功能梯度材料

介绍了功能梯度材料的提出，开发流程，研究现状，对于当前功能梯度材料的设计过程，制备方法，性能评价方法和实验手段进行了详细叙述，提出了功能梯度材料应进一步发展的方向。     

功能梯度材料热应力研究进展

梯度功能材料的热应力问题贯穿梯度功能材料设计、制备、性能评价及应用整个研究领域,其中,热传导问题是热应力研究基础。介绍了梯度功能材料的概念及热传导和热应力问题的研究背景,重点分析了梯度功能材料热传导和热应力问题在数学模型、物性参数模型、解析方法、数值方法等方面的国内外研究进展,并展望进一步研究方向。     

Non-Local Theory Solution for an Anti-Plane Shear Permeable Crack in Functionally Graded Piezoelectric Materials

In this paper, the non-local theory solution of a Griffith crack in functionally graded piezoelectric materials under the anti-plane shear loading is obtained for the permeable electric boundary conditions, in which the material properties vary exponentially with coordinate parallel to the crack. The present problem can be solved by using the Fourier transform and the technique of dual integral equation, in which the unknown variable is the jump of displacement across the crack surfaces, not the dislocation density function. To solve the dual integral equations, the jump of the displacement across the crack surfaces is directly expanded in a series of Jacobi polynomials. From the solution of the present paper, it is found that no stress and electric displacement singularities are present near the crack tips. The stress fields are finite near the crack tips, thus allows us to use the maximum stress as a fracture criterion. The finite stresses and the electric displacements at the crack tips depend on the crack length, the functionally graded parameter and the lattice parameter of the materials, respectively. On the other hand, the angular variations of the strain energy density function are examined to associate their stationary value with locations of possible fracture initiation.     

Simulation of Crack Propagation in Functionally Graded Materials Under Mixed-Mode and Non-Proportional Loading

Automatic simulation of crack propagation in homogeneous and functionally graded materials is performed by means of a remeshing algorithm in conjunction with the finite element method. The crack propagation is performed under mixed-mode and non-proportional loading. Each step of crack growth simulation consists of calculation of mixed-mode stress intensity factors by means of a novel formulation of the interaction integral method, determination of crack growth direction based on a specific fracture criterion, and local automatic remeshing along the crack path. The present approach requires a user-defined crack increment at the beginning of the simulation. Crack trajectories obtained by the present numerical simulation are compared with available experimental results.     

A Moving Mode-III Crack in a Functionally Graded Piezoelectric Strip

In this paper, the problem of a functionally graded piezoelectric strip with a constant-velocity Yoffe-type moving crack is considered. By using the Fourier transforms, the problem is first reduced to dual integral equations and then into Fredholm integral equations of the second kind. The electroelastic field near the crack tip is obtained for electrical impermeable boundary conditions and electrical permeable boundary conditions, respectively. The results obtained show that the gradient of the material properties can increase or decrease the magnitudes of the stress intensity factors, and the velocity can disturb the stress distribution near the crack tip.     

玻璃-氧化铝功能梯度材料的研究进展

综述了国内外玻璃-氧化铝功能梯度材料的最新进展,详细总结和分析了国外该系材料的制备技术、组成、结构及性能以及国内通过湿法成形制备的材料的烧结行为及机理.国外主要通过渗滤和等离子喷涂2种方法制备该系材料,已经证明,该系材料弹性性能呈梯度变化,能有效抑制Hertzian锥形裂纹生成.与国外等离子喷涂方法制备的材料相比,湿法成形制备的材料不存在分层,无明显的界面问题.已经证明,氧化铝的含量对于该系材料的烧结行为有决定性影响,能够改变基体的烧结机理、抗收缩性能及裂纹扩展行为.最后,阐述了国内外的差距并展望了玻璃-氧化铝功能梯度材料的发展趋势.     

A Review of Dynamic Fracture Studies in Functionally Graded Materials

Abstract:  This article presents a review of dynamic fracture studies on functionally graded materials. A brief literature review on the fracture mechanics of graded materials is presented first. This is followed by a discussion on the higher-order asymptotic analysis of the transient elastic field surrounding the tip of a dynamically growing crack in a functionally graded material. A comprehensive experimental study of dynamic crack growth in model functionally graded material using the optical method of reflection photoelasticity and high-speed photography is then presented. The results are analysed to establish a generalised relationship between the crack velocity and the dynamic mode-I stress intensity factor (SIF). This relationship is found to be unique and is distinctly different from that previously established for the matrix material (polyester). Finally, an innovative experimental procedure is used to demonstrate the necessity of employing a fully transient stress-field representation in the analysis of optical data for an accurate prediction of the dynamic SIF history.     

