In order to investigate the effect of microstructure in the surface layer produced by shot peening on fatigue properties of a maraging steel, rotating bending fatigue tests were carried out using shot-peened specimens and electro-polished ones of a 350 grade 18% Ni maraging steel in the relative humidity of 25% and 85%. The shot-peened specimen tested had a fine-grained structure and a small amount of reversion austenite in the work affected layer. The shot-peened specimens showed a unique fatigue fracture surface with a ring-shaped fracture one along the surface layer in the wide range of fatigue lives. The formation mechanism of the unique fracture was explained from the coalescence of many surface cracks over the entire circumference initiated from dimples formed by shot peening at the specimen surface and the difference in the microstructure between the fine-grained surface layer and the matrix. Fatigue strength in the shot-peened specimen increased due to the grain refinement in addition to hardening and formation of compressive residual stress at the surface layer. The fish eye size, i.e., the internal crack length, increased and the depth of a surface crack inversely decreased with increasing in the fatigue life. The value of stress intensity factor obtained from the fish eye size increased with increasing in the fatigue life and approached to the one of the fatigue fracture toughness of the maraging steel in longer life beyond 10⁷ cycles. This suggested that the fracture mode in the shot peened specimens was changed in the order of a fracture controlled by a propagation of the surface crack, a combined fracture due to propagation and coalescence of a surface crack and an internal one, and an internal fracture induced by an internal crack propagation with decreasing in the stress level.

In this study, the threshold stress intensity factors for the hydrogen assisted crack initiation, K_IH were compared using the high and low toughness welded joints simulated under two different PWHT conditions within the 2.25Cr-1Mo-V steel reactor fabricating specifications by reproducing the hydrogen embrittlement factors predicted under each operating conditions such as startup, steady-state operation and shutdown into 1T-C(T) specimens, rising and holding load tests. First of all, in the reproduce of startup conditions, the rising load tests were performed under 20 MPa hydrogen pressure at room temperature. As the results, quasi-cleavage crack initiation mode was observed during slow rising load in both high and low toughness welded joints. However, in the low toughness welded joint, fast fracture before the onset of 5 % nonlinearity occurred, and the fracture toughness due to hydrogen embrittlement, K_IC-H was recognized. Secondary, in the reproduce of steady-state operating conditions, the threshold for hydrogen assisted crack initiation was determined in the same way as reproduce of startup conditions, and the holding load tests were conducted where the hydrogen environment and load for the threshold for hydrogen assisted crack initiation were maintained for up to 10 days. As the results, it was observed that quasi-cleavage crack growth continued during the load holding period in both high and low toughness welded joints. The crack growth rate in the high and low toughness welded joints were modeled respectively, by numerically introducing the relationship between da/dt and K based on the correlation between the quasi-cleavage crack growth and the load line displacement. Finally, in the reproduce of shutdown conditions, the rising load tests were performed in air at 150 °C using the 1T-C(T) specimen that had been pre-charged with hydrogen. As the results, there was almost no difference in the values of K_IH between high and low toughness welded joints.

It is known that the sound absorption performance of resonant type acoustic liners is affected by glazing flow, which interferes with the motion of fluid particles. In order to prevent the effects of glazing flow, we propose new design concepts, which apply with a special thin film called Fine-Perforated-Film (FPF) to the surface of the acoustic liners. We made two types of liners. Typical resonant type acoustic liners are “Baseline” which has round holes and “V-Slit” which has slit holes. New resonant type acoustic liners have a gap fixed between the FPF and “Baseline” liner surface. Each liner was tested using the flow duct rig of Japan aerospace exploration agency (JAXA). From the data obtained, the sound absorption coefficient Δ and the drag coefficient were calculated. The results show that the drag coefficient can be reduced without changing the sound absorption coefficient by changing the hole shape of the FPF. It is suggested that small hole size of FPF reduces the peak value of the sound absorption coefficient and the drag coefficient. These results show that acoustic liners combined with FPF can be superior to conventional acoustic liners in both acoustic and aerodynamic performance. To find the mechanism of drag reduction due to hole shape change, we performed visualization tests using PIV on acoustic liner models. It was found that shortening the length of the hole in the flow direction suppresses the flow into and out of the cavity and reduces the occurrence of turbulence.

In the routine maintenance of piping systems in power plants, maintenance management priorities are determined based on quantitative indicators, such as safety classification guidelines and probabilistic risk assessments, as well as qualitative metrics, such as supply reliability, operating experience, and work safety. In power plants, quantifying the level of maintenance criticality for areas that pose little risk to safety is difficult. Assuming damage to the piping system due to deterioration, the internal fluid flowing to the surrounding area may affect the functions of the peripheral equipment and work safety at the site. If the fluid temperature is high, the risk of burning increases. This study was aimed at quantifying the indicators of human burns that may pose a risk to work safety. Based on indicators related to the severity of human burns, we constructed an evaluation model using the results of fluid experiments and analysis of heat conduction in the skin to estimate the PBI, which in turn can be used to estimate the prognosis of burns. It was found that, especially under the condition for the evaluation of flashing, when a phase change occurs before and after a leak, the fluid diffusion range is large, and the fluid temperature is also high near the leak source. Such flow conditions can induce serious burns over a wide area. Based on the trends of the indicators related to human burns obtained in this study, we will construct a model to evaluate work safety risks in power plants using design information like temperature, pressure, and piping layout of the system.

