Stresses in multilayered ceramics subjected to biaxial flexure tests

Although standard test methods for biaxial strength measurements of ceramics have been established and the corresponding formulas for relating the biaxial strength to the fracture load have been approved by American Society for Testing and Materials (ASTM) and International Organization for Standardization, respectively, they are limited to the case of monolayered discs. Despite the increasing applications of multilayered ceramics, characterization of their strengths using biaxial flexure tests has been difficult because the analytical description of the relation between the strength and the fracture load for multilayers subjected to biaxial flexure tests is unavailable until recently. Using ring-on-ring tests as an example, the closed-form solutions for stresses in (i) monolayered discs based on ASTM formulas, (ii) bilayered discs based on Roark's formulas, and (iii) multilayered discs based on Hsueh et al.'s formulas are reviewed in the present study. Finite element results for ring-on-rings tests performed on (i) zirconia monolayered discs, (ii) dental crown materials of porcelain/zirconia bilayered discs, and (iii) solid oxide fuel cells trilayered discs are also presented to validate the closed-form solutions. With Hsueh et al.'s formulas, the biaxial strength of multilayered ceramics can be readily evaluated using biaxial flexure tests. ? (2009) Trans Tech Publications, Switzerland.