A non-standard circumferentially cracked round bar (CRB) specimen has been examined for replacement of the standard fracture toughness CT specimen since 1981. In the case of a material with low fracture toughness, the CRB specimen can be substituted for the CT specimen. However, when it is applied to those with medium or high fracture toughness, there are many problems: the specimen size required, the strain constraint equivalent to plane strain, the measurement of crack length and the procedure to obtain the J-R curve. In this investigation, fracture toughness testswere conducted on a medium fracture toughness material using the CRB specimens. The normalization method was tested for the first time on CRB specimens and was considered adequate to measure its J–R curves. The CRB specimens with about (the ratio of ligament to radius) b/R₀=0.3 showed the better strain constraint and almost the same fracture surface as the CT specimen within Δa=0.2mm: blunting, initial crack growth and the grown crack blunting. On the other hand, after Δa=0.2mm, the latter half of the stable crack growth region showed a difference in fracture surfaces between two specimens: the void growth was dominant, or the shear dimple was dominant. Therefore, for fracture toughness indexing of CRB specimens, J_0.1 is preferable to J_0.2 which is typically used for the standard CT specimens.

Our study systematically evaluated the microstructure evolution which depended on the shape of the welding tip. And then, it was revealed that the different microstructure was generated in the slope and flat regions of the welding tip. In the slope region corresponded to the end of the joints, the wavy behavior due to the intense plastic deformation was observed, and the grain refinement occurred near the weld interface in the slope region at the welding conditions. It was associated that the expansion of the weld diameter was led by the enhancement of the plastic deformation in the slope region, and the weld strength increased. On the other hand, as the welding process progresses, the grain growth occurred in both the slope and flat regions. It was revealed that the {1012} deformation twin and the twin growth were the main deformation mechanism in the process which the grains became coarse during the high strain rate processing such as the ultrasonic spot welding.

In this study, aluminum alloy specimens were subjected to bending vibrations at different vibration frequencies near the first resonance frequency in order to investigate the vibration changes associated with crack propagation. Bending displacement, crack length, and strains at several parts of the specimen were measured during the bending vibration tests. As a result, it was confirmed that when the vibration frequency was lower than the initial first resonance frequency, the vibration amplitude increased with the crack length, and when the vibration frequency was higher than the initial first resonance frequency, the vibration amplitude decreased with an increase in the crack length. This is due to the decrease in the first resonance frequency due to the material damage. The relationship between the change of bending displacement amplitude and the crack length during vibration of the specimens can be organized using the slope (dΔε_x2/df_v) of the relationship between the strain range and the vibration frequency for the undamaged specimen. This might be due to the strong correlation between the decrease in the first resonance frequency and the crack size when the crack initiation location is limited in the material. Moreover, based on the relationship between the change of bending displacement amplitude and the crack length, the stress intensity factor range (ΔK) was estimated by incorporating the load change into the crack length. By using the modified ΔK, the crack growth rate during bending vibration could be predicted.

The 3D printer using Fused Deposition Modeling (FDM) is attracting attention as a manufacturing technology that is able to reduce the production time and the manufacturing costs. However, the information on the mechanical properties and the process parameters that affect to the safety and the reliability of the shaped object is less than that for metallic materials. Therefore, it is desirable to detect and evaluate the phenomena such as “Craze occurrence/growth” and “In- or Inter-layer failure/fracture”. In this study, tensile tests were conducted to the two type specimens with different stacking directions. Then, it was attempted to extract the characteristics of those phenomena from the results of chaos analysis of AE signals detected during the test. The following findings were made clear. (1) The frequency ranges that characterize the respective phenomena were determined. (2) The chaos parameters of AE waveforms in which the signals were separated into the frequency range of each phenomenon using the Empirical Mode Decomposition (EMD), enabled the characteristics of that phenomenon. (3) Differences in stacking direction affect the chaotic characteristics of AE waveforms emitted by each phenomenon.

