The shape memory effect (SME) in Fe-Mn-Si based alloy is associated with γ ⇄ ε martensitic transformation which is caused by motion of the Shockley partial dislocation. The variants in Fe-Mn-Si based alloy could appear the four orientations according to Shouji-Nishiyama (S-N) relation in the transformation from the austenite phase (A-phase) to the martensite phase (M-phase). It was reported that a single variant formed under the stress induced transformation in the SME and that is the advantage for the shape recovery in the variant selection behaviors. In this study, the variant selection of Fe-Mn-Si based alloy under stress applied is investigated on the basis of crystallography in the SME with Electron Backscatter Diffraction (EBSD). The amount of shape recovery was quantified by means of bending tests and the best recovery ratio was run into 83% for the specimen annealed 873K. The SME is improved by not only the increase of A-phase but also the promotion of the single variant under stress induced transformation. The single variant orientation is selected by the degree of Schmid's factor in the behaviors. In the specimen annealed at 873K, the increase of M-phase concentrates at 0.475 of the Schmid's factor, the single variant orientation, and that suggests the single variant formation.
In our previous study, it was found that the wear life of the DLC/AlN hybrid film compared with a DLC film deposited directly onto Al-alloy could be improved by controlling the hardness of the AlN intermediate layer film. However, the hard coating like above films has a possibility to decline the fatigue strength of based material. In the present study, to ensure the fatigue reliability of Al alloy coated with DLC/AlN hardness gradient hybrid film, the fatigue strength and the fatigue failure mechanism were investigated. Fatigue strength of A7075 alloy coated with DLC/AlN hybrid film in lower stress side was higher than the untreated material, but that in higher stress side was almost the same as the untreated material. Compressive residual stress of A7075 alloy coated with DLC/AlN composite film was larger than the untreated material. From the observation of crack initiation part in the fracture surface of the A7075 alloy coated with DLC/AlN hybrid film by SEM, micro cracks in AlN film were found to be generate from the interface between Al base material and AlN film by the local plastic deformation in Al base material. Since the DLC film with a high fracture toughness values obstruct that micro cracks came out to the film surface, the initiation of a main crack was delay. As the result, the fatigue life of DLC/AlN hybrid coating material was improved. DLC/AlN hybrid coating is considered to represent a simple and effective means of improving the wear resistance and fatigue reliability of Al-alloy components commonly used within the aerospace and automotive industries.
Low cycle fatigue tests were performed for austenitic stainless steel, SUS316L. The effect of machined surface layer on low cycle fatigue life was investigated. In order to separate the effect of surface morphology and material property variations, fatigue tests were carried out for specimens, which had three different surface finishes. Fatigue test results show plastic deformation caused by machining had small influence on fatigue lives. On the other hand, scratches reduced the fatigue lives. If there were scratches on specimen surface, cracks initiated from corner of valley of scratches. Many cracks initiated in the scratch. Cracks grew almost as large as scratch in early stage of fatigue life. Fatigue tests were performed for specimen which had a few small scratches. Fatigue lives of that specimen was similar to those of specimen which was removed scratches. Fatigue crack propagations were predicted based on elasto-plastic fracture mechanics. Assuming that initial crack depth was equal to scratch depth and aspect ratio was 1, fatigue lives of predictions were longer than experimental results. When crack propagations were predicted using scratch depth and length as initial crack depth and length, fatigue lives of prediction was close to experimental results. We can predict safety side fatigue lives using scratch length and assuming that aspect ratio is 1.
An external load applied to a rolling bearing is distributed among the rolling elements. This rolling element load distribution is changed according to the way the external load is applied or the internal clearance of the bearing. And, it will affect the rolling contact fatigue life of the bearing. Therefore, several experimental methods for determining the load distribution of rolling bearings have been proposed so far. Their methods, however, could not provide dynamic load distributions while the rolling elements make one revolution along the raceway. Besides, there has been little research on measuring the rolling element load distribution in detail by changing the internal clearance variously. In this work, the rolling element load has been measured by using an optical fiber sensor mounted on a roller of a double row tapered roller bearing to be measured, and the effect of the internal clearance on the rolling element load has been investigated. As a result, it has been clarified that the load distribution factor decreases with the increase in the axial clearance, and as the radial load becomes small, the degree of reduction of the load distribution factor due to the increase in the axial clearance increases. Further, this tendency has been confirmed to be consistent with the numerical results.
