This paper presents a method to improve accuracy of measuring through–thickness residual stress for welds through deep hole drilling (DHD) technique. The focus of this study is the effect of dimensions of the hollow cylinder, which is manufactured by drilling and trepanning processes, on residual stress measurement at the welds. First, stress concentration–induced plastic region around a reference (drilled) hole was theoretically quantified according to value of existing stress. The plastic region around the hole is not negligible for the welds at where high tensile residual stress exists. In order to reduce the influence of the plastic region, it is considered effective to set a large ratio of trepanning diameter to drilling diameter. Another noteworthy thing is that weld residual stress is present in a relatively narrow region along a weld line. Then, DHD technique was applied to measure through–thickness residual stress at the welds of melt–run welded–plate specimens under conditions of various drilling and trepanning diameters. These DHD residual stress measurement results were compared with those measured by X–ray diffraction and contour methods and calculated by weld thermal elastic–plastic analysis. As the results, it was shown that through–thickness residual stresses measured by DHD technique were obviously influenced by dimensions of the hollow cylinder. Measurement accuracy becomes higher with increasing the ratio of trepanning diameter to drilling diameter. Meanwhile, trepanning diameter should not be larger than width of generation area of high tensile residual stress to be measured at the welds. It was concluded that a method for determining appropriate dimensions of the hollow cylinder to be drilled and trepanned was successfully proposed to accurately assess through–thickness residual stress at the welds through DHD technique.

Press forming is a mass production method that is used to manufacture many machine components such as automobiles, industrial machinery, and various plants. However, there is a limit to the degree of shape freedom that can be applied, so countermeasures against cracks, wrinkles, spring-back, etc., must be taken in the development process. It is well known that it is difficult to apply it economically in the case of small-lot production because of its high capital investment. In a previous report, the author reported that the folding line processing by press method / bending has a high degree of shape freedom, requires little capital investment, and can be expected to be applied for experiments and prototypes from small to mass production. This paper shows that press folding line processing using V-shaped punch can be applied as deformation induction based on experiments and FEM results. To improve the impact energy absorption performance in the event of a collision, notches and uneven surfaces called beads have been formed in the crush boxes and front side members as automobile parts manufactured by press forming. The bead has the function of inducing deformation so as to improve the impact energy absorption performance during the axial crushing process. However, bead setting for inducing deformation by the press forming, in addition to the difficulty of mold design/manufacturing, needs to correct the bead design after impact experiments using prototypes. This paper shows press folding line processing as deformation induction is very convenient and effective.

Thin high-strength steel sheets are increasingly being applied to vehicle frames in order to increase the strength and reduce the weight. The thinner the plate, the more likely it is to occur buckling. So it is important to understand the structural properties based on buckling theory in order to efficiently design for buckling in the early stages of vehicle development. The authors have addressed the issue of theoretically determining the shear buckling stresses in torsion of thin-walled square cross-section beams. In the previous paper (Budiansky, et al., 1948) for determining shear buckling stresses in torsion of infinitely long thin-walled square beams, two adjacent plates were treated collectively, the buckling modes were expressed as an infinite series in the width direction and a single sinusoidal wave in the infinite length direction, then, the method of Lagrange multiplier was used to consider the constraint condition in the center line, finally the shear buckling stress was obtained by the energy method. However, this process cannot be applied to finite-length beams because a single sinusoidal wave cannot satisfy the boundary conditions at both ends in the longitudinal direction. So, the purpose of this paper is to theoretically determine the shear buckling stress in torsion of a thin-walled square beam of finite length. First, based on the previous process, two adjacent plates are considered to be a single plate, and the buckling mode is represented by an infinite Fourier series as in the shear buckling of a single plate. The shear buckling stress in torsion is obtained by the energy method, taking into account the constraint condition in the center line of the width direction of the plate by the method of Lagrange multiplier. The validity of the derived values is compared with the FEM results, and the results are in good agreement.

In this paper, the critical buckling temperature of a lattice sandwich panel was investigated using FE analysis. In the previous study[Sebata, Y., Ushijima, K., Study on thermal buckling temperature of a lattice sandwich panel, Transaction of the JSME (in Japanese), Vol. 88, No. 905 (2022)], a Pyramid-shaped core unit was selected and the effects of unit-cell height and width on the buckling temperature were investigated. In the present study, two kinds of lattice core, BCC and f₂BCC were added for investigation, and the effects of the core stiffness and micro-architecture on the buckling temperature were discussed. It was revealed from this study that the constraint of rotational angle at the connection point between the face sheet and the core strands could enhance the local buckling temperature. Also, enlarging the core stiffness could enhance the local buckling temperature. Moreover, the local buckling temperature can be predicted theoretically based on the thick shell theory by considering the effective width of the face sheet for one unit-cell reflected by the cross-sectional area for a strut.

