Jump to content
tiya

linear stress simulation problems

Recommended Posts

hello, I'm studying a support element (midplane section below). On the left, a vertical load is applied and the two red elements are radial supports.

image.thumb.png.d4aab99c8c03a3c94cceba6c34ea0ba9.png

Herebelow a view of half-model (symmetric with respect to the XY plane below).

image.thumb.png.08836a8b373a4e3f1458d0b3c9671cbe.png

 

Calculation performed on standard fem software show smooth stress concentration in the throat section.

image.thumb.png.fd5b9778ed8744060db56322079ff3d2.png

 

With simsolid:

1 - first problem: the hemi-cylindrical surface is imported as a single surfaces (even if it is separated in order to apply the support restraints).

image.thumb.png.85b5cc3190361e161032e9d7c9aba2eb.png

 

2 - stress distribution is unrealistic, even worse if I set forther refinements (activate feature adaptation or increase the number of adaptive solutions). Here is the von Mises stress with default options

image.thumb.png.893183b154e15f4c9f7186b7f02a9f14.png

 

Any idea? here annexed the model (test.zip).

 

Tyia

test.zip

Share this post


Link to post
Share on other sites

Couple of things:

  • Wrong boundary condition. You were using elastic foundation. Better just to apply sliding on 3 surfaces
  • Under converged. When looking for stress, better to use 4-passes and check on Adapt to features. See results below.

image.thumb.png.37ba17223cc7b485c28684dec9f9705b.png

 

Now stress are located in the slot as expected. Note: due to the fact SimSolid uses a fixed results plotting grid for contour display, stress distribution can appear more fragmented in narrow slots as compared to FEA. This is an artifact of the viz and not of the solution. 

 

Here is one more plot with the legend adjusted close to that used in FEA.

 

image.thumb.png.bfd64f830913bf4c2666e8ef57f1a818.png

Share this post


Link to post
Share on other sites

Thank you Ken for your kind reply.

 

In my opinion, soft spring elastic foundation  is a proper way in order not to influence excessively the stress distribution near the throat. Anyway this is due to the fact that I'm unable to import correctly the support faces, that are properly defined (in red, herebelow). Probably a simsolid limitation. I attach the geometry file (test.stp), if you want to try debugging the problem (or add a feature in simsolid to avoid collapsing surfaces when importing).

image.png.02e19ce3d41c6c2a1eb79a83294ed076.png 

 

With a slider on three faces (that in my opinion is less accurate near the throat section, at least on a standard FEA calculation), 4 passes and feature refinement, I obtain only a qualitative approximation of the result, that I would not approve as a design calculation (I subsequently perform a strain-life fatigue assessment, so I need the peak stress value, or better, the peak value about 0.5 mm, where the crack enucleates). In simsolid the peak stress 516 MPa is well above the real stress (about 350 MPa).

image.thumb.png.b9f78f2a39ad6b80043c39cef26eecf8.png

 

If I try to refine the solution (during postprocess) on the surface I do not obtain any better/smoother stress distribution.

 

If I perform another simulation,  increasing the number of adaptations to 5 (herebelow), I do not obtain a smoother solution. The peak stresses in the throat are better in line with FEA but the distribution is unacceptable: the results in the throat are too much scattered, and not uniformly varying.

The artefact (within the revision cloud) is probably due to the slider condition that, in my opinion, is not a good condition in this case.

image.thumb.png.24197c2f8e44e5c343d3ab08b39b8300.png

 

My conclusion is that, at the moment, for this kind of calculations, I will better rely on a standard FEM model.

Any consideration/suggestion?

Best

Tyia

test.stp

Share this post


Link to post
Share on other sites

Hello,

 

you can try to use a "Spot" for a region to apply boundary conditions and loads. See attached picture.

And as Ken has already noted, use more passes and use "Adapt to feature".

 

Best Regards,

Mario

 

 

image.pngimage.png.fe7980a87dcc9003b5bc0dcd82e4bfb0.png

Share this post


Link to post
Share on other sites

Hello Mario

 

6 minutes ago, Mario said:

you can try to use a "Spot" for a region to apply boundary conditions and loads. See attached picture.

 

 

Ok I see.

But why a soft spring is a wrong boundary condition if I'm just interested in the maximum stress in the throat? I'm a PhD mechanical engineer with more than 20 years of experience on FEA, and I wrote FEA codes myself: I can state that in standard FEA it is a perfectly acceptable condition.

 

9 minutes ago, Mario said:

use more passes and use "Adapt to feature"

 

Yes, the results shown in my post of yesterday are with "Adapt to feature" turned on and with 4 and 5 passes, as I explicitly wrote. So you suggest more than 5 passes?

 

Ok, a simulation with 6 passes (apart using 3.5 GB of RAM, that is too much for that kind of solution). Stress are unacceptably scattered in the throat section. I don't see any benefit if compared to the 5 passes solution previously shown. In classical FEA there exists a concept called grid convergence. I'm not sure if it is demonstrated that increasing the passes, the linear stress simulation performed with simsolid converges to the theoretical exact solution.

image.thumb.png.b02e3336fa2f77cf8fc856c3c9d2dc0e.png

 

Best,

Tyia

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
You are posting as a guest. If you have an account, please sign in.
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...