News Article | May 25, 2017
Figure: Trial of the simulation technology in comparison with a pouring experiment with Die Casting shot sleeves: The simulation (below) correctly replicates the differences in motion of water and aluminum alloy, observed in the experiment. Fujitsu Limited and Daido University Professor Yasuhiro Maeda have jointly developed new simulation technology that can accurately replicate splash and wave behavior in the surface of molten metals when they are being poured. In the casting process, which is used in component manufacturing in a variety of fields, such as automobiles and IT devices, molten metal is poured into a mold to be cast into a shape. The way molten metal flows through the interior of a mold significantly effects casting quality, but because the interior is impossible to see, there has been a demand for a simulation that can clarify how molten metal flows within the mold. However, simulation of this flow has been difficult to achieve as the way molten metal flows can change greatly depending on the oxide film that forms when metal contacts the air. Now, based on a simulation technology known as the particle method, Fujitsu and Daido University have developed a new way to calculate flow variations with physical properties (viscosity) near the boundary between it and the air. This technology was then verified, comparing it to an actual experiment modeling a process where aluminum alloy melted at high temperatures is poured into casting equipment, which confirmed that the manner of splash suppression in line with the oxide film on the poured liquid metal could be accurately simulated. This technology creates a simulation to clarify how molten metal flows inside casting equipment and molds, a process which cannot be observed from the outside. This will make it possible to change metal pouring procedures so as to more quickly manufacture high quality products, which is expected to contribute to improving casting productivity. Details of this technology will be announced at the 169th JFS Meeting (Japan Foundry Engineering Society), which will be held on the Setagaya campus of Tokyo City University on May 26-29. Casting, which is used in the manufacturing of components for a variety of fields, including automobiles, appliances and IT devices, is a process in which metal that has been melted at high temperatures is injected into molds, and the way the metal is injected is known to have a significant impact on the quality of the component. In a casting method known as die casting, for example, if the liquid metal inside the shot sleeves that inject the molten metal into the die at high pressure violently splashes, oxides or other impurities that form on the surface where it meets the air can be mixed in, leading to the casting defects in the shaped component that make them prone to breakage. For this reason, in order to prevent severe splashing of the liquid metal surface within the shot sleeve, the timing of the injection into the mold is adjusted based on estimates of the splashing of the liquid surface in the parts of the sleeve that cannot be seen, creating a need for technology to accurately simulate how the liquid metal flows. Metal that has been melted at high temperatures reacts with oxygen the instant it comes into contact with air, generating an extremely thin oxide film less than 0.1mm on the surface, which greatly reduces fluidity. For this reason, it was not possible to get accurate results with previous commonly used technology, which simulated it as the flow of a uniform liquid. In order to calculate the impact of the thin oxide film formed as the liquid surface splashes, it was necessary to separate out the thin film for calculations using a technology that can simulate the splashing. In order to calculate at the extremely high rate of precision that enables distinguishing the thin film, however, computations of over one thousand times greater than that of a uniform liquid simulation would be necessary, meaning timely simulations were not realistic. Overview of the New Simulation Technology Fujitsu and Daido University have developed simulation technology that can calculate the impact of lowered fluidity in liquid metals due to the thin oxide film without significantly increasing computation cost. This technology combines a method known as the particle method, in which fluids are represented as collections of particles in calculations, with a new computational model that dynamically changes the physical property values of particles located on the surface of the liquid. With this computational model, the physical property values related to fluidity (viscosity) for the particles located on the liquid surface are set based on the ratio between the size of the particles representing the liquid metal and the thickness of the film. Because the impact of lowered flow properties due to the formation of the thin oxide film can be calculated with this method without changing the particle size, which is the base unit of calculation, the computational time required for the simulation can be kept to about the same level as a simulation of a flow of a uniform liquid. In a technology trial in which the simulation was compared with an experiment modeling the pouring of aluminum alloy melted at high temperatures into a Die Casting shot sleeve, it was confirmed that a simulation that correctly reproduced the way molten metal flows, which is significantly different from water, could be accomplished in about eight hours of computational time (see figure). Explore further: A cheaper, greener way to grow crystalline semiconductor films
Imai K.,Daido University
Journal of the Physical Society of Japan | Year: 2013
The n-dimensional homogeneous Lotka-Volterra (HLV) ladder equation possesses Lie symmetries that generate a Lie algebra isomorphic to sl n(K) [J. Phys. Soc. Jpn. 71 (2002) 2396 and 72 (2003) 973], where K = C or R. In this work, using the Lie algebraic structure of the HLV ladder equation, we derive new n-dimensional dynamical systems and prove their integrability from the viewpoint of Lie symmetries. © 2013 The Physical Society of Japan.
Oono Y.,Daido University |
Sounai A.,National College of Technology, Suzuka College |
Hori M.,Daido University
Journal of Power Sources | Year: 2012
The mechanism underlying the decline in cell voltage over time was investigated for high-temperature proton exchange membrane fuel cells. Five identical cells were prepared and long-term power generation tests were conducted at an operation temperature of 150 °C and a current density of 0.2 A cm -2 for periods of up to 17,860 h. Each of the cells was then analyzed using transmission electron microscopy and electron probe micro-analysis (EPMA). The results indicated that growth of the Pt catalyst particles occurred during operation, in addition to oxidation of the carbon support. Degradation of the catalyst layers was investigated by EPMA of cross sections of the membrane electrode assemblies, allowing the mechanism of cell performance reduction to be clarified. © 2012 Elsevier B.V. All rights reserved.
