Papers by Author: Moe A. Khaleel

Abstract: Statistical continuum approach is used to predict effective conductivity of anisotropic random porous heterogeneous media using two-point correlation functions. Probability functions play a critical role in describing the statistical distribution of different constituents in a heterogeneous media. In this study a 3-dimensional two-point correlation function is utilized to characterize the anisotropic porous media of a Cathode materials to incorporate all the details of the microstructure. These correlation functions are then linked to the effective properties using homogenization relations. An anisotropioc Green’s function solution is used to solve the set of field equations. Examples in this study demonstrated how the model captured the anisotropy in effective conductivity of the random heterogeneous media. Predicted results showed the influence of microstructure on the effective conductivity tensor.

Abstract: In this work, we propose a comparison between two different approaches for the simulation of the large deformation response and crystallographic texture evolution in polycrystals. The first approach is the well-know self-consistent scheme. For this, we used the Visco-Plastic- Self-Consistent (VPSC) approach. The second approach is based on a recently developed intermediate modeling. In a first part of this paper, we present the VPSC model. In a second part, we define the intermediate linear modeling which is based on a linear combination of Taylor and Sachs models using a weight parameter. For the comparison of these two approaches, we present different results in the case of uniaxial tests for an FCC polycrystal for different values of the weight parameter for the intermediate modeling and for different formulations of the macroscopic moduli in the self-consistent model.

Abstract: The arrangement of ceramic layers in laminated structures is an interesting way to enhance the flaw tolerance of brittle ceramic materials. The interfaces are expected to deflect cracks, increasing the fracture energy of the laminate compared to a monolithic material and thus raising the toughness. The target of this study is to predict the volume fraction of pores, in porous layers, required to cause crack deflection. Formulation of the fracture toughness and fracture energy as function of the material porosity is presented for random and ordered pores distribution. The effect of crack tip-flaws interaction is considered to estimate the pores volume fraction needed for crack deflection. In this work, dense and porous layers of NiO-YSZ material similar to the one used in the fuel cells technology are considered. The fracture energy of a porous material with an ordered distribution of pores shows a possibility of crack deflection at a porosity of 22.5%. However for a system with randomly distributed pores this possibility can be seen at 36% of porosity.