In recent years, renewable energy resources have been attracting the people’s attention in order to prevent global warming. We have been developing a small but flexible wave power generator. This device takes a form of tetrapod incorporating with power generation units. This device generates by the force from waves vibrates. This generator also has a surface moving capability in order to move back to the home station and to discharge the stored electricity. In this study, we present a new surface moving mechanism of the generator for the purpose of improving the moving performance. We numerically evaluate the equipment dimensions and magnet weight required for the generator to rotate and to move on water. In addition, we simulate the device behavior, using a particle (SPH) -based CFD method developed in our laboratory, and compared the results with the experiments.
In the Great East Japan Earthquake, the tsunami caused huge damage to the Tohoku area. One of the reasons is that the people forgot the risk of tsunami over a million years from the previous tsunami. Therefore, we have developed a portable but realistic tsunami experience system (TSUNAMI VR) using recent HMD technologies and CFD techniques. In the Great East Japan Earthquake, thousands of people were sacrificed because they tried to escape from tsunami by a car and cars on the street prevented people from escaping on foot. We numerically analyzed the car drifting motion by flood using SPH method, which is one of the particle methods, and confirm the accuracy of analysis by comparison with the previous experimental study. We finally computed the behaviors of tsunami attack to the Miyako City. In the computation, we compared the car drifting motion by tsunami with the actual video during the Great East Japan Earthquake.
This paper is concerned with the ultrasonic wave propagation in a solid propellant. Solid propellants are fuels which can be motive force of solid rocket motor. In the production process, no critical defects in solid propellants are required. In general, the radiographic testing (RT) has been used to detect a defect in solid propellants. However, RT needs much inspection time and cost, and may be troublesome task. The ultrasonic testing (UT), which is simple and widely used for various inspections, may have a potential for detection of a defect in solid propellants. Therefore, in this research, 2-D simulation of ultrasonic wave propagation and scattering in a solid propellant is implemented by using the finite element method (FEM). After the fundamental isotropic elastodynamic theory is discussed, the finite element formulation with Rayleigh attenuation used in this study is introduced. Some numerical results are demonstrated to understand the ultrasonic wave propagation phenomena and to verify the developed FEM code.
The creep curves of superalloys as conventional high temperature materials consist of three regions which are
transient creep, steady state creep and accelerating creep. However, unlike this, it was reported that anomalous
strengthening phenomena appeared in the creep of the superalloy in high temperature and low stress regions, and creep curves repeating unique unevenness were drawn. Although no single equation representing such anomalous creep curves has been found so far, we succeeded in expressing the above-mentioned anomalous creep curves with single equation using discrete cosine transform. Therefore we report the above in this paper.
CAE is indispensable in the current field of engineering, and the development of computational mechanics calls for the addition of functions, but by continuing to add functions without taking measures, program complexity and functions Some of the computational mechanics researchers can not afford to take measures or are not familiar with the program, so the laboratory maintains the maintainability of existing programs, By making additional functions independent of each other, research is being conducted on how to add functions that prevent these problems, and this method is advocated as the Option pattern. Maintaining existing program maintainability in the Option pattern. There are three conditions that the additional functions can be made independent and can be combined multiplely, and the additional functions can be described in one place. To. In this study use, by adding a geometric nonlinear functions and dynamic analysis function in FEM program
according to the Option pattern, to verify the validity of the function addition method. The class to be added is called Option class, and in this research, four Option classes are added to the existing FEM program. By performing this research, functions are added independently while maintaining the maintainability of the existing program. I was able to confirm that.
In this paper, a shape reconstruction method based on the time-reversal technique is developed for the purpose of quantification of the ultrasonic non-destructive testing (UT). First, a forward analysis of 3-D scalar wave scattering by multi scatterers under the use of a matrix array transducer is solved by using the convolution quadrature time-domain boundary element method (CQBEM), which can produce higher accuracy better than conventional time-domain boundary element method (BEM). In the corresponding inverse analysis, the topological sensitivity proposed by Bonnet is used to identify the shape and position of defects in the 3-D scalar wave field. In this process, the scattered waves at the matrix array transducer obtained by the CQBEM are time-reversed numerically, and sent back to the defects to implement the defect detection. As numerical examples, some defect shape reconstruction results are presented, and the reconstruction ability of the proposed method is investigated by changing the radiation pattern of ultrasound from a matrix array
This paper is concerned with the 2-D large-scale elastic wave scattering by many cracks in general anisotropic elastic solids using a parallelized convolution quadrature time-domain boundary element method (CQBEM). Anisotropic materials such as fiber reinforced plastics (FRPs) have received attention in many engineering fields. However, it is difficult to use ultrasonic non-destructive testing (UT) for detection of cracks in anisotropic materials which have acoustic anisotropic property. Therefore, in this research, the CQBEM for 2-D pure SH wave scattering by defects in general anisotropic elastic solids is proposed. The CQBEM involves the convolution quadrature method (CQM) which is applied to the time discretization of the time-domain boundary integral equation. The CQBEM can produce stable numerical solutions better than the classical time-domain boundary element method (TD-BEM) if we use a small time increment. In addition, the CQBEM is parallelized by using the hybrid method of OpenMP and MPI (Message Passing Interface) to improve the computational performance.
