In this study, best-fit fatigue curves are constructed considering material properties and loading modes. Three common fatigue test methods (rotating bending, axial load-control, and strain-control) are compared, and their scopes of application are clarified. The best-fit fatigue curves, expressed as functions of ultimate tensile strength, have been constructed based on strain-controlled fatigue test data. A comparison of the best-fit fatigue curves with axial load-controlled test data reveals that both deviated from each other for the carbon and low-alloy steels and austenitic stainless steels. Therefore, the best-fit fatigue curves are reconstructed by integrating data from both rotating bending and axial load-controlled fatigue tests. For the carbon and low-alloy steels, the best-fit fatigue curves are classified according to two types of microstructures, whereas for the austenitic stainless steels, the best-fit fatigue curves are classified according to two types of loading modes. Finally, design factors based on the reliability of the best-fit fatigue curves are explicitly presented.

In this study, we focused on the high fracture toughness of nacre, which has a microscopic structure consisting of calcium carbonate lamellae and protein stacks. We performed deformation and fracture analysis on a compact tension (CT) specimen, where a brick-like structure, with lamellae modeled as bricks and proteins as a cohesive model, was placed at the tip of an artificial crack. First, a CT specimen with a single brick-like structure was printed using an FDM 3D printer and subjected to tensile loading. Next, a finite element (FE) analysis was performed on an FE model with the same shape. As a result, it was confirmed that the nonlinear deformation behavior and fracture process obtained by the FE analysis were in good agreement with the test results. Then, using the verified FE model, finite element analysis was performed on brick-like structured CT specimens with different brick aspect ratios. The results showed that the maximum load and the maximum displacement to failure increased as the brick aspect became more elongated along the tensile loading direction. This was attributed to the resistance as the brick was pulled out of the matrix. Consequently, a finite element analysis was performed on a CT specimen with a multilayered brick-like structure, where a certain area around the tip of the artificial crack was filled with a brick-cohesive model. The results confirmed that, similar to the single brick-like structure, the pull-out resistance of the brick and the zigzag crack propagation path were effective in improving the fracture resistance. However, when the brick aspect exceeded a certain value, the brick itself cracked, causing the crack to propagate linearly and reducing the maximum load.

To clarify the mechanisms underlying unsteady aerodynamic forces related to train vibrations of high-speed trains running through tunnels, large-eddy simulations of large-scale flow structures around a simplified six-car train model were conducted. Since actual trains run on one of the double track lines, the position of the train model was set to deviate from the tunnel center and hence the gap between one side of the train and the tunnel wall is narrower than that on the opposite side. A train running in the open-air was also calculated for comparison. The results of this study shed light on the generation mechanism of the pressure fluctuations acting on the side of high-speed trains as follows. Firstly, in the open-air, the air velocity in the space between the underbody and the ground gradually decreases from the head toward the tail of the train. Thus, the air velocity is slower than that on both sides of the train, which generates shear flows near the bottom edges of both sides of the train. The shear flows cause large Kármán vortex-like structures forming a staggered vortex street, which in turn lead to a meandering airflow beneath the underbody of the train. Secondly, in the tunnel, the air velocity not only in the gap between the underbody and the ground but also in the narrower gap between the side of the train and the tunnel wall gradually decreases from the head toward the tail of the train. In the same mechanism as the open-air, a meandering airflow is generated throughout the side and underbody of the train and causes pressure fluctuations along the side of the train. Finally, the present LES results indicate that the wavelength of pressure fluctuations along the side of the actual train can be reasonably estimated.

