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Makoto Yoshida - One of the best experts on this subject based on the ideXlab platform.
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Thermal Stress Analysis of residual Stress in a cylindrical aluminum casting with cast in gci liner taking recovery behavior effect into account
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2018Co-Authors: Yuichi Motoyama, Naoyuki Ebihara, Hidetoshi Shiga, Takeshi Sato, Hiroshi Kambe, Makoto YoshidaAbstract:Most aluminum cylinder blocks produced using high-pressure or low-pressure die-casting processes require gray cast iron liners (GCI liners) to compensate for their insufficient wear resistance and heat resistance of the Al-Si-Cu alloys. However, the cast-in liners cause excessive residual Stress at the cylinder bore region. The resultant residual Stress induces distortion of the cylinder liner. These inconveniences hinder development of more efficient engines. Therefore, an accurate Thermal Stress Analysis technique has been sought to predict the residual Stress and distortion of the cylinder liner. For accurate Thermal Stress Analysis, we have already developed an elastoplastic-creep constitutive equation for which the inelastic strain developed at high temperatures does not contribute to strain hardening that occurs at low temperatures by duplicating the recovery behavior. Our earlier investigation using this equation has already revealed that incorporation of the recovery in the alloy constitutive equation is effective for improving the prediction accuracy of the Thermal Stress developed during casting. However, this conclusion was obtained only for a simple shape casting with a uniaxial Thermal Stress state. Effects of the developed constitutive equation have not been discussed for a casting closer to an actual cylinder block. For this study, a cylindrical aluminum casting with GCI (ISO 300) insert was produced. Then, the circumferential strain of the GCI liner was measured in-situ during casting. Measurements were taken of the residual Stresses of the cylindrical aluminum casting and GCI liner, and of the liner deformation at a room temperature. The experimentally obtained results supported a discussion of the predictive accuracies of the elastoplastic-creep constitutive equation and the classical elastoplastic constitutive equation. A comparison revealed that the elastoplastic-creep constitutive equation for the aluminum casting has better predictive accuracy than the classical elastoplastic equation for residual Stress, liner deformation, and the circumferential strain of a GCI liner during casting. Investigation of the simulated strain components of the cylindrical aluminum casting during casting indicated incorporation of the recovery in the alloy constitutive equation as a main factor improving the predictive accuracy.
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Crack prediction for a partially solidified lead-free bronze casting using Thermal Stress Analysis
Journal of Materials Processing Technology, 2017Co-Authors: Akira Matsushita, Tomoaki Nakazawa, Toshimitsu Okane, Makoto YoshidaAbstract:Abstract For crack prediction in permanent mold casting of lead-free bronze, elasto-viscoplastic and elasto-plastic Thermal Stress analyses were performed and compared with the casting tests. The elastoviscoplastic model was constructed by the method which enables to determine rheological properties without steady state Stress in experiments. Maximum deviatoric principal (only by the elastoviscoplastic Analysis) and hydrostatic Stress were in reasonable agreement with the locations of cold cracking and hot tearing in the casting tests, respectively. It was suggested that considering the rheological properties of semi-solid alloys was important especially to predict cracks during and after solidification
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effects of recovery behavior and strain rate dependence of Stress strain curve on prediction accuracy of Thermal Stress Analysis during casting
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2017Co-Authors: Yuichi Motoyama, Hidetoshi Shiga, Takeshi Sato, Hiroshi Kambe, Makoto YoshidaAbstract:Recovery behavior (recovery) and strain-rate dependence of the Stress–strain curve (strain-rate dependence) are incorporated into constitutive equations of alloys to predict residual Stress and Thermal Stress during casting. Nevertheless, few studies have systematically investigated the effects of these metallurgical phenomena on the prediction accuracy of Thermal Stress in a casting. This study compares the Thermal Stress Analysis results with in situ Thermal Stress measurement results of an Al-Si-Cu specimen during casting. The results underscore the importance for the alloy constitutive equation of incorporating strain-rate dependence to predict Thermal Stress that develops at high temperatures where the alloy shows strong strain-rate dependence of the Stress–strain curve. However, the prediction accuracy of the Thermal Stress developed at low temperatures did not improve by considering the strain-rate dependence. Incorporating recovery into the constitutive equation improved the accuracy of the simulated Thermal Stress at low temperatures. Results of comparison implied that the constitutive equation should include strain-rate dependence to simulate defects that develop from Thermal Stress at high temperatures, such as hot tearing and hot cracking. Recovery should be incorporated into the alloy constitutive equation to predict the casting residual Stress and deformation caused by the Thermal Stress developed mainly in the low temperature range.
