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# Limiting node translation

Pioneer

I have a FE model in which a pin is constrained. In reality, the pin goes thru a soft bushing which let the pin translate 0.5" in xy plane (pin free to move in Z dir). Currently, to take the bushing into account, i'm using zero length cbush with stiffness values. Now, i would like to try a different method where i want to let the node on the pin translate 0.5" in xy plane before it starts to take any load. To acheive this, i tried gap elements  (only in xy plane) with an initial gap. I have "use gaps as contact " checked in. As the reactions on the pin is not inplane, the gaps are not really working. Picture attached. Is there a easier way to acheive what i'm trying to do. Thank you very much.

8 REPLIES

# Re: Limiting node translation

Siemens Phenom

I've done this in the past my making the CBUSH's stiffness nonlinear, where I define a Stiffness vs. Displacement Function.

Create the function first, I use Displacement vs. Force

On the CBUSH Property, I entered a DOF 1 Stiffness as 1.0, and then press the "Nonlinear/Freq Resp.." button, and hook the same DOF to the stiffness funtion -

When a NASTRAN nonlinear job is run, there's no stiffness until the two nodes are 2.0 apart in the CBUSH's x-direction -

(view in My Videos)

Attached is the FEMAP v11.3 .modfem -

# Re: Limiting node translation

Pioneer

Thank you. My model is huge and it takes hours to run non-linear analysis. Will it give it a try and keep you posted.

Thanks

KR

# Re: Limiting node translation

Phenom
You say "the reactions on the pin is not in plane". Assuming you mean not in plane to the plane of the four gaps in your image, then this, by definition, is a nonlinear effect. The useful thing about Mark's suggestion is that (unlike gap elements) the CBUSH rotates properly and its stiffness effect rotates with it. Note that the CBUSH needs to be finite length (not zero length) for the stiffness to rotate as the element orientation changes with deflection.

# Re: Limiting node translation

Pioneer
Hi, I'm not able to load your model. Says "invalid model database or model is corrupted". Can you please share the .dat or .nas file. Thank you.

Siemens Phenom

# Re: Limiting node translation

Pioneer

Hi,

I took a similar approach to your example model, but i still have the CBUSH translating lot more than what the function defines. I have the screenshot of function and property attached. I also tried to run with finite length. Am i missing overlooking something? Thank you.

# Re: Limiting node translation

Pioneer
Thanks EndZ. I understand that mark's approach is lot better and I'm trying to get it solved the same way. Do you think I should be worried abt stiffness to rotate as I want the bush to freely translate till a particular displacement is reached and then completely stop irrespective of loading. If you look at the function, I say there is no stiffness for translation < 0.3984 and applied a stiffness (making it very stiff) of 1000000 for translation > 0.3984. Appreciate any thoughts.

# Re: Limiting node translation

Phenom
Looks like the results are negative? You may need to specify this function for the negative values as well.