Push of a body on another body

[biricio]

Hi, I have to do an analysis of a small assembly.
As you can see from the image the cylinder pushes with a certain force on the plaste.
I want to know the stress I get ONLY on the plate.
How do I set-up the analysis?
I have to apply a material to the cylinder?
There is a command in Ansys that let me get the stress of a body although there are + bodies?

thanks

 

[Calcul8it]

As a start I would divide the force you are applying on the cylinder with the combined contact area of the four slabs you have between the cylinder and the plate. Unless you have other loads or constraints not mentioned here, this number would give you the stress on the plate exactly where the slabs touch the plate.

As far as I know, you need to apply a material to all bodies in the analysis that is going to be part of the solution process.

I would model the geometry of the plate, the four slabs and the beginning of the cylinder as solids in Ansys Designmodeler (I assume you have Ansys since you posted here), mark the three bodies as one part, click Share Topology and go to Workbench Mechanical. In Mechanical, I would use standard meshing settings, leave the default material (structural steel). Click the bottom face of the plate and constrain as fixed. Apply your force perpendicular to the cylinders flat face far end (opposite the contact face with the slabs).

Click solve! When solved you would have to add stress plots to Solution (right-click on Solution and select the stres type you wanto display).
Iin the interface of plate and slab you should have the same stress as your initial hand calculation.

And now you can inspect the stress distribution in the plate - you should probably change the material in the plate and the slabs (the cylinder is not so important) if you want to get a more exact stress distribution in the plate.

Christian Hansen
Twitter: @ChrHansen



FEA consulting made easy -

http://www.calcul8.it

 

[biricio]

Hi, thanks for the reply.
Perhaps the image is not clear but the bodies are just 2: the plate and the cylinder.
The 4 slabs are part of the plate.
In reality the plate is in POM material and the cylinder in PC.
I did a test like this:
I deleted the cylinder from the analysis and I distribuite the force in the 4 areas of contact. What do you think?

 

[Calcul8it]

Ok. It depends where you are interested in seeing the stress. It you are interested in the stress near the contact on the four upstands then I would add a piece of the cylinder and put force on the cylinder or alternatively put force only on contact part of the four upstands.

If you only want to see some order of magnitude stress level throughout the plate then probably it's ok to apply force over the whole surface of the upstands, put the contact is rather localized on the upstands.

Christian Hansen
Twitter: @ChrHansen


FEA consulting made easy -

http://www.calcul8.it

 

[biricio]

Hi, I want to see the stress of the plate (no cylinder).
I attach a pdf

 

[biricio]

I have made a 2 test.
If I add the cylinder and I put the force on the cylinder, the stresses that I see in the plate are different from the Test 1. Why?
Thanks

 

[Calcul8it]

Two reasons:
Reason 1)
The force on the upstands are very different from Test1 to Test2, by far.
Test1: You have 4 areas of approx. 5 mm X 5 mm = 0.0001 m2, with a pressure of 2 MPa -> total force of 200 N (check it!)
Test2: You have 1 area of approx. area = Pi * r^2 = Pi * (50 mm)^2 = 0.0079 m2, with a pressure of 22 MPa -> total force of 173800 N (check it!)

i.e. a 800-900 times the force is applied to Test 2 compare to Test 1.

Reason 2)
This, I expect, is very insignificant (especially compared to the above
There will be a small difference in the freedom of the upstands when the cylinder is present and bonded. This will give a different stress distribution, but the magnitude should stay the same away from the contact area.

I suggest you do the hand calculation, mentioned above so you know what to expect. Then if you know the force apply that instead of the pressure. 1 X full force on cylinder or 4 X quarter force on the upstand, the force will give you more certainty what you are applying.

If you only know the pressure, check the pressure area on the Project Outline on the left of the screen in Mechanical.

Good luck!

Christian Hansen
Twitter: @ChrHansen


FEA consulting made easy -

http://www.calcul8.it

 

[biricio]

Hi, I have only a datum: the pressure of 2 MPa that pushes the cylinder against the plate.

I have understood the reason 1.
The question is:
if I put, in the test 1, a force of 173800 N/4 (number of contacts area) I have the same results of the tst 1?

2° question:
I have understood where I can check the pressure area on the Project Outline on the left of the screen in Mechanical.

thanks

 

[Calcul8it]

You, have to check the actual area of the cylinder where the 2 MPa is applied and then calculate the actual force - I just estimated the area. Also, as I said the constraints on the upstands will be slightly different, but otherwise the stress should be the same.

Christian Hansen
Twitter: @ChrHansen

FEA consulting made easy -

http://www.calcul8.it

 

[biricio]

Hi, I have calculated the force in the two tests.
I have not understood because, to page 8 of the pdf, have two diffrentis stress.

Perhaps because I have two force values:
Test 1 > 240 N
Test 2 > 15080 N

How I do to have the same stress value in the TEST 2 (ugual of TEST 1)?
thanks

 

[Calcul8it]

Think the link doesn't work.

But if you want to make an analysis without the cylinder (and only have the pressure on the cylinder) you have to work out what corresponding pressure to apply on the upstands. Guess you just scale up the pressure with the ratio between the big cylinder surface and the smaller upstands contact areas.

Christian Hansen
Twitter: @ChrHansen


FEA consulting made easy -

http://www.calcul8.it

 

[biricio]

Hi, I attack again the file pdf.
I have calculated the force in the two tests.
I have not understood because, to page 8 of the pdf, have 2 diffrentis stress.

Perhaps because I have two force values:
Test 1 > 240 N
Test 2 > 15080 N

How I do to have the same stress value in the TEST 2 (ugual of TEST 1)?

 

[biricio]

Ok

 

[Calcul8it]

Hi Biricio

You have to make sure that you use the 1/4 force on each upstand compare to the force you put on the cylinder.

I.e. if you put 15080 N on the cylinder you put 15080 N / 4 = 3770 N on EACH of the upstands.

Or

If you put 240 N on each upstand you should put 4 x 240 N = 960 N on the cylinder top.

Christian Hansen
Twitter: @ChrHansen

FEA consulting made easy -

http://www.calcul8.it

 

[biricio]

Ok, When I have made the calculation I founded 15080 N on the cylinder top.
If I divide 15080/4=3770 N I have the force in each upstands.
Instead I have calculated 240 N in ALL upstands.