Dynamic FEM and DEM simulations are carried out to investigate dynamic penetration of a projectile into a target of granular medium. Spatial distribution and time dependence of ejecta are clarified together with their trajectories in medium. Highly densified region is generated just ahead of the projectile and propagates leaving rarefied regions. Force on the projectile is fully discussed in connection with dynamic behavior of granular target.
This work deals with the time-dependent creasing characteristics of coated paperboard. The correlation between the bending strength (resistance) and time-dependent problems on the actual processing phenomenon has not been sufficiently discussed in the past. In this study, therefore, a prototype testing apparatus has been applied to investigate about the dynamic relaxation of bending moment. In order to reveal the relaxation characteristics of the bending resistance during the folding motion from an initial position up to a specified tracking angle, a white-coated paperboard of 0.3 mm thickness was scored with a creasing rule and then the bending test was carried out by varying the number of folding repetitions. Through this work, the followings were obtained: (1) The relaxation of the bending resistance was characterized by an exponential coefficient which was independent to the nominal shear strain while it varied with respect to the number of folding repetitions; (2) The relaxation coefficients of logarithmic approximation with the elapsed time are linearly characterized by the nominal shear strain and the number of folding repetitions; (3) The relaxation depends on the bending velocity.
This paper describes the joining phenomena and the tensile strength of friction welded joint between type 1070 pure aluminum (CP-Al) and oxygen free copper (OFC). When the joint was made at a friction pressure of 30 MPa with a friction speed of 27.5 s-1, the upsetting (deformation) occurred at the CP-Al side. When the joint was made at a friction time of 2.0 s, the whole weld interface on the OFC side had the transferred CP-Al, and it was obtained approximately 30% joint efficiency. Then, the joint efficiency increased with increasing friction time, and it was obtained approximately 63% joint efficiency at a friction time of 12.0 s. The joint fractured at the weld interface, which had a CP-Al adhering to the weld interface on the OFC side. When the joint was made with friction times of 2.0 s and 6.0 s, the joint efficiency increased with increasing forge pressure and then the joint was obtained the CP-Al side fracture at a forge pressure of 135 MPa or higher. However, the joint did not achieve 100% joint efficiency because the adjacent region of the weld interface at the CP-Al side was softened. In addition, the joint at a friction time of 2.0 s had no intermetallic compound (IMC) layer at the weld interface although the not-joined region was slightly observed. On the other hand, the joint at a friction time of 6.0 s did not have the not-joined region at the weld interface although the IMC layer was slightly observed. In conclusion, to obtain higher joint efficiency with fracture on the CP-Al side, the joint should be made with higher forge pressure, and with the suitable friction time at which the entire weld interface of the OFC side had the transferred CP-Al.
Formation behavior of bubbles and its effect on strength in PET/SUS304 dissimilar materials laser spot lap joint was studied. Surface of SUS304 was irradiated through transparent PET with fiber laser. Static and cyclic contact force was applied at the welding region during the joining process. Strength of the joint was evaluated by conducting tensile shear test. The formation behavior of bubbles inside PET nearby the interface changed with change in condition of contact force. In case of applying lower static contact force, welded area and failure load of the joint increased with increase in contact force. This result might be due to flow of molten PET by applying compressive force. On the other hand, when higher static contact force was applied, welded area and failure load of the joint decreased, because suppress of the flowing for molten and softened PET occurred. The joint joined with applying cyclic contact force showed lower values of welded area and failure load compared to the joint joined with applying the same maximum static contact force. According to fracture surface observation, crack mainly passed through bubbles to failure in all joints. Apparent strength was calculated by failure load and welded area obtained. The strength of the joint decreased with increase in bubbles density, except the joint joined without contact force. In case of joint joined without contact force, large bubbles were formed and decreased strength. Bubble size formed was small when contact force was applied. Density of bubbles affected strength of the joint and changed by applying contact force, particularly that decreased by applying cyclic contact force. It is considered that applying the contact force is an effective way to control formation behavior of bubbles and results in improvement for reliability of the dissimilar material joint between plastic and metallic materials.
