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Old 08-01-2014, 07:21   #151
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Re: Load Testing Results

Testing reaving splices.

Last night I tested some reaving splices (cover only) in old line; I got to thinking, if the cover is shot, how weak are they? At the same time I thought, in a conventional double braid splice the load on one leg is carried by only the cover at the throat; not easy for the casual user to see, but the core does not re-enter the main rope. Is this spot also vulnerable to UV?

Test line: 14-year old blue 5/16" Sta-Set with a bad looking cover. It tested at only 40% of new strength.
  • The reaving splice (2 repeats) tested at the same strength as the line, breaking at the apex of the eye instead of in the line. But the same strength!
  • The cover-only tested at 58% of the total (2 repeats). I'm sure the distribution of strength (cover vs. core) varies with size and I do not know what it was for new line).
What can we take away from this?
  • A cover-only splice can be pretty darn strong. It was 2x as strong as a bowline in the same line. Not that I'm recomending this, if only for wear reasons.
  • The UV and oxidation damage is more than skin deep. Granted this is small line, but the core is as degraded as the cover, in spite of apearances.
  • Conventional splices may not be so vulnerable at the root. Expereince supports this.
  • The cover suffers little loss over the carabiner because it is flat, like webbing.
  • Cover damage in the eye is serious; in some early testing I used a shackle that was not well rounded; at high load it would cut a rope like a knife, reducing strength by half or more.
High mod line, of course, is completely different and more complex. Still, it's nice to know that reaving splice will hold more than a ton in new line.
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Old 08-01-2014, 07:59   #152
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Re: Load Testing Results

Quote:
Originally Posted by thinwater View Post

Test line: 14-year old blue 5/16" Sta-Set with a bad looking cover. It tested at only 40% of new strength.
  • The reaving splice (2 repeats) tested at the same strength as the line, breaking at the apex of the eye instead of in the line. But the same strength!
  • The cover-only tested at 58% of the total (2 repeats). I'm sure the distribution of strength (cover vs. core) varies with size and I do not know what it was for new line).
What can we take away from this?
[LIST]
[*]The UV and oxidation damage is more than skin deep. Granted this is small line, but the core is as degraded as the cover, in spite of apearances.

.
Interesting . . .not what I would have guessed. . . . I would have guessed that the cover would have protected the core from 'most' of the UV damage.

I am not completely clear on your results . . . .am I right that:

1. That the entire line (Core + Cover) was at 40% of original strength (did you test this with class 1 DB splices on each end)?

2. That of the 40% in #1, the cover provided 58% - eg 23% (how did you test that?).

3. That the reaving splice (which is a cover only splice - correct?) tested the same as the whole line (eg core + cover) - eg 40% of the original line strength. I am not so surprised by this because the reaving splice is doubled. Would be interesting to know if it is true even in new line. But I would have thought this suggested that the cover equaled 50% of the total line strength, rather than 58%?

On adhesive . . .3M 5200 is speced to provide 700 psi, and I suspect will bond to polyester webbing nicely.
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Old 08-01-2014, 08:58   #153
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Re: Load Testing Results

Quote:
Originally Posted by estarzinger View Post
Interesting . . .not what I would have guessed. . . . I would have guessed that the cover would have protected the core from 'most' of the UV damage. Exactly.
I am not completely clear on your results . . . .am I right that:

1. That the entire line (Core + Cover) was at 40% of original strength (did you test this with class 1 DB splices on each end)? YES. Sewn, since tucking would be impossible. In some tests the sample broke between the splices, so it was true line strength.

2. That of the 40% in #1, the cover provided 58% - eg 23% (how did you test that?). YES. I pulled the core and spliced only the cover into a dogbone. It failed at the edge of the splice in both tests, indicating reasonably high efficiency.

