Bolt preload followed by pressure load 1

[rob768]

Hi there,

I'm stuck in a Femap model. I modelled a section of a connection of two flanges, connected to each other by a pre-loaded bolt. Symmetry is applied to simulate a full model. In the pre-loaded model, i want to apply an internal pressure load. I tried to do this with a restart command, but i can't get it to work.
Is there an option to calculate the two steps (preload followed by a pressure load) in one sequence?

 

[rb1957]

How are you applying preload ? I assume you're torquing the bolt, and are using standard analysis to infer the preload applied ? In the olde days it was difficult to get the bolt tension load to be reacted by joint compression, a common work around was to use thermal loads. But maybe these days there are better tools ?

How did you determine the pressure load ? Are you applying pressure to a surface and letting FeMap figure out the bolt load, or have you determined a pressure load by calc ?


If so why FE ?

In any case, you could work in the time domain ... apply the preload, let things stabilise, then apply the pressure load.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[rob768]

Bolt preload is a simple command in Femap, and the pressure load is a given design pressure. Working in the time domain isn't possible, because the combination non-linear and contact surfaces is not supported.

I'm trying to figure out how the restart function might help me, but I can't get that to work.

And why FE? On specific customers request.

 

[TG_eng]

What solution sequence are you using? Why are you using a restart?

 

[rob768]

I thought i needed a restart, because i wanted to add pressure AFTER applying preload. I now understand that, in a combined load case using bolt preload, The effect of preloading is calculated first, after which any other load is applied.
So, i can simply use a single loadcase.
Happy days.

 

[rb1957]

Humm, I don't understand the "single loadcase" particularly with your non-linear components. You can't apply a %age of preload and pressure load, solve that, then move on. You need AIUI to complete the preload then apply the external load. But then maybe FeMap solves the preload "widget" then applies your other loads ... I'd want to have FeMap confirm this (as it sounds "odd").

Are we talking about an isolated bolt, or one of many ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[rob768]

The calculation is lineair. But i wanted it done in the right order. Preload first, with related lengthening of the bolt and compression of the structure, then pressure load.
Apparantely NAstran does that automatically.