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Modeling surface constraints


I am trying to model a constraint that similar to a surface constraint but not exactly the same. It is shown in the attached figure. I would like the constraint to function like this:

1. When it pushed in along the +Z direction, the constraint should works like a surface constraint.

2. When it moved along the -Z direction, the model should be constrained by the the four bolts.


I am not sure how to model a constraint like this. Any suggestion would be greatly appreciated.


Re: Modeling surface constraints

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom


Basically what you need is to define contact between your model and a fixed base: when working in traction only bolts will support load, when working in compression only base will support load. You need to add a support body (a simply fixed plate meshed with Shell elements) and define contact surface-to-surface, and define spiders in the holes using RBE2 elements to simulate the bolt effect, constraining the master (Independent) node of the RBE2 element doing TX=TY=TZ=0 to simulate the pin joint.

Using contacts you unload bolts when supporting compression loads, but alternatively you can directly avoid definition of any surface-to-surface contact: this way bolts (well, the spider RBE2 simulating the bolt effect) will support all loadings (tension & compression) and you will have to dimension bolts properly based in the computed reaction forces (shear & tension/compression).

Best regards,

Blas Molero Hidalgo, Ingeniero Industrial, Director
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