Recently, it has become more important to develop vacuum cleaners which achieve both high suction power and low noise along with comfortable sound quality. To reduce the noise of centrifugal blowers, the authors investigated the pressure fluctuation in vaned diffusers using unsteady pressure measurement and compressible flow simulation. From the tracking analysis of the results of noise, it was confirmed that the rotational speed at which the pressure fluctuation in diffuser becomes maximum matches a resonance rotational speed. The pressure fluctuation in the diffuser has a node at the downstream of the overlapped region at any resonance rotational speed. On the other hand, the node position near the inlet of the overlapped region and the amplitude of the pressure fluctuation depend on the resonance rotational speed. Furthermore, it was revealed that stationary wave modes were dominant in the pressure fluctuation and governed the positions of the maximum and minimum pressure fluctuations along the flow direction.
In this study, we developed a simultaneous measurement system for measuring the concentration fluctuations of two species using pulsed laser diodes in the light absorption spectrometric method. Conventional methods utilize halogen lamps or continuous laser diodes as light sources for concentration measurements. These light sources require multi-monochrometers or dichroic mirrors, which makes these methods rather expensive. However, using pulsed laser diodes as the light sources eliminates the need for additional multi-monochrometers and dichroic mirrors. A diffusion field consisting of two dye species in an axisymmetric turbulent jet was measured using the developed concentration measurement system. To ascertain the validity of our concentration measurements, we compared the present measurement results with those of a single dye species and previous studies. It was observed that the concentrations of the two dye species were measured accurately by the present measuring system. Therefore, such low-cost concentration measurement systems can be developed and applied in various simultaneous measurements of concentration fluctuations of multiple species such as in turbulent reactive flows.
The resolution and efficiency of the finite-difference lattice Boltzmann method (FDLBM) is improved to deal with wall-bounded turbulence, which is characterized by the strong shear and anisotropy. FDLBM puts the merit of LBM, which is the explicit and non-iterative algorithm, into practice on the body-fitted coordinate in the conventional solvers based on Navier-Stokes equation of motion. Thus the performance of FDLBM is mostly affected by the finite-difference scheme for the advection terms of LBM, which has to be an upwind one from a stand point of numerical stability. Particularly in this study, the influences of the the order of accuracy and upwind method are assessed by the direct numerical simulation of fully-developed turbulent flow in a plane channel. We introduce a discretization method with numerical flux similar to the finite-volume method, and a nonlinear scheme which localizes the effect of the numerical diffusion. Our method successfully reproduced the mean velocity and turbulence statistics in comparison with standard database. We confirmed that the nonlinear scheme improved the resolution. Increase of reproducibility with the higher order scheme surpassed increment of its computational cost. The 7th-order scheme, for example, provided a comparable result to that by the 3rd-order scheme using 4 times finer grid, though the calculation time increases just 20 % at the same resolution. This higher-order nonlinear scheme proposed in this study, by reducing the requirement of computational resources, can extend the applicability of LBM for DNS and LES of turbulent flows.
Bioethanol can be used as alternative fuel for an internal combustion engine. However, the price of bioethanol per calorific value is generally higher than that of gasoline. Therefore, it is necessary to improve thermal efficiencies of engine using bioethanol and reduce the refining cost of bioethanol. This study aims to improve thermal efficiency in a fuel reforming engine system using low concentration hydrous ethanol (less than 60 wt%). Low concentration hydrous ethanol can reduce the fuel cost because it can be generated from biomass with reduced number of distillation process for refinement. The fuel reforming engine system installs the reformer in the exhaust pipe of an engine, and hydrous ethanol and exhaust heat are supplied to the reformer, which generates the reformed gas containing hydrogen. Part of the hydrous ethanol is supplied to the engine cylinders. This system has three features: (1) exhaust heat recovery by fuel reforming, (2) hydrogen mixed combustion for lean burn, (3) high compression and low temperature combustion using hydrous ethanol with high octane number. This system can be combined these three features. Therefore, this system can the thermal efficiency can be dramatically improved. In this study, thermal efficiency improvements of this system are examined by experimental analysis. As a result, the reformed gas containing hydrogen improves thermal efficiency because the hydrogen in the reformed gas promotes the combustion of low concentration hydrous ethanol. And exhaust heat recovery using fuel reforming improves thermal efficiency. In addition, NOX emissions of this system using low concentration hydrous ethanol were lower than that of using pure ethanol fuel (1150ppm⇒650ppm) because the combustion temperature of hydrous ethanol is lower than that of pure ethanol. Low concentration hydrous ethanol in fuel reforming engine system could achieve high thermal efficiency and low NOX emissions.
