Effect Of Surface/Interface On The Dynamic Stress In Nano Composites

With the rapid development of nanotechnology, nano composites are widely applied in engineering. To increase the working stability and serving life of nano structures, it is urgent to understand and predict the response under the various types of dynamic loads in nano composites. Unlike the conventional composites, when the size of low-dimensional materials approaches the nano-scale, the fracture and destruction will firstly occur in surface/interface region due to the high ratio of surface/interface area to volume. In order to analyze the surface/interface effect on the dynamic strength and stability of nano composites, in this dissertation, the effect of the surface/interface on the dynamic stress concentration in nano composites is investigated systematically by using the model of the linearized surface/interface elasticity, and the multiple scattering theory of elastic wave is described. The main research contents are as follows:Multiple scattering of anti-plane shear waves and dynamic stress concentration in nano-fiber reinforced composite material are investigated. The cylindrical wave function expansion method is employed to express the elastic wave fields, and the expanded mode coefficients are determined by satisfied the boundry conditions between the reinforcing phases and matrix material. The analytical solution of the dynamic concentration factor is derived. The effect of surface/interface on the distribution of dynamic stress around the reinforcing phases is analyzed by taken the different physical and geometrical parameters.Based on the typical characteristic of bounded structures in engineering application, the model of the semi-infinite slab with a nano-scale circular inclusion is presented, and surface/interface effect on the dynamic stress around the inclusion is investigated. Image method is employed to satisfy the traction free boundary conditions of the semi-infinite slab. The addition theorem for cylindrical Bessel function is used to accomplish the superposition of wave fields, and the analytical solution and numerical examples of the dynamic stress concentration factor are obtained. The effects of the distance between the inclusion and the structural boundaries, the incident wave number and the material parameters on the distribution of dynamic stress around the inclusion are analyzed.Combined with the wave function expansion method and image method, the propagation of the anti-plane shear wave in the semi-infinite structure with a core-shell nanowire is investigated. The multiple interfaces effect of nanowire is considered. The expanded mode coefficients and the analytical solution of dynamic stress concentration factor are obtained by satisfied the boundary conditions around the inner interface and outer interface of the nano-scale coating layer. The effects of the material properties of the nanowire with the annular coating layer and the surfaces/interfaces, the frequency of incident wave and the size of the semi-infinite structure are analyzed. Comparision with the previous results is also presented.