At the poultry farm, oxygen supply and temperature control by ventilating indoor air are very important. The
method by which the inside of a poultry farm becomes negative pressure is used in many cases. In order to equalize the internal air temperature, the designer adjust and design the amount of inflowing air from the vent provided in the front and the side by the number of the blower and vent. In this study, we used the flow analysis system OPENFOAM to predict the flow conditions in the poultry farm with various ventilation methods. And we examined each method from the viewpoint of velocity distribution and temperature distribution.
Oscillations of gas bubbles in bubbly liquids induce a wave dispersion effect into weakly nonlinear propagation of pressure waves and its propagation process is described by KdV-Burgers (KdVB) equation. We numerically solve the KdVB equation via a finite difference method. As a result, the initial waveform is firstly distorted due to a nonlinear effect, and is separated into some solitary waveforms due to a dispersion effect. Finally, the solitary waveform is attenuated by a dissipation effect. It is implied that the appearance of nonlinearity induces the dispersion and this does the dissipation. The formation of an attenuated soliton as the time lapse is accomplished by a competition of nonlinear, dispersion, and dissipation effects, and its amplitude strongly depends on the initial void fraction.
Open cell polyurethane foam is used in various products. Product design method of open cell foam by numerical analysis has not been established because the mechanical properties of the material are complicated. In this study, FEM analysis method is proposed to predict the mechanical properties of polyurethane foams considering the matrix and its microstructure. The polyurethane matrix were assumed to be approximated by the isotropic hyperelastic model. The Yeoh model was applied to the potential energy function of the hyperelastic model. The microstructures of two polyurethane foams were obtained by the CT-scanning system. FEM analysis models were prepared from the CT-scanning data. From simulated results, the influence of analysis area and the boundary condition were evaluated.
Fiber-reinforced materials such as natural leathers, artificial leathers, fiber-reinforced rubbers, and so on are widely used in the sports fields. Now, it is expected to develop the new artificial materials which have higher performance than the existing ones. However, fiber-reinforced material has reinforcing fibers in the body. Since the effect of fiber orientations, the mechanical property shows anisotropy. Also, the directions of the reinforcing fibers are dispersed. Due to the characteristics, it is difficult to predict the mechanical property of fiber-reinforced materials. Then, our research group proposed an anisotropic hyperelastic model of fiber-reinforced materials. The modeling was conducted to the mechanical characteristics of natural leathers. In order to consider the fiber orientation dispersion in the material, circular normal distribution was applied to the proposed model. In this paper, from the results of uniaxial tensile loading tests of natural leathers, fiber orientation dispersion was presumed by circular normal distribution. Also, numerical analyses were conducted and the applicability of circular normal distribution to the estimation of fiber orientation dispersion was evaluated.
In this study, the stiffness in the out-of-plane direction of the string surface of the badminton racquet was evaluated by finite element analysis. Three types of badminton rackets with different frame shapes and different string intervals were modeled. The models were analyzed to analyze the out-of-plane displacement of the string plane by finite element analysis programs. The stiffness derived from the analysis results were compared with racquets, and the relationships between the out-of-plane stiffness of the string surface, the shape of the racquet frame and the string interval were investigated. As the results of investigation, the stiffness increased as the string spacing became wider. In addition, the distribution of stiffness of the string plane changed depending on the shape of the racquet frame.
The phenomenon in which the dimensions of the magnetic material change due to the addition of a magnetic field is called magnetostrictive effect. Conversely, the phenomenon that the internal magnetic flux changes by the expansion and contraction of the shape of the magnetic material is called inverse magnetostrictive effect. Magnetostrictive materials can be driven without contact and have a high response speed, so they are also attracting attention in IoT applications and sensing. Therefore, considering application to evaluation of axial force of bolt which is a fastening part, tightening test of bolt using magnetostrictive material FeCo alloy and finite element analysis are performed, and proposal of direct bolt axial force evaluation method by change of magnetic flux density, evaluate the fastening characteristics of the magnetostrictive bolt.
