Compressive residual stress formed by fine particle peening improves the fatigue properties of steel. However, it is relaxed during the fatigue process particularly during the first cycle of fatigue because of the compressive residual stress layer yield. In this study, the compressive residual stress was induced for specimens with different yield strength by fine particle peening, and the residual stress relaxation behavior was measured and compared using in situ X-ray stress measurement. The results showed that the higher the hardness of the base metal, the higher was the compressive residual stress formed. Moreover, the residual stress was more stable during the fatigue process for a substrate of higher hardness compared to that formed for a substrate of a lower hardness. This is due to the difference in the yield stress.

In this study, in order to investigate the effect of grain size on fatigue crack propagation in CrMnFeCoNi high-entropy alloy (HEA) fabricated by spark plasma sintering, stress intensity factor-K decreasing tests were conducted under the force ratios from 0.1 to 0.8 in ambient condition. Crack profiles were observed by scanning electron microscopy, and microstructures around crack profiles were analyzed by electron backscatter diffraction. Threshold stress intensity factor ranges ΔK_th in HEA tended to decrease with increasing the force ratio and decreasing grain size. Effective threshold stress intensity factor ranges ΔK_eff,th were lower than ΔK_th and almost the same value regardless of the force ratio and grain size. The fatigue crack path in the coarse-grained structure was more tortuous than that of fine-grained structure. The effect of grain size on fatigue thresholds in CrMnFeCoNi alloy was disappeared by eliminating the crack closure phenomenon.

Ni-based auperalloys are used in harsh high-temperature creep-fatigue environments. It has been reported that the lifetime is drastically decreased under creep-fatigue loads. However, the details of the mechanism of significant strength degradation in these environments have not yet been clarified. In this study, the authors focused on the strain rate during the creep-fatigue loads as a new dominant factor in the damage acceleration mechanism of Ni-based superalloys. Electron backscatter diffraction (EBSD) was used for continuous observation of the change in Image Quality (IQ) value of grains and grain boundaries under the different strain rate, 10 N/s and 100 N/s. As a result, it was found that the IQ value decreased significantly at grain boundaries perpendicular to the load when the strain rate was high. In the creep-fatigue test, the initial intergranular cracking started to appear at the grain boundaries perpendicular to the load when their IQ value degraded to 80 % of that of the received material. In addition, intergranular cracking occurred at grain boundaries which consisted of the difference in Schmid factor larger than 0.03.

In order to estimate the fatigue limit of carburized steels having surface compressive residual stress and surface texture generated by peening, we investigated the effect of surface texture and residual stress relaxation on the fatigue limit of carburized steels. In this study, rotating bending fatigue tests were conducted for the carburized steels treated with electrochemically polishing, fine particle peening and shot peening prior to gas carburizing. In the proposed fatigue limit estimation method for carburized steels, the surface texture formed by peening and the sum of mean stress and compressive residual stress experiencing relaxation are considered. The method shows that the maximum value of fatigue limit of carburized steels increased with decreasing the waviness in the surface. Additionally, the lower the waviness in the surface, the lower the maximum value of compressive residual stress contributing to the increased fatigue limit of carburized steel. These results indicate that fatigue limit of the carburized steel depends on the surface texture formed by peening.

Gas blow induction heating (GBIH) nitriding is a rapid nitriding method, but there are few researchs to evaluate its fatigue properties. In this study, hourglass-type fatigue specimen made of beta-rich alpha+beta-type titanium alloy (SP700^®) was treated with GBIH nitriding to evaluate axial loading fatigue properties. GBIH nitriding was performed at 1173 K for 60 s in a controlled nitrogen atmosphere, and its effect on the surface characteristics and fatigue properties was investigated. The formation of the nitrogen compound (TiN) layer with the thickness of approximately 2 μm was clearly observed using an optical microscope and an X-ray diffraction. The formation of the nitrogen diffusion layer (approximately 70 μm) was recognized using a micro-Vickers hardness tester. Axial loading fatigue tests were performed at a stress ratio of -1. The fatigue strength of the GBIH nitrided titanium alloy (GBIH series) exhibited a considerable decrease as compared to that of the mirror-polished alloy (P series). This was attributed to grain coarsening and the formation of the compound layer. Additional fatigue tests were performed for the GBIH+P series in which the compound layer from the GBIH series was removed to determine the effect of the compound layer; however, the fatigue strength was still lower than that of the P series. These results indicated that grain coarsening was the dominant factor in decreasing the fatigue strength.

