Contact US

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!

*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

Shell Pairs in mechanica

Shell Pairs in mechanica

Shell Pairs in mechanica


I am having a minor issue with Mechanica, and I am hoping someone who has had the same issue can share their experience with me.

I have a simple assembly of a solid object sitting on a sheetmetal object. I simplify the sheetmetal part down to a shell pair (not doing so is not an option, the part is too big and too thin), and run the model. Success.

However, the problem is, due to the shell pair my result shows a 1/2 thickness "gap" between the top of the sheetmetal part and the bottom of the solid, since Mechanica shrunk the sheetmetal part down 1/2 thickness on each side of the midsurface.

So, to solve the problem, I went into my assembly, and moved the solid part "into" the sheetmetal part 1/2 thickness, and run the model again, with vastly different results.

Now, my only problem is, I have no idea which one of these represents the true results. Does anyone have some insight into this, as to which of these is actually correct, and why? Any help would be greatly appreciated. Thanks!

RE: Shell Pairs in mechanica

When mixing solid and shell elements make sure that in your assembly the face of the solid part should be coincidently constrained to the face of the sheetmetal part.  I belive mechanica recommends the use of the mate constraint (not sure why though).

During the meshing process Mechanica will compress the sheetmetal part as you have seen into a midsurface shell model.  The edges of the solid part that were originally touching the sheetmetal part will be connected to the shell elements with link elements, which are shown in pink if you view the mesh.  An excessive number of link elements is not recommended by PTC, given that link elements are computationally intensive.  They start out with an element order of 9 (the maximum equation order possible in Mechanica).

Moving the solid part into the sheetmetal part will not bond the two surfaces together when using mechanica to perform mid surface compression.  Thus, the explination on why your results differed.

Good Luck,


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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close