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Enforced displacement loads

Experimenter
Experimenter

Hi everyone,

I'm trying to simulate the behavior of a plastic component in Nastran NX 10. This component has some clips, and I need to enforce a displacement of 1 mm in X and Y direction on the top edge of the clip, in order to simulate its working position.
I was able to run the simulation (using SOL106 - Global Constraints), and the stress of the clip results as expected. 
However, I need to know the force needed (in X and Y) to compress the clip.
I looked everywhere in the post processing, but I can't find the values of the load.

Am I missing something? Attached you can see a picture of how I set the enforced displacement. The only other constraint is a fixed support on the bottom of my plastic component.

Thanks in advance,

 

/Daniele

5 REPLIES 5

Re: Enforced displacement loads

Siemens Phenom Siemens Phenom
Siemens Phenom

If you request SPCFORCE output, you can sum the SPC forces using the Identify command in post processing to get the total reaction force.

Re: Enforced displacement loads

Experimenter
Experimenter

Hi Jim,

thanks for the quick reply. I already tried it (see attached picture): I get a force (on axis Y it's -2.5 N), but if I remove the enforced displacement constraint, and apply a force of -2.5 N, the re-run the simulation, I dont get 1 mm of displacement (I get 0.644).

So I assumed that reaction force output wasn't what I was looking for.

Again, am I missing something?

Thanks a lot,

 

/Daniele

Re: Enforced displacement loads

Gears Phenom Gears Phenom
Gears Phenom

This is nonlinear problem. Maybe this clip have snap-through behavior. Save intermediate results and plot diagram Reaction vs. Time. Maybe you have peak somewhere in the middle of diagam. Try to use peak value instead of end value.

Re: Enforced displacement loads

Experimenter
Experimenter

I run the simulation using 10 subcases. I tried to plot the reaction force on Y over the iterations (see attached picture), but as expected, the peak is at the last iteration. Plus, I need to know the force on the edge when the clip is in its working position (X and Y displacement = 1 mm), not in a different one.

After many attempts applying a simple load on the edge, I found that I need a Force of Fy=-4,5 N along (axis Y) and Fx=2.25 N (along axis X), in order to get the correct displacement of -1 mm along Y and 1 mm along X.

But then again, if I set the required enforced displacement, and in the last subcase I use the identify command on the whole edge, the sum of the reaction forces on the nodes is Fx=0.6 N and Fy=-2,5 N. these values are not correct.

Any suggestions?

Thanks,

 

/Daniele

Re: Enforced displacement loads

Gears Phenom Gears Phenom
Gears Phenom

Dont use subcases. Search for option "Output Control" -> Intermediate ->All in solver setting.

Chose biger force like 10 N. Request 100 timesteps and check at what step you get 1 mm displacement.

Here is screen of nonlinear setting in Femap, yesterday I search this option in NX.