Evaluation of Thermophysical Properties of Functionally Graded Materials

In this work, by considering four-layered functionally graded material (FGM) specimens of Cu/Ni and PSZ/NiCrAlY, the transient characteristics and homogeneity of heat conduction media have been studied. The thermal diffusivities of the considered specimens have been measured by the laser flash method. As the temperature response curve of a FGM is very similar to that of a homogeneous material, it is difficult to distinguish a FGM from a homogeneous material by the shape of the temperature responses. Therefore, the thermal diffusivity obtained from the half-time method is usually taken as the corresponding value of the thermal diffusivity. The apparent thermal conductivity, obtained from the corresponding value of the thermal diffusivity and the average of the heat capacity of each layer, is different from the effective thermal conductivity, obtained from the sum of the heat resistances of each layer. As the values of the heat capacity of materials exist over a certain range, and the heat capacity distribution can be predicted when the materials in a FGM are known, the amount of error that will be caused when the effective thermal conductivity is replaced by the apparent value can be determined. Also, the heterogeneity of a FGM, based on an evaluation of thermophysical properties, has been discussed.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui,P. R. China.     

Crack Spacing Effect on the Brittle Fracture Characteristics of Semi-infinite Functionally Graded Materials with Periodic Edge Cracks

The effect of crack spacing on the brittle fracture characteristics of a semi-infinite functionally graded material (FGM) with periodic edge cracks is discussed. The incompatible eigenstrain induced in the material due to mismatch in the coefficients of thermal expansion is considered in the analysis. The nonhomogeneity of the material is simulated by an equivalent eigenstrain, whereby the problem is reduced to that of a cracked homogeneous material with incompatible and equivalent eigenstrains. A method is then formulated to calculate the stress intensity factor of periodic edge cracks in such a semi-infinite homogeneous medium and applied to calculate apparent fracture toughness of a semi-infinite FGM from its prescribed composition profile. Inverse calculation is also carried out to compute composition profile from prescribed apparent fracture toughness of the semi-infinite FGM. Numerical calculations are carried out for semi-infinite TiC/Al₂O₃ FGM and the results are shown in the figures.     

Metallic Functionally Graded Materials:A Specific Class of Advanced Composites

<正>Functionally graded materials,including their characterization,properties and production methods are a new rapidly developing field of materials science.The aims of this review are to systematize the basic production techniques for manufacturing functionally graded materials.Attention is paid to the principles for obtaining graded structure mainly in the metal based functionally graded materials.Several unpublished results obtained by the authors have been discussed briefly.Experimental methods and theoretical analysis for qualitative and quantitative estimation of graded properties have also been presented.The article can be useful for people who work in the field of functionally graded structures and materials,and who need a compact informative review of recent experimental and theoretical activity in this area.     

梯度热电材料的研究进展

热电材料梯度化是在保证各组分单一材料的热电性能的基础上,拓宽其应用温度范围,使各组分材料都能工作在最佳温区,以确保热电材料在一定的工作温度范围内具有较高的ZT值,保证其高的热电转换效率.介绍了热电材料的研究基础及其梯度化设计,对梯度热电材料在国内外的研究进展进行了综述并对未来的研究趋势进行了展望.     

流延法制备梯度功能材料的研究进展

简要介绍了梯度功能材料的产牛背景和发展历程,综述了梯度功能材料的制备方法的原理及优缺点.重点阐述了梯度功能材料的流延法制备及流延法制备梯度功能材料的国内外的研究动态和进展.     

Impact Energy of Functionally Graded Steels with Crack Divider Configuration

Functionally graded steels were produced via electroslag remelting process using the primary electrodes of plain carbon and austenitic stainless steels. Charpy impact energy of as-prepared specimens was measured in the form of crack divider. The obtained results show that the impact energy of the specimens depends on the type and the volume fraction of the present phases. Based on the rule of mixtures, a mathematical model, which correlates the impact energy of functionally graded steels to the impact energ...     

