Testing the strength of cordage

I have a wide variety of types of cordage I would like to test for load bearing capabilities. I am looking for ideas on how to test this without a laboratory. If anyone knows of a good piece of equipment, please let me know. I found a machine that can do it, but it measures in tons, and I need to measure in small increments, from zero to about 1000 pounds (US). The unit of measure is not important as it all can be converted, but the range is essential.

I am not worried about testing without knots as I will always be using the cordage with knots, and I feel this is actually a more accurate measure for practical applications.

I thought about using a car and a strong stationary base as an anchor, I just need to find the piece of equipment to measure the amount of tension. I have also thought about a jack or hydraulic lift, but they either don't have a gauge for measuring or they don't measure in small enough increments.

This forum has always been good for discussing ideas such as this, and I look forward to any and all thoughts on the matter. No idea would be too crazy for the discussion. Thanks.

I will enjoy this thread.

Yes, indeed. Clearly the tension will build to unbearable levels....


Come on Montanero! You didn't really expect help from the likes of us, did you?

Just don't stretch the truth about the results.

In the absence of any helpful suggestions, I will be forced to hang the stuff and put weights on it. I think I will run into problems when I approach the limits of some of the cordage. The Technora claims 950 pounds, and I don't have nearly enough weights for that. I am not sure my rack will hold that much anyway. I will definitely find the limits of several of the components that I have at hand.

Didn't I see the Myth Busters do this with tanks? The gauge displayed the maximum load after it broke. I can't find any such gauges on the internet though.

I have a wide variety of cords: 550 Milspec, 550 commercial, a variety of kevlar thicknesses, technora in 400 and 950, Spectra, and the usual hardware store selection of twines, strings, and ropes.

I would just like to see how strong each really is, and then find the best strength to volume ratio. It is also about really understanding the limits of your gear.

Humor is expected, and even welcome. My fingers and toes would appreciate a better option than hanging weights on it though.

this sounds like a really hi tec project.the stuff you would need would be found in a testing lab.outside of finding a spring scale that handles 100's if not 1000's of pounds and attaching the rope and pulling with a car and watching the results i can't think of any sort of home made gizmo.i would not want to be the guy watching the spring scale when the line busted!!!


i used this old spring scale when i was deer hunting years ago.
it go's up to 500 pounds,more or less.

Joking aside, you might want to do some web searching on field testing of climbing anchors. Folks who do that sort of thing seem to use some combination of hydraulic device for an steady, even, slowly incrementing pull. For the actual measurement they use a various devices called a "load cell" or "pull gauge". Might cost a couple of $K to buy it all, but maybe you can rent or borrow? You also might try to find a college engineering department who will let you do it in a lab as a project by your boy scouts?

Good luck. We are all pulling for you!

I'd use weights from a weight set. Back when I had a home weight set, I could stack 350 pounds on there. The weights would tell me how much tension is on the rope. I'd also try to simulate a knot-less rope, as much as that's possible. Round turns around a large diameter pipe would simulate the no-knot. My old weight set had a weightlifting cage. So, I'd rig the pipe to the cage somehow.

Anything higher than 350 pounds, then I'd take the manufacturer's word for it. At that weight, you're messing with a dangerous amount of tension (not worth risking serious injury). Then, I'd multiply the manufacturer's posted limit by 2/3, and use that as my working max. For example, If the manufacturer says the break strength is 900 pounds without a knot, then I wouldn't push a Bowline past 600 pounds (900 x 2/3).

On the other hand, if I put some fishing-type knot in the rope (which would be a huge knot in regular rope), then I might use that rope at a higher tension than 600 pounds if I absolutely needed to do so.

A few things to consider...

Unfortunately, the results of your test won't really provide meaningful information over the manufacturer's posted limit (assuming the rope is in good condition). Think about it. In the real world, how much tension do you really know you're putting on the line? Plus, on a real job, you're going to subject the rope to shock loading, the effect of which cannot be predicted by a slow load test. You can only make a rough guess, at best, about the effects of a shock load. Personally, I'm more concerned about breaks due to shock loading, rather than breaks due to slow loading. I figure a break due to a shock load is much more likely.

The physics of the rope materials has a lot to do with how the rope responds to a shock load. For example, nylon is quite stretchy. So, a nylon rope will be able to handle a shock load better then a hemp rope for example.