A lab-scale two-stage light-oil burner has been developed to obtain the fundamental data required for designing burners to heat a diesel particulate filter when exhaust gas temperature of the main engine is low. Regenerative-heating and pre-evaporation premixing combustion were adopted to this burner for downsizing and reducing cost. Two-stage combustion was realized in the burner to reduce the heat-load of the combustion chamber for the first stage combustion. The combustion chamber volume is about 66 mL. Observations of flame-holding condition and temperature measurements of the burner and combustion gas were performed with varying the fuel flow rate and air flow rate. Three types of secondary air nozzle and three secondary air nozzle positions were tested to understand the effect of the secondary nozzle on combustion gas temperature and combustion gas compositions. It was found that the burner in the single-stage combustion mode was able to stabilize a flame in the range of 2 to 14 mL/min in fuel flow rate at adequate equivalence ratio in the range of 1.4 to 1.8. Combustion gas temperature of the burner in the two-stage combustion mode is determined by the total equivalence ration and is independent on the equivalence ratio of the first stage combustion. It is possible to suppress CO and NOx emissions when the burner is operated at 0.8 in the total equivalence ratio.
Increasing the electric power of nuclear power plant is important for the economy and the environment. Pressurized water reactor (PWR) exchanges the heat of primary system with secondary system in the steam generator (SG) to generate vapor. In this study, the steam generator of PWR was focused on. A prediction method to estimate the vapor mass flow rate of steam generator has been developed. In the method, the heat transfer from the primary system to the secondary system can be categorized into the following types. (1) Heat transfer from the primary system to the heating tube. (2) Heat conduction of the heating tube. (3) Heat transfer between the heating tubes and the secondary system. The liquid in the primary system is in the single-phase, while the liquid in the secondary system is in both single-phase and two-phase. In this research, the Colburn's equation and the Chen's equation to calculate the heat transfer coefficient for both single-phase and two-phase were used, while using the Saha-Zuber's equation and the Clark-Rohsenow equation to calculate the vapor mass flow rate at the sub-cool region. In addition, vapor mass flow rate of the steam generator with the axial economizer is compared with that of the current SG to evaluate the merit of the axial economizer. Moreover, we added fins and twisted tape to the current steam generator with the axial economizer as an approach to increase the vapor mass flow rate. Then, the rate of heat transfer and the temperature difference between the primary system and the secondary system were compared to inspect the economizer, fin, and twisted tape. As a result, vapor mass flow rate has increased about 3% by the combination of the external fin and twisted tape.
The aim of the present study is to investigate the relation between the positions of flow reattachment and maximum heat transfer at flow reattachment region. Flow separation and reattachment at downstream of an orifice (bore ratio d/D ≈ 0.5, ReD ≈ 13000) in a pipe was chosen as a flow field. A technique using high-speed infrared thermography was used to measure the spatio-temporal heat transfer to a turbulent water pipe flow around an orifice. In this work, we attempted to evaluate the convection velocity of the heat transfer structure on the heated surface, which is considered to be associated with the convection of the vortical structure in the near-wall region. As a result, it was confirmed that the maximum position of the time-averaged heat transfer was not coincide with the time-averaged flow reattachment position, as it has been reported in the literature. In order to investigate the mechanism of this, ensemble-averaged heat transfer coefficients were calculated on the condition that instantaneous reattachment appeared at specific streamwise positions. The ensemble-averaged heat transfer coefficient shows a noticeable peak at the flow reattachment position. Also, the peak value of the ensemble-averaged heat transfer coefficient tended to decrease toward downstream. This trend indicates that the flow reattachment at upstream contributes to the heat transfer enhancement more significant than that at downstream. This is the reason why the maximum position of the time-averaged heat transfer exists upstream of the time-averaged flow reattachment position.
Heat flux measurement method with thin film resistance sensor in a premixed gas combustion field has been studied to develop an accurate heat flux sensor, and to grasp and improve a heat transfer loss of the engine in SIP (Cross-ministerial Strategic Innovation Promotion Program) innovative combustion technology project. The MEMS technology was introduced to satisfy the requirement of the accurate heat flux measurement with high temporal, spatial and heat flux resolution for a turbulent heat transfer in the engine. The thin film resistance sensors of 250 to 1000 micron scale were fabricated on the Si substrate, and then a calibration method, measurement characteristics and response to the combustion were studied. Since the heat flux was measured through the surface temperature measurement and the transient heat conduction analysis of the sensor, accurate data and an exact thermal model are required. The heat flux calibration using self-heating showed a good agreement between the excited heat flux of 400 kW/m2 level and measured one with an error less than 10 kW/m2 for the wide frequency range from 200 Hz to 8 kHz by introducing an interfacial thermal resistance in the thermal model. The developed measurement system showed heat flux peak of 250 kW/m2 level with noise of 10 kW/m2 level against a butane-air premixed gas combustion in an open chamber. Heat transfer analysis showed that the heat flux trend after the peak can be explained by heat conduction between the burnt gas and the sensor wall. It was also demonstrated that the developed system can measure heat flux down to 10 kW/m2 and up to 5 kHz frequency range. Good prospect of the heat flux sensor for the engine application was obtained with the sufficient accuracy and the resolutions.
