maybe something like - if you isolate a ten foot section of the line (say, by having two people hold their fingers under it so it wont sag under load) and hang a two pound weight on it (roughly the weight of a full nalgene, im guessing), a line with XX pretension will sag XX cm, etc. this would crossover to ropes and rescue back-ties and whatnot, and if it was even a little bit repeatable without your tools would be an interesting and possibly useful thing to have on hand.
finally, im guessing a quick look at how various types, ages, etc of webbing and how they compare would be useful to anyone who cares strongly about SL tensions. for instance, new ribbed nylon, vs smooth nylon (which im guessing is milspec vs climb spec), and various vintages of those two. pretension all to some mid-range and see how they act (do they lose/hold tension the same? do they sag the same?)
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slacklinejoe
Jun 28, 2009, 5:11 AM
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sixleggedinsect wrote: im guessing you are doing this for your own line production, so a lot of the oddball scenarios id enjoy seeing numbers from are probably not interesting to you.
Actually, I'm game for a fair amount of testing. I don't have a dedicated pull tester system and I see no reason to compete with the existing testing systems, but I've got an accurate dynometer and interest in dynamic loads, elasticity and anything slackline related.
One of my proposed tests right now is testing the efficency ratios of various techniques for pulling a line tight. 3:1, 4:1, 5:1 whatever with carabiners, pulleys. I've ran into a lot of bullshit claims regarding it and I'm legitamently interested in how much pulling power the average person really has at their disposal. Anyone have rigs they'd like to see set up and tested? How would you like it done?
I was thinking of using a verticle rig with the dynometer in load and using a known weight (such as several 25lb weights) on the system to generate effective mechanical advantage. Is that something people would find interesting? What guidelines would you want to see to ensure it was fair testing?
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sixleggedinsect
Jun 28, 2009, 5:24 AM
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slacklinejoe wrote: One of my proposed tests right now is testing the efficency ratios of various techniques for pulling a line tight. 3:1, 4:1, 5:1 whatever with carabiners, pulleys. I've ran into a lot of bullshit claims regarding it and I'm legitamently interested in how much pulling power the average person really has at their disposal. Anyone have rigs they'd like to see set up and tested? How would you like it done? I was thinking of using a verticle rig with the dynometer in load and using a known weight (such as several 25lb weights) on the system to generate effective mechanical advantage. Is that something people would find interesting? What guidelines would you want to see to ensure it was fair testing?
oh, hell yes. id be very curious about real-world hauling setups. you want to pull your line tight. i want to have an idea waht works best for field self-rescue and finagled haul rigs. for instance- i can build a 5:1 quickly to haul my partner past a roof he can't follow, but is it worth it with the additional friction vs. a 3:1?
id be curious to see the maximum forces that could be generated by various 3:1, 6:1, 5:1, and 9:1 rigs built with no pulleys and standard rope-diameter biners. i dont know how well it would work with hanging weights, as i imagine that the static vs kinetic friction thing would make a huge difference and those weights wont be heave-ho'ing. maybe you could mock up a 'heave' with standarization by effectively dropping weights from a given height. id also use more than 25, as we pull harder than that most times.
or, its unscientific, but the 'control' could be the same guy/gal heaving on the line in similar circumstances. just dont tucker her out.
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slacklinejoe
Jun 28, 2009, 5:25 AM
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sixleggedinsect wrote: I am curious about the forces seen in dynamic falls onto the slackline
sixleggedinsect wrote: id also be curious if you could make a field-quantifying mech for guessing line tension.
I think the most unusual part of these equations is that preload seems completely independant. If you place high pre-load on the system to reduce deflection, when you stand on it, the numbers are still on part with what you'd expect if you were using static line. Basically, if the weight of slacker, line length and deflection (sag) are the same, you pretty much have the same effective load in the system. I'm sure there's something I'm forgetting though, but I haven't tested a slackline scenario that this wasn't the case.
sixleggedinsect wrote: a quick look at how various types, ages, etc of webbing and how they compare would be useful to anyone who cares strongly about SL tensions. for instance, new ribbed nylon, vs smooth nylon (which im guessing is milspec vs climb spec), and various vintages of those two. pretension all to some mid-range and see how they act (do they lose/hold tension the same? do they sag the same?)
Honestly, without a standardized elasticity testing load, I'm not sure it'd be practical for comparisons. For ropes we have a UIAA testing process to determine a % elongation. To my knowledge, we don't have the same universal standardization for % elongation for webbing.
