Showing papers on "Functionally graded material published in 1997"

Functionally graded metals and metal-ceramic composites: Part 2 Thermomechanical behaviour

Abstract: Following a review of the processing of functionally graded metals and metal-ceramic composites in Part 1; this Part 2 of the two part series focuses on the thermomechanical behaviour. The paper begins with an overview of the fundamentals of thermoelastic and thermoplastic deformation in metal-ceramic composites. Various approaches, including the rule of mixture approximations, mean field theories, crystal plasticity models, discrete dislocation models, and continuum finite element formulations of the constitutive phases of the composites, are discussed, and the significance and limitations of these approaches are highlighted. Issues specific to the thermomechanical analyses of graded materials are then addressed. It is reasoned that the introduction of a new length scale to the problem due to compositional gradients inevitably calls for detailed micromechanical analyses of the size, shape, continuity, and spatial dispersions of the constituent phases of graded metal-ceramic composites. Models for...

Functionally graded materials synthesis via low vacuum directed vapor deposition

Abstract: The spatially distributed microstructures needed to implement many functionally graded material (FGM) designs are difficult to realize affordably with today's materials synthesis/processing technologies. To address this need, a new directed vapor deposition (DVD) technique has been developed and explored as a potential FGM synthesis tool. The technique exploits supersonic helium jets in combination with electron beam/resistive evaporation under low vacuum (10−3-10 Torr) conditions to atomistically spray deposit a wide variety of monolithic and composite materials. Two of the most important processing parameters (the carrier gas velocity and the deposition chamber pressure) that control deposition are identified, and their effect upon deposition efficiency for flat and fiber substrates is explored systematically. Under certain conditions, the DVD approach is found to deposit vapor onto fibers with a significantly higher efficiency than traditional high vacuum line-of-sight vapor deposition techniques. It can even deposit material onto surfaces that are not in the line-of-sight of the source. A computational fluid dynamics model has been used to interpret the experimental observations and to identify the role of carrier gas dynamics in controlling deposition efficiency and spatial distribution.

Characterization of functionally gradient epoxy/carbon fibre composite prepared under centrifugal force

Abstract: Centrifugal force was employed in order to induce a spatial gradient of fibre distribution in the epoxy/carbon fibre system. The gradient structure of the epoxy/carbon fibre composite can be controlled by varying the rotation time and the material parameters, such as fibre length, fibre content and matrix viscosity. The spatial gradient distribution of carbon fibres in an epoxy matrix was achieved by the combined mechanism of packing and settling. The mechanical properties of the functionally gradient epoxy/carbon fibre composite were also investigated. At the same content of carbon fibre, the flexural strength of the functionally gradient composite was higher than that of conventional isotropic composite.

Residual stress and thermal properties of zirconia/metal (nickel, stainless steel 304) functionally graded materials fabricated by hot pressing

Abstract: To analyse the residual stress and the thermal properties of functionally graded materials (FGMs), disc-type tetragonal zirconia polycrystal (TZP)/Ni- and TZP/stainless steel 304 (SUS304)-FGM were hot pressed, and compared with directly jointed materials (DJMs). The continuous interface and the microstructure of FGMs were characterized by electron probe microanalysis, wavelength dispersive spectrometry, optical microscopy and scanning electron microscopy. It has been verified that the defect-like cracks in FGMs are induced by the preferential shear stress and shown to cause fracture. These facts have corresponded well with the residual stress distribution analysed by the finite element method. The thermal diffusivity and the thermal conductivity of FGMs and DJMs were also measured by the laser flash technique. As a consequence, this work has described the interfacial stability, the residual stress release mechanism and the thermal protection characteristics of FGMs via a compositional gradient.

Bending strength of an AlAl3Ni functionally graded material

Abstract: The gradient of bending strength of an Al-Al3Ni functionally graded material (FGM) has been examined using 3-point bending tests. Specimens with rectangular cross-sections of 6 × 6 mm2 were machined from a thick-walled FGM tube such that the thickness direction of the specimen coincided with the radial direction of the tube. Thus the specimens had a graded composition of the A13Ni phase in the thickness direction. Four types of specimens characterized by four nominal volume fractions of the Al3Ni phase at the crack initiation plane, namely Vf= 0, 24, 49 and 53 vol%, were employed in the study. Fracture surfaces consisted of cleavage facets of the Al3Ni phase surrounded by dimples of the aluminum phase. Brittle fracture of Al3Ni dominated the fracture process of Al-Al3Ni FGM. Fracture strengths of the four types of specimens were plotted on the standard normal and Weibull probability paper. The trends of each data set exhibited good linearity, making it difficult to determine the differences in the fit between the two kinds of probability papers. Maximum average fracture stress of 156 MPa was obtained from the Vf= 24 vol% specimen, and decreased in the following order with specimen type: Vf= 24, 49, 53 and 0 vol%. Fracture strength of Al-Al3Ni FGM attained a maximum value of 160 MPa at Vf≈10 vol% and decreased with an increase in the A13Ni volume fraction due to the size effect that controls the strength of the brittle Al3Ni phase.

