Effect of porous interlayers on crack deflection in ceramic laminates

Ceramic layered systems with interlayers of various porosities were fabricated using tape casting technique. Submicron size alumina powders were used to make the tapes for both the strong dense laminae and the weak porous interlayers. Porosity was introduced into the interlayers by the addition of PMMA powders. The pores generated were found to be spherical and uniformly distributed. The crack deflection capability of the layered systems with interlayers of different porosity were then investigated. To facilitate the study, the fracture energies of the different porosity monolithic porous layers, and also the dense alumina layer, were quantified using four point bending tests. It was observed that there exists an optimum porosity that the crack deflection, hence the fracture energy of the system, can be maximized. Theories proposed in the literature on crack deflection in layered systems were also discussed and compared with the present experimental findings.