Although elastic limit and tensile strength are essential for mechanical strength design, the measurement of high hardness materials is a challenge due to their sensitivity on notches. As an alternative, the tensile strength can be easily assumed from hardness using the conversion table (e.g. SAE J 417); however, the table does not include the data for high hardness region, namely tempered materials at low temperature. We performed tensile tests and obtained elastic limits and tensile strengths of quenched martensitic medium-carbon steel with tempering at several temperatures. The hardness was monotonically decreased with the increase of tempering temperature. However, the tensile strength and elastic limit improved as the increase of temperature at low tempering temperature. In contrast, at high tempering temperature, the tensile strength and elastic limit were decreased with increase of tempering temperature. Consequently, the ratios of hardness to tensile strength or elastic limit were changed below or above the transition point. The ratios were constant below a tempering temperature (290 ℃ for elastic limit and 200 ℃-300 ℃ for tensile strength in the present experiments) and increased with the increase of the tempering temperature above the temperature. The variation of the ratio, hardness to tensile strength, is due to the brittle fracture on high hardness specimens before reaching the threshold to start plastic instability. In addition to, it is considered that the variation of the ratio, hardness to elastic limit, is caused by another mechanism, a decrease in elastic limit due to mobile dislocations.

SiC fiber reinforced SiC matrix composites (SiC/SiC composites) are a kind of ceramic matrix composites (CMC) and have attracted attention as a new material for aerospace engines because of their high strength, high temperature resistance, and oxidation resistance. The dry-spinning method for SiC fibers is one of approach to reduce the fabrication cost of SiC/SiC composites. In the dry-spinning method, the raw material, polycarbosilane (PCS) is dissolved in a volatile solvent and spun. This method can skip the curing process, which is the cause of high cost. In this study, dry-spun SiC fibers were fabricated by changing molecular weight of PCS and heat-treatment temperature. The mechanical properties of SiC fibers were determined by monofilament tensile tests. The highest tensile strength and elastic modulus of the dry-spun SiC fibers were 2.88 GPa and 270 GPa, respectively. These mechanical properties strongly effected the molecular weight of PCS, the heat-treatment temperature, and the fiber diameter. As the molecular weight of PCS was higher than a certain threshold, the excessive crystallization was observed causing the decrease of mechanical properties. In addition, the defects inside the fiber increase when molecular weight is higher. The heat-treatment temperature also affected the crystallization and the increase of defects with depending on the molecular weight of PCS. The crystal size enlarged with increasing the heat-treatment temperature, while the fracture morphology remained unchanged.

From the viewpoint of suppressing global warming, it is required to reduce CO₂ emissions during driving by improving the fuel efficiency of automobiles. For that purpose, it is necessary to reduce the weight of the vehicle body frame to reduce running resistance. The most important function required of the frame member is the strength function to secure a space for the occupants to survive in the event of a collision. In general, the weight reduction and strength functions of the frame are in conflict, and structural design technology that suppresses cross-sectional collapse is important. We studied the plate shape that controls the in-plane bending buckling of the vertical plate of the cross section with the aim of suppressing the cross-sectional collapse of the automobile body frame formed of thin and high-strength steel sheets and utilizing the material strength of the steel sheet. From the theory of post-buckling strength of thin plates, we focused on the support conditions of the vertical plate and clarified the relationship with the shape of the peripheral structure. In addition, we derived a new shape proposal that suppresses buckling based on the shape of the vertical plate itself, and confirmed that it is possible to develop a buckling resistance that approaches the theoretical value that directly constrains the periphery.

Low stiffness in the axial direction is required to suppress stress shielding, whereas high stiffness in the torsional direction is required to promote bone healing in metallic implants. Therefore, two types of 316L stainless steel additive manufactured plates having a low Young’s modulus in the longitudinal direction and high Young’s modulus in the lateral direction were fabricated via selective laser melting. Their crystallographic orientations were tried to be controlled being <100>/<110> and <110>/<111> along two in-plane orthogonal directions. Although the degrees of <110> orientations perpendicular to the laser scanning direction and parallel to the stacking direction were slightly reduced, a strong <100> orientation was obtained parallel to the laser scanning direction. Therefore, the additive manufactured plates with the Young’s modulus higher in the lateral direction than that in the longitudinal direction could be obtained successfully. However, with regard to the directions along <100> and <111> orientations, the difference in Young’s modulus between the additive manufactured plates and the single crystal were more than 30%. This difference can be decreased by optimizing the fabrication parameters for selective laser melting and changing the building direction. On the other hand, many similar aspects could be observed between the plastic deformation behaviors of additive manufactured plates fabricated in this study and that of single crystal reported in the literature. However, the microstructure of additive manufactured plates was heterogeneous, containing equiaxed and columnar grains, depending on the laser scanning direction and stacking direction. Therefore, the strength and ductility of additive manufactured plates were probably affected by not only crystallographic orientation but also the relationship between tensile loading direction and crystal grain morphology.

