By using an aligned multi-walled carbon nanotube (MWCNT) reinforced epoxy composite, an electrothermal bimorph actuator was fabricated and its load and deformation capacities were investigated. The composite has a negative coefficient of thermal expansion (CTE) as well as large Young’s modulus. To evaluate the actuator property, a composite/aluminum laminate was prepared and a U-shaped actuator was formed by cutting off the middle part of the composite/aluminum laminate. The Young’s modulus of the composites increased linearly with increasing MWCNT volume fraction, and that of the composite containing 27 vol.% MWCNTs reached 56.8 ± 3.9 GPa. We also demonstrated that the actuator showed a large bending displacement and force output under low voltage stimulation. The bending displacement and force output of the actuator with the free length of 16 mm reached 7.6 mm and 9.0 mN under a DC voltage of 5.2 V, respectively. Furthermore, the actuator fabricated in this study showed higher values of work output per unit volume compared to the actuators reported in previous studies within the frequency between 0.05 Hz and 0.5 Hz. The enhanced performance was attributable mainly to the high Young’s modulus of both composite and aluminum layers and the huge mismatch of the coefficient of thermal expansion in the composite/aluminum laminate.
When local compressive load is vertically applied on the face sheet of the sandwich panel, the face sheet will be deflected and the core layer will be crushed at relatively low load. In order to evaluate the mechanical property of the sandwich panel subjected to the local compression, it is important to estimate the reaction on the face sheet supported by the core layer. However it is difficult to directly measure the support reaction because the core layer has been crushed. This paper describes a novel method to estimate the support reaction on the face sheet of the sandwich panel by inverse analysis of the deformed shape data of the face sheet. In this method, the finite element method based on strain increment theory is applied to the face sheet using the measured deflection of the face sheet as the boundary condition. Then it estimates the nodal load of the finite element model of the face sheet that is equivalent to the support reaction by the Tikhonov regularization. In order to demonstrate the validity of the proposed method, numerical simulations have been performed. In the numerical simulations, the several support conditions of the face sheet were given in advance. Then the direct analysis was applied to obtain the correct support reaction and the deformed shape of the face sheet in each condition. The inverse analysis was applied on the simulation data of the deformed shape to estimate the support reaction. The results show that the support reaction estimated by the proposed method has good agreement with the correct value. Moreover, it is concluded that the proposed method requires the location of the support point as a priori information.
In this study, based on the Orowan equation and the principle of Bergstrom dislocation evolution, the plastic mechanical response of single crystalline micropillars is investigated by considering dislocation evolution. According to the single-arm source model, a physically revised Peirce-Asaro-Needleman (PAN) hardening model is proposed that can describe size-dependent hardening flow. The dislocation evolution parameters greatly affect the size-dependent plastic behavior of the single crystalline micropillars. Linking to the crystal plasticity finite element (CPFE) method, a physical plastic constitutive model with the framework of the CPFE method is proposed to solve the size-dependent boundary value problem. Compared with the results based on the original PAN hardening model, the proposed constitutive model can provide mechanical responses in different sizes, depending on the shear strain in each slip plane. If the non-friction condition between the rigid punch and the top surface of the pillar under uniaxial compression is considered, the results show that the shear band of the pillar mainly results from shear deformation on the slip plane with the maximum Schmid factor. Otherwise, the actual shear band deformation of the micropillars is complicated and combined with the other slip planes, that is, a multislip system. The results also indicate that friction affects size-dependent hardening.
