FEM deformable objects bending and shearing


I would like to know if iMSTK contemplates the possibility of applying shear and bending (dihedral and area) constraints to deformable bodies simulated with FEM. I cannot avoid FEM elements bending with gravity even modifying Youngs modulus, poissions ratio, or dt.

Pd: Using dihedral, area or bend constraints while using FEM causes runtime errors. Yes, I can use distance and volume constraints with no problem, but they doesn’t avoid the bending.



So, conceptually, they should work together, but I’m not sure that would solve your problem. If a body is fixed at one end and free at the other under gravity it will always bend to some degree. What is your goal? Would you like the body to be rigid?


Mi body is fixed by two sides, like this:

Simple explanation

Runtime deformation

Space constraints not in runtime

And yes, it isn’t not a cloth with pbd constraints, it’s a thin tetrahedral body with FEM constraints.
Basically I want it to behave as a “cloth”, being tighten, but with the stability that FEM offers in the simulation, because the PBD restrictions cause, with certain actions colliding or grabbing, the simulation to break completely.

Ah. Thanks for the clarification. The simplest fix for this problem would be to turn off gravity for the deformable PBD object. @Harald_Scheirich added a flag to set that in iMSTK-Unity recently. Its handy for when we don’t want to arbitrarily stiffen the body.

Also, what is the nodal mass of the PBD object, and the total mass? It could be that it is just too heavy.

I don’t want to turn off gravity, I want the body to react to gravity forces, but not that way. What I really need is some bending restriction but it doesn’t seem like it’s compatible.

The global mass is 0.01, is the minimum mass I can set, because the uniform particel mass is the lowest to reach 0.01 global mass.

What units are you using?

imstk-Unity doesn’t specify units, idk.

The units are based on the inputs you are using. What are you using for gravity? Also, what value are you using for youngs modulus in the FEM constraints?

-9.81, the default one. And I have tested from 10 to 10¹⁰, and behaves the same

Hi Nacho! I’m Maria and I’m currently working in a project similar to what you’ve shown you did in the unity imstk asset review page (the youtube video). I’m having some difficulties implementing this functionalities and, considering it looks like you are the person with most knowledge of this tool internetwide, I was wondering if you could maybe help me somehow. I’m open to any request you have to aknowledge your service. If you think you are able to help me, please contact me at maayza@gmail.com Thanks in advance! Your work is amazing!