It is difficult to predict the earthquake loading so the effect of pre-strain on fatigue strength was required to investigate. Especially, surface shape was changed when large plastic strain was applied. Strain concentration may be occurred by this surface changing. In this study, the effect of pre-strain on micro-scale strain concentration was investigated using in-situ observation. Tensile test for austenitic stainless steel, SUS316L, was performed under laser microscope to measure the height distribution. In addition, micro-scale strain distribution was measured using digital image correlation method. Pre-strains were applied range of 0-56 %. Loads were applied in the range of plastic strain after pre-strain. The results show that height of roughness due to pre-strain became large when the pre-strain was larger than 16 %. High strain area due to pre-strain did not depend on pre-strain because strain concentration was dominated by ease of plastic deformation of each grain. When plastic strain was applied after pre-strain, which was smaller than 8 %, strain distribution was not affected by pre-strain. This is because surface shape changing was small and strain concentration was dominated by ease of plastic deformation of each grain. On the other hands, local strain was increased when pre-strain was large. This is because surface shape changing became large and strain concentration due to surface changing was also occurred.

In the sport of curling, various mechanisms in curl of rotating stones have been proposed; however, the essential understanding of the mechanism has not been clarified. In this study, we attempted to explain the curl of a rotating stone by focusing on the contact area between the stone and many small ice protrusions known as pebbles which artificially produced by spraying water droplets onto the flat ice surface of lane. Specifically, a novel model so-called contact area model, which assumes that the contact area between the stone and pebbles differs between the front and back side of the stone, was proposed to explain the curl of stone. It has been experimentally shown that the heights of pebbles decrease an average 1.1 μm with each pass of the stone. The sliding stone and pebbles contact each other firstly in the front side of the stone and then in the back side. Pebbles contacted in the front side of stone may also contact in the back side, resulting in a potentially larger contact area in the back side of stone compared to that in the front side. The difference in contact area between the front and back side creates a frictional force difference between the front and back side of rotating stone, creating the force that causes it to form a curved trajectory. We evaluated the force required for a rotating stone to curl based on the relationship between a stone-trajectory experimentally obtained and time estimated by solving the equation of motion of the stone, and investigated whether the magnitude of the force could be explained using the contact area model. The result shows that the difference of contact area between the front and back side probably contributes to the curl of rotating stones.

In this study, LES calculations by OpenFOAM were performed using five blade models with different blade thicknesses (original, quarter, half, 3-quarters, and filled) to investigate the characteristics of separated and reattaching flow between blades of two-dimensional cascade. The results showed that the type of separation changes from leading edge separation (original - half models) to on-blade separation (3-quarters and filled models) as the blade thickness increases. The size of the separation bubbles and the distribution of mean and RMS values of pressure on and between the blades varied continuously within the three models for leading edge separation and within the two models for on-blade separation, respectively. The changes in the vortex structure were captured by considering the spectral shape of pressure between the blades. In the case of leading edge separation, vortex shedding, merging, reattachment, and collapsing were detected while in the case of on-blade separation, they were hardly detected. In the case of leading edge separation, the vortex merging prevented the increase of the RMS value of the pressure. In the case of leading edge separation, with increasing the blade thickness, two dimensionality of the vortex was weakened and irregularity of the vortex structure was strengthened, and therefore, the periodicity of the vortex merging was weakened.

Controlling frictional drag, noise, mixture, and chemical reaction in flow is an important issue in various engineering fields. In recent years, many investigations have been carried out to control the frictional drag by external stimuli, such as light and electricity, from the point of view of rheology and physical property. Flow control by the external light stimulus has a great advantage in that there is no contamination of the flow field. Some experiments of a photoresponsivity surfactant solution CTAB/C4AzoNa have been conducted for the basic study of flow control. The viscosity of the surfactant solution increased with the irradiation of ultraviolet (UV) light and decreased with visible light. First, we attempted to control the vortex height in the rotating flow by irradiating with UV and the visible light. The vortex height repeatedly increased and decreased by the reversible change in viscosity of the CTAB/C4AzoNa solution. Next, a thin layer of this solution in a vessel was exposed to blue laser sheet irradiation of 405 nm wavelength. As a result, the viscosity of the CTAB/C4AzoNa solution in the thin layer was locally increased at only the irradiated portion of the laser sheet. Finally, the CTAB/C4AzoNa solution filled a thin gap of the rotating two axial cylinder represented as a simple shear flow model. The torque acting on the inner cylinder surface was changed by local UV irradiation. These results proposed that this surfactant solution has the potential to achieve local and reversible flow control of drag.

