Stress tensors in Cylindrical coordinate system

[aleer766]

I am a fairly new user to Autodesk.

I'm trying to simulate a straight pipe that is subjected to internal pressure and gravity. No fluid inside the pipe(this is how stream could be modeled). Boundrary condition are modeled such that the edges can expand in radial direction and are free in roational, to avoid large moment from the internal pressure, but not translational along gravity such that the moments won't be exluded.

Boundary conditions:

RS: Ty and Tz locked in cylindrical coord, the rest free

LS:  Ty and Tz locked in cylindrical coord, the rest free

However when I look at the Von Mises representation and on the cylindrical tensors it doesn't add up. By my hand calculation I should have much higher Axial load from internal pressure than it is shown in Autodesk Simulation Mechanical 2014. Why?

When I compare Hoops and VMstress they are almost the same.

My best guess that something is off with my boundary conditions. To make a FE-model represent analytical values can be hard since the expressions for hoop and axial stress doesn't include any boundary conditions. 

Or is the something I am completely missing here?

sig_hoop=pd/2t

sig_axial=pd/4t

Take note: All stresses are represented in Membrane Stress in plate display options. 

By hand calculation:                        From Autodesk(max value):

Hoop= 16.89 MPa                            16.76 MPa

Axial=  8.44 MPa                              5.5 MPa

VM=     14,64 MPa                            15.09 MPa

Thank you

Material Data:

Density d=7850 kg/m^3

poisson's ratio v=0.3

Young's modulus E=212 GPa

Input Data:

Internal pressure p=1 MPa

Gravity

Diameter d= 212.8mm

thickness t=6.3mm

Dimensions correspond to DN-200

Model made in PV/Designer thus the elements and mesh that are used is the predefined defaults.

[AstroJohnPE · Accepted solution]

Hi,

My suggestion is to setup three load cases:

1. pressure and gravity
2. pressure only
3. gravity only

This is done from the "Multipliers" tab under the "Setup > Model Setup > Parameters" command on the ribbon.

Hopefully you can see what the issue is by looking at the results individually (load cases 2 and 3) and then understand the combined loading (load case 1).