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Confused ?? Axial Force - Contact Pressure - Axisymmetric Solution SOL 601

Either I'm missing something obvious... or there is an error.
I'm using NX 7.5 SOL 601.

Simple setup:

Two cylindrical rods stacked on top of each other, one short on top and one bit longer under it. (10 mm and 20 mm, diameter 20 mm, respectively).
A symmetry plane in the bottom of the long one. An axial force (500N) applied to the top short rod. A contact setup between the two rods. This yields a contact pressure between the top rod and the bottom rod.

Now - Just doing a simple calculation the ideal pressure should be approximately 1.6 MPa over the contact surface. However, the pressure in the results is approximately 10 MPa.

Something is very wrong or I'm doing something wrong.
As I believe - When I apply an axial force in an axisymmetric solution, I apply this force along the edge of the 2D reresentation of the surface onto which this force acts, as if I would apply tha force to the surface in a 3D simulation. The program accounts for the difference in solution (2D axi- 3D).

Am I doing someting wrong?? I'm totally confused and can't find any information about this anywhere.

Greatful for help!

Re: Confused ?? Axial Force - Contact Pressure - Axisymmetric Solution SOL 601

In an axisymmetric analysis, forces are defined per radian. Your force of 500 N is applied to a 1 radian segment of the total structure. The total applied load to the full 360 degree structure is 500 * 2*pi.

Note that your pressure results are also 2*pi larger than expected:

10/1.6 = 6.25, which is approximately 2*pi.

If you want to apply a 500 N total load to the full structure, a force of 79.58 N should be applied to the axisymmetric model.

Jim Bernard
Advanced Applications Engineer

Siemens PLM Software
2000 Eastman Dr., Milford, OH 45150-2712

Re: Confused ?? Axial Force - Contact Pressure - Axisymmetric Solution SOL 601

Hi Jim,

Thanks for the input. Eventually I figured out just that. Why I got confused is that I thought the conversion was included in program.

So Now I have things working.

Thanks again!