×
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

Isotropic strain failure?

Isotropic strain failure?

Isotropic strain failure?

(OP)
I'm trying to define strain based failure criteria for an isotropic elastic material, using CAE. The suboption 'Fail Strain' gives me a table with five values: Tensile and Compressional failure strain for directions parallel and transverse to fibres, plus shear strain failure.
But as my material is defined as isotropic, there are no 'parallel and transverse' directions. What to do?

I've tried entering the same values for both transverse and parallel, and I've also tried leaving either one of them blank. But whenever I run the model, I get the following:

"Anisotropic material properties without a local orientation system have been defined for 5710 elements. Anisotripic material properties must be defined in a local orientation system. The elements are identified in element set ErrElemAnisotropicMaterial."

How can I make it clear to ABAQUS that I want this material to be isotropic? The manual section about this doesn't offer any answers.

RE: Isotropic strain failure?

Hi,

The fail stress and fail strain suboptions under ELASTIC are normally intended to be used with orthotropic materials like fibre-reinforced composites. These work in plane stress conditions. For details, please refer to the Abaqus Analysis user's Manual 18.2.3 (v6.8).

Now the error message you are receiving is just saying that you need a material orientation system for any non-isotropic material you define. This can be done in CAE in property module Assign -> Material Orientation.

If you are trying to model an isotropic material damage and failure, I would recommend looking at ductile damage or a similar material model.

Regards

Aamir

RE: Isotropic strain failure?

(OP)
Ok, I've managed to get the thing to run now, by defining and assigning CSYS for the material orientation in each part. But somehow, the failure criterium isn't showing any effect. I'm still getting an aborted model due to excessive distortion, even though the distorted elements have strain rates way over what I set as failure limit. Shouldn't the elements over the fail strain be removed from the analysis?

RE: Isotropic strain failure?

Hi,

You have to request field output variable CFAILURE to see the output of failure criteria. Also note that these failure criteria are indicators of material failure.

Aamir

RE: Isotropic strain failure?

(OP)
Am I understanding that correctly? It would just show me where material failure occured? Not remove the elements that have strain above the limit?

That's not really what I had in mind. The problem is that elements are excessively distorting after they have left the region of interest. These distorted elements are then causing the model to abort, even though the deformation in the interesting part is still way within tollerance.

Guess I've been barking up the wrong tree, huh?

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