Hardness is evaluated using the damping behavior of a Herbert pendulum swung on the specimen in Herbert
hardness test. Currently, swing angle of the pendulum is detected by two laser displacement meters installed outside of the pendulum during hardness test. In this study, a compact size acceleration sensor is installed to the pendulum to improve portability of the Herbert hardness testing system. Herbert hardness test was carried out to the metal specimens using the pendulum with the compact size acceleration sensor. Swing angle was detected by both laser displacement meters and compact size acceleration sensor. Hardness obtained by the compact size acceleration sensor was compared with that by the laser displacement sensor. Hardness obtained by the compact size acceleration sensor corresponds with that by the laser displacement meter. Therefore, portability of the Herbert hardness testing system can be improved by installing a compact size acceleration sensor to the Herbert pendulum because Herbert hardness test can be carried out without the laser displacement meters as outside equipment.
A flange structure is often used when joining cylindrical members. And these flange joints are joined by bolts.
Therefore, in order to allow this joint to maintain its original function, it is important to evaluate the strength of the bolt appropriately. On the other hand, when a cylindrical member is used as a large-sized structure, the diameter of the bolt for flange connection also inevitably increases. However, there are many studies on the strength of conventional bolts in the dimension of M20 or less, and there are almost no studies on the evaluation of strength of large diameter bolts. In this study, we analyze tightening process of M48 bolt using FEM. The relationship between the axial force and the rotation angle during tightening, the torque coefficient, and the share rate of fastening force were compared with the theoretical ones. In addition, the impact of the coefficient of friction on the relationship between the axial force and the rotation angle and the share rate of fastening force are obtained.
The lifestyle of Jomon people is changed by invention of Jomon ware. Jomon ware is a very interesting device from the view point of materials strength. However, mechanical test cannot be carried out to Jomon ware due to its high historical value. The purpose of the study is to investigate the effect of aging time on strengths of Jomon ware materials after kneading clay in manufacturing process. The specimens are manufactured based on the reproduction process of Jomon ware. Bending strength and fracture toughness are experimented by four point bending testing. Conclusions are as follows; 1) These strengths seem to become higher with increase in aging time. 2) Jomon people had proper knowledge for the view point of materials strength. 3) The changing of mixing ratio and aging time affect the strength and easiness of molding.
A modeling method for buckling FE analysis of plate structures with corner dimension was proposed. The model for a plate with corner dimension consists of an edge plate with equivalent length and constant thickness. The equivalent length is derived from the efficient buckling length by comparing with buckling forces of plates with corner dimension and consistent thickness under the condition of both fixed edges. The equivalent thickness is derived from comparing with support stiffness of the plates with corner dimension and constant thickness. The proposed method was applied to single plates and plate structures with corner dimension, and the buckling forces of the given structures and structures modeled by the proposed method were compared by buckling FE analyses. It was found that the buckling forces could be evaluated within errors of 1.9 % and 2.7 %.
IIn late years, the law about the energy consumption performance gain of the building is promulgated, and the house which had the high insulation performance more than the energy saving standard is bought. Thermal insulation material applies it to the outer wall of the building and is effective in lowering the indoor temperature of the building by reflecting light of the sun. Therefore, it is cost-cut the air conditioner and is connected for saving energy by using it for the outer wall of a house and the building of the warm area. As for the study to evaluate thermal insulation performance of such paint, a lot of reports are accomplished. On the other hand, I can expect that I am effective in raising indoor temperature by performing an insulation of the temperature of the room when I apply thermal insulation material to the inner wall of the house. Thus, insulation effect of thermal insulation material is necessary for the saving energy of the chilly local house and building. However, it is necessary to demonstrate that paint has insulation effect because there are few reports on insulation performance examples of the paint. We tested it to assume a chilly local house in this study, and to apply thermal insulation material to the inner wall of the examination device, and to evaluate a heat reply characteristic of the room space.
When the liquid in the vertical pipe is heated, depending on the conditions, the liquid inside will be boiled rapidly, and the geysering phenomenon which repeats ejection and re-inflow of liquid occurs. The geysering phenomenon is classified as a kind of unstable flow phenomenon that occurs in the pipeline, and may occur in the pipeline of a power plant that uses boiling phenomena such as boilers, and it is can be a problem. In this study, we investigated the influence of the heating amount of the heater, the water level at the start of the experiment, the temperature of the cooling water, and the volume of the boiling part on the geysering phenomenon. The experimental device consists of a boiling vessel, a vertical tube and a sub plenum. The experiment is started by heating the working fluid with a heater installed at the bottom of the boiling vessel. The experimental conditions are the input power, the water level at the start of the experiment, and the
temperature of the sub plenum. In addition, we created mathematical models and compared the results of numerical analysis and experiments. As a result, liquid temperature and water level fluctuation showed similar tendency.