Linear stability analysis and 3-D temporally developing direct numerical simulations are performed to study the transitional structure and the resultant acoustic emission caused by interactions between the unstable modes related to Kelvin-Helmholtz (K-H) instability in a supersonic fully expanded round jet with “top-hat” velocity profile at high Mach number. Numerical results for the Mach number M_j = 2.0 and Re_r = 2000 based on the jet half-radius r₀ are presented. For DNS, two types of initial disturbance are examined. The first type is the jet forced by only one linearly unstable mode (one of m = 0, 1, 2, 3 and 4). The second type is the jet flow forced by a pair of helical modes (one of m = ±1, m = ±2 and m = ±3). Numerical results show that staggered structures of positive radial velocities are generated between the regions where Λ-shape vortices are closed in the supersonic jet. This structure exists in each jet forced by a pair of helical modes. Therefore, the formed positive radial velocities of the structure cause a spreading in the radial direction of the jet and a rapid expansion of the jet shear layer. Furthermore, numerical results indicate that the phase velocity of the linearly unstable mode greatly affects the magnitude of the pressure fluctuation radiated from the jet. In a comparison between the pressure fluctuations radiated from each jet, the magnitude of the pressure fluctuation radiated from the jet forced by a pair of the helical modes of m = ±2 and m = ±3 with a transonic/subsonic phase velocity is about 10 dB lower than that of the jet forced by a pair of the helical modes of the m = ±1 with a supersonic phase velocity.

The heat generation density of electronic components has increased as they have become smaller and more powerful. Various types of heat pipes have been used as thermal control devices, utilizing heat transport by the gas-liquid phase change of refrigerant. Pulsating Heat Pipe (PHP) has attracted much attention because of its compactness and high heat transport performance. This study is on Low Filling Ratio Pulsating Heat Pipe (LFR-PHP), which can realize more efficient heat transport than conventional PHP. The appearance and experimental outline are the same as those of the conventional PHP, but the amount of working fluid filled is extremely low (10 vol.%), which is considered to cause dry-out in the conventional system. Although the LFR-PHP achieves highly efficient heat transport, the details of the heat transport characteristics, such as the operating principle, have not yet been clarified. In this report, the effects of the installation posture of LFR-PHP (bottom-heat, horizontal-heat, and top-heat posture) on the heat transport performance were investigated. As a result, In the bottom-heat position, the minimum thermal resistance of LFR-PHP was 0.18 K/W, which was about 1/5 times higher than that of conventional PHP and it was confirmed to operate at filling ratios of 3 to 10 vol.%. Experiments with different heat exchange section ratios in the bottom-heat and horizontal positions showed that the heat transport distance was increased and the heat transport performance was improved by adding 60 area.% of adiabatic section area. in the horizontal position, the LFR-PHP was cooled efficiently by placing the heating section in the center of the LFR-PHP, and heat transport performance of it was approximately the same as that of bottom-heat position. In the top-heat posture, it operated when the heating section was 50 area.%, with a minimum thermal resistance of 0.22 K/W.

The drum cable engines with DO/HBs (Draw off hold back gear) have been indispensable equipments to lay and recover the optical submarine cables and the optical submarine repeaters. When use them, the back tensions by the DO/HB have been set at relative high tensions because of the empirical knowledge to pass repeaters and cable couplings safely through the drum. However there had been no papers on the minimum back tensions for the DO/HB. If we could know them for the various kind of repeaters, the preparation and operations of the drum cable engines and DO/HBs would be improved and get security. Therefore the author solved forces and moments acting on the repeaters and the cable couplings on the rotated drum cable engines using the linear system of equations. And found that there were the negative longitudinal axial forces acting on the repeaters when the repeaters passed around 85 to 100 degrees from the top of the drum of the first turn in the lay, and around 80 to 110 degrees from the top of the drum of the last turn in the recovery if the back tensions by DO/HB were set below specific values. If there were the negative longitudinal forces, the repeaters would not face the drum and not be wound correctly on the drum. Then here the author clarified the minimum DO/HB back tensions for the drum cable engines based upon more than zero longitudinal axial forces acting on the optical submarine repeaters during lay and recover. These calculations can apply to almost all kind of repeaters if they are connected to the cable coupling with the gimbals joints.

