Dear Natanael Lanz,
It seems to me on the figure you provide that the maximum stress is
located on the part of the tooth where probably the load is applied and
at the hollow between two teeth which a priori is quite normal.
Additionnally, you have a stress distribution compatible with Hertz's
theory on the part where the load is applied (do you use a contact
condition ?). So my question is : what minima and maxima do you refer to ?
I suppose you use a quadratic approximation, right ? Is your mesh a
quadratic one also ? Having small oscillations is quite usual and may be
due to the fact that you use a linear mesh if it is the case. Did you
try to interpolate the stress on a discontinuous fem ? The interpolation
on a continuous fem make intervene some local average of the values on
each element.
Best regards,
Yves
Le 12/09/2017 à 14:04, Lanz Natanael a écrit :
Hello dear getfem++ users,
I have a question, some of you may know an answer to:
I solve a linear elastic problem using getfem, where first the
displacement of a gear tooth under load is computed an from this the
von Mises and principle stresses are computed using
compute_Von_Mises_or_Tresca(md, …) for von Mises and a slightly
adopted own version of it for the computation of the principle
stresses. Both functions basically call
compute_gradient(mf_U,mf_ST,U,GRAD).
My problem ist, that also if the computed displacement looks very
smooth (figure is attached), the computed stresses have local minima
and maxima where they should be quite constant. Also at certain single
nodes the stress values show unexplainable peaks. As I look for the
maximum stress, this peaks are not good. Does anybody know where these
local peaks are coming from? How exactly does the interpolation on the
quadratic elements work? Is there may be a numerical problem?
Under the following link you can download some pictures of the
displacement and stress results:
https://polybox.ethz.ch/index.php/s/cWKcMznQmYQLLda
Following link leads to an example results vtk file:
https://polybox.ethz.ch/index.php/s/ht3dfd5qniYrTZP
And this link to the imported gmsh mesh file:
https://polybox.ethz.ch/index.php/s/hG90v8SeLNlvTb4
As mentioned quadratic elements are used (FEM_PK(3,2)) are used, in
order to get continuous stress values at the nodes.
Thank you for any help in advance.
Natanael Lanz
MSc Masch. Ing. ETH
IWF ETH Zürich
Technoparkstrasse 1
PFA E82
CH-8005 Zürich
[email protected] <mailto:[email protected]>
www.iwf.mavt.ethz.ch
Tel. +41 44 6325714
Mob. +41 79 5862958
Natanael Lanz
MSc Masch. Ing. ETH
IWF ETH Zürich
Technoparkstrasse 1
PFA E82
CH-8005 Zürich
[email protected] <mailto:[email protected]>
www.iwf.mavt.ethz.ch
Tel. +41 44 6325714
Mob. +41 79 5862958
--
Yves Renard ([email protected]) tel : (33) 04.72.43.87.08
Pole de Mathematiques, INSA-Lyon fax : (33) 04.72.43.85.29
20, rue Albert Einstein
69621 Villeurbanne Cedex, FRANCE
http://math.univ-lyon1.fr/~renard
---------
