Fatal error message in FEBio knee joint file

[brockeubanks60]

I know that there is already a post about the error message " Fatal Error: Rigid body rotations cannot mix prescribed and free components", but I was wondering how exactly you would fix the rotational degrees of freedom in the PreView environment.

[maas]

Hi,

First, you need to add a rigid material (in FEBio, rigid bodies are defined implicitly by adding a rigid material).

1. Select Physics/Add Material from the menu.
2. In the dialog box, select Other from the Category and then Rigid Body from the material property type.

Then, to fix degrees of freedom from a rigid body:
3. Select Physics/Add Rigid Constraint from the menu.
4. In the dialog box, select Fixed Rigid body displacement/rotation from the options.

Let us know if you have any further questions.

Cheers,

Steve

[brockeubanks60]

I'm still having an issue with joints not being rigid. Is there a way to add rigid constraints without changing the material properties?

[maas]

I'm not entirely sure what you are asking, but you can only apply rigid constraints to rigid bodies, which are defined implicitly via a rigid material. So, my answer to your question would be no, but perhaps if you elaborate on what the problem is, or what you are trying to do, maybe I can offer some more help.

Cheers,

Steve

[brockeubanks60]

Is it possible to change the material type to a rigid body but keep the same property values that it had before? I'm just trying to figure out how to run force simulations on knee joint but parts of the knee joint such as the cartilage, mcl, and pcl are giving me the fatal error. At least, that is what I'm assuming.

[maas]

No, you cannot transfer material properties between types. That wouldn't make a lot of sense for the vast majority of materials in FEBio, since each material defines its own set of properties that have no relationship with any other material.

Cheers,

Steve