During the use of asphalt pavement, the water in the pavement produced a freeze-thaw cycle due to the change of temperature, which caused a large number of early diseases on the pavement. In this paper, the water stability of the asphalt mixture of three kinds of asphalt were tested after multiple freeze-thaw cycles. The results show that under the same number of freeze-thaw cycles, the asphalt mixture’s cracking strength, freezing-thawing splitting test strength ratio (TSR), and water stability were, from large to small: SBS modified asphalt > asphalt with anti-stripping agent > base asphalt.

In order to investigate the fatigue properties under varying loading conditions in a heat welding joint by friction stir spot welding of aluminum alloy and CFRP, this study was carried out repeated two-step loading test. Moreover, this study was established a fatigue damage evaluation method with safety and high accuracy under two-step loading conditions. As a result, a fatigue life of joints under constant force amplitude conditions was 2.85 times the difference between the regression line by the least-squares methods and the fatigue life having the failure probability from 10 to 90 %. Moreover, the cumulative damage of the joints based on the Miner’s law was much lower than 1, the effect of load interaction on fatigue life of the joints was confirmed under varying loading conditions. Therefore, the fatigue damage evaluation of the joints with the safe side and high accuracy under varying loading conditions could be achieved by considering a variation of the fatigue life of the joints using confidence intervals and correcting the effect of load interaction using Corten-Dolan method.

Laser welding has many advantages, such as the ability to achieve high-quality welds with low deformation, but it has been confirmed that welding defects occur depending on the welding conditions. The welding defects are likely to be the initiation point of damage, it is necessary to optimize the welding conditions and evaluate the fatigue characteristics to ensure the safety and reliability of welding joint. This study focused on evaluation of fatigue strength based on dissipated energy. This evaluation method can evaluate the fatigue strength in a short period of time. So, this study investigated the applicability of this evaluation method to laser welding joint by SPCC. As a result, evaluation of fatigue strength based on dissipated energy of SPCC base metal and laser welding joint was realized, and it was clarified that evaluation of fatigue property based on dissipated energy for laser welding joint was effective. The fatigue fracture origin of laser welding joint was the area of base metal, and it is found that the fatigue strength in the welded area is higher than that in the area of the base metal. As a result of evaluating the fatigue strength of the laser welding joint based on the dissipated energy, it is found that the fatigue strength of the laser welding joint is almost the same as the fatigue limit obtained from the fatigue test.

We experimentally characterize the strain energy release rate (G) and the crack-tip local strain field of a hydrogel under various types of imposed biaxial strain. We also reveal that the features of the local crack-tip strain field, including crack-tip opening displacement, strain field area, strain magnitude resulting from crack opening, are governed exclusively by G, independent of the biaxial loading type.

Paper sheet is a kind of soft material with high flexibility compared to the bulk counterpart. The flexibility comes from the geometry of thin shape, rather than the mechanical properties of the material itself. In this study, we develop a method of constructing curved surfaces using the flexible deformation of paper sheet. The target surface is divided into several pieces using space curves which are characterized as a straight line on a parameter space. The geodesic curvature, which is the projection of the normal curvature of the space curve onto the tangent plane, is used to approximate the piece of surface on a flat paper. We made several curved surfaces including hemisphere, torus and catenoid.

A new double-network hydrogel has been prepared by one-pot method. The hydrogel possesses 3D porous structure with pore sizes in the micrometer range. The unique double-network ensures the hydrogel with favorable mechanical performance.

