[Kratos] ConstitutiveLaw interface

Riccardo Rossi rrossi en cimne.upc.edu
Jue Jun 3 10:53:14 CEST 2010

On Wed, 2010-06-02 at 18:29 +0200, Janosch Stascheit wrote:
> Hi all,
> Nelson's proposal looks quite fine in principle. As far as I can judge
> from a first glance, the principle is very similar to the one we are
> actually using. I have prepared the draft of a nee base class definition
> for the constitutive law.
> Three comments:
> 1. I guess that the abbreviations used are referring to a kind of
> enumeration? In this case, a complete list of variables and enumerations
> would be nice. As far as I remember, we agreed to use Kratos variables
> for the most common material parameters (like Density, Young's modulus)
> and the MATERIAL_PARAMETERS vector for the specific ones of particular
> models, right?

I completely agree about 1

> 2. A more formalised description of the input format would be handy. In
> the file Nelson sent, I am still not quite sure about how to actually
> define the material models

Not sure i understand your point...

> 3. This one is essential: please stick to English language comments and
> names; and please use correct names if referring to particular persons
> (like, for example "Mohr-Coulomb" and not "Morh-Colulomb"). This may
> sound stupid as it is not important for the compiler. But it improvest su
> usability and comprehensibility a lot. With respect to this issue, maybe
> we should think about installing a kind of glossary to make sure we are
> talking about the same things (e.g. fluency criterion <-> flow rule).

Concerning the naming of Mohr-Coulomb, Von Mises etc i completely agree.
This is very important also because of the image it gives of the group!

concerning fluency criteria etc, could someone write a comment about
that? in any case not all constitutive laws will use the fluency
criteria stuff ... well the word is to Nelson on the subject

> Attached, you will find my draft base class constitutive_law_new.h, a
> respective constitutive model von_mises_3d_new and a respectively
> changed kinematic_linear_element as a proof of concept. Some
> explanations can be found in the additional text file.
> Any comments and suggestions will be appreciated.

Comments on the proposal for the 

do we really need a template parameter? if it is not 100% needed than
better to remove it to reduce the computational time

if we decide that GetValue has to give back something from the base
class, than
it should return Vector() and Matrix() empty objects. I don't think it
makes sense they return objects of size 1

concerning the SetValues, we could think of making them "pure" so to
oblige people to implement them. 
Pooyan, what's your opinion about this?

We need also the functions
FinalizeSolutionStep (here for example we need to save the values)

In my opinion CalculateMaterialResponse should have flags like 
bool calculate_stress
int calculate_tangent (this could be a int so to use it for algorithmic
tangent or any other choice)
bool save_internal_variables 

Volumetic response should work with doubles ...
virtual void CalculateVolumetricResponse( const double&
                                                      double& pressure,
                                                      const ProcessInfo&
                                                      const Properties&
GeometryType& geom,
                                                      const Vector&
ShapeFunctionsValues )

and i think that the deviatoric one should assume a deviatoric strain
tensor is provided

i believe that CalculateStressAndTangent is not needed anymore ...
although one can implement it and use it internally as a private

on the other hand i think that CalculateCauchyStress should be public

furthermore i would like to propose the functions (virtual pure!!)


finally we were discussing with Pooyan the possibility of introducing a
"ValidateMaterial" (virtual pure once again)
to be used in checking that the properties provide all of the variables
needed for the calculations. If we like we could even check in there if
numbers given make sense or not...

okk ... i wrote a lot ... 
hope this can be useful


> Best regards
> Janosch
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