The role of interfacial interactions on the mechanical behaviors of materials

The mechanical properties of a material strongly depend on its microstructure, such as grain and grain boundaries in polycrystalline materials, or organic-inorganic interface in biological nanocomposites like bone or nacre. To understand the contribution of interface on mechanical response of nanocomposite materials, it is necessary to develop a generalized interfacial zone model, which could describe difference material interface behaviors and properties. This work developed interfacial zone models to define a variety of material interface behaviors (e.g. brittle, ductile, rubber-like, elastic-perfectly plastic behavior, etc.) and interface properties (e.g. stiffness, strength, toughness). The proposed interfacial zone models were verified and validated through analytical solution and experimental measurements. Through modeling of the organic interface of extrafibrillar matrix in bone, it is found that the opening mode is the dominant failure mode under tensile loading and the intergranular sliding between the mineral crystals is the dominant failure mode under compressive loading. Also, the hydration status of the organic interface in the extrafibrillar matrix may con- tribute to the plasticity of bone. Through modeling of the grain boundary of polycrystalline Al2O3, the simulation results show that intergranular to transgranular fracture transition is sensitive to the ratio of fracture energy and strength between grain boundary and grain. In addition, through modeling of the cell-cell interaction in collective epithelial cells, it is found that the following cells can sense the motion of leading cells through intercellular force transmission.