Also, if you bring your rope to its breaking limit, then you have weakened that rope. It's kind of like the Heisenberg uncertainty principle. The closer you get to understanding what you're testing, you inevitably CHANGE what you're testing. So, how does your test give you information about the rope sitting over there on your shelf? It really doesn't. The rope you just tested could have had a random imperfection, or perhaps something is not right with your testing setup. This goes back to the manufacturer's posted limit being the best rough estimate you have.

I do it by comparison.

I take a web/rope of known strength and attach it to the cord in question and then chain with a logging chain to a very large tree (blocked to prevent damage to the tree) and my tow hook on my truck and then slowly pull until something fails.

If the tow hook pulls off--- you have some strong 550 cord.

Mythbusters did this with interwoven phone books, some sort of tension scale and an APC. I don't think you are going to find that kind of scale here in Fayetteville, but one never knows.

Try calling around to some of the machine shops and see if they have one. Failing that, call a local gym and ask if you can use a lot of weights for a short term at their facility.

Good luck

A 55 Gal. drum will hold about 450 Lbs. You could string up the empty drum and start filling it. Note the level of water as you go until it breaks. Fill the drum from a platform beside it so no body parts can get under the drum. Water is about 8.3 Lbs. I think.
Good luck.

The manufacturers of the cord/ropes will provide reasonably accurate breaking strain forces for their cords/ropes especially where there is a safety issue.

Breaking strain forces are not the be and end all of manufacturing cords and ropes. There are elongation, dynamic loading, creep, environmental specifications as well. i.e. Mil spec Paracord being nylon has a 30% minimum elongation specification before breaking etc.

https://en.wikipedia.org/wiki/Parachute_cord

There are many types of paracord with a wide range of breaking load forces.

Dyneema cord/ropes will have a much higher breaking strain forces and improved minimum elongations etc.

Kingfisher evolution race 4mm Cord have a breaking strain of 720 Kg or 1580 lbs. i.e. 3x MIL-C-5040H 550 type III cord.

http://yachtropes.co.uk/race.php

Are you intending to do some emergency abseiling? Using paracord is probably not a good idea!

http://www.youtube.com/watch?v=OeF-Vcq2g5Y

I am more concerned with the cords I find that do not have manufacturer information. I find the 550 in the surplus stores and the other types of cord on line. It is as much about checking the veracity of marketing claims as it is knowing about different types of cord. I find some at good prices, but I would like to verify their claims to a reasonable degree. I was just looking for techniques for doing so.

It seems that if you're looking to verify manufacturer claims, then maybe you need to look into how manufacturers rate their ropes. Does 500 lbs mean static tension, holding indefinitely? Or does it mean a one foot drop with 500 lbs attached?

It seems like anything involving more than a few hundred pounds could be very dangerous. I started thinking about how I'd design a tester, and then I thought, hey, someone's probably done that. Lo and behold:

http://www.youtube.com/watch?v=JVRI45AXOHA

It seems that the company (http://admet.com) sells a bunch of testing machines. Buying one of these is probably the best thing to do, though it may not be the cheapest.

If you can work with metal, you may be able to make a similar tester with gears.

If only approximate testing of the strength of cordage is required, then you can make your own test rig fairly easily.

Obtain a short length of substantial RSJ or timber, and support each end of this on a small pier or column of bricks or concrete blocks.

Attach the sample to be tested to this support, and attach weights to the sample until it fails.

To avoid danger from the end of the tested cord whipping around, or from the weights falling, arange such that the weight will only fall an inch or so.

A suitable weight up to about a ton is an IBC of known empty weight. Suspend this from the sample, and fill with water from a safe distance by use of a garden hose.
Either measure the volume of water added by a water meter, or use a container with markings as to volume.

With a little ingenuity, other methods can be devised. Use of a water container that can be emptied or filled remotely has much to commend it as no close approach during testing is needed.

How you apply the force depends on what you want to measure. Do you want to test a static load or a dynamic load?

A static load requires you to slowly and gently add weight and you are measuring a weight.
A dynamic load, depends on what kind of dynamic load you want to test. But you test with a force, so newtons instead weights.

Anyone know the aprox. strength of jute? I am curious about replacing some of my synthetic cord on shelters with jute. Need something with a strength of about 80 lbs. Wondering what diameter would be needed.

The only tool you really need is a set of max recording spring scales in the ranges (at 50% of full scale) that you need. You can get by without them by using an increasable load (the water barrel or weight plates suggested above). You need something to provide the load, but many good ideas have been recommended for that. The way you use it will certainly depend on the information you need. There are standards for testing that will make the information consistant. NFPA, UIAA, ASTM, CEN and many others have their testing protocols. In order to understand and compare strength you need to know how the rated strength is obtained.