We conducted friction experiments between a compliant gel and a rigid cylinder at sliding velocities comparable to the Rayleigh wave or Secondary wave velocity of the gel. We found that, when the sliding velocity exceeds the wave velocities, the contact state transitions from Hertzian like to flat punch like, resulting in the breakdown of the lubricating oil film and the abrupt increase in the friction coefficient. We succeeded in deriving theoretical solutions for the contact pressure distributions and the deformation profiles in the presence of friction.

Hydrogel is a 3D polymer network swollen by water, and it is expected as biomaterials like artificial cartilage. It is important to research on mechanical properties of hydrogel for its application, but difficult to evaluate its wear because the change in surface morphology, mass, and volume by wear is not retained due to swelling after the sliding test. In this report, we focused on the released polymer from the hydrogel by wear into the lubricant and quantitate the amount of polymer by UV spectrometry or TOC measurement. We prepared Poly(vinyl alcohol) (PVA) hydrogel and conducted its wear test using the strain-controlled rheometer. Then, UV spectrometry was performed for the lubricant to determine the quantity of PVA polymer using the absorbance at 280 nm that corresponds to the absorption of the carbonyl group at the unsaponified part of PVA. Also, TOC measurement was demonstrated for the lubricant with very low PVA content. First, we confirmed that we could determine the concentration of PVA in the lubricant using the calibration curve of PVA aq. solutions acquired from UV spectrometry. As a result of sliding of PVA gel against glass substrates with various surface roughness, specific wear rate depended on the size of surface roughness. In addition, the wear rate of the gel with surface concave patterns was lower than that of the gels with flat surface. This is because the surface holes of concave hydrogel reduce the contact area and promote the lubrication by trapped water.

Biological tissue composed of numerous cells has a variety of structures closely related to its mechanical functions. The tissue structures are determined through cellular dynamics, which is affected by stage-dependent mechanical and biochemical environment during morphogenesis. Towards understanding the mechanism of physiological tissue morphogenesis, in this study, we aimed to develop a mechanical model of tissue morphogenesis caused by cellular dynamics depending on the environment. To explicitly express cellular activities, including hypertrophy and proliferation, we extended the material point method (MPM), which is the simulation method based on continuum mechanics using particles for discretization. By performing the MPM-based simulation of tissue morphogenesis, we successfully expressed tissue deformation induced by hypertrophy and proliferation of the composed cells. Further extension of this mechanical model is expected to enable prediction of the change of tissue structures and functions in response to the surrounding environment. This study will contribute to providing better understanding regarding the relationship between tissue morphogenesis and mechanical environment.

The helical coiling of plant tendrils has fascinated scientists for centuries, yet the formation process of the inverted helical structure is still unclear and further investigation is required. In this study, we investigate the formation mechanism of the helical structure from experiments and finite element analysis. First, we measured the geometry of the tendrils using photogrammetry technique. This analysis yields a distribution of curvature and torsion from a least square fitting of a space curve to the point cloud data. The formation process is then estimated from inhomogeneous evolution of the curvature and torsion. We also conducted finite element analysis on a Riemannian manifold. This analysis reveals that the formation of helical structure is explained by development of internal curvature.

Surface energy of a polyhedral crystal is evaluated depending on the energy of the faces, edges, and vertices of the polyhedron, and the relative contribution varies with increase in particle size. Therefore, the stable shape changes with growth of the crystal. In this study, the surface energy of the polyhedral crystal was formulated using the number of constitutive elements. The standard energy of each element was evaluated using molecular dynamics simulation, and then the size dependency of the surface energy was estimated. Finally, the change in shape during the crystal growth was simulated, and it was shown that a drastic change in shape could occur.

Fiber reinforced thermoplastics (FRTPs) are widely used in a variety of molding methods because of their good specific elasticity and specific strength. As an index to evaluate the interface strength, the interface shear strength (IFSS) has been concerned by people all the time, and many evaluation methods have been put forward. These methods aim at a single fiber and ignore the interaction between fibers. In this paper, a short beam method based on three-point bending test is proposed, and it is directly evaluated by FRTP injection molded parts. The fiber distribution angle and interfacial shear strength were obtained and compared with the previous evaluation results. This angle showed the orientation of the fibers with the highest frequency in the central layer. Combined with the welding strength, IFSS and heat flows from DSC measurement, the solidification temperature of PP/GF composites is observed, and it was clear that the solidification temperature of PP/GF composites is agreement with the crystallization completion temperature.