Pool boiling is used for cooling in numerous thermal energy dissipation systems because of its high heat flux removal capacity. However, the heat removal in a pool boiling is limited by the occurrence of critical heat flux conditions (CHF), the primary concern in the thermal management requiring high heat flux removal is CHF enhancement. For such systems, we have ever proposed a technique to enhance the CHF in saturated pool boiling using a honeycomb porous plate. This cooling technique enhanced the CHF by more than a factor of two (2.5 MW/m2) compared with that of a plain surface. The plausible mechanisms for the CHF enhancement are liquid supply through (1) capillary action and (2) vapor escape channels from the top surface due to gravity. In the present study, in order to quantitatively clarify the effect of the two liquid supply mechanisms on the CHF enhancement, experiments to identify the elementary processes were conducted, and the CHF obtained in the experiments using the honeycomb porous plate was compared with a proposed capillary limit model. Based on the results, the following conclusions were obtained: (1) In the high heat flux region, the liquid supplied through capillary action was shown to be the dominant factor leading to the CHF enhancement in saturated pool boiling, and the results calculated using the proposed model were found to be in good agreement with the experimental results. (2) Liquid supplied through vapor escape channels had a strong effect on the heat transfer coefficient.
Nanofluids are suspension dispersed nano-scale particles in a base fluid. In this study, natural convective heat transfer characteristics of Al2O3-water nanofluids in a vertical cylindrical container heated from below and cooled from above are investigated by transient three-dimensional numerical computations. Thermophysical properties of Al2O3-water nanofluids are estimated by either the conventional prediction equations or the experimental correlation equations reported by Khanafer and Vafai. The validation of the analysis program developed in the present study is carried out by comparing the computed average Nusselt numbers of the Rayleigh-Benard convection of water for Ra = 2500, 5000, 7500, and 10000 with Silveston's experimental data. A grid independency study is also carried out by computing the natural convection of water for Ra = 105. When thermophysical properties estimated by the conventional prediction equations are applied, the heat transfer rates of Al2O3-water nanofluid natural convection increase with the increase of the volume fraction of the nanoparticles for Ra = 104, and 105 compared with those of water. When thermophysical properties estimated by the experimental correlation equations are applied, the heat transfer rates of Al2O3-water nanofluid natural convection decrease with the increase of the volume fraction of the nanoparticles. The decrease of the convective heat transfer rates agrees with the experimental results reported by Li and Peterson qualitatively. Thermophysical property equations for estimating both at least effective viscosity and effective thermal conductivity are necessary to compute natural convective heat transfer characteristics of Al2O3-water nanofluids more accurately.
This study reports a vibrational energy harvesting system applied for low-speed vehicle tires on the asphalt road. The systematic model was analyzed under the measured road noise, in which a cantilever beam pasted piezoelectric film and magnets with the same polarity are fabricated as a nonlinear bistable vibrating system, when vehicle travels on the asphalt road at the different speeds of 10-20 km/h. By the theoretical investigation and simulation study, in the case of combination of a periodic modulating force which is autonomously offered from the gravitational effect of the magnetic end mass with the tire rotation and a vertical road noise excitation which is produced by the interaction of the tire and road surface, it can be observed that the potential becomes practically realizable to stimulate stochastic resonance, which can apparently enhance energy harvesting at the angular velocity of 14.4 rad/s. With consideration of the theory of stochastic resonance in this research, the vibrating responses become significantly strong to generate more available energy, where the energy captured from not only the road ambient, but also its gravitational acting. Hence, the proposed energy harvester model is capable of being utilized under the vehicle tire rotation circumstances. Furthermore, the suggested application for this harvester is to provide electrical power for tire pressure sensors.
