Investigation On The Interaction Mechanism Of Reinforcements With Typical Defects In The Nanocomposites

With the emergence and development of nanotechnology, nanocomposites have showed a lot of excellent properties, which makes them to be applied in many fields of mechanics, microelectronics, optics, chemistry, medicine and others. However, the quantitative correlation between the microstructure and the macromechanical properties is lack of systematic and comprehensive study due to the complexity of the nanocomposite microstructure, which delays the further development and application of nanocomposites. Thus, building quantitative models to study the interaction between nanoparticle reinforced phases with various defects in nanocomposites is a very important and urgent task at present.In this paper, taking nanocomposites as the research object, we systemically study the interaction of nanoparticle reinforced phase with dislocation, disclination and crack in nanocomposites, and their relativity with the strengthening and fracture toughness mechanism of nanocomposites. Based on the experimental observation, all kinds of complex mechanical models are established. Utilizing the elastic complex potential method and the distributed dislocation technique, the solutions of a series of complex microstructure problems are obtained. The influences of the inhomogeneity radius, the inhomogeneity distribution, the dislocation position, the crack length, the coating thickness, the material elastic dissimilarity and the interface stress on the dislocation image force, the dislocation equilibrium position, the stress intensity factor(SIF) at the crack tip, the energy release rate are analyzed. The research not only contributes to the elastic complex potential method, but also can serve as a guide in the design of the nanocomposites. The main achievements are summarized as follows:(1) The interaction between the screw dislocation dipole in the nanoscale coating layer and the nanowire is investigated by utilizing the surface/interface stress model. The analytical solutions of the complex potential functions in the coating layer and the nanowire and the explicit expression for the dislocation image force are derived by means of the complex variable method. The influences of the nanowire size, the coating layer thickness, the material elastic dissimilarity and the interface stress on the screw dislocation dipole motion and equilibrium stability in the nanoscale coating layer are analyzed. The results show that the local hardening and softening effects at the interface of the nanowire due to the interface stress are remarkable, the stiff nanowire can attract the dislocation dipole, and the soft nanowire can repel the dislocation dipole. As the nanowire size decreases, the impact of the interface stress upon the dislocation image force increases. When the nanowire size is very small, the impact of the interface stress on the image force becomes significant. Addtionally, the interface stress can change not only the number of the equilibrium positions of the screw dislocation dipole in the coating layer, but also the value of the critical coating layer thickness.(2) The interaction between a Griffith crack and a circular inhomogeneity in the presence of an edge dislocation is investigated by means of the distributed dislocation technique. The SIFs at the crack tip are determined by solving the formulated singular integral equations numerically. The influences of such parameters as the elastic mismatch between the inhomogeneity and matrix, the edge dislocation position and the inhomogeneity size on the SIF at the crack tip are revealed in detail. The results indicate that the edge dislocation can shield or anti-shield the crack tip, depending on the position of the edge dislocation. As the edge dislocation approaches the crack tip, the effect of the edge dislocation will be getting stronger. The stiff and soft inhomogeneity both can shield or anti-shield the crack tip with the edge dislocation, and as the edge dislocation approaches the inhomogeneity, the effect of the inhomogeneity on the SIF of the crack tip will be getting stronger. The hard inhomogeneity shields the crack tip while the soft inhomogeneity anti-shields the crack tip under the uniaxial tensile load. There is competition between the effects of the inhomogeneity and the edge dislocation on the crack propagation. When the distance between the edge dislocation and the crack is less than a certain value, the edge dislocation is more distinct factor that influences the crack propagation. When the distance between the edge dislocation and the crack is equal to the certain value, the edge dislocation and the inhomogeneity counteract each other’s efforts. When the distance between the edge dislocation and the crack is more than the value, the effect of the inhomogeneity is more dominant.(3) Interior crack of a nanoscale cylindrical inhomogeneity with interface stress under the uniaxial tensile load is investigated. The influences of the interface stress, the material elastic dissimilarity, the crack length and the nanoscale inhomogeneity radius on the SIF of the crack tip are evaluated. The results show that both the positive(negative) residual interface tension and the interface elastic constants suppress(promote) crack propagation under the uniaxial tensile load. The stiff matrix decreases(increases) the SIF of the crack tip while the soft matrix increases(decreases) it under the negative(positive) residual interface tension. As the crack tip approaches the interface, the effect of the elastic mismatch will be getting stronger. The effects of residual interface tension and interface elastic constants on the SIF of the crack tip increase with decreasing the inhomogeneity radius. When inhomogeneity radius reduces to a small value, even with the remote load, the crack does not propagate due to the positive residual interface tension.(4) The effect of the nanoinhomogeneity on the nanocrack generation and the Zener crack propagation in the nanocrystalline matrix is theoretically investigated. The deformation twin is modeled by the wedge disclination quadrupole. The boundary condition at the interface between the nanoinhomogeneity and the matrix is modified by incorporating interface stress. The influences of the nanoinhomogeneity shear modulus, the nanoinhomogeneity radius, the nanoinhomogeneity position, the interface stress and the external stress on the nanocrack generation and the Zener crack propagation is investigated in detail. The results indicate that the stiff nanoinhomogeneity suppresses the nanocrack generation and the Zener crack propagation, while the soft nanoinhomogeneity promotes the nanocrack generation and the Zener crack propagation. Therefore, the stiff nanoinhomogeneity can enhance the tensile ductility of the nanocomposites while maintaining high strength. As the nanoinhomogeneity radius increases and the nanoinhomogeneity approaches the twin, the effect of the nanoinhomogeneity on the nanocrack generation and the Zener crack propagation will be getting stronger. Both the positive(negative) residual interface tension and the interface elastic constants suppress(promote) the nanocrack generation and the Zener crack propagation. However, the interface elastic constants have a weak effect on the nanocrack generation and the Zener crack propagation. The influence of the residual interface tension is greater than the interface elastic constants.