Yasuyoshi Fukui

Control of Composition Gradient in a Metal-Ceramic Functionally Graded Material Manufactured by the Centrifugal Method

The motion of ceramic particles in a molten metal of a viscous liquid under a centrifugal force is numerically modeled to study the formation process of composition gradients. The simulated results are in good agreement with those of experiments that used a plaster-corundum model functionally graded material (FGM). It is found that greater gradients are obtained in cases of thinner thickness, greater applied centrifugal forces and smaller mesh size particles. In addition, the processing of mixed mesh size particles is examined. We conclude that the use of a mixture of particle sizes is particularly useful to control the composition of metal-ceramic FGMs manufactured by the centrifugal method.

Computer evaluation of sprinkler irrigation uniformity

SummaryA method for evaluating the water application rate (WAR) and uniformity coefficient (Cu) of overlapping irrigation sprinklers is given for realistic field conditions which includes wind drift of the sprinkler spray. The method requires as input — the geometry of the sprinkler arrangement, trajectories of water drops from the sprinkler nozzle as calculated by the equations of motion and the WAR distribution (discharge) profile of a single sprinkler experimentally observed under windless conditions. Wind direction with respect to the main sprinkler line is shown to have a small effect on Cu and is assumed to be parallel to the main line. Results show that the effect of wind drift of sprinkler spray on Cu can be neglected for wind velocities less than 1 ms−1 (Fig. 8). Analysis of simulated discharge profiles (Table 1) shows that the maximum value of the uniformity coefficient was obtained with triangular sprinkler discharge profiles at low values of spacing, changing to trapezoidal profiles as the spacing increases (Figs. 8 and 9). The effect of nozzle pressure on WAR was evaluated for the pressure range between 294 and 490 kPa and an optimum layout of overlapping sprinklers, designed to minimize the effect of wind drift and nozzle pressure on the uniformity of WAR distribution, is presented.

Analysis of thermal residual stress in a thick-walled ring of duralcan-base Al-SiC functionally graded material

A ring-cutting test and an elastic theory were applied to evaluate the macroscopic residual stress in a thick-walled ring made of Al-SiC functionally graded material (FGM). The FGM ring specimens, with outer diameter 90 mm, radial thickness approximately 8.4 to 10 mm, and width 30 mm, were fabricated by the centrifugal casting method from an ingot of Duralcan F3D.20S of Al-20 vol pct SiC master composite. Because of a difference in centrifugal forces of SiC particles and of molten aluminum alloy, the rings had a graded composition of SiC particles in the radial direction. The volume fractions of SiC particles in each ring specimen varied in the range of 0 to 43 vol pct from the inner to the outer surface of the ring, depending on the applied mold spin speed. A ring diametral compression test was performed to validate an analytical formula based on the curved beam theory that can account for the graded properties of the material. Excellent agreement between the theory and the experiment was found. The residual stress was found to be generated by a cooling of Δt=140 K, which was from half the melting point corresponding stress-free condition to the ambient temperature. The hoop residual stresses in the FGM ring varied in the range of −50 to +35 MPa and from tension at the inner surface to compression at the outer surface because of the graded composition. With an increase in wall thickness and/or composition gradation, the residual stresses were found to increase.

Bending strength of an AlAl3Ni functionally graded material

Abstract The gradient of bending strength of an Al-Al 3 Ni functionally graded material (FGM) has been examined using 3-point bending tests. Specimens with rectangular cross-sections of 6 × 6 mm 2 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 A1 3 Ni phase in the thickness direction. Four types of specimens characterized by four nominal volume fractions of the Al 3 Ni phase at the crack initiation plane, namely V f = 0, 24, 49 and 53 vol%, were employed in the study. Fracture surfaces consisted of cleavage facets of the Al 3 Ni phase surrounded by dimples of the aluminum phase. Brittle fracture of Al 3 Ni dominated the fracture process of Al-Al 3 Ni 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 V f = 24 vol% specimen, and decreased in the following order with specimen type: V f = 24, 49, 53 and 0 vol%. Fracture strength of Al-Al 3 Ni FGM attained a maximum value of 160 MPa at V f ≈10 vol % and decreased with an increase in the A1 3 Ni volume fraction due to the size effect that controls the strength of the brittle Al 3 Ni phase.

