How much gap between parts in assembly?

[johnsmith2]

Hello all,

I am working on the assembly with different parts. I know this is the contact nonlinear problem. What is the amount of the gap need to be in order to model the real case? I know the gap will strongly affect the contact pressure between parts. The problem is not press-fit, should I use the tolerance in the design to put into FEA? Thanks for help.

 

[corus]

If you leave a gap then the two surfaces may never contact, so what have you proved then? It's best not to assume tolerances will leave a gap but assume the worst and have the surfaces in contact (if that is the worst case). There's also an option to move the nodes so that they touch and don't overlap. It's best to use that.

corus

 

[johnsmith2]

corus,

Thanks for your quick response. I am quite curious if I make two parts contact with each other, do the auto-meshing mesh the whole parts together, like one parts, instead of two parts. Just like two parts welded together. Of course, I know, I need to define the "slave" and "master" contact surface, tangential behavior, frictionless, sliding formulation options!

The option that you mentioned is "slave node adjustment"?

 

[corus]

No. Abaqus meshes parts separately. If you want a single part and can't be bothered creating it in the part module, then you can tie the nodes together.
The slave node adjustment is the option to move nodes to be touching, initially. Be careful with this though, as if you have a gap then the model will be distorted as the nodes from the slave surface are moved to the master surface. Too big a gap and you can get odd results or even the job failing due to element distortion.

corus

 

[johnsmith2]

Thanks corus, it seems you are the chairman for this particular group. In short, you means no gap between parts is the worst case and common practise for the contact problem in the large assembly.

 

[corus]

"To be or not to be, in contact, that is the question" as Shakespeare once said (later edited).
If you had a beam resting on three supports , ie. one support was redundant, then you cannot guarantee that all three supports are in contact. For a case like that I might consider the worst case of only having two supports for a design case scenario.

corus