Cordage Breaking Strengths

[Aussie Forager CQ]

Hi All,

G'day everyone. Long story short, I work as a rope access technician. The employer I work for owns 'The Rack' - a hydraulic test bed designed for pulling rope, carabiners and rope access/height safety related equipment until they break and recording the force required to do so. My employer has kindly agreed to allow 'The Rack' to be used to break/test natural fibre cordage and rope made by BushcraftOZ members.

This would allow BushcraftOZ members to send in rope/cordage that they have made and have it tested and the breaking strength recorded. Then the results of the tests would be posted for viewing and use of the forum.

'The Rack' will allow the tests to be done quite scientifically, I would suggest all the interested BushcraftOZ members, together, arrange specifications for the tests and come up with a process that everyone is happy with, we could have more than one set of criteria for certain circumstance, different diameters...... whatever really, the possibilities are endless. Mainly I would suggest the aim is for collating results on the different type of fibers available in OZ.

I am happy to give some ideas that may help, from experience I've already had from seeing 'The Rack' in action.

So if anyone has any thoughts, yell out....all that is needed is people to be keen, make some cordage, send it through and we can see some results.

Anyone keen??

 

[Wentworth]

Great idea and offer! I wonder how we'd standardise the cordage, in terms of thickness of the component strands etc?

 

[Aussie Forager CQ]

Yeh I have had the same thoughts, so far I have thought we can set ideal diameters that we try to make e.g 3mm and 6mm or whatever we come up with, and then put the verniers on the test piece when we break it, maybe a system of taking an average diameter of a standard length of cord....

 

[Greatbloke]

Great idea and offer! .***

That ^.

 

[Corin]

Keen as Mustard!!!!

How long do samples need to be?

Do you knot the samples onto the machine or splice, or some other method of attaching that won't weaken the rope?

 

[Aussie Forager CQ]

Keen as Mustard!!!!

How long do samples need to be?

Do you knot the samples onto the machine or splice, or some other method of attaching that won't weaken the rope?[/

To get an actual breaking strength of a rope without a knot it is usually tested with a 'no knot' or a tensionless hitch type set up and you would know what the actual strength of the rope is - without a knot. However this would mean we need a little more cordage per piece to enable the wraps for the hitch. We can test pieces like this.... Anoher option is that when we use the cordage it would no doubt have a knot in it so we can test each piece with a knot, it would be easier, not as much material needed and we can repeate it easily. It would also give us a relative 'worst case' for each type....an 'overhand on the bight' is an easy knot to tie (especially in small cordage) and would give a good worst case as it does reduce strength quite a lot.......either way it won't be hard to work out what length is needed for either test. (there doesn't have to be much in the middle of the knots/hitches e.g 100mm from knot to knot)........

 

[Corin]

sounds good, I probably have some samples for you already...

I would suggest rather than worst case, we test best case. this stuff is not exactly synthetic, we will be talking breaking strains of around 20-40???kg or so and if we weaken that by 60% or so the process will be less than impressive. if the rope is spun in such a way that it can be spliced, in my opinion it should be tested spliced. (ie I would like my samples tested spliced if possible) I will see what I have about tomorrow...

 

[Aussie Forager CQ]

Corin,

Yeh point taken, best case sounds good. I'm happy to run with that if everyone else is....it does make sense, then allowances can be made by the user as per what knot is chosen (we can always do tests with a knot if someone wants to). I'm assuming most of us are making two ply cordage, in that case I'm not sure of any great ways of splicing loops or ends to an object with two ply. Having said that, i am not an expert with splicing, much more experience with modern kernmantle and braided ropes, there may well be a good way of splicing two ply that we can use. I know that if you imagine feeding the tail of the cordage around an object - or to make a loop, and pass it through it's two ply's, and then through itself again the other direction (and again if wanted) quite good strength can be gained. I have not tested this though, but it may be an option.... Three ply would be easy.... There is definately nothing stopping us from using a 'no knot' to do the test, this would give us 100% strength of the material, we just need a little more cordage per test that's all.

