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Recently, casting simulations have been used to improve the product quality and the yield during casting. However, there are cases in which the simulation results do not reproduce the defects in the product. Although accurate physical property values are necessary for highly accurate simulations, some physical property values are not dependable. Recently, the occurrence of defects, such as shrinkage porosity, has been compared between simulated results and actual products by varying the physical property values given in the simulation. It has been shown that the heat value of the exothermic sleeve in the catalog used to reduce defects may be approximately one-seventh of the actual heating value. In this study, we developed an adiabatic calorimeter with a simple configuration that can realize actual casting conditions. The heat generated by the three types of exothermic sleeves was measured. No difference in calorific value was observed between the three types of samples, and all were approximately 2 kJ·g−1. This value is less than the half of that provided in the catalog.

The laser flash technique is a standard method to measure the thermal diffusivity of solid samples especially at high temperatures. To understand the reliability of thermal diffusivity evaluation at high temperature for solid samples with low-thermal-diffusivity values, we analyzed the effect of radiative heat loss using the logarithmic method. The results revealed that when the Biot number was 0.1, the deviation from the input thermal diffusivity value was approximately −1.6%. In addition, when an aluminum silicate (AS) sample was heated to 1,273 K, the maximum deviation was approximately −0.35%. In contrast, the difference between the input value and the thermal diffusivity evaluated by the halftime method when AS was heated to 1,273 K was approximately 2.38%. Thus, since the effect of radiative heat loss was found to be negligible, it is concluded that the normalized logarithmic method should be very useful for the thermal diffusivity analysis of low-thermal-diffusivity solid samples at high temperature.

（閲覧はこちらから→）https://www.sciencedirect.com/science/article/pii/S0022311521002257

One of the key issues in a core disruptive accident (CDA) evaluation in sodium-cooled fast reactors is eutectic reactions between boron carbide (B4C) and stainless steel (SS) as well as its relocation. Such behaviors have never been simulated in CDA numerical analyses in the past, therefore it is necessary to develop a physical model and incorporate the model into the CDA analysis code. This study focuses on B4C-SS eutectic melting experiments, thermophysical property measurement of the eutectic melt, and physical model development for the eutectic melting reaction. The eutectic experiments involve the visualization experiments, eutectic reaction rate experiments and material analyses. The thermophysical properties are measured in a range from solid to liquid state. The physical model is developed for a CDA computer code based on the measured data of the eutectic reaction rate and the physical properties. This paper describes the project overview and progress of experimental and analytical studies conducted until 2019. Specific results in this paper are the validation of physical model describing B4C-SS eutectic reaction in the CDA analysis code, SIMMER-III, through the numerical analysis of the B4C-SS eutectic melting experiments in which a B4C block was placed in a SS pool.

The earthquake (Mw 7.3) that struck Nepal on April 25, 2015 caused damage to many civil engineering and architectural structures. While several road gabion retaining walls in mountainous regions incurred damage, there was very little information that could be used to draw up earthquake countermeasures in Nepal, because there have been few construction cases or case studies of gabion structures, nor have there been experimental or analytical studies on their earthquake resistance. Therefore, we conducted a shake table test using a full-scale gabion retaining wall to evaluate earthquake resistance. From the experiments, it was found that although gabion retaining walls display a flexible structure and deform easily due to the soil pressure of the backfill, they are resilient structures that tend to resist collapse. Yet, because retaining walls are assumed to be rigid bodies in the conventional stability computations used to design them, the characteristics of gabions as flexible structures are not taken advantage of. In this study, we propose an approach to designing gabion retaining walls by comparing the active collapse surface estimated by the trial wedge method, and the experiment results obtained from a full-scale model of a vertically-stacked wall, which is a structure employed in Nepal that is vulnerable to earthquake damage. When the base of the estimated slip line was raised for the trial wedge method, its height was found to be in rough agreement with the depth at which the gabion retaining wall deformed drastically in the experiment. Thus, we were able to demonstrate the development of a method for evaluating the seismic stability of gabion retaining walls that takes into consideration their flexibility by adjusting the base of the trial soil wedge.

In developing countries, gabions are widely used in several construction works, like road, river, countermeasures against slope failure and so on, because of their easy operation and low cost. In 2015 Nepal Gorkha Earthquake, a lot of retaining walls using gabions were not damaged against the strong earthquake because of their high flexibility. However, some deformation or declination were reported dpending on retaining wall types and ground conditions behind retaining walls. Therefore, in order to evaluate the earthquake resistance and residual deformations of retaining walls using gabions widely observed in Nepal, full-scale shake table tests and laboratory tests were conducted in previous studies. In this study, elemental simulations for determination of the analysis parameters based on the results of triaxial compression tests were carried out to check the validity of parameters. Then, a series of numerical analysis using proposed model was performed to reproduce the dynamic behaviors of full-scale shake table tests and evaluate the earthquake resistance of retaining wall using gabions. According to the results of these numerical analysis, it was confirmed that proposal model adequately could simulate the dynamic response of retaining walls in the full-scale shake table tests. and it was also cleared that the stepwise type retaining wall was superior to that of vertical type from the standpoint of earthquake stability against sliding and overturning.