This paper introduces a distance-based observation model for standing and sitting behaviors by using a proximity sensor as an interface function toward the development of a novel lower-limb assist robot. The proposed observation model employing relative distances to each part of a human body enables to determine a behavioral state transition from sitting to standing, or conversely. When the observation model capable of monitoring these behaviors continuously is applied to the assist robot, it would be very convenient to employ the device due to not requiring any manual control devices. Specifically, the observation model without visual data will be a great help to decrease mental burdens such as privacy. Practically, to verify the effectiveness of the observation model, the evaluation experiments were conducted by 30 subjects including 17 persons over the age of 60 and the results are described in detail. As a result, we could confirm that the observation model provides the assist robot with reliable recognition without the use of any manual controls or wearing a specific device.
In aging society, welfare personal vehicles have been widely used to improve the quality of life of elderly and handicapped persons. However, it is difficult for the users to steer the vehicle in narrow buildings. Accordingly, platoon driving of welfare personal vehicles has attracted attention as one of the effective leading methods. The platoon driving system consists of the longitudinal control and the lateral control. The longitudinal control is based on Adaptive Cruise Control. If the vehicle parameters are adjusted for each user’s driving ability, the longitudinal control will be string unstable in the worst case. As for the lateral control, the following vehicle tracks the preceding vehicle according to the target point following algorithm. The following vehicle may collide with a wall due to the large tracking error at a sharp corner in buildings. In this paper, the robust and precise platoon driving system is proposed to realize the safe platoon driving. Firstly, the longitudinal controller stably keeps the inter-vehicle distance regardless of the short time-headway. Secondary, the lateral controller precisely tracks the wheel track of preceding vehicle by using way-points. Thirdly, the robust platoon control for the different vehicle dynamics is designed by Model Error Compensator. Finally, the effectiveness of our proposed system is evaluated by the driving experiments.
We studied the sensing technology that detected the pan bottom temperature through a top plate made of crystallized glass. We did the sensing with three sensors of the reflection sensor that measured the reflectance and the thermistor that agitation such as that at the top plate temperature of the thermopile and the pan bottom to detect radiant energy from the pan bottom and located it in the lower part of the top plate we were able to confirm that we could detect a different pan bottom temperature of the emittance at ±10°C by revision of the emittance using the reflection sensor output. As for the structure of the reflection sensor, the emission of light scattered the LED emission of light with a concave lens in the pan bottom side, irradiated it, and the light receiving region with to locate in the upper part of the emission of the light region. 40-60% of the heat agitation was included in the radiant energy that the thermopile that we placed in the lower part of the top-plate received. We were able to confirm that we could correct the heat agitation based on the correlation that we measured with the thermistor of the top-plate back side temperature and thermopile output. As a result of putting the pan bottom temperature sensing that put three sensors together on an induction cooktop, and having inspected the measurement accurately, we were able to confirm that we could detect the pan bottom temperature with an error of approximately ±10°C in the range of 140-260°C regardless of the emittance of the pan bottom.
The approximate analytical method using the maximum entropy method (MEM) is proposed to estimate the stationary probability density function of nonlinear systems subjected to non-white random excitation. The MEM is often used to estimate the response distribution of nonlinear systems subjected to Gaussian white noise. In order to obtain the response distribution, the moment equations are used as the constraint conditions on the MEM. However, in the case of nonlinear systems under non-white random excitation, the term of the cross-correlation between the excitation and the response in the moment equations is generally not able to be calculated. In the proposed method, the equivalent linearization technique is applied to calculate the cross-correlation approximately. Using the method, we estimate the stationary response probability density functions of a Duffing oscillator and an asymmetric nonlinear system subjected to non-white excitation with the exponentially decaying correlation function. In the analysis, a wide range of the excitation bandwidth is considered. To demonstrate the effectiveness of the method, the results are compared with those of Monte Carlo simulation.
A novel method to identify anisotropic elastic constants for friction materials of automotive disk brake pads is proposed. This method identifies accurate elastic constants of friction materials in a non-intrusive way using the inverse analysis. To solve this inverse analysis, eigenfrequencies and mode shapes are measured with the hammering test. In order to make this problem well-posed, the original measurement system is developed. This new system reversibly constrains the sliding surface of the pad to the metal block using ice with refrigerating the metal block. Measured eigenfrequencies and mode shapes of the constrained pad make this problem well-posed. The Response Surface Method (RSM) is applied to reduce computational time of the eigenvalue analysis using FEM. In order to increase regression accuracy of response surfaces, the Modal Assurance Criterion (MAC) is applied to correlate measured and calculated mode shapes. Identification accuracy is performed with simulated measurement. Identification of elastic constants of an actual brake pad is performed. Calculation results are smoothly converged to reasonable values.
