×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

How to get a stress-strain curve?

How to get a stress-strain curve?

How to get a stress-strain curve?

(OP)
I have a nonlinear buckling model, and I am trying to generate a stress/strain curve. How should I go about doing this? When I run the study I dont seem to get stress or strain that I can plot as my X and Y data.



RE: How to get a stress-strain curve?

In Comsol it’s not that easy because it doesn’t save results for each increment, like other programs do. Most likely you will have to use auxiliary sweep with load as a parameter to obtain the stress-strain curve.

RE: How to get a stress-strain curve?

(OP)
"I employed a displacement control strategy. The average load on the boundary is considered as a global degree of freedom. I defined a global equation in the Solid Mechanics>Global Equations 1 node in terms of the average displacement at the boundary to get the applied load value. To calculate the average displacements on the upper boundary I defined an average nonlocal coupling under the Component 1>Average 1 node."





He creates an average displacement at the boundary to get load value? And he uses a nonlocal coupling to calculate the average displacement?

RE: How to get a stress-strain curve?

This is related to the postbuckling modeling approach we discussed in one of the previous threads here. Its details are described in the article "Buckling, When Structures Suddenly Collapse" on Comsol’s website but there are also some examples in Application Gallery that you can open in Comsol and review. They feature pdf files with instructions as well.

RE: How to get a stress-strain curve?

(OP)
Hi FEA way, for the auxiliary sweep, when I stop my range at 0.6 it runs fine, but when I increase it to for example 0.66 to make sure the model buckles, I get the following error message:



RE: How to get a stress-strain curve?

Regular Newton-Raphson method without any support usually won’t be able to complete the whole equilibrium path, including the postbuckling regime. Comsol has very limited capabilities when it comes to such analyses and it doesn’t have an arc length (Riks) solver which could be very helpful to overcome convergence issues. However, you can try replacing it with the approach described in previous threads and on Comsol’s website (the approach that uses the continuation parameter).

RE: How to get a stress-strain curve?

(OP)
Hi FEA way, I have been trying to follow the article and set up my model the following way. It seems to run fine when the equilibrium path is linear, but does not seem to give me the full equilibrium path when I turn up the load/displacement - it does not run and gives an error message. Do you know what might be wrong?






RE: How to get a stress-strain curve?

You may have to add imperfections in form of scaled linear buckling mode shapes to this model in order to get the complete post-buckling response. In Comsol this can be done using Deformed Mesh —> Deformed Geometry module.

RE: How to get a stress-strain curve?

(OP)
Do you know why it doesnt run when I dont have imperfections? Does it have to do with COMSOL itself?

RE: How to get a stress-strain curve?

It might be Comsol’s fault since it has limited capabilities for such analyses. However, in many cases imperfections are necessary to obtain the whole equilibrium path regardless of the software.

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


Resources

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