Bolt Preload with Femap and NX Nastran

Bolt preload adds quite a bit of complexity to any model since the analysis procedure is nonlinear (geometrically nonlinear) and that two sequential nonlinear runs are required to arrive at the final “bolt preload solution”. The utility of this approach lies in its ability to quantitatively calculate the bolt axial and shear forces for any type of bolted connection. Additionally, if bolt fatigue is important, then a bolt preload approach is invaluable.

What is bolt preload?
Bolt preload is used to clamp together two plates or two structures and create a frictional lock between the members and reduce the effects of cycling loading on the bolt. With respect to the laWer (i.e., bolt fatigue), bolt preload can make all the difference between a safe, long-­‐lasting structure or catastrophic failure.

Where to use bolt preload?
Bolt preload is not a free lunch. To effectively use bolt preload on FEA connections requires many additional steps and it converts a linear run into a nonlinear run that requires two sequential nonlinear analysis where (i) the bolt preload is applied and then (ii) the external structure load is applied.

What is covered in this white paper?
This white paper will cover a the basics of setting up you model for bolt preload, theoretical foundation, examples of its use and a bolt fatigue primer.

Engineering Comment:
Bolt preload adds quite a bit of complexity to any model since the analysis procedure is nonlinear (geometrically nonlinear) and that two sequential nonlinear runs are required to arrive at the final “bolt preload solution”. The utility of this approach lies in its ability to quantitatively calculate the bolt axial and shear forces for any type of bolted connection. Additionally, if bolt fatigue is important, then a bolt preload approach is invaluable.