Determinig bolt forces

[izax1]

I'm in the process of calculating bolt forces from loads applied to a FEM model. The FE model is basically built from 3D tet elements. In order to save CPU time, I'm wodenring: Will the bolt forces be influenced by using linear tet elements and not higher order tets?
Any with experience in this?

 

[canwesteng]

In structural engineering bolt forces are determined using elastic assumptions generally - see instantaneous centre of rotation method. In this field using 3D tet elements is generally inappropriate, and even 2D plates might be overkill.

 

[izax1]

Thank you, canwesteng

Sorry for not being clearer. The bolts itself are modelled with beam elements. The structure to be bolted are modelled with Tets. So, I am wondering. Would it be OK to use linear Tets for finding the bolt forces. Would using higher order tests make a difference to the bolt forces?

 

[rb1957]

generally TET4s are a bad element to use, and TET10s are recommended.

another day in paradise, or is paradise one day closer ?

 

[izax1]

I am aware of the restriction for a TET4 element when calculating stresses, but I need to reduce DOF's in my model to save computong time. Hence my question: Will TET4 do the job of giving me the "correct" bolt forces?

 

[rb1957]

TET4s over estimate the stiffness they are trying to represent. This will affect your bolt forces. Significantly ? I don't know.

Are the bolts in tension or shear ?

another day in paradise, or is paradise one day closer ?

 

[canwesteng]

What is the structure you are modeling? I would try a more appropriate forum, what you have described is generally not done in structural engineering, even in research papers. Solids modeling in the field of structural engineering is generally limited to large concrete structures, such as dams or block foundations.