Fastner connections in WF 2.0

[johnsmith2]

Hi,

I am the user of both abaqus and Pro/Mechanica. As fastner connections was introduced in the version 2.0 in pro/M. I found compared with abaqus, it is rather simple to make connection between two parts by screws or bolts, what you need to define is edges of the holes, materials, diameter of the bolts, or/and spring stiffness properties, etc. Most important, I don't need to model the real physical bolt parts in Pro/mechanica, I don't need to define the contact pairs between bolts and the parts.

However, I am not sure about the results in Pro/M, especially the contact pressure between bolts and parts. Of course, in Pro/M, bolts take all shear, so, no friction between parts exist.

In abaqus, you need to define surface-to-surface or node-to-surface contact, you need to model the bolts in beam elements, define the master and slave surface.

If my purpose is to ensure that the bolts are strong enough to hold or support under pressure/force between two parts, do you think Pro/M can fulfil my requirements. Thanks for ideas and opinions.

 

[brep]

Since you cross posted this in another forum, here's the same reference I posted as reply:

http://www.patentstorm.us/patents/5920491-fulltext.html

Furthermore, you are not quite correct when you describe what is "required" to model bolts in ABAQUS.

In fact, the complete answer is way too long for this forum. It is suffice to say that analysts model bolts, rivets, welds (fasteners, connectors... the names are somewhat interchangeable) in a variety of ways for a variety of purposes. What are you trying to learn? The load transfer between components? The stress distribution around the connection? The stress in the connector itself? What happens to the structure should a connector fail? Statics? Dynamics?

Depending on your analysis goal, the "correct" way to model the bolt/rivet will vary wildly. In some cases, using a tie constraint between nodes is sufficient. Otherwise you might use a rigid beam, or maybe a deformable beam. You'll have to decide how to attach the rigid/deformable beam to the rest of teh structure. Old-schoolers might use more rigid beams in a wagon-wheel (spider web) configuration. Perhaps you might like to include plasticity in the beam(s)? And also damage? Further, you might want to use a bushing type connection with stiffness,damping, damage and failure that is multi-axial?

Ok, so that's point to point methods. Now you could consider using shell element abstractions, or even solid elements. For these you might like to include contact (back to your original point - you see, contact is not always required unless...).

For bolts modeled as solids, what are you going to do with the threads? Are you going to discretize them? Or ignore them? What is your rationale for doing one or the other? If you ignore them how will you connect the bolt to the nut? If you use a tie constraint between them, what effect does this have on the spreading of the threads that is a real-life phenomenon when you torque up the bolt? Tie constraints completely miss this effect, by the way.

So the real questions (i.e. mechanics related) need to be answered before you can decide which FE tool will do the job. Mechanica may well be the right tool, but if decide friction in contact, plasticity, damage, failure etc... are going to influence your analysis, then you might have to look further...

 

[johnsmith2]

Thanks for your information and explanation. You are very true to point out what I should try to do in the problem.

1) Load transfer between components?
2) stress distribution around the fasteners?
2) stress in fasteners itself?

After reading the manual, in Pro/M, I think what they can do is (1,2), not (3). Because we don't need to model bolts as solid or shell elements. So. we have no idea to see whether they are strong enough to hold external forces. Also, bolts take all the shear, without friction between parts involved. Moreover, linear analysis cannot catch the behavior where the preload is overcome and the joints start to open up.

It seems that most people rely on the theoretical calculation to predict the bolts stress. For example, based on the tensile area of bolts, the bolt stress can be calculated based on the force or torque applied to bolts.

thanks again to make me think!