Set the compressive yield point? 1

[chris10000]

I am new to abaqus and trying to run some very simple models. I have managed to run a plastic analysis with a tensile load, I am now interested in running an analysis with compressive yielding. I have tried setting the yield stress to -xxx (*Plastic -xxx,0) but get an error to say the yield stress must be greater than zero. How do you set the stress at which a material will deform in compression or is it assumed that the material yields at the same stress in both tension and compression?

Thanks
C

 

[Cansand]

what model are you using
MohrColoumb, Drucker Prager, Metal . It depends

 

[chris10000]

Thanks for your reply, its a metal part

 

[Yoman228]

If you looking for some basic steel like material behavior, in most cases, you can assume that the material have isotropic hardening. Then all you need is the material data from tensile test (need to transfer the engineer stress and strain to true stress and strain for ABAQUS model)

If there is no details of the material data, using Ramberg-Osgood behavour is a good start.
I personally will not use perfectly plastic material behavior if I know the material will going to yield.

 

[gurmeet2003]

Yoman,

If for steel one just inputs stress strain data in tension, how is the data interpreted by ABAUQS in compression (for metals). Is the yield in compression assumed to be same as yield in tension? What is failure criterion for ductile metals in tension? Your reply to above questions will be appreciated.

Thanks,
Gurmeet

 

[Yoman228]

For "isotropic" hardening material, the yield in tension and compression is the same. and the yield surface will grow under cycling loading, it does not take into account of the Bauschinger effect.

when doing cycling load such as a low-cycle fatigue situations. it is better to use Kinematic hardening material modelling, where the yield surface will shift.

 

[Yoman228]

Failure criterion? usually that is defined by the project scrope. when a material get pass yield does not mean it have fail.
Moreover, steel started to have noticeable non-linear behavior below its yeild (my gusses is appoximately 80% of yield strength)
Notice that, after the last stress strain data. ABAQUS assumed that it will be perfetly plastic afterward.

 

[gurmeet2003]

yoman,
Sorry there was a mistake in my earlier post. My question was about failure criteria in comprssion not tension.
Thanks,
Gurmeet

 

[Yoman228]

If it is isotropic" hardening material, what the different between tension and compression? They both will have not be able to take more load when it gets to perfetly pastic.

 

[Cansand]

Yoman228
just for your info that a material can have both isotropic (yield/loading surface is expand or contract in the same magnitude at all directions) and kinematic hardening (the yield surface being expanded is also translating in a specific direction) at the same time, although i do not thing that this case is applied to questionor's problem.

 

[Yoman228]

I do agree with you Cansand. However, I do not think ABAQUS have a sample build in material model that do that. I was told to use Isotropic when I have single cycling model and kinematic for mutli-cycling as it gives the best estlimate solution. Hope this is correct as I used this concept for years.