Residual Stress Fields in Mullite Based Laminated Structures

Mullite is an interesting material with several potential applications, as it is inert and refractory. However, its full exploitation as structural material is hindered by the poor mechanical properties. To overcome this problem, a laminated structure has been prepared by tape casting in order to induce compressive residual stresses on the sample surface, therefore enhancing tensile strength. Two types of samples have been prepared: one using pure kaolin as starting powder and a second one using kaolin with an excess of alumina, in order to obtain (after sintering) a composite with an excess of alumina as secondary phase. Mullite obtained from kaolin had 1ower thermal expansion and was used as the outer layers in the laminated structure in order to induce a compressive residual stress field on the surface. A piezo-spectroscopic technique based on the linear shift with stress of selected Raman and fluorescence bands of the constituent materials was used for assessing the residual stress field distribution in different layers of the laminated structure.