Oxygen additional system was examined for CO₂ capture system in gas fueled engine. In this study, the effect of the oxygen supply on combustion was investigated to increase CO₂ concentration of the exhaust gas. As the amount of supplied oxygen increased, the more EGR was required for the higher thermal efficiency. Exhaust temperature increased as the amount of supplied oxygen increased under same G/F condition. The supplied oxygen could increase the CO₂ concentration and the temperature of the exhaust gas.

The characteristics of a differentially-operated optical displacement sensor developed for wind-tunnel using magnetic suspension are studied both analytically and experimentally. The target sensor measures the three-dimensional displacement of the suspended object (floator) from the variations of the shadow of the floator. It is composed of eight optical systems. First, the output characteristics of the fabricated sensor are measured. As to linearity, it is good in the direction of light (x-axis) but inferior in the other directions (y and z axes). In addition, interferences among the axes are observed. Because the differences in characteristics among the optical systems cause such errors, adjustments by software are carried out. They reduce the nonlinearity and interferences. However, residual errors still remain. To clarify the reasons, the output characteristics are studied analytically by investigating the movement of the shadow of the floator and the variations of the illuminated area on the lenses. The results suggest that nonlinearity and interaxial interferences exist on some extent in the sensor, which was observed in the experiments.

This study concerns establishing a mathematical model to analyze and design tensegrity structures built from repetitions of elementary structures, called the truncated regular octahedral tensegrity (TROT). The TROT has three pairs of parallel square faces, each perpendicular to the others, and is preferable to build three-dimensional (3D) tensegrity lattices. The squares of each the pair are twisted for the structural stability purpose, and one simple way to form a lattice is to use the mirror image as its neighbor. Another connection type is also possible by employing the quadruplex prismatic tensegrity (QPT) as a bridge between the TROT. The connectivity matrix plays a central role in the analysis and design of tensegrity structures. This paper provides a systematic way to construct the connectivity matrices for these TROT tensegrity lattices. For a given space to fulfill and a force to bear, the number of the TROT, node locations (shape), length of the QPT bridge, etc. can be chosen arbitrarily. The provided connectivity matrix formulae allow us to automatically change these parameters during the evaluation process in the structural design. To show the effectiveness of the proposed formulae, for identical compressive forces from all sides, a minimal-mass design subjected to the force equilibrium (force balance) and yielding/buckling stress constraints is shown. A dynamical simulation of a TROT lattice under a uniaxial compressive force is also shown to evaluate the equilibrium state of the system.

Control of large structures often involves the use of hydraulic equipment due to the large power requirements. In this study, a large telescope is taken as an example of a large structure. A large telescope is equipped with hydraulic support systems to adjust the deformation of the structure, as changes in its pointing direction and ambient temperature deform the structure and reduce the telescope's observational performance. In previous studies, hydraulic support system elements and piping paths have been discussed, but quantitative evaluations and design considerations for the overall system performance of multiple hydraulic support systems and telescope structures have not been discussed. In this paper, simple transfer function models are derived for a coupled system of multiple hydraulic support systems and telescope structures, which allow the static and dynamic transient response characteristics to be evaluated. A design example using these transfer function models is also proposed and it is shown that the selected design parameters enable the large telescope to meet the specifications.

We have developed a Flexible Mono-tread Mobile-Track (FMT), which exhibits an inherent capability for flexed posture in three dimensions and can traverse over rough terrain, particularly in post-disaster scenarios. The flexion mechanism of the FMT passively adapts to irregular ground surfaces, reducing overall weight, degrees of freedom for operation, and the operator's workload. Rigorous testing of legacy prototypes confirmed the remarkable mobility, following the National Institute of Standards and Technology (NIST) guidelines. The FMT’s performance is notably influenced by the flexibility of the vertebral body structure and the shape of the track belt. For instance, the asymmetric track belt results in anisotropy of forward and backward movement, while the layered body cannot achieve uniform three-dimensional flexion. Additionally, the asymmetric or simple circular head shape poses challenges in ensuring consistent climbability over steps with overhang walls. This paper proposes a solution involving a new vertebral body structure and symmetric track belt for the FMT. The resulting prototype, MRT03-GEJIY, addresses these challenges and improves upon the performance of the legacy FMT prototypes in the following: 1) Establishing a reliable vertebra for achieving wide and uniform curvature, facilitating smooth track belt movement. 2) Implementing a symmetric track segment to enhance the isotropy in forward and backward movement. 3) Introducing a horizontally symmetrical head shape equipped with passive obstacle-crossing capability. Furthermore, we conducted performance evaluations of MRT03-GEJIY, including tests such as step-climbing.