The nanoparticles whose diameter is less than 100 nm are used as the ceramics, electrical material and cosmetics. It is important to produce homogeneous characteristics of the particles for high performance property. The particle generation method to form homogeneous characteristics is difficult. The nanoparticle generation method with the flame has several advantages such as easy to accomplish high temperature by using simple apparatus construction and continuous produce. The authors proposed that the novel nanoparticle synthesis method by using flashing spray with flame in order to improve the problems. In this method the precursor and low boiling point organic solvent mixed solution is used as the start solution to improve the characteristics of the precursor evaporation characteristics. The injected solution from the nozzle is evaporated by flash boiling and form the homogeneous vapor. The nanoparticles are produced by the combustion energy of the flame. In this paper, the relationship between the flame and injection characteristics, and TiO2 particle characteristics were investigated to demonstrate the method. As the result, the particle distribution has two peaks as 0.1 and from 1 to 3 μm when the low injection frequency and the anatase phase of mass fraction increases by increasing injection frequency. The particle diameter distribution has wide distribution in the case of high equivalence ratio because the aggregation is promoted. The anatase phase of mass fraction changes at the equivalence ratio equal to 0.4, drastically.
A high-reliability design method for a MEMS accelerometer using a stretchable beam structure was proposed to prevent sensor property variations due to stresses from device fabrication and packaging. To achieve a compact piezoresistive three-axis accelerometer using a low-cost resin-mold packaging, beam buckling due to compression forces originating from residual stresses of thin films and shrinkage of mold resin must be overcome. The proposed stretchable beam structure, which gives axial flexibility by adding a ring-shape part at the center of the beam, has advantages in which it is effective against not only packaging stress but also inner stress such as thin film stress, and it does not sacrifice compactness. Formulations with a simple accelerometer model revealed that large and nonlinear variations in sensitivity occur due to beam compression. Such large variations have to be avoided to stabilize sensor performances. Besides, it is expected to enhance sensitivity up to about 1.5 times while maintaining linearity by arranging an appropriate compression force using the stretchable beam. The effects of the stretchable beam were verified using simulations and experiments on test samples. The designed stretchable beam, which has two rings connected serially, has five times the axial flexibility compared with a conventional straight beam without significant change in bending stiffness. A preferable increase of about 1.4 times and small deviations in measured sensitivity were achieved with the developed stretchable beam, compared with the straight beam with an unstable increase of about seven times and extremely large deviations. These large deviations seem to come from shape variation due to non-uniformity of dry etching technologies commonly used for MEMS devices. Thus, the effects of the proposed stretchable beam to the MEMS accelerometer design were confirmed to prevent large variations and deviations in sensor properties and to enhance sensitivity.
A parameter identification issue for Hill's orthotropic model to characterize plastic and creep properties of reinforced plastics is revisited on the premise of the practical use of the numerical material testing (NMT) in decoupled multiscale analyses based on homogenization theory. Specifically, the use of optimization methods is suggested to determine the Hill's constants that represent elastic limits followed by plastic flows in anisotropic plasticity and stress-relaxation in anisotropic creep. To examine the effectiveness of the present strategy, NMTs are conducted on three separate periodic microstructures (unit cels) to obtain the macroscopic stress-strain or time-creep-strain curves and the particle swarm optimization (PSO) algorithm is employed for parameter identification. In each of the unit cells, polyamide and epoxy resins, which are assumed to respectively exhibit plastic and creep deformations, are selected for matrix phases, while carbon is taken as a reinforcing material in unidirectional-fiber, plain-weave-fiber and particulate-dispersion reinforced plastics. During the course of the examination, we also discuss the implication of the ratios of orthotropic elastic constants in the determination of Hill's constants for the creep model in terms of the relaxation spectrums in the directions of material axes.
