Wire breaking strength and pin diameter

[Jim Cate]

All this theorizing is interesting, but in the end there is a practical observation: I've seen a fair number of failed wires but never a single case of a clevis pin shearing. Not one, either personally or anecdotally. Have any of you other CFers seen one fail?

Jim

[Snowpetrel]

https://youtu.be/d-jqwkNXMIY

Is very interesting to see just how far they had to go to get the rig to fail.

Be aware that the wire forming process considerably strengthens the thin strands over the normal bar stock as used for Clevis Pins.

[Cheechako]

It's not a factor of two necessarily, the chain plate/pin is a factor of one. However the CP is likely thicker material than the fork. But is it 2x as thick as one side of the fork? Sometimes yes, sometimes no. All this comes into play I suppose. I would just use what your chainplates are already drilled for!

[phorvati]

I am fabricating my chaniplates. I need to up my wire from 8mm to 10mm for V2s and D1s. 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 especially compact one. I am in the process of drilling clevis pin holes on the chainplates. And was purchasing reamers to finish the hole. I ended up getting adjustable reamers for both 5/8" finish hole and 3/4" finish hole. These adjustable ones can go from 1/32" below 5/8" to 1/32" above. Same with 3/4" pin. So I have options and I need to decide before purchasing turnbuckles. So the only question is do I drill to ream to 3/4" or 5/8" finish diameter hole. I am also aware of letting 1/64" more on the finish diameter for the clevis pin hole to account for dents and scratches in the pin. Point loading does not come into play until freeplay is much larger than 1/64".

[DumnMad]

Originally Posted by Jim Cate

All this theorizing is interesting, but in the end there is a practical observation: I've seen a fair number of failed wires but never a single case of a clevis pin shearing. Not one, either personally or anecdotally. Have any of you other CFers seen one fail?

Jim

Exactly. Its not the design strength that counts becasue large factors of saferty deal with that.
Its corrosion and brittle fatigue failure that can easily occur inside ss wire due to salt trapped inside the strands where there is also a lack of oxygen to maintain the protective layer of oxide.
Crevis corrosion can occur inside the shackle but the shackle is usually well rinsed by rainwater whereas the rain fails to clean out the inside of the wire strand.

[Cheechako]

Originally Posted by phorvati

I am fabricating my chaniplates. I need to up my wire from 8mm to 10mm for V2s and D1s. 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 especially compact one. I am in the process of drilling clevis pin holes on the chainplates. And was purchasing reamers to finish the hole. I ended up getting adjustable reamers for both 5/8" finish hole and 3/4" finish hole. These adjustable ones can go from 1/32" below 5/8" to 1/32" above. Same with 3/4" pin. So I have options and I need to decide before purchasing turnbuckles. So the only question is do I drill to ream to 3/4" or 5/8" finish diameter hole. I am also aware of letting 1/64" more on the finish diameter for the clevis pin hole to account for dents and scratches in the pin. Point loading does not come into play until freeplay is much larger than 1/64".

I'd ream if you can. You want a nice clean bore.

[Thumbs Up]

The clevis pin size is tied to the turnbuckle size which should match the wire size. 8mm (5/16) 1x19 wire gets 5/8" turnbuckle and pin. If you are reaming your chainplate holes you need to make sure that you will have enough "meat" between the edge of the hole and the top and sides of the chainplate. A 5/8" hole needs 5/8" of meat. Don't ream the hole though until you have the clevis pin because they don't quite measure 5/8". Toss was saying that even though they make smaller fittings for a given wire size that it is not all right to use them. I have seen a failed pin but it wasn't sheared. crevice corrosion caused it to fracture diagonally. A rigger showed it to me.

[Jim Cate]

Toss was saying that even though they make smaller fittings for a given wire size that it is not all right to use them. I have seen a failed pin but it wasn't sheared.

If they don't shear why is not all right to use them? Failure from crevice corrosion might take a bit longer with the larger pin, but those cracks just keep propagating until something breaks.

