Re: [Getfem-users] Uncontinous stress problem (next try)

[Yves Renard]

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

 

address@hidden

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

 

address@hidden

www.iwf.mavt.ethz.ch

Tel. +41 44 6325714

Mob. +41 79 5862958

 

 

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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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