The purpose of this study is to investigate how affect the hot needle punching on bending strength and inter-laminar fracture toughness of CFRTP. Four types of needle in which tip shape were different was used to investigate the effect of needle shape on bending strength and interlaminar fracture toughness of CFRTP. CFRTP specimen was heated to soften the matrix of PA6, and then needle punching was conducted to specific number of times per unit area. The bending characteristics and interlaminar fracture toughness of CFRTP were evaluated by four point bending test and double cantilever beam (DCB) test, respectively. Test results showed that when punching was done using a needle with a notch at the tip, it resulted in the realignment of the yarn fibers along the out-plane direction of the punched specimen. It also led to the breakage of the fibers, owing to excessive bending. Moreover, due to the high viscosity of the matrix resin, the void was generated when the needle was pulled out from the composite. The interlaminar fracture toughness of the CFRTP specimens improved when punching was performed at stab density of 12 cm-2 or more. Finally this paper revealed that the mode I fracture toughness of the needle-punched CFRTP specimens is dependent on both of crack bridging of the realigned fiber and pin-like resin structure.
In this paper, we applied a multiscale numerical scheme called the seamless-domain method (SDM) to nonlinear elliptic boundary value problems. Although the SDM is meshfree, it can obtain a high-resolution solution whose dependent-variable gradient(s) is sufficiently smooth and continuous. The SDM models with only coarse-grained points can produce accurate solutions for both linear heat conduction problems and linear elastic problems. This manuscript presents a simple nonlinear solver for the SDM analysis of heterogeneous materials. Although the solver can easily approximate the solutions to nonlinear multiscale problems, it does not require an iterative multiscale analysis at every convergence calculation. In other words, the proposed scheme does not completely interactively couple the multiple scales. We present numerical examples of nonlinear stationary heat conduction analyses of heterogeneous fields and compare the SDM model, the direct finite-element model, and the homogenized model based on the homogenization theory. For a real heterogeneous structure (graphite fiber composite) that did not have strong material nonlinearities, the SDM model using only 925 points gave a solution with similar precisions as an ordinary finite element solution using hundreds of thousands of nodes. To investigate the limitations of the method, we also applied the SDM to imaginary materials with various strengths of thermal property nonlinearities.
Corrugated cardboards are used in many fields. The design of corrugated cardboard, however, is based on experimentations. The subject of this paper is developing the technique for high accurate analysis of corrugated cardboards. The corrugated cardboard is complicated structures and its property is unknown. Therefore, it is difficult to analyze this structure. We did bending tests of corrugated cardboard and its homogenized analysis using finite elements. We estimated its property by comparing both results. The experimentations include a lot of variation because the sample varies widely. Therefore model verification and validation is necessary. We used Bayesian inference for this purpose. In Bayesian inference, a priori probability is important. We compared three a priori probabilities. The first one is a uniform distribution which means no a priori information. The second one is a normal distribution which indicates a priori information about ambiguous data of the property. The third one is a normal distribution of which mean is the exact property. It is not realistic to use the third one. Numerical results show a uniform distribution is useful for estimating the property. The variance of Bayesian inference using a uniform distribution is wide, but the mean value becomes exact value quickly. The numerical results show the validity of Bayesian inference.
Analyses of magnetic field help find out internal states noninvasively and there are many applications of the analyses for nondestructive inspections. In the field of power sources, there has been a great discussion about behaviors of an internal short circuit in a lithium-ion battery. Since lithium-ion batteries supply or preserve high energy, the visualization of the current flow in the batteries is an important issue to prevent serious incidents by such short circuits. The basic structure of lithium-ion batteries is a type of laminated constructions of thin sheets. This study has developed a novel estimation method of the current density between laminated thin sheets by the inverse analysis of the magnetic field, and investigated its applicability to the short circuit localization. In the proposed method, the boundary element method (BEM) for thin plate, the Tikhonov regularization and the Kullback-Leibler divergence are applied. The BEM calculates the observation equation relating the current density to the magnetic flux density in high accuracy and high speed. The Tikhonov regularization reduces the influence of the measurement error on the estimated value. By using the Kullback-Leibler divergence as the criterion to determine the Tikhonov regularization parameter, it makes the standard deviation of the magnetic flux density useful to the evaluation of the estimated current density. In order to verify the proposed method, numerical simulations and actual measurements were performed. From the results of the numerical simulations and the actual measurements, it is concluded that the proposed method provides the location of the short circuit between the thin sheets through the estimation of the current density. Moreover, the limitation of the proposed method was observed in terms of the standard deviation of the magnetic flux density.
