This paper presents a novel technology called ‘double-action bending (DAB)’ to eliminate springback in hat-shape forming of advanced high-strength steel sheets (AHSS). It consists of four steps: (1) ...clamping of a sheet between an inner punch and a counter punch, (2) U-bending under a constant clamping force, (3) pushing-up the sheet by the counter punch from the bottom end, and (4) bending of the flange by an outer punch. A great advantage of this technology over other hat-bending processes, such as draw bending and crash forming, is that perfect hat-shaped channels are easily obtained for any type of AHSS just by determining two controllable process parameters, namely, the bottom pushing-up force and outer-punch stroke in flange bending. An accurate finite element (FE) simulation allows us to determine these process parameters prior to experimental tryout. The validation for this process was shown by performing the hat-shaped DAB experiments on a dual-phase 980-MPa AHSS and the corresponding FE simulation.
Research and development on the thermochemical water-splitting cycle using iodine and sulfur, a potential large-scale hydrogen production method, is reviewed. Feasibility of the closed-cycle ...continuous water splitting has been demonstrated by coupling the Bunsen reaction, thermal decomposition of hydrogen iodide and that of sulfuric acid. Studies are in progress to realize efficient hydrogen production. Also, development of chemical reactors made of industrial materials has been carried out, especially those used in the corrosive process environment of sulfuric acid vaporization and decomposition.
The three-dimensional simulations of the combustion of self-propagating hydrogen-air premixed flame are performed by an open-source CFD code. The characteristics of the flame such as flame ...propagation behavior, flame radius, temperature, and pressure are analysed by varying the initial laminar flame speed and grid size. When the initial laminar speed increases, the thermal expansion effects become strong which leads the increase of flame radius along with the increase of flame surface area, flame temperature, and pressure. The fluctuation of pressure appears and it leads the temperature to fluctuate further. The increase in flame radius is directly related to the flame temperature. A new laminar flame speed model derived previously from the results of experiment is also introduced to the code and the obtained flame radii are compared with those from the experiments. The formation of cellular flame fronts is captured by simulation and the cell separation on the flame surface vividly appears when the grid resolution becomes sufficiently higher. The propagation behavior of cellular flame front and the flame radius obtained from the simulations have the reasonable agreement with the previous experiments.
In this study, it was evaluated the long-term catalytic effect and catalyst poisoning effect of gamma-ray irradiation on zirconium molybdate hydrate in the presence of three-way catalysts. The ...results indicated that the three-way catalyst was effective in suppressing the increase in hydrogen concentration due to radiolysis without being affected by poisoning. In addition, hydrogen diffusion analysis of the compressed hull and endpiece waste shows that hydrogen flows well through the waste and is suppressed by a three-way catalyst located in the center of the waste headspace.
Dissimilar linear friction welding (LFW) of AA5052/AA6061 was performed at different applied pressures. A dissimilar joint obtained at a high applied pressure of 200 MPa exhibited a tensile strength ...equivalent to that of the AA5052 base material, mainly because of the high density of low-angle grain boundaries (LAGB) per unit area at the weld regions. Meanwhile, the joints obtained at low applied pressures of 30 and 100 MPa softened at the weld regions because the LAGB density decreased because of the increased peak welding temperature. Therefore, the joints fractured in the weld regions, and the tensile strength of the joints decreased. Because dissimilar AA5052/AA6061 joints have metallurgical inhomogeneities and strength mismatches, plastic strain constraints near the weld interface of the soft material inevitably occur during tensile testing. Although the Vickers hardness at the weld interface on the AA5052 side had the lowest value, fracture was suppressed owing to the plastic strain constraint. At 100 and 200 MPa, the average grain diameters as a function of Z on the AA5052 side of the dissimilar AA5052/AA6061 joints matched the plot obtained from the similar AA5052 joint. At an applied pressure of 30 MPa, the average grain diameter was much larger than that of similar joints because the dissimilar joints underwent lower strain during LFW compared to similar joints, which resulted in the suppression of grain refinement during continuous dynamic recrystallization (CDRX).