In recent years, new measurement and inspection techniques using infrared thermography are applied in various research and development fields. One of the advantages of infrared thermography is the ability to measure time series two-dimensional surface temperature distributions without contact. In this report, three kinds of different silicone oil (100cs, 1000cs, 5000cs) are used as test fluids. The silicone oil is filled in a horizontally open rectangular container and the heat flow phenomenon while heating from the bottom is visualized by an infrared camera. Heat transfer characteristic of natural convection obtained by experiments are compared with the conventionally proposed heat transfer correlation formula. Experimental results show that the natural convection does not develop as Prandtl number increases. The Rayleigh number increases as the amount of heating increases, and the heat flow phenomenon is related to the Rayleigh number.
The heat transfer characteristics of natural convection of magnetic ionic liquid in a horizontal enclosed rectangular container are evaluated experimentally. The validity of the heat transfer coefficient based on the thermophysical properties is examined and compared with the conventionally proposed heat transfer correlation equation. It is found that the heat transfer coefficient ratio (with and without a magnetic field) is less than 1, therefore, the heat transfer suppressed after applying a magnetic field. In addition, the stronger the external magnetic field in the vertical direction is, the higher the heat transfer suppression is.
Sewage pumps used in sewage treatment facilities need to prevent the blockage of foreign matter because they transport fluid containing a large amount of various foreign matter. Because single blade centrifugal pump can form a large passing particle size in the pump, it is generally used as a sewage pump. The internal flow of the single blade centrifugal pump is very complicated. Elucidation of the internal flow is important for improving the efficiency of singleblade centrifugal pumps, but the open type has hardly been investigated. In this study, CFD analysis were performed to investigate the relationship between flow structure and hydraulic loss in casing of an open-type single blade centrifugal pump. As a result, in the open-type impeller, the vortices generated from near the volute winding start and near the tongue continued to develop up to around the blade phase angle of 120°. Therefore, it is suggested that the mixing loss increases rapidly to around 120°of the blade phase angle, and becomes larger than that of the closed-type impeller.
We have developed an axial flow hydraulic turbine with a collection device aimed at high output by collecting and accelerating the flow of shallow open channels such as agricultural waterways and small rivers. The hydraulic turbine has excellent portability, but when the output is improved, the hydrodynamic force increases. The multi-objective optimization method is effective for such problems. By applying it to this hydraulic turbine, it is expected to decrease the hydrodynamic force while increasing the output. In this study, the multi-objective optimization design method was applied to the collection device of an axial flow hydraulic turbine with a collection device. As a result, the optimized hydraulic turbine has almost the same axial thrust coefficient as the prototype hydraulic turbine, the power coefficient is improved, and the effectiveness of this multi-objective optimization design method is confirmed.
In recent years, power generation using natural energy has attracted attention. Among them, hydroelectric power can be stably supplied with little effect of weather and can supply high density energy. In our laboratory, we have been conducted on the research on the undershot cross-flow water turbine applied to an open channel by removing the casing and guide vane from the cross-flow water turbine which is a water turbine for pipelines. Previous studies have shown that placing a straight blade, which is easy to manufacture, radially relative to the water turbine can provide relatively good performance. However, the details of the effect of the straight blade angle are not clear. So, in this research, we researched the effects of blade angle on turbine performance and we examined the effect of it on each component of torque. As a result, the water turbine performance improved as the blade angle increased. Also, the gravity component was dominant in each mechanical component torque and it increases as the blade angle increases.
Noise reduction is a major issue because small propeller-type wind turbines are placed near the lives of people in urban areas. However, the elucidation of the generation mechanism of aerodynamic noise of a small propeller-type wind turbine is not enough. In this study, we conducted noise experiments by changing the tip speed ratio of a small propellertype wind turbine, and conducted RANS analysis and acoustic analysis using FW-H, and compared the results of the two. As a result, SPL increased in the high frequency band as the tip speed ratio increased. The APL around the wing increased with the increase of the tip speed ratio as the blade tip was approached. However, in the vicinity of the blade tip, APL increased on the pressure surface side, but did not increase on the suction surface side due to the effect of tip vortices, and the high APL region decreased.
