material parameters for fabric

Dear all,

sometime ago I put a discuss about a simulation of material properties:

http://www.grasshopper3d.com/group/kangaroo/forum/topics/how-to-kee...

after some explanation from Daniel I found a very interessting simulation from Daniel named 'tablecloth', which is exactly what I wanna do:

http://vimeo.com/51169678

In that video you see how a fabric deformed without(?) changing its material property.

I made a similar defination using Kangaroo, the result:

In my definition I give the connection and rest-length for kangaroo separat.

after the fabric streched the length in both direction dosent changed so much. and it is exellent!

But it just looks too perfect/smooth then in the reality. I was expecting some 'folding' happen, like this:

I am not sure if it is naccesary to expecting those 'folding'. Just wondering coz in Daniels Simulation 'tablecloth' you can see fabric-folding!

If anybody have explanation or give some advice/ discuss about that? I am mean e.g. prestress the material in GH/ Kangaroo...(?)

thx guys!

Attachments:

membran.gh, 24 KB
Movie.wmv, 2 MB

Replies to This Discussion

Permalink Reply by Nick Cole on April 13, 2014 at 3:21am

Shear stiffness! When your model deforms there is nothing preventing all the rectangles in the grid warping to form parallelograms. It is behaving like a chain net. You're trying to model a material that has resistance to this shear deformation and this is what causes the creases. You can easily add this to your model by including diagonals to the rectangular grid. By altering the stiffness of the diagonals you will change the shear stiffness. Very flexible = chain net, very stiff = solid material, somewhere in between = fabric.

Permalink Reply by Daniel Piker on April 13, 2014 at 3:57am

Hello Frank,

That tablecloth video was created as a response to this question in the forum:

http://www.grasshopper3d.com/group/kangaroo/forum/topics/table-clot...

In that thread you can find a bit more explanation, and the definition used.

(Nick is absolutely right - shear stiffness is the key here. See also this video for a comparison of with/without shear resistance: https://vimeo.com/15022048)

Depending how much your fabric folds onto itself, you may also want to include self-collision - see here:

http://www.grasshopper3d.com/video/kangaroo-collisions

http://www.grasshopper3d.com/group/kangaroo/forum/topics/new-exampl...

I hope that helps,

Daniel

Permalink Reply by Jon on April 15, 2014 at 3:35am