In this research, we improved the fatigue test method for copper alloy strips which was standardized by Japan Copper and Brass Association. In order to increase test frequency and obtain repeatable test results for 108 cycles, the design of fixed block jigs was improved and the tolerance of the knife edge shaper was restricted. Also, lubricant was used for reducing wear on the specimen. From results from the fatigue tests, it shows that the fatigue life of specimens created by a transverse rolling direction was longer than that of specimens created by a rolling direction. To investigate this reason, fracture surfaces of specimen were observed. The areas where the cracks began were found inside the copper alloy strip, not on the edge, and they were consistent with the stress concentration areas estimated with finite element analysis. In addition, we found that in specimens created in the rolling direction transgranular fractures occurred, while in specimens created in the transverse rolling direction intergranular fractures occurred. The difference in fracture mode between the rolling directions is thought to be due to the fact that the grain size is slightly larger than that in the rolling direction due to rolling during strip fabrication, and it is assumed that the degree of plastic strain mismatch at the grain boundary is larger in the orthogonal direction than in the rolling direction, creating resistance to crack propagation. Moreover, the effect of specimen thickness on the fatigue life was investigated. Regardless of the rolling directions, it was confirmed that fatigue strength decreased with increasing thickness. The relationship between thickness and fatigue strength of the strip in the rolling direction tended to decrease at an almost constant rate with increasing cycles, but in the transverse rolling direction, the amount of decrease in fatigue strength decreased with increasing thickness with increasing cycles.

In the manufacture of electronic devices and MEMS, a wide variety of materials are jointed. For light-weight automobiles, CFRP materials are jointed with metallic materials. In these products, jointed interfacial corners are singular stress points, and sometimes fractures occur from such corners. Evaluating the severity of the singular stress field is important to protect these corners from fracture. In our previous studies, we proposed a definition of the stress intensity factors (SIFs) of two-dimensional (2D) jointed interfacial corners. We can use this SIFs formula to evaluate the singular stress field around a jointed interfacial corner with a smooth edge front in a three-dimensional (3D) object. However, fractures sometimes occur from sharp 3D jointed corners. In our previous paper, we proposed a numerical method for calculating the scalar parameters that describe the singular stress fields around sharp 3D corners. In this study, we propose a unified definition of SIFs at sharp 3D jointed corners between anisotropic dissimilar materials. The definition is compatible with the SIFs of 2D corners, of interfacial cracks and of cracks in uniform material. Furthermore, the proposed SIFs can describe the singular stress along any directions around a sharp 3D jointed corner.

Fatigue strength of resistance spot welded high-strength steels does not improve with increasing base metal strength. Therefore, cold-working method and tempering treatment have been proposed as methods for improving fatigue strength. These methods control residual stress, hardness, and both of them to increase fatigue strength. However, it is difficult to say that the effects of hardness and residual stress on the fatigue strength of resistance spot welded joints have been clarified. In this study, to clarify the effects of hardness and residual stress on fatigue strength, these factors were controlled independently by using cold-working method and tempering treatment. As a result, the fatigue life was improved in the joints to which compressive residual stress was applied by cold-working. On the other hand, the fatigue life decreased with the joint where the press load increased and the hardness increased. From these results, it was clarified that the compressive residual stress is a factor for improving the fatigue strength and the increase in hardness is a factor for decreasing the fatigue strength in the resistance spot welded joint.

TiAl (titanium aluminide) has been applied to turbine blades in aerospace industry, because it is a promising lightweight material with high strengths at high temperatures. In recent years, the production method of TiAl by additive manufacturing has been studied. In this research, the effect of dimensions of TiAl specimens by additive manufacturing had on the tensile and creep properties was studied. It was confirmed that the near-net specimen showed higher tensile strengths and lower creep resistance and life than those of the specimen cut from the block with larger cross section and volume than near net specimen. The results showed that the difference of the mechanical properties was because of the different microstructure caused by the powder melting process including hatching to melt inside the cross section and contouring perimeter. The difference in microstructure is considered to be due to the energy density. The energy density of contours is nearly 4 to 10 times higher than that of hatching. Therefore, it is considered that rapid heating and rapid cooling occur in the contour process, resulting in a fine structure.

