Lot's of options here... but what we generally do is compute the _average_
stress and strain (pick a component) and store it per element using
CONSTANT, MONOMIAL's in an ExplicitSystem... that way we can view the
stress/strain in your visualization tool.

This is pretty similar to what Abaqus and other solid mechanics codes do.
 libMesh will even output a nodal interpolation of that CONSTANT, MONOMIAL
field by default if you are using Exodus... which again matches what Abaqus
typically does...

Computing the average is trivially easy... just integrate whatever
component of stress/strain you are interested in (or compute Mises or
whatever) over the element (loop over qp's, multiply by JxW and add it up)
then just divide by elem->volume() to get the average on that element and
store the result into the ExplicitSystem solution vector at the
corresponding element DoF for your CONSTANT, MONOMIAL...

Derek

On Sun, Jun 24, 2012 at 1:19 PM, John Peterson <jwpeter...@gmail.com> wrote:

> On Saturday, June 23, 2012, Kyunghoon Lee wrote:
>
> > Hi all,
> >
> > I wonder what is the best way of computing strain and stress values with
> > displacements obtained by solving linear elasticity problems.  I can
> simply
> > follow displacement-strain and strain-stress relationships (using finite
> > difference to compute gradients), but I guess it would be more natural to
> > use basis function information.  I'd appreciate it if someone can suggest
> > me some reference examples.
>
>
> What about using some kind of gradient recovery method like Zienkewicz-Zhu
> to postprocess the solution?
>
> Libmesh also has the patch recovery error estimator machinery that may be
> inspirational.
>
>
> --
> John
>
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