Magnetostrictive materials of the Fe-Ni-Cr ternary system for sensitivity enhancement of force sensors were searched by using a combinatorial method. Magnetostrictive materials for force sensors require large magnetostriction, high relative permeability, and high resistivity. This research is an attempt to find composition ranges that satisfy the following requirements: magnetostriction greater than 20×10 -6, relative permeability greater than 4,000, and resistivity over 90 μΩ cm. A novel combinatorial deposition method, known as Combinatorial New Facing Targets Sputtering (Combi-NFTS) method was applied to fabricate libraries of samples with various compositions. Samples for measurement of the relative permeability and resistivity were synthesized with a composition distribution by using Combi-NFTS onto a 108 mm×76 mm glass substrate. After deposition of thin film, each sample is divided into 10 mm×10 mm. The relative permeability and resistivity were measured by using a vibrating sample magnetometer and the four probe method, respectively. Bilayer cantilever samples for evaluation of magnetostriction were fabricated onto a 6 mm×20 mm×0.1 mm Si substrate, whereby deflection of the samples changes when a magnetic field is applied. The laser lever method was used to measure the cantilever deflection. The results indicate that the composition range with an Fe content of 26-36.5 at.%, a Ni content of 61-66 at.%, and a Cr content of 7.5-9.5 at.% satisfy the requirement criteria.
By assisting with resistance heating, the material formability can be improved, and more homogeneous material flow can be obtained. In this study, finite element (FE) models for an analysis of microbending process assisted by resistance heating were developed. Coupled thermal-electrical procedure and coupled thermal-displacement dynamic explicit procedure were conducted to analyze the temperature distribution and material deformation, respectively. And static implicit procedure was carried out for the analysis of springback behavior. The simulation results show that the temperature distribution of the blank is caused by the difference in electrical current density, which influences the material deformation as well as springback behavior. And the spingback angle decreases with increasing forming temperature. The temperature distribution and springback angle obtained from the simulation show the same tendency with the experiments, which confirmed the feasibility of the developed FE models. By using the developed FE models, the effects of the temperature distribution on material behavior can be obtained, and the springback angle for microbending process assisted by resistance heating can be predicted precisely. The possibility of reducing springback and improving the accuracy of the products by designing the process efficiently is demonstrated.
In this study, to promote stress relaxation effect by the servo actuated step motion that stops the die motion at regular interval, a novel microforming process with combining ultrasonic vibration and the step motion was proposed. To investigate the effect of ultrasonic vibration on stress relaxation by step motion, a micro-compression test was carried out in different scale dimension with the specimen size of 0.5, 1.0 and 2.0mm in diameter and height. Stress relaxation by step motion was repeated for 6 times at constant strain interval. Ultrasonic vibration with amplitude of 1.2 and 2.4 μm was applied on the axial direction during the stress relaxation by step motion. As results, in the all process conditions, the stress drop increased with decreasing the specimen size. To investigate the size dependency of the effect of ultrasonic vibration on stress relaxation, the stress drop in the surface and inner grains was calculated based on the surface grain theory. The result showed that the stress drop in the surface grains was larger than that in the inner grains in similar scale dimension. Additionally, the stress drop in the surface grains increased with decreasing the specimen size. The possibility of improving the material formability by this process was experimentally demonstrated.
The bonding quality of an adhesive component was estimated using the frequency of zero-group-velocity (ZGV) Lamb waves, which can be generated and detected with a laser ultrasonic technique. Two distinct peaks corresponding to ZGV Lamb waves in the amplitude spectrum were obtained for well- and weak-bonded adhesive plate samples. The frequency difference between the measured low frequency mode and the calculated frequency, which can be obtained by assuming a continuous stress and strain at a bonding interface, linearly increased with shear strength, as obtained by the shear-tensile test. The frequency of ZGV Lamb waves was also calculated with reduced shear modulus of the bonding layer to express a weak bonding, and the change in the calculated frequency in low frequency ZGV Lamb waves showed a similar tendency to that in measured one.