Lots of options....either way there will most likey be a 'learning period' when we start testing things that havent been done before, to really fine tune the system. Mind you I'm happy we can get good results very quickly.

I am in the process of changing address so it wont be until mid next week that I can put the postal address up, I shall put it up as soon as I can and we will be underway!


Chutes,

Yeh mate I do have a great boss, I'll pass it on. I like the idea of testing those materials you mentioned. Definately would be interesting to know, I will ask the boss, I'm hopeful he won't mind doing the odd piece here and there, he does like breaking things after all. I think it would be helpful for our natural cordage tests as well...to give us something to compare against....

 

[Wave Man]

excellent offer mate, I will be interested in seeing the results

 

[GTVi]

I'm keen to see some numbers.

 

[Corin]

I will have three samples for you on Monday, Giant Stinging Tree, Blackfellows Hemp, Illawarra Flame tree. When you have an address we will get things rolling I will supply the samples at 100mm long + an eye splice on each end. Thickness for each sample will vary some, as I did not make them with testing in mind. but they will get you started.

 

[Blake]

Awesome offer mate. Please thank your employer.

I could offer some also. Out of interest. How do people feel about testing some leather cordages? I have quite a few different leathers and hides here, chrome and veg tan that I could strip and make into cordage as well. Roo, with and without fur, Rabbit, fox, bovine etc. I would be happy to make some with different variations. I have been playing with some different variations of leather twists and plaits as it stretches alot. Sometimes this is desirable, sometimes not and I use different plaits depending on if I want it to stretch or not. I have also been working on making a "braiding soap' which makes the leather bind alot tighter and theoretically stronger but ive never seen numbers that back this up. It would be great to put my theory to the test under controlled conditions.

Would that be ok with everyone? I think it would still come under natural cordage despite not being a plant fibre? Thoughts?

 

[auscraft]

I would be keen on the results Blake and yes I say natural cordage

 

[Aussie Forager CQ]

Blake, leather cordages sound like a great idea,I would be definately keen to see some results with the different variations. Definately in the same category I reckon. I'll be able to rustle up some wallaby raw hide.....maybe some different raw hide strip breaking strengths.... Got me thinking as well!!

I should have the postal address sorted by the end of the week, so as soon as I know ill post it up.

I have a few more notes for when people send stuff in as well, let me know what yous think.

- firstly and obviously, be aware that your pride and joy will not be coming back, at least not in the same piece (literally). I am happy to post back the pieces after they are broken, if so just include a self addressed envelope and l will send them back. Otherwise they will be thrown out or kept for reference eg. Take a photo of a selection together to put names to numbers.

- If we make each piece the same length we will get some good comparative results. So i think 100mm will work good if the material is already knotted or spliced, so 100mm between the base of each knot or the base of each splice.

- If we choose to break a length without a knot or splice it will have to be a minimum of 1000mm long to allow for wrapping of the tensionless hitch type set up.

- When we send pieces in just make sure they have a label on them to describe what they are made of and which one is which.

- The more information we can gather for each piece we break the better :-
- senders name (Aussie Forager CQ etc)
- material of plant (inner bark, leaf fibre, stalk fibre etc)
- construction (Z lay reverse twisted 2 ply, thigh rolled 2 ply, 3 plait etc
- average diameter
- age - date collected, date made (made on xx/xx/xxxx or just a rough time line, 1 moth old etc)
- condition (anything that you think may be worthy of note - brand new and not used, light use, has been used alot and may have been overloaded, good condition, was left in sun for two weeks etc)
- process for obtaining fibers (retting, pounding, scraping, peeling direct from source etc)
- solutions used during process
- is the piece spliced or is it a full length of fibers
- whatever else yous can think of

All the above information does not have to be included but the more info we have the better and we will be able to get some relatively scientific results, just include whatever you think worthy on a bit of paper or post it onsite.

