Genetic Algorithm for the Thermal Stresses Optimum Design ofFunctionally Gradient Material Plate

Based on the thermal stress distribution for functionally gradient material (FGM) plates, a Genetic Algorithm (GA) method for the thermal stresses optimum design of FGM plate with computer technologies is given. The minimum thermal stresses combination distribution for FGM is obtained.

Optimization design and residual thermal stress analysis of PDC functionally graded materials

The distribution of thermal stresses in functionally graded polycrystalline diamond compact (PDC) and in single coating of PDC are analyzed respectively by thermo-mechanical finite element analysis (FEA). It is shown that they each have a remarkable stress concentration at the edge of the interfaces. The diamond coatings usually suffer premature failure because of spallation, distortion or defects such as cracks near the interface due to these excessive residual stresses. Results showed that the axial tensile stress in FGM coating is reduced from 840 MPa to 229 MPa compared with single coating, and that the shear stress is reduced from 671 MPa to 471 MPa. Therefore, the single coating is more prone to spallation and cracking than the FGM coating. The effects of the volume compositional distribution factor (n) and the number of the graded layers (L) on the thermal stresses in FGM coating are also discussed respectively. Modelling results showed that the optimum value of the compositional distribution factor is 1.2, and that the best number of the graded layers is 6.

Electrical, Thermal, and Mechanical Properties of Cu/Ti3AlC2 Functional Gradient Materials Prepared by Low-temperature Spark Plasma Sintering

Cu/Ti3AlC2 composite and functional-gradient materials with excellent electrical conductivity and thermal conductivity as well as good flexural properties were prepared by low-temperature spark plasma sintering of Cu and Ti3AlC2 powder mixtures. The phase compositions of the materials were analyzed by X-ray diffraction, and their microstructure was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Further, the electrical conductivity, thermal conductivity, and flexural properties of the materials were tested. Results show that, for the composite materials, the resistivity rises from 0.75 × 10^-7 Ω·m only to 1.32 × 10^-7 Ω·m and the thermal diffusivity reduces from 82.5 mm^2/s simply to 39.8 mm^2/s, while the flexural strength improves from 412.9 MPa to 471.3 MPa, as the content of Ti3AlC2 is increased from 5 wt%to 25 wt%. Additionally, the functional-gradient materials sintered without interface between the layers exhibit good designability, and their overall electrical conductivity, thermal conductivity, and flexural strength are all higher than those of the corresponding uniform composite material.

Finite Element Analysis of Thermal Stresses in Ceramic/Metal Gradient Thermal Barrier Coatings

This paper studied the thermal stresses of ceramicl metal gradient thermal barrier coating which combines the conceptions of ceramic thermal barrier coating （TBC） and functionally gradient material （FGM）. Thermal stresses and residual thermal stresses were calculated by an ANSYS finite element analysis software. Negative thermal expansion coefficient method was proposed and element birth and death method was applied to analyze the residual thermal stresses which have non-uniform initial temperature field. The numerical results show a good agreement with the analytical results and the experimental results.

INFLUENCE OF TEMPERATURE-DEPENDENT PROPERTIES ON THERMAL STRESSES RESPONSE AND OPTIMUM DESIGN OF C/M FGMS UNDER THERMAL CYCLIC LOADING

The influence of temperature-dependent properties on thermal stresses response and optimum design of newly developed ceramic-metal functionally graded materials under cyclic thermal loaning and high temperature gradient environment is studied. The thermal conductivity of material is considered to be dependent on the temperature. In this paper, the thermal stresses response of the material is calculated rising a nonlinear finite element method. Emphasis is placed on the influence of temperature-dependent properties on the thermal stresses response characteristics, the thermal stresses relaxation property and the thermal stresses history under the different graded compositional distributions and different heat flux magnitudes. Through tile analysis. it is suggested that the influence of temperature-dependent properties can not be neglected In the thermal stresses response analysis and the optimum design process of the material must be based on the temperature-dependent thermo-elastic-plastic theory.

THERMAL STRESSES ANALYSIS OF CERAMIC/METAL FUNCTIONALLY GRADIENT MATERIAL CYLINDER

In this paper, the composite cylinder system is made of three layers: metal, functionally gradient material (FGM) and ceramics is studied. The formulas of the steady_state temperature distribution and the associate thermal stress distribution in the cylinder are obtained. For ZrO 2/Ti_6Al_4V system, the distribution of steady_state temperature and thermal stress are calculated and discussed.

Experimental analysis for thermal stress in functionallygradient material

Studies of displacement fields and stress concentration, due to uniform temperature change in a functionally gradient material (FGM) specimen and bimaterial (NFGM) specimen, have been made by Moire interferometry and finite element method. Results show that the thermal stresses concentration has been effectively reduced, and the distribution of the thermal deformations and thermal strains have also been relaxed and improved by transition layer of FGM.

