how to design a model with multiple properties and user subroutine

[vinnuram]

hey all,
I guess it's a small question for most of them.I actually wanted to know how could i design a 2d shell with inner part as viscoplastic and outer part as elastoplastic,a user subroutine UMAT is applied on this model.
I am actually trying to apply a user subroutine on a cell structure of a material in which matrix and unit cell are in elastoplatic region and the particle in the center is a viscoplastic.
Should i have to mention while giving the properties that these are viscoplastic and elastoplastic separately and should i have to just specify the USER DEFINED MATERIAL AND CAN I SPECIFY THE PROPERTIES IN THE SUBROUTINE....
PLZ LET ME KNOW..
VINNU ARIGE

 

[xerf]

You need to define two user materials and assign them to different element sets (or different parts, depending on your modeling approach).

In UMAT you will have to identify to which material (model area) the integration point belongs to, by cheking the CMNAME parameter vs. the assigned material name (put in *USER MATERIAL definitions).

Depending on this check one of the coded constitutive responses (viscoplastic or elastoplastic) will be used.

The material proporties are typically specified on the definition
*USER MATERIAL, NAME=viscopl, CONSTANTS=no_of_constants1
c1,c2,c3....etc

*USER MATERIAL, NAME=elplast, CONSTANTS=no_of_constants2
k1,k2,k3....etc

when UMAT is called, the constants you put in the *USER MATERIAL definition will be found in the PROPS vector which will have the length NPROPS= CONSTANTS.

Generally the first thing in UMAT to be done, after identifying the material is to recover the constants,say:
E=PROPS(1)
NU=PROPS(2)
S_YIELD=PROPS(3) and so on

Alternatively ....of course if you identify the material you could specify the material properties within the UMAT , but then you'll have to update the subroutine each time you want change material properties.