Is this application considered Single Shear or Double Shear?

[Pirate2719]

I've been having a discussion with fellow work mates. I am trying to determine (in the picture below) if the pin is in Single or Double Shear based on the fact the center section is a square tube?

All comments and help are appreciated.

Thanks,

Pirate

 

[rb1957]

I'd say there are two shear faces reacting the load (in single shear). I see the middle element applying 1/2 the load local to each face.

For me, double shear is more like a pin in a clevis.

another day in paradise, or is paradise one day closer ?

 

[EdStainless]

Agree, 2 cases of single shear.
And I am sure that this one has quite a bit of deflection before anything actually shears.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Pirate2719]

Thanks for the input!! I was taking the position of Single Shear as well. Given the Single Shear application, I am running some basic numbers and have results in image below. I have adjust some of materials to both .250" to support the required design load. My next question is weather or not Allowable Stress Value shown is less than Bearing Area Stress will result in failure with 3:1 Safety Factor? Allowable Stress is greater than Bearing Stress using a 2:1 Safety Factor.

 

[Compositepro]

This looks very much like a pin a clevis arrangement to me. Imagine replacing this one pin with two separate pins (which would clearly be single shear). I think this is closer to double shear because the pin will not rotate significantly.

 

[msquared48]

Agreed - single shear twice.

Mike McCann, PE, SE (WA)

 

[dvd]

Manufacturing tolerances and misalignment whatnot - I would design for single shear at full load if possible.

 

[desertfox]

Hi

I would call it double shear and not single shear because you have calculated one side of the pin shear stress based on 3500lb, if it were single shear then the full load of 7000lb would be acting on both halfs of the pin.

See this site

http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

To call it single shear twice and do the calculation as in your post is double shear.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Nescius]

To call it single shear twice and do the calculation as in your post is double shear.

Yes.

For those saying "two instances of single shear", are you using a formula for single shear that outputs more stress than would be given by simply dividing the load by the cross-sectional area of the pin?

 

[dvd]

Also, if there are any chances of load reversal, I would recommend to investigate block shear of the tube.

p.s. avoid putting the hole through the tube weld

 

[rb1957]

@pirate,

your calc. are you saying your design is down ('cause 22222 > 16433) ? I don't think so. Your allowable stress (49ksi) looks like a shear stress, not a bearing stress. I think you're ok ('cause 11228 < 16433).

Is it just me or is this an "odd" way to preform the calc ? I'm used to calculating the MS form the allowable and the applied and seeing the FoS that falls out from that. I see the logic of requiring a FoS of 3, and so reducing your allowable ... just not what I'm used to.

another day in paradise, or is paradise one day closer ?

 

[BrianE22]

I get a bending stress of about 75 ksi. This is assuming about .5" between the applied load and the reaction near the end of the pins. I've messed up a lot of calculations lately though, so check my numbers.

 

[rb1957]

Moment would depend on the gap around the central tube, no?
and on the loading assumption (conservative = uniform across the thickness, "sporty" = triangular, centroid at 1/3 thickness).

bending + shear interaction is, in my mind, somewhat nominal ... peak bending stress at zero shear stress, peak shear at zero bending ...


another day in paradise, or is paradise one day closer ?

 

[desertfox]

Hi
From the link I gave earlier :-

Single shear is = 4*F/(pi*d^2)

Double shear = 2*F/(pi*d^2)

The difference between double and single shear if everything remains constant geometry wise is the force is effectively halfed.


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[ESPcomposites]

The resolved free body loads are the SAME, no matter what you want to call it. So the question is why do we say "single shear" and "double shear". One simple reason is just to be aware that the double shear case has two shear planes (but again a FBD will always tell you this for both cases).

The more meaningful distinction between "single shear" and "double shear" has to do with the how the fastener fits/bends within the members, how the fastener and nut/collar react moments, and the effect of eccentricity. These conditions affect the static strength to some degree and may affect the fatigue strength to a greater degree. In general, a double shear configuration usually has improved static/fatigue strengths (ASIDE from the simple effect of having two shear planes). Therefore, for typical configurations, you may compare the loads to two different sets of allowables.

Classifying it as two cases of "single shear" or a single case of "double shear" won't change the FBD loads, but there could be a tendency to directly jump to a scenario like the picture in the 4th post. But your case has no fastener head/nut on each end and there is no preload. Instead, you need an intermediate consideration based on judgement, test, or a safety factor to address the fact that you don't have a typical single shear case. In the end, it is better not to classify it at all (especially if fatigue is a concern). This could be misleading. That said, using single shear allowables would be better than double shear allwoables (though neither are actually correct).

Brian

http://www.espcomposites.com