Von Misses Stress is below Yield Strength but construction was bended

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1

Dear SimScale People,

Von Mises Stress is below Yield Strength but construction was bended
Is this construction safety or not? How should our approach be to handle this result?

Bending is indicated with red line at atttached screenshot.

Best regards

Ekran Alıntısı
Ekran Alıntısı1919×896 154 KB

Project Link:

2

Hi, this is Fillia :smiley:

Tagging the @power_users group so they can provide you with some insights.

Best regards,
Fillia

5

I tagged the group, no worries :slight_smile:

6

Dear @moguzhan ,

I can see no problem here.
There is a maximum of 16mm deflection of this structure for the given load. Von Mises Stress below yield strength simply indicates that once the load is not applied the structure will return to it’s original shape.

If this deflection is too much then the inertia need to be increased in the bent area to make it stiffer (thicker material, additional braces etc.).

I hope it helps.

Best regards,
Jani

7

Dear @jhorv_th ,

My mind is confused.

I am not a mechanical engineer. I am just trying to do something safety by searching and learning from several reference books or google searches, etc.

I know von mises stress like this:

The von Mises yield criterion states that if the von Mises stress of a material under load is equal or greater than the yield limit of the same material under simple tension then the material will yield.

Your von mises stress definition is totally diffrent.

8

Dear @moguzhan ,

it is nice to hear that you explore new disciplines!

I am a mechanical engineer and I know the von Mises yield criterion. The quoted definition is the one I share too. Why do you think I defined it differently?

Let’s see a simple example: if you have a car and you sit on the hood it is most likely that the hood will deform elastically under your weight. So once you get off the hood, it will hopefully spring back to it’s original shape. It is because the load due to your weight did not exceed the yield strength of the sheet metal. However if there is a big hail and ice impacts the hood it will probably have permanent/irreversible/plastic deformation. Simply because the hood locally yielded.

The point is that it is absolutely normal that you have (even large) deflections of structures under load below yield stress.

Best regards,
Jani

9

Hi @moguzhan, you may have over constrained your model.

I’ve run your simulation again, but changed the feet constraints so that your structure can move more in line with how I would expect. I may be on the wrong track here because I’m not familiar with your application.

Here is a top view of your original model (20x deformation).

image
image1612×635 100 KB

Here is a top view of the modified simulation (20x deformation).

image
image1658×664 147 KB

You can see that the stress in the structure is higher with the new constraints. However, the stress is still not high enough to explain the failure you’ve observed. Are you sure your load magnitude and direction is correct?

Here is a link to my copy of your project.
https://www.simscale.com/projects/BenLewis/200-80_tekrar/

10

Good Morning @jhorv_th ,

When I read again your definition. Yes, you are right. Both definitions are same. I understood your definition very different. Thats all because of my poor english skills. Sorry for that.

I supposed that the displacement in my result was plastic. So thats why I suprised.

Thank for your time and patient

Wish you all success and healhty days also for everyone in this forum.

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