Analysis of Frame bolted on trailer 1

[Belisario_G]

Hi everyone,
I'm working on performing some static analysis on the frame shown in the picture.
Can you guys assist me in pick the correct constraint for the bolt holes ?
Also, which constraint will be suitable to represent the contact between the trailer and the frame ?

Thanks!!!

 

[JGard1985]

ANSYS Academic Huh? Coursework?

Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[Belisario_G]

The post is not coursework or project. We are during summer break right now, I am simply learning the software package ANSYS. Would you be able to help with the small question I asked?

 

[JGard1985]

Sure, spherical joint for trailer hitch. Revolute for bolt holes

Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[Belisario_G]

Thanks Jeff!
Do you have a reason why I wouldn't be able to use a cylindrical support on the bolt holes?
Also this framing will be modeled to rest on a flat surface, which constraint will be fit that condition ? I was thinking on using a frictionless support (Applies constraint normal to the surface selected).

 

[JGard1985]

Cylindrical support allows translation along length of joint (axial movement). Nuts & bolts prevent translation in this direction.

Yes frictionless contact is the easiest to do. Don't bond it because then your bolt holes won't take tension/shear force that you would expect them to.

On a side note, as you learn ANSYS or any other FEA package, think about your mesh and how well it converges to a steady state solution. Read these two articles to understand how to apply validation, verification and mesh convergence in FEA

https://www.xceed-eng.com/finite-element-analysis-verification/

https://www.xceed-eng.com/finite-element-analysis-convergence-and-mesh-independence/

Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[Belisario_G]

Splendid!
Great links, I am aware of how important the meshing is. Do you have any book recommendations that address these factors ?

Also,
I will try the Revolute for the bolts hole. Do you have a better recommendation on how to model a surface contact (Contact between frame and flat surface) ?

Thanks!!!

 

[L_K]

As was said before, frictionless support is not able to open in Ansys in which case bolt holes would not take as much tension force as in reality. Revolute joints in bolt holes are sufficient
to constrain the model, in my opinion.

For a more detailed analysis, the lower surface should also be modelled. Then you could use nonlinear surface-to-surface contacts (frictionless or frictional) which would allow opening.

 

[JGard1985]

Belisario_G

Easiest way to do mesh independence is plot it yourself. Just pull on model in 1 direction, and record deflection. Then remesh to a finer mesh, pull, and record deflection. Plot deflection vs. number of elements, Eventually you will get to a point where adding elements has no appreciable effect on stress. I have a plot of this in blog post mentioned in previous post

You also want to do something like this at your connections (areas of high stress intentsity). Keep remeshing these areas and monitor stress (such as Von Mises). Eventually localized stresses should level off. Then you know you have a good mesh.

ANSYS also has tools to help you. In the tree on the left hand side (of workbench) click on Mesh. Then in the details window (below) click on Display Style and choose element quality. With element quality ranging from 0 (bad) to 1.00 (best) ANSYS will tell you areas of the mesh that are bad and may need a finer mesh.

Also Surface contact is the "true way" to model this configuration. If you wanted to remove contacts you could apply supports (Zero Displacement) to base plates you expect to be in compression and apply revolute joint to the bolt on the plate subjected to tension. Its an approximation, but gets you out of contact space. You just want to make sure that:
1. Tension forces act at the bolt hole only (not over entire plate)
2. Compression forces act across entire surface of plate
Jeff

Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[L_K]

You could take a look into "compression only" support. This might achieve the points 1 & 2
mentioned in the post above.