To achieve reliable logistics, the construction of transportation infrastructure is essential, and the safety guarantees of various types of poles are required as well. A cyclic bending loading test is commonly conducted to investigate the fatigue strength of lighting poles. In the actual service environment, the loading mode may be not only simple bending but also torsion or a mixture of both. In addition, the base plate of the lighting pole is strengthened by a rib weld, and it is essential to understand the cracking from the stress concentrated point at that section and to obtain the fatigue property data. In the present work, we designed and developed a fatigue testing system that can conduct cyclic loading using two hydraulic actuators in a desired loading mode to the actual lighting pole. The fatigue strength property investigation in an arbitrary loading mode was made possible by controlling the movement of the two hydraulic actuators. The effect of the shape of the strengthening ribs on the fatigue strength of the base of lighting poles was investigated using two different rib shapes, and it was confirmed that the U-shaped ribs had a better fatigue life than the triangular-shaped ribs.

As a simple and highly accurate axial force management method during manufacturing and maintenance of bolt-tightened structures, we examined a method to calculate the axial force from images of the bolt head. In this method, the axial force is calculated using the strain on the bolt head measured by digital image correlation (DIC) technique from images of the bolt head and the relationship between strain on the bolt head and axial force calculated by finite element analysis (FEA). In this report, we have proposed a method for calculating axial force considering bending force on a bolt. Specifically, we have proposed a method for calculating the axial force and bending force ratio using the least squares method, based on a 5th-order approximation curve consisting of two variables: the axial force and the bending force ratio, which is obtained by numerical calculation with the bending force as a parameter, and the strain distribution measured by DIC. In bolt tightening tests using M20 bolt and tapered washers to reproduce bending force, the bending force ratio and direction obtained using the proposed method were in good agreement with those obtained from the strain gauges attached to the bolt shank, confirming that the proposed method can be used to evaluate bending force on bolts. In addition, the axial force calculated with the proposed method was in good agreement with that calculated with the bolt gauge, and the average absolute difference between the two was 4.9 kN for all tests. For test results with a large bending force ratio, the deviation in the axial force calculated before and after considering the bending force was around 14%, and it was confirmed that the proposed method enables more accurate evaluation of axial force in bolted structures where bending force occurs.

In this study, we investigated the propagation and reflection behavior of thermal and elastic waves based on a dynamic thermoelastic equation coupled with a non-Fourier heat conduction equation for two-dimensional plate problems under plane stress condition. This paper focuses on numerical simulations of photoacoustic microscopy and reports the results of assuming circular defects near the surface of a two-dimensional plate to investigate the effects of differences in defect size and depth on the temperature and particle velocity along the plate surface and stress distribution in the plate. It was found that the presence of defects caused thermal and elastic waves to be reflected and synthesized, resulting in large oscillations in these distributions. In particular, it was observed that the temperature distribution was concentrated at the tip of the defect, and it was confirmed that the defect shape has a strong influence on the surface temperature distribution.

Critical resolved shear stress (CRSS) is one of the most important parameters in the field of plasticity in metals, and the CRSS ratios between slip systems govern the plastic anisotropy, workability, and so on. Therefore, it is highly valuable to develop a system that can predict CRSS ratios with high accuracy in a short period of time. With the above background, Sato et al. (Transactions of JSME (in Japanese), (2023)) developed a system to predict CRSS ratios using distributions of strain and crystal orientation. However, the system requires much time to predict CRSS ratios. In this study, a new CRSS ratio prediction system with low computational cost has developed by devising a calculation method and introducing the covariance matrix adaptation evolution strategy (CMA-ES), a method of meta-heuristics. The validation of system was conducted by prediction of CRSS ratios in virtual hexagonal close-packed (HCP) materials from the strain distributions obtained by a crystal plasticity finite element method (CPFEM) and crystal orientation distributions. The validation results showed that the prediction of CRSS ratios for <a> slip systems was success and the accuracy was similar when information from all measurement points and when representative values for individual grains were used. The prediction accuracy was also the same level when the method introducing CMA-ES was employed. These results indicate that the developed system can predict CRSS ratios for <a> slip systems in HCP metals within seconds.

Recently, EGR (Exhaust Gas Recirculation) combustion has been used to enhance the thermal efficiency of internal combustion engines. However, EGR combustion causes ignition instability, leading to increased cycle-to-cycle combustion variability and misfire rates. To improve ignition stability under high EGR conditions, it is essential to elucidate the ignition mechanism and develop a predictive model that incorporates this mechanism. In particular, short-circuiting and restriking of spark channels are critical elements to model, as they directly influence flame kernel formation. Experiments using the RCM (Rapid Compression Machine) has demonstrated that ignition stability varies with changes in the flow velocity near the spark plug and the EGR ratio. Additionally, when misfire occurs, the flame kernel forms in small pieces due to a spark short circuit and then extinguishes. The model developed in this study combines a space potential model and a discharge path search model, which can reproduce the flame kernel behavior and EGR limits observed in experiments.

