What is the difference between joint and contact connections?

[tlewis3348]

I am modeling a hinge in ANSYS and have not been able to get it to run without crashing. So far, I've been modeling the relationship between the two sides of the hinge and the hinge pin using just contact connections, but when I did a modal analysis, I found that the contact connections were not being obeyed between the hinge pin and the two sides of the hinge. Only after switching to a joint connection would the simulation run without crashing. Can someone tell me what would cause ANSYS to ignore a contact connection? I'm relatively new to using ANSYS (though I've used other FEA systems before), so if there is a default that I need to change to account for things like slop in the hinge, or some such thing, I would not be aware of it.

 

[L_K]

Please post a picture of your model (including the contact definitions).

 

[rickfischer51]

In Ansys, non-bonded contact is a nonlinearity,and I think that in Ansys, modal analysis is valid for a linear model only. I think Ansys turns contact into bonded automatically, but maybe not. Joints are created with constraint equations.

I find joints in Workbench a little tricky to use, but I dont use them very often. But they are much nicer to use than contact for something like a hinge. You probably want some combination of Revolute and Cylindrical joints to model your hinge.



Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[tlewis3348]

My biggest concern is that the joint will not behave the same way as it would if is actual contact. Will the hinge pin and the sleeve through which it passes see the same stress? Also, in the details pane for the revolute joint, there is a "Effective Length" field. Is this the length along the shaft that the sleeve can slide, or the length of the sleeve that is in contact with the shaft?

Finally, I've recently removed several bolts to simplify the model and reduce the amount of contact, but I'd like to have them in the model. As far as the complexity of the geometry goes, my model is small enough that modeling the bolt and nut as a cylindrical shaft with an extruded hexagon on both ends and modeling the washers separately doesn't add too much complexity. My question is, what is the best way to deal with the contact of the bolt with the bolt's clearance hole? I've tried doing this with just contact connections, but that ran into all kinds of problems. I'm not sure whether that was the result of selecting the entire surface of the plate for the washer to have contact with, or if there was something else going on.

 

[rickfischer51]

best way to learn this stuff is make a simple model and try it.

Rick Fischer
Principal Engineer
Argonne National Laboratory