I have addressed a magnetic Janus particle suspension in the thermodynamic equilibrium situation. The magnetic moment of Janus particles treated in the present study is shifted from the particle center, which is perpendicular to the magnetic moment direction. From the viewpoint of elucidating the internal structure of particle aggregates in a three-dimensional (3D) system, I have treated a dispersion composed of magnetic Janus particles with a full 3D rotational ability in a quasi-two-dimensional (2D) system. The quasi-2D Monte Carlo simulations have been performed in order to investigate the dependence of a regime change in the aggregate structures on various factors such as the magnetic particle-particle interaction strength, magnetic particle-field interaction strength and the distance of the magnetic moment from the particle center. In no applied magnetic field, the Janus particles aggregate to form a stable cluster unit composed of 2-4 particles if the magnetic particle-particle interaction strength is increased. As the magnetic field is increased, the cluster units collapse and chain-like clusters are formed aligned in the magnetic field direction. In the situation of a strong magnetic field, the chain-like clusters composed of Janus particles tend to be thicker as the magnetic moment is shifted away from the particle center. This is because the magnetic interaction between neighboring particles increases due to the magnetic moments of constituent particles in chain-like clusters being closer to each other. The present results are useful for elucidating the internal structure of complex aggregates in a 3D system.

It is known that flaming combustion duration of highly densified single cylindrical biomass briquette is proportional to the product of the inverse square of the specific surface area and briquette density. It was suggested that the proportional constant C_f can be correlated with the mass percentage of holocellulose in the biomass. On the other hand, the char combustion duration is almost proportional to the product of the inverse square of the specific surface area and the fixed carbon content of the briquette. It was suggested that the proportional constant C_c can be correlated with the mass percentage of the ash content in the biomass. However, the individual influences of cellulose, hemicellulose and ash content on the flaming and char combustion durations, and thus on C_f and C_c, have not been clarified yet. In the present study, to investigate the effects of holocellulose content, ash content in raw materials, and cellulose (hemicellulose) content in holocellulose on C_f and C_c in detail, briquettes made of artificial raw materials adding cellulose, hemicellulose powder, cypress ash or rice husk ash to cypress or rice husk were burned in the hot air flow. It was confirmed that C_f increases with increasing the holocellulose content, however, there is less effect of the cellulose content in holocellulose, in the scope of this study. And it was suggested that low boiling component in briquette affects the C_f value. It was confirmed that increasing the ash content decreases 1/C_c, and the dependence decreases as the ash content increased. And it was confirmed that there is less effect of the holocellulose content, the cellulose content in holocellulose, ash type and low boiling point component on 1/C_c value.

This paper describes a practical design of a novel Stirling engine generator and 1kW machine test data. This machine’s configuration is a 4 cylinder double acting Stirling engine coupled with a Halbach PM generator in line. This machine operates on the Stirling thermodynamic cycle and electromagnetic cycle established in 19^th century by Carnot and Faraday. This machine’s unique function is bidirectional exchanging between thermal energy and electric power, as a same rotating direction of a same shaft. And the shaft speed can be controlled by three phases voltage source PWM inverter during both function such as the motor cooler mode and the engine generator mode. So, this unit can generate an electricity by using to many kinds of external heat source. As the heat source temperature changes as the shaft speed changes for the amount of absorbed heat changing in order to keep a cylinder temperature (700 ℃) and a heater tube temperature (<770 ℃). Consequently, the unit will achieve a highest efficiency keeping as a creep rapture strength limit level of the heater tubes. This unit has achieved 1.1 kW effective electric power, and 20.1% efficiency using LPG fuel, and 23.7 % thermal energy to electrical energy. This unit can connect to a commercial AC grid line by another inverter and, also connect a high voltage battery and a solar cell on the high voltage DC bus line in the PWM inverter.