The feasibility of ultrasonic in-situ measurement of friction surface temperature has been examined. The ultrasonic thermometry that is a method providing nondestructive temperature measurements by ultrasound is applied to temperature measurements of a friction surface at which temperature rise occurs due to friction, and an attempt is made to demonstrate in-situ monitoring of transient variations in the friction surface temperature and temperature distribution beneath the surface. Those temperatures are quantitatively determined by a combined method consisting of ultrasonic pulse-echo measurements and a finite difference calculation for estimating one-dimensional temperature distributions along the direction of ultrasound propagation. To demonstrate the practical feasibility of the method, the ultrasonic pulse-echo measurements at 2 MHz are performed for an acrylic resin plate of 10 mm thickness whose single side is being heated by friction with a felted fabric plate. The temperature profile near friction surface and its transient variation are measured during the friction heating under different applied loads to the friction surface. It has been observed that the temperature at friction surface increases quickly and significantly just after the friction started, and the maximum temperature rise at the friction surface increases markedly with the applied load. Thus, in-situ measurement of friction surface temperature by the ultrasonic thermometry has successfully been demonstrated.
We propose a novel measurement method for directly measuring the lateral displacement of structures by using air-coupled ultrasound transducers. The normally-distributed far field of an ultrasound transducer in a lateral direction is taken advantage of for the purposes of measuring lateral displacement. The measurement system is composed of three flat-type air-coupled ultrasound transducers and a steel wire as a target. The ultrasound transducers are immobilized at a fixed point, whereas the steel wire is separately arranged on the opposite side. When the steel wire is displaced laterally, the lateral displacement is calculated utilizing the intensity ratio of the reflected ultrasound waves. The accuracy of the lateral displacement measurement is experimentally assessed to be within ± 0.5 mm and the feasibility of the measurement system is discussed. The results show that a developed displacement measurement method will be usable in the field of structural health monitoring due to its accuracy and wide measurement range through the use of several ultrasound transducers.
The present study introduces the numerical simulation of mechanical sensors using IPMCs (ionic polymer-metal composites). IPMCs can be applied into both of actuators (from electricity to deformation) and mechanical sensors (from deformation to electricity), but the existing models of the actuators cannot be inversely applied to the mechanical sensors. The mechanical sensors generate very much smaller electric potential compared to the supplied electric potential of actuators with respect to the same displacement and structure. The non-invertible response of the mechanical sensors is numerically simulated, and the simulation considers hydration and transient behaviors. IPMCs have hydration effect that volume and mechanical stiffness are significantly changed with water uptake. In order to consider the volume swelling due to hydration, the total strains and pore pressure of IPMCs are respectively decomposed into stress-induced and hydration-induced parts. The hydration-induced strain is considered as eigen-strain, and the stress-induced strain and stress-induced pore pressure are employed into Biot poroelastic constitutive equations. The mechanical stiffness of a hydrated IPMC is expressed as empirical relations with water uptake. Furthermore, mechanical sensors using IPMCs show transient response with the relaxation and time lag of reaction force and electric potential. The transient response is modeled with a set of basic equations, e.g. layered Timoshenko beam model, Biot poroelastic model, Darcy-flow model, Poisson-Nernst-Plank model. The instantaneous peak of reaction force is estimated on undrained condition, the relaxation of reaction force is considered with pore pressure and its Poisson effect, and hydration-induced water migration is modeled with hydration potential. The hydration potential is modeled with an empirical chemical potential at free swelling equilibrium and is expressed as a function of water uptake. Next, discretization and numerical formulation with layered finite beam elements is introduced. Lastly, the transient responses of a Flemion-based mechanical sensor are numerically simulated with different deflections, and the distributions of stress, pore pressure, ion concentration and electric potential are obtained with time. Lastly, the numerical simulation is compared with the experiments of a reference.