An air twisting nozzle was investigated by modifying the horizontal connection angle (α) and vertical connection angle (β) of the air orifice relative to the yarn channel, using computational fluid dynamics. Here, α represents the horizontal (rotational) connection angle of the air orifice relative to the yarn channel axis, while β denotes the vertical inclination angle between the air orifice and the yarn channel. A yarn channel with double air orifices was also analyzed under different connection angles. Airflow vorticity and velocity within the air twisting nozzle were evaluated to assess the influence of these connection angles. The connection angles were set at α=30° and α=90°, while β was fixed at 40°. At α=30°, the velocity decreased by approximately 8%, and vorticity dropped by about 12%, which disrupted the air twisting process. Next, β was varied (25°,30°,35°,40°,45°) while α was fixed at 90°. The velocity and vorticity reached their highest values when α=90° and β ranged between 30° and 40°, with the maximum vorticity recorded at 1.58x10⁶ 1/s for β=30°, an 18% increase compared to β=25° (1.34x10⁶ 1/s). The diameter of the yarn channel and the air orifice geometry remained constant throughout these computations. These connection angles were optimized to enhance airflow velocity and vorticity, with highest values were observed near the air orifice. Connecting the air orifice to the yarn channel at these optimized angles significantly increased both velocity and vorticity. The addition of double air orifices further improved flow dynamics, increasing average channel vorticity by approximately 20% compared to single air orifice designs. The developed air twisting nozzle with double air orifices was fabricated as a prototype and tested on a spandex winder at 900 m/min and 10 kPa inlet pressure. Compared with an existing single air orifice nozzle, the developed design achieved a 30% increase in twist number, reduced running tension by 14%, and improved flux uniformity, resulting in more stable yarn processing. These results demonstrate that the developed nozzle can significantly enhance twisting efficiency and yarn quality in industrial applications.

An experimental study was made on burning velocity in powder-gas hybrid combustion in order to investigate the determination factor to alter the burning velocity caused by the addition of power in the premixed gas. A burner system was newly developed to visualize the dynamic flame behavior originally stabilized in a stagnation point flow field. Using the system, the instantaneous burning velocity and burning area by powder loading were obtained and analyzed. It was found that the burning velocity and burning area changed in accordance with the powder loading amount. Data analyses exhibit that a positive correlation was found between them, suggesting that wrinkling is a major cause of the change of the burning velocity. To understand the mechanism of wrinkle formation, the change of the flow field ahead of the flame with powder loading was measured. It is suggested that the wrinkles could be attributed to the pyrolysis gases evolved in the preheating zone, which could both increase the local burning velocity by increasing the local equivalence ratio and change the flow field due to the divergence flow generated by each powder. Further study would be needed to go deep on the mechanism of wrinkle formation.

ASME Boiler and Pressure Vessel Code Case N-875 provides a rational in-service inspection (ISI) approach for liquid-metal cooled reactors. This is a risk-informed approach that establishes ISI requirements including acceptance criteria by considering features of respective plants in terms of the effects of flaws on the plant safety. In this approach, fracture mechanics is essential. Not only part-through-wall cracks but also through-wall cracks need to be evaluated, for example, to determine the maximum allowable size of flaws in reactor internal components and investigate the applicability of continuous leakage monitoring to flaws in sodium-retaining components. The basic procedure of the Code Case has also been incorporated in Fitness-for-service code (Section XI, Division 2) in ASME, which provides requirements for reliability and integrity management programs for nuclear power plants, including advanced reactors. The demonstration sodium-cooled fast reactor currently under development in Japan is expected to be designed with thin wall and large diameter to reduce the thermal stress. For some components, the ratio of radius-to-thickness is expected to exceed 100. There are currently no generalized Stress Intensity Factors (SIFs), which are required for fracture mechanics, applicable to components with such a large ratio of radius-to-thickness. In this study, as a part of the development of a flaw evaluation method applicable to components with large ratio of radius-to-thickness, the conservatism of applying the SIF solutions for through-wall cracks in plates to circumferential through-wall cracks in cylinders with large ratio of radius-to-thickness was discussed. As a result, it was clarified that the SIF solutions for plates should not be used for circumferential through-wall cracks. Therefore, a new SIF solution for circumferential through-wall cracks in cylinders was developed by using Finite Element Analysis.

