Papers by Author: Zhi Ying Ou

Abstract: The residual stresses induced in fiber-reinforced functionally graded composites cooling down from the processing temperature are determined with concentric cylinder model and analytical solutions of inhomogeneous governing equations for displacement components, which include particular solution and general solution of the corresponding homogeneous equations. The analytical solutions presented here are general for power-law variations of the elastic moduli of the functionally graded matrix. With a power exponent, analytical expressions for the residual stresses of fiber-reinforced functionally graded composites can be obtained. By changing the power exponent and the coefficient of the power terms, the solutions obtained here could be applied to fiber-reinforced functionally graded composites with different properties. The results show that the large difference exists between functionally graded composites and common-used composites consisting of two phases of homogenous materials. The variation of matrix modulus and fiber percentage have a great deal of effects on the residual stresses in functionally graded composites.

Abstract: Axisymmetric nonlinear bending of the functionally graded circular plates is investigated in the present work. The material properties of plates are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and to be temperature-dependent. Based on the classical nonlinear plate theory, the governing equations for the problem are derived, and then a shooting method is employed to numerically solve the equations. Effects of material constant, temperature- dependent properties and boundary conditions on the nonlinear bending behavior of the FGM plate are discussed in details.

Abstract: The elastic field around a nanosized spheroidal cavity is derived on the basis of surface elasticity theory. The effects of surface energy, shape and size of the cavity are discussed. It is seen that the stress field near the nanosized cavity depends on the shape and the size of the cavity as well as the properties of the surface. These new characteristics are different from those predicted by the classical elasticity and may illuminate some new mechanisms at nanoscale.

Abstract: A simplified approach for calculating the stress field of the fiber-reinforced composites is developed to improve the work of Theocaris et al. (1985) in this paper. This approach considers that the main factor affecting the stress field of composites is the existence of interphase between fiber and matrix, which possesses different Young’s modulus than those of the constituent phase. A parabolic law is adopted for the variation of Young’s modulus of graded interphase, versus the polar radius from fiber to matrix, while the Poisson’s ratio of the interphase is assumed as constant. Space axisymmetric model is applied to the Representative Volume Element (RVE) of the fiber-reinforced composites to evaluate stress field of the composites. Also, the effective longitudinal modulus of the fiber-reinforced composite can be obtained.

Abstract: The residual stresses induced in functionally graded medium (FGM) with inhomogeneity cooling down from the processing temperature are determined with concentric cylinder model and analytical solutions of the inhomogeneous governing equations for displacement components. The analytical solutions derived here are general for power-law variations of the elastic moduli of the FGM. With a power exponent, analytical expressions for the residual stresses of FGM with inhomogeneity can be obtained. By changing the power exponent and the coefficient of the power terms, the solutions obtained here could be applied to different properties of FGM with inhomogeneity. The results show that the huge difference exists between FGM with inhomogeneity and homogeneous medium with inhomogeneity. The variations of FGM and inhomogeneity size have a great deal of effect on the residual stresses in FGM.