Load Testing Results

[fgd3]

Originally Posted by estarzinger

Splice to splice test

Before: two pieces, each with two splices, joined loop to loop, with 1:1 bend radius

Attachment 73133

After: broke at the end of the taper of one of the splices and not the 1:1 radius. Broke at 98% of rated strength (rated average strength with two splices). Big bang

Attachment 73134

Surprising . . .tentative conclusion . . .1:1 bend radius is just fine and anything bigger is gravy.

It would be interesting to see if there is any difference between a 1:1 bend radius around another rope or around a metal pin. You could test that by inserting a chain link or similar metal part between your two splices. I would expect the hard bend (rope to metal) would fail sooner than the soft bend (rope to rope).

Fabbian

[Paul Elliott]

Originally Posted by estarzinger

Yes, that was my first thought and is logical . . . EXCEPT the piece I was testing was only 400mm between the two knots. So there was not a lot of room for relative slipping between the cover and core. Unless the core is slipping right thru both knots.

If internal slipping was a problem with 400mm, imagine what it would be on a 40m halyard!

The core could have slipped through either or both of the knots. If you look at the ends of the lines did the core slip inside the cover? It wouldn't take much slippage before the cover is carrying all the load. Of course the core might not have buried itself at the line ends, but instead the cover could be bunched up.

Obviously I wasn't there, so this is pure conjecture. I really appreciate your work here -- I've learned a lot.

[Paul Elliott]

Originally Posted by estarzinger

If internal slipping was a problem with 400mm, imagine what it would be on a 40m halyard!

Yes, I've wondered how the dyneema (etc.) halyards manage to not slip through the covers when they're in a clutch. The cover sections are usually sewn on, aren't they? I don't use stripped lines on my boat so I've not seen this up close.

Is it possible that the clutches grip the core/cover more tightly than a good knot does?

[estarzinger]

Diagnostic info . . .

The core is still flush with the cover on both ends of piece one . . .so the core was not slipping thru the knots.



On piece 2, one end is still flush but the other has the core slipped in about 3/8".



Given piece 1, I don't think the core slipping thru the knots is the primary cause here.

[Paul Elliott]

But if the core had slipped, would it have slid into the cover, or would it have pulled the cover so it bunched up? It wouldn't have to bunch up very much before the cover on the other side of the knot was taking all the load.

As I see it, if the cover is breaking first then the core almost has to be slipping through the knots. Otherwise the cover never sees much load (since it is able to stretch more than the core).

[HappyMdRSailor]

Originally Posted by thinwater

The line is wrapped around a large diameter drum and secured under a clamp, after several wraps. Sort of like using a winch. I've done this sort of testing with New England ropes. One down side is that samples need to be 6'.

When I test thread or small cord (to 170#) that is how I do it... sort of. Wrap the string around a pull-up bar at one end and a broom stick at the other, stand on an acurate annalog bathroom scale, and pull (subtract your own weight). For smaller stuff I use loops to get ~ 50-100 pounds. Repeat and you get a good number.

Like this.... I've used these and similar others....

I'll look up an ASTM standard that I would have in my standards library...

[estarzinger]

On my cover breaking . . .

. . . . on closer examination . . . when I milked the cover back hard on the tails . . . the core did pull thru one knot about 1/4" and thru the other knot 1/2". So that's about 3/4", and I have about 2 1/4" of core exposed at the cover break (when I milk that cover back toward the break) That leaves about 1 1/2" unexplained.

[thinwater]

Originally Posted by estarzinger

On my cover breaking . . .

. . . . on closer examination . . . when I milked the cover back hard on the tails . . . the core did pull thru one knot about 1/4" and thru the other knot 1/2". So that's about 3/4", and I have about 2 1/4" of core exposed at the cover break (when I milk that cover back toward the break) That leaves about 1 1/2" unexplained.

I suspect the knot also tightened differentially; the cover slipped only a little at the non-load end of the knot, but slipped progressively more toward the load end.

[HappyMdRSailor]

Evans,

I think you're ready to graduate to the next level......

[estarzinger]

Originally Posted by HappyMdRSailor

Evans,

I think you're ready to graduate to the next level......

No thanks . . . I am happy with my "toy puller". I am learning quite a bit even with such a small machine. And I could not afford the rope to break on a "real" size puller.