Stress Analysis In A Two Materials Joint With A Functionally Graded Material

Abstract: In this paper the stresses in a joint with a functionally graded material (FGM) are analyzed. In the middle of a joint with FGM the stresses have been calculated analytically by using the plate theory. The effect of the thickness of the FGM layer and the effect of the transition function form on the stresses in the joint is discussed. Near the free edges of the interface in a joint with FGM, the stresses are described analytically by using the Mellin transform method. Some examples are presented to show the good agreement of the stresses calculated from FEM and with the analytical description in a joint with graded material.

Evaluation of thermomechanical performance for thermal barrier type of sintered functionally graded materials

Abstract: Thermomechanical properties of metal/ceramic functionally graded materials were evaluated by a burner heating test using a H 2 /O 2 combustion flame, which simulated the real environment of the heated inner wall of a rocket combustor. Disk-shaped graded samples of a material combination of partially stabilized zirconia and stainless steel were used for the test, in which the ceramic surface of the sample was heated with a burner flame and the back surface was cooled with flowing water. The critical temperature of the first crack formation, which was always observed on the ceramic surface during cooling, was determined in the test. The stress distributions in the sample during heating and cooling cycles, calculated by the finite element method, show the generation of large compressive and tensile stresses during heating and cooling, respectively, which are attributed to the non-elastic deformation of the heated sample surface due to an excess compressive stress. The fracture mechanism in terms of crack formation and spalling in the FGMs is discussed on the basis of the stress distributions in addition to a fracture mechanics approach.

Orientation of Al_3Ti Platelets in Al-Al_3Ti Functionally Graded Material Manufactured by Centrifugal Method

Abstract: Al-Al 3 Ti functionally graded materials (FGMs) were manufactured by the centrifugal method with a commercial ingot of Al-5 mass% Ti master alloy. The alloy was melted at a liquid/solid coexisting temperature, at which Al 3 Ti remains as a solid, and then it was cast into a thick-walled ring. It was found that the Al-Al 3 Ti functionally graded material can be successfully fabricated by the centrifugal method. It was also found that the volume fraction of the Al 3 Ti can be increased by repetition of the centrifugal method. Since the shape of Al 3 Ti particles in a commercial alloy ingot is that of a platelet, the Al 3 Ti particles are arranged with their platelet planes nearly perpendicular to the radial direction. The orientation effects become stronger when the G number becomes larger. Although the final centrifugal casting was conducted under a very large centrifugal force for the specimen cast three times, the orientation effects were weaker than those in the specimen cast one time. From these observations, it is concluded that the origin of orientation of Al 3 Ti platelets can be attributed to the angular velocity gradient of the melt along the radial direction produced by the difference in the viscosity.

Application of poly(methylsilane) and Nicalon® polycarbosilane precursors as binders for metal/ceramic powders in preparation of functionally graded materials

Abstract: For the first time, ceramic precursors were applied in the powder metallurgy (P/M) preparation of Functionally Graded Materials (FGM). Two types of FGMs were prepared: Al/SiC for possible aerospace applications and Cu/SiC for dynamic seal applications. There are two main advantages of using ceramic precursors for P/M preparation of FGMs (1) avoidance of the commercially used debinding step and (2) shrinkage control of the individual layers of the composite.

Thermally induced stress waves in functionally graded materials with temperature-dependent material properties

Abstract: This article is concerned with the dynamic treatment of thermally induced stress waves in an infinite elastic plate subjected to impulsive electromagnetic radiation. The plate is assumed to be a functionally graded material (FGM), meaning that the material is composed of multiconstituents in ceramics and metals, the volume fractions of which distribute continuously inside the material. The mathematical problem is one of wave propagation in a typical nonhomogeneous material The radiation absorption is assumed to occur at a constant rate for the duration of the pulse and to diminish exponentially with distance from the surface of the plate, assuming negligible heat conduction. In treating problems, the nature of the stress-wave buildup in the plate is studied for the case of a temperature-dependent solid, that is, when material properties vary with temperature. The numerical procedure employs the characteristic method based on the integration of the governing equations along the characteristics. Numerical c...

