Re: [Getfem-users] Stress tensor / normal stress on surface

[Yves Renard]

Dear Stephan,

The easiest way to do this now (but for that you have to download the svn 
version of Getfem) is to use the generic interpolation (see 
http://download.gna.org/getfem/html/homepage/userdoc/interMM.html#interpolation-based-on-the-high-level-generic-assembly-langage
 and 
http://download.gna.org/getfem/html/homepage/userdoc/gasm_high.html#ud-gasm-high).

For instance the interpolation of the whole stress ca be done with the string
"lambda*Trace(Grad_u)*Id(meshdim) + mu*(Grad_u + Grad_u')"

if u is the variable representing the displacement and lambda, mu the Lamé 
coefficients. So you can use the function

getfem::ga_interpolation_Lagrange_fem(md, "your expression to be interpolated", 
mf, result, rg=mesh_region::all_convexes());

to perform the interpolation (mf should be a Lagrange fem). If rg is a boundary 
region, you can use the keyword "Normal" to refer to the unit outward normal to 
the boundary.

The Von Mises stress can be obtained with the string
"sqrt(3/2)*Norm(Deviator(lambda*Trace(Grad_u)*Id(meshdim) + mu*(Grad_u + 
Grad_u')))".


Yves.




----- Original Message -----
From: "Stephan Gekle" <address@hidden>
To: address@hidden
Sent: Monday, April 28, 2014 5:53:16 PM
Subject: [Getfem-users] Stress tensor / normal stress on surface

Dear all,

I am using the 'isotropic linearized elasticity brick'.
Is there an easy way to obtain the local stress tensor sigma throughout 
the material? And similarly the tangential / normal stress on the surface?
Or is it necessary to compute that manually using the derivatives of the 
displacements... if so, has anybody a piece of code at hand to do this?

Thanks a lot for any help,

   Stephan


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