Preload of Bolts and Nuts

[sprashanth]

I'm trying to do an FEA which involves an assembly of two steel plates which are bolted-onto each other. The preload due to tightening of the nut & bolt is applied in the form of tensile force or pressure on the contact areas (acting in opposite directions to each other) between the bolt & plate and the nut & plate.

I'm wondering if the above inputs are enough for my FEA, or do I have to also include the forces that each plate applies onto the other due to the tightening preload?

I have attached a drawing which illustrates my question. Basically Option-1 is where I include only the preload force between bolt & plate and nut & plate (the arrow marks indicate the forces applied on the faces of the components). Option-2 is where I also include the forces that one plate applies onto the other due to the tightening.

So which option should I go with for my FEA - Option-1 or Option-2?

 

[sprashanth]

Oh, and the above attachment opens only if you have Office 2007 installed. For those with Office 2003 and older, I am attaching the drawing/document in a compatible format for your reference.

 

[corus]

I'd do option 1 where you apply the pressure from the bolt to the surfaces. If you adopt option 2 then you're assuming something about the contact pressure distribution, which you don't know. Of course with option 1 you assume you know what the pressure distribution is from the contact there, but that'll be a reasonable assumption to assume a uniform load.

corus