Load Testing Results

[Jim Cate]

Wow, guys, this is really interesting!

Evans, when you quote breaking loads relative to thread tensile, is that on a per stitch basis? It sounds like it... so does the strength of the stitched join vary linearly with stitch count... and over how big a range? And do you think that these numbers will transfer to stitched splices in line? I've used such eye splices with an arbitrary number of hand stitches in heavy waxed sail twine for years, never having a very good idea of how strong they were! Kinda scary, that,but none have ever failed (and I don't use those sorts of splices in critical areas).

Another area of interest might be strength of seized eyes, with either plain or racking whippings. Kind of old fashioned, I know...

And thanks again to you and Thinwater and the others who are contributing to this investigation.

Cheers,

Jim

[estarzinger]

Originally Posted by Jim Cate

when you quote breaking loads relative to thread tensile, is that on a per stitch basis?

Yes, lbs/stitch.

Which I then 'normalize' (so it can be applied to other thread) into % efficiency by dividing by (2 x thread tensile strength)


so does the strength of the stitched join vary linearly with stitch count... and over how big a range?

It appears to be linear (85% adj R^2, and normal distribution residuals), except in the very high stitch density/count samples, where the efficiency falls off


And do you think that these numbers will transfer to stitched splices in line?

I do not have good apple to apples data on that yet. I have data on stitching in polyester line and nylon webbing. The polyester line stitching has higher efficiency than the nylon webbing. But I need (and will test) some samples in polyester webbing to be able to compare directly to the polyester line.

My intuition is that there are sharper bends in the stitching in webbing than in line, so I would think the line stitching would tend to be equal or stronger but not weaker than the webbing.

Many of us have machines that can do webbing stitching, but few of us have machines that can do line stitching, so those will mostly be done by hand. It appears that hand stitching is stronger (higher efficiency) than machine stitching. ThinWater is proposing (if I understand him correctly) that this is because machine lock stitching cannot equalize thread tension as well as hand stitching. That sounds logical but I don't have enough information (either about the failure modes or the stitching geometry) to have any certainty.

Thinwater . . . Gore does in fact make #35 Tenara thread, but I have never used any of it. Sailrite appears to sell the #25 thread (model M1000H).

[thinwater]

Originally Posted by estarzinger

Thinwater . . . Gore does in fact make #35 Tenara thread, but I have never used any of it. Sailrite appears to sell the #25 thread (model M1000H).

Yes, I see that, but the Sailrite specs, when I search M1000H, say 15 pounds. If there is a retail source for the 35#, I've not seen it.

And unfortunately, I don't want to buy a cone of something I may not like. I doubt many folks would unless they knew it to be the bees knees. What do you know of it's abrasion resistance; I've never thought of Teflon as being cut resistant.

[estarzinger]

Originally Posted by thinwater

Yes, I see that, but the Sailrite specs, when I search M1000H, say 15 pounds. If there is a retail source for the 35#, I've not seen it.

What do you know of it's abrasion resistance; I've never thought of Teflon as being cut resistant.

No, I don't know anything about abrasion. Like you, I would guess it is nothing special in that regard. The UV resistance is not something to sneer at though - you know how UV eats both polyester and dyneema.

I just looked at the cone of Tenara I have from sailrite, and it is part number M1000HTR, which gore spec sheet agrees is 14 lbs. This is different than the same size thread part M1000H, which is 25lb.

Gore's spec sheet lists the the "original" styles and the "TR" styles. The TR's are about 40% weaker and about 140% stretchier that the "original". The TR styles only go up to 19lbs.

So, it looks like they "cheapened" the product while still maintaining the high price. I am curious what they did to the formulation - my guess is it had to do with environmental mfg problems. I know PTFE has had really toxic mfg processes. Their spec sheet does say the TR style is still completely UV resistant.

[Ocean Girl]

What about using the actual tread from the core that you are splicing to lock stitch?

[thinwater]

Originally Posted by estarzinger

I just looked at the cone of Tenara I have from sailrite, and it is part number M1000HTR, which gore spec sheet agrees is 14 lbs. This is different than the same size thread part M1000H, which is 25lb.

The UV resistance is sure keen.

I spoke with several guys at Sailrite today; the heavier Tenara weights are "only in a magazine" at this time.

I've put samples of waxed twine and sewn samples in yard for 4 years of aging. They're right next to the Strataglass, Regalite, O'Sea, and 20/20 panels. I'll be breaking them in 2 years and in 4 years. Time will tell.

[Cotemar]

Originally Posted by thinwater

The UV resistance is sure keen.

I spoke with several guys at Sailrite today; the heavier Tenara weights are "only in a magazine" at this time.

I've put samples of waxed twine and sewn samples in yard for 4 years of aging. They're right next to the Strataglass, Regalite, O'Sea, and 20/20 panels. I'll be breaking them in 2 years and in 4 years. Time will tell.

There is a reason Terara thread is warrantied that it will not be damaged by exposure to sunlight, weather or water during the lifetime of the fabric with which it is used.

Most thread used on boat canvas can become brittle and break after a few years.

I started using Tenara thread ten years ago when I got sick of stitching and re-stitching the same areas that had been stitched with regular marine grade thread. The sun just eats regular thread up.

