Learning Forum

[Soliman]

Good afternoon everyone,

 

I am trying to perform a very simple task on Ansys 19.2. I am trying to simulate the bond between concrete and embedded steel bar inside concrete cube by predicting the force-slip relationship. However, when I set the contact area between concrete and steel to "Bonded" the model works very fine but it gives me very exaggerating results  in terms of no slippage and very high stresses, while when I set the contact area to frictional with friction coefficient of either higher (0.6) or low (0.2), the model gives me multiple errors. I did everything as per this discussion "https://forum.ansys.com/forums/topic/bar-pull-out-analysis-in-ansys/"  but I could not find the problem. I started learning ansys three weeks ago so may be this is the problem lol.

Attached is my model.

 

Thanks in advance.

[Soliman]

Here is a picture of my model.

[SaiD]

Hi,

Using if you use Bonded contact then the two surfaces in contact will not have any relative motion between them irrespective of the force applied i.e. even if you apply a very high force, there will be no slippage.

So a frictional contact is best suited for your analysis. What errors do you get? Have you checked the Initial Contact status? In the contact pair, which surface is the Contact side and which one is the Target side?

Sai

[Soliman]

Hi,

Contact body is the steel bar and concrete block is the target body.

 

And how to check the initial contact status?

 

I get these errors :

 

1- An internal solution magnitude limit was exceeded. Please check your Environment for inappropriate load values or insufficient supports.  Please see the Troubleshooting section of the Help System for more information.

2-The unconverged solution (identified as Substep 999999) is output for analysis debug purposes. Results at this time should not be used for any other purpose.

3- (it is highlighted in orange) One or more contact pairs are detected with a friction value greater than 0.2. If convergence problems arise, switching to an unsymmetric Newton Raphson option may aid in convergence. 

4-Contact status has experienced an abrupt change.  Check results carefully for possible contact separation.

 

Thanks for your help

[SaiD]

The Contact and Target side assignment seems correct. 

To get Initial Statu, right-click on Connections -->Insert-->Contact Tool. Then right-click on the Contact Tool and choose Generate Initial Contact Results. You can check if initial contact is Closed.

Based on messages 1 and 4, it appears that the bar gets pulled out during the simulation (resulting in an abrupt change of contact status from closed to open). I am guessing you apply a force to the bar and not a displacement. Once the bar is pulled out, since there is nothing constraining the bar, it undergoes rigid body motion which results in the error message 1. Static Analysis is not meant for cases which undergo rigid body motion. 

To fix this, you should change the simulation from force-controlled to displacement-controlled. Also ensure that there is no rigid body motion happening throughout the simulation.

Hope this fixes it,

Sai

 

[Wenlong]

Hi, 

Apart from the suggestion Sai provided, you can also refer to this thread to get an idea about interference fit and dynamic/static friction coefficient https://forum.ansys.com/forums/topic/friction-contact/

Regards,

Wenlong

 

[Soliman]

Thank you all for my help.

 

When I apply displacement, the bar slides inside the concrete. I think I am missing something. I will go dig in this area.

 

I appreciate you time.

 

Regards,

Ahmed

[Soliman]

That is What I got from the Contact Tool.

[SaiD]

Hi,

The Initial Contact information looks good. Your contact is Closed as it should be since it's a Bonded Contact. The Geometric Gap is of the order 1e-15 and hence very small, which is also great!

I am not sure why the bar slides into the hole. Did you check the direction of the displacement applied? You can apply Displacement By Component and defined displacement in the correct direction.

Sai

 

[Soliman]

Hi,

The displacement direction is correct.

I really appreciate your help. I tired to do this model using APDL platform and it kinda gave me better results.

Ahmed

[to2020]

Hi Soliman, nDid you model the ribs of the bar too? If so, did you have to like do contacts for each rib face? nWhen you changed from Force to displacement-controlled, how did you do that? nThis is my problem:nI want to model the pull out of a reinforcement bar from a concrete (cylindrical specimen). I have designed the ribbed pattern on the bar in Solidworks and need to do the simulation in Ansys. Anyone know how I can do this? I would like to apply a constant force on the bar:nDuring a period of 2 minutes, steadily increase the axial force in the bar until the tensile stress in the bar reaches the yield stress (560MPa).nThen I need to measure the Free-end slip of the barnStress in the cylindernI am quite new to Ansys as well, any help would be greatly appreciated! nThanks! n