One of the engineering challenges in developing more reliable electrodes in solid oxide fuel cells is to reduce residual stresses generated during electrode fabrication. The Young's modulus of porous ceramic materials employed in the electrodes is a fundamental property essential for evaluating the residual stresses of electrodes. In this study, the correlation between Young's modulus and the microstructure of the cathode material La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ was evaluated numerically using a voxel-based finite element method in conjunction with the three-dimensional mesoscale techniques, including a kinetic Monte Carlo and a discrete element method. The results of simulations utilizing the FIB-SEM reconstructed microstructures are in good agreement with those of micro-indentation experiments, indicating that our methodology is effective for estimating the Young's modulus of porous ceramics at room temperature. Furthermore, we reveal that the porosity dependence of Young’s modulus can be well described by an empirical power law based on the percolation model. In particular, our findings indicate that the dependencies on porosity are highly related to the homogeneity of the initial powder microstructures before sintering. Finally, our results suggest that the effective Young’s modulus of the porous materials at any porosity has a correlation with the tortuosity factor.

Rotating machineries supported in journal bearings are operated at a rotational speed between the one where the minimum oil film thickness is ensured to prevent direct contact of the journal and bearing surfaces and the one where self-excited vibration occurs, while avoiding the critical speed of the rotor-bearing system. When a rotating shaft is supported in a cylindrical journal bearing, which has the simplest structure among journal bearings, the upper operational speed will be approximately twice the critical speed. In the present report, focusing on a rotating shaft supported in the bearing with fluid slip regions on part of the bearing surface, those speeds are numerically calculated by applying a hydrodynamic lubrication theory, then the effects of the fluid slip region on the range of stable operation are evaluated. It is found as follows; (1) the detachment speed of the journal from the bearing is not affected by whether or not the fluid slip regions are given, (2) the stability threshold speed is significantly enhanced when several fluid slip regions are given at intervals up to the apex of the bearing downstream from the direction of attitude angle at the detachment speed, and (3) the enhanced stability caused by the fluid slip region is attributed to a reduction in oscillating journal motion. The range of the safe operation of a rotating shaft can be significantly extended simply by giving fluid slip regions on a part of the bearing surface, without replacing complicated journal bearings or employing stabilization method such as adjusting the amount of oil supplied.

Impedance control has been extensively used in robot control in physical human–robot interactions between humans and robots. To achieve smooth operation, various evaluations of operator responses have been performed during robot operation under impedance control. Although conventional studies have extensively employed assessments of motion characteristics based on manipulation force and hand tip positions and subjective evaluations, limited research has been conducted on physiological indicator evaluations to objectively assess human sensibility. During robot operation, humans plan control strategies for bodily movements by perceiving impedance parameters in the brain. Consequently, brain activity measurements have been extensively used to investigate the impact of impedance parameters on operators. In addition, recent research has elucidated control strategies based on human hand tip motion based on motor characteristics and muscle activity. However, conventional research has seen limited efforts in elucidating control strategies based on human hand tip motion, and simultaneous measurement and evaluation of motor characteristics and brain/muscle activity are seldom performed. Therefore, in this experiment, the forces, hand tip positions, muscle activity, and brain activity of the operators were measured during physical interactions, and statistical evaluations were performed on the operator’s physiological responses and motor characteristics arising from differences in impedance parameters. The experiment results indicate that impedance parameters influence motor characteristics and brain/muscle activity. Furthermore, the brain and muscle activity measurements indicate a correlation between brain activation and muscle force output, suggesting that insights into control strategies based on human manipulative forces and hand tip motion can be partially elucidated through temporal data analysis of hand velocity.

This paper aims to clarify the behavior and damage conditions of batteries when multi-rotor unmanned aerial vehicles (drones) in horizontal flight collide with a structure to obtain the engineering knowledge that serves to consider the method of the safety performance evaluation of drone batteries in the collision. Drones with maximum takeoff weight of 15.5 kg, 24.5 kg, and 50 kg for aerial photographing, agricultural chemical spraying, and material transporting were used in the experiment analysis. The drones were ejected from an ejection system and collided with a barrier. The behavior of the drones and the batteries were captured on high-speed cameras. In addition, collision loads on the barrier and accelerations of the drones and their batteries were measured. The behavior of the drones and the batteries were considered based on the analysis results of the high-speed cameras. When the drones collided with the barrier, the batteries attached to the drones with snap-fit, rubber bands, and hook-and-loop fasteners separated from the drones. The separated batteries subsequently collided with the barrier. In the collision of the batteries and the barrier, the acceleration of the battery attached to the front of the drone by snap-fit was maximum. The acceleration was approximately 2.2 times larger than the acceleration given to the battery by the impact testing machine in the JIS standard (JIS C62133-2) that defines the test method for the safe operation of lithium secondary batteries used for portable devices. The damage conditions of batteries were presented and discussed from the viewpoint of the collision safety of batteries.