: An armadillo demonstrates non-Newtonian behavior similar to a cornstarch solution-resisting large stresses, it initially bounces on the ground, but when the stress is reduced it flows readily. In this paper we describe a point-based approach for animating elastoplastic materials. Our primary contribution is a simple method for computing the deformation gradient for each particle in the simulation. The deformation gradient is computed for each particle by finding the affine transformation that best approximates the motion of neighboring particles over a single timestep. These transformations are then composed to compute the total deformation gradient that describes the deformation around a particle over the course of the simulation. Given the deformation gradient we can apply arbitrary constitutive models and compute the resulting elastic forces. Our method has two primary advantages: we do not store or compare to an initial rest configuration and we work directly with the deformation gradient. The first advantage avoids poor numerical conditioning and the second naturally leads to a multiplicative model of deformation appropriate for finite deformations. We demonstrate our approach on a number of examples that exhibit a wide range of material behaviors.
REF proposed a new method for calculating the deformation gradient based on approximating the affine transformation between the original structure and the current structure.
A point-based method for animating elastoplastic solids
SCA '09
Mathematics Computer Science