In recent years, adhesives have been applied not only in our daily lives but also in various fields such as automobiles, aviation, and electrical products. In addition, adhesives are expected to be used to join various mechanical parts for the purpose of weight reduction. Although a polymer adhesive such as epoxy resin or urethane resin has high bonding strength, it cannot be used in high temperature environments of 400°C or higher. Therefore, inorganic adhesives with excellent heat resistance are attracting attention for joining components that are exposed to high temperatures. However, inorganic adhesives become hard and brittle after heat curing, and their bonding strength cannot be improved by increasing adhesion area in overlap bonding. In this study, the bonding strength of the joint which are made of a stainless steel rod fitted into a stainless cylinder with an inorganic adhesive was evaluated analytically and experimentally. In this paper, we report the effect of the thermal stress on the joint strength which was investigated by stress analysis.

Directly joining metals and thermoplastics using the anchor effect of micro-roughness has the advantage that it does not require any components for bonding. This paper fabricated single lap joints by injection molding polyamide 6 (PA6)/carbon fiber (CF) composites onto an anodized aluminum alloy. The joint strength of specimens was examined as a function of injection temperature and CF content by subjecting to tensile shear tests. The shear strength of the PA6, which was determined from the Huber-Mises-Henchy yield criterion and the pore area density (PAD), was considered the maximum joint strength and compared with the experimental data. The results show that the CF reduced the joint strength because it inhibited the anchoring process.

Dimple Spot Welding (DSW) is a novel method for dissimilar metal joining, which has been developed for advance multi-materialization of automotive body structure. In this study, fatigue tests were performed for DSW dissimilar metals joints of steels and aluminum alloys. In fatigue tests, all specimens were failed in aluminum alloy plate, and the fatigue life was determined by the strength of the base material used for aluminum alloy plate. As a result of observation of the failed aluminum alloy plate, black wear mark was formed near the crack initiation point, which suggested that the fatigue failure of the DSW joint was affected by the fretting fatigue damage caused by the contact between the steel plate and the aluminum alloy plate. For comparison, the same tests were also performed for SPR (Self-Pierce Riveting) dissimilar metals joints of steels and aluminum alloys. It was found that the fatigue strength was higher in the DSW joint compared with the SPR joint.

Adhesives widely used for internal adhesion of industrial products have a problem of decreasing tack force due to thinning. Therefore, it is necessary to investigate the factors that govern the tack characteristics in order to develop new adhesives and explore appropriate storage methods. In this study, we focus on the bubbles inside the adhesive that are generated when the tack force is generated and clarify the relationship between the tack characteristics and the generation of the internal bubbles and the environmental conditions that dominate them. The probe tack test was performed under different conditions such as pressure and aging of the sample, and the relationship between the tack characteristics and internal bubbles was investigated from the obtained load displacement curve and the observed image. Furthermore, theoretical fingering wavelength and loads are compared with experimental results.

Interfacial strength was evaluated in multi-layer dissimilar materials explosive welding joint. The joint was composed with five different material layers, two aluminum alloys, titanium alloy, nickel alloy and stainless steel. A crack was successfully propagated along interface between titanium alloy and nickel alloy by applying fatigue loading, and plastic deformation at an aluminum alloy layer was suppressed. A crack grew for certain length along the interface and then deflected to titanium alloy side. Direction for crack propagation might be decided by tangential stress and threshold stress intensity factor. Interfacial strength can be evaluated as crack growth resistance on fatigue crack growth curve arranged by a complex stress intensity factor for an interfacial crack.