Performance demonstration certification of non-destructive inspection for cast stainless steel (CASS) has been planned but the target flaw depth to be detected has not been determined yet in Japan. The target flaw size is closely connected to the allowable flaw size which is determined by flaw evaluation of the rules on fitness-for-service. However duplex micro-structure of CASS makes low permeability of ultrasonic wave and large flaw size of UT detectability, which might not be acceptable by flaw evaluation. The current JSME rules for fitness-for-service allow only deterministic procedure. For rational mitigation of the acceptable flaw size, application of probabilistic fracture mechanics (PFM) is one of the useful countermeasures. In the paper, benchmark problems for a CASS pipe were proposed with intention applying and verifying PFM codes to CASS pipe's issue. As the fracture modes, fatigue crack extension, plastic collapse and ductile crack initiation were assumed. The PFM analyses were performed in the condition of the combination of crack extension and plastic collapse or ductile fracture to verify the basic functions of the PFM codes. Six organizations participated in the benchmark analysis and failure probabilities from them were compared. As a result the failure probability of each problem by each code showed good agreement and the code for application of CASS issue has been verified. The sensitivity of the failure criterion on the failure probability was discussed.
In this study, four multilayer film samples of polyimide/Mg, polyimide/Mg/Ti, polyimide/Mg/Pd, and polyimide/Mg/Ti/Pd were prepared by pulsed laser deposition and evaluated for hydrogen absorption-desorption properties. Polyimide/Mg and polyimide/Mg/Ti samples did not absorb hydrogen under conditions of 0.8 MPa and 200°C, while polyimide/Mg/Pd and polyimide/Mg/Ti/Pd samples absorbed hydrogen under the same conditions. The polyimide/Mg/Pd and polyimide/Mg/Ti/Pd samples desorbed hydrogen in the temperature ranges of 430-440°C and 140-200°C, respectively. The addition of Pd was necessary for the absorption of hydrogen because Pd promoted the dissociation of molecular hydrogen. The addition of Ti was necessary to decrease the temperature of dehydrogenation. The improved hydrogen absorption-desorption behavior could be caused by the structural change of MgH2 from bct to fcc and the decreased thermal stability of fcc MgH2 compared to that of bct MgH2. The hydrogen storage amount of the polyimide/Mg/Ti/Pd film was determined with pressure-composition-temperature measurements. The sample absorbed 0.42 wt.% hydrogen at 200°C and 2.0 MPa and 0.49 wt.% at 200°C and 10 MPa; hydrogen desorption was incomplete under both conditions. While the hydrogen storage amount of the polyimide/Mg/Ti/Pd film is less than that of pure Mg, it may be increased by omitting the base material of polyimide film.
Although titanium alloys are known to possess low density, high specific strength, and excellent corrosion resistance, their low specific stiffness and wear resistance have restricted their widespread application. Cost-effective discontinuously reinforced titanium and its alloys containing titanium boride (TiB) are emerging as possible candidates for overcoming these limitations. The mechanical properties of titanium matrix composites (TMC) are mainly dependent on the matrix composition, and on the volume fraction, and distribution of reinforcements. The distribution of reinforcements in the matrix depends on the particle shape and size of the Ti matrix powder. The purpose of this study was to investigate the effect of Ti powders produced by different manufacturing processes on the tensile behavior of titanium compacts and TiB reinforced Ti matrix composites (TiB/Ti). The Ti powders were produced by the hydride-dehydride (HDH) or the gas atomization (GA) process with particle sizes of <45 μm and <150 μm. The TiB/Ti composites were produced by a spark plasma sintering process. The Ti compact using Ti particle sizes of <45 μm, with higher oxygen content, possessed high tensile strength. This is because of the influence of oxygen as an interstitial strengthening element in the titanium alloy, which is well known. The TiB/Ti composites using HDH Ti powder with a particle size of <45 μm had the highest Young's modulus, tensile strength, and Vickers microhardness. For the HDH Ti powder with a particle size of <45 μm, small TiB clusters connected like a network were uniformly distributed around the Ti matrix particles. Cracks in the composites initiated at the TiB clusters when a tensile load was applied to the composites. The presence of small TiB clusters inhibited the formation of cracks.