Unmanned excavation or remote excavation require an autonomous control design. In addition, a semi-autonomous system that can be operated by human intervention in emergency situations is necessary. We have designed an autonomous system using an nonlinear dynamics with an orbit attractor and embedded multiple orbits by extending the dimension of the dynamics. In this paper, we extend the conventional method to design a semi-autonomous system for area excavation. We design an autonomous system whose attractor is a cylindrical surface by helixing trajectories in the extended dimension using index value that represents the operation progress and further multiple helixing. A semi-autonomous system that changes its trajectory by human operation is designed by estimating state variables including index values using an Extended Kalman Filter based on human operation input. The effectiveness of the proposed method is evaluated through experiments using a leader-follower system.

Automotive torsional dampers are designed to absorb torque fluctuations generated by the engine and deliver a smoother torque to the components located toward the rear. During the torsion evaluation test of these dampers, torsional torque is repeatedly applied while the damper rotates. Given that torsional dampers consist of dead zone elements and multi-stage spring elements, achieving effective torque control can be challenging during these evaluations. In this study, we proposed a method to enhance the performance of the torque control system used in traditional torsional evaluation test machines. Our approach involves modifying the target torsional torque reference by adding a one-pulse signal. Then, the shape of this one-pulse signal is determined through Bayesian optimization. We validated the effectiveness of this proposed method through both simulations and an experiment conducted on actual equipment.

Various devices have been developed in recent years to assist human jumping using plate springs, rubber tubes, and other means. Nevertheless, using products of many kinds is difficult because they generate jumping force with human ankles fixed. Cooperating with human users is favorable for enhancing both usability and jumping height. Some researchers have adopted this approach. Unfortunately, the jumping height remains insufficient. As described in this paper, we have developed devices of two types that emphasize cooperation with the human user: a rotational model and a linear model. The former, which is used for comparison purposes, provides floor reaction force using a rotational mechanism similarly to a human ankle joint. The latter provides normal force using the Scott–Russell mechanism, which moves in the vertical direction. Moreover, this mechanism enables the user to generate floor reaction force for a longer duration. Experimentation demonstrated that the jumping height with the linear model increased by approximately 0.8 – 35% (0.4 – 12.4 cm) compared to that without a device. Moreover, the duration generating the jumping force when using the linear model increased by approximately 34% compared to that obtained when using the rotational model.

This study concerns a diaphragm mechanism for the deformation (expansion/contraction) of dielectric elastomer generators (DEG). The DEG converts mechanical energy to electrical one owing to the capacitance change according to its deformation. One of the typical mechanisms for the deformation is a diaphragm mechanism, which utilizes the difference of fluid pressure to inflate a DEG sheet. Diaphragm mechanism devices have no moving part for deformation, and thus are expected to reduce the device size and maintenance frequency compared to mechanical ones employing moving parts. In the literature of the DEG diaphragm, free deformation of a circular membrane up to a hemisphere is often considered. However, the hemisphere deformation is usually far less than its maximum stretch coming from the material limit, and there is a possibility to improve the power generation efficiency. This paper proposes a new type of the DEG diaphragm mechanisms, which employs a segmented deformation space to increase the material stretch up to its maximum. The proposed device has cavities for deformation in its upper cover, and the sheet deforms along their walls. These cavities make the sheet deform like the folds in the stomach, and can increase the DEG surface area as desired. We first show that the voltage and energy increments per cycle by the DEG increase with respect to the area change ratio of the DEG sheet. The area change ratio for the proposed DEG diaphragm can be represented as a function of the numbers of segmentation, which is then utilized for the optimal design of the segmentation. The area change ratio can be continuous by introducing a protrusion in each cavity, which allows us to achieve the DEG stretch up to its maximum. Experimental results show the efficiency of the proposed mechanism.

In the field of die and mold machining, determining appropriate cutting conditions is crucial. Factors such as tool geometry, machining path, work material characteristics, machining efficiency, and finishing accuracy must be taken into consideration. However, the current method of determining cutting conditions relies heavily on the intuition and experience of skilled engineers, and there is a need for a system to replace such knowledge. One of the critical factors affecting machining accuracy and efficiency is the tool overhang length, which is directly related to tool geometry. Unfortunately, there is no clear guideline for its determination. In a previous study, researchers developed a system to quickly derive cutting conditions using a data mining method and Random Forest Regression (RFR) applied to a tool catalog database. In this study, we constructed a new cutting condition compensation system based on the existing model, which accounts for the tool overhang length. The results of cutting experiments under high aspect ratio overhang lengths confirm that the correction coefficients proposed by the system are significant.