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a parameterization method of recovery behavior based on initial yield Stress pre strain diagram for an al si cu high pressure die casting alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Yuichi Motoyama, Gota Saito, Hiromi Ono, Makoto YoshidaAbstract:Abstract Consideration of recovery behavior in the constitutive equation of alloy is crucially important for accurate Thermal Stress Analysis of the casting process. However, previously reported empirical equations present difficulties when including a coefficient that determines the ratio of the recovery (or strain-hardening) strain component because the alloy recovery behavior has not been investigated systematically. First, this study systematically revealed effects of the temperature and amount of inelastic strain at 200–440 °C on the increase of the initial yield Stress of the room temperature (RT) in an Al-Si-Cu high-pressure die casting alloy. Secondly, from those results, an initial yield Stress – pre-strain diagram was proposed, demonstrating the effect of the amount of the inelastic strain given at each temperature on the increase of the initial yield Stress of RT. Finally, this study newly defined a temperature-dependent contribution ratio of strain hardening to parameterize and duplicate the alloy recovery behavior based on the initial yield Stress – pre-strain diagram for the constitutive equation of the alloy. Using this ratio as the coefficient to determine the proportion of the strain contributing the strain hardening for the constitutive equation, Thermal Stress Analysis can produce more accurate duplication of the experimentally determined recovery behavior. Thereby, the residual Stress and deformation of the component in the casting process can be predicted more accurately than when using conventional empirical constitutive equations.
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A verification of the Thermal Stress Analysis, including the furan sand mold, used to predict the Thermal Stress in castings
Journal of Materials Processing Technology, 2013Co-Authors: Yuichi Motoyama, Yuki Inoue, Gota Saito, Makoto YoshidaAbstract:Abstract The restraint exerted on a casting by a furan sand mold on the casting and the contraction of the casting during cooling was dynamically and simultaneously measured using a device that we developed. The measurements were compared during cooling with Thermal Stress analyses. The Thermal Stress analyses were based on the representative mechanical models for the furan sand mold, i.e., the elastic and elasto-plastic models used in previous studies. The comparison demonstrated that the elasto-plastic model simulates the restraint force more accurately than the elastic model. In the Thermal Stress Analysis, it was important to describe the development of inelastic deformation and the fracture of the sand mold. However, the simulated restraint force was still twice as large as the measured force even in the elasto-plastic model. This error is most likely attributable to using the temperature-independent mechanical properties of the furan sand mold and the mechanical model of the casting alloy, which neglected the viscoplasticity at high temperature in the Thermal Stress Analysis.
Joon Hyung Shim - One of the best experts on this subject based on the ideXlab platform.