A method for connecting a driving shaft to a three-dimensional composite disk via a polymer ring was examined to achieve stable rotation at high rotation speeds. Polyoxymethylene (POM) was adopted as the polymer ring material. Compression test was conducted to determine the limit of linear viscoelasticity, and creep resistance of POM was examined to evaluate its long-term durability. Structural design using finite element analysis including long-term creep resistance has shown that this method was predicted to be effective up to a tip speed of 1210 m/s. A three-dimensional composite disk was reinforced to three directions in accordance with the cylindrical coordinates. A trial composite disk with outer and inner diameters of 304 and 41 mm, respectively, was manufactured and tested up to a tip speed of 908 m/s. Vibration amplitudes were measured using gap and laser sensors. The vibration phenomenon and methods of suppressing vibration were discussed for higher rotation speeds.
The equipment and operation planning of a compound energy system (microgrid) with renewable energy sources is a dynamic, multivariate, nonlinear problem. Genetic algorithms (GA) provide a facile method for solving such problems and can be easily adapted to complicated energy systems; however, conventional GAs require a long runtime when the microgrid contains numerous energy sources and the solution must be highly accurate. This work introduces a preliminary step in which experimental design techniques, namely, an orthogonal array experiment and a factorial-effect chart are used to find an operation method that is close to the optimal solution for the energy system. The optimal operation solution is determined by using the operation method obtained from the orthogonal array experiment as the initial generation of chromosomes for the conventional GA. This proposed method does not find a strictly mathematical optimal solution, but the quasi-optimum solution is far more accurate than that from convention GAs and can be used industrially. The characteristics of the output power sources are found to strongly affect the analytic accuracy for the example of a microgrid.
In this study, a method to evaluate the effectiveness of adaptive driving beam (ADB) to enhance a driver's perception level for detecting pedestrians in a driving simulator is proposed. First, we investigated a driver's reaction time for applying brakes and the time taken to detect pedestrians stepping out from sidewalks. Next, we evaluated the effectiveness of ADB in terms of likelihood of collision mitigation using this reaction time based on the system reliability concept that we have proposed in previous studies. Using a driving simulator, we verified that it is almost possible to simulate the distribution of illuminance on the road surface by headlights and that it is useful to investigate the reaction time of drivers to detect obstacles such as pedestrians walking on a drive lane during the night.
In this study, a method of modeling the frequency characteristic of a ball-screw-driven stage in a design phase is proposed, targeting a printed-circuit-board drilling machine. A ball-screw driven stage is widely used as a precise positioning mechanism mounted in inspection devices or manufacturing equipment. When a controller of the stage is being designed, the frequency response of the stage is needed first, and it is generally measured with actual stage equipment. Therefore, the positioning performance of the stage cannot be estimated in the design phase. A method for predicting the frequency characteristic of the stage on the basis of its design specification is required for developing the stage structure and controller and the method will be useful for shortening development period or lowering development costs. At the beginning of this study, it was revealed that the frequency response of the stage is affected by not only the stiffness of the ball screw but the natural modes of the structure, and it cannot be represented with just a lumped-parameter model of the ball- screw driving system. Subsequently, a modeling method for a ball-screw driven stage was proposed. The model consists of a lumped-parameter model of a ball-screw drive system and vibration models of its structural components (which are analyzed by FEM models), and these models are connected by mode synthesis. Finally the effectiveness of the proposed model was demonstrated in comparison with experimental results, and it is concluded that the proposed model can represent similar frequency-response characteristics as represented by measured values.
