Interfacial crack problems in layered materials

Interfacial cracking and toughening in metal/ceramic layered materials are investigated in this dissertation. This work stems from the fact that mechanical properties of metal/ceramic layered materials are, to a large extent, determined by the deformation and failure mechanisms at the interface. With the wide use of metal/ceramic layered materials in electronic packaging, ceramic actuators, coatings of fine length scale, the characterization of the basic properties of the layered materials can be quite different from that of the corresponding bulk materials, and provides challenges for both theoretical modelling and experimental measurements. Two fundamental issues are analyzed in detail in present work with considering the fine length scale (from micrometer to nanometer): ductile versus brittle behaviour of metal/ceramic layered materials, and interfacial toughening in metal/ceramic layered materials under mixed mode load condition.; The ductile versus brittle behaviour of the metal/ceramic layered materials is examined by considering the energy conditions for dislocation initiation (layered materials behaviour is denoted as ductile) and interface debonding (layered materials behaviour is denoted as brittle). It is demonstrated that dislocation emission is obvious when the metal layer thickness is above several micrometer; on the other hand, the metal/ceramic layered material is brittle when the metal layer thickness is in the order of nanometer. The mode mixity effect on this ductile versus brittle behaviour is also investigated in terms of loading phase angle. The interfacial toughening in metal/ceramic layered materials is analyzed by considering the dislocation behaviour in the metal layer. Superdislocation approach is employed to analyze the effects of blunting and shielding on the interfacial crack. A model of periodically enabling dislocation emission and interface debonding is established to simulate the interfacial crack initiation and propagation process. The interface fracture toughness is investigated and steady-state interfacial crack propagation is achieved such that provides some basic parameters, such as length scale and mode mixity, for the safe design of metal/ceramic layered materials.