3. That the reaving splice (which is a cover only splice - correct?) tested the same as the whole line (eg core + cover) - eg 40% of the original line strength. I am not so surprised by this because the reaving splice is doubled. Agreed. I would expect a little lower, because ofthe bend, but close, since the cover should behave like webbing. Would be interesting to know if it is true even in new line. But I would have thought this suggested that the cover equaled 50% of the total line strength, rather than 58%? Yes, it tested the same (expermental variability means it was most probably a bit less). I'm betting the core/cover strength distribution is variable in the 40-60% range.

On adhesive . . .3M 5200 is speced to provide 700 psi, and I suspect will bond to polyester webbing nicely. I was just about to mention that. I have used 3M on fabric assymblies where I wanted some stiffening in non-critical applications (placing grommets in sheet bags--works very well for this, perhaps better than multiple fabric layers). I simply glued a layer of fabric on the back and it lasted longer than the bags. But placing a grommet through 3M is not the same as stitching through it. My greatest concerns are the inability to inspect and the long term affect of flexing. It would be fun to clamp a splice in the vice untill cured (no stiching) and then pull. I think I'll do that, perhaps with another urethane I have (PL).
Though I was surprised, only so much. PS did some testing of old docklines that showed great strength loss, enough that core damage had to contribute. Perhaps there is some other mecanism (internal wear?) that damages the core more than the cover (there are more dried salts in the core), evening things up. I know that old polyester lines can really squeak when loaded up (spinning lubes gone) Maybe it is common for the core to be just as bad, apearances deceiving. Not long ago I posted a photo of a line with a failed core with the cover still intact, and that is not the first time I've seen that.

I have not the slightest idea how this might relate to Specra/Dyneema core ropes. Everything is different. I suspect the cover provides better protection, since Dyneema should be less prone to internal wear. But if the cover helps the line hold dried salts--stopping rain--I wouldn't be so cocky about it! A larger uncovered line with a lose braid (Amsteel) might very well do better in some applications, where snagging and low friction don't matter. A fun long-term test project.
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Old 08-01-2014, 10:06   #154
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Re: Load Testing Results

^^ Interesting. I have not come to grips yet how to do something meaningful with old line, but testing how degraded the core is, is a good idea . . . there is quite a bit of debate right now about whether cover dyneema life lines are better than single braid (of the same total diameter). The argument for covered lines is that while they start out weaker, the core will not be UV damaged or chafed, but your result is suggesting there may well be significant core damage.

My new beam is suppose to arrive Friday, so I should be back up and pulling over the weekend.
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Old 08-01-2014, 10:25   #155
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Re: Load Testing Results

^^ Yes, testing used line is a bugger, but in many ways, it is the only thing that matters, since it will fail whe used. The bit I have been working with is now gone and the next bit will be different. That was a boom-end traveller line (mechanical wear along full length) and the next bit may be a mainsheet or halyard.
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Old 08-01-2014, 10:55   #156
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Re: Load Testing Results

Webbing carrying load web-to-web friction, cause by thread induced compression.

Some, but I think we are jumping to a conclusions without calculation or testing.

Friction from pre-tension. If we have 200x2 thread stitches carrying 5000 pounds, we have 25 pounds holding per stitch and 12.5 pounds per strand. If you look at the dents in the fabric and try to duplicate them with a small dull metal tool, it is aparent the pre-load per stitch is perhaps 1 pound, perhaps less. More than that and the machine will break thread at speed. If we take the coeficient of friction of nylon/nylon as 0.2 (slippery stuff) this gives 100*1*.2=20 pounds of holding force. We can neglect this.

Friction over the carabiner. The math is more complicated here, but basically the force on one leg is less than the other. If sliding, the difference is about 30%, but I'll take it as 15% for calulation purposes. Thus the shear force on the eye is 0.85*5000=4250 pounds.

Threads in shear. I'd have to see a photo to believe it. In my expereince, when they are close to failure, they are angles. Tubular webbing is not that hard. Could be a minor factor. But by the time there is enough stitchin to creat that situation, you're not going to see failure.