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three dimensional Thermal Stress Analysis of the re oxidized ni ysz anode functional layer in solid oxide fuel cells
Journal of Alloys and Compounds, 2018Co-Authors: Stefan Stenfelt, Joon Hyung Shim, Fritz B PrinzAbstract:Abstract Nickel-yttria-stabilized zirconia (Ni-YSZ) cermet is widely used as an anode material in solid oxide fuel cells (SOFCs); however, Ni re-oxidation causes critical problems due to volume expansion, which causes high Thermal Stress. We fabricated a Ni-YSZ anode functional layer (AFL), which is an essential component in high-performance SOFCs, and re-oxidized it to investigate the related three-dimensional (3D) microstructural and thermo-mechanical effects. A 3D model of the re-oxidized AFL was generated using focused ion beam-scanning electron microscope (FIB-SEM) tomography. Re-oxidation of the Ni phase caused significant volumetric expansion, which was confirmed via image Analysis and calculation of the volume fraction, connectivity, and two-phase boundary density. Finite element Analysis (FEA) with simulated heating to 500–900 °C confirmed that the Thermal Stress in re-oxidized Ni-YSZ is concentrated at the boundaries between YSZ and re-oxidized NiO (nickel oxide). NiO is subjected to more Stress than YSZ. Stress exceeding the fracture Stress of 8 mol% YSZ appears primarily at 800 °C or higher. The Stress is also more severe near the electrolyte-anode boundary than in the Ni-YSZ cermet and the YSZ regions. This may be responsible for the electrolyte membrane delamination and fracture that are observed during high-temperature operation.
Yaupin Chyou - One of the best experts on this subject based on the ideXlab platform.
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Thermal Stress Analysis of planar solid oxide fuel cell stacks effects of sealing design
Journal of Power Sources, 2009Co-Authors: Chihkuang Lin, Liehkwang Chiang, Linghao Huang, Yaupin ChyouAbstract:Abstract A three-dimensional multi-cell model based on a prototypical, planar solid oxide fuel cell (pSOFC) stack design using compliant mica-based seal gaskets was constructed in this study to perform comprehensive Thermal Stress analyses by using a commercial finite element Analysis (FEA) code. Effects of the applied assembly load on the Thermal Stress distribution in the given integrated pSOFC stack with such a compressive sealing design were characterized. A comparison was made with a previous study for a similar comprehensive multi-cell pSOFC stack model but using only a rigid type of glass–ceramic sealant instead. Simulation results indicate that Stress distributions in the components such as positive electrode-electrolyte-negative electrode (PEN) plate, PEN-supporting window frame, nickel mesh, and interconnect were mainly governed by the Thermal expansion mismatch rather than by the applied compressive load. An applied compressive load of 0.6 MPa could eliminate the bending deformation in the PEN-frame assembly plate leading to a well joined structure. For a greater applied load, the critical Stresses in the glass–ceramic and mica sealants were increased to a potential failure level. In this regard, a 0.6 MPa compressive load was considered an optimal assembly load. Changing the seal between the connecting metallic PEN-supporting frame and interconnect from a rigid type of glass–ceramic sealant to a compressive type of mica gasket would significantly influence the Thermal Stress distribution in the PEN plate. The critical Stress in the PEN was favorably decreased at room temperature but considerably increased at operating temperature due to such a change in sealing design. Such differences in the Stress distribution could be ascribed to the differences in the constrained conditions at the interfaces of adjacent components under various sealing designs.
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Thermal Stress Analysis of a planar sofc stack
Journal of Power Sources, 2007Co-Authors: Chihkuang Lin, Tsungting Chen, Yaupin Chyou, Liehkwang ChiangAbstract:Abstract The aim of this study is, by using finite element Analysis (FEA), to characterize the Thermal Stress distribution in a planar solid oxide fuel cell (SOFC) stack during various stages. The temperature profiles generated by an integrated thermo-electrochemical model were applied to calculate the Thermal Stress distributions in a multiple-cell SOFC stack by using a three-dimensional (3D) FEA model. The constructed 3D FEA model consists of the complete components used in a practical SOFC stack, including positive electrode–electrolyte–negative electrode (PEN) assembly, interconnect, nickel mesh, and gas-tight glass-ceramic seals. Incorporation of the glass-ceramic sealant, which was never considered in previous studies, into the 3D FEA model would produce more realistic results in Thermal Stress Analysis and enhance the reliability of predicting potential failure locations in an SOFC stack. The effects of stack support condition, viscous behavior of the glass-ceramic sealant, temperature gradient, and Thermal expansion mismatch between components were characterized. Modeling results indicated that a change in the support condition at the bottom frame of the SOFC stack would not cause significant changes in Thermal Stress distribution. Thermal Stress distribution did not differ significantly in each unit cell of the multiple-cell stack due to a comparable in-plane temperature profile. By considering the viscous characteristics of the glass-ceramic sealant at temperatures above the glass-transition temperature, relaxation of Thermal Stresses in the PEN was predicted. The Thermal expansion behavior of the metallic interconnect/frame had a greater influence on the Thermal Stress distribution in the PEN than did that of the glass-ceramic sealant due to the domination of interconnect/frame in the volume of a planar SOFC assembly.
