Maximum Von Mises Stress Point / Average - Max / Inventor Nastran 2021

[Anonymous]

Hello,

We are using Inventor Nastran 2021 version.

In my analysis, when I select Plot --> Data Conversion to "Average"; Maximum Von Mises Stress is indicated as 190,906 (Data Max).

However when I select Plot --> Data Conversion to "Maximum"; Maximum Von Mises Stress is indicated as 305,419 (Data Max).

Furthermore, the 305,419 high stress point is located at an irrelevant location.

What is the reason of this high stress point? 

Is it due to the modelling quality or is it a real stress point?

If it is due to modelling, what I can do to eliminate it?

Thanks!  

[Roelof.Feijen · Accepted solution]

Hello @Anonymous ,

There is an article on the website (see this link) that explains Data Conversion, Data Type, and Contour Type.

Reading that article first might be helpful in this case.

If you still have questions after reading this article, please let us know.

[John_Holtz · Accepted solution]

Hi @Anonymous 

A separate stress is calculated in every element based on the displacement calculated at the nodes. Therefore, the stress is two adjacent and connected elements is rarely the exact same value.

The calculated stress is highly affected by the shape of the element. A distorted element will cause a distorted stress. By averaging the stress between adjacent elements, those differences tend to average out. But this also means that if you look at the "maximum" result from the N elements connected to a node, the result is likely to be higher than the theoretical result. Therefore, you should probably not use the maximum result for any purpose (other than to get an idea of how much variation occurs at a node).

Since the mesh is created automatically and you have very little control over the quality of the solid mesh (which is the source of the distortion), there is very little that you can do to eliminate it. My advice is to ignore it, especially if it occurs in a location that is not important and has a low stress otherwise.

[firas.abdelahad]

Can the higher stress results be hidden or not reported in the published report ? Anyway of doing that without hiding the actual member ?

[John_Holtz]

Hi @firas.abdelahad 

I think you do not have any control over what is created by the automatic report, but you can replace the images that it creates after the report is generated. The best that you can do to "hide" the high stress singularities are things like this:

• Hide the max and min markers so that the "Max" is not shown at the singularity.
• Change the legend range so that the high value from the singularity is not "shown" in the legend.
• Rotate the model so that the singularity is not visible.

The first two items are done by editing the contour plot.