Jim

[Thumbs Up]

Because the pin size is tied to the turnbuckle size (when you buy new fittings). Toss is saying that the pin and the turnbuckle are undersized.

[Adelie]

Originally Posted by phorvati

I'm going over turnbuckle pin diameter vs. breaking strength of wire for relevant turnbuckle.

For instance for 8m wire, standard turnbuckle options are those with pin/screw diameters of 5/8" and 1/2".
Breaking strengths for various flavors of 8mm wire are in the range of 11.8k to 13.5kpsi or so.

if you look at 1/2" pin, breaking strength would be considered a shear strength which is usually 60% of tensile strength of SS (75-80)kPSI. Usually number used for shear strength is 45kpsi.

so shear area of a pin is Pi*r^2.
So for pin of 1/2" diameter, area would be 3.14*.25*.25 = 0.19sq-in.
So its shear strength would be only 8.8kpsi. Somehow West marine lists Hayn 1/2" clevis pin at 11kpsi breaking strength. Not sure how they got that number since hayn does not list it in their catalog.

It appears that 1/2" pin would break before 8mm wire. But they are a standard option for 8mm wire.
Idk what i'm missing but if anyone could chime in that would be great.
Petar

Let's clarify several things.

There are 2 different stainless steels in common use for rigging wire, A304 & A316. There is a strength difference between the 2 of about 15%.

There are 3 different strengths: yield, ultimate and breaking. For our purposes Ultimate and Breaking can be treated as the same. Yield strengths are when the material in question starts to plasticly deform but it hasn't failed. If the load on the piece is removed the piece will be permanently deformed. Generally breaking strength or breaking load are the valules provided by vendors.

This brings us to terminology and units. Breaking load and breaking strength are not the same thing. They are related but they are not the same. I've been known to mix and match some and certainly vendors do all the time but for this discussion we need to be a more careful.
Breaking strength is function of the material in question: A304, A316, A992, A36, concrete, T6061, jello, rubber bands. This is expressed in units of psi or ksi (if you want metric I can cough those up).
A304: 90ksi
A316: 75ksi
A316L: 70ksi

http://www.integritystainless.com/wp...e-316-316L.pdf
http://www.aksteel.com/pdf/markets_p...data_sheet.pdf

Material strengths are provided in psi or ksi so that you can easily determine breaking loads for pieces that do not have a 1 sq-in area. Multiply the area of the piece times the breaking strength of the material the piece is made of will give you breaking load. Breaking loads are in lb, pound or kips (1,000s of lb).

When considering strengths the wire is in tension and will fail in tension for which a value can be looked up.

Pins on the other hand fail in shear. Is shear strength the same as tensile strength? Nope. However they tend to be related.
"Usually for isotropic metallic materials shear strenght τ depends on tensile strenght σ .
The value adopted by von Mises yield criterion is τ = σ / Sqrt [3]
The Tresca criterion gives the value : τ = σ / 2"
Another rule of thumb from industry is τ = σ * 80%

50% to 80% is a pretty wide range.

https://www.researchgate.net/post/Ho...aterial_SS_304

Once again we are talking the strength of the material here so units are in psi or ksi.

We don't care about the strength of the material, we care about breaking load for the particular piece we are using and matching all the different pieces and knowing which is going to be the weak link. Don't try to analytically figure this out from tensile strength, use test data.

For pins, use the vendor's breaking load (which will probably be labelled breaking strength but if the units are lb or kips then it's really load). The big ambiguity here is whether the value provided is for single or double shear. That is was the test apparatus a fork on one side and and eye on the other so there are 2 planes of failure in the pin, or were there eyes on both sides and a single plane of failure in the pin? You can call the vendor and find out who then manufacturer was then call them and see if they can tell you who does the testing for them and call the testing agency, or you can tack a sample to a local testing lab and have it done, or you can be conservative and assume the value provided is for double shear. I would do the last.

