topic Re: Zero Stress On Shell Element in a shell/solid assembly in Inventor Nastran Forum

Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Fri, 05 Apr 2019 19:35:11 GMT

Hi Everyone,

I am running a FE analysis of a structure, the shell part where the load is applied on, shows zero stress. Could anyone let me know what is the reason or what I am doing wrong?

Any comment is appreciated in advance. The shell and solid Von Mises results are presented in these photos.

Re: Zero Stress On Shell Element in a shell/solid assembly

Roelof.Feijen — Fri, 05 Apr 2019 20:02:11 GMT

Did you check the material properties of the shell idealization. Be sure not to use the Generic material property. The pictures shows a min / max value. Does the shell results maybe show a stress singularity on one node for example?

Re: Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Fri, 05 Apr 2019 20:58:39 GMT

@Roelf.Feijen Thanks for your comment. I don't use generic material. a snapshot of shell material is added.

Re: Zero Stress On Shell Element in a shell/solid assembly

Roelof.Feijen — Sat, 06 Apr 2019 08:20:32 GMT

Hi @Anonymous,

It is hard to tell what is going on, based on some images.

Could you share your model?

Re: Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Sat, 06 Apr 2019 21:30:16 GMT

Hi @Roelof.Feijen ,

Not really. If you have such a problem in an analysis which areas do you check? what do you think could be the reason of this.

any thoughts?

Kind Regards,

Ali

Re: Zero Stress On Shell Element in a shell/solid assembly

Roelof.Feijen — Sun, 07 Apr 2019 08:10:33 GMT

It is not so easy to give advise if I don’t understand your problem.

From the title of this post I thought that all shell results are zero. But I am right that there is only one node that has a zero value?

Also I don’t see a displacement value at the summary at the bottom of your results plots. Did you check the displacement results?

If it comes to stress note that by default we are looking at the average nodal results. Is your stress plot showing the average, the min, the max?

Re: Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Sun, 07 Apr 2019 12:01:30 GMT

hi @Roelof.Feijen

The displacement is:

Stress distribution definition:

Thanks in advance,

Ali

Re: Zero Stress On Shell Element in a shell/solid assembly

John_Holtz — Sun, 07 Apr 2019 20:12:33 GMT

Hi @Anonymous

Are you sure that the 0 stress is in the shell? From your title, you have solids and shell elements. If I remember correctly (I am answering from home and do not have access to the software), I think the minimum value of 0 is in the solid, not the shell element.

In other words, it is possible that In-CAD displays a value of 0 in all of the solids because the solids do not have a "shell stress". If you edit the contour plot, choose "Part View", and select only the shell parts, then the minimum marker will show the true minimum value in the displayed parts.

Re: Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Sun, 07 Apr 2019 22:09:35 GMT

Hi @John_Holtz

I checked part view, but I don't know why I can not pick shells!!!. So that, I just used the probe to pick a node stress. The stress on shell element could be seen in the following snapshot which is almost 0:

Thanks for you comment John,

Ali.

P.S: Just in case if it helps, this is the version of my Nastran:

Re: Zero Stress On Shell Element in a shell/solid assembly

shigeaki.k — Mon, 08 Apr 2019 05:23:22 GMT

Hello @Anonymous ,

currently "part view" only works for parts with solid idealization. An idea has already been submitted to the Product Team to allow for the selection of shell and beam parts in "part view" as per,

Ability to select shell or beam meshed parts in "part view" for result plot

Are you also able to share the model?

Regards,

Shigeaki K.

Re: Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Mon, 08 Apr 2019 06:09:58 GMT

hi @shigeaki.k,

I can not share it publicly, but I can do it privately for Autodesk support team.

Thanks,

Ali

Re: Zero Stress On Shell Element in a shell/solid assembly

shigeaki.k — Mon, 08 Apr 2019 07:31:16 GMT

Hello @Anonymous ,

I have sent a private message with regards to uploading the file(s).

Regards,

Shigeaki K.

Re: Zero Stress On Shell Element in a shell/solid assembly

shigeaki.k — Tue, 09 Apr 2019 10:38:24 GMT

Hello @Anonymous, thank you. We have received the file. I am wondering if your analysis completed successfully. When I ran the last analysis, I noticed that it was struggling to converge. I removed the "arc length method", and all the contact definitions that you had. I then set up a single "solver" contact with activation distance of 50mm and the analysis seems to be chugging along nicely. I will need to wait until the analysis completes to check the shell von mises results. Regards, Shigeaki K.

Re: Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Tue, 09 Apr 2019 22:18:43 GMT

hi @shigeaki.k

Unfortunately it didn't converge. I am going to update my model to match your suggestions and check the analysis.

Thanks for your try.

Ali

Re: Zero Stress On Shell Element in a shell/solid assembly

shigeaki.k — Wed, 10 Apr 2019 13:16:35 GMT

Hello @Anonymous ,

the model completed successfully. In the meantime, could you send @John_Holtz or myself a link to a file sharing site you are using via private message for this forum.

Regards,

Shigeaki K.

Re: Zero Stress On Shell Element in a shell/solid assembly

John_Holtz — Thu, 18 Apr 2019 12:49:47 GMT

Hi @Anonymous

I wanted to follow up with you to find out where you stand with the analysis. Did you get it to work using Shigeaki's suggestion? Did you provide the updated model that is not working? (Sorry if I missed a message somewhere. )

Re: Zero Stress On Shell Element in a shell/solid assembly

Anonymous — Mon, 22 Apr 2019 22:22:55 GMT

Hi @John_Holtz,

Thanks for your follow up. Yes, I got the analysis working. I used @shigeaki.k comments and it worked.

His comments were:

use solver contact for contact defenition,
avoid "arc mesh method".

I provided the model and he worked on that, too.

Regards,

Ali