Gabion structures are used in a variety of ways in Japan and around the world because they allow for the creation of simple structures at highly reasonable construction costs and completion periods. Previous earthquake damage surveys have shown that, in many cases, gabion structures did not collapse even though deformation was allowed, and have demonstrated that the wire mesh used in their construction has a high confinement effect on the stones filling the gabion. Despite this, gabions have not been actively utilized, nor have they been used to construct permanent structures in Japan because the design and construction of such structures are based on experience, and a standardized design method has not been developed. Hence, in order to facilitate development a design method for gabion-based structures, we must first go back to the basics and establish a detailed explanation of the wire mesh deformation mechanism of such structures. In this study, we performed tensile tests on wire meshes of different shapes in order to determine their strength and deformation characteristics and then conducted numerical analyses using the results obtained. The tensile tests revealed that deformation characteristics differed depending on the mesh shape and tensile direction. We also showed that the direction in which the tension acts and the mesh nodes are important, and that the test results could be reproduced via numerical analysis with the finite element method by using beam elements.

Borosilicate glasses are candidate materials for the immobilization of high-level radioactive waste. The values of thermal conductivity of different borosilicate melts are thus indispensable inform...

Thermal conductivities of alkali–silicate (R2O–SiO2 (R = Li, Na, K)) and calcium–alkali–silicate (CaO–R2O–SiO2 (R = Li, Na, K)) melts were evaluated by combining their thermal effusivities measured using the front-heating front-detection laser flash method with their density and specific heat capacity. Results of the evaluation revealed that the temperature-dependences of the thermal conductivities of the R2O–SiO2 and CaO–R2O–SiO2 (R = Li, Na, K) melts are small over the temperature range investigated. Moreover, the thermal conductivities of the CaO–R2O–SiO2 melts are almost equal to those of the R2O–SiO2 melts. Therefore, the network frame of the CaO–R2O–SiO2 melts can presumably become dense owing to the ion bonding between Ca2+ and the non-bridging oxygen.

This study aimed to measure the thermal effusivity distribution on a lunar regolith simulant (FJS-1) using a thermal microscope and to calculate the average thermal effusivity and thermal conductivity using density and specific heat. Moreover, discussions were conducted based on the results of the microstructural analysis of the sample. The FJS-1 particles were embedded in an epoxy resin and polished to a mirror finish. The samples were analyzed using scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM–EDS). X-ray diffraction (XRD) was performed to identify the mineral phases in FJS-1. The results of SEM–EDS and XRD showed that a single sand particle was composed of several minerals, such as anorthite and olivine. Then, the thermal microscope was used to obtain the distribution of the thermal effusivity of a particle from the mirror-finished sample in a 1 × 1 mm2 area with intervals of 10 μm. The measured thermal effusivity correlates with the SEM image of the sample. Anorthite has a small thermal effusivity of 1.99 ± 0.31 kJ·s−0.5·m−2·K−1, while olivine has a large thermal effusivity of 2.73 ± 0.35 kJ·s−0.5·m−2·K−1. In both cases, the thermal effusivity was found to be of the same order of magnitude as the reported values. The average thermal effusivity and conductivity of a single particle were determined to be 2.4 ± 0.6 kJ·s−0.5·m−2·K−1 and 2.6 ± 1.3 W m−1·K−1, respectively, based on the proportion of existing phases.

A spot periodic heating method is a highly accurate, non-contact method for the evaluation of anisotropy and relative thermophysical property distribution. However, accurately evaluating thermal diffusivity is difficult due to the influence of temperature wave reflection from the whole surface of the sample. This study proposes a method to derive thermal diffusivity using a parameter table based on heat transfer equations using the concept of optimum distance between heating-point and measurement point. This method considers finite sample size, sensitivity distribution of infrared ray detector, intensity distribution of heating laser and sample thickness. In these results, the obtained thermal diffusivity of pure copper corresponded well with previous literature values. In conclusion, this method is considered highly effective in evaluating the thermal diffusivity in the horizontal direction.

One of the key issues in a core disruptive accident (CDA) evaluation in sodium-cooled fast reactors is eutectic reactions between boron carbide (B4C) and stainless steel (SS) as well as its relocation. Such behaviors have never been simulated in CDA numerical analyses in the past, therefore it is necessary to develop a physical model and incorporate the model into the CDA analysis code. This study focuses on B4C-SS eutectic melting experiments, thermophysical property measurement of the eutectic melt, and physical model development for the eutectic melting reaction. The eutectic experiments involve the visualization experiments, eutectic reaction rate experiments and material analyses. The thermophysical properties are measured in a range from solid to liquid state. The physical model is developed for a severe accident computer code based on the measured data of the eutectic reaction rate and the physical properties. This paper describes the project overview and progress of experimental and analytical studies conducted until 2018. Specific results in this paper are boron concentration distributions of solidified B4C-SS eutectic sample in the eutectic melting experiments, which would be used for the validation of the eutectic physical model implemented into the computer code.

