Papers by Keyword: Functionally Graded Material (FGM)

Abstract: Analytical solutions of stress fields in functionally graded circular hollow cylinder with finite length subjected to axisymmetric pressure loadings on inner and outer surfaces are presented in this paper. The cylinder is simply supported at its two ends. Young's modulus of the material is assumed to vary continuously in radial direction of the cylinder. Moreover, numerical results of stresses in functionally graded circular hollow cylinder are appeared.

Abstract: Based on the first-order shear deformation theory of plate, governing equations for the axisymmetric buckling of functionally graded circular/annular plates are derived. The coupled deflections and rotations in the pre-buckling state of the plates are neglected in analysis. The material properties vary continuously through the thickness of the plate, and obey a power law distribution of the volume fraction of the constituents. The resulting differential equations are numerically solved by using a shooting method. The critical buckling loads of circular and annular plates are obtained, which are compared with those obtained from the classical plate theory. Effects of material properties, ratio of inter to outer radius, ratio of plate thickness to outer radius, and boundary conditions on the buckling behavior of FGM plates are discussed.

Abstract: The dynamic anti-plane crack problem in a functionally graded smart structure is considered. Integral transforms are employed to reduce the problem to the solution of singular integral equations. Numerical results are presented to show the nfluences of electrical crack condition, crack position, electromechanical combination factor and material gradient parameter on the fracture behavior.

Abstract: Accurate crack propagation simulation requires critical fracture parameters to be known a priori. For elastic-plastic materials, two fundamental parameters are the separation energy and the peak stress required to generate new crack surfaces. In general, both are difficult to quantify since direct determinations are not possible in experiments. For inhomogeneous materials, such as graded materials, determination is even more complex since these parameters vary spatially. In this paper, a novel method based on an inverse analysis technique is proposed to estimate the fracture parameters of elastic-plastic and graded media. The method utilizes the Kalman filter to process measured data and extract best estimates of the unknown parameters. The accuracy of the method is examined in a verification study where a dynamically propagating crack in double cantilever beam type specimen is modeled. In the study, time variation records of crack opening displacement, opening strain, crack advance distance, and load point reaction force are used as possible measurements. Despite large noises in data, the results confirm accurate estimation. The estimates improve when multiple measurements are supplied to the inverse technique.

Abstract: Compositionally graded Al-SiC_p composites were fabricated using pressureless infiltration process. Microstructure was examined and thermal properties were characterized for Al-SiC_p composites. Al-SiC_p composites with fairly uniform distribution and compositional gradient of SiC reinforcement in the Al matrix though the thickness direction was successfully fabricated. The thermal conductivity of Al-SiC_p composites was measured at room temperature, 200°C and 400°C using laser flash method. Thermal conductivity of Al-SiC_p composites increases non-linearly with decreasing the volume fraction of SiC. Cyclic thermal shock fatigue tests were performed by immersing Al-SiCp functionally graded materials(FGM) into water from the various heating temperatures of 400°C , 300°C and 200°C , repeatedly. After cyclic thermal shock fatigue tests, micro-hardness was measured and formation of cracks was investigated.e fati

Abstract: Interfacial strength distribution and thermal residual stresses in multi-layered or compositionally graded NiCrAlY/ZrO₂ coatings are analyzed. These coatings are fabricated by detonation gun spraying using mechanically alloyed, plasma-spheroidized composite powders. The problems in design of functionally graded materials (FGMs) are outlined and their modeling approaches are reviewed. Due to the concentrational or structural gradients in FGMs, the normal approximations and models, used for traditional composites, are not directly applicable to graded materials. The goal is to show the efficiency of the simplest models to provide the most accurate estimates of the properties and even to make simple elasto-plastic analysis of FGM components without vast computations by finite element methods with an arbitrary non-linear distribution of phases and corresponding properties is presented. Results showed that bonding strengths increased gradually with increase of the composition of metals in the FGM coatings. The FGM coating was more stable on the mechanical properties than normal duplex composites. And, the maximum compressive radial stress is found to be at or near the surface of the specimen where surface cracking may be generated. The maximum axial stress is at the edge of the specimen where spallation may occur. The maximum shear stress is also at or close to the edge.

Abstract: Centrifugal casting method was used to fabricate composites with graded structures in alumina-zirconia system. The composition profiles of the graded composites showed three distinct regions, with a greater part of the specimen showing nearly linear variation of compositions. The composition profile can be varied by using zirconia powder of different size ranges. The top of the specimens showed nano-scaled microstructures. The composition profiles can also be varied by altering zirconia content in the starting suspension. It was found that the composites with graded structures showed higher bending strength than that of uniform composites. On the other hand, the specimens fractured with the lower zirconia content region being the crack initiate plane showed higher bending strength than that of fractured form higher zirconia content region.

Abstract: Capability of the X-ray scattering for study of low-dimensional structures is illustrated on few examples. They are focused to the phase analysis, residual stress measurement, calculation of the stress-free lattice parameters, investigation of the anisotropic lattice deformation and preferred orientation in UN thin films. Further, the study of concentration profiles in functionally graded hard-metals and investigation of the multilayer degradation caused by soft annealing are discussed.