Viscoelastic material behavior: models and discretization used in process simulator DIOS

It is a known fact that melted glass, such as SiO/sub 2/, shows viscoelastic behavior. But in the range of processing temperatures the mechanical properties of SiO/sub 2/ vary strongly. While below 800/spl deg/C the material behaves like an elastic solid, at temperatures above 1000/spl deg/C it shows nearly pure viscous properties. In this paper, the governing equation, the so-called constitutive equation, describing viscoelastic behavior, and its discretization are presented. The oxide viscosity depends on the local amount of shear stresses which leads to inhomogeneous material behavior and a nonlinear theory. This new mechanical model was implemented into the process simulator DIOS-ISE. Some obtained simulation results are shown and discussed.