Going back to the OP's values. He/she indicates the 8mm wire breaking strength is 11.8kips to 13.5kips.\
8mm is a touch smaller than 5/16"
WestMarine lists
5/16" A316 wire breaking load as 11,855lb.
5/15" A304 wire breaking load as 13,340lb

https://www.westmarine.com/buy/alps-...93?recordNum=4
https://www.westmarine.com/buy/alps-...79?recordNum=2

Looking at Hayn in the WM site I consistently see 5/16" swaged end fittings with 5/8" pins in double shear but no breaking load listed. All materials A316.
https://www.westmarine.com/buy/hayn-...6?recordNum=11

Looking at pin breaking loads:
5/8" pin, A316 Breaking load 15,575lb
https://www.westmarine.com/buy/hayn-...80?recordNum=7
1/2" pin, A316 Hayn, breaking load 11,125lb.
https://www.westmarine.com/buy/hayn-...2?recordNum=16

Hayn Turnbuckles
1/4" to 5/16" wire, 1/2" pin, breaking load: 12,500lb
5/16" to 5/8" wire, 5/8" pin, breaking load: 17,000lb
https://www.westmarine.com/buy/hayn-...05?recordNum=1
https://www.westmarine.com/buy/hayn-...05?recordNum=1

Comparing Hayn turnbuckle breaking loads and pin breaking load, the turnbuckles have higher breaking loads than the pins they use. I assume the testing did not involve loading thru the pin but directly thru the screws in the turnbuckle.

So if you used 5/16" A304 wire with 1/2" dia pin turnbuckles the weak link(s) in each stay would be the pins, then the turnbuckles then the wire when the stay is NEWLY installed.

My take is that after maybe 3yr fatigue and corrosion will make the wire the weak link. If you start with A316 wire the order is pin, wire, turnbuckle but the rate of corrosion for the A316 is way less than A304 if in a tropical or semitropical environment so the change is worth the extra cost in the long run.

Recent article in GoodOldBoat discussed a rigging failure related to failure of a clevis pin. Cotter pin corroded in the clevis pin with the corrosion products expanding and breaking off the end of the pin. Thus a regular maintenance item needs to be replacing all cotter pins every 3-5yr, and the clevis pins every 10y.

[barnakiel]

I have never seen a pin fail on any boat.

I have never seen a pin even bent on any boat.

Are you not over engineering your fears?

Bigger pin = bigger screw = bigger wire.

Why do you think you need bigger wire than the one designed in?

Pins fit the terminals of the screw and that's that. You want bigger pins, you imply getting bigger screws and bigger wires.

Some screws have two optional terminals/pins. I have seen 3/8 screws some with bigger pins some with smaller pins.

b.

[a64pilot]

Originally Posted by Cheechako

I'd ream if you can. You want a nice clean bore.

I’d even break out the Dremel with a cotton wheel and jewelers rouge and polish the bore if I were real concerned about strength and failure.
Reasoning is to remove any stress risers, almost always high cycle fatigue failure is cracking, that propagates from a stress riser.

[barnakiel]

Originally Posted by Adelie

(...)

Thus a regular maintenance item needs to be replacing all cotter pins every 3-5yr, and the clevis pins every 10y.

Why should a clevis pin need replacement every 10 years?

a) It gets no work hardening,
b) It can be fully inspected.

I agree that since most any part of the rigging may need replacement after 10 years of heavy use, the pin could go as well. When we buy terminals new pins come with each anyways. But I am not sure the pin HAS TO be replaced, unless it is bent, dented or pitted, etc.

As a side dish, I always find it funny in our musings at CF when most of us agree most of the rigging has to go every 10 years but we very often overlook the mast tangs in the process. I say this as in our short catalogue of failures the tangs are 33% of the cases.

Cheers,
b.

[hellosailor]

Having once had a turnbuckle rupture rather dramatically and take off skyward, still attached to the shroud (accidentally tightened when it was supposed to be loosened) I have to say that there's something to be said in favor of having the turnbuckle fail instead of pulling down the rigging.

Not necessarily a bad way to "program" the failure mode.

[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.