Isotropic strain failure?

[rmettier]

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.

 

[amubashar]

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

 

[rmettier]

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?

 

[amubashar]

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

 

[rmettier]

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?