Functionally Graded Materials VIII

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Authors: Daniel T. Butler, Marek-Jerzy Pindera, Jacob Aboudi
Abstract: The Higher-Order Theory for Cylindrical Functionally Graded Materials is employed to investigate the effectiveness of thermal barrier coatings in mitigating deformation mechanisms in thrust cell liners leading to experimentally observed failure modes. The results indicate that under the employed thermo-mechanical loading histories coating thickness has a great impact on temperature and deformation fields within the cooling channel wall of a thrust cell liner, with thicker coatings producing more desirable temperature and deformation fields. Functional grading of metallic substrate and coating materials does not produce improvement in terms of overall thrust cell liner performance. Further, the application of grading is potentially detrimental due to likely roughening of the thrust cell liner wall in the combustion chamber as a result of local deformations around relatively coarse inclusions. The homogenized approach to analyzing the graded coating effectiveness is incapable of capturing these localized effects, leading to erroneous conclusions.
Authors: Glaucio H. Paulino, Emílio Carlos Nelli Silva
Abstract: The concept of functionally graded materials (FGMs) is closely related to the concept of topology optimization, which consists in a design method that seeks a continuum optimum material distribution in a design domain. Thus, in this work, topology optimization is applied to design FGM structures considering a minimum compliance criterion. The present approach applies the so-called “continuous topology optimization” formulation where a continuous change of material properties is considered inside the design domain by using the graded finite element concept. A new design is obtained where distribution of the graded material itself is considered in the design domain, and the material properties change in a certain direction according to a specified variation, leading to a structure with asymmetric stiffness properties.
Authors: Jian Ping Wang, Gang Chen, Peng Cheng Zhai
Abstract: This paper studies the optimization problem of composition distribution of functionally graded material (FGM) coating subjected to steady heat flux loading. The investigation object of the paper is an infinite plate substrate with FGM coating in the surface. The materials are heated at the ceramic surface (upside) with a steady high-intensity heat flux input, and cooled at the metal surface (underside) with flowing liquid nitrogen. The thermal stress distribution and the temperature distribution are obtained by formulation. For optimization, the design variables are the thickness of each interlayer and the volume fraction distribution of the coating. The objective function is the danger coefficient and the restricted condition is the total thickness of FGM plate and heat insulation coefficient. In the paper, three different optimization schemes are considered and compared. The µGA and related parameters are discussed in detail. Optimizing the thermal stress distribution and minimizing the danger coefficient are carried out by µGA. The optimization results of composition distribution are gained, and the results show the optimum composition distribution can distinctly reduce the danger coefficient.
Authors: Glaucio H. Paulino, Zheng Yu Zhang
Abstract: This paper presents a Cohesive Zone Model (CZM) approach for investigating dy- namic failure processes in homogeneous and Functionally Graded Materials (FGMs). The failure criterion is incorporated in the CZM using both a ßnite cohesive strength and work to fracture in the material description. A novel CZM for FGMs is explored and incorporated into a ßnite element framework. The material gradation is approximated at the element level using a graded element formulation. A numerical example is provided to demonstrate the eácacy of the CZM approach, in which the inàuence of the material gradation on the crack branching pattern is studied.
Authors: Li Sheng Liu, Qing Jie Zhang, Peng Cheng Zhai
Abstract: The reflected coefficient of functionally graded layer to waves is very important as the design of impact-resistant FGMs. In the paper, the Optimization problem of propagation characteristic of elastic wave in FGM has been investigated. The relation between the top layer’s stress and displacement and the bottom layer’s is deduced from elastic propagation equation as the incident wave is a plane and harmonic elastic stress wave, then the reflected coefficient of gradient layer is obtained, and the reflected coefficient is selected as object function of optimization. The thickness of each layer is selected as optimization design parameter. The conjugate gradient method is used to get the optimal results about gradient layers’ thickness.
Authors: Shin-ichiro Tsuru, Noriyuki Hayashi, Tomohiko Onoda, Yasushi Sakamoto, Masanori Hara
Abstract: A new numerical method to simulate the centrifugal process of fabricating functionally graded materials (FGMs) from solid-particles/viscous-matrix mixtures is proposed, and the simulation method was successfully applied to a practical fabrication process of FGM from an alumina-fillers/epoxy-resin mixture. Gradient profiles of dielectric constant of the resultant FGM were estimated by using the proposed method and compared with the experimental ones, resulting in reasonable agreement between them. Based on the numerical results, gradient pro- files of the number density and size of the dispersed fillers were confirmed, and contribution of the filler size toward the gradient in the packing fraction was demonstrated. It is concluded that the gradient in the filler distribution can be intentionally regulated by changing not only the centrifugal conditions, but also the size distribution of the fillers.
Authors: M. Rohde, O. Baldus, D. Dimitrova, S. Schreck
Abstract: Laser supported processes can be used to modify the electrical and thermal properties of ceramic substrates locally. These processes are characterised by a strong thermal interaction between the laser beam and the ceramic surface which leads to localised melting. During the dynamic melting process an additive material is injected into the melt pool in order to modify the physical properties. The heat and mass transfer during this dynamic melting and solidification process has been studied numerically in order to identify the dominant process parameters. Simulation tools based on a finite volume method have been developed to describe the heat transfer, fluid flow and the phase change during the melting and solidification of the ceramic. The results of the calculation have been validated against experimental results.
Authors: Zhi Guang Zhou, Lian Meng Zhang, Qiang Shen, Dao Ren Gong
Abstract: From the process of sedimentation the mathematical relationship between deposition volume and powder properties as well as sedimentation parameters was deduced in this paper. The relationship was expressed by using indirect method. Based on the formula, design model and prediction model were set up. The models can be used to design powder properties and predict the volume fraction of FGM. Programs to solve the models were developed in numerical methods. As examples, TiC-Ni system FGM were designed and predicted. The prediction results fit well with the design. Experiment of Mo-Ti system FGM was used to validate the prediction model.
Authors: Kazunari Shinagawa, Yasushi Hirashima
Abstract: During sintering of metal/ceramic functionally grade materials, cracks are often formed on the surface on the top ceramic layer due to the internal stress produced by mismatch shrinkage and warpage. The ways to reduce the internal stress are examined by using the finite element method as well as the plate theory for sintering. Uniaxial pressing, which gives the counter moment against the warping, can decrease the bending stress but only in the middle of the surface. Thinning the top layer is found to be effective in reducing the tensile stress on the surface when the sintering properties of some layers are modified appropriately. The suppression of the surface cracking in the improved graded powder compacts is confirmed by experiment.
Authors: Bao Sheng Zhang, Michael M. Gasik, A. Facchini, M. Pressacco, P. DallaPria, S. Posocco
Abstract: Computer-integrated safe design of FGM component for hip replacement prosthesis was presented based on principle of optimal stresses distribution in the FGM component. The goals were to create an FGM structure with reasonable compressive stresses on the surfaces (subjected to wear) and to keep them during the entire manufacturing cycle (sintering, machining, assembling and application). The residual stresses developed in the different parts of the composite were implemented into the subsequent process of the surface grinding and assembly to simulate properly the whole processing route to ensure optimal combination of the processing parameters.

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