  This paper describes a 2D and 3D simulation engine that quantitatively models
the statics, dynamics, and non-linear deformation of heterogeneous soft bodies
in a computationally efficient manner. There is a large body of work simulating
compliant mechanisms. These normally assume small deformations with homogeneous
material properties actuated with external forces. There is also a large body
of research on physically-based deformable objects for applications in computer
graphics with the purpose of generating realistic appearances at the expense of
accuracy. Here we present a simulation framework in which an object may be
composed of any number of interspersed materials with varying properties
(stiffness, density, etc.) to enable true heterogeneous multi-material
simulation. Collisions are handled to prevent self-penetration due to large
deformation, which also allows multiple bodies to interact. A volumetric
actuation method is implemented to impart motion to the structures which opens
the door to the design of novel structures and mechanisms. The simulator was
implemented efficiently such that objects with thousands of degrees of freedom
can be simulated at suitable framerates for user interaction using a single
thread of a typical desktop computer. The code is written in platform agnostic
C++ and is fully open source. This research opens the door to the dynamic
simulation of freeform 3D multi-material mechanisms and objects in a manner
suitable for design automation.