梯度结构热电材料的研究动态

为了获得高的热电能量转换效率,可以把不同单体联接制成多段热电装置形成梯度结构(FGM),能有效扩大工作温度区间;同时又可以使每段材料工作在其最佳温度范围内,获得最佳的热电优值,有效提高热电转换效率.概述了梯度结构热电材料的设计与研究现状,并简要介绍了梯度结构中的界面稳定性和性能表征.     

Alumina/Ce-Tzp Functionally Graded Materials by Electrophoretic Deposition

Cylindrical Al2O3/Ce-TZP functionally graded composites were fabricated by electrophoretic deposition and pressureless sintering in air. A continuous change in composition was realized by changing the composition of the suspension during deposition. In order to achieve full densification, a temperature above 1550℃ was necessary. The resultant FGM cylinder with a diameter of 5.6 mm shows the following structure: a central hole with a diameter less than 0.5 mm, a tough Ce-ZrO2 core with a diameter of about 3 mm, a gradient layer of about 1 mm, and a hard Al2O3-rich surface layer. The Ce-ZrO2 core has a Vickers hardness between 10and 11 GPa and an excellent toughness (＞10 MPa√m). In the gradient layer, hardness and toughness vary continuously along the radius. The surface layer has a hardness of 15.5 GPa and a modest toughness of 2.5MPa√m.     

Numerical Calculation of Stress Intensity Factors in Functionally Graded Materials

The finite element method is studied for its use in cracked and uncracked plates made of functionally graded materials. The material property variation is discretized by assigning different homogeneous elastic properties to each element. Finite Element results are compared to existing analytical results and the effect of mesh size is discussed. Stress intensity factors are calculated for an edge-cracked plate using both the strain energy release rate and the J-contour integral. The contour dependence of J in an inhomogeneous material is discussed. An alternative, contour independent integral is calculated and it is shown numerically that , the strain energy release rate G, and the limit of J as approaches the crack tip (where is the contour of integration) are all approximately equal. A simple method, using a relatively coarse mesh, is introduced to calculate the stress intensity factors directly from classical J-integrals by obtaining lim_{#x0393; 0} J.     

含裂纹功能梯度材料梁结构的振动功率流特性分析

功能梯度材料(FGM)梁在工程中应用日益广泛,而梁中裂纹的存在改变了局部刚度等特性,使得功能梯度材料梁的振动和波传播特性发生改变。以含有张开型裂纹的功能梯度梁为对象分析其波传播和振动功率流特性。利用转动弹簧模型模拟裂纹,给出由裂纹引起的局部柔度表达式。建立无限长FGM欧拉梁结构的动力学方程,采用波动法结合梁的连续条件计算得到FGM欧拉梁的振动特性,对无缺陷梁和裂纹梁的输入功率流和传播功率流进行分析。讨论了材料梯度指数、激励频率、裂纹深度和裂纹位置等信息与输入功率流、传播功率流之间的关系,为基于振动功率流的裂纹FGM梁的损伤识别提供理论基础。     

梯度热电材料的优化设计及研究进展

将2种不同的单体材料连接起来,制备成梯度结构热电材料(FGTM),不仅能扩大材料的应用温区,而且能极大地提高材料的热电转换效率.介绍了梯度热电材料优化设计的理论基础及方法,综述了梯度热电材料的研究进展及应用前景.     

功能梯度材料的制备与应用进展

功能梯度材料(FGM)是由日本人首先提出的一种新型复合材料,从提出后到现在已经得到了深入的研究和广泛的应用.阐述了功能梯度材料的概念及其产生背景,重点评述了功能梯度材料各种制备技术的原理和特点,以及国内外在应用方面取得的各种成果,探讨了功能梯度材料的发展方向.     

Fracture Mechanics Analysis Model for Functionally Graded Materials with Arbitrarily Distributed Properties

Functionally Graded Materials (FGMs) have been developed as super-resistant materials for propulsion systems and airframe of space-planes in order to decrease thermal stresses and to increase the effect of protection from heat. It has been experimentally observed that surface cracking in FGMs is the most common failure mode of a metal-ceramic FGM when it is subjected to a thermal shock. Therefore, it is very important to consider the thermally induced fracture behaviors of FGMs. In this paper, a functionally graded material strip containing an embedded or a surface crack perpendicular to its boundaries is considered. The graded region is treated as a large number of single layers, with each layer being homogeneous material. The problem is reduced to an integral equation and is solved numerically. Unlike most of the existing researches, which considered only certain assumed material distributions, the method developed in this paper can be used to investigate functionally graded materials with arbitrarily varied material properties.