Severe vibration may occur in structures such as high-rise buildings and bridges according to wind and seismic excitations, and in large space structures due to their lightweight and flexible constitution. Generally, when several vibration modes are simultaneously excited, application of the model-based control strategies become difficult. In this study, we propose a wave absorption control method for reducing vibrations in multi-degree-of-freedom systems semi-actively using a magnetorheological elastomer-based dynamic absorber. The stiffness of the absorber is changeable according to the applied magnetic field strength. The value is tuned adaptively so that the mechanical impedance at the boundary meets an absorptive boundary requirement. Analytical investigation clarified relationship between the excitation frequency and absorber stiffness that could eliminate the wave reflection from the boundary and maintain no resonant state in the system. Based on this stiffness condition, numerical simulation and experiment for the wave absorption control were performed. The proposed absorber to be used with the wave control scheme was found to significantly reduce structural vibrations within the stiffness variable range.

A mechanism has been proposed that utilizes the gyroscopic moment generated by tilting the rotation axis of a flywheel for stabilization control of unstable system. In this study, we investigate the effectiveness of feedback control which drives a gimbal mechanism to maintain the standing posture of an unstable structure such as a two-wheel vehicle. Although a simple feedback of posture angle enables a two-wheel structure to keep standing, both posture and gimbal continue shaking little by little. This is because the gimbal temporarily stays at a constant angle due to the action of Coulomb friction, and the system becomes unstable in the interim. We propose a method to estimate both the length of time when the motion of the gimbal stops and the amplitudes of the vibration of posture and gimbal. Here, we assume that the first-order mode poles obtained from the linearized model are complex numbers and that the second-order mode response converges immediately. From the experimental results, it is found that if the gimbal stays at a constant angle for a long time, the structure tends to fall over. We show that state feedback is necessary to realize to shorten the time when the gimbal stays at a constant angle and to reduce the amplitudes of oscillations at the same time.

This paper proposes a method for a robot to recall multiple action candidates for an object by learning object manipulations based on observation of human actions. When learning, multiple answers to a single input in supervised regression manner, it is usually necessary to map all correct answers to the same input. However, only one action can be observed for an object at a time in observing object manipulations, and other possible actions are not always observed for the identical object. It is, therefore, important to automatically share various observed actions between similar-shaped objects by recognizing common shape cues among individual objects. The proposed method learns the code descriptions of object shapes by a variational auto-encoder (VAE) with an object image as input data, and the code descriptions of actions by a conditional VAE with object shape as a condition and an action as input data. Since the action is unknown recall target, it is desirable to obtain the code description of the action from only the object shape during recalling. The distribution of the code description of actions conditioned by input object shape on the obtained code description space is obtained by marginalization of the distribution learned by the encoder part of CVAE. However, since this marginalization is difficult to analytically and numerically operate, a deep regression model that “imitates” this marginal distribution is trained by using a maximum likelihood method based on sampling. Common actions of similar-shaped objects are shared among the similar objects in this “marginalization by imitation” process. Various possible actions for the input object shape can be recalled by repeatedly sampling from the imitated marginal distribution. This paper describes the results of experiment using actual object images and manipulation actions, and demonstrates the effectiveness of the proposed method.

When a mechanical system collides with the ground, the impact force may cause damage to its components. Generally, springs and elastic members are installed to prevent the impact. However, it is difficult to overcome this problem because hard springs have a large mass, a spring with a large mass cannot suppress the impact force, and the energy stored in the spring has to be dissipated. On the other hand, Momentum Exchange Impact Damper (MEID) aims to reduce the momentum of the main body by transferring momentum to the weight, and are effective for shock mitigation. From this point of view, we have proposed a passive MEID so far. This is a passive mechanism that achieves momentum exchange and prevents the propagation of the impulsive force by utilizing the singularity of the mechanism. The mechanism does not require any additional actuators or sensors, and is extremely effective in mitigating the impact force. However, there is a problem that the acceleration generated in the body during the motion of the mechanism is not small. In this paper, we propose a passive MEID that reduces the acceleration generated in the main body by changing the constraint of the mechanism, and design it by optimization. The effectiveness of the proposed mechanism is verified through experiments using a prototype.

In this paper, a concurrent optimization method of shape and topology for natural vibration design of shell structures is presented. The fundamental vibration eigenvalue is maximized under volume constraints for shape and topology optimization. The free-form optimization method for shells and the solid isotropic material with penalization (SIMP) method are respectively employed and combined effectively for shape and topology design, in which shape and fictitious homogenized-density variations are used as design variables and simultaneously determined. In other words, the optimal topology is determined in the variable design surface optimized by shape optimization. The optimal design problem is formulated as a distributed-parameter optimization problem, and the sensitivity functions with respect to shape and density variations are theoretically derived. Both the optimal shape and density variations are determined with the unified H¹ gradient method, where the sensitivity functions are respectively applied as the Robin condition to the design surface in order to determine the optimal shape and topology. We also show an improved method for the spurious (or localized) mode problem of shell structures, which often occurs in the lower density region in topology optimization for vibration design. With the proposed method, shell structure for light weight and improved low-order vibration characteristics can be obtained without any design parameterization, free of numerical instabilities such as checkerboard pattern and zigzag-shape problems.