Safe working load may vary from 25% of the breaking strength for non-critical situations to about 7% (15:1 ratio per NFPA) for supporting humans (climbers have traditionally used a 10:1 safety factor). Knots can reduce breaking strength by as much as 50% or as little as 15 or 20%.

Respectfully,

Jerry

If you are looking for a natural fibre rope/cord to replace synthetic paracord then hemp would be a better bet with a higher breaking strain over Jute.

A 5mm braided Hemp rope/cord has a 190kg breaking strain.

http://www.jaderope.co.uk/natural-hemp-rope-5mm-braided.html

Why on earth would you want to do this?

Sustainable, provides jobs in poor countries like Bangladesh, can be used as tinder, bits left around decompose quickly, processing the plants just takes water.

Hemp is hard to come by, don't know how it works as tinder, also don't know how "green" industrial hemp manufacturing is.

Figure I need about 80 lbs breaking strength as force on tarp cords attached to tarps of silnylon in high wind gusts generally do not exceed 40 lbs.

I'll bet jute comparable in size and weight to 550 cord would be strong enough.

The jute is going to be a lot less stretchy the synthetic nylon (e.g., most paracord). That's something to consider if you're tying down a tent, tarp, etc. You may get the jute taught. Then, the wind blows the wrong way, and suddenly there's slack in the line. That's just something to keep in mind.

Just want to try it out. I currently use 1mm polyester and it works great and has little stretch. Paracord is way overkill. The parachute nylon of the tarp is super stretchy and would limit dynamic loading just as a climbing rope limits strain on wire stoppers.

Natural fibers like jute and manila are obsolete for rope and cordage. They degrade more quickly and unpredictably than synthetics and in every respect are inferior.

I'll bet the force exerted on a tarp in high winds can easily snap jute in the size range of paracord. Actually, there are now better materials than paracord for light cordage suitable for shelters and similar. I've got some stuff that is one half the size and twice the strength of 550 - "ironwire" is what the supplier calls it. It's actually pretty hard to beat braided mason's twice for most uses.

Big gusts can pull out stakes, bend or break poles, blow tents away, and cause all sorts of havoc. A strong gust could easily break jute.

One trick I learned is to tie a short loop of shock cord through the tie in points on your tent or fly. Then tie the guys in to that, and stretch them snug. The shock cord keeps the guys tight, and creates a bit of give when the wind gusts hit. Less wear and tear on the tent or fly. And you sleep better with less distraction from a flapping fly.

Unless you use very heavy shock cord, it will provide too much stretch and increase the sawing motion on stakes etc. You need to pre-stretch the fabric to keep flapping to a minimum.

Check out these tarps backpackers are using made from shrink wrap and tape.

http://www.backpackinglight.com/cgi-bin/...le_pagination=1

You use stout shock cord and very short little loops (perhaps 2-3" in diameter). Because they are loops, you effectively have double shock cord. When you set up the tent, you pull the guys snug, so the shock cord is stretched slightly. When wind gusts hit, it stretches a bit more, but softens the jerk.

The method has worked quite well, in my experience. Way better than tying the guys directly to the fly.

The excellent book "On Rope" by Bruce Smith and Allen Padgett (about North American vertical rope techniques, published by the National Speleological Society) has a section on measuring rope strength, and here are a few points it mentions:

• There is a U.S. test standard: 191A, Method 6016
  
• It involves wrapping rope around two cylinders that are pulled apart at a fixed rate. All the parameters/dimensions are spelled out.
  
• Lots of factors affect strength, and lots of different things can be measured as "strength"
  
• Practical, real-world values may be significantly different from what is measured in a lab

From my own brief experience measuring Nomex thread strength in a university Textile Engineering lab, ideally what you might like to get is not a single number, but a graph of the relationship between elongation and pulling force.

Steve

Montenero - I like the suggestion of suspending a steel drum and filling it with water. You can calibrate the height of the water level against the total weight (drum plus water). You can suspend the drum with extra strength paracord, and then you only have to loop the cordage you are testing through the paracord.

good luck,
Pete

Here you go, just out:

http://rockexotica.com/enforcer/index.html

Pete

That is very cool. Test whole systems, Falls, Fabrics, Thread, Stress on joints from different activities. Bunch of stuff could be measured.

What is the price of the "enforcer?"? I could not find it anywhere...

About $700.

Thanks. That is exactly the type of thing I was looking for.