Modelling the viscoelastic response of ceramic materials by commercial finite elements codes

Abstract

A very prominent patented technology permits to obtain bent porcelain stoneware tiles by a proper combination of machining and secondary firing in a kiln. During this firing, the ceramic materials show a viscoelastic behaviour. The viscoelasticity permits the tiles to be bent without further interventions: just using the gravity force in a so-called pyroplastic deformation. Both the viscoelastic response in general and pyroplastic deformation in particular are complex aspects of material behaviour to be modelled with accuracy. In general, the theory of viscoelasticity can be considered extremely large and precise, but its application on real cases is extremely tricky. A time-depending problem, as viscoelasticity naturally is, has to be merged with a temperature-depending situation. It means that, even if the constitutive equations could be set as general formulation, all the fundamental parameters inside these formulas change in function of both entities. Finite Elements codes could help to pass by this impasse, permitting to discretize the variability on temperature. But several cautions have to be taken into account, especially considering that few commercial codes developed proper algorithms. This paper investigates how the viscoelastic response of ceramic materials can be modelled by commercial Finite Elements codes, defining limits and proposing solutions.