Saida H.,Daido University
Entropy | Year: 2011
This paper consists of three parts. In the first part, we prove that the Bekenstein-Hawking entropy is the unique expression of black hole entropy. Our proof is constructed in the framework of thermodynamics without any statistical discussion. In the second part, intrinsic properties of quantum mechanics are shown, which justify the Boltzmann formula to yield a unique entropy in statistical mechanics. These properties clarify three conditions, one of which is necessary and others are sufficient for the validity of Boltzmann formula. In the third part, by combining the above results, we find a reasonable suggestion from the sufficient conditions that the potential of gravitational interaction among microstates of underlying quantum gravity may not diverge to negative infinity (such as Newtonian gravity) but is bounded below at a finite length scale. In addition to that, from the necessary condition, the interaction has to be repulsive within the finite length scale. The length scale should be Planck size. Thus, quantum gravity may become repulsive at Planck length. Also, a relation of these suggestions with action integral of gravity at semi-classical level is given. These suggestions about quantum gravity are universal in the sense that they are independent of any existing model of quantum gravity. © 2011 by the author.
Komori K.,Daido University
Procedia Engineering | Year: 2014
A crack becomes stationary during blanking when the clearance between the punch and the die is relatively small. In this work, a simulation of the stationary crack during blanking was performed using the node separation method. When a crack becomes stationary, one fracture surface contacts another fracture surface in the region near the stationary crack. Therefore, a simplified simulation method is proposed for the material contact. Special attention was paid to the effect of the various kinds of ductile fracture criteria on crack initiation and crack propagation during blanking. The shapes of chips and holes and the relationship between punch displacement and punch force calculated from the simulation agree well with those obtained experimentally. © 2014 The Authors. Published by Elsevier Ltd.
Komori K.,Daido University
Computational Materials Science | Year: 2013
A void model that can be used for the evaluation of ductile fracture in the simulation of sheet metal-forming processes is proposed. This void model is an extension of the Thomason model of void coalescence, which is based on the internal necking of the matrix between voids. In sheet metal-forming processes, the material is subjected to a complex strain path. Hence, the prestrain should be considered for the evaluation of ductile fracture in the simulation of sheet metal-forming processes. In the present paper, the prestrain is first introduced in the proposed void model. The simulation of the hole expansion test, which is a fundamental material test in sheet metal forming, is performed while paying special attention to the void configuration and the void shape. Finally, the validity of the proposed void model is confirmed by comparing the simulation results with the experimental results. © 2011 Elsevier B.V. All rights reserved.
Komori K.,Daido University
International Journal of Mechanical Sciences | Year: 2013
A crack is arrested during blanking when the clearance between the punch and the die is relatively small. Simulation of the arrest of a crack during blanking is performed using the node separation method. When a crack is arrested, one fracture surface contacts another fracture surface in the region near the arrested crack. Therefore, a simplified simulation method is proposed for the material contact. Special attention is given to the effect of various kinds of ductile fracture criteria on crack initiation and propagation during blanking simulations. The shapes of the scraps and blanks and the relationship between the punch displacement and the punch force calculated by the simulation agree fairly with those obtained in the experiment. © 2013 Elsevier Ltd.
Komori K.,Daido University
Mechanics of Materials | Year: 2013
An ellipsoidal void model, which is based on a parallelogrammic void model, is proposed for simulating ductile fracture behavior. It is used to analyze ductile fracture behavior in three plastic deformation modes: plane strain tension, uniaxial tension, and simple shear. The relationship between the fracture strain and the initial void volume fraction in uniaxial tension calculated using the void model agrees with that calculated using a finite-element void cell and agrees reasonably well with experimentally determined relationships in previous studies. For a specified initial void volume fraction, plane strain tension and simple shear respectively have the smallest and largest nominal fracture strains of the three plastic deformation modes.© 2013 Elsevier Ltd. All rights reserved.
Imai K.,Daido University
Journal of the Physical Society of Japan | Year: 2014
In this paper, a new n-dimensional homogeneous Lotka-Volterra (HLV) equation, which possesses a Lie symmetry, is derived by the extension from a three-dimensional HLV equation. Its integrability is shown from the viewpoint of Lie symmetries. Furthermore, we derive dynamical systems of higher order, which possess the Lie symmetry, using the algebraic structure of this HLV equation. © 2014 The Physical Society of Japan.
Komori K.,Daido University
Mechanics of Materials | Year: 2014
The ductile fracture in the simulation of sheet-metal-forming processes is evaluated by the ellipsoidal void model previously proposed by the author. In the present study, the simulation and experiment of the hole expansion test are performed using six types of metals. For an alloy, the relationship between prestrain and hole expansion ratio calculated using the ellipsoidal void configuration and ellipsoidal void shape and that calculated using the ellipsoidal void configuration and circular void shape agree with the relationship obtained experimentally. For a pure metal, the relationship between prestrain and hole expansion ratio calculated using the average void configuration and average void shape agrees with that obtained experimentally. Furthermore, the method of introducing prestrain to an as-rolled sheet is proposed, and the prestrain in this sheet is estimated. © 2014 Elsevier Ltd. All rights reserved.