I now use Tenara thread and it’s done until the canvas falls apart.

I also use Tenara for whipping the ends of my Amsteel lines

TENARA Sewing Thread ORIGINAL STYLE is Gore’s first generation of outdoor sewing thread. The ORIGINAL STYLE sewing thread is un-lubricated, with an elongation or stretch of 5 to 7 percent. Some customers prefer un-lubricated thread for their particular applications.

TENARA Sewing Thread TR STYLE is our second generation of outdoor sewing thread, engineered for high-speed sewing applications such as awning production. The patented TR STYLE sewing thread has an elongation or stretch of approximately 17 percent, aiding high-speed sewing. The TR STYLE is lubricated in all but the largest size.

[DumnMad]

I'm thinking the joint strength must be proportional to the clamping force, or web on web friction, rather than shear on the thread or thread pattern. - Can you vary your tension on the stitching to get increased clamping force?

[estarzinger]

Originally Posted by DumnMad

I'm thinking the joint strength must be proportional to the clamping force, or web on web friction, rather than shear on the thread or thread pattern. - Can you vary your tension on the stitching to get increased clamping force?

Yes, adjusting tension is really the one and only skill in machine sewing. And I am not very good at it . . . I basically have one general purpose tension setting that works find for medium dacron thread in 'normal' fabrics, but is probably not right for webbing.

In cloth you can tell if the tension is right by visually inspecting the stitching, but I am suspecting its not that easy with webbing, and that to truly get it right (max breaking strength) you need to run sames at various tension and then pull test them.

I have also been told by people who stitch webbing professionally that sewing speed matters, with faster = stronger and more repeatable.

I have 100' of dacron webbing ordered and will play around with all this when it comes and I get my test bench back together (I got the new high strength bolts today).

[thinwater]

Originally Posted by DumnMad

I'm thinking the joint strength must be proportional to the clamping force, or web on web friction, rather than shear on the thread or thread pattern. - Can you vary your tension on the stitching to get increased clamping force?

No, I think that is too great a stretch without data or calculation.

If we wished to confirm such an assertion, we would need to sew something lose enough so that there is little clamping force (I've done this) and show that it is very weak. Hard to do with a machine, since things tangle up at very low tension. However, you will be surprised, I think at how much the thread can carry in tension. It will be perhaps 70% of thread strength, sometimes more.

That said, there are some excellent reasons you don't want to sew loosely, the first of which is wear; with repeated movement you will break thread. Threads will snag and wear on the surface; tight threads are drawn further into the weave, somewhat protected. On the other hand, there is a point when pretension damages and stresses thread.

It boils down to trial and error. Finding a process that is robust and wears well. Bar tacking is the gold standard and Estar is tracking down other possibilities. I think it is a mistake to over think this. Better to systematically try everything. Much of science is about not leaping too far.

[DumnMad]

Would be interesting Evans. Its like frictions grip bolts versus shear bolts. The thing with thread is that side compressive strength is nothing compared to axial tensile strength so creating friction grip from thread tension seems logical.

[thinwater]

Originally Posted by estarzinger

... I have also been told by people who stitch webbing professionally that sewing speed matters, with faster = stronger and more repeatable....

That sounds dead-on and may be at the heart of the problem, even with some commercially sew items that have failed; it's hard to do that on a small sample. Interesting. My gut tells me that machine sewwing will require a massive safety factor because variability will be hard to iron out. But perhaps that is not a serious short coming, as it goes fast. The solution may involve finding patterns that allow enough stitching without too much over sewing.

Good luck!

[estarzinger]

Originally Posted by DumnMad

creating friction grip from thread tension seems logical.

that leads me to the thought . . . that with webbing perhaps it should be all about adhesive (like with modern sails), with the sewing just clamping the adhesive to prevent peeling.

I will have to try some contact adhesive.

Edit . . . looks like 300 psi is a typical shear strength for the spray adhesives, so a 12" glue bond (on 1" wide webbing) would give 3600lbs . . .strong but not enough by itself for say jacklines. A 15" bond would theoretically get to the required 4500lbs for jack lines.

Adhesive (probably) will not work with sewn line splices though.

[thinwater]

There seems to be a lot of talk about thread in shear, but I'm not so certain that is the case. I know with hand stitching it is not. Comparing a bolt with thread is obviously or intuitively valid, given the enormous difference in flexibility.

Might I suggest stitching near the edge, loading a sample up to ~ 80% of breaking, and then taking some macro pictures from the edge. I'm guessing (that's why we take pictures) that the thread is angled a good bit. I'm also guessing that the bend radius is not very sharp for thread.

[Cotemar]

Originally Posted by estarzinger

that leads me to the thought . . . that with webbing perhaps it should be all about adhesive (like with modern sails), with the sewing just clamping the adhesive to prevent peeling.

I will have to try some contact adhesive.

Edit . . . looks like 300 psi is a typical shear strength for the spray adhesives, so a 12" glue bond would give 3600lbs . . .strong but not enough by itself for say jacklines.

Adhesive (probably) will not work with sewn line splices though.

Interesting.

I used contact cement to glue on a sunbrella patch on a sunbrella lazy sail bag.

Just contact cement and no stitches. It’s in the direct sun and weather and it’s been perfect for five years now.

Interesting test on glue bonding.