Positional finite element method analysis of residual stresses in partially crystallized lithium disilicate glasses

Abstract

Glass ceramics, polycrystalline ceramics obtained from controlled crystallization of glasses, have several advantages over precursor glasses and same composition ceramics obtained by the traditional method from powdered raw materials, due to the variety of special microstructures that cannot be produced in any other material. However, residual stresses arise during crystallization and can cause the propagation of cracks and micro-cracks, affecting their mechanical properties. Predicting the effect of crystallization on such materials is important for their development and their performance maximization. However, as the overlapping of the stress fields resulting from the growth of a given number of crystals in the volume quickly evolves into a very complex scenario, the theoretical models of residual stress calculations, which are based on simplified geometries, do not always coincide with the observed experimentally. This research project aims, therefore, to better understand and model the effect of the phenomena associated with the controlled crystallization of glass on its mechanical properties. For this, we intend to develop a computational tool for nonlinear geometric analysis that simulates the effect of residual stresses generated due to thermal and elastic incompatibility between crystalline precipitates and the glass matrix on the mechanical resistance of lithium disilicate glass ceramics for volumetric fractions of crystals between 0 and 5%. The numerical basis of the work is the formulation in Positional Finite Element Method, which should be complemented/adapted for (i) immersion of crystals in the glass matrix; (ii) inclusion of residual stress models generated by the crystals (iii) implementation of damage models. (AU)