Calculating sheer strength of clevis pins + chain plates.

Ceirwan

Ceirwan

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As per the title, assuming 316 grade stainless steel, I'm looking for how to calculate the sheer strength of a clevis pin of the type used in the rigging, and the strength of chainplate based on the thickness of the material.
I believe to maintain material strength of the chainplate, I need to allow at least 2x the material thickness between the edge of the hole and the edge of the material.

I'm struggling to find the calculations online.
Its for a Solent Stay system I'm planning out.

I know I could just use the same size that everything else is onboard, but I'm curious as to the strength of the various bits.
 
For the chainplate,

You need to look up the UTS of 316 ss, and calculate your CSA in m^2

If you multiple the UTS by the CSA that will give you the failure load in N, assuming there is no hole in it, which there is.

So next you have to work out what allowance has to be made for the stress concentration caused by the hole. There are graphs for this, they look like this:

http://www.biscarri.cat/openALYA_tutorials/case_XFEM.html (scroll down to stress concentration factor ).

The pin is a lot more complicated, to the point where I'm not going to try and describe how to do it on here. If the chain plate will take the load then look at one of your other clevis pins/ chain plates, and make the new pin in the same ratio of CSA and then it will be fine :).
 
Rough guide, shear strength of steel is between half and two thirds of tensile strength and about 60% of yield strength. The yield strength of 300 series stainless steel is proportionately much lower than for carbon steels so I am guessing that the value will be higher in this case. Some values here http://www.bssa.org.uk/topics.php?article=127

Makes a difference if the component is in single or double shear. Double would be normal for a clevis pin, which perhaps means you can take the YS or UTS value.
 
Thanks people, given me plenty to read up on.

vyv, yes I believe, double sheer, fork slid over the chainplate.
 
Ideally you shouldn't be anywhere near the limits for either the clevis pin or the chainplate. The rigging wire (or rod) should fail before these items. When I replaced the chainplates on Snark, the holes in the chainplates were elongated and the clevis pins were worn but there was no sign of plastic deformation of either.

Replacements should be like for like. The yacht designer should have done the calcs with a good safety margin.
 
Topcat47 said:
Ideally you shouldn't be anywhere near the limits for either the clevis pin or the chainplate. The rigging wire (or rod) should fail before these items. When I replaced the chainplates on Snark, the holes in the chainplates were elongated and the clevis pins were worn but there was no sign of plastic deformation of either.

Replacements should be like for like. The yacht designer should have done the calcs with a good safety margin.
Click to expand...

Well my backstay is a U-bolt in the deck with minimal backing and an unfair load because of the angle of the shroud, so I wouldn't trust him fully!

But I get what you're saying, if I match the rest of the rig with the solent stay chainplate it will be fine, i'm more interested in working it out as a curiosity.
 
If the connected parts are thin the bearing of the connected parts on the pin could be critical rather than shear .

On M10 bolt or pin the connected parts 4mm thickness and allowing for a factor of safety the safe load would be about 5kN or half a tonne.

The edge distance from the hole on the connected parts to the edge depends on the quality of the edge but typically 1.5 to 2 x bolt diameter from centre of hole.
 
Ceirwan said:
Well my backstay is a U-bolt in the deck with minimal backing and an unfair load because of the angle of the shroud, so I wouldn't trust him fully!
Click to expand...

I would be more concerned about the "minimal backing" aspects of your backstay u-bolt. Mine goes to a chainplate on the transom. The backstay takes the brunt of the forces on the mast, driving the boat.
 
Holy cow.... I remember doing those calcs at Uni..... that was such a long time ago I would not like to have to try to do it again...... not for real anyway. Wasn't there a cunning formula for "H" section steel???
 
Topcat47 said:
I would be more concerned about the "minimal backing" aspects of your backstay u-bolt. Mine goes to a chainplate on the transom. The backstay takes the brunt of the forces on the mast, driving the boat.
Click to expand...

I am concerned about it, because the design in general is rubbish.
The U-bolt is bolted through the deck hull join onto a backing plate that hangs half on and half off the deck hull join!
Thoughtful early engineering from Sadler yachts!

I'm thickening up the laminate on the transom and as you said the plan is for a chainplate bolted to the transom and then bent to match the angle the backstay intersects the transom.

I've been told of 2 failures on the u-bolt, both of the u-bolt itself, its mounted horizontally to the load, which means its trying to bend the U section towards the mast, eventually it fails.
 
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