Microstructures of functionally graded materials fabricated by centrifugal solid-particle andin-situ methods

Functionally graded materials (FGMs) belong to a relatively new class of inhomogeneous composite materials, in which the composition and/or microstructure undergo a gradual change along some directions. In this review article, the microstructures and composition gradients in Al/SiC, Al/Shirasu (volcanic eruptions commonly found in south Kyushu in Japan), Al/Al3Ti, Al/Al3Ni, Al/Al2Cu FGMs have been investigated. The Al/SiC, Al/Shirasu and Al/Al3Ti FGMs are fabricated by the centrifugal solid particle method where the distribution particles of SiC, Shirasu and Al3Ti are solids in the melts. On the other hand, Al/Al3Ni and Al/Al2Cu FGMs are fabricated by the centrifugalin-situ method where Al/Al3Ni and Al/Al2Cu systems have lower liquidus temperatures than the processing temperatures. The feature of Al/(Al3Ti−Al3Ni) hydrid FGM, which is fabricated by a method combining both the centrifugal solid-particle andin-situ methods, is also shown.

Evaluation of Particle Size and Particle Shape Distributions in Al-Al3Ni FGMs Fabricated by a Centrifugal in-situ Method

This paper reports on the variation of particle size, particle shape and volume fraction distributions in AlAI^Ni functionally graded materials (FGMs) fabricated by a centrifugal in-situ method. Eight specimens of AlAI3N1 FGM were systematically selected for the experimental analysis. The microstructures of AI3Ni primary crystal particles were observed and then gradients of volume fraction of AI^Ni particles towards centrifugal force direction were measured. A detailed evaluation of particle size was done considering the area-equivalent diameter from cross-sectional area of each AI^Ni particle. Moreover, particle shape distributions were also conducted using functions concerning with both fractal dimension and circularity of particles. It is revealed that both particle size and particle shape of AI^Ni had graded distributions as well as volume fraction distributions within the FGMs. Those results were explained considering the effect of applied G number, Ni content in Al-Ni master alloy, cooling rate and stirring of melt. Key w o r d s : Functionally graded materials (FGMs), AI-AI^Ni, centrifugal in-situ method, particle size, particle shape, cooling rate, fractal dimension, circularity, stirring

Homogenization method for heterogeneous material based on boundary element method

Abstract In this paper, formulations for homogenization method based on the boundary element method, for heterogeneous elastic materials having periodic microstructure, are presented. The formulations are developed using a novel use of the method of weighted residuals. Both the trial and test functions are expressed by asymptotic expansions with respect to the size e of the unit cell. Two types of boundary element formulations for the analysis of unit cell, are proposed; single-region boundary element method with volume integrals and multi-region boundary element method. Convenient formulae to compute effective (homogenized) elastic constants, are presented.

Numerical analysis on near net shape forming of Al-Al3Ni functionally graded material

Abstract The results of numerical studies on the near-net shape forming of Al–Al3Ni functionally graded material (FGM) are presented and are compared with the experiments. FGM billets at an elevated temperature of semi-solid condition are set in a container and are subject to backward extruding, and FGM cups are obtained. Due to the composition gradient of FGM the effective viscosity of semi-melt FGM billet varies spatially. The flow/deformation of semi-melt FGM billet is strongly influenced by the spatial variation of effective viscosity. Some characteristic behaviors of flow/deformation of FGM during the semi-solid process are presented and 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.

Novel Concept to Detect an Optimum Thixoforming Condition of Al-Al3Ni Functionally Graded Material by Wavelet Analysis for Online Operation

A novel technique to characterize the transition phenomenon from solid to melt of Al-Al3Ni functionally graded material (FGM) through a wavelet analysis for the development of a thixoforming system is investigated. Identification of an optimum semi-solid condition for thixoforming is necessary not only for the construction of a system but also the fabrication of a near-net-shape product with fine microstructure. An online wavelet analysis system using Haar’s wavelet function, which is applied for its simplicity compared with Daubechies’ wavelet function, is developed to find the optimum operating condition. A thixoforming system, which is constructed adapting a threshold value as an index, monitors successfully a discontinuity of deformation of Al-Al3Ni FGM with the temperature rise. Thus, the timing of an operation is not at pre-fixed temperature but at the time when the index related to a wavelet function is satisfied. The concept is confirmed to be suitable from the micro-structural observation of the Al-Al3Ni FGM product, because the product under the optimum condition is found to have refined Al3Ni grains, which change from coarse grains and are expected to improve the mechanical properties.