Bolt Connector Functionality within Static Stress Simulation

[david.pritchard]

Hi all, 

I am having a problem within the simulation workspace currently and it is all to do with how the bolt connectors work and their impact on the simulation results.

For example, I can set up a model with a solid acting as my support structure (i.e. a wall) with brackets being fixed to the wall using bolt connectors. I then place two of these brackets at 1m centres for instance and then join a panel with bolt connectors to the two brackets.

I then run the simulation with a pressure acting on the panel to then produce some results. I am looking for the resultant deflection in the panel, but at the same time I want to see how the bolt connectors impact the brackets being fixed to the wall. It seems that whatever value I put in for the preload on the brackets has no bearing on the simulation results, as if the bolt connector element of it is being ignored and it just sees it as a 'Bonded' contact for instance.

I could really do with some assistance on this, as one of the main things I want to experiment with is the bolt connector preload value and see how it fares within the model. This is so I can select an appropriate fixing from a list of options. (Ideally I want to see the bracket bolted connection fail when the preload is too low for example)

Any help would be appreciated, as this feels like a major flaw within the simulation workspace, however someone with more knowledge of the software may be able to point at where it is I am going wrong.

The model I am referring to can be downloaded using this link.

https://a360.co/417WkQA

Many thanks in advance, 

David

[John_Holtz]

Hi David,

The contact force results shows what I would expect. With a higher preload, the contact force has a larger value (614 N max) and surrounds all three bolts. With a lower preload, the contact force is smaller (25 N max) and only appears at two bolts. If the bracket were bonded, I would expect to see a more uniform contact force over the entire area.

Figure 1: Preload = 2000 N

Figure 2: Preload = 2 N

So now some questions:

1. Physically, how does the bolt preload affect the behavior of the bracket? 
2. In the simulation, what needs to be done to duplicate that behavior?

Bear in mind that the bolt head is "bonded" to the bracket, and the bolt threads are "bonded" to the hole. The bolts in the simulation will support the bracket even if there is a gap between the bracket and the wall. (The same is true in real life except the bracket can slide on the real bolt if there is a gap between the bracket and wall. Also, a loose bolt has a tendency to unscrew out of the hole.)

Normally, the purpose of a bolt preload is to put the bolted components in compression and keep them in compression. When an external load P is applied, the bolt load increases by x*P and the compression of the components decreases by (1-x)*P, where x is typically 10% to 20%. A minority of the load is taken by the bolt, and therefore the bolts (ideally 🙂 remain below the allowable stress.

John