For an example though, polyester tubular webbing woven in a mil-spec pattern (not technically mil-spec since it isn't nylon) has 15% elongation at 1,500 lbs. Subjectively though, this stuff is less elastic that nylon. Is that what you are looking for, or are you looking for more subjective data?
To subjectively answer the question, actual ability of webbing to hold a load without losing tension over time (a situation that I call "Preload Decay") varies all over the place depending on the weave, humidity, material used and even between colors of the same batch of webbing. How much of a difference is worth noting, that I don't know. My feet seem far more indifferent to sutble line tension changes, something that suprised me considering the amount of time I spend on a line.
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slacklinejoe
Jun 28, 2009, 5:32 AM
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Just thinking outloud here, but what about first measuring someone just yanking on the dynometer with webbing, that'd give us the ballpark of what type of loads to introduce into the system. It'll vary all over the place so we'd need to find a number we could live with for static testing. Thoughts?
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sixleggedinsect
Jun 28, 2009, 5:32 AM
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slacklinejoe wrote: Good idea, but from experience there is going to be wild variation in that number, both over time and due to the variability of elasticity in webbing.
pipe dreams, hm? i figured it might not be reasonable. thanks though.
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slacklinejoe
Jun 28, 2009, 5:37 AM
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sixleggedinsect wrote: pipe dreams, hm? i figured it might not be reasonable. thanks though.
Actually, give me a bit more time with that thought before writing it off. Here's a scenario I have in my head that needs testing.
If say for instance we take a fish scale, and introduce 25 pounds of pull onto the center of the line measuring deflection, we may have a high enough number to enter it into the static calculation formulas. I don't know if this number would be useful or not, but as long as the line enters an elastic state, we may have a usable field test.
For the record, I don't think 2 lbs is close enough to force most lines into an elastic state. It's actually an elasticity curve, until you hit at least 400 lbs, you don't see much system stretch at all in most mil-spec or climb-spec lines.
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sixleggedinsect
Jun 28, 2009, 5:37 AM
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slacklinejoe wrote: Just thinking outloud here, but what about first measuring someone just yanking on the dynometer with webbing, that'd give us the ballpark of what type of loads to introduce into the system. It'll vary all over the place so we'd need to find a number we could live with for static testing. Thoughts?
sure- have a few people heave the amount they think is reasonable for tensioning a line, or raising a haulbag, etc. then see what it takes to make that same dynamic 'heave' with bits of rope and string and weights with a repeatable standardized setup.
then see if homemade purchase rigs are as efficient as we hope. test multiple 'heaves' of course because if the results are all over the place it would be hard to trust the data. and i can imagine with all the friction with biner pulleys it might be tricky to get good results.
i admit im more interested in seeing haul rigs made out of rope than out of webbing, like i see most lines setup with. (no climber would ever use those multiple-overlapping-loop purchase systems for a climbing application). id be pleased to sned you some used dynamic rope if you thouht youd ever get around to this.
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sixleggedinsect
Jun 28, 2009, 5:40 AM
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slacklinejoe wrote: sixleggedinsect wrote: pipe dreams, hm? i figured it might not be reasonable. thanks though. Actually, give me a bit more time with that thought before writing it off. Here's a scenario I have in my head that needs testing. If say for instance we take a fish scale, and introduce 25 pounds of pull onto the center of the line measuring deflection, we may have a high enough number to enter it into the static calculation formulas. I don't know if this number would be useful or not, but as long as the line enters an elastic state, we may have a usable field test. For the record, I don't think 2 lbs is close enough to force most lines into an elastic state. It's actually an elasticity curve, until you hit at least 400 lbs, you don't see much system stretch at all in most mil-spec or climb-spec lines.
sounds tempting. the important idea i had was to be able to do it in the field without any special gear. estimating weight with water might be doable, but i dont bring a scale with me on a regular basis. although maybe i could protect tight chimneys with it, come to think of it..
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slacklinejoe
Jun 28, 2009, 5:43 AM
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Well, I could always do dynamic rope and static rope as well. Some people still use either in slackline tensioning, mostly in Australia though. They seem to have a passion for those silly little orange petzl pulleys that I broke a dozen off trying to get short lines set.
Granted, no matter what I do, I'll run into the problem of claims of product bias so I'm tempted to find someone on here in the boulder area to oversee the testing.
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