Odd shear design part.

[RoarkS]

Howdy,
As seen in the attached picture, I have a rod with two "ears" that will support a normal load on the green face, by making contact with the transparent collar on the red faces.

I have calculated out the shear force, based upon the shear area created by the arc*length of the ear. Most everyone around here seems to think that this is enough. I am worried about the Height of the ears (major Radius of the ear)-(shaft radius). I Don't want to be broaching out the collar.

Background info.
Force normal to green face is a 24,000 lb impact strike.
Safety factor of 2.5 or better required.
in current config the shear force to fail the ears is sitting at 70,600 lb.
Both materials are a type of steel with a yield in hardened state of no less than 90ksi.

...but that doesn't tell me how tall they need to be.
Any ideas for some sound formulas I can throw at this?

 

[hydtools]

Is the collar intended to absorb all the impact force? Looks like an impact tool retaining arrangement. Does the elongated end contact anything to deliver impact?

Calculate the ear/collar contact area.

Evaluate the interface stress against the material strength. Face compression. Projected shear area through the collar.

Ted

 

[RoarkS]

The collar does absorbs all the impact force, delivering it to a fixed mount that fully constrains the collar. The elongated end is just floating sliding fit constrained by the collar merely for alignment.

I have a nasty excel sheet for calculating the ear collar contact area to back up the solid model.... should be able to project the profile without hassle and check it with the model.

The arcs will remain constant, and by adding length, that will add to the perimeter of the shear profile in the collar giving a positive correlation between increase in length and increased shear resistance.

That sounds like it's a real good step in the right direction! Thanks!

Will check out face compression, but I already calculated the flex of the ears to be a little less than .002"... I'm hoping that will be the weaker of the two.

Thanks!

 

[Ron]

The ear height only impacts the collar...contact surface area of ear onto the collar. This is a compression/bearing issue. If contact area meets allowable stresses, not an issue..if not, then raise the height of the ears or widen. Widening the ear would be a bit more efficient as less deformation is likely.

 

[GregLocock]

My guess is that the collar will be wedged outwards by the ears. As such there is a sort of 4 point bending failure of the collar, and the other option is shear along an inclined plane of the ears, that is, with the proportions shown, the failure area for each ear is more like w*h*1.4, rather than L*w, where w*h is the red bit.





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[hydtools]

Don't forget to remove or reduce the stress concentrations. Inside corners and outside corners.

Ted

 

[ornerynorsk]

Hmmmmm. Also looks like locking locks in a bolt action receiver.

 

[Twoballcane]

Just checking...first did you divide the strike load by two (you will have two reaction loads) and this will be the load on the ears, did you calculate the shear stress (psi) due to the reaction load, and finally the shear yield is half of the yield strength of the material.

Tobalcane
"If you avoid failure, you also avoid success."

 

[RoarkS]

@ ornerynorsk, we have a winner. You would be surprised to know how many of our dimensions are... just because that's how it was done. There are a lot of new calibers that have normal chamber pressures close to proof load pressures from when the guns were designed. It's making me kind of nervous to put my name on the prints.

@Twoballcane

here is a link to what I have been working with...

http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm

 

[ornerynorsk]

Designs have not changed much in bolt actions in the last 100 to 110 years or so. That pops into my mind everytime I pull the trigger on my Remington 700 .300 Winmag at the target range. I had a 50 BMG single shot bolt gun about 10 years ago, and this thing was clearly engineered with safety factor. The bolt had roughly 6 times the mass of what the more conventional "little" calibers have, and the lugs were massive. Still the 2 lug design, though. Fun stuff!