A liquid mercury target system for the megawatt-class pulsed spallation neutron source in installed in the J-PARC. In the system, cavitation damage induced by pressure waves that are generated by proton beam injection at the beam window of the mercury target vessel is a key factor to decide lifetime of target because the damage degrade the structural integrity of the vessel. A double-walled structure with a narrow mercury channel was adopted to the vessel for expecting to reduce cavitation damage. In this study, the cavitation bubble behaviors of the growth and collapse under water flow field were investigated by using the combination of a spark discharge for bubble formation and a high-speed photography in order to determine the effective factor for mitigating cavitation damage in narrow channel. It showed the bubble collapse behaviors that the bubble was divided into two at the bubble central part under stagnant condition, while the bubble collapsed as a single in the case of flowing condition. Furthermore, we measured the equivalent diameter and wall vibration due to the cavitation bubble collapse with parametrically changing flow velocity. It was found that the maximum equivalent diameter of the cavitation bubble and the response vibrational acceleration of the wall are decreased with the increasing velocity. As the results, it was found that cavitation bubble collapse pressure was affected by flowing condition in the narrow channel.
An effect of the liquid viscosity and the thermal conductivity on weakly nonlinear propagation of pressure waves
in an initially quiescent liquid containing many small spherical gas bubbles is theoretically elucidated especially
focusing on the wave dissipation effect. Based on the derivation of the KdV-Burgers equation for a long wave and the nonlinear Schrödinger equation for a short carrier wave, the following results are obtained: (i) The installation of energy equation affects nonlinear, dispersion, and dissipation effects; (ii) The liquid viscosity and the thermal conductivity lead to change considerably the explicit form of coefficient in the dissipation term.
An effect of mass transfer at a bubble-liquid interface on weakly nonlinear propagation of pressure waves in
bubbly liquids is theoretically investigated. We focus on a low frequency long wave and derive a KdV-Burgers equation incorporating the effect of mass transfer. The effect of a mass flux across the bubble interface is taken into account as a simple classical model. Although the heat conduction is considered, the effect of viscosity of gas inside the bubble is neglected. The set of basic equations for bubbly flows is composed of the conservation law of mass, momentum, and energy, radial oscillations of bubble, and so on. From the method of multiple scales, the KdV-Burgers equation can be derived from the second order of approximation in the basic set.
In this study, in order to determine the effect of double bonds in fuel molecule on ignition and combustion of nheptane, HCCI combustion experiments were performed using n-heptane/air mixture in co-existence with three kind of alkenes with different carbon number of 2 – 4, ethylene, propylene and 1-butene. A single cylinder research engine with compression ratio of 14.7:1 was used for the experiments at a constant speed of 960 rpm. When these alkenes co-exist, the low temperature oxidation was delayed and the low temperature oxidation heat release was almost equally reduced compared with n-heptane alone, regardless of carbon number of alkenes. This is unlike in the case of alkane co-existence, in which the effect of the low temperature oxidation differs widely depending on the carbon number.
To investigate the effect of bio-fuels addition on autoignition characteristics of gasoline, ignition delay times of gasoline surrogate mixtures, S5H, consisting of isooctane, n-heptane, methylcyclohexane, toluene and diisobutylene, S5H/ethanol, S5H/ETBE, S5H/2-methylfuran blended fuels were measured using a rapid compression machine at an equivalence ratio of 0.5 and oxygen concentration of 21% at the pressure of 4 MPa and in the temperature range 660 - 720 K. The measured ignition delay times were compared with the simulated ones using detailed chemical kinetic model of gasoline surrogate mixtures (SIPGd2 model). Ignition delay times of bio-blended fuels were longer than those of S5H over the entire experimental conditions. Simulated ignition delay times of ethanol blended gasoline had the same tendency as those of experiments, while simulated ignition delay times of ETBE blended gasoline had the different tendency as those of experiments. From the chemical kinetic analysis, it is found that the inhibition of the ignition under the ethanol blend conditions was derived from the OH consumption of ethanol.
APOM (Axial Plane Optical Microscopy) can directly image a sample’s cross-section parallel to the optical axis of an objective lens without scanning. In the present research, the principle of APOM system and its applicability to practical application is confirmed. Axial plane images of glass fiber and micro ruler are recorded and the relationship between the angle of mirror and the degree of deformation is obtained.
Water jet that spouted from nozzle attached to bottom of air pressurized water reservoir naturally draws air from free surface of water in the reservoir and becomes a gas-liquid mixture jet when the free surface of water in the reservoir makes low into some height from the bottom with time elapsed. In such a gas-liquid mixture jet, depending on the conditions, a phenomenon occurs in which aligned droplets from the jet splash explosively and periodically to radial outside of the jet. In this study, we changed nozzle shape and added pressure and analyzed the droplet splashing phenomenon by photography and pressure measurement. As a result, it was found that the added pressure range of occurring water jet with aligned droplets changes by difference of the nozzle shape.
