Material Matters

Hey Everyone,

So this past week I've worked on two things: memory and material properties.

Memory has been a massive pain in the butt, which is surprising because I thought it would be easy to work with. In my previous post about memory my only somewhat successful memory attempt was done through relaxing the rest length of bend springs. I was relatively happy with that to capture a piece of paper that is incredibly curled up. But it was hard to get it to get slightly bent. So I spent a lot of time trying to get the rotational springs to be added procedurally but regardless of what I did it seemed like it would not work. So I decided to just hard program it and I realized that it required very slight adjustments of the rest angles of the rotational springs to get that slight curl. Take a look at the video below:

So in conclusion of the memory, you can get strong results for memory by playing with the rest lengths of bend springs and this can be done procedurally. However if you want to get slight curl due to moisture or it is light paper, you are better off putting rotational springs in there manually and tweaking them.

So when I say "material properties" I of course mean something that is more visual than something that is grounded in physics. I found this webpage : http://www.paperonweb.com/paperpro.htm and it has a great amount of physical properties of paper.

• The major thing that you have to deal with here is the weight of the paper. So I spent some time playing around with the mass of my particles. What this did visually was it mainly affected how great the forces were acting upon the particles. Mostly this just slowed down or sped up the folding process. However because it changed the speed of the fold, it did make the paper slump or stiffen a little more than usual. So changing the mass definitely had an effect.
• The second property that I deal with is curl. I talk about the curl in my memory portion above. This website lists three different types of curl with regards to paper. When I add rotational springs this is sort of like structural curl, where a difference in the fibers causes the paper to pop up. When I change the bend spring's rest length that is sort of like moisture curl, where fibers in the paper either collapse or expand due to exterior forces or moisture.
• The third major property I deal with is the dimensional stability. Dimensional stability is basically how the fiber in the paper keeps the paper together and affects how it folds. This is akin to my spring constants. I spent a lot of time playing with settings of spring constants to get different affects. Reducing the constants of the shear and bend springs will make the paper much more cloth. Reducing just the shear springs will make the paper more like tissue paper. Reducing just the bend springs will make the act like it is more moist. Reducing the constants of the structural springs is just bad because then the paper no longer holds its form.
• The last property I got from that website was formation. Formation is the alignment and distribution of the fibers in paper. I wrote code that offsets the points in the lattice by a random but clamped epsilon. However this did not seem to change much in my simulation. I think it would be more important if I worked in a very large lattice.

I've attached videos of some the presets I've created for my simulation and showing what I described above.

Next week I am going to just concentrate on rendering. I have a problem where the paper can be folded at odd angles, causing breaking. I need to look at Joe's Maya export code before I can come up with a firm idea of how to solve this problem. After I do the rendering I am going create my poster and get ready for my final presentation. Yay!