Preparation and properties of polyimide/Cu functionally graded material

Abstract: A polymer/Cu functionally graded material (FGM) was prepared from thermosetting polyimide and Cu powders using a spark plasma system. These powders were consolidated at different temperatures. A FGM of Cu and polyimide was prepared under a graded temperature using a graphite die, the diameters of which were different at the top and bottom. A dense polyimide/Cu FGM was formed under the graded temperature. There were no cracks in the FGM prepared by stacking three graded layers. Thermal properties of the thin FGM were measured.

Application of an intermetallic compound Ti5Si3 to functionally graded materials

Abstract: Ti–Ti 5 Si 3 -functionally graded materials (FGMs) have successfully been fabricated by utilizing bonding through a eutectic reaction which occurs between Ti and Ti 5 Si 3 , where Ti 5 Si 3 was employed because of its high heat and oxidation resistance. The bonding by the eutectic reaction has been investigated to bond a plate of pure Ti and of Ti 5 Si 3 together. A compositionally and microstructurally graded region, where the volume fraction of Ti 5 Si 3 changes continuously, has been obtained between these plates after bonding at 1613 K. Subsequently, a similar method has been utilized to make coating on Ti plates and semi-round rods through the eutectic reaction with Ti 5 Si 3 powder. In this case, a similar compositionally and microstructurally graded region has been obtained. No macroscopic defects, including observable cracks, have been detected in these FGMs fabricated.

Al2O3/Y-TZP continuous functionally graded ceramics by filtration-sedimentation

Abstract: The filtration-sedimentation method is applied as an alternative route to obtain functionally graded ceramics (FGCs) without defined interfaces. Using this technique a fully dense Al2O3/Y-TZP continuous functionally graded ceramic has been obtained after sintering at 1550 °C. The concentration gradient shows a parabolic distribution of phases which depend on the starting slurry solid concentration.

An Analytical Solution to Transient Temperature Field in a Functionally Graded Material Plate by Piecewise-Linear Nonhomogeneity Approximation Method.

Abstract: An analytical solution is presented to the transient temperature field in a functionally graded material plate (FGM plate) heated at its surface. The FGM plate has arbitrary nonhomogeneities of thermal properties and temperature variation only through the thickness. The transient temperature field is determined by solving the nonhomogeneous heat conduction problem in a multilayered plate with piecewise-linear nonhomogeneous thermal conductivity, and different, homogeneous specific heat and density in each layer. Numerical calculations in order to demonstrate the applicability of the present analytical method are carried out for transient temperature distributions in PSZ/SUS304 FGM plates with linear and ceramic-rich compositional distributions.

Production of a functionally graded artificial tooth root by unique sequence of processes

Abstract: A unique sequence of processes is used to produce a prototype of a functionally graded artificial tooth root: (1) Dry-jet spraying of the mixture of Ti and Al2O3 ultrafine particles (UFPs) produced by radio-frequency plasma onto the surface of a cylindrical Ti rod, where the composition of the UFPs is changed gradually in the outward radial direction from Ti to Al2O3; (2) Temperature-gradient sintering of the deposited composite, where the Ti – and the Al2O3– rich sides are heated simultaneously at about 1400 K and 1800 K, respectively; (3) Plasma spray coating of hydroxyapatite (HAP) onto the outermost Al2O3 surface of the sintered composite. The final product has compressive strength of more than 200 MPa and is durable against fatigue test of 107 stress cycles at 1000 N. The adhesion strength between the Ti substrate and the Ti-Al2O3 functionally graded layer exceeds 65 MPa. No contamination with heavy metals is detected throughout the processes and biological cell growth is confirmed to occur on the HAP surface. With these mechanical and biochemical properties the composite produced here is considered to be highly suitable for an artificial tooth root. A series of processes developed here are expected to be applied to the production of various kinds of fine-grained functionally graded materials with complicated forms.

Computer design of thermoelectric functionally graded materials

Abstract: The results of the optimal control theory use have been presented for program creation of functionally graded material computer modeling. Modeling results such as limiting values for FGM generators efficiency, functionally graded material advantages resulting from the computer modeling have been.

Mechanical Performance of ZrO2-Ni Functionally Graded Material by Powder Metallurgy

Abstract: The mechanical performance of a ZrO2-Ni functionally graded material (FGM) developed by powder metallurgy was investigated by means of three-point bending test. It was shown that the mechanical behavior of ZrO2-Ni system strongly depends on constitutional variation, exhibiting typical behavior of elasto-plastic deformation similar to metallic material in the Ni-rich composition and typical behavior of elastic deformation and macroscopic brittle fracture in the ZrO2-rich composition. The mechanical properties of ZrO2-Ni system also display various gradient distributions corresponding to constitutional change. With the rise of Ni content, Vickers hardness decreases, but fracture toughness increases remarkably. Young’s modulus changes corresponding to the distribution of porosity. Bending strength is quite sensitive to microstructural factors, and its peak and valley point are relevant to the dispersion strengthening of ZrO2 particles and the distributional transition of components, respectively.

