First attempt at material nonlinearity, problem with plastic region

[bogiedreamer]

Hi all,

I finally got my model of helical spring compression to run.

Initially to keep the model simple, I define only E = 29,000,000 psi and PR = 0.3. The result seems a little high especially at the toward the end with larger compression (see attached graph).

Then I attempted to define both the Elastic and Plastic regions.
Elastic:
E = 29,000,000 PR = 0.3

Plastic:
Yield Stress Plastic Strain
1 29,000 0
2 35,600 0.000235
3 42,600 0.000474
4 63,400 0.001377
5 69,600 0.0018

With the plastic region included, the result is too low (the final force is only 40% of test data).

What am I doing wrong? Many thanks,

 

[abaqusmaster]

I have made many comparisons like that between ABAQUS results and practical results, but have not seen more than 5% difference between them. there are many details must be noticed in modeling, I think there is something wrong in your modeling or material definition.
Please leave your model here to be considered.

Good Luck,

Mohammad Shahbazi

http://www.omranafzar.com

shahbazi@omranafzar.com
----------------------------------
Please DO NOT respond to me directly but post all responses here in the newsgroup so that all can share the information.

 

[bogiedreamer]

Here is the file, thanks,

 

[abaqusmaster]

I have seen the model already. I can not help you.

Mohammad Shahbazi

http://www.omranafzar.com

shahbazi@omranafzar.com
----------------------------------
Please DO NOT respond to me directly but don't hesitate to post your response here so that all can share the information.

 

[bassmanjax]

Couple of things to check;

1) Where is the stress-strain data that you are basing the material model on? Is it from a tensile test..?

2) Are you using true stress and strain?

Regards

Martin Stokes CEng MIMechE

 

[vumat721]

What are the strains in your simulations? You only define material data up to a strain of (0.001 + 0.0018 = 0.0028) which is a pretty tiny strain. Does the experimental data continue to harden past this point? Or does it flatten out? If it continues to harden, they I'd recommend adding some more points to your *plastic card.

 

[corus]

I'm not sure why you didn't use a structured mesh for this problem with quadrilateral elements. In the model you have linear triangular elements which are useless. As well as the other suggestions, I'd suggest you change your mesh.

corus