Wire breaking strength and pin diameter

[Adelie]

Originally Posted by phorvati

I get why 5/8"pin turnbuckle is standard for 5/16" wire. That math works out. But why is 5/8" pin turnbuckle standard for 10mm and 3/8" wire. In fact hayn does not list larger pin turnbuckle for 3/8" wire or 10mm wire. This is from Hayn catalog for turnbuckles and imperial and metric wire. The point is if i get 10mm or 3/8" wire and 5/8" pin turnbuckles, pin breaking strength is lower than wire breaking strength if you do the Pi r squared as area. and factor 60% for shear stress.
Yet this is the standard option. Also how is it that turnbuckle has higher breaking strength than the pin itself?

While this may sound like theory, it is what keeps the rig from collapsing. So I am trying to understand how is it that my math does not work out. The fact that clevis pins never fail is irrelevant. Undersized clevis pin will fail.

Did you account for pins being in double shear rather than single shear?

[Jim Cate]

Undersized clevis pin will fail.

Well, I guess this means (since they don't fail in practice) that they must not be undersized... which is likely why folks continue to sell and use them.

I don't think the lack of failure is irrelevant at all... it is the real world!

Jim

[phorvati]

I didnt. Now that I thought about it some more, it is two. There are two shear surfaces that the pin sees. One for each side of the turnbuckle fork. So that's how the numbers work out.

[phorvati]

Just because they don't typically fail, it doesn't mean they are correct. I see bad designs work ok all the time. In many mechanical or electronic aspects of engineering, but this is one of those that I would not use lack of failure as any kind of input for a design decision. I'm just glad I was able to understand how the math works out.

[Thumbs Up]

Yes it is in double shear. I think that it does work harden as it's a pivot point. They make those fittings for other types of weaker wire configurations than 1x19. I am going to stick to what brian toss says. Which I will paste (again):

"If you run pin strength (pi x r squared x strength of metal), you will see that a 1/2" pin is stronger than 5/16" 1x19. The problem is that it is not stronger enough. Pins -- and chainplates and tangs -- need to be at least a third stronger than the wire, in order to deal with vulnerability to fatigue and corrosion, as well as the weakening effects of threading rod for studs, and shaping barrels, for instance. Taking all this into account, it is not impossible to end up with a turnbuckle that is weaker than the wire. That is why 5/8" is the standard pin size for 5/16" 1x19.
The reason that you can nevertheless get 1/2" terminals for that diameter is that those terminals are meant for 7x19 and similar constructions, which are much weaker than 1x19. 1/2" is the appropriate pin size for those constructions. "

I am upgrading all of mine (1/2" turnbuckles and pins to 5/8" on my four shrouds and forestays, 5/16 wire). You (op) are going from 5/16(8mm) wire to 3/8(10mm) wire but want to know if it is ok to use 5/8 pins and turnbuckles instead of 3/4". Neither Hayn nor Stalok list a larger than 5/8" screw and pin for 3/8" or 10mm wire. Only the 5/8". So I am assuming that is the standard pin size for 10mm wire (as well as the 5/16 and 8mm). So you will want use your 5/8" reamer but check the actual pin size before you do because those pins are not quite 5/8.

[barnakiel]

Originally Posted by phorvati

(...)

I have two lower shrouds. 5/8" pin turnbuckles are listed for both 8mm wire and 10m wire as well as 3/8" wire if you like imperial units. But I am questioning strength of 5/8" pin for use on a 10mm wire (...)

Start with not mixing metric and imperial terms. Make it easier on the reader.

You can find the correct choices e.g. here:
Stud/fork : Seldén Mast AB

and wire strength from e.g. here:
https://www.harken.com/uploadedFiles...oads_HORIZ.pdf

10mm wire is BL 7250 kg, the screws are rated at 9500 kg. Implicit the pins are rated at least 9500 kg. Yes/No/Maybe? YES.

In fact at least 12500 kg. Just look up Selden's.

Where is the problem?

Cheers,
b.

[B-Baysailer]

You can buy 3/4 stud terminal for 3/8 and 10mm wire from hi-mod if you want 3/4 turnbuckles

[Thumbs Up]

In fact at least 12500 kg. Just look up Selden's.

Where is the problem? That 12500kg on the Selden page is for the 3/4" pin and screw. The 5/8" pin and screw show a 9500kg. The op's dilemma is whether to go with the 3/4" or the 5/8" Now I see that Selden offers both fittings for 10mm wire. Hayn and Staylok only have one choice: 5/8". If you follow Toss's recommendation of sizing the fittings to be 1/3 stronger than the wire (7250kg) then you would need them to have 9667kg (breaking load) which is more than the 9500kg listed for the 5/8" (but just barely). I thought that I had solved the problem by pointing out that you cannot buy 3/4" fittings for 10mm wire (hayn and staylok don't sell them). Since the op is up sizing his wire from 8mm to 10mm I think that he is fine with the 5/8" (especially since that is the standard size for Hayn and Stalok and we are splitting hairs over this 1/3 safety factor) but now we see that that Selden does carry the 3/4" and that to get a full 1/3 safety margin you would need to use the 3/4"

[phorvati]

From riggers apprentice...

[loquin]

I know it's an old thread, but I was looking at shear forces on clevis pins, came across this thread, and was intrigued. I had also found a related discussion pertaining to the drawing process involved in creating steel cable wire, and how the tensile strength of the cable greatly increases. Ref: "Wire drawing induces the development of dislocation density, reduction of interlamellar spacing and the refinement of grains size which leads to a strong hardening of the wires. That explains the increase of the tensile strength from 1242 MPa to 2618 MPa with higher deformation."
https://www.researchgate.net/figure/...%20deformation.