Friction at load. This is MUCH harder to figure. If we assume the threads are actually at a 45 degree angle when at full load, 70% of the stress on the thread translates into holding force and 70% of the stress translates into clamping force (trig). If the total stress on the thread is 5000 pounds (assume 100% efficiency of stitch, which testing suggests is conservative), 3500 is dirrected in line, and 3500*.2=700. The total is 4200 pounds, a good match for the 4250 pounds we have in shear.

Thus, only about 700 pounds is carried by web-to-web friction and most of the load is carried by the strands in tension at an angle.

What about efficiencies we see over 100%? Well, the 0.2 coeficient of friction will vary with the weave. Sure enough, I've found higher efficiencies in rough used line than new slick webbing. With 3-strand rope in a seizing it is considerably higher. Friction over the pin can vary; is the pin fixed or can it rotate (it wont rotate, though unless the friction of the bearing under lad is less than the friction of the nylon)? Lots of variables.

If higher thread pretension helps it will be because we have increased uniformity. There is simply no way we can add enough pre-tension, unless we over stitich a ton (which isn't a bad idea) for it to effect ultimate holding strength. Pretension is proven to reduce wear (less movement and less abrasion) and improve drop test results (less movement).

Test, test test....
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Old 10-01-2014, 10:37   #157
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Re: Load Testing Results

Ok, the test bench is back in business . . . first up were some webbing adhesive samples I glued and clamped up yesterday. I made loops (four samples with each adhesive) with 5 sq in of adhesive, no sewing at all

5200 fast cure = 191 psi, stdev 5
3M Spray 90 (high strength) = 110 psi, stdev 11
3M Spray 80 = 78 psi, stdev 13

For reference:

sewing 9 rows of zigzag = 567 psi, stdev 18
water knot = 511 psi, stdev 4

I would say the 3M spray 90 was clean and easy to use, quick curing, and perhaps adequate for light duty.

The 5200 is quite messy to work with and a 24 hr cure

The water knot was both fast and strong.

The stitching can be as strong as the webbing but takes some time and/or a machine.
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Old 10-01-2014, 11:15   #158
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Re: Load Testing Results

Second test for the day . ..brummels . . . just the brummel with no bury. . . .

single brummel 49% of line strength (supporting what NER suggested that the single may be just under 50%, but very close, within normal statistical variation). This does indicate that the brummel splice with bury might be just less strong that they straight bury if load is allowed onto the brummel.

double brummel 66% of line strength

five brummel 78% (supporting Brian's claim of "about 80%")

None slipped.
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Old 10-01-2014, 12:38   #159
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Re: Load Testing Results

Quote:
Originally Posted by estarzinger View Post
Ok, the test bench is back in business . . . first up were some webbing adhesive samples I glued and clamped up yesterday. I made loops (four samples with each adhesive) with 5 sq in of adhesive, no sewing at all

5200 fast cure = 191 psi, stdev 5
3M Spray 90 (high strength) = 110 psi, stdev 11
3M Spray 80 = 78 psi, stdev 13

For reference:

sewing 9 rows of zigzag = 567 psi, stdev 18
water knot = 511 psi, stdev 4

I would say the 3M spray 90 was clean and easy to use, quick curing, and perhaps adequate for light duty.

The 5200 is quite messy to work with and a 24 hr cure

The water knot was both fast and strong.

The stitching can be as strong as the webbing but takes some time and/or a machine.
I've got to admit it, I'm completely confused. I'm sure your data is good, but I'm not understanding the comments.

100-200 psi. It would take 2-3 feet of 1 inch webbing, assuming no deterioration or pealing force, to reach 4000 pounds. Did I slip a decimal? I would also wonder if 24 hours was nearly long enough for 5200; I would give that 2 weeks to reach full strength in good conditions.

Stitching. I generally get about 150 pounds per full stitch in webbing, and about 3000 pounds in 1 inch (4*5*150=3000). 2 inches of hand stitching will break webbing. Clearly, we don't need a machine, though a bar tacker does nice work.

Stitching plus adhesive. There should be a strong synergistic affect, since the coefficient of friction is dramatically changed. Adhesive could also reduce wear, since the fibers won't move. But I don't understand how to sew through most adhesives; could very well be I had a wimpy machine.