Chihkuang Lin - One of the best experts on this subject based on the ideXlab platform.
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Thermal Stress Analysis of planar solid oxide fuel cell stacks effects of sealing design
Journal of Power Sources, 2009Co-Authors: Chihkuang Lin, Liehkwang Chiang, Linghao Huang, Yaupin ChyouAbstract:Abstract A three-dimensional multi-cell model based on a prototypical, planar solid oxide fuel cell (pSOFC) stack design using compliant mica-based seal gaskets was constructed in this study to perform comprehensive Thermal Stress analyses by using a commercial finite element Analysis (FEA) code. Effects of the applied assembly load on the Thermal Stress distribution in the given integrated pSOFC stack with such a compressive sealing design were characterized. A comparison was made with a previous study for a similar comprehensive multi-cell pSOFC stack model but using only a rigid type of glass–ceramic sealant instead. Simulation results indicate that Stress distributions in the components such as positive electrode-electrolyte-negative electrode (PEN) plate, PEN-supporting window frame, nickel mesh, and interconnect were mainly governed by the Thermal expansion mismatch rather than by the applied compressive load. An applied compressive load of 0.6 MPa could eliminate the bending deformation in the PEN-frame assembly plate leading to a well joined structure. For a greater applied load, the critical Stresses in the glass–ceramic and mica sealants were increased to a potential failure level. In this regard, a 0.6 MPa compressive load was considered an optimal assembly load. Changing the seal between the connecting metallic PEN-supporting frame and interconnect from a rigid type of glass–ceramic sealant to a compressive type of mica gasket would significantly influence the Thermal Stress distribution in the PEN plate. The critical Stress in the PEN was favorably decreased at room temperature but considerably increased at operating temperature due to such a change in sealing design. Such differences in the Stress distribution could be ascribed to the differences in the constrained conditions at the interfaces of adjacent components under various sealing designs.
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Thermal Stress Analysis of a planar sofc stack
Journal of Power Sources, 2007Co-Authors: Chihkuang Lin, Tsungting Chen, Yaupin Chyou, Liehkwang ChiangAbstract:Abstract The aim of this study is, by using finite element Analysis (FEA), to characterize the Thermal Stress distribution in a planar solid oxide fuel cell (SOFC) stack during various stages. The temperature profiles generated by an integrated thermo-electrochemical model were applied to calculate the Thermal Stress distributions in a multiple-cell SOFC stack by using a three-dimensional (3D) FEA model. The constructed 3D FEA model consists of the complete components used in a practical SOFC stack, including positive electrode–electrolyte–negative electrode (PEN) assembly, interconnect, nickel mesh, and gas-tight glass-ceramic seals. Incorporation of the glass-ceramic sealant, which was never considered in previous studies, into the 3D FEA model would produce more realistic results in Thermal Stress Analysis and enhance the reliability of predicting potential failure locations in an SOFC stack. The effects of stack support condition, viscous behavior of the glass-ceramic sealant, temperature gradient, and Thermal expansion mismatch between components were characterized. Modeling results indicated that a change in the support condition at the bottom frame of the SOFC stack would not cause significant changes in Thermal Stress distribution. Thermal Stress distribution did not differ significantly in each unit cell of the multiple-cell stack due to a comparable in-plane temperature profile. By considering the viscous characteristics of the glass-ceramic sealant at temperatures above the glass-transition temperature, relaxation of Thermal Stresses in the PEN was predicted. The Thermal expansion behavior of the metallic interconnect/frame had a greater influence on the Thermal Stress distribution in the PEN than did that of the glass-ceramic sealant due to the domination of interconnect/frame in the volume of a planar SOFC assembly.
