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# Is this a plane strain case?

## Is this a plane strain case?

(OP)
Hi!

I cannot fully wrap my head around if I can use plane strain to calculate the stresses in my pressure vessel:

- Suppose a cylinder that will see hydrostatic pressure
- The housing is made in a stainless steel
- But the front lid is made up of a "sandwich" consisting of different thin plates in various materials (supported by a steel backing plate)
- thickness of thin plates range from 1-4mm

My interest is the behaviour and stresses arising in the thin plates at various water depths.

Cross section of pressure vessel:

I was thinking of using plane strain and model the cylinde like this:

Does this case look look like a plan strain case?

(I'm using Autodesk Nastran, and i'm skeptical that 3D tet elements will to the job for the thin plates)

### RE: Is this a plane strain case?

I’d suggest axisymmetry for this case, plane strain assumes that the structure extends far in the thickness direction like a long pipe. For comparison you can use a 3D model with planar symmetry.

### RE: Is this a plane strain case?

3d 4-noded tets are horrible elements, do not use.
3d 10-noded tets are ok for solid modeling; can be ok for thin shells provided several are used thru the thickness.

### RE: Is this a plane strain case?

I'd scrap the partial 3D model and model the full vessel with 2D shells.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

### RE: Is this a plane strain case?

Hello!,
Plane strain elements are two-dimensional elements with membrane only stiffness and in-plane loading. The plane strain element idealization has zero strain in the thickness direction. These elements represent structures that are very thick relative to their lateral dimensions. If you are modelling a cylincrical vessel please consider the simplification option of axisymmetric analysis, ie, body of revolution 2-D plane elements where the stiffness, mass and loads are based on a per radian section basis. You mesh the cross section with 2-D solid plane elements and you are considering 1 radian:

Also is possible to study axisymmetric problems with 1-D Shell line elements in cases where the thickness is very small:

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog de FEMAP & NX Nastran: http://iberisa.wordpress.com/

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