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Single direction DOF


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I want to constrain a part like it is bolted to a flat surface. I want to optimize the tension in the bolt to eliminate ANY separation between the part and the flat surface.

I would like to add a roller type constraint that would allow (+) y-axis displacement, (+/-) x-axis displacement, but NOT (-) y-axis displacement.

Can anyone give me some advise? Or possibly a better method of attacking the problem?


Roger Raetzman

Bombardier Recreational Products

did you try to make a plane in assembly mode, in purpose to contrain your part by this plane
It sounds like you need to do a contact analysis. This is available in Mechanica Structure, you need to set up contact regions between the mating surfaces. Run times are likely to be longer than a standard linear analysis, as it is an iterative process. If you are interested in bolt preload, you will need to run a prestress analysis. The 'trick' is usually to apply a thermal load to get the bolt to have the right preload, but set the CTE of the other parts to zero so they are not affected.

Alternatively if all you want to know is what size the bolt should be and it is a simple enough part, and it can be assumed to be 'rigid', you could could just do a hand calc on the bolts.

If the problem is likely to be deflection of the flange between bolts, even it they are fully clamped, you could do a 'quick and dirty' linear analysis on one part, holding it at the bolt positions and just look at the deflection between the bolts.

It all depends how deeply you want to get into this and how much time you want to spend on it.

Bolted joints, whilst simple in real life are one of the most complicated things to analyse, to the extent that we run a special course on analyzing assemblies, which takes a day, so it is hard to compress all that into a 5 minute email answer, but I hope this helps.


It is a course that we have written ourselves as we know that bolted (and welded) assemblies can cause a lot of heartache. It runs at our centre at East Midlands airport in England and the next one is scheduled for 21st Nov. Have a look at, or email me [email protected] and I will send you details.



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