Dear all,
I notice something in my simulations and I wanted to share it with you. I appreciate if I could have your thoughts on it: In one simulation, when I uniaxially strectch a plate and change the mesh size, I noticed that the nodal stresses and strains remain in the same range. However, once I added an elliptical hole in its center, it seems that as I decrease the mesh size, stress and strain especially at the sharp edges of the ellipse goes up and do not reach to a plateau. My understanding is that it shouldn't be real and in fact should reach to a steady state. Please let me know what you think.
Best, Ali
Hi Ali,
stresses and strains are primarily calculated in quadrature points, because the derivatives of basis functions are evaluated there, and then interpolated into the mesh nodes. For uniaxial loading, the stresses and strains are usually constant or linear in the whole domain and the change in the size mesh has no effect. Around sharp edges, there is a nonlinear distribution of stresses/strains and the results of FE simulations are sensitive to the mesh size. This is quite common behavior. It is an "artifact" related to the FE approximation.
Regards Vladimir
On 15. 09. 21 22:18, kshargh.ali@gmail.com wrote:
Dear all,
I notice something in my simulations and I wanted to share it with you. I appreciate if I could have your thoughts on it: In one simulation, when I uniaxially strectch a plate and change the mesh size, I noticed that the nodal stresses and strains remain in the same range. However, once I added an elliptical hole in its center, it seems that as I decrease the mesh size, stress and strain especially at the sharp edges of the ellipse goes up and do not reach to a plateau. My understanding is that it shouldn't be real and in fact should reach to a steady state. Please let me know what you think.
Best, Ali
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Hi Vladimir,
Thank you very much for the response. Regarding "Around sharp edges, there is a nonlinear distribution of stresses/strains and the results of FE simulations are sensitive to the mesh size. ", let's say I'd like to estimate the strength based on LEFM according to the local failure strain of the elements, ( i.e. once the per element strain reaches to a specific value during the loading, we say the material fails), then since the local strain/stress around the edge changes with the change of mesh size, it means that I cannot define a unique strength value independent of mesh size. In that case, is there another way I can define the strength or any other way to avoid/weaken this mesh dependency ?
Best, Ali
Hi Ali,
On 9/16/21 3:26 PM, kshargh.ali@gmail.com wrote:
Hi Vladimir,
Thank you very much for the response. Regarding "Around sharp edges, there is a nonlinear distribution of stresses/strains and the results of FE simulations are sensitive to the mesh size. ", let's say I'd like to estimate the strength based on LEFM according to the local failure strain of the elements, ( i.e. once the per element strain reaches to a specific value during the loading, we say the material fails), then since the local strain/stress around the edge changes with the change of mesh size, it means that I cannot define a unique strength value independent of mesh size. In that case, is there another way I can define the strength or any other way to avoid/weaken this mesh dependency ?
FWIW, it depends on the precision you need - to resolve such a stress concentration "exactly", you might want a code with hp-adaptivity (e.g. deal.II, mfem, ...).
r.
participants (3)
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kshargh.ali＠gmail.com -
Robert Cimrman -
Vladimír Lukeš