This study evaluates the effects of forced chatter vibration on the shape of bamboo fibers for the production of 100% bamboo molds. Considering that fiber shape variation during end milling affects the mechanical properties of the molded product, we first determined the effect of bamboo cylinder shape on natural vibration through impact testing and finite element analysis. Based on these results and the temperature at the time of cutting, cutting conditions that do not resonate with the natural frequency were examined, and it was found that a ratio of approximately 4.5 between the natural frequency and intermittent cutting frequency was appropriate. Next, we investigated the effect of the relationship between the endmill's intermittent cutting frequency and the natural frequency of bamboo on fiber shape. The results showed that when the ratio of the endmill's intermittent cutting frequency to the bamboo's first- and second-order natural frequencies was an integer multiple, resonance increased the vibration of the bamboo cylinder, which decreased the average width of the extracted fibers and increased their standard deviation. It was also shown that the effect of third-order natural frequencies was small. Further investigation of the effect of height variation confirmed that at heights below 125 mm the vibration amplitude was sufficiently small to have no effect on the mean or standard deviation of the fiber widths.

Optimizing stiffened panel structures used in ships and aircrafts are becoming increasingly important for reducing material costs while maintaining or enhancing structural strength. These structures require simultaneous optimization of continuous design variables (panel thicknesses) and discrete design variables (stiffener cross-sectional shapes), making gradient-based methods less applicable. Consequently, heuristic approaches such as Genetic Algorithms (GA) are often employed; however, GA typically imposes a high computational burden in large-scale optimization problems. To address this, the use of deep reinforcement learning (DRL) has been investigated for large-scale combinatorial optimization. Among DRL approaches, Double Deep Q-Network (DDQN) has been reported as effective, yet its application to structural optimization involving high computational demands from Finite Element Analysis (FEA) remains limited. To overcome such an environment, in this study, an optimization flow for structural optimization is considered, and states, actions, and rewards appropriately representing design variables, constraint conditions, and objective functions are discussed. In addition, this study also proposes incorporating an elite-preservation algorithm into DDQN to reduce the computational load of structural optimization. Experimental results show that the proposed method yields designs under various load conditions that are up to 6% lighter than those obtained using GA, with a computational time reduction of approximately 81%. These findings confirm the feasibility of efficient and effective optimization for stiffened panel structures and suggest potential benefits in cost reduction and performance enhancement in future structural designs.

Various training techniques have been devised to capture motion data during real-time walking and provide feedback to trainees, allowing them to adjust their gait to align the measured gait parameters with target values. However, these methods may not suit all individuals owing to physical differences. To address this, in our previous research, we used a MC-DCNN to classify gait based on ideal and non-ideal features. Activation maximization was applied to generate target gaits; however, the method did not account for human walking dynamics, thereby sometimes resulting in unnatural gait patterns. Consequently, some generated data exhibited unnatural values for human gait. Additionally, the constructed model was based on experimental data from eight young males wearing age-simulation suits, raising concerns about its applicability to actual older adults. In this study, we addressed these limitations by collecting gait data from adults aged over 65 years, including 10 males (70.6±2.5 years) and 8 females (70.6±2.8 years), as well as younger adults, including 8 males (22.1±0.8 years) and 7 females (20.7±0.5 years). Based on this dataset, we utilized the structure of a generative adversarial network (GAN) and leveraged identity loss and cycle consistency loss from CycleGAN to generate target gaits. Additionally, the generator model was designed to reflect both the temporal features of gait and the dependencies between gait variables. Consequently, the proposed model successfully converted gaits frequently associated with stumbling into gaits rarely associated with stumbling, depending on the degree of gait instability.

Instrumented wheelsets are widely used in the railway industry for the purpose of measurement of the wheel-rail interaction forces, which are crucial factors in a running safety assessment. Recently, the author proposed a new configuration of bridge circuit for measuring wheel-rail lateral force, which are categorized as “axially-asymmetric bridge circuit.” The merit of this type of bridge circuit is to reduce the measurement error associated to the lateral contact point shift. In this study, we propose a highly accurate continuous measurement method of the derailment coefficient based on “orthogonal weighting functions” that utilizes the characteristics of an axially-asymmetric bridge circuits. A continuous measurement method for the lateral contact position is also proposed utilizing the concept of the orthogonal weighting functions. The validity of the proposed method was confirmed through roller-rig tests.