Carbon Fiber prosthetic foot - STIFFNESS

[kukogoba]

I have made a FEM model of a prosthetic foot. And i want to obtain the stiffness of the model.
I´m thinking of doing a Force vs Displacement graph, but i´m still not sure how to accomplish my purpose.
I need some help.

Thanks in advance.

 

[ebdoep2]

If you really want to boil it down to a single number for stiffness then all you need to do is apply a small load run the model and look at the deflection at the point of interest (likely where the load was applied). Assuming you have small deflections and therefore run a linear simulation your disp vs. force graph will also be linear, so you will only need to run the model once.

Of course nonlinear you will need to try several loads across the range of operating loads.

The one part that will be difficult/take some thinking is what do you want to consider to be the "stiffness" if are really looking for a single scalar value. Most structures will have a different stiffness depending on how they are loaded.

 

[Michael279]

You can create a force displacement graph for any point of your model, for any direction and force of interest.
To do this you can request displacement at a point in the model via the history output.
Then you can plot this by: visualization module -> create XY data -> plot. Now you get a displacement vs. time graph, where time is proportional to force.

When using a nonlinear analysis (Step -> nlgeom = on ) you can press "Save as" after plotting the XY data.
Then also save the load of interest in the same way.
Then you can combine the displacement-time and force-time plots by: Tools -> XY Data -> Create -> Source: operate on XY Data -> Combine(X,X) -> Select the two history outputs of interest and "Save as".
Then Tools -> XY data -> Plot