Hertzian contact behavior of alumina-based trilayer composites: experimental observation and FEM analysis Original Research Article

Two different alumina-based trilayer composites were fabricated with the aim of elucidating the influence of a quasi-ductile interfacial layer on the nature of the Hertzian contact damage. In each case the composites were designed to promote cone cracking in a more brittle outer layer (consisting of fine-grain alumina), and distributed microcracking in a quasi-plastic core layer (composed of alumina with 30 vol.% calcium hexaluminate platelets). Experimental observations of the indentation induced cracking behavior were complemented by FEM analysis of the principal stress and plastic strain contours. It was observed that for the trilayer with an intermediate coarse-grain alumina layer, the depth of cone cracking was reduced, which correlated with an improvement in the as-indented strength. Finite element modeling analysis confirmed that due to the presence of the interlayer, modification of the subsurface stress state took place, resulting in a more shallow predicted cone crack trajectory. Implications for design of trilayers with improved contact damage resistance are discussed.