17th December 2018

Carbon 9.0.0 introduced the ability to control the plastic deformation of cloth. This is a crucial feature for believable cloth simulation. There are three key parameters:

1) The Yield (an angular value) controls the angle at which plastic deformation kicks in.
2) The Plasticity (fraction) determines how much angular deformation can be elastically recovered vs plastically deformed, once you are beyond the Yield angle.
3) The Stiffness of the cloth.
Past the Yield angular value, a fold will take the current deformation and add the Plasticity fraction into a plastic angle that is the reference angle + deformation x Plasticity. While the fraction corresponding to ( 1 - Plasticity ) can still be elastically recovered.
So, if Plasticity is 0 then no plastic deformation will ever occur and if Plasticity is 1 then all deformation gets converted into plastic deformation and no deformation can be reverted elastically.
So, if you use a low Yield, then each fold can easily record plastic deformation, but it also works the other way around and they can be ironed back by an opposite small deformation. So low Yield angles kind of sucks up fast rotation energies, generating gentle and short term memory folds. While high Yield angles will not produce lots of plastic deformation due to the big angular threshold, but in return the deformations have a much longer life.
The Stiffness is also very important, because it works in combination with the Yield.
For example -
  • A very stiff cloth is very hard to deform already so a strong Stiffness combined with a high plastic Yield will produce metal thin shell plastic deformations.
  • A high Stiffness with a low Yield will produce the behavior of an unlively thick cloth.
  • A low Stiffness with a high Yield will produce a lively cloth, but dissipative behavior. And
  • A low Stiffness with a low Yield will look silky.
The amount of Plasticity has less impact on the behavior than the Yield and the Stiffness. 
The amount of Plasticity amplifies the intensity / smoothness of the plastic deformation.