Calculation of thermal stresses in glass-ceramic composites

Opto-electronics make intensive use of composite materials based on amorpho us materials, which can be considered as smart materials since they are cap able of high performances in their final state. Particularly, glass-ceramic composites involved in welding operations for microelectronics application s are subjected to important thermal stresses during their production, whic h can deteriorate their properties at room temperature, until the failure s tage is reached. It is then essential to be able to predict the evolution o f the internal stresses generated during the cooling. We have performed fin ite-element simulations in order to quantify the stress evolutions for diff erent composite geometries: a ceramic fiber embedded within a glass matrix, a spherical particle located at the center of a spherical glass matrix, an d a dispersion of spherical ceramic particles, this last case being the mos t representative of reality. The thermomechanical modeling of the glassy ma trix takes into account its viscoelastic behavior, and the glass transition is described by the decrease during cooling of the free volume as a functi on of the temperature history. The combined effect of the differential ther mal strain during the transition and mechanical relaxation of glass on stre ss evolutions is evidenced. It is shown that the consideration of a periodi cal or random distribution of spherical ceramic particles leads to similar stress profiles.