EXPERIMENTAL APPROACH TO STUDY THE THERMAL INDUCED STATE OF STRESS IN A MEDICAL CERAMIC BILAYER

摘要

An experimental study is presented to provide a basic analysis of the causes and key thermo-mechanical parameters of residual stress development in ceramics medical implant. For simplicity, a bilayer planar geometry is considered, that is constituted by a veneering porcelain and tetragonal zirconia (Y-TZP). A novel non-contact optical based instrument was adopted to measure the thermal expansion as well as the deflection upon heating of the bilayer fabricated from these two materials. This non-contact technique enables to determine the thermal behavior below and above the glass transition temperature (T_g) of the porcelain and to evaluate the coupling attitude of the materials. The approach is then used to investigate the influence of cooling rate during initial fabrication of the porcelain-zirconia bilayer upon the subsequent heating and cooling. Breaking off the acquisition before the dilatometric softening in order to avail any plastic deformation of the sample and following the cooling process also, the optical dilatometer allowed in fact to study the thermal expansion dependence on the prior thermal history. The observations of the bilayer deflection enable to investigate the crucial role of the neo-formation interface between the layers and to analyze its effects upon cooling.