Torsion and Inflation Analysis of a Hollow Tube ?

[osman]

Dear Feap Users,

I have been dealing with a input file problem regarding torsion&inflation test of a cylindrical tube modeled with modified neo-Hookean material (MNEO) on  FEAP 8.3.

The torsion is implemented by the use of SPIN command in Feap which starts at time t=0 and goes until t=0.2. The rotation angle/time in degrees reads 30.

The inflation is merely the application of internal pressure on the inner surface elements by means of follower load. It starts right after torsion, i.e. t=0.2 and proceeds until t=1 with a magnitude of 180 [mm Hg].

My problem is to reset the boundaries for the inflation after  the application of  the torsion where edge boundaries and displacements (EBOUN & EDISP) are

   EBOUNdary
  3  -12.5   1 1 1
  3   12.5   1 1 0

  EDISPlacement
  3  12.5   1.0  1.0  0.0

for torsion. However, it  should become

  EBOUNdary
  3  -12.5   0 0 1
  3   12.5   0 0 1

for inflation.

Whenever I simulate, I end up with honey pot-like shape due to the fact that  the boundaries at the bottom (z=-12.5) and the top (z=12.5) resume to be restrained in x- and y-direction  ( which should be only the case for torsion) during inflation analysis.

Can someone help me solve this issue? I am basically up against the wall  for the time being.

I attach the mesh and the input file necessary to simulate the problem.

I appreciate your help.

Sincerely,
Osman Gültekin

[FEAP_Admin]

I think you need to more clearly define your boundary conditions.  For example the way you have presented what you want to do seems to leave you with a singular system (roller plates top and bottom leave the system with 3 rigid body modes).

Please provide a description of what you want for boundary codes and boundary loads/displacements for the time intervals [0,.2] and [.2,1].  For example it is completely unclear what you want to happen with the imposed torsion during the time interval [.2,1].

[osman]

Hi again,

Regarding boundary conditions for inflation test, linear stiffnesses in x- and y-direction are attached to the entire outer surface. With the range of pressure applied I did not have any problems.

If we focus on my real problem, maybe I can simplify the issue by a generalization.

1) The hollow tube is going to be under torsion for a certain time; the state of deformation will be from reference state to deformed state, say def1.

2) I would like to use  the mesh associated with the deformed state, i.e.  def1 as an input for  the inflation . Then, the state of deformation will read say def2.

In summary, it needs to be a superposition of the two loads.

Now, how can I store and reuse the mesh data after the torsion ? Is there a command to achieve it?   

The input file attached above unfortunately can not carry out it.

I hope that it is now a little bit more clear

Thanks,
Osman

[Prof. S. Govindjee]

For the torsion, do you want to hold the rotation angle or the applied torque during the inflation step?

Solution states can be saved for later use using the SAVE command.

[Prof. R.L. Taylor]

try: OUTM DEFOrmed  to get the deformed mesh after your first step.  But I assume when you input the mesh from this it will be stress free, which is not physically correct.

[osman]

Dear Prof. Govindjee and Taylor,

For the question whether i want to hold the angle I say yes, the applied torque ( implemented by SPIN command) should be retained; therefore the stresses need to be preserved as well.

Tomorrow (almost midnight in Austria now:) ), I will give it a try and implement your suggestions.

The version I have been  using is Feap 8.3.

Thanks for your help.

Best regards,
Osman

[Prof. R.L. Taylor]

Ver 8.3 does not support OUTP DEFOrm; it may be able to do one LOAD GROUP;

The most expedient solution is to upgrade your version, for this contact the usual feap order process at the web site.