Re: [Getfem-users] material law with non-symmetric stiffness

[Yves Renard]

Dear Andriy,

Since grad_sigma should be the hessian of an elastic energy, it as to be 
symmetric, at least in the hyperelastic framework. I am not a specialist of 
orthotropic material, what is the difference is that case ? You mean that you 
are not in an hyperelastic framework ?

The symmetry is assumed in assembly routines 
(asm_nonlinear_elasticity_tangent_matrix use "M(#1,#1)+=sym(...)") for the 
stiffness matrix.


Yves.


On lundi 2 mai 2011, Andriy Andreykiv wrote:
> Dear Getfem users,
> 
> I would like to use a non-linear elasticity brick with my own material
> law that has non-symmetric stiffness matrix.
> It's non-symmetric if you write it with Voigt notations, but of
> course, two other "standard" symmetries of a full C_{ijkl} tensor are
> present (i-j symmetry and k-l symmetry).
> When I looked into getfem_nonlinear_elasticity.h I  found a comment
> (next to virtual void grad_sigma declaration):
> 
> "// the result of grad_sigma has to be completely symmetric."
> 
> Does this comment imply the above mentioned two symmetries or it means
> that a non-symmetry that also reveals itself
> in material matrix, written in  Voigt notations, is also not allowed?
> A simple example would be: Can I use a fully orthotropic material in
> non-linear elasticity brick?
> I browsed through the code of "getfem::nonlinear_elem_term " but it
> doesn't look like any symmetry is required.
> However, I would like to be sure.
> 
> Thank you in advance,
>                                      Andriy
> 
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-- 

  Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
  Pole de Mathematiques, INSA-Lyon             fax : (33) 04.72.43.85.29
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  69621 Villeurbanne Cedex, FRANCE
  http://math.univ-lyon1.fr/~renard

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