Papers by Keyword: Functionally Graded Material (FGM)

Abstract: Functionally graded materials (FGM) are often an integral part these days in many engineering applications, such as, nuclear structural components, spacecraft and marine structures, thermal barrier coatings used for military applications, etc. These structures are also susceptible to dynamic loads varying from harmonic to impulse type of loadings which are in the form of rotating engines, sudden blasts and others. These loadings often pose serious threats to the structural systems by inflicting fatigue damages or by driving the system in tune with its resonating frequency that eventually lead to the complete collapse of the structure. Therefore, a vibration control strategy needs to be devised to protect these structures from unwanted vibrations due to the external loading. A passive vibration control strategy is proposed in the present research work to control the vibration response of a flat panel made of functionally graded material. At first, the FG plate is numerically modelled using the finite element (FE) method to calculate its response due to a point harmonic force. Ceramic (Alumina) is used for the top part of the FG plate while the bottom is made of metal (Aluminium) and the material property is smoothly varied from ceramic to metal using the power law distribution. Then, several resonators consisting of spring-mass system and parallel to each other are attached to both sides of the panel to isolate the response in the resonating frequency ranges. The FE model for the FG plate with resonator is developed and the controlled vibration response is obtained. The controlled response indicates that the resonators are efficient to produce band-gaps in the resonating frequency regime compared to the bare FG plate.

Abstract: The process of fabricating reliable materials according to efficient usage has become one of the most vital concerns. In this paper, the fabrication of functionally graded materials (FGMs) is the target using a specified application of an internal combustion engine piston model to achieve such a gradient. With a convenient rotational speed under the concept of centrifugal casting technique, the required gradient piston was successfully produced from two pure aluminum alloys A336 and A242 by such a new mechanical technique for having the required gradient. The percentages of internal ingredients, mainly, silicon were controlled axially through the piston. Chemical composition analysis, micro-hardness and wear resistance tests were performed to check the gradient and to know the difference between mechanical properties for each piston portion from its top combustion chamber to its skirt, achieving compatible results through performed tests. Obvious opposite direction gradient of silicon content to copper content appeared. Micro-hardness, wear resistance and coefficient of friction values showed a successfully gradient in the axial direction of the piston model.

Abstract: This paper presents how to calculate the overall heat transfer coefficient of a very long functionally graded hollow circular cylinder subjected to steady state heat transfer. Thermal conductivity coefficient of the functionally graded cylinder (FGC) vary radially and continuously according to an exponential form, which is supposed to be independent of the temperature. Overall heat transfer coefficient is found analytically in terms of the radial coordinate, thermal conductivity, material parameter, inner surface and outer surface temperatures of the cylinder. Once the overall heat transfer coefficient is found, calculation of the heat transfer rate across the cylinder wall is quite straightforward. The equation derived for the overall heat transfer coefficient can be applied to any type of functionally graded hollow circular cylinder playing with the material parameter term.

Abstract: This paper presents how to derive Airy stress function to obtain the thermal stresses in a tungsten-steel functionally graded solid cylinder with fixed ends in elastic region. Once Airy stress function is derived, the thermal stresses can be found due to the related equations. There is uniform heat generation inside the tungsten-steel functionally graded solid cylinder. Material properties of the functionally graded cylinder (FGC) are assumed to vary radially according to a parabolic form and assumed to be independent of the temperature. These properties are yield strength, modulus of elasticity, coefficient of thermal conduction and coefficient of thermal expansion (CTE). Poisson’s ratio is assumed to be constant as an average value between tungsten’s and steel’s. Airy stress function is derived in terms of these properties to characterize the FGC entirely.

Abstract: The paper participates in a development of composites. A composite tungsten-steel is studied as materials suitable for a first wall of tokamak, a composite FeAl + Al₂O₃ is a possible material for fourth generation of a nuclear power plant and a composite Al₂O₃ + YSZ is a potential implant material. The focus of our study is change of material properties near the interface and a determination of area size which is influenced by the adjacent material. Material properties are investigated by nanoindentation. The task is simulated using finite element method. Simulated specimen is composed of a tungsten part and a steel part. The sharp boundary between materials is a plane which is located parallel to the loading force direction. Elastic modulus is determined in dependence of a distance between the interface and a tip of the indenter. The simulated results are verified experimentally.