A brake that presses a friction material against a rotating disk is called a disk brake. And it is widely used in industrial machines and automobiles. A noise called squeal may occur during braking. Squealing is generally unpleasant and can impair the performance of the machine on which the brake is mounted. When a machine squeal occurs, countermeasures such as provide dampening may be taken. However, it is difficult to take effective countermeasures unless the mechanism of squeal generation is clear. It has been clarified in previous studies that the natural vibration of the disk greatly affects the generation and frequency of the squeal. In particular, the generation mechanism of out-of-plane squeal, which has been extensively studied for a long time, has been elucidated and countermeasures have already been taken. On the other hand, when out-of-plane squeal was dealt with, in-plane squeal became a problem. In-plane squeal is characterized by large vibrations in the in-plane direction and small vibrations in the out-of-plane direction as if the disk were twisted. In this study, we clarified the generation mechanism of in-plane squeal using a low-degree-of-freedom analysis model. Since the conditions under which in-plane squeal occurs have also been investigated, it will be useful for eliminating in-plane squeal in the future.

Infrastructure facilities have been deteriorating and require a vast number of inspections conducted by skilled engineers. Inspection robots are now necessary because of a shortage of skilled engineers. To improve the inspection efficiency of outdoor infrastructure facilities, we investigated an omni-directional mobile robot that can move freely in all directions. However, it is necessary to design a vibration-isolation mechanism because the positional-inspection accuracy of underground objects is adversely affected by vibration in an outdoor environment. We constructed an experimental setup to evaluate the vibration properties of the robot’s wheel and evaluated the acceleration characteristics due to the difference between the direction of movement and speed of the wheel. Experiments using the omni-wheel as the robot’s wheel were performed. We clarified that the input vibration is transmitted to the robot body by the wheel. We also compared the experimental results and theoretical estimation and confirmed that vibration generated from the wheel could be estimated using the formula for calculating the period of vibration. In consideration of the external environment and vibration properties such as the irregularities of the road surface and the structure of wheel, we confirmed that it is possible to estimate input vibration in the upper housing of the wheel.

In order to apply resist patterns fabricated by electron beam lithography to nanoimprint molds, it is necessary to consider not only line widths and hole diameters observed two-dimensionally from the exposure top surface, but also three-dimensionally including resist cross-sectional shapes. In this study, we focus on the dose distribution inside the pattern and the development time, and investigate the effects of these on the cross-sectional shape of the resist. An exposure method was employed to produce a resist pattern with a line width 100 nm, in which the total dose within a line is the same, but the electron beam scanning position and number of times within a line are changed. The results of a comparison between the dose distribution analyzed by electron scattering simulation and the sidewall shape of the pattern after resolution showed that the dose distribution and the actual resist shape agreed with each other within ±5 nm accuracy under certain conditions. The results showed that the actual shape of the resist sidewalls can be changed by local dose distribution in the resist depending on the scan position and number of scans, even if the average dose is the same for the entire pattern. Furthermore, we investigated the resolution mechanism of the resist by observing the development process of the resist after exposure at different development times. The results showed that the difference in the development speed caused by the difference in the dose inside the pattern affects the cross-sectional shape of the resist. The results of this study indicate that the resist cross-sectional shape is significantly affected by the dose distribution inside the resist and the difference in development speed caused by it, and that these parameters can be expected to be applied to the fabrication of the desired cross-sectional shape in the future.

The purpose of this study is to create micro-texture on the surface of various mold materials by ultrasonic-assisted grinding. The effects of materials properties (hardness and fracture toughness) on micro-periodic structure were investigated by performing ultrasonic-assisted grinding, in which ultrasonic vibration is assisted in the axial direction of the grinding wheel in surface plunge grinding. The results showed that periodic structures can be formed without plastic flow on the surface after machining only in the case of cemented carbide with high hardness and low toughness. Furthermore, by modeling the abrasive grain shape and arrangement of the general purpose diamond grinding wheel without special treatment used in the experiments, we attempted to simulate the grinding groove shape formed by a multi-grain grinding wheel when ultrasonic vibration is assisted. The periodic structure formed on the cemented carbide surface was compared with the simulation results, which were in good agreement in terms of the period of the sinusoidal wave and the width of the grinding groove, confirming the validity of this simulation method. From the above, basic knowledge about the machining mechanism of grinding groove in ultrasonic-assisted grinding was obtained.