MICROSTRUCTURE AND THERMAL STRESS RELAXATION OF ZrO_2－Ni FUNCTIONALLY GRADED MATERIAL

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Relationship Between Thermal Shock Behavior and Cutting Performance of a Functionally Gradient Ceramic Tool

Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in this paper, according to which an Al 2O 3-TiC functionally gradient ceramic tool material FG-1 was synthesized by powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al 2O 3-TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al 2O 3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shock resistance. The experimental results were supported by the calculation of transient thermal stress field. The cutting performance of the Al 2O 3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning the cylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al 2O 3-TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.

THERMAL STRESSES RELAXATION DESIGN OF Ni/NiFe_(2)O_(4) SYSTEM FUNCTIONALLY GRADED CERMET INERT ANODE

The thermal stresses relaxation of Ni/NiFe2O4 system functionally graded cermet inert anode for aluminum electrolysis was optimally designed. The transient thermal stresses of the inert anode under complex boundary condition during high-temp （955℃） electrolysis were calculated using the finite-element software ANSYS, the influence of different parameters on the distribution of the thermal stresses were analyzed. The results showed that, during the process of thermal shock, the thermal hoop tensile stress on the surface of the anode is very large, which is possibly the major cause of anode crack; when the radius of the anode is between 0.05-0.15m, a range that can be realized by recent manufacturing technology, the optimum composition distribution exponent p is 0.25; The hoop tensile stresses reduce with the decrease of anode scale and also decrease with the decrease of the convection coefficient between the electrolyte and the anode.

COUPLED THERMAL/MECHANICAL ANALYSIS FOR THE FRACTURE OF FUNCTIONALLY GRADED MATERIALS UNDER TRANSIENT THERMAL LOADING

A comprehensive treatment of fracture of functionally gradedmaterials (FGMs) is provided. It is assumed that the materialproperties depend only on the coordinate perpendicular to the cracksurface And vary continuously along the crack faces. By using alaminated composite plate model to simulate the ma- Terialnon-homogeneity, an algorithm for solving the system based on Laplacetransform and Fourier transform Techniques is presented. Unlikeearlier studies that considered certain assumed propertydistributions and a Single crack problem, the current investigationstudies multiple crack problem in the FGMs with arbitrarily Varyingmaterial properties. Transient thermal stresses are presented.

ANTI-PLANE SHEAR CRACK IN A FUNCTIONALLY GRADIENT PIEZOELECTRIC MATERIAL

The main objective of this paper is to study the singular natureof the crack-tip stress and electric displacement field in afunctionally gradient piezoelectric medium having materialcoefficients with a discontinuous derivative. The problem isconsidered for the simplest possible loading and geometry, namely,the anti-plane shear stress and electric displacement in -plane oftwo bonded half spaces in which the crack is parallel to theinterface.

ANTI-PLANE FRACTURE ANALYSIS OF FUNCTIONALLY GRADIENT MATERIAL INFINITE STRIP WITH FINITE WIDTH

The special case of a crack under mode Ⅲ conditions was treated, lying parallel to the edges of an infinite strip with finite width and with the shear modulus varying exponentially perpendicular to the edges. By using Fourier transforms the problem was formulated in terms of a singular integral equation. It was numerically solved by representing the unknown dislocation density by a truncated series of Chebyshev polynomials leading to a linear system of equations. The stress intensity factor （SIF） results were discussed with respect to the influences of different geometric parameters and the strength of the non-homogeneity. It was indicated that the SIF increases with the increase of the crack length and decreases with the increase of the rigidity of the material in the vicinity of crack. The SIF of narrow strip is very sensitive to the change of the non-homogeneity parameter and its variation is complicated. With the increase of the non-homogeneity parameter, the stress intensity factor may increase, decrease or keep constant, which is mainly determined by the strip width and the relative crack location. If the crack is located at the midline of the strip or if the strip is wide, the stress intensity factor is not sensitive to the material non-homogeneity parameter.

Method of lines for functionally gradient materials

The method of lines(MOL) for solving the problems of functionally gradient materials(FGMs) was studied. Navier’s equations for FGMs were derived, and were semi-discretized into a system of ordinary differential (equations(ODEs)) defined on discrete lines with the finite difference. By solving the system of ODEs, the solutions to the problem can be obtained. An example of three-point bending was given to demonstrate the application of MOL for a crack problem in the FGM. The computational results show that the more accurate results can be obtained with less computational time and resources. The obvious difficulties of numerical method for crack problems in FGMs, such as the effect of material nonhomogeneity and the existence of high gradient stress and strain near a crack tip, can be overcome without additional consideration if this method is adopted.

Design of DLC/Titanium Alloy Bio-Functionally Gradient Coat

The material design is used to direct the magnetron cosputtering process. At first, according to the particularity of functionally gradient coat (FGC) the thermal elastic stress analysis for FGC was carried out based on the plane stress hypothesis. It is obtained that the peak value of plane thermal stress within FGC is only determined by the physical properties of materials of FGC and substrate, the composition distribution coefficient only influences the distribution and trend of plane thermal stress. And the plane thermal stress criterion for design of FGC was presented. Then the plane thermal stress of diamond like carbon/titanium alloy FGC was calculated.