The flame structure and NOx formation of the inversed diffusion flame (IDF) and MILD combustion formed in the secondary combustion area of waste incinerator were experimentally investigated in order to clarify the NOx generation mechanism in the waste incinerator. The flame structure of secondary combustion near the nozzle exit was characterized by visualization, OH planar laser induced fluorescence (PLIF), and temperature distribution. Besides, ammonia was used as the additives in fuel for understanding the effects of flame structure on NOx formation. The amount of NOx in the exhaust was sampled and analyzed. Results showed that both the IDF and the MILD combustion were successfully formed under the same volume flow rate of oxidizer at the nozzle exit. In the case of MILD combustion without ammonia, the NOx concentration in the exhaust gas was lower than that in IDF without ammonia because the temperature of MILD combustion was more uniform and lower. On the other hand, MILD combustion with ammonia showed higher NOx concentration than that of IDF with ammonia because the spatially homogeneous reaction region was formed in the condition of MILD combustion.

While lean combustion in SI engine is one of the promising methods to increase the thermal efficiency and reduce the pollutant emissions, it causes instability of ignition and combustion due to the low burning velocity. Thus, we propose to increase the combustion intensity by incorporating oxygen enrichment with lean combustion. The objective of present study is to investigate the effects of oxygen enrichment on lean combustion behavior in SI engine. Premixed methane-air-oxygen mixture was combusted in a rapid compression expansion machine with varying their concentration. Experimental conditions were determined by identifying the conditions where the laminar burning velocity significantly changes by oxygen enrichment with 1-D simulation of premixed combustion. Histories of pressure were measured to evaluate heat release rate. Luminous flame was captured by a high-speed camera to observe the flame propagation. As a result, laminar burning velocity increased with oxygen concentration, which caused reduction of combustion period and enhancement of the indicated thermal efficiency. On the other hand, this trend was suppressed when the fuel concentration is lower than 6.85 %. In addition, when the fuel concentration is relatively large, flame propagation speed increased with increase in oxygen concentration, which can cause autoignition of end gas. NOx emission decreased or kept almost constant with increase in oxygen concentration, which might be due to the shortened combustion duration.

In the control of a large structure, hydraulic equipment is often used because it requires a large output. In this study, we focus on the telescope as an example of a large structure, and model its hydraulic support system and analyze its characteristics based on the proposed model. In recent years, the structure of telescopes and the size of the primary mirror have been increasing in dimensions. However, as a telescope is made of steel, changes in ambient temperature cause the structure to expand, thereby deteriorating its observational performance. To address this problem, a hydraulic system to adjust the deformation of the structure has been proposed. Traditionally, this design has relied on static performance studies and pre-installation adjustments. However, to implement the optimal design and achieve high performance, the structure and the system need to be considered in conjunction with each other. Therefore, it is necessary to represent the system in a dynamic and simple model. In this study, a new method for calculating the transfer function is proposed. First, the pipes, pistons, and accumulators are modeled to derive the low-order transfer function. Next, the transfer function is derived at a constant volume or pressure. Finally, the transfer function of the system in combination with the telescope mass is derived and evaluated.

In the control of a large structure, hydraulic equipment is often used because it requires a large output. In this study, we focus on a telescope as an example of a large structure, and experimentally verify the basic characteristics of the hydraulic support system for the telescope. Large telescopes are equipped with a hydraulic system that adjusts the deformation of the structure, because the change in ambient temperature causes the expansion of the structure, thereby degrading the observational performance of the telescope. In another report of the authors, a dynamic and simple transfer function model of this system has been derived. In this report, an experimental apparatus simulating the system is built, and the static and dynamic transient response characteristics are evaluated. The transfer function model is evaluated using the experimental response results. As a result, it is confirmed that the system has sufficient properties to achieve a high observational performance of the telescope and that the proposed transfer function model adequately represents the properties.

