Break Test Extravaganza(s)

[Brion Toss]

Hello all,
Thanks to those who have sent in pieces to break. We are getting ready to send them on to Treestuff, so if you have been planning to participate, it is time to get in gear. And it isn't just for soft shackles, so if you have any sort of experimental rope structure to test, there is room.
Fair leads,
Brion Toss

[MarkG]

Thew were sent priority mail today and should be there by Monday.

Mark

[Anton B]

Do I send them to 313 Jackson Street PT WA?

Anton

[Brion Toss]

zip is 98368

[asdf777]

Hi, did I miss the results or the tests haven't been done yet?

Thanks!
Gleb

[Brion Toss]

Hi,
And oops, sorry not to have kept you posted. After some delay, Treestuff will be breaking the samples very soon, maybe even by tomorrow (Friday, 12 June).
Fair leads
Brion Toss

[Brion Toss]

Hello all,
The good folks at TreeStuff sent results of the break tests today. With over 30 samples of various constructions, diameters, and materials, it will take a bit to analyze the data. So for the moment I'll just say that a new "bifocal" configuration broke the 300% mark. This configuration is the brainchild of Mark Gardiner. The samples he made did not do so well (average of about 100%), but a variation on it, which is also easier to make, broke all previous records. Thanks, Mark!
I'll be posting details on all the breaks, as soon as I sort things out.
Fair leads,
Brion Toss

[allene]

So, how is it going?

[Brion Toss]

Hello all,
My apologies for neglecting to report on the break tests. No excuse; I've had the results, but just hadn't gotten around to organizing them. So, a brief, most belated summary:
First, rate of pull. In previous tests, at New England Ropes and elsewhere, the hydraulic cylinder was set to move at about 12"/minute, while the cylinder at TreeStuff, where the current tests were done, moved more than twice as fast, at 27.5"/minute. At the slower speed, the knot has a chance to "set" before a serious load comes on. At the higher speed, we wanted to see if the set of the knot and the rate of pull had an effect on the strength of the shackles; in the real world, people might not take the time to set shackles they build, and the load will tend to come on faster than in the lab. Sure enough, the average break strengths were lower than had been reported in previous tests. The "standard" Lanyard Knot configuration averaged 106% of rope strength, instead of at least 120%, for instance.
Interestingly, the results for the button-knot-and-bury shackle were not significantly different than the slow-rate tests; I am guessing that this is because all four parts of the button version draw up under load, while only two parts of the lanyard version do.
We can't do much about bringing the load on gradually, but it seems pretty clear that setting a new shackle is an important step, at least for the lanyard version.

Next, effects of diameter. In all of our tests so far, the bigger the rope, the lower the relative break load. For instance, with 5/32" rope it is not uncommon to get breaks of 280% with the button version, but by the time you get to 11mm results are down to about 160%. The only explanation I have is that it is much harder to produce a fair, snug knot in larger materials than in smaller. This scaling factor seems to explain the range in break strengths we seen from other people's tests. For instance, the estimable Evans Starzinger was getting, as I recall, about a 150% average for the lanyard version, while New England was showing more like 120%. With larger rope than Evans could break on his machine.
If further tests confirm this scaling effect, then we will need to scale shackle strength to rope size, instead of using a blanket average number for all sizes. Further, the scaling effect argues for the use of the inherently stronger button version, because with it we can use smaller rope, with a higher efficiency, for the same load. This effect also seems to undo, to some extent, the advice to use the lanyard knot version, but with larger rope, if greater strength is required, because greater rope size does not seem to result in correspondingly greater strength.
I am trying to avoid confirmation bias here (the button version is my baby), but must also note that smaller rope simplyfits into places that larger rope can't, which matters in things like connecting rope to chain for rodes. It is also easier to get an acceptable radius for the bearing point of smaller rope. So even though the button version is more difficult to make, it seems to be worth the effort for many applications.
Next, operator skill. For a given configuration, how well the knots were formed made a huge difference. One tyer, skilled at making the lanyard version, and with a 135% break average to prove it, got a less-than 100% average for his attempt at the button version, instead of the over 200% results that skilled tyers of that knot obtained. His buttons looked malformed to my eye, but not everyone knows how to judge that kind of thing. Therefore I urge people to get destruction tests done. Or, if they are buying soft shackles, ask to see test results from the vendor.
Finally, the +300% Grail. In no previous tests have we gotten over 300% efficiency for any shackle, but a Mr. Gardner came up with the idea of a"bifocal" version, in which two pieces of rope are used, instead of one. Sadly, his version averaged only 99%, but the concept was compelling, so I played around with it. One variation averaged 328%(!). I have some further samples ready to test, and will try not to delay in getting them out. Or in getting back to you re results.
If you submitted samples for the tests, please be in touch for detailed numbers on your work.
Again, I regret taking so long in getting these results out.
Fair leads,
Brion Toss

[allene]

Brion,

Thanks for filling us in. I would like to see some details. One thing that would be very interesting is the range of results for each type of knot. I assume you had a range of skill levels so this would give a good indication of what we could expect to see for a range of users. Averages are perhaps not as interesting as the minimum strength. The average doesn't mean a thing if the shackle you are using is at minimum strength. Personally, I would rather use a shackle that had an average strength of 110% and a minimum strength of 100% than one with a average strength of 200% and a minimum strength of 50%. This example is exaggerated and I am not suggesting it represents the results. Of course, if the shackles are inspectable such that any user could judge a good shackle from a bad one then bad ones could be excluded from the results. But lacking some usable criteria, I think they need to be included.

You say that going to larger line causes a loss in efficiency but is that loss enough to erase the increase in strength of the larger line? Going up in line size gives 50 to 60% increase in strength. Is the loss in efficiency enough to negate this increase in raw line strength? That would be surprising. Perhaps the combination in added strength and lost efficiency is not enough to equal the superior button knot strength. Does this hold for the minimum strengths as well as the average?

And finally, if it is possible to give each person the results of the units they submitted that would be nice. You have my permission to publish any of my results if that would help. To tell you the truth, it has been so long I can't remember what or even if I sent any samples.

Allen
L-36.com