Analytical solution for functionally graded anisotropic cantilever beam under thermal and uniformly distributed load

The bending problem of a functionally graded anisotropic cantilever beam subjected to thermal and uniformly dis-tributed load is investigated,with material parameters being arbitrary functions of the thickness coordinate. The heat conduction problem is treated as a 1D problem through the thickness. Based on the elementary formulations for plane stress problem,the stress function is assumed to be in the form of polynomial of the longitudinal coordinate variable,from which the stresses can be derived. The stress function is then determined completely with the compatibility equation and boundary conditions. A practical example is presented to show the application of the method.

THERMAL FRACTURE OF FUNCTIONALLY GRADED PLATE WITH PARALLEL SURFACE CRACKS

This work examines the fracture behavior of a functionally graded material （FGM） plate containing parallel surface cracks with alternating lengths subjected to a thermal shock. The thermal stress intensity factors （TSIFs） at the tips of long and short cracks are calculated using a singular integral equation technique. The critical thermal shock △Tc that causes crack initiation is calculated using a stress intensity factor criterion. Numerical examples of TSIFs and △Tc for an Al2O3/Si3N4 FGM plate are presented to illustrate the effects of thermal property gradation, crack spacing and crack length ratio on the TSIFs and △Tc. It is found that for a given crack length ratio, the TSIFs at the tips of both long and short cracks can be reduced significantly and △Tc can be enhanced by introducing appropriate material gradation. The TSIFs also decrease dramatically with a decrease in crack spacing. The TSIF at the tips of short cracks may be higher than that for the long cracks under certain crack geometry conditions. Hence, the short cracks instead of long cracks may first start to grow under the thermal shock loading.

功能梯度复合材料的制备及隔热性能模拟研究

基于航空航天热防护技术对多功能隔热材料的需求,制备了由力学缓冲层、高温隔热层和核心隔热层构成的功能梯度复合材料,材料应力适应性强、耐温性高、隔热性能优异。通过模拟计算的方法对复合材料的隔热性能进行研究,结果表明,30mm厚的复合材料在1000℃、1000s的热载荷下隔热性能优异,各功能层厚度影响复合材料的传热背温。随着力学缓冲层/高温隔热层相对厚度的增大,复合材料背温和核心隔热层热面温度均增大,由于核心隔热层耐温极限的限制,力学缓冲层厚度最大为12mm,此时复合材料背温为26.10℃。力学缓冲层/核心隔热层、高温隔热层/核心隔热层相对厚度增大时,复合材料背温增大,核心隔热层热面温度减小,力学缓冲层的厚度最小为6mm,此时复合材料背温为20.21℃,高温隔热层的厚度最小为10mm,此时复合材料背温为22.58℃。

功能梯度阳极固体氧化物燃料电池热应力数值模拟研究

固体氧化物燃料电池(SOFC)各部件间的材料属性差异导致电池在制造和运行过程中应力过高,使用功能梯度材料电极可以减小SOFC的残余应力和热应力。本研究基于COMSOL Multiphysics 6.0软件建立完整结构的SOFC多物理场耦合模型,采用四种不同的分布曲线表征阳极材料的组分分布,对功能梯度阳极SOFC的残余应力和运行热应力进行数值计算。结果表明,电池在制备过程中,使用功能梯度材料能显著减小阳极所受的拉应力,该现象在常温下更加明显。二次曲线分布相比于无梯度分布,还原前阳极的室温最大拉应力减小47.69%,还原后室温最大拉应力减小35.74%。电池在运行过程中,电化学反应产热和气体对流换热导致入口和出口形成温差,金属框在出入口以及肋与电极接触的位置存在较大的应力集中现象。功能梯度材料可以显著减小阳极、金属框及电解质所受的最大应力,其中材料组分为二次曲线分布时效果最明显。本研究对设计制造SOFC具有潜在的理论意义和工程价值。

热环境下功能梯度梁力学特性分析

为探究轴向功能梯度梁在热环境下部分力学特性,利用Gauss-Lobatoo节点与Chebyshev多项式建立功能梯度梁的轴向变形场,通过Chebyshev谱方法和Lagrange方程推导其轴向变形场在热环境下的离散控制方程,结合投影矩阵法对模型施加边界条件,并利用均匀Timoshenko材料的对比结果进行辅助验证,分析得到系统固有频率在不同温度场、材料梯度指数、固支条件的变化情况,同时研究了结构的热屈曲温度.结果表明:在相同条件下,系统的各阶固有频率随着温度的升高呈下降趋势,且一阶频率的减小幅度最大.四阶固有频率减小幅度最小;悬臂梁的固有频率变化趋势与材料软化趋势相同,且三阶频率减小幅度较一二阶频率更明显;通过调节材料梯度指数可以优化结构的各阶固有频率;随着材料梯度指数的增大,材料的热屈曲温度不断提高,但对于不同的功能梯度材料,表现出不同的热屈曲温度变化趋势.本文研究可为功能梯度材料的研究与工程应用提供支撑.