Residual stresses and deformations are usually encountered in all forming processes, after the shaped object is cooled. While they can be neglected or discarded in some applications, their prediction and anticipation can at times be of utmost importance. This is true in the glass industry in particular, where residual stresses and deformations may induce weaknesses and/or visual surface defects. It is therefore important to be able to identify and quantify these physical properties.

A significant part of residual stresses and deformations originate from the cooling phase in a process. The thermal history often differs according to the location, as well as the material response to such a thermal history. Typically, physical properties in regions that cool slowly will more often reach an equilibrium value, while they may be frozen in another state in regions that cool faster. This behavior is observed for the density, which may reach different values at room temperature, even though it was uniform within the forming process at high temperature.

This chapter will mainly address the behavior of glass during the cooling process, and with the resulting development of residual stresses and deformations. The simulation of the flow behavior of molten glass per se is described in other chapters. For additional information on residual stresses and deformations, see Residual Deformations and Stresses and Inputs for Residual Stresses and Deformations.