High-speed and high-precision actuator control is required for industrial manufacturing equipment. In such systems, the control operation cycle needs to be shortened to 100 μs or less. Recently, the quantity of sensors and actuators is increasing because new control methods have been developed. Therefore, the amount of information input/output to/from sensors and actuators is also increasing. Any electromagnetic noise occurring inside the equipment due to using high-voltage power or various actuators affects the system performance. The authors are thus developing a network communication system for high-speed and high-precision mechatronics control considering electromagnetic noise. The network communication adopts an original protocol operating in the 40-MHz band with 8B10B coding for SerDes logic implemented on an FPGA. In this paper, a method for the K-code usage of 8B10B coding to reduce packet transmission overhead is proposed, as well as a data transfer scheduling method that can reduce communication delay by setting a communication period for each data and distributing the amount of data transfer per communication cycle. Evaluation results show that the cycle-to-cycle jitter in sampling between the main controller and the control device was 260 ns. In addition, the data transfer scheduling reduced communication delay by 36% compared to the case without the scheduling.

In recent years, high-precision gears are expected to be used in vehicles and robots. Currently, gear hobbing is widely used as a roughing process while shaving and grinding are used as finishing processes to improve the accuracy and surface quality of the gears. The increasing demand for gears requires a gear machining method that is more efficient than the conventional machining processes. In this study, high-speed gear hobbing that achieves accuracy comparable to shaving and grinding was performed at a cutting speed 12 times that of conventional hobbing. Experiments were conducted using Cr-Mo steel as the workpiece and cemented carbide as the hob cutter in the cutting speed range of 200 - 2450 m/min. The relationship between the hardness and the depth from the gear surface was investigated with a comparison with the change in the material structure of the gear surface layer. The results showed that the hardness of the gear surface layer increased in the high-speed hobbing process compared to the conventional hobbing due to the strain and crystal grain refinement caused by the high cutting speed. In addition, experiments were performed at each cutting speed in the range of 400 - 1200 m/min to investigate the possible changes in machining characteristics when the number of machined pieces increased to 30. The results showed that despite the number of machined gears, the surface hardness increased at high cutting speeds. The effects of the number of machined gears on tool wear and surface roughness were also insignificant, indicating that high-speed hobbing is a promising efficient production method of gears with high surface quality.

Nuclear deformation caused by external mechanical stimuli has been suggested to impact cellular activities, such as cell migration, gene expression, and proliferation; however, the underlying mechanisms remain largely unknown. Since cells reside in dynamic mechanical environments, investigation of viscoelastic behaviors of nuclei under mechanical conditions is believed to be key to understanding the mechanisms of the cellular responses to mechanical stimuli. In this study, we developed an in-situ observation system for the dynamic deformation behavior of the cell nucleus caused by mechanical substrate stretching. Human dermal fibroblasts cultured in a custom-made PDMS chamber were subjected to 5% strain by using a newly developed stretching system mounted on the stage of an inverted microscope. To obtain sequential "in-focus" fluorescent images of the nucleus during the cell stretching condition, the height of the stretching chamber was continuously controlled with a polynomial interpolation method during image acquisition. Intranuclear strains were then calculated from the fluorescence images obtained. As a result, compared to a lower strain rate condition, the whole nucleus strain in the direction of stretching tends to decrease during the application of stretching at a higher strain rate. In addition, the intranuclear strain showed heterogeneous magnitude distribution under the higher strain rate condition, while a uniform strain distribution was observed at the lower strain rate. The system we developed will help elucidate the role of the viscoelastic behavior of intranuclear structures in the cellular response to substrate stretching.

Aerators are necessary for the conservation of water quality in dams, as they increase water circulation and oxygenate the water. To estimate aerator performance characteristics in the field, the optimal spatial range, resolution, and sampling time interval need to be determined for the targeted water mass. In this study, we conducted precise field experiments at Hiyoshi Dam in Kyoto, Japan, by employing a new type of aerator in the summer of 2012. Initially, the water temperature distribution near one aerator was observed using an automatic temperature profiler capable of horizontal movement on the water surface over a distance of 90 m at a speed of 0.1 m/s during a sampling cycle of 15 minutes. The vertical temperature distribution was determined by a series of thermocouples suspended in steps of 0.1 to 1 m on a 10-m-long cable beneath the surface. Subsequently, the water temperature distribution between two identical aerators located 275 m apart was observed using 6 pairs of vertically suspended thermocouples connected horizontally with a cable at 25-m intervals. Finally, the water flow distribution near one aerator was observed with an electromagnetic flowmeter. Analysis of the results clearly showed how an entrained water mass intruded into a thermocline that formed at a depth of 2.5 m. In addition, details regarding the speed and flow rate of the intrusion, the mixing efficiency, and the estimated number of days required for shallow layer circulation were estimated.