Having problem in definiing support for my analysis

[aminhed]

I tried to do a static structural analysis. My model consists of a lead screw, a nut and a pintle over lead screw. In reality Nut rotates around an axis (lets name this axis Y). Since lead screw supports are in such a way that it cannot rotate, this rotation causes the screw moves along the same axis (Y). So the Nut support is fixed at all directions except rotation around Y and lead screw support should be fixed at all direction except along Y axis.

I have problem in defining these supports. I used remote displacement for this purpose and set other directions constant and set rotation around Y or linear movement along Y to free.
After doing analysis, I deal with following warning message:

One or more bodies maybe underconstrained and experiencing rigid body motion. Weak springs have been added to attain a solution. Refer to Troubleshooting in the Help System for more details.

I attached a photo of the model to this messagewhich shows loading and supporting conditions.

Can anyone help me to solve this problem and find right way to define supports?

Thanks in advance

 

[GeorgeKTR]

Hello Aminhed

First of all, what output do you want from you analysis?


Since you're in static analysis, if you want reaction force in the axial direction it doesn't matter if you lock the bolt in the axial direction, let's say with a frictionless support. You just have to add a "force reaction" inquiry from your boundry condition, under solution. I don't think that the error message should come up then. The harder part in this case would be to declare the contact conditions in a realistic way with friction and all.

//George

 

[aminhed]

Dear George

Thank you very much for your response. Actually, it is a lead screw which should change the rotation of the Nut to a linear motion to move 15 N force which is applied over it. I want to substitute the material of the lead screw which is stainless steel 304 with a special type of plastic (Poly Amide). I want to extract stress tensors over the lead screw to know if this substitution is possible or not. So I need to use exact supports. I think one of the major problems is that two bodies (Nut and Screw) do not know each other as a body and Nut passed from screw and vise versa. Dou you know any way which I could define bodies know each other and do not pass from each other?

Thanks again

 

[GeorgeKTR]

Sorry for the late response,

ANSYS should recognize the the 2 bodies (or more) if you import the assembly from some cad-software and even automatically set up contact-conditions... Do you have an assembly?

 

[aminhed]

Thank you so much for your response.

I imported geometry from MECHANICAL DESKTOP and ANSYS already recognized contact regions. I defined a frictional contact for contact between screw and nut and after some searches I found out in 'define contact details' section under 'advanced menu', if 'interface treatment' be set as "Add Offset, No Ramping" bodies would not recognize each other and pass through each other. If this parameter be set as "Adjust to Touch" they cannot pass through each other. Any way I did my analysis with "Adjust to Touch" but I faced with a new problem as you can see in attached file There is no frictional stress between two parts, it means that still no contact is a occurred between them. What is your idea about this problem?

Thanks