The thermal conductivities of borosilicate melts, which have scarcely been measured, are one of the important thermophysical properties for optimization of temperature distribution in a glass melting furnace. In this study, the thermal effusivities of B2O3-SiO2 and CaO-B2O3-SiO2 melts were first measured using a front heating–front detection laser flash method. Then, the thermal conductivities, which were obtained by combining the measured thermal effusivity data with specific heat capacity and density, could be evaluated through an equation using the least-squares method. As such, the thermal conductivities of the B2O3-SiO2 and CaO-B2O3-SiO2 melts were found to slightly linearly decrease with increasing temperature over the investigated temperature range of 1248–1723 K. In addition, the thermal conductivities of the samples of CaO-B2O3-SiO2 melts were higher than those of the samples of B2O3-SiO2 melts. Furthermore, the network models of the thermal conductivities for the B2O3-SiO2 and CaO-B2O3-SiO2 melts were discussed using the boron-11 NMR spectra of the glassy samples for the B2O3-SiO2 and CaO-B2O3-SiO2 samples.

In the 2015 earthquake in Gorkha, Nepal, damaged different kinds of structures around the Kathmandu Basin. On the other hand, in mountainous areas, it was confirmed that gabion structures such as retaining walls along roads showed their high flexibility by performing their functions. In this paper, based on the results of the damage field survey on gabion retaining walls, a full-scale shake table test is conducted to evaluate the earthquake resistance of gabion retaining walls on roads, which are a common site in Nepal. The soil container used for the full-scale shake table test has the following internal dimensions: 4.0 m height, 3.1 m width, and 11.5 m depth. Earthen bank retaining walls with height of 3 m were arranged in three rows in a perpendicular direction to the cross-section, and the ground behind the retaining wall was prepared. The sinusoidal waves of 3 Hz were applied, consisting of 2 s of gradual increase, 4 s of steady part, and 2 s of gradual decrease; the input waves were provided in four stages of acceleration amplitude. Three types of gabion retaining walls were considered, i.e., vertical-type, stepwise-type and gravity-type, and 3D terrestrial laser measurement was conducted before and after shake table test of each case. Comparison of the residual deformations of the gabion retaining walls measured by 3D terrestrial laser showed that the vertical-type wall did not collapse but tilted forward after the shake teble test. A similar damage situation was confirmed by the field survey in Nepal. The other two cases suffered only slight deformation and are considered to be effective structures for application on sites. Finally, the trial wedge method was applied to the experimental results of the vertical-type of gabion retaining and useful suggestions for future earthquake-resistant design were made by comparing the active collapse angle with the positions of deformation, such as cracking which occurred in the ground behind the retaining wall after shaking. Then, the applicability of trial wedge method and its problem in the design of gabion retaining wall were shown.

The thermal conductivity of silicate melts was evaluated using a thermal resistor network model, which consisted of a diamond lattice. Based on the assumption that the mean free path of phonons is shorter than the interatomic distance, the thermal conductivity of the silicate melts was calculated through a Monte-Carlo simulation based on the non-bridging oxygens to tetrahedral cations (NBO/T) ratio and the ratio of the conductance of silicon with NBOs (CSi-NBO) to that of silicon with bonding oxygens (CSi-BO). For NBO/T

A compositionally graded alloy in the PbTe–Sb2Te3–Ag2Te system was fabricated by the Bridgeman method. In the sample obtained for analysis, the length of the graded area was of the order of several tens of nanometers. Its thermal effusivity was measured with a thermal microscope, which required sputtering of a Mo film on the surface of the sample. The measured values of thermal effusivity depended on the thickness of the Mo film. However, it was difficult to sputter the Mo film uniformly in the wide area. Even though a relatively large target was used in the sputtering apparatus on the laboratory scale, the thickness of the Mo film just under the center of the target was larger than that in other areas. In this study, the measured thickness of the Mo film was calibrated with a high degree of accuracy against the reference glass slide. The thermal effusivity of the PbTe–Sb2Te3–Ag2Te alloy was in the range of 400–800 Ws0.5 m−2 K−1.

The influences of crystal orientation on phonon transport properties were analyzed by nanoindentation using single-crystal Si wafers. The elastic moduli and group velocities of [100]-oriented Si were lower than those of [111]-oriented Si. The phonon mean free path (MFP) exhibited the opposite trend. Phonon transport properties were calculated using the Hooke's law with a stiffness tensor. The measured phonon MFP of the [100]-oriented Si were approximately 13% different from the corresponding semi-theoretical values, while those of the [111]-oriented Si were comparable to the corresponding semi-theoretical values, according to the difference in atomic density of each crystal plane of Si.