A vertical counter-flow heat exchanger with mist injection is newly designed and fabricated in a vertical double cylinder in order to reuse waste thermal energy discharged from various environment, such as factories, commercial facilities and houses, as effective resources. In the present study, the performance of the prototype is elucidated using a series of parametric heat transfer experiments and flow visualization. Through several kinds of comparative experiments with different flow regimes (falling liquid film, 20μ m of mean-particle-diameter , 50μ m of mean-particle-diameter, 100μm of mean-particle-diameter, 500μm of mean-particle-diameter) at the hot water inlet section of the heat exchanger, it is obvious that the thermal exchange effectiveness (or temperature efficiency) becomes maximum for the case of the mist of 50 𝜇m of mean-particle-diameter even though the heat exchange flow rate is comparatively small at the hot water section of the heat exchange
Pouring air bubbles from nozzle is used for the industrial field such as promotion of the heat transfer and
equalization of liquid components. Therefore, many studies on characteristic of the air bubbles were reported. Main parameters that affect bubble formation are air flow rate, nozzle diameter, physical properties of surrounding liquid and the most importantly wettability of nozzle surface that is gas-liquid interface. If this can be understood and controlled, we can use bubbles effectively according to the purpose of use it. In this study, we use super water repellent nozzle like over 120-degree to confirm experimentally about bubble frequency and detachment characteristics in order to clarify the wettability of the nozzle surface that has effect on bubble detachment. In detail, we measured a nozzle exit pressure in each flow rate using 4 kinds of nozzles. In addition, we photographed the state of bubble departure of nozzle with a high- speed camera. As a result, we could compare with not processed nozzle and water repellent nozzle. Moreover, we evaluated surface wettability focusing on contact angle changing as the bubble grows from the viewpoint of image processing.
This paper describes a finite element method (FEM) analysis for cold burring process of large diameter SGP pipe. The large diameter pipes are used for a plant as a flow channel of gas and liquid. A burring process of pipe is generally for forming the branch. The burring process is achieved by drawing of die from prepared hole. And the branch pipe is welded to the formed pipe. This process has some problem. One is the forming limit of pipe, and the other is needed to machining the end surface to be welded. Since each problem depends on the shape of the pilot hole, the optimum pilot hole shape is required. In this study, FEM analysis was operated to estimate the optimum prepared hole shape. At first, the length of longitudinal and circumferential direction of ellipse was estimated. Secondly, the measurement of the other point that was effected on the end surface shape was estimated.
This paper describes a finite element method (FEM) analysis for cold burring process of large diameter SGP pipe. The large diameter pipes such as ϕ165.2 mm are used for a plant as a flow channel of gas and liquid. A burring process of pipe is generally for forming the branch. The burring process is achieved by drawing of die from prepared hole. And the branch pipe is welded to the formed pipe. This process has some problem. One is the forming limit of pipe, and the other is needed to machining the end surface to be welded. Each problems are depend on the prepared hole shape, thus the optimum prepared hole shape is required. In this study, FEM analysis was operated to estimate the optimum prepared hole shape. Prepared hole has two dimensions because of ellipse. At first, the length of longitudinal and circumferential direction of ellipse was estimated. Secondly, the measurement of the other point that was effected on the end surface shape was estimated. By performing burring and ironing process with a tapered punch using a stepped mold, appropriate pre-hole shape that enables welding only in the process of rigid body drawing that does not require end face cutting of the branched part in the post process estimated.
Stress relaxation resistance is often required in application of electrical parts for copper and its alloys. The stress relaxation behavior should be influenced by stored strain through manufacturing process. In the present study, Cu-Ni-Si alloy solution-treated sheet was subjected to continuous cyclic bending (CCB), which was proposed as a useful straining technique to produce the higher strain on the surface and the lower strain in the center layer of metal sheets. Samples were analyzed by scanning electron microscope/ electron back scatter diffraction (SEM/EBSD) technique to investigate stored strain and stress relaxation process. CCB raised up the strength of Cu-Ni-Si alloy sheets at room temperature. The stress relaxation ratios of the CCBent sheets increased with an increment of holding time. The stress relaxation process was accompanied with change in kernel average misorientation (KAM) of the samples. The change in KAM through the stress relaxation test was understood as a result of release of residual and applied stresses with consumption of stored strain
Magnesium alloy is the lightest metal among practical metals and has superior specific strength and rigidity. Thus, it has recently expected as a promising metallic material for the low carbon society. With this background, forming into various shapes is required to apply the magnesium alloys for decreasing the product weight. However, magnesium alloys suffer from their poor plastic deformability because their crystal structure is close-packed hexagonal, and the basal plane is the only slip plane. Although there have been a number of reports on tensile ductility and formability in bending, deep drawing, extrusion and budging, none on spinning has been seen according to the authors’ survey. Spinning, one of the incremental forming processes, has an advantage in cup forming with smaller tensile stress in bottom-R area than deep drawing. In this study, the spinning workability of AZ31 alloy is investigated.