The properties of three thermal sprayed coatings (Coating①: Top coat; Al2O3, Bond coat; Ni-Cr, Coating②: Top coat; YSZ, Bond coat; CoNiCrAlY, Coating③: SUS316) were compared to select the effective sprayed coating for giving the thermal barrier to the Al alloy components of internal-combustion engine. The results are as follows. (1) After thermal cycle test, there was not any crack and delamination in the coating③, and a partial cracks and delamination were observed at the top coating in coating① and ②. (2) The coating①, ② and ③ have sufficient adhesion strength. The adhesion strength of coating② was specially high. (3) The thermal barrier property of the coating② was better than that of coating① and coating③. (4) In the result of comprehensive evaluation, the coating② had good thermal barrier property and the coating③ was a reasonable material because of low cost as the thermal sprayed coating applied to the Al alloy components of internal-combustion engine.
When the honeycomb core sandwich panel (hereafter, HSP for brevity) is used as a floor panel, a dent is formed on the surface of it. If the depth of dent was deeper, it is changed into a new one. In order to change it efficiently, it is necessary to study a period for use as the floor panel applied the repetition of local compression load for the longitudinal direction of honeycomb core (hereafter, fatigue life for brevity). The local compression fatigue tests of peripherally clamped HSPs were carried out. In this study, it is attempted to clarify the local compression fatigue property of roll core sandwich panel which was superior to the honeycomb core sandwich panel in the manufacturing cost and the mechanical property. From the obtained results, the follows were summarized; 1) There were three fracture patterns such as a tensile and a shearing types that fractured on the border of the indenter contact region and the noncontact region of specimen and a shearing around dent type that fractured on the periphery of a dent formed during the indentation. 2) The stress state at a crack initiation site governed a fatigue life. 3) Not a core shape but a cell size influenced the fatigue life.
Mixed-mode thermal stress intensity factors (SIFs) are investigated at various temperatures using the method of caustics. First, theoretical caustic patterns are obtained for various types of optical systems in addition to the mode II SIF KII and mode I SIF KI ratios. Next, the values of the SIF are experimentally investigated at various temperatures for glass plates with an inclined artificial notch or a natural crack, and the effect of the crack on the sign of the SIF is considered. Then, it is determined whether or not crack extension occurs. It is shown that a negative value of the SIF KI occurs at the notch tip under high-temperature conditions. In contrast, the sign of the SIF KI at the natural crack tip under high-temperature conditions is positive. At low temperatures, the signs of the SIFs at the notch and the natural crack tip are positive. Crack propagation is observed when the sign of KI is positive. The direction of crack propagation initiating from the natural crack at high temperatures is in accordance with the theory of maximum circumferential tensile stress (σθ)max. At low temperatures, the crack extends slightly, and thereafter, the direction of crack propagation abruptly changes because of the compressive stress in front of the notch and the natural crack tip.
This study deals with an application of blazed plate heat exchangers to a condenser used in a heat pump water heater. The heat transfer performance was experimentally evaluated by using a pump driven two-phase flow loop in the operating condition for water heating at the environmental temperature. The effects of number of refrigerant paths and setting orientation, such as a vertical orientation with downward refrigerant flow or a horizontal orientation, were evaluated. HFC134a was used as the refrigerant. Superheated vapor was supplied to the condenser, and heated water, and then subcooled liquid was exhausted. Water was supplied to form a counter flow heat exchange. Three kinds of heat exchangers with different refrigerant paths of 6, 10, and 14 were used. Refrigerant temperatures at the exit of each path were measured by inserted thermocouples to evaluate the flow distribution. As a result, it was shown that vertical orientation produced higher heat transfer rate than the horizontal orientation. For the horizontal orientation, heat transfer rate decreased with an increase of refrigerant channels from 10 to 14. The reason would be due to a maldistribution of the refrigerant. The deterioration in heat transfer performance for the horizontal orientation could be improved by the inclination of 15° of the heat exchanger.