----

I've got some adhesive samples curing too, I will report, but it will be a few weeks.
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Old 11-01-2014, 11:06   #160
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Re: Load Testing Results

Quote:
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100-200 psi. It would take 2-3 feet of 1 inch webbing, assuming no deterioration or pealing force, to reach 4000 pounds. Did I slip a decimal?

Well, 40" at 100psi and 20" at 200psi. Why is that "confusing"?

I would also wonder if 24 hours was nearly long enough for 5200; I would give that 2 weeks to reach full strength in good conditions.

Sorry, that it was 5200 fast cure. Instructions say cured in 24hrs. You are exactly right about the regular (eg not fast cure) 5200 - instructions say 7 days, which I thought too long for practical use in this case.


Stitching. I generally get about 150 pounds per full stitch in webbing, and about 3000 pounds in 1 inch (4*5*150=3000). 2 inches of hand stitching will break webbing. Clearly, we don't need a machine, though a bar tacker does nice work.

This was V69 thread - tensile 10.6lbs, at the machines biggest zig zag. I suspect you are using stronger thread. And I could easily have used smaller stitch length to cram more stitches in per inch. It is clearly NOT the "strongest possible sewing", but does look very like some of the commercial sailing webbing sewing I have seen (the rock stuff looks consistently stronger than the sailing stuff).

Stitching plus adhesive. There should be a strong synergistic affect, since the coefficient of friction is dramatically changed. Adhesive could also reduce wear, since the fibers won't move. But I don't understand how to sew through most adhesives; could very well be I had a wimpy machine.

----

I've got some adhesive samples curing too, I will report, but it will be a few weeks.

Will be interesting to hear the results, but for me at least, practically speaking, a week long cure is too long for me when making up stuff like this when I can sew it or knot it in some minutes
........
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Old 11-01-2014, 11:12   #161
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Re: Load Testing Results

Just looking at the downside of 'bad' splice construction:

My results were that the splice with no taper was 86%. That was in 7/64" amsteel. I suspect this will get worse with bigger line (eg there will be a bigger stress riser with bigger line).

I also tested the "whoppie sling splice with end sticking out" and got 80%. Which is exactly consistent with Samson's results, which I only looked up after doing my own test because I thought their result was 60% (and is another data point suggesting my testing is not grossly inaccurate).

Samson's comment on the Whoppie are: "Using Amsteel Blue whoopie slings for suspending hammocks is a very interesting application. Thanks for the link to the thread on the hammock forum, it's a good discussion.

Recently the (popularly believed) reduction to 60% of average break strength for Amsteel Blue whoopie slings was suspected to be a low value. Testing showed that it is actually around 80% depending on the size of the rope. On every test done the break location was at the point of the adjustable whoopie tail exit.

In collusion, the locking brummel has less impact on break strength reduction than the "sudden transition in size where the adjustable section exits the bury". If a traditional buried eye replaced the brummel, the same strength reduction would be expected because the adjustable bury exit is the weakest link."
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Old 11-01-2014, 11:37   #162
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Re: Load Testing Results

No contact cement tests ?
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Old 11-01-2014, 12:18   #163
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Re: Load Testing Results

The water bowline was suggested as a fixed loop that does not slip in amsteel.

Water bowline test (this is only 3 pulls):

Figure 8: 44%
Waterbowline: 46% (statistically the same as the figure 8)
Waterbowline with modification (tail tucked thru the knot): 53% (statistically stronger)

None of these slipped . . . so you were correct to identify there are two ways to make the water bowline, one of which slips and the other (the one shown on the animated knots site) does not.
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Old 11-01-2014, 13:39   #164
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Re: Load Testing Results

I just pulled a couple knots in WarpSpeed (dacron covered dyneema). The cover beaks, and pretty much exactly at the same load as the RobLine (for example with the buntline 41% for the warpspeed and 42% for the RobLine).
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Old 11-01-2014, 13:46   #165
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Re: Load Testing Results

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........
I'm not confused any longer. All makes sense.
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