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Poission's ratio problem related to Structural Mechnics
Posted 17 ago 2012, 00:34 GMT-4 Structural Mechanics Version 5.1 7 Replies
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I just started to learn COMSOL and tried to conduct a simple simulation of deformation of an elastic plate by a face load. I used Solid Mechanics model in 4.3 edtion.
1. When I set the material property, poission's ratio as 0.3, the simulation worked well and I could check the deformation plot. But when I change the ratio to 0.5, the problem came. It said,
- Detail: Undefined value found in the equation residual vector.
.There are 4885 degrees of freedom giving NaN/Inf in the vector for the variable mod1.u
. at coordinates: (-0.01,-0.005,0.0002), (-0.01,-0.005,-0.0002), (-0.01,-0.005,0), (-0.01,-0.00426971,-0.0002), (-0.01,-0.00463486,-0.0002), ...
There are 4885 degrees of freedom giving NaN/Inf in the vector for the variable mod1.v
. at coordinates: (-0.01,-0.005,0.0002), (-0.01,-0.005,-0.0002), (-0.01,-0.005,0), (-0.01,-0.00426971,-0.0002), (-0.01,-0.00463486,-0.0002), ...
There are 4885 degrees of freedom giving NaN/Inf in the vector for the variable mod1.w
. at coordinates: (-0.01,-0.005,0.0002), (-0.01,-0.005,-0.0002), (-0.01,-0.005,0), (-0.01,-0.00426971,-0.0002), (-0.01,-0.00463486,-0.0002), ...
No matter how I change other parameters, like load value or mesh, it always got wrong. But the 0.5 is the one I really need. Hope someone could help me figure out the reason.
2. And there's another question. when I changed the value of load to the surface and compute for result, I found the plot didn't change. I mean in reality, when the load increases, the displacement should be also increased. But in the plot, the shape of plate is never changed. Is this problem related to scale ratio or something?
Here I attach my mph and I really appreciate the help!
Attachments:
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The shape of the plate is not changing because COMSOL scales the displacements (to make the deformation visible). If you put a bigger load you get a small displacement scaling factor and the deformed geometry looks the same. You should manually set the displacement scale factor and activate “Include Geometric Nonlinearity” if your displacements are not very small.
Nagi Elabbasi
Veryst Engineering
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The shape of the plate is not changing because COMSOL scales the displacements (to make the deformation visible). If you put a bigger load you get a small displacement scaling factor and the deformed geometry looks the same.
Hello Nagi, I just want to ask something about that: Is there a way in Comsol that we could see the actual displacement for instance, if we would want that?
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Nagi Elabbasi
Veryst Engineering
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It's too excessive though, but that's probably another mistake I made, I'll find it sooner or later.
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i am photonic student and i have question about structural mechanic. may you give me your email that i be in contact with you.
regard
amir
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Poisson ratio has to be between 0-0.5 it cant be 0.5
That is a common misunderstanding. Actually -1 < Poisson's ratio < 0.5
Materials with Poisson's ratio < 0 are called "auxetics".
See also www.comsol.com/blogs/modeling-linear-elastic-materials-how-difficult-can-it-be/
Henrik