In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. This process ends up damages on the heat transport equipment in the SFR. Therefore, the study on sodium-water chemical reactions is of paramount importance for security reasons. This study aims to clarify the sodium-water reaction mechanisms using an elementary reaction analysis. A quasi one-dimensional flame model is applied to a sodium-water counter-flow reaction field. The analysis contains 25 elementary reactions, which consist of 17 H2-O2 and 8 Na-H2O reactions. Temperature and species concentrations in the counter-flow reaction field were measured using laser diagnostics such as LIF and CARS. The main reaction in the experimental conditions is Na+H2O→NaOH+H and OH is produced by H2O+H→H2+OH. It is demonstrated that the reaction model in this study well explains the structure of the sodium-water counter-flow diffusion flame.
Ammonia is a carbon-free fuel and its application to internal combustion engines is expected. However, few studies on ammonia flames, especially at high pressures, have been carried out because ammonia has not been considered to be a fuel owing to its lower combustion intensity. Most of NOx, which is formed by ammonia combustion, is considered to be the fuel NOx. The objectives of this study were to investigate the fundamental characteristics of NOx experimentally, such as NO emission and chemiluminescence of ammonia/air flames not only at the atmospheric pressure but also under high pressures and to explore NO formation/reduction mechanisms using numerical simulation. Experiments were carried out using a nozzle-type burner. NH2 ammonia α band spectra were observed, and it was clarified that the color of ammonia flame is mainly determined by the NH2 ammonia α band and H2O spectra. Burned gas was sampled from ammonia flame stabilized at the burner. The mole fraction of NO decreased with the increase in equivalence ratio at atmospheric pressure. Reaction flow analysis was performed, and it was clarified that the decrease in the mole fraction of NO for rich mixtures was caused by NHi (i = 2, 1, 0). High pressure experiments were performed using a high pressure combustion facility for stoichiometric ammonia flame. Consequently, the decrease in the mole fraction of NO was experimentally observed and its tendency was found to qualitatively agree with the results of the numerical simulation. It was clarified that the third body reaction of OH + H + M ⇔ H2O + M plays an important role in the reduction of the mole fraction of NO at the high pressure.
The dragonfly wing is passively deformed under flapping and has the strength to withstand high flapping frequency simultaneously. These characteristics of deformation and vibration of the wing are important for flapping flight. However, the effect of these characteristics on flapping flight has not been well understood. The purpose of this study is to investigate deformation and vibration characteristics of the dragonfly wing, and then to develop an artificial wing suitable for flapping flight on the basis of the dragonfly wing. In this study, natural frequency and deformation of the dragonfly wing are measured, and the artificial wing is fabricated on the basis of the results. From the measured results, the dragonfly wing has the high natural frequency of about 120 Hz, and thereby, it does not resonate with flapping. Although base-side of the wing is hardly deformed, the tip-side of the wing is greatly deformed because of the torsional deformation from the nodus of dragonfly wing. On the basis of characteristics of the dragonfly wing, the deformable artificial wing that can deform in the same manner of dragonfly wings was fabricated. Then, aerodynamic force and power consumption under flapping when using the deformable artificial wing was measured. As a result, the power efficiency of aerodynamic force using the deformable artificial wing is five times greater than the power efficiency using a non-deformable wing.
In order to prevent global warming, the emissions of greenhouse gases must be reduced. In public transportation systems, electric buses can help to achieve this. However, the deployment of electric buses has been limited to public corporations as a result of the weight of the required energy storage devices. One approach to addressing this problem is rapidly charging the electric bus at every bus stop, thereby reducing the required energy storage and weight. In addition, charging buses using electrical power generated from renewable energy sources could further reduce emissions of greenhouse gases. For such a system, the required energy for each bus route must be estimated and the storage device designed to minimize the weight of the bus. In this study, the feasibility of the proposed system is confirmed by a demonstration experiment using a converted electric minivan. Then, a simulator to calculate the energy consumption of a full-size bus is developed by extrapolating the parameters used in a simulator for the electric minivan, which were validated experimentally. A trial bus-mounted storage device for the route is also designed.
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