In this paper, we propose a simple plasma-less fabrication and integration method for biomicrodevice applications. For optogenetics, microlenses and pinholes irradiating local sight of biological tissue with focused visible light and electrodes measuring a biological electropotential are integrated by using organic materials such as polymer. The proposed fabrication method consists of photolithography and wet-etching process only. The shape of fabricated microlenses measured by a white light interferometer was the diameter of 111.5 μm, the depth of 45.5 μm, and the focal length 320 μm. The impedance of Platinum black electroplated on the fabricated electrode pads was reduced to 200 kΩ. As the results, it is succeeded to integrate electrode pads, microlenses and pinholes without plasma etching process. The fabricated dish is assembled with a light irradiation device having two LEDs. By the light irradiation test, the fabricated dish is expected to be utilized in a variety of neuroscience researches. By the test for cytotoxicity, it is succeeded to create neural network on the fabricated dish.
We have developed a speech-driven embodied entrainment character called “InterActor” that has functions of both speaker and listener for supporting human interaction and communication. This character would generate communicative actions and movements such as nodding, body movements, and eyeball movements by using only speech input. In this study, we focus specifically on the pupillary responses related to human emotions in embodied interaction and communication. Pupillary responses in human face-to-face communication are analyzed using an embodied communication system with a line-of-sight measurement device. Based on the analysis results, we enhance the functions of the character and develop an advanced speech-driven embodied entrainment character system for conveying empathy. Using only speech input, this system changes the pupil size of characters based on the analysis. Through sensory evaluation, we perform experiments to determine the effects of the developed system. The results reveal that the system is effective in human interaction and communication.
Muscle fatigue should be quantitatively evaluated in order to design an optimum work environment and work-rest scheduling and prevent musculoskeletal disorder of workers. The aim of this study was to formulate a relationship for the dependence of perceived muscle fatigue (PMF) on time and external load. Three differential equation models―saturate, non-saturate, and hybrid of saturate and non-saturate―were proposed for the PMF function. An elbow flexion task was performed with varying load amplitude (percent of maximum voluntary contraction, %MVC), and the PMFs were measured every 30 s during the task execution. The three models were applied to the measured PMFs and compared in terms of their PMF prediction accuracy. In addition, the maximum endurance times (METs) predicted by the three models were compared with the existing MET models. The measured result showed that the PMF increased logarithmically at the relatively low %MVC and linearly at the relatively high %MVC. The hybrid model was selected for the PMF function, because it showed a better fit to the measured PMFs and a higher interclass correlation with the existing MET models. Individually approximated PMF functions for males and females did not show an improved accuracy compared with the PMF function for both genders. Therefore, a single PMF function was applied irrespective of the gender.
This study is aimed at the development of civil engineering materials such as pavement blocks and building tiles that can moderate the heat island phenomenon. This is achieved by exploiting properties such as the material porous structure, high water absorption capacity and high strength of ceramics produced by mixing clay and crushed waste glass fiber-reinforced plastic (GFRP) before firing. Fundamental properties, such as pore size distribution, water absorption capacity, solution pH after ceramic immersion, bending strength, freezing resistance performance and thermal conductivity of ceramic specimens with varying ratios of clay and GFRP were clarified. The radiant heat reduction performance of the ceramic was examined by measuring the surface temperatures of a ceramic sample made from clay, a ceramic sample made by mixing 20% GFRP with clay, and a mortar sample in water-saturated and dry states while their surfaces were irradiated with infrared light. To clarify the difference in temperature-reducing ability by evaporation heat on each sample, the amount of water evaporated from a sample that had absorbed water and was irradiated with infrared light was measured. The rate of heat-absorption from the sample by water evaporation was estimated. The temperature-reducing effect by evaporation heat of the sample during water-absorption was verified quantitatively by thermal conductivity analysis using finite element methods. While water-saturated, a 20% GFRP/clay ceramic sample could reduce the increase in temperature caused by radiant heat considerably, and for an extended duration. It is expected that such ceramics could be used in civil engineering materials to counteract the heat island phenomenon.
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