FEA for LMDPE (Linear medium desnsity polyehthylene)

[Sanjay]

Hello all,

I am conducting FEA analysis for tank (LMDPE material) with the help of ansys software. Dimension of my tank is app. 5ft X 4ft. I am applying pressure gredient (0 to 6 psi linearly from top of tank to bottom) form the inside of the tank it shows me 10 inch displacement. However, we alredy installed this tank on our machine but we didn't have displacement more than 2". I don't know what is wrong on my analysis and why i am getting to much displacement.

I am trying NLGEOM option ON any OFF (for small tank or less pressure gradient value) and it will give huge difference in displacement. I know for big tank i should NLGEOM option ON so it will give me lesser value of displacement but when i am putting this option ON, ansys will not converge this and stop in between the analysis.

Some experts gave me advice that you need exact stree-strain curve values and enter in to ansys then it will converge.

Can anyone give me some advice to me. My approach seems right on not.

One more thing do need put young's modulus value in ansys or Flexural modulus because i hard that if you get lot of bending then use flexural modulus value.

Please help me. I am new to that analysis. My boundary condition is right.

Thanks
Sanjay

[Jorgen]

I recommend that you set NLGEOM to ON, and that you use real experimental data for your material to calibrate an appropriate material model. Depending on how accurate you need your simulation results, a simple plasticity model might be sufficient. You should not experience convergence problems.

- Jorgen

[Sanjay]

Hello,

Thanks for reply. I tried to put all stress-strain curve value but Ansys is not converging. It is converging for lesser pressure gredient (0-2 psi) value but not for if bigger pressure gredient (0-6 psi).

[Jorgen]

Does the mesh start to deform very fast when you get the convergence problems? There are certain geometries and loading conditions in which you get a true instability in the response and the pressure cannot be larger than a specific value.

- Jorgen