In adaptive cruise control (ACC), it is important to improve ride comfort and safety. Distance and acceleration have a significant influence on ride comfort and safety, and there is a trade-off relation between distance and acceleration. Therefore, driving characteristics of ACC should be changed according to various driving scenes. This paper proposes control strategy and design method considering a trade-off between distance and acceleration. In proposed control strategy, driving behavior of ACC is expressed by combination of transient behavior and steady behavior. An example of transient behavior is approaching to a slow vehicle, and an example of steady behavior is following to a breaking vehicle. The proposed control is based on 2-degree of freedom control, it consists of feedforward and feedback controllers. A feedforward controller is designed for transient behavior, and a feedback controller is designed for steady behavior independently. In proposed control design method, driving characteristics for transient behavior is defined by 2-stage moving average filter. Time constants of the filter are theoretically linked to the required distance response and acceleration response. Simulation results show that driving scenes of ACC is expressed by combination of transient behavior and steady behavior. In addition, 2-stage moving average filter defines the response of ACC directly, it contributes to consider a trade-off between distance and acceleration.

A tethered system, which is a multibody system in which multiple rigid bodies are connected via a flexible tether, is currently used for space and deep-sea exploration. In order to perform accurate work with such tethered systems, the ability to comprehend tether dynamics behavior with large deformation/displacement and time-varying length is crucial. Numerical analyses are beneficial in that it is difficult to carry out experiments in such environment. In this paper, an efficient numerical approach is proposed for a flexible body motion with time-varying length using a dimensionless equation of motion. Generally Absolute Nodal Coordinate Formulation (ANCF), which is a nonlinear finite element method is effective for dynamic simulation of a flexible body motion. VFE-ANCF, which applies variable-domain finite element (VFE) as a method of expressing time-varying length to ANCF, was proposed to represent the motion of a flexible body with large deformation, displacement and time-varying length. However, conventional approach using VFE-ANCF has a problem that the accuracy changes depending on the length change. So in this paper, to avoid this problem, dimensionless variables are introduced using representative value that changes with time-varying length. In addition, the usefulness of this method is shown by comparing the numerical results using this method and the conventional method.

As a method for cleaning the nozzle of clinical analyzers with high cleaning efficiency, ultrasonic cleaning was selected because the cleaning mechanism can be miniaturized and the effect on dispensing accuracy is negligible. As for nozzle cleaning, it is necessary to meet two requirements: (i) suppress the wetting range of the nozzle inserted in the chamber of the ultrasonic cleaner and (ii) generate cavitation at a depth of a few millimeters from the liquid surface. To meet those requirements, a new ultrasonic cleaner with an L-shaped cleaning head as a small and high-efficiency cleaning nozzle is proposed. The shape of the cleaning head, which enables the vibration phase of the ultrasonic irradiation surfaces to be reversed even with a single ultrasonic transducer (BLT), is composed of two vibration plates at the tip of the cleaning head to concentrate the sound pressure in the cleaning area. The BLT with cleaning head has three resonant frequencies: f_BLT, f_L-P, and f_U-P. At f_BLT, the ultrasonic transducer expands and contracts in the longitudinal direction.At f_L-P and f_U-P, deformation of each vibration plate is large. By setting the resonance frequencies in the increasing order of magnitude f_L-P, f_BLT, and f_U-P, the phases of the two vibration plates are reversed by driving at f_BLT. It was confirmed by experiment that the sound pressure can be concentrated in the cleaning area by driving the cleaning head at f_BLT.

In the structures whose bottoms is not fixed such as home appliances and furniture, the falls and the slip movements are caused by vibrations such as earthquakes. There is an urgent need to develop fall prevention measures in order to reduce the damage caused by falls and slip movements of structures. The purpose of this study is to clarify the effect of changes in the coefficient of friction on the falling and slipping of structures by analyzing the coefficients of static and dynamic friction separately about dynamic behavior when slipping occurs during rocking vibration. As a result of analyzing the rocking vibration that changed the shape of the structure, it was clarified that the structure wasn’t fall and the slip displacement was the smallest under the conditions when rocking vibration occurred and the height of the structure was low regardless of any degree of freedom. It was clarified that the slip displacement was smaller in 2-DOF system by comparing 1-DOF system and 2-DOF system. It is thought that one of the reasons for this is the fact that the rocking angle reduces and collision frequency increases. 2-DOF system has many collisions because it collides not only between grounds and the structure but also between the upper and lower structures. Therefore, it is considered that the energy consumption of 2-DOF system is larger and the slip displacement is smaller than that of 1-DOF system.

