changing material properties in abaqus

[mami826]

Hi All,
I am going to model density that is changing through the thickness for graded plates.
Before, I wrote UMAT to model variation of elastic modulus through the thickness and I solved my bending problem. But at this moments I want to add density to solve vibration as well.
I dont know how can I modell that. I mean if I define the density as a function of z in UMAT how abaqus define density in its solution. because in UMAT, elastic modulus can be related to stress and strain but there is no calling for density.

I would greatly appreciate if you help me.
please see the attached file for UMAT for variation of elastic modulus for bending analysis

 

[akabarten]

Hi,

I have no experience with UMAT but I agree density is not a part of UMAT definition.

Base on Abaqus documentation it looks like density is independent to UMAT.
Abaqus Analysis User's Manual, 26.7.1 User-defined mechanical material behavior, Material constants

Just add *DENSITY keyword into your *MATERIAL definition and then you can use field variable and/or distribution:

http://www.eng-tips.com/viewthread.cfm?qid=407697

Regards,
Bartosz

VIM filetype plugin for Abaqus

https://github.com/gradzikb/vim-abaqus

 

[mami826]

Dear akabarten,
many thanks foe your help.
I wrote USDFLD for E and density based on your previous comments in the following thread:

http://www.eng-tips.com/viewthread.cfm?qid=385982

but I gave different frequency compared with by-hand solution. I think it could related my BC.
actually, BC is simply supported. I am thankful if you let me know how can model simply supported plate correctly?

Regards

 

[Mustaine3]

Just to mention that again: It is not possible to change the density during the simulation.

 

[akabarten]

Hi,

It is not possible to change the density during the simulation.

Good point, I did not know this.

Thanks,
Bartosz

VIM filetype plugin for Abaqus

https://github.com/gradzikb/vim-abaqus

 

[mami826]

Hi,
what is the meaning of that? """Just to mention that again: It is not possible to change the density during the simulation.""
You mean density cannot define as a field variable in the USDFLD? what do you think about the following thread:

http://www.eng-tips.com/viewthread.cfm?qid=385982

they used density in USDFLD and I don't know why you said it is not possible.

then, what should I do to model density variation?
thanks

 

[IceBreakerSours]

Could you take a few steps back and just explain what you want to accomplish? What is the ultimate purpose of this modeling exercise? Please leave out the subroutines.

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[Mustaine3]

@mami: Just try it by yourself. Make your density dependent of a field variable, assign initial conditions and then use *Field with an amplitude to change the value of the field variable. Request mass output, run the job and then look at the mass.

The manual is also pretty clear about that.

 

[DrBwts]

Could you change the density using a User Routine? Using a continuum damage model?

 

[Mustaine3]

No, I don't think so. During a structural analysis the density is something like a constant. I assume that otherwise basic equations would not work, like the energy balance.