When we break it I will record and post the following:-

- breaking strength in Newtons (very closely 1000N : 100kg)
- approximate stretch at time of failure
- failure point
- any other worthy notes and all the information sent in

An example of a perfect world report might be something like this.....

Test # 1 (I will number them)
Maker - AFCQ
Plant/material - Rubber vine, Cryptosetia Grandiflora
Part of plant/material - Inner bark
Process - pulled strips of bark (inner and outer) direct from plant and twisted into cordage while fresh
Construction - Z lay Reverse twisted two ply.
Average diameter - 2.5mm
Age - collected and made on 25/04/12
Condition - never been used and stored out of sunlight
Splices used for length? - yes
Testing process - wraps around bollards to achieve 100% breaking strength
Length - 100mm distance between bollards

Breaking strength - for example 200N
Stretch - 50mm
Failure point - suspected faure in a splice point

If there is anything else people think would be good to see here just let me know.

As I said the more info the better, I would imagine this sort of testing is hard to come by....
Having said that, if all you can or want to do is send something in as is, we will break it and tell you what it broke at. Either way we get to break stuff!

 

[Aussie123]

@Blake. I'd like to see the leather breaking strains - very interesting. There may some other types of material too, but I'm not sure what ?

Bailing / fencing wire has to be a common enough "binding" material, but there are quite a few types about ?

 

[Greatbloke]

I have a suggestion; it's not natural cordage, but it is something that we could use in the bush, and would be an interesting comparison. If someone sending in cordage would also send in some platted strips of plastic supermarket shopping bag, and/or or garbage bags, it would be interesting to compare..for that matter you could plat strips of the green enviro bags.

The list is endless really..platted duct tape, bandages....

 

[Blake]

I have a suggestion; it's not natural cordage, but it is something that we could use in the bush, and would be an interesting comparison. If someone sending in cordage would also send in some platted strips of plastic supermarket shopping bag, and/or or garbage bags, it would be interesting to compare..for that matter you could plat strips of the green enviro bags.

The list is endless really..platted duct tape, bandages....

True enough. Cotton shirt material etc could be used in a fix?

 

[Aussie Forager CQ]

Hi All,

Bit of a delay but I now have the postal address for BushcraftOZ members to send their home made materials for testing. It is:

PO Box 9807
FRENCHVILLE QLD 4701

Refer to my earlier post for additional details. Feel free to start sending items in. Looking forward to seeing some work and
results!

 

[Corin]

Hi All,

Bit of a delay but I now have the postal address for BushcraftOZ members to send their home made materials for testing. It is:

PO Box 9807
FRENCHVILLE QLD 4701

Refer to my earlier post for additional details. Feel free to start sending items in. Looking forward to seeing some work and
results!

Sorry, I missed the post with your address. I will post out 2 samples today.

2 x Illawarra Flame Tree
1 x Blackfellows Hemp.

 

[Aussie Forager CQ]

Sorry, I missed the post with your address. I will post out 2 samples today.

2 x Illawarra Flame Tree
1 x Blackfellows Hemp.

Cool mate, look forward to seeing them, just let me know what terminations you want them tested with.

I thought I'd get the ball rolling today as well with a synthetic test. Definately setting the benchmark high but gives us something to go off. I have used this Chute cord as it is relatively common and something most people have had something to do with.

1kN ~ 100kg

Test # 1
Manufacturer - Sterling rope
Material - Nylon 550 GI Chute cord (as per below photo)
Diameter - Aprrox 4mm at widest point.
Age and condition - brand new and unused

Conducted three tests.....

1. Overhand on the bight Vs Figure 8 on the bight

Result - Figure of 8 was victorious......overhand broke at 1.75kN

2. Clove hitch with two half hitches Vs Inside Bowline

Result - Clove hitch is the winner! Bowline broke at 1.63kN

3. Loop....joined with double overhand bend.

Result - Loop broke at 3.77kN

Just keep in mind knots are always variable and will give different results with different material but it gives us a good rule of for this cord though. Hope that is usefull Keen to hear you thoughts!