×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Shear Pins Calculations

Shear Pins Calculations

Shear Pins Calculations

(OP)
I have 3 shear pins 120 deg. apart connecting to concentric pieces of pipe. I want to shear the pins at a given force. My questions are: How do I calculate the shear and do the 3 pins sahre the shear load or individual. If that makes sense?

RE: Shear Pins Calculations

torque or direct shear ? i guess "given force" means direct shear.

in a failure case all three would share the load. it is common in these "structural fuses" to cut a sharp notch right at a shear plane to provide a predictable failure. using the shear ultimate of three bolts is a very coarse estimate of failure load (since three specimens will vary quite a bit in actual failure load).

what tolerance on the "given load" ? 10% ? 1% ? 0.01% ??

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

RE: Shear Pins Calculations

(OP)
I am not aware of any tolerance for the given load. It will actually ramp up to a given force then shear. I hope. I do not know how fast the operator can achieve the given force, to shear the pins. I am concerned that they will not shear simultaneously. It is a prototype piece. The pins will be subjected to vibration and forces unforseen, as the medium changes constantly. Thanks for all your help.

RE: Shear Pins Calculations

it wouldn't shear at 3*ultimate allowable, the real structure will fail at a higher load. tolerance depends on how critical it is that the thing fails at the described load.

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

RE: Shear Pins Calculations

How well they share the load depends, in part, on how accurate the hole locations are. Can you get by with 2 pins?

RE: Shear Pins Calculations

(OP)
I am told I have to have 3 due to the design. It is critical that they shear that is why I was thinking to use the ultimate shear strength of the material.

RE: Shear Pins Calculations

true enough ... the minimum load would be 1*ult allow ... each pin bearing in turn. there's a case for saying 2* as the minimum, that eccentricities would cause the joint to pivot and the 2nd fastener would bear up ... but now the failure load is < 2*allow as we're taking some (unknown/unknowable) eccentricity into account, which implies in my mind some sort of couple (adding to the direct shear).

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

RE: Shear Pins Calculations

Unless they are a brittle material there will be a continuous amount of deformation with the shear load supplied.

When one pin starts to shear, the movement to allow that to continue depends on the remaining pins also shearing.

If this mode of failure is used as a fuse, the expected shear load will be 2-3X what the pins will nominally fail to make up for variability. They can be more precise with careful dimensional and material properties control.

In your case if there is ductility to the pins, the load will rise up with increasing torque and little relative rotation, plateau with increasing relative rotation, then drop off a little while the relative rotation vs torque ramps up as less and less material remains un-sheared. At the end the torque abruptly drops and relative rotation rises the maximum input rotation rate.

Typically materials are considered failed when there is 1/3 material thickness displacement, but that will vary considerably depending on the material.

RE: Shear Pins Calculations

How are the loads going through the pins? It would be good to check the pins for bending to make sure it's 'pure shear' that causes the failure.

RE: Shear Pins Calculations

Hi

This link shows how to calculate single shear on bolts etc.
http://www.roymechx.co.uk/Useful_Tables/Screws/Bol...

I doubt very much that you will be able to shear three pins simultaneously because tolerances on holes and pins and material properties will have an effect on how the load is shared between pins, why do you need three pins and not one pin what is the reason?

RE: Shear Pins Calculations

What is the orientation of the shear pins relative to the pipe axis? Are the shear pin axes parallel or radial to the pipe axis? And what kinematic constraints are there between the pipes and shear pins? If the only positional constraint between the two pipes is that provided by the shear pins, then the initial torque force applied to the pipes will be reacted between just two of the shear pins. After there is sufficient deflection at the contact points of the two shear pins, the third shear pin will start to pick-up some of the loads.

RE: Shear Pins Calculations

(OP)
The shear pins are perpindicular to the axis of rotation. Thank all of you for your advice. My concern, of not being able to get the pins to shear like we want, have been answered. On to the next project.

RE: Shear Pins Calculations

with radial pins, the shear load on the pins is axial (along the pipe) ?

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources