CRACK SUPPRESSION IN STRONGLY BONDED HOMOGENEOUS HETEROGENEOUS LAMINATES - A STUDY ON GLASS GLASS-CERAMIC BILAYERS

A study is made of a glass/glass ceramic bilayer as a model homogeneou s/heterogeneous laminate. The underlying objective is microstructural design of ceramic layer systems with optimum mechanical properties, al ternating hard layers, for wear resistance, with tough layers, for fra cture resistance, Mica flakes in the glass-ceramic layer inhibit the p ropagation of well-developed intrusive cracks, by bridging; these same Bakes render the structure susceptible to distributed damage, by prov iding discrete weakness at the microstructural level. A major distingu ishing feature of the bilayer design is the incorporation of a strong interface, so that cracks are inhibited by the underlayer rather than deflected between the layers, Vickers and Hertzian indentation tests o n specimen cross sections demonstrate the capacity of the glass-cerami c layer to arrest radial and cone cracks penetrating from the adjacent glass layer, Additional Hertzian tests on the outer surfaces of glass layers in a coating/substrate configuration show diffuse damage accum ulation in the glass-ceramic substrate layers, This diffuse damage abs orbs energy and shields cone cracks in the glass from the applied load ing, Implications concerening the design of damage-tolerant laminate s tructures are discussed.