I am curious how well my results and learning scale up. I am guessing fine thru "yachting sizes", but I am going to check that with some 1/2" size pulls.

I was just thus morning looking at "screw pullers" because I am wondering at what point the seals are going to blow out on my hydraulic rams when they go from say 5tons to zero instantly.

[HappyMdRSailor]

Originally Posted by estarzinger

No thanks . . . I am happy with my "toy puller". I am learning quite a bit even with such a small machine. And I could not afford the rope to break on a "real" size puller.

I am curious how well my results and learning scale up. I am guessing fine thru "yachting sizes", but I am going to check that with some 1/2" size pulls.

I was just thus morning looking at "screw pullers" because I am wondering at what point the seals are going to blow out on my hydraulic rams when they go from say 5tons to zero instantly.

Your info is INVALUABLE.... Way more initiative than I think any of us have... For that.... THANK YOU!

Boy... I think it would be pretty crazy for any "un-engineered" (actual sailor common use) application for much over 1/2-5/8"

I'm no expert authority... But here's what I know about testing rams... Most seal failure was high stroke travel/high cycle stuff... OR heat generated cyclic failure/dirty fluid... Never saw a dramatic seal failure...

We had an MTS hydraulic actuator that would do 50k tensile to compression at just about any frequency you could program depending on travel (in load controlled mode). i.e. delta 100,000 lbs, 1" stroke 20hz.... Talk about noise! leak eventually? Yes... no blowouts...

You had to be VERY careful programming that machine.... because it would do "anything" you told it to....Load/frequency/stroke (oh yes... many ruined samples)

Re screw driven.... I did preferred those machines... Instron and Dillon

[Paul Elliott]

Originally Posted by estarzinger

On my cover breaking . . .

. . . . on closer examination . . . when I milked the cover back hard on the tails . . . the core did pull thru one knot about 1/4" and thru the other knot 1/2". So that's about 3/4", and I have about 2 1/4" of core exposed at the cover break (when I milk that cover back toward the break) That leaves about 1 1/2" unexplained.

Total wild guess, but did the cover fibers heat up and shrink? Not enough to show globs on the fiber ends, but perhaps enough to shrivel a bit?

[estarzinger]

Here is another pull of the RobLine . . .

Here is the set-up at 150lbs tension. Two bowlines, quite short (15cm) section between them and 4:1 bend radius at both ends inside the loops.I have inked marks on the cover around each knot.



Here at about 500lbs, the left knot has tighten up a bit and I have inked on another mark there. Nothing else seemed to be moving



Here at about 1500lbs (41% of rated strength) I head a breaking noise. The left knot looks fine



But if you look closely at the right knot you can see cover ripped. The photo is not very good but I have drawn an arrow at some obvious cover damage.



Then at 1920lbs (52%), most (but not all) the core breaks in this same knot, and you can see much more cover damage.



the cover has sucked in/bunched up the cover on the tail of the broken right knot. Its hard to measure exactly, but I am estimating a bit less than 1/4"

So, each of my three samples has failed in a slightly different way, but the cover has clearly failed first in all. I wonder if any knots are 'easier' on the cover than others. Note, the final break, at 52% is actually not bad compared to the dyneema single braids.

I guess I am/was just surprised by the failure mode here. I expected the cover to stretch (not break), and the core to explode.

[estarzinger]

Back to the questions I was trying to answer with the covered line . . .. some interest in the halyard knot. I did three pulls. Failure mode the same in all cases. Cover broke and then core pulled right thru the knot. Averaged 48% - a bit more than the buntline but a bit less than the bowline (which seems the 'softest' on the cover I have tested).

[attachment=201916:halyard.JPG]

So far, the plain old bowline looks like a pretty good choice for these high modulus covered lines. . . . very unlike how bad a choice it is for the high modulus single braids.

[estarzinger]

attaching jib sheets to jibs

some people take one long sheet and 'luggage tag' it to the jib in the middle. There has always been some question if/when that will slip.

I had a piece of dacron double braid with two bowlines in it sitting right by the bench, so . . .

I luggage tagged it to a sail ring, and pulled on both ends to 1000lbs to 'set" it. This is 2200lbs rated line.



Then I started pulling on one end. It started slipping very slowly at 900lbs, and quickly at 1000lbs.



will do some more tomorrow.