stone05
Structural
- Sep 15, 2005
- 2
Hi all,
I have a muffler assembly with heatshield on it. The heatshield is tied up on the muffler top through straps. I intend to apply pretension on the strap to tie up the heatshield in the first step. The strap has a thickness of 0.5 mm. Because of the thickness of the strap, I can not mesh it with brick elements. Instead, I replaced part of the straps with beam elements in order to apply pre-tension.
The muffler body was constrained on both ends but not in the strap or heatshield. I defined contact pairs in muffler-heatshield, strap-heatshield, and strap-muffler. I've made sure there is no initial penetration in the contact. Well it showed overclosure and DOF singularity errors when applied pre-tension. Initially, I thought it was due to the unconstrained heatshield and strap, so I added some weak springs on the contact pairs. But the overclosure still kept coming up when pre-tension applied. I am pretty sure the normal direction and contact pairs setup were correct.
In order to understand the contact problem, I made some simple tests on Abaqus. I created two thick flate plate (meshed w/brick elements)coated w/think shells. These two plates were both constrained on one end (like cantilever)and contact each other (no clearance) initially. I then applied load on one end, well it converged w/o problem. But,if I seperated both plates a tiny bit, it will show overcloseure error even they are still technically penetrated (because of the coating). If I replaced both plates with shell elements, it will overclose either way. Why is that?
I have tried couple contact control cards and changed the time step on the model, but none of them worked out.
I got a suggestion from friend to use thermal contraction or "shrink fit". Does anybody use them before? How to use?
If I use thermal contraction, will the overclosure still linger?
Thanks
I have a muffler assembly with heatshield on it. The heatshield is tied up on the muffler top through straps. I intend to apply pretension on the strap to tie up the heatshield in the first step. The strap has a thickness of 0.5 mm. Because of the thickness of the strap, I can not mesh it with brick elements. Instead, I replaced part of the straps with beam elements in order to apply pre-tension.
The muffler body was constrained on both ends but not in the strap or heatshield. I defined contact pairs in muffler-heatshield, strap-heatshield, and strap-muffler. I've made sure there is no initial penetration in the contact. Well it showed overclosure and DOF singularity errors when applied pre-tension. Initially, I thought it was due to the unconstrained heatshield and strap, so I added some weak springs on the contact pairs. But the overclosure still kept coming up when pre-tension applied. I am pretty sure the normal direction and contact pairs setup were correct.
In order to understand the contact problem, I made some simple tests on Abaqus. I created two thick flate plate (meshed w/brick elements)coated w/think shells. These two plates were both constrained on one end (like cantilever)and contact each other (no clearance) initially. I then applied load on one end, well it converged w/o problem. But,if I seperated both plates a tiny bit, it will show overcloseure error even they are still technically penetrated (because of the coating). If I replaced both plates with shell elements, it will overclose either way. Why is that?
I have tried couple contact control cards and changed the time step on the model, but none of them worked out.
I got a suggestion from friend to use thermal contraction or "shrink fit". Does anybody use them before? How to use?
If I use thermal contraction, will the overclosure still linger?
Thanks