The Japan Atomic Energy Agency (JAEA) is performing research and development on the thermochemical water-splitting iodine–sulfur (IS) process for hydrogen production with the use of heat ...(temperatures close to 1000
°C) from a nuclear reactor process plant. Such temperatures can be supplied by a High Temperature Gas-cooled Reactor (HTGR) process. JAEA's activity covers the control of the process for continuous hydrogen production, processing procedures for hydrogen iodide (HI) decomposition, and a preliminary screening of corrosion resistant process materials. The present status of the R&D program is reported herein, with particular attention to flowsheet studies of the process using membranes for the HI processing.
In this study, a comparison between the well-established Lagrangian approach and the Arbitrary Lagrangian–Eulerian (ALE) approach is presented. This comparison aims to verify the ALE's approach ...suitability for modeling thermomechanical processes. After that, a study on the material's stress state evolution inside the specimen is provided. The stress state is evaluated through the triaxiality factor and Lode parameter. Ideally, under pure compression, these parameters' values are − 1/3 and − 1, respectively. However, it is not possible to achieve ideal conditions in actual experiments. The Lagrangian model was done in QForm, and the ALE model was done in LS-Dyna. The results from both models are in good agreement between them and agree with the force vs. stroke measured during the experiments. Two paths were defined to study the stress state inside the sample, in the radial direction (equator line) and axial direction (axial line). It was concluded that some areas in both paths might be considered as approximately under pure compression stress state. In addition, the ALE approach accuracy for thermomechanical modeling was verified.
Article highlights
Cylindrical compression test is modeled by finite element method and compared with experimental results.
The Lagrangian and the Arbitrary Lagrangian–Eulerian (ALE) approaches are used to model the experiments.
The ALE approach's suitability for modeling thermos-mechanical phenomena is verified by comparing it with the Lagrangian approach.
Two dimensional unsteady calculations of reactive flows were performed in large domain to investigate the unstable behaviors of cellular premixed flames at low Lewis numbers based on the ...diffusive-thermal (D-T) model and compressible Navier-Stokes (N-S) equations including one-step irreversible chemical reaction. The relations between the growth rate and wave number, i.e. the dispersion relations, were obtained. The growth rates obtained by the compressible N-S equations were large and the unstable ranges were wide compared with those obtained by the D-T model equations. This was because both hydrodynamic and diffusive-thermal effects were taken into account in the compressible N-S equations. A disturbance with the maximum growth rate was superimposed on a stationary planar flame to generate the cellular flame. The cellular flame formed, and the overshoot of temperature evolved. When the length of computational domain increased, the number of small cells separated from large cells of the cellular flame increased drastically. As the results, flame surface area and average burning velocity increased. The stronger unstable behaviors and the larger average burning velocities were observed especially in the numerical results based on the compressible N-S equations. In addition, the fractal dimension obtained by the compressible N-S equations was larger than that by the D-T model equations. Moreover, we confirmed that the radiative heat loss promoted the instability of premixed flames at low Lewis numbers.
Magnesium alloys usually exhibit low ductility at the room temperature due to its hexagonal close-packed structure, but it will be improved at elevated temperature. Therefore, warm press-forming of ...magnesium alloy sheets is quite attractive. In order to determine the optimum condition of press-forming for magnesium alloy sheets, in the present work, the effects of strain rate, temperature and sheet thickness on the yield locus were experimentally investigated. The yield loci of magnesium alloy (AZ31) sheets with different sheet thickness (0.5 and 0.8
mm) were obtained by performing biaxial tensile tests, using cruciform specimens, at temperatures of 100, 150, 200, 250 and 300
°C at strain rates of 10
−2, 10
−3 and 10
−4
s
−1. Based on the experimental results, the effects of strain rate, temperature and sheet thickness on the yield locus were discussed. The size of yield locus drastically decreases with increasing temperature and decreases with decreasing strain rate. In contrast with the temperature and strain-rate dependence of the yield locus, sheet thickness has no influence on the yield locus. The shape of the yield locus of magnesium sheet is far from the predictions calculated by the yield functions of von Mises, Hill and Cazacu. Instead of these, the yield functions of Logan-Hosford or Barlat is a better choice for the accurate description of biaxial tension stress–strain responses at high temperature.
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