For the purpose of clarifying the water vapor effect on brake pad wear, two experiments were performed. In the first set of experiments, wear tests were conducted using four pads under three relative humidity conditions (0.8%RH, 35%RH and 65%RH). The tested pads were simplified formulation of commercial brake pad, each of which contains either CeO2, CuO, graphite as additive or no additives. Wear test results showed that wear amount of the three pads containing CeO2, CuO and non-additive at 0.8%RH was larger than those of pads at 35%RH and 65%RH. Analyses of wear debris and of the worn surfaces of both pad and disk showed that adhesion between pad and disk was relatively high at 0.8%RH. In the second set of experiments, adsorption tests of pad specimens left under 35%RH and 65%RH conditions were conducted. Test results indicated that water vapor in the environment physically adsorbed the pad materials. From the two sets of experiments, it is concluded that water vapor in ambient air adsorbed on the worn surfaces of pad and disk contributed to reduce the adhesion between them. On the other hand, adding graphite to the pad material decreased pad wear even at 0.8%RH. In order to elucidate this mechanism, the specimen of pure graphite was rubbed against disk material at 0.8%RH, 2.5%RH, 3.5%RH, and 65%RH. Wear of graphite at 0.8%RH and 2.5%RH was by some orders of magnitude higher than that at the other humidity conditions. On the disk specimen, graphite was clearly transferred at 0.8%RH. These results mean that the adhesion of graphite is very high at 0.8%RH. Therefore, the wear reduction mechanism of the pad with the addition of graphite at 0.8%RH was concluded as follows. Degraded gases from phenolic resin adsorbed the graphite surface at frictional interface, which caused to reduce its high adhesion to the disk material under very low humidity condition.
Authors proposed new system comprises a combination of a gear and a rolling bearing into a traction drive system because the rolling bearing has a function that reduces rotational speed and supports gear reaction forces. The system requires preload to use a rolling bearing as a traction drive. Adding preload axially requires an extra space for the spring to preload. In this study, preload in radial direction was induced to save space by placing a ring outside the outer ring utilizing shrink fitting. When a rolling bearing used as a traction drive, friction between a rolling element and the retainer becomes important. To improve transmission efficiency of the new system comprises a combination of a gear and a roiling bearing, it is necessary to improve a profile of the retainer. By this study, optimization of the curvature radius of the retainer when it contacts a rolling element was investigated. Optimization of the curvature radius of the retainer showed that the improvement of the oil film thickness and the contact pressure. By using the retainer with improved curvature radius, it was found that the transmission efficiency improves to 93.2%. The result observed on the surface condition of the retainer after examination was also reported. The major improvement could be confirmed more than the original flat surface.
We construct a structural optimization method targeting lattice structures composed of a sufficiently large array of unit cells where each unit cell consists of several beam elements, with the aim of maximizing the stiffness of the entire structure under a volume constraint. In this method, micropolar continuum theory is introduced for continuum modeling of the lattice structures because micropolar continua and beam elements both have rotational degrees of freedom in addition to translational degrees of freedom. That is, the material behavior of a micropolar continuum that is equivalent to the lattice structure is obtained so that the strain energy density of the micropolar continuum is equal to the volume average of the strain energy stored in a unit cell of the lattice structure, which is derived from the framework of classical beam theory. The conventional finite element method is expanded for numerical analyses of the micropolar continuum to take the rotational degrees of freedom into account. The optimization algorithm has the width of each frame element set as a design variable and represented as a continuous distribution in the modeling of the micropolar continuum. Finally, two design examples are provided to confirm the validity and effectiveness of the proposed method.
This study evaluates a robust optimum design of a compliant mechanism considering uncertainty of the load direction. For the topology optimization, this study adopts a level set based approach incorporating a fictitious interface energy term. The method is known to have several advantages such as the allowance of topological as well as shape changes, and the ability to qualitatively control the geometrical complexity of the obtained optimum configurations. The design objectives are to maximize the displacement at the gripping position and the robustness under variations of the applied load direction. In addition, the eigenfrequency maximization is considered to acquire the structural stiffness. The design problem is formulated as a multiobjective design problem. Conventionally, the robust design problem has been formulated as a weighted sum of the mean value and the standard deviation of the performance index. Integrating the multiobjective optimization to the level set-based topology optimization method, this study adopts the lp-norm method that can obtain the Pareto solution even when the Pareto frontier is a non-convex form. Through numerical examples of a compliant mechanism design, validity of the proposed method is verified. Then, the robustness of the obtained optimum configuration is discussed.
For several decades, factory automation or unmanned factory productivity has been progressed to realize much higher productivity in manufacturing. However, human centered manufacturing system is getting attention to realize much more flexibility for manufacturing of wide product variety and volume. So it is necessary to provide the safe and efficient environment to workers considering their own physical properties. This study investigated a mechanism of muscle fatigue and proposed a muscular fatigue model to evaluate muscle fatigue progress under several muscular force patterns. Previous studies have already proposed a muscular fatigue model. However, these previous studies discussed about the condition of maximum voluntary contraction. The new point of this study is considering several muscular force patterns including muscle recovery progress. This study proposed the method to estimate the endurance times for keeping constant forces considering the physical characteristics. This study also proposed the method to estimate the iteration numbers for keeping constant forces with interval. To validate the effectiveness of the proposed method, experimental verifications were conducted. The experimental results had a good agreement with the evaluation of muscle fatigue progress using the proposed method although it is necessary to consider the method to raise the precision of determining the physical parameters and the method to decrease the dispersion of experiments derived from the subjective judgement of participants. Success of resolving these issues will provide ergonomically safe and efficient working environments considering the physical properties of each worker.
