Bolt Pre tension and joint simulation using ABAQUS/std

[Theanalyst]

Hello, I have modeled a simple bolted joint with 3 parts: two rectangular plates with 2mm holes in the center stacked on top of each other and a bolt with shank of 2mm and a round 4mm head. The top plate has a slightly bigger hole than the bolt shank's diameter hence there is no thread engagement up top here. All half symmetric parts.

I have also defined contact where ever there is one, between the head and the top plate, between the plates and between the bottom part of the shank and the hole in the bottom plate. I also applied a coupling constraint using a point on the bolt shank away from restraints and the pretension section (is that right way of chosing?) and the hole surface on the bottom plate so that the threaded areas in engagement move together.

When I apply a positive pretension bolt load to the pretension section surface of the shank, the part of the bolt shank below the pretension section appears to be moving up and the top of the bolt above it is moving down. Although the rest of the results on other parts make sense because the inner top region of the hole in the top plate is being pulled down near that edge by the bolt head thats moving down, and the bottom plate's hole surface is being pulled up axially because of the coupling constraint I had applied. So all of this makes sense but what I don't understand is the way the two shank parts are moving in opposite directions? Is that simply how the pretension in a bolt is simulated in ABAQUS?

Another issue is the stress concentration on a point on the shank that I used to define the coupling constraint. Also, get a ton of overconstraint check messages but it does go through a lot of them and then finish the step OK. I also checked and unchecked any coupling directions on the nodes on the bottom plate hole surface that are restrained in those directions. I still get those overconstraint messages.

Any comments..suggestions would help. Thanks a lot, Sunny.

 

[Theanalyst]

...since I have posted this message no one has responded, quite dissappointing. Took me a while, but I found out a number of things on my own, the summary of which is below.

1) You do not define contact between the bolt shank and the panel holes.
2) A typical joint has the bolt pulling the bottom part up and pushing the top part down as you load it and thus forces the joint together. The top panel's hole is typically larger for the bolt to simply slide in.
3) Go through the bolt load section in the analysis user's manual or the online manual, it will tell you how to apply a bolt lod on a bolt.
4) Most important is that you have to use something called "tie" constraints on the surfaces of engagement on the bolt shank and the hole of the bottom panel.
5) This will allow the bototm part to get pulled up as the bolt pretension is gradually applied on the bolt pre tension section.
6) Also remember that the nodes lying on the pretension section should not be used in the tie constraint at the the same time, it will spit error messages at you.

Hope this helps.