Papers by Keyword: Functionally Graded Material (FGM)

Abstract: The propagation behavior of Love waves in a functionally graded material layered half-space with initial stress is taken into account. The Wentzel-Kramers-Brillouin (WKB) asymptotic technique is adopted for the theoretical derivations. The analytical solutions are obtained for the dispersion relations and the distributions of mechanical displacement and stress along thickness direction in the layered structure. Firstly, these solutions are used to study effects of the initial stress on the dispersion relations and phase velocities, then influences of the initial stress on the distributions of mechanical displacement and shear stresses along thickness direction are discussed in detail. Numerical results obtained indicate that the phase velocity of Love wave increases with the increase of the magnitude of the initial tensile stress, while decreases with the increase of the magnitude of the initial compression stress. The effects on the dispersion relations of the Love wave propagation are negligible as the magnitudes of the initial stress are less than 100MPa. Some other results are shown for distributions of field quantities along thickness direction. The results obtained are not only meaningful for the design of functionally graded structures with high performance but also effective for the evaluation of residual stress distribution in the layered structures.

Abstract: Idea of functionally gradient material (FGM) theory was used to the design of ceramic nozzle. The purpose was to increase the erosion wear resistance at the entrance of the nozzle in dry sand blasting processes. The SiC/(W,Ti)C gradient ceramic nozzles fabricated by conventional hot pressing. The erosion behavior of the SiC/(W,Ti)C gradient ceramic nozzles were investigated in comparison with the common homologous ceramic nozzles. The experimental results have shown that the ceramic nozzles with a gradient structure have superior erosion wear resistance to that of the common homologous ceramic nozzles under the same test conditions. It was shown that the mechanical properties of the gradient ceramic nozzle materials were greatly improved in comparison with that of the common homologous nozzles. The surface Vickers hardness and indentation fracture toughness of gradient ceramic nozzle were greatly improved compared with that of the common homologous nozzles. Therefore, it is indicated that gradient structures in ceramic nozzles is an effective way to improve the erosion wear resistance of the common homologous nozzles.

Abstract: Ceramic composite armour in general utilises a front layer of dense ceramic, typically backed by a second layer of metal. Thereby creating a sharp interface that is the weakest link within the material system and would result in cracking of the ceramic prematurely and hence not able to provide the requisite protection. One promising possibility has been found is the use of functionally gradient materials as armour materials. In such materials, the high hardness of ceramics is combined with the ductility of metals. Laboratory scale experiments were being performed to exhibit the potential of this material in terms of physical and mechanical properties. A comparison was made with the current ceramic armour system and it was found that the new material system had better ballistic properties.

Abstract: Using the processes of field-activated and pressure-assisted combustion synthesis (FAPACS), FGM materials (FGMs) were prepared under the conditions of field-assisted and the hot-press. The microstructure and the phase composition of the interface of the graded materials were investigated and the results showed that the metallurgical joining layer was formed in the interfaces of the (TiB2)pNi/Ni3Al/405 steel. The mechanical characterization of the gradient materials showed that the composition and the micro-hardness of the gradient material were gradient distributed, and its surface Rockwell hardness and wear resistance are better than that of hardened 20Cr steel.

Abstract: Multilayered mullite/Mo cermet functionally gradient material (FGM) was fabricated through a powder stacking process and sintering in vacuum up to 1500°C. The composition distribution, microstructure and microhardness of the FGM were analyzed. The results indicated that the mullite/Mo FGM was well densified with composite graded distribution and there was no new phase appeared. The microhardness of the FGM increase from 467HV to 1543HV, the density from 2.919 to 7.106 g/cm3 as the content of mullite increase from 20% to 80%. The relative density exceeded 90% as the content of mullite reached 80%. Thermal shock test showed that the cracks passed through the joint without deflection.

Abstract: The fabrication of electrodes is one of the key techniques in constructing thermoelectric elements for the practical applications. In this work, the commercial active brazing alloy “Incusil-ABA” was used for the joining of CoSb3 to the Cu surface of the graded electrode materials (Cu/AlN/Cu) by using spark plasma sintering (SPS). The bonding was performed in vacuum at temperatures 500°C for 10min. The brazing and diffusion bonding process were investigated by analyzing the crystal structure and microstructure of the bonding interface using X-ray diffraction and scanning electron microscopy, and its composition distribution was also analyzed by energy dispersive X-ray.

Abstract: TZP/SUS304 functionally graded material (FGM) was developed by slip casting. Microscopic observations demonstrated that the chemical composition and microstructure of TZP/SUS FGM distributed gradually in stepwise way, eliminating the macroscopic ceramic/metal interface occurred in traditional ceramic/metal joint. Each interface of layers connected well without evident defects, and the mechanical properties of TZP/SUS system strongly depended on constitutional variation.

Abstract: In this paper, the transient heat conduction and transient thermal stresses in an infinite plate with double-sided functionally graded coatings (FGM coatings) under the convective boundary condition are investigated. The thermo-physical properties of the two symmetrical FGM coatings are assumed to have distributions of power forms along the thickness direction of the plate, the effects of which on the thermal shock resistance of the FGM coated plate are analyzed via numerical calculations. And consequently some design rules for the double-sided FGM coatings are put forward, which provide a guidance for the development of FGM coated cutting tools.

Abstract: Using the development tool C++ Builder and adopting object oriented programming method, the ceramic/metal gradient thermal barrier coating design software (CCDS) is developed according to software engineering criterion. The CCDS, which has user-friendly interface, is composed of three functional modules: preprocess module, analysis module and post process module. In addition, this software is attached with an optimal design module and an expert module. The calculation and design of the ceramic/metal gradient thermal barrier coating can be carried out by the CCDS, and the numerical results show good agreement with the analytical results.

Abstract: This study systemically presents an inverse homogenization method in the design of functional gradient materials, which gained substantial attention recently due to their layer-by-layer defined physical properties. Each layer of these materials is unilaterally constructed by periodically extended microstructural elements (namely base cells), whose effective properties can be decided by the homogenization theory in accordance with the material distribution within the base cell. The design objective is to minimize the summation of the least squares of the difference between corresponded entries in target and effective elasticity tensors. The method of moving asymptote drives the minimization of this positive objective function, which forces the effective values approach to the targets as closely as possible. The sensitivity of the effective elasticity tensors with respect to the design variables is derived from the adjoint variable method and it guides the minimization algorithm efficiently. To guarantee the connectivity between adjacent layers, non-design domains occupied by solid materials acting as connective bars are fixed in the design of base cells. Furthermore, nonlinear diffusion technique is introduced to avoid checkerboard patterns and blur boundaries in the microstructures. A series of two-dimensional examples targeted for the elasticity tensors with same extreme Poisson ratios but different densities in each layer are illustrated to highlight the computational material design procedure.