Abstract: Light weight aluminium alloys and low-density materials have drawn the attention of researchers as potential structural materials for transportation sector due to the requirement of effective reduction in fuel consumption, stringent emission norms and higher payload capacity. Functionally Graded Materials (FGM) provides variation in properties and better functional performance within a component. Sequential casting is fairly a new technique to produce functionally graded materials and components by controlled mould filling process. Bimetallics of aluminium alloys are prepared by sequential casting using A390-A319 alloy (cast-cast alloy) and A390-A6061 alloy (cast-wrought alloy) combination and solidified under gravity. The effect of temperature of the two melts and gap between pouring of the melts on microstructure and properties of the bimetals are investigated. The microstructures show good interface bonding between the two different alloy metals. The hardness testing shows higher hardness at hypereutectic alloy region. The process described in this study shows potential and effective approach to create good bonding between two different aluminium alloys to develop advanced functional and structural materials which can be used in various automobile components to reduce the overall weight of the vehicle, by which better fuel efficiency and performance can be achieved.

Abstract: A390 functionally graded material (FGM) pistons were fabricated by centrifugal casting, where the silicon particles were segregated in the head portion of the pistons by appropriate design and their density differences. Centrifugal casting offers casting of cylindrical structures with gradation in its properties. In centrifugally cast A390, a suitable die design can lead to the formation of hard primary Si particles gradually distributed towards the head region producing a particle rich zone, transition zone and matrix rich zone. Microstructure and chemical composition analysis confirms the composition gradation. Hardness and wear test results revealed that the gradation positively helps to improve the desired properties with the presence of in-situ primary silicon reinforcements.

Abstract: The present study describes the processing and characterization of hypoeutectic A319 functionally graded Aluminium metal matrix composite (FGMMC) reinforced with 10 weight percentage SiC_p particles of 23 μm size. FGMMC’s are processed by liquid stir casting method followed by vertical centrifugal casting. Metallographic analysis of FGMMC casting reveals the influence of the centrifugal force on the gradation of various phases in the matrix and an increasing gradient distribution of SiC reinforcements gradually from inner towards the outer periphery forming different zones. Tensile and the compressive tests show that the variation in properties are structure sensitive and is confirmed by the dry wear tests. The study clearly depicts the gradient nature in the structure and mechanical properties of the FGM castings produced by centrifugal casting method.

Abstract: A study of the effect of material gradient on the performance of a functionally graded endodontic prefabricated parallel post (FGEPPP) is the main goal of the current study. Elastic modulus (E) of FGEPPP is considered to vary continuously from lower to upper surfaces. This variation is performed according the volume fraction. Based on a modified sigmoid function, the volume fraction will be defined in the present work. The primary goal of the current investigation is to analyze the difference between the performance of a homogeneous endodontic prefabricated parallel post (EPPP) and a FGEPPP through finite element analysis (FEA). In the current investigation, von Mises stress, and shear stress in FGEPPP case with a modified sigmoid function and in homogeneous EPPP case are carried out. After that, the effect of material gradient on the performance of an EPPP made of FGM was carried out through FEA in the current investigation. The simulation cases shown that, the maximum values of von Mises stress, and shear stress increase when increasing the value of “D”, and decrease when increasing the value of “w”.

Abstract: Formed in the semi-solid state, materials can obtain unconventional microstructures and properties compared with traditional method. In this paper, semi-solid billet of 9Cr18 steel was obtained through a wavelike sloping plate. Microstructure analysis of the semi-solid billet was conducted through scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). X-ray diffraction (XRD) test and microhardness test were also used to analyze the properties. The results showed that the structure of 9Cr18 semi-solid billet contained globular primary austenite and secondary austenite-Cr₇C₃ eutectic. Globular primary austenite grains were first formed during partial solidification in the sloping plate, and then the rest liquid metal formed secondary austenite and Cr₇C₃ eutectic structure surrounding the primary grains. Cr atoms had a concentration in the rest liquid side, which along with C atoms contributed to the formation of the Cr₇C₃ carbide. Hardness in the primary solid grain area and the eutectic area was about 330 HV and 650 HV, respectively. These specific properties were important for subsequent thixoforming of the functional graded materials.