The goal of this study is elucidation of propulsion mechanism of small creatures by ciliated swimming legs. For this purpose, a ciliated pereiopod of an opossum shrimp was introduced and it was modeled with a straight cylindrical stem with 10 much narrower cylindrical poles perpendicularly projecting on the stem. Flow drag acting on the pereiopod in a steady flow, which corresponds to the thrust force by paddling of the pereiopod, was computed with a variety of clearance between each adjacent pair of cilia d and the flow velocity U. It was found that the drag increased with the increase in d to be saturated with a certain value in the range of d ≥ 0.04 mm where influence of boundary layers of adjacent cilia is negligible, and the drag agreed well with that estimated from drag of a two-dimensional cylinder. This result suggests that the opossum shrimp is propelled with the drag-based swimming and the ciliated pereiopods supply greater thrust force than tabular pereiopods with the same projection area. It was also found that the drag decreased in the range of d > 0.07 mm in which some cilia come into the boundary layer of body of the shrimp. It was optically observed that distance between adjacent cilia is around 0.07 mm on the stem and cilia near the root of the pereiopod are shorter than those near the tip. The present results suggest that the ciliated pereiopod is well designed to efficiently generate the thrust force within a limited length and mass by preventing influence of the boundary layers.
Indoor thermal quality affects the conditions of the occupant who is doing tasks in an indoor environment, and also task performance. Therefore, appropriate control of thermal factors is important to improve the conditions of occupant, such as thermal comfort sensation and the arousal level which is related to task performance. In order to determine guidelines how to control the thermal factors for improving the comfort sensation and arousal level, it is necessary to evaluate the condition of occupant by using quantitative and continuously measurable indices such as physiological indices. In this study, we aimed to clarify the relationship between the condition of occupant and physiological indices which is affected by changes in thermal factor and task level. We measured subjective evaluation and physiological indices such as electroencephalogram (EEG), electrocardiogram (ECG), respiration, and skin temperature of 10 participants in 4 experimental conditions consisted of different temperature and arithmetic task level. From the result of time-series analysis and correlation analysis among the experimental conditions, the subjective evaluation value, and physiological indices, it is showed that difference of task level can affect to the correlation between the conditions of occupant and physiological indices. These result suggests that the effect of task level on physiological indices should be considered in order to evaluate the conditions of occupant by using physiological indices.
This research is a study of the new steering system to improve maneuverability during low speed driving. First, we investigated the problem of the steering operation during low speed driving. As a result, it was found that the changing of steering grip position is one of the workload. Therefore, we developed the new steering system to solve the problem. We can operate a vehicle without the changing of steering grip position by using the proposal system that is changed upper limb motion and grip position's shape. We conducted driving simulator experiment to investigate driver characteristics change between the proposal system and the conventional system with low gear ratio. As a result, operation by the proposal system makes low driver gain. Therefore, the system is maneuverable even if it is low steering gear ratio. Finally, we conducted subjective experiment using an actual vehicle. As a result, it was indicated that the driver can operate a vehicle by using the proposal system even if he has never driven an actual vehicle.
This study numerically evaluated the effect of green phase countdown timer (CDT) on the reduction of driver's dilemma at signalized intersection. The proposed system provides the remaining green time to the drivers in real-time to support the stop or pass decision-making. Driving simulator experiment equipped with the CDT indication system was carried out to collect the drivers' data when approaching to a signalized intersection. It was confirmed that the CDT encouraged most drivers to reduce their approaching speed and to prevent falling into the dilemma zone. A logistic regression analysis (LRA) showed that the remaining distance and acceleration rate significantly contributed to their decision making after amber onset. Especially, it contributed to decreasing the approaching velocity for the drivers who travels at high speed. Also, the intent estimation was carried out using the LRA to infer whether they stop or pass the intersection. Most of the drivers aided by the assistance system terminated their decision much earlier far from the stop line. It was concluded that the CDT was quite effective in reducing drivers' approaching speed and preventing falling into the dilemma zone in most cases. Also, it contributes to shift their stop/pass decision much earlier to safely stop or pass the intersection without any confusion.