Computer Animation and Simulation ’97

Abstract

Existing techniques for real-time simulation of object deformation are well suited for animating soft materials like human tissue or two-dimensional systems such as cloth. However, simulation of deformation in malleable materials and fracture in brittle materials has only been done offline because the underlying equations of motion are numerically stiff, requiring many small steps in explicit integration schemes. In contrast, the better-behaved implicit integration techniques are computationally expensive, particularly for volumetric meshes. We present a stable hybrid method for simulating deformation and fracture of materials in real-time. In our system, the effects of impact forces are computed only at discrete collision events. At these impacts, we treat objects as if they are anchored and compute their static equilibrium response using the Finite Element technique. Static analysis is not time-step bound and its stability is independent of the stiffness of the equations. The resulting deformations, or possible fractures, are computed based on internal stress tensors. Between collisions, disconnected objects are treated as rigid bodies. The simulator is demonstrated as part of a system that provides the user with physicallybased tools to interactively manipulate 3D models.