The design method for reference trajectory calculation and flight control system development of the autonomous hammer-head turn maneuver and verification results applied to unmanned helicopters are described. The whole maneuver is divided into four processes. Polynomial of the load factor is formulated by using trigonomeric functions and the given attitude trajectories. Coefficients of the polynomial are calculated by solving simultateous equations which include velocity/load-factor terminal conditions at the beginning and the end of each process. It is introduced in the velocity control law that the reference thrust is selected by looking a value of a reference load factor. This reduces effects to the desired attitude delivered from velocity tracking errors to complete vertical pitch-up motion around the turn process. The results of computational simulations and outdoor flight tests by using the experimental apparatus including a small flybar-less electric helicopter show that the desired maneuver which covers low-to-high speed and load over 2-G is safely achieved by using the proposed methods. On the other hand, velocity tracking performance deteriorates for a while after turn because of priority of pitch up. Rotor-speed drop-down often occurs during climb up against the wind because of lack of motor torque of the experimental helicopter.

This study proposes a multiobjective stacking sequence optimization method for an unsymmetric laminated plate using for a torsion-box structure of an aircraft wing. The objective functions are to minimize the thermal warping occurred during molding process and the bending stiffness ratio that empirically corresponds to the compression after impact strength. The constraints considered are a limited set of ply orientation angles, the allowable number of contiguous plies, and the allowable orientation angle difference between neighboring plies that empirically derived from several strength criteria as delamination, matrix crack and so on. Thus, the design problem is formulated as a combinatorial multiobjective optimization problem with several empirical constraints. To solve this problem, this study adopts a multiobjective genetic algorithm. To consider the empirical constraints on the genetic algorithm, new searching strategies that arrange mutation and gene repair strategy are proposed. Furthermore, lamination parameters and binary trees are introduced to improve searching performance. Through numerical examples, the performance and efficiency of the proposed method are demonstrated. Then, features of the obtained Pareto set are discussed for several design conditions with different thicknesses.

This paper proposes a solution to a multi-material robust topology optimization problem of density type considering material uncertainties based on H¹ gradient method. A material interpolation with respect to the density is introduced using the rational approximation of material properties (RAMP) and generalized it for the case with an arbitrary number of materials. Material uncertainty is considered by introducing random variables in the material interpolation scheme. The probability density functions of the random variables are assumed to be given. The topology optimization is formulated using the density which is given by a sigmoid function of the design variable. A weighted sum of the mean and standard deviation of the mean compliance is used as the objective function to control the tradeoff between optimality and robustness. To evaluate statistical moments of the objective function effectively, the univariate dimension reduction (UDR) and the Gauss-type quadrature sampling are introduced. A scheme to solve the robust topology optimization problem is presented using an iterative algorithm based on the H¹ gradient method for reshaping. Examples of a two-dimensional cantilever beam under various material uncertainty exhibit the efficiency and flexibility of the approach. The accuracy of UDR is validated by comparing the results to the Monte Carlo approach.

The number of whiplash injuries in rear-end collisions is still high worldwide. Since the 1990s, many researchers have studied the mechanisms of injury occurrence in which were focused in the early stage of the rear impact. However, the current situation is that it has not led to a significant reduction in the number of injuries. The authors created a head-neck FEM model with muscles and accurately reproduced the head-neck behaviors of male and female volunteers in the rear impact tests. Then, using the same model, it was clarified that the difference in muscle strength is a large factor in the gender difference in frequency of whiplash injuries. In this paper, we focused on nerve damage, which is the cause of chronic whiplash, and examined the possibility of nerve root damage in the early stage of rear impact. It is generally known that living soft tissues such as nerves have viscoelastic behavior. Using animal axons and nerve root characteristics, it was found that a hyperbolic relationship was established between the velocity and the deformation under compression load on nerve root. The higher the loading rate, the stronger the locality at the compression site, and the greater the possibility of damage even if the deformation is small. Next, we studied the possibility of nerve root damage during a rear impact using a C4-C5 spinal unit FEM model including nerve root model (nerve-spinal unit model). First, in the same model, it was confirmed that there is no nerve root damage during a daily head extension. Then, using male head-neck behavior data in rear impact, it was confirmed that there is a possibility of nerve root damage when the compression speed of the vertebral body increases. Finally, we also analyzed using female data and found that there was a higher possibility of nerve root damage than in male.