fluid pressure and metal plasticity

[Newuser2006]

hi to all again,my first question is how to define a fluid pressure and temperature acting on a piece of metal?is this possible in ABAQUS?and my second question is about the different plasticity models which one is to use and for what
thanks in forward

 

[Cansand]

For modelling metal: It depends on the Loading (Cyclic or static) and on the Lab data available to you
Do you have creep results?
Conventional insenstive to hydrostatic pressure model ,e.g , Tresca (or Mises) with isotropic hardening can be used if you only have Stress-Strain curve under static load

 

[Cansand]

For applying Fluid pressure: are you analyzing porous medium..?

 

[Newuser2006]

yes for metal i habe a lab data,thats why it did not work in the default model for plasticity,it gave me that the numbers should be increasingly ordered,but the stress-strain curve i have is of course not so.so yes i have a lab result for stress-strain curve?how to model it in abaqus with the young modulus.

for the fluid modeling,no it is not a porous medium.i want to model a fluid pressure on a definied area of a piece of metal.any idea. thanks for the reply

 

[Cansand]

What model are you using in ABAQUS ?
what material data do you have ?
For the fluid pressure: you can simulate it by applying hydrostatic pressure on the edge (surface) of the metal part this fluid pressure operating on.

 

[Newuser2006]

thanks cansand and please read what i wrote,i told you i have stress-strain data for a metal at many temperatures.these are experimental results from the lab and i want to model them in abaqus.so what is the best way to define elasticity and plasticity in abaqus.how to introduce these curves in abaqus. and thanks

 

[Yoman228]

I have to agree with Cansand that we need to know that the loading is static or cyclic. Are you expected the material to yield? The material model for static and cyclic loading is quite different.
Beaware that ABAQUS use true stress and longitudital strain. so you many need to convert them from the engineering stress and strain from test

 

[Newuser2006]

yes iam expecting the material to yield and the load on the specimen is static.yes i transformed the experimental data from nominal strain-stress to engineering strain-stress.so now how to model the material data exactly please give me where i can host for you some of my material curves. and thanks alot for help

 

[Cansand]

Alright
You can use simple elasto-plsaticity model that is temperature-dependent
Get the young modulus from the stress strain curve.
If you notice the Curve, you find it at early loading stage linear. So get the slope of this linear part of the curve . That will be your Young modulus (E )if the stress- strain curve is for tension/compression and is Shear modulus (G) if shear test was performed. Assume Poission ratio for the material you have.
Enter the elastic information under Elasticity information
Go to plasticity and select Plastic . Choose isotropic hardening and tick at temperature-dependent data box
enter the first stress-plastic strain curve (taken at the first tempertaure)
enter the second curve for the second temperature
and so on

 

[Newuser2006]

thannks consand for the long post,but first of all my curves have almost no linear region at the beginning and thats why i have difficulty calculation the e-modulus,secondly the isotropic model for plasticity is not working with my curves especially when the stress values start to decrease after the ultimate stress value,it gives me that values should be increasingly ordered.have you reallly tried it before.any idea about the other plasticity models?? and thanks

 

[Cansand]

In terms of elasticity :
For stress strain curve ,do you have loading and unloading paths

If you do not have unloading path then this would be the only way to get elasticity modulus if you only have stress-strain curve data. Alternatively, You may want to get the approximate elasticity modulus looking for a similar material from literature.
"secondly the isotropic model for plasticity is not working": Keep the same model and just try to use the Step :Static Riks instead of Static General
and please let me know what happens.

 

[Yoman228]

You need to read ABAQUS menu

18.2.2 Models for metals subjected to cyclic loading.

and you will need to use the kinematic hardening modelling for cycling yielding.

In ABAQUS standard, the material only model up to the ultimate tensile strength, hence the loading that you see where it drop will not be modelled normally.

Beware that the plasticity will become perfetly plastic from the last of the plastic strain value specified.