High-strength steel sheets for weight reduction and safety improvement of vehicles have been developed. Highstrength TRIP-aided steel with transformation induced plasticity of the retained austenite has high strength and ductility. Conventional TRIP-aided steels are subjected to austempering process after austenitizing. Generally, elongation and formability of TRIP-aided steel are improved by finely dispersing retained austenite in BCC phase matrix. The finely dispersing retained austenite and grain refinement of TRIP-aided steel can be achieved by rolling with heat treatment. TRIP-aided steel having higher strength and ductility by combining heat treatment and rolling can be expected to be obtained. In this study, thermomechanical treatment was performed by combining hot rolling and austempering process in the manufacturing process of TRIP-aided steel. The mechanical property of the new TRIP-aided steel were investigated, and the effects of thermomechanical treatment on the properties were discussed.
Recently, various high strength steel sheets for weight reduction of vehicles have been researched and developed. High-strength TRIP-aided steel has high strength and ductility due to the transformation induced plasticity (TRIP) of the retained austenite. Since the amount of retained austenite in the low alloy TRIP steel with a matrix of martensite is small, it is necessary to increase the amount of retained austenite to obtain a higher TRIP effect. In this study, with the aim of increasing the amount of retained austenite, the samples were prepared by the cooling process passing just below the Ms temperature at various cooling rates, and their microstructure and mechanical properties were investigated.
The properties of steel materials can be widely changed by the composition, processing method, heat treatment, etc. The cold-rolled Fe-Ni-Al-C alloys is reported to have a good balance of strength and ductility because the strength is significantly increased while the decrease in ductility is suppressed. Effect of hydrogen on mechanical properties of the alloys have been examined in previous studies. It has been also reported that the mechanical properties are affected by the second phase whose distribution can be controlled by heat treatment before cold rolling. In this paper, a Fe-Ni-Al-C alloy was heat-treated and subsequently cold-rolled to control the distribution of the second phase. The effects of cold rolling on the microstructure and hydrogen embrittlement behavior has been investigated by microstuctural observation and evaluation of mechanical properties by SSRT (Slow Strain Rate Technique) tensile test after hydrogen charging.
The divertor materials, which receive the highest heat flux load in the next large nuclear fusion experimental devices are considered to use carbon fiber reinforced carbon composites (C/C composites) and tungsten material. C/C composites have the highest heat resistance (sublimation at 3,650K) and the highest thermal shock resistance in materials, and are considered to be the only material which can bear up against the highest heat flux load such as a plasma disruption. In this research, an isotropic graphite, a pyrolytic graphite and a C/C composite were irradiated by neutron with a low temperature and a high neutron flux in the research reactor (BR2) of Belgium. The fundamental knowledges about the neutron irradiation effects on mechanical properties and microstructures of carbon materials were obtained.
Spot welding is an important process in industry. The high conductive materials such as copper and aluminum need huge current in the welding, therefore tungsten is used for the electrode. In this study, the welding operations were repeatedly carried out up to 3,000 cycles using a copper-tungsten electrode and a cerium-tungsten electrode, where the constant temperature of the boundary between the electrode and the work metal was maintained at the initial cycle of welding with different forces applied onto the work metal. The influences of the alloying elements of the tungsten electrode and the applied pressure on cracking behavior of the electrode surface were examined, and then the durability and the lifespan of the electrode were discussed. As the results, the total crack length and the maximum crack width of the copper-tungsten electrode and the cerium-tungsten electrode were smaller than those of the unrecrystallized tungsten electrode at 180N applied pressure. Therefore, the copper-tungsten electrode and the cerium-tungsten electrode have the high durability and the long lifespan in the welding at high applied pressure.
With the problems of exhaustion of fossil fuels and global warming, weight reduction is required to improve the fuel efficiency of automobiles and railway vehicles. Weight reduction is expected by using magnesium alloys, the lightest material among ones for practical structural use. However, magnesium alloys are inferior to conventional materials in mechanical characteristics. Magnesium alloys are known to be strengthened by grain refinement. In friction stir process (FSP), which is one of the methods of grain refinement, a workpiece is subjected to severe plastic straining by a highspeed rotating tool, and mechanical characteristics in the agitation section can be improved by grain refinement. In this study, FSP is applied to a flame resistant magnesium alloy whose flame retardancy has been improved by adding Ca, and the influence of FSP conditions on the grain size is examined.