Liehkwang Chiang - One of the best experts on this subject based on the ideXlab platform.
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Thermal Stress Analysis of planar solid oxide fuel cell stacks effects of sealing design
Journal of Power Sources, 2009Co-Authors: Chihkuang Lin, Liehkwang Chiang, Linghao Huang, Yaupin ChyouAbstract:Abstract A three-dimensional multi-cell model based on a prototypical, planar solid oxide fuel cell (pSOFC) stack design using compliant mica-based seal gaskets was constructed in this study to perform comprehensive Thermal Stress analyses by using a commercial finite element Analysis (FEA) code. Effects of the applied assembly load on the Thermal Stress distribution in the given integrated pSOFC stack with such a compressive sealing design were characterized. A comparison was made with a previous study for a similar comprehensive multi-cell pSOFC stack model but using only a rigid type of glass–ceramic sealant instead. Simulation results indicate that Stress distributions in the components such as positive electrode-electrolyte-negative electrode (PEN) plate, PEN-supporting window frame, nickel mesh, and interconnect were mainly governed by the Thermal expansion mismatch rather than by the applied compressive load. An applied compressive load of 0.6 MPa could eliminate the bending deformation in the PEN-frame assembly plate leading to a well joined structure. For a greater applied load, the critical Stresses in the glass–ceramic and mica sealants were increased to a potential failure level. In this regard, a 0.6 MPa compressive load was considered an optimal assembly load. Changing the seal between the connecting metallic PEN-supporting frame and interconnect from a rigid type of glass–ceramic sealant to a compressive type of mica gasket would significantly influence the Thermal Stress distribution in the PEN plate. The critical Stress in the PEN was favorably decreased at room temperature but considerably increased at operating temperature due to such a change in sealing design. Such differences in the Stress distribution could be ascribed to the differences in the constrained conditions at the interfaces of adjacent components under various sealing designs.
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Thermal Stress Analysis of a planar sofc stack
Journal of Power Sources, 2007Co-Authors: Chihkuang Lin, Tsungting Chen, Yaupin Chyou, Liehkwang ChiangAbstract:Abstract The aim of this study is, by using finite element Analysis (FEA), to characterize the Thermal Stress distribution in a planar solid oxide fuel cell (SOFC) stack during various stages. The temperature profiles generated by an integrated thermo-electrochemical model were applied to calculate the Thermal Stress distributions in a multiple-cell SOFC stack by using a three-dimensional (3D) FEA model. The constructed 3D FEA model consists of the complete components used in a practical SOFC stack, including positive electrode–electrolyte–negative electrode (PEN) assembly, interconnect, nickel mesh, and gas-tight glass-ceramic seals. Incorporation of the glass-ceramic sealant, which was never considered in previous studies, into the 3D FEA model would produce more realistic results in Thermal Stress Analysis and enhance the reliability of predicting potential failure locations in an SOFC stack. The effects of stack support condition, viscous behavior of the glass-ceramic sealant, temperature gradient, and Thermal expansion mismatch between components were characterized. Modeling results indicated that a change in the support condition at the bottom frame of the SOFC stack would not cause significant changes in Thermal Stress distribution. Thermal Stress distribution did not differ significantly in each unit cell of the multiple-cell stack due to a comparable in-plane temperature profile. By considering the viscous characteristics of the glass-ceramic sealant at temperatures above the glass-transition temperature, relaxation of Thermal Stresses in the PEN was predicted. The Thermal expansion behavior of the metallic interconnect/frame had a greater influence on the Thermal Stress distribution in the PEN than did that of the glass-ceramic sealant due to the domination of interconnect/frame in the volume of a planar SOFC assembly.