From the machining center (MC) user’s point of view, the authors propose a practical approach to estimate the trajectory error of a linear interpolation cutter path produced by the linear acceleration/deceleration (Acc/Dec) processing for a target MC in this paper. Firstly, a simple and convenient motion model is established for describing the behavior of the servo axes corresponding to the linear Acc/Dec procession of a linear segment, which can be applied to any linear segment regardless of length. Based on the model and a linearity assumption on the dynamics of servo system, a simulation method is developed to precisely calculate the cutter path trajectory in detail together with the servo axis speed from the motion parameters commanded in NC program. The algorithm not only has a very simple structure but also demonstrates high efficiency in actual calculation. In order to confirm the effect of the approach, verification experiments have been performed on the target MC, in which specially designed cutter paths were inspected by a cross grid measuring device with high resolution in non-contact state. These measured trajectories are compared and discussed with the ones simulated under the same motion parameters, from different perspectives. The examination results sufficiently demonstrate the effectiveness of the proposed model and simulation method. Therefore, as a useful tool, the approach provides a potential application possibility, i.e. beforehand estimating the influence of the NC Acc/Dec processing on cutter path accuracy or judging the motion conditions for the machining purpose without performing an actual machining with the target MC.

A lack of the application of appropriate mechanical stimuli to cells within healing tissue in tendon defects has been proposed as a possible mechanism of incomplete defect healing with scar formation. This suggested that different mechanical environment in a tendon defect with a different geometry may result in different healing outcome. Therefore, the present study adopted a slit injury model in a mouse patellar tendon model and performed macroscopic and microscopic mechanical analysis on tissue regenerated in the central slit defect. Tensile strength and tangent modulus of the tissue in the defect at 3 weeks of healing were lower significantly than that of normal patellar tendon, which recovered to a level still lower than the normal level but without statistical significance at 6 weeks of healing. Micromechanical analysis on local strain field revealed that microscopic tensile strain was not different between normal patellar tendon and healing tissue at 6 weeks. However, microscopic transverse and shear strain was significantly lower in healing tissue than normal tendon tissue. The former may indicate that collagen fibers in healing tissue exhibit no crimp morphology, and the latter demonstrates that collagen fibers were not aligned to the long axis of the tendon. Although healing tissue in the slit defect possessed better strength that that in a rectangular defect examined in our previous study, microscopic strain field was similar between two models, possibly due to that healing tissue in both models was still immature structurally at 6 weeks of healing when compared to the normal patellar tendon.

Vascular smooth muscle cells (VSMCs) in the normal vascular wall regulate vascular contraction and dilation due to their contractility. But they change their phenotype from contractile to synthetic state and actively remodel the vascular wall in pathological conditions. Findings on the phenotypic change mechanism of VSMCs have been reported by many in vitro studies, however, mechanical environments in vivo vascular wall are quite different from those of in vitro culture condition: VSMCs in vivo exhibit an elongated shape and form a tissue that aligns with the circumferential direction of the walls, while VSMCs in vitro spread randomly and form irregular shapes during cultivation on flat culture dishes, and dedifferentiate into synthetic phenotype. To clarify the mechanisms of the phenotypic changes in VSMCs, it is essential to develop a cell culture model that consider the mechanical environment of in vivo vascular wall. Here, we fabricated the polydimethylsiloxane (PDMS)-based micro-grooved substrate with 5 or 20 μm of groove width and 5 μm of groove depth to induce cell elongation and alignment observed in vivo. We established the coating method with cell adhesion protein only on the surface of groove concaves, and found that VSMCs adhering into the concaves formed uniform cell tissue and allowed remarkable elongation. In particular, the micro grooves with 5 μm groove width and depth facilitated a significant nuclear deformation and volume reduction of the nucleus due to a lateral compression by the side wall of the groove concaves that is relatively similar to a sandwich-like arrangement of in vivo elastic lamellae, resulting in the cell proliferation inhibition and VSMC differentiation. These results indicate that our cell culture model with the micro-grooved substrates can be useful to study the mechanisms of the phenotypic changes in VSMCs under consideration of in vivo vascular mechanical environment.