Simulating nut & bolt preload in FEA
Simulating nut & bolt preload in FEA
(OP)
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 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 also have to include the forces that one 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?
I'm wondering if the above inputs are enough for my FEA, or do I also have to include the forces that one 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?





RE: Simulating nut & bolt preload in FEA
Aamir
RE: Simulating nut & bolt preload in FEA
RE: Simulating nut & bolt preload in FEA
RE: Simulating nut & bolt preload in FEA
RE: Simulating nut & bolt preload in FEA
replaced with the weasle words "... student posting are not allowed ..."
RE: Simulating nut & bolt preload in FEA
The best way to solve this problem is to apply negative thermal forces on the bolt. The bolt will then shrink, and compress the plates together. The full solution is available only if you define contact planes/elements between the plates. In that way you should get the surface pressures between the different planes.
An interesting test case for your FEA training.
RE: Simulating nut & bolt preload in FEA
I would like to also clarify a few things for those who have mistaken my question as "student posting" - I am not a college student who's trying to cheat in his homework or exams, I'm an Engineer working at a Manufacturing firm for the past 4 years. The major problem is that our company is relatively new to the field of FEA & unfortunately, where we live there is very limited training resources available (more specifically, when it concerns FEA). The training we have recieved in FEA is very poor & there is virtually nobody to approach when we need help for complicated FEA problems. Other than the internet & specifically informative forums such as these, how else can I seek FEA knowledge for self-improvement?
RE: Simulating nut & bolt preload in FEA
At our company, we have so far been following option-1, but we are not satisfied with the results - therefore, we are looking at alternate options of simulating the fastener preload that will give us satisfactory results. We're looking at option-2 as one alternative, since it accounts for compressive forces that each plate applies onto the other due to tightening of the fasteners.
RE: Simulating nut & bolt preload in FEA
the key point about preload is to control gapping of the joint under tension loads (and also to control the fatigue life of the bolt under tansion loads). i'd use the FEM to evaluate the tension loads in the bolt form the external loads, then i'd design the preload to account for these tension loads.
you Could apply thermal loads, but you Must understand the variability of preload; depending on how you control the preload (PLI washers, torque wrench, nut rotation, etc, size of the guy with the wrench in his hand, his eye-sight, and so on) you have a different variability in preload (up to 50%). you would be beguiled if you model one value of preload and think you've got a really accurate solution (because you're using FEA).
RE: Simulating nut & bolt preload in FEA
I think that Solid works could do a kind of iterative linear analysis. I'm not experienced in Solid Works but I think should be something similar to a linear gap analysis in Nastran with PARAM CDITER.
The solver iterate until all the gaps are in a know status. Giving a very high stiffness if they are closed and no stiffness if they are open.
Then the model is resolved as a normal linear model.
For some contact analysis you don't need a true non linear with large displacement or material non linearity.
In the link below you can find a very interesting pdf about bolt connection:
http://w
hope this help.
Onda
RE: Simulating nut & bolt preload in FEA
RE: Simulating nut & bolt preload in FEA
I you have the experience in performing bolt connection calculations, this should be straight forward. Don't bother with FEA if you can use bolts with sufficient preload (Bolts with large diam or hight strength capbilities)
RE: Simulating nut & bolt preload in FEA
One thing to consider if the parts are being pulled apart is load spikes. We reverse engineered a part on a logging machine that kept breaking bolts and warped the plate. The first run we fixed the bolts and applied a load where the boom attached and the design was adequate. The second run we fixed the part at the boom attachment and applied a load on one washer equal to the breaking strength of the bolt. The results were the plate was too thin.
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: Simulating nut & bolt preload in FEA
i guess your joint was loosening, and vibration loads turned into impact loads.
RE: Simulating nut & bolt preload in FEA
corus