Thermal Stresses in Functionally Graded Material of Particle-Reinforced Composite.

Abstract: Functionally graded materials (FGMs) have been developed for case as ultrahigh-heat-resistant materials in aircraft, space and nuclear engineering fields. The composition of FGMs varies, but most FGM are particle-reinforced FGMs. In the study of FGMs, the material properties due to macroscopic combine-low have been adopted. However in order to obtain more correct thermal stresses in the FGMs, it is necessary to analyze thermal stresses by use of the microscopic combinelow. Using the constitutive equations for the particle-reinforced composites, the stress-strain relations of particle-reinforced composites taking into account the effect of the manufacturing process, and the stress distribution in an FGM plate subjected to heating are discussed. The number of damaged particles and the possibility of crack generation taking into account the manufacturing process are also discussed.

Fabrication of Magnetic Functionally Graded Material by Martensitic Transformation Technique

Abstract: It is known that the paramagnetic phase in an austenitic stainless steel, such as Fe-18Cr-8Ni, transforms into a ferromagnetic α ′-martensite phase by plastic deformation at low temperature. The amount of saturation magnetization due to the martensitic transformation increases with increasing plastic strain. Thus, a manufacture of magnetically graded materials based on the concept may require the inhomogeneity of plastic deformation. In the present study, it is aimed to obtain a suitable gradient of the magnetization by introducing inhomogeneous deformation and to examine the relationship between the magnetization and applied plastic strain using Fe-18Cr-8Ni. A simple model to evaluate the distributions of strain and saturation magnetization is obtained in order to clarify the results mentioned here.

Research on Enhancement of Thermoelectric Figure of Merit through Functionally Graded Material Processing Technology in Japan

Abstract: For useful thermoelectric elements, the figure of merit should be high over wide temperature range. In order to realize such a thermoelectric performance, Functionally Graded Material (FGM) approach has attracted engineers’ attention. The research activities on the enhancement of thermoelectric figure of merit through FGM processing technology in Japan are reviewed in the paper. After the fundamental design guideline of FGM thermoelectric element is presented, the experimental results for several kinds of FGM approach are introduced mainly based on the FGM projects named “Development of Energy Conversion Material though Formation of Graded Structures” promoted by Science and Technology Agency and “Physics and Chemistry of Functionally Graded Materials” supported by Ministry of Education and Culture. The technological problems and future prospects are also discussed.

Mode I interaction of a periodic array of parallel cracks in a functionally graded nonhomogeneous plane

Abstract: The mode I interaction of a periodic array of parallel cracks which are uniformly spaced apart in a functionally graded material is investigated. The two-dimensional theory of nonhomogeneous elasticity is employed as the basic framework for this study. The material nonhomogeneity is represented in terms of the spatial variation of the shear modulus in the exponential form along the direction of cracks, while Poisson’s ratio is assumed to be constant. Formulation of the proposed mixed boundary value problem is reduced to solving a hypersingular integral equation with the crack surface displacement as a new unknown function. As a result, the variations of stress intensity factors are illustrated as a function of possible range of periodic crack spacing in conjunction with the different values of the material nonhomogeneity parameter. Furthermore, crack opening displaccements are presented for various geometric and material combinations.

Trial Manufacture of Functionally Graded Si-Ge Thermoelectric Material

Abstract: A functionally graded material of SiGe was manufactured by using spark-plasma-sintering(SPS) in a trial. The studied material was mainly a p-type 80Si-20Ge alloy in which doping concentration of B were graded stepwise in three levels of 0.027, 0.2, and 0.58 at %. Preliminary evaluation was made for the manufactured material samples in terms of their Seebeck coefficients together with electrical resistivities. Measurement of resistivity distribution around the FGM boundary was carried out to localize the boundary.

Mathematical Model for Axial-Symmetrical FGM

Abstract: Analytical procedure for empty cylinder of Functionally Graded Material(FGM) with axial symmetry has been investigated. Based on thermal elasticity theory and computational mathematical method, temperature distribution has been obtained and thermal stress of FGM in ring section has been calculated.

Micromechanical approach to the thermomechanical analysis of FGMs

Abstract: The thermoelastic fields in a functionally graded material (FGM) are derived semi-analytically by the use of the eigenfunction expansion method. The eigenfunctions are approximated by a linear combination of admissible functions each of which satisfies the homogeneous boundary condition. The eigenfunctions can also be used to construct the Green’s function for the FGM which enables the handling of various boundary conditions and source terms. A numerical example is presented to show thermal stress distributions in a 2-D rectangular FGM under steady-state heat transfer subject to the first kind of displacement boundary condition.