Jump to content
Sign in to follow this  
Crashphys

Composite thickness increasing stress??

Recommended Posts

Hi,

 

I am modelling sandwich panels applied to a wall with loading in various cases. In sandwich theory, the stress should decrease with core thickness. However when the core is thick here, the minimum principal stress is much higher than when the core is thin. 

 

I am aware there is a high load specifically at this point in specific so stress is high, however stress should still decrease with increased thickness. I am wondering if anyone has an explanation to help me understand?

 

Thin Composite:

image.thumb.png.ef38ebcef728517ae438c9b24c449ff3.png

 

Thick Composite:

 

image.thumb.png.bb2581ed3758b094120256016107f558.png

 

forum.zip

Share this post


Link to post
Share on other sites

Hi,

 

These counterintuitive results can be explained if the displacements are imposed: the thicker structure is stiffer and develops more stress under the same imposed displacements.

 

For similar reasons when optimizing for stiffness:
-imposed loads= minimize compliance
-imposed displacements= maximize compliance

Crashphys likes this

Share this post


Link to post
Share on other sites

Hi Simon,

 

Thanks again for the help. In this case, loads are applied and not displacements. That's what makes it all the more confusing...

 

Worth mentioning also: For all load cases, compliance appears to increase with increased core thickness. 

Share this post


Link to post
Share on other sites

Hi Simon,

 

I guess this is not so much a software problem but a theoretical one but:

 

Considering there are both loads and displacements applied here, if I wanted to optimize this is there a way to address this if I wanted to run OS optimization with stress constraints?

Share this post


Link to post
Share on other sites

I haven't done breakout model optimization yet so take this with a grain of salt:

 

One way coupling is a limitation of breakout modeling: the boundary conditions transferred from the global model may not be valid in a local model, if the local model's stiffness is changed significantly (in a way that alters global behavior).

Check how the global response changes at upper when compared to lower bound stiffness (thickness). Afterward, perform optimization with a narrower stiffness range for which boundary conditions are still valid. 

Also try including a more extended transition region.

 

You may find the following article useful:

https://www.digitalengineering247.com/article/global-local-modeling-fea/

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.

Sign in to follow this  

×
×
  • Create New...