Electric vehicles (EVs) produce different cabin noise than internal combustion engine (ICE) vehicles during low-speed driving. To identify the cause of the interior noise of an EV at low speed (30km/h) and to reduce it, a Helmholtz resonator made of pulp mold was fabricated, and its noise-reduction effect was evaluated. First, a Helmholtz resonator is investigated numerically to reduce the tire's cavity resonance. Numerical calculations demonstrated that a stable noise-reduction effect could be achieved by installing multiple Helmholtz resonators. Next, we fabricated a Helmholtz resonator using a pulp mold and installed multiple resonators in the tire. In the experiment, the resonators reduced the tire cavity resonance by 13.8 dB to 9.7 dB. When driving tests were conducted with these tires installed, noise at the front-seat ear positions was reduced by 11.3 dB. From these results, we identified that tire cavity resonance is the cause of cabin noise at low speeds. In addition, a driving test in which the same number of Helmholtz resonators as installed in the tires were installed on the cabin ceiling resulted in an 8.1 dB reduction in cabin noise. We demonstrated that it is possible to reduce tire cavity resonance noise, even with parts inside the vehicle.

This study proposes a risk-predictive path planning and control framework for autonomous driving (AD) and advanced driver-assistance systems (ADAS) operating on narrow urban roads with limited visibility. When driving through unsignalized intersections, buildings or parked vehicles often create blind spots where pedestrians or other road users may suddenly dart out, becoming a significant safety risk. To address this challenge, this research defines a method to simultaneously determine the safe speed and safe lateral distance based on the geometric relationship between the ego vehicle and the occluded area. The safe speed is defined as the maximum velocity at which a collision can be avoided through emergency braking, while the lateral gap ensures avoidance of side-faced collisions. Using these risk-predictive parameters, a non-linear polynomial path generation method is formulated, in which cubic and quartic functions describe the vehicle’s speed profile and trajectory, respectively. The coefficients of these polynomials are optimized to minimize deviations from desired paths while preventing the vehicle from entering the predicted high-risk zones by the proposed method. Comprehensive MATLAB simulations were performed using a 3-DoF vehicle model to validate the proposed method. Results show that the framework successfully generated smooth and safe trajectories, allowing the vehicle to avoid potential collisions under various road widths and darting-out conditions. Even in constrained road scenarios, the system maintained stability and avoided frontal collisions. The proposed method effectively balances safety and mobility, demonstrating strong adaptability for future integration into real-world AD/ADAS systems.

This paper proposes a new structural design method to obtain an optimized shape of a compressor mount in a wide operating range. To eliminate the resonant frequencies of the structure in the wide operating frequency range, maximization and minimization of the natural frequency are performed simultaneously, and it is important to define an objective function that can derive a clear structural shape in both optimization cases. In this study, a multi-objective optimization method is proposed that combines dynamic compliance at sub-frequencies as well as at target frequencies to obtain an optimized structure, sufficiently clear to be applied for manufacturing while achieving the desired frequency response. The sub-frequencies are selected near the natural frequencies generated within the operating frequency range and are used to reduce the number of gray-scale elements and to prevent the creation of discontinuous structures. The material properties without the damping coefficient SIMP method are used and the frequency response of the structure is calculated using the mode superposition method. The proposed optimization method is applied to the natural frequency minimization problem of a cantilever, which was mentioned in previous studies as being difficult to derive a clear structural shape, to confirm its effectiveness, and a compressor mount design problem simply modeled in two dimensions is introduced.

In recent years, personal mobility vehicles (PMVs) have attracted attention as a new means of transportation for the elderly. In general, PMVs have the advantage of being compact and maneuverable, but both the rider and vehicle have a high center of gravity, which may cause the rider to lose balance. In this study, we investigated the dynamic characteristics of PMV riders during acceleration and braking and conducted vehicle experiments to clarify differences in dynamic characteristics depending on age and driving conditions. Measurements of the change in position of the body center of gravity showed that the elderly riders tended to have a greater change in their center of gravity toward the front of the vehicle during braking than younger riders, resulting in a greater risk of falling. An analysis of correlations and time-series changes in joint moments revealed that the elderly riders tended to control their posture by applying force to the joints of the lower body, such as the ankles and knees, whereas the younger riders tended to stabilize their posture by effectively applying force to the joints of the upper body, such as the elbows and wrists, in addition to joints of the lower body. Furthermore, the results show that applying a force in advance to counteract movement before braking helps minimize joint displacement and the shift in the center of gravity.