Fasteners on symmetry plane

[gfraulini]

Hi all,
if I want to analyze an assembly with the symmetry constrain I need to "cut" the entire assembly before to enter in Mechanica.
But if the cut is passing trough a hole where I want to put a screw with the fastener proE feature, I can't; because that feature needs an entire circle and not only one half.
In this case what I do?
In each case, the preload force of a screw, cutted at half from the symmetry, should be the half?

Regards

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[346gnu · Accepted solution]

Hi,

You cannot 'cut' a fastener idealisation in half.

If you have a symmetry plane that passes through the fastener then you have to mode the fastener as a solid.

Regards

[gfraulini]

How can I set a preload force modeling the screw as a solid?

I suppose I need to set a free contact region between screw and hole.

Can you explain better this concept, please?

I have this assembly, already simplified for the FEM analysis.

It is an equipment testing.

I need to see the displacement (especially the vertical one) ander the mass load of the components.

Some components are suppressed and replaced directly with their forces.

The symmetry plane is named TAGLIO; there is the symmetry of geometry and loads.

[sdensberger]

I believe you said in your other thread that you're using WF5 (I'm not too sure if this feature was added in), but there is a pre-load for solid elements.

If this feature isn't in WF5, then you could make your fastener out of beams and links (or solid elements) and use a temperature load to cause the fastener to go through thermal contraction. This will be an iterative process to ensure that you've got the correct pre-load (just like with the fastener tool). Make sure that you restrict the thermal load to just the fastener (you don't want the result of the model to contract), or define a material property on the rest of your system that has a zero coefficient of thermal expansion.

[gfraulini]

You're right, in WF5 that function there isn't.

However your idea of to make that with a beam is interesting...I will try to do it and I'll post the results.

[gfraulini]

I've tried with beams that simulated the screws with the thermal load for make them shorter but you can't do an analysis like this because you need to have contact regions as "contact", and ProE tells that you can't use them into an analysis that includes thermal loads.

[sdensberger]

Really? I don't have WF5 installed on my machine, but I know you can do this (thermal and contact) in Creo. Can you either post your model or show how you set your model up?

[gfraulini]

I've retried yesterday and it works but you have to specify, also in thermal mode, a contact region between pieces since you have a contact region in structure mode.

The problem is the good design of the link of the beam (points) with the solid geometry, so you have to make some surface regions and rigid links.

I've done a little simple model for analyze the differences between a model modeled with a fastener and a link made with beam.

There are differences around the link, caused by the rigidity of the link (I've put a rigid link); from here the importance of the design.

[sdensberger]

I've retried yesterday and it works but you have to specify, also in thermal mode, a contact region between pieces since you have a contact region in structure mode.

You shouldn't need to go into the thermal mode to do this; the structural side of Mechanica was a thermal load that you can use.

The problem is the good design of the link of the beam (points) with the solid geometry, so you have to make some surface regions and rigid links.

Correct, although you can also used weighted-links (avoids the singular issues with rigid links).

I've done a little simple model for analyze the differences between a model modeled with a fastener and a link made with beam.

There are differences around the link, caused by the rigidity of the link (I've put a rigid link); from here the importance of the design.

Try a weighted-link; this will prevent the infinite stiffness discontinuity. At the end of the day, regardless of whether you're doing it with beams or with Mechanica's fastener tool (which uses a network of springs), you're creating a linear representation of something that is very non-linear.

[gfraulini]

Nobody else have never tried something like this and can give some suggestions?