Physical-mechanical Properties of Inorganic Nano-crystal Structure in Bio-materials

Abstract: At nanoscale, study of biomimetic materials is a frontier science. In the biosystem, structural mimetic and functional mimetic is a new multi-discipline. Nacre in the shell is an extraordinary example of a hierarchical biological nanocomposite, as well as bones and teeth. In the biomimetic materials, mineral at nanoscale enables outstanding mechanical performance including an excellent combination of stiffness, strength and toughness. The shell materials comprise about 95% aragonite (a mineral form of CaCO3), with only a few percent (about 5%) of biological macromolecules, consisting of alternating layers of mineral tablets separated by thin layers of a biomacromolecular“glue”. Its laminated structure achieves approximately a two-fold increase in strength and a 1000-fold increase in toughness over constituent materials. In the shell, mineral form of calcium carbonate is calcite and aragonite. In this thesis, mechanical performance of calcite had been simulated. It is the base of researches of the interaction of calcium carbonate and protein with organic molecules.In the thesis, the ab initio quantum mechanics method based on Density Functional Theory was used. The ideal tensile and shear strength of calcium carbonate crystal was calculated. The stress-strain curve of calcite was calculated from simulations of tensile strain, shear strain and coupling of tensile and shear deformation. From stress-strain curve of calcium carbonate crystal, nano-calcium carbonate crystal is strong anisotropy and nonlinear characteristic. In the supercell structure of calcium carbonate, the tensile strength at [001] direction is more 22GPa, others perpendicular to [001] direction and themselves are about 15GPa. The tensile strain at [001] direction is 69%, the stress-strain curve is smooth. The shear stress is, separatively, 10.285GPa、9.767GPa and 7.343GPa for applied critical shear strain 0.28、0.40 and 0.31. It indicated that the tensile strength, the shear strength and toughness of calcite is superior. They are foundation that we design the high strength composites. On the base of this work, if we investigated the interaction of calcium carbonate and organic molecules, it is hope that we find new high strength composites. The linear elastic stress-strain curve applied tensile strain and shear strain was fitted, the elastic constants of calcite are estimated. Result shows how well the constants estimated reproduce experimental data. In the thesis, it is the first that we obtain the high toughness of calcium catrbonate crystal and the data of its strength nonlinear and anisotropy stress-strain relations. It provides the foundation of the nonlinea…
Key words: Shell; Aragonite; Calcite; Tensile strength; Elastic constants; Quantum mechanics; Graphite; Composite

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