Papers by Keyword: Microstructure Design

Abstract: Automobile exhaust is one of the sources of PM2.5, which can merely be catalytically decomposed by a "post-treatment" three-way catalytic device at present. Afront-treatment device based on rare earth-alumina nanocomposite in gasoline was innovatively introduced. nanoalumina and rare earth elements are function as the backbone and carrier, respectively. Microscopic molecular assembly and catalytic mechanism were studied to synthesize metastable ordered mesoporous with high degree of aggregation. Mesh filter of rare earth-alumina nanocatalytic composite with self-sustained release function is formed by sintering, which can be solidified in an automotive air intake system. Results show that rare earth-aluminum nanocomposite contributes to catalytic combustion and makes combustion more complete. Moreover, it has a better effect of reducing PM2.5 than a "post-treatment" device in terms of catalytic effect.

Abstract: The microstructure design satisfying the mass constraint can reduce the structure weight more directly and effectively in comparison with the volume constraint. This paper is devoted to the topology optimization of microstructures with multiphase materials under the mass upper limitation constraint for maximizing the equivalent elastic tensors and their combinations. Firstly, the strain energy method is applied to compute the effective elastic properties of microstructures. In order to make sure that the formulation of mass constraint is linear with separable design variables, DMO (Discrete Material Optimization) model is adopted for the element density interpolation. Therefore, this optimization problem can be solved efficiently by means of mathematical programming approaches, especially the convex programming methods. Besides, the filtering technique is adopted to avoid the checkerboard pattern. There are two categories of numerical examples. In the first category, the modulus and the stiffness ratio of the solid material phase 1 are smaller than the solid material phase 2. In the second category, the modulus of the solid material phase 1 is still smaller than the solid material phase 2, but its stiffness ratio is bigger than the solid material phase 2.

Abstract: In this paper, the microstructures with extreme properties are designed through the generalized shape optimization, which is implemented with the help of the smooth curves representation of the level set description and the numerical analyses of the eXtended Finite Element Method (X-FEM) with the fixed mesh work. The parameters of basic level set features are defined as the design variables. To calculate the given effective computation of microstructures, the energy method and homogenization method are physically identical. But the energy method is advantageous in computing efficiency and numerical implementation. Combining with the CONLIN algorithm, the periodic microstructures with the maximum elastic properties are obtained with the flexibility of handling the topological changes and solid-void boundaries. Numerical examples show the great interests in the microstructure design with the level set method and X-FEM.

Abstract: Inoculation is the most common grain refining technique during metal/alloy castings. However, only a small fraction, typically 1~2%, of inoculants serve as nucleation sites while most of them do not participate in the nucleation event and hence they are usually termed ‘inactive’ inoculants. But ‘inactive’ does not mean ‘useless’. Our recent studies revealed some extra merits of these ‘inactive’ particles in Mg-Al-Y cast alloys. The current results represent a new approach to microstructure design through manipulation of inoculated particles during castings.

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: For steel with combination of high strength (~2000MPa) and toughness, along with low cost, the designed structure should be low-temperature tempered, fine lath martensite with high density of dislocation, coated by film of austenite with considerable thickness and distributed with fine ε (η) or (and) complex carbide. Correspondently, the steel should contain less than 0.5 (wt%) of carbon, certain amount of alloying elements for lowering Ms, such as Ni, Mo and (or) Mn, carbide forming element, e.g. Nb, as well as Si or (and) Al, the element depressing the formation of cementite, the brittle phase in high strength steel. The heat treatment process is suggested as: austenitizing at a temperature slightly above Ac3, followed by quenching at Ms-Mf, partitioning either at quenching temperature or at slightly above Ms for a few minutes, cooling down to room temperature and tempering at low temperature about half an hour.

Abstract: Microstructure Sensitive Design (MSD) offers a rigorous mathematical framework for representing the relevant statistical details of the material microstructure for a given design problem, and for developing quantitative invertible relationships between these microstructure representations and the macroscale properties of interest. The methodology makes extensive use of Fourier representations of the distribution functions representing the material internal structure and existing homogenization theories. In this paper, we describe the application of the MSD framework to fcc polycrystals with a specific focus on the crystallographic texture as the microstructure design variable. The advantages of the MSD approach are demonstrated through a number of elastic-plastic property closures for cubic metals.

Abstract: A mathematical framework called Microstructure Sensitive Design (MSD) has been developed recently to solve inverse problems of materials design, where the goal is to identify the class of microstructures that are predicted to satisfy a set of designer specified objectives and constraints [1]. This paper demonstrates the application of the MSD framework to a specific case study involving mechanical design. Processing solutions to obtain one of the elements of the desired class of textures are also explored within the same framework.