The 2219 aluminum alloy has been used in aircraft components, liquid oxygen tank for rockets, etc. In general, agehardened Al-Cu alloys, called 2000 series aluminum alloys, are known to have high strength. So far, the effects of heat treatment and cold working on mechanical properties of 2000 series aluminum alloys have been reported. Hydrogen embrittlement has been known to be a significant problem in some high strength aluminum alloys, where tensile strength and especially elongation are reduced in humid air environment. It has been considered that the 2000 series aluminum alloys are not influenced by hydrogen embrittlement. However, recent research reported hydrogen embrittlement in 2000 series aluminum alloys. In this study, 2219 aluminum alloy specimens were solution treated at 535℃ for 1 h, waterquenched and aged at 130℃ for 24 h to control the microstructure in the vicinity of grain boundaries, which might affect hydrogen embrittlement behavior. Slow strain rate technique (SSRT) tensile test was made in humid air environment to evaluate susceptibility to hydrogen embrittlement.
When the aluminum alloy is strengthened by precipitation treatment, coarser phases are precipitated at grain
boundaries than in the grains. At the same time, a precipitation-free zone occurs near grain boundaries. Such grain boundary precipitation structure is known to affect toughness and resistance to hydrogen embrittlement. Conventionally, grain boundary precipitation structure has been evaluated by transmission electron microscopy. However, it is difficult to observe statistically significant numbers of grain boundaries by this method. In this study, we tried to reveal and evaluate the precipitate microstructures for many grain boundaries in three Al-Mg-Si alloys by scanning electron microscopy observation after infiltrating the liquid metal Ga that causes intergranular fracture with no plasticity.
This paper describes a commercial scale twin roll strip casting process for producing aluminum alloy strip of AC7B. Twin roll casting process is able to produce a strip from molten metal directly. Thus this process has a possibility to reduce total cost of sheet making. However strip casting process has some disadvantages. Casting speed depends on the material properties. It is difficult to decide the casting conditions. Many paper on the strip casting are reported. However there are few reports on the commercial scale machine. In this study, the effect of roll speed on the strip casting was investigated. Continuous strip could not be produce at the roll speed 10 m/min. Continuous strip was produced at the roll speed 20 m/min. This strip consisted of an opaque part and a metallic luster part. However, cracks were observed. Continuous strip was produced at roll speed 30 m/min. However, cracks were observed too.
A laser cutting technique is expected to be utilized for separation and volume reduction of the radioactive
wastes from the benefits of non-contact and remote control system. However, a demerit of laser cutting is the
spatter and fume spreading which contain radioactive particle during cutting. The physical behaviors in molten
pool accompanied by spatter and fume generation have not been elucidated in detail because of the complicated
phenomena, including the multi-phases dynamics of solid, liquid, and gas. In order to suppress the spreading
fumes and spatters during laser cutting, in this study, as a fundamental study to construct a physical model, a
phenomenon at molten area during laser cutting was visualized using a high-speed video camera by changing
beam power. The result showed that the area of the molten pool and the solidification time of the molten metal
depend on the beam power, whereas the time when the molten area reach the maximum depend on the pulse
Recently, low friction diamond like carbon (DLC) coatings are prevailed for engine parts improving the fuel efficiency of automobiles. The quality control for the adhesion strength of DLC coatings is very important because of higher internal stress in the film. In this paper, a new method to evaluate the adhesion by using a simple pin / disk sliding test with acoustic emission (AE) equipment are introduced. Not only for the determination of the delamination strength, but also for the estimation of the cause of delamination by analyzing the frequency profile of AE signals with FFT are attempted. As a result, we found that peaks in 350-600 kHz is a signal of delamination and peaks in 8 kHz /30 kHz are due to droplets on surface.
Nano-diamond (ND) particles with the average diameter of 4 nm by the detonation method is known as the friction reducer adding to water. But since the mechanism has not been elucidated, how to design the formulation of ND contained engine oils is not clear. In this paper, after the friction test in water, ND particles were extracted by centrifugation and direct observation of the particle surface was attempted, in addition to the surface analysis (SEM / EDX / XPS) of the sliding surface. We found that the change of the functional group of the ND particles and the adsorption of the ND on the surface of the sliding portion were observed, resulting in the conclusion that both factors are the influence factors.