on the first part, are you looking for somethign INSIDE the software to do the FOS calc for you like there is in linear? i'm not clear on why you can't extract the data and do what you're describing manually, but maybe you want to do this automatically somehow?
regarding the second part about a dynamic analysis with bolts, someone asked that recently. it is a limitation. your best bet is to model the bolts and pull the info manually.
I disagree with the statement that the bolt load will remain 2kN until the external load exceeds the preload. What happens at that point is that the joint separates.
Unless I'm mistaken (this is off the top of my head), the bolt load is Pi + Pe*kb/(km+kj)
Pi = preload
Pe = external load
kb = bolt spring constant
kj = joint spring constant
You can get the external loads from simulation
Sorry, missed that this was a dynamic study.
Thanks guys for your replies.
@ Jared. I need to take the loads into a spreadsheet and apply my Factors of Safety and Fitting Factor (as per NASA-STD-5020) to calculate my Margins of Safety against Joint Seperation...so I need compare the forces on bolts from the load case and calculate the difference between that and my preload to show my margins. My model only provides the resultant absolute force on the bolts (preload).
Let say for example I am preloading the bolts as per the bolt material proof stress but I am only applying a 1-G load...then there will be a large positive margin of safety against joint seperation...I need to calculate this...
Thanks in advance,
Why not run the analysis with pins (and contact) instead of bolts and get the loads sans the preload and use that as the loads required to be resisited by the preload to compute the margins on joint separation.
I have modelled the bolts in place and bonded them accordingly. The non-linear model is solving and I am extracting the Von Mises. I have calculated the load on the bolts from this (say 400 N)
I am running the non-linear model with preloaded bolt connectors at 350 N to verify if the joint seperates (looking for forces in excess of this or close to 400 N).
Does this sound like a viable route to go with this study?
What I would do is:
- remove the bolt gemnoetry (as you would have with the bolt connectors).
- Add pins to all the holes and lock them for rotation though this could go eitehr way and probaly doesn't make a difference if it is a multi fastener joint.
- Run the NL analyis - extract the pin loads.
- compare the bolt loads you computed earlier to the pin loads the pin loads should be lower than the preloads.
The above isn't bullet proof in logic for what you want but should be a reasonable approximation in my view but frankly I haven't thought about all that hard. Your call.
Can't you run with preload of 0 to get what you want?
Or I Thibk you said originally run with preload only, then run with your load, the delta is the difference that you are looking for. The software does not know the difference so it doesn't report them differently.
But this is all moot if you need to do a dynamic analysis.