Composites structural failure usually involves a complex interplay of intralaminar and interlaminar damage. In this paper, we investigate the development of a particle-based, Non-Ordinary State-Based (NOSB) formulation of Peridynamics to predict the failure mechanism of carbon fiber composite laminates subjected to high-velocity impacts. In NOSB-peridynamics, the bonding energy set between particles can be introduced as a fracture parameter associated with the energy release rate. The accuracy of the NOSB-Peridynamics was verified for a simply supported beam, It was shown that the stress-displacement curves of the Peridynamics and the commercial FEM software were consistent. Furthermore, a dynamic delamination calculation of a laminated structure was performed using the NOSB-Peridynamics. The elastic wave which can induce delamination were suppressed by the viscous damping introduced to stabilize the Peridynamics simulation. It was found that the coefficients of the NOSB Peridynamics should be chosen appropriately to simulate the phenomenon correctly.

Carbon nanomaterials were applied to the development of biochemical sensers for detecting plural gases and molecules in an environment. In order to further improve the selectivity of a target gas or molecule, carbon nanotube was applied to the catalyst on a graphene nanoribbon. In this study, CNTs were synthesized by thermal CVD using acetylene gas. Since it was found by the first principles calculation that the electronic conductivity of graphene and graphene nanoribbon varies drastically under the application of strain, mechanical properties of the grown CNTs were evaluated. As a result, the surface stress newly generated by CNT synthesis was very low of 32 kPa, and the macroscopic Young's modulus of the synthesized CNT layer was 4.2 MPa and the linear expansion coefficient was 5.8×10^-6 K^-1. It was found that the CNT layer synthesized by the thermal CVD method did not cause significant stress on the synthesized surface, and the low density of the CNT layer provided sufficient specific surface area for exposure to gas molecules.

Geckos have ability to climb up easily and speedy on smooth vertical surface such as window glass. Gecko's foot has thousands of nano size hairs. They cause strong attractive van der Waal’s force. Normal polyethylene (PE) molecules are vertically transplanted on a carbon plate. Two of this structure are interlocked like as zip fastener. Aihara and Chibana name this connected structure Super Gecko structure. In present study, formation process of the Super Gecko structure is simulated by molecular dynamics (MD) method. The Super Gecko structure has been formed from two separated structures consisting of the PE molecules with distributed electric charge which are vertically transplanted on a carbon plate. The electric charges cause attractive force between two separated structures.

Anodizing was widely used to prepare porous alumina oxide films structure through the thickness and interpore distance. Porous aluminum anodic oxide films fabricated by anodizing in oxalic acid electrolyte containing organic acid were investigated. By controlling them in phosphoric acid corrosion solution for 45 min, high tensile strength alumina templates were obtained. Compared with the surface coating of mild anodization, the tensile strength could be effectively increased from 20.02 MPa to 24.42 MPa.

In this paper, an atomic-scale loading test model was developed using first-principles calculations based on density functional theory, and the effect of the difference in the reactive groups on the bond strength between the metal surface and the silane coupling agent was numerically investigated. Copper was used as the metal, 3-aminopropyltrimethoxysilane and 3-mercaptopropyltrimethoxysilane were used typical the silane coupling agents. We compared the bond strength between the hydrolyzing group and the organic functional group (-NH2) or (-SH), which have high affinity to copper. As a result, it was found that the bond strength of 3-aminopropyltrimethoxysilane decreased by 11.1% and that of 3-mercaptotrimethoxysilane decreased by 15.3% when the organic functional group was bonded in comparison with the case where the hydrolyzing group was bonded. In both cases, delamination due to interatomic cracking at the interface with the metal was observed. The results obtained by first-principles calculations are in qualitative agreement with experimental results.

In order to investigate the relationship between strain distribution and fatigue crack growth behavior, the digital image correlation (DIC) method was applied for strain distribution measurement at crack tip during SEM in-situ observation fatigue crack growth test. The result showed that a straight crack had an elliptical strain concentration area at the fatigue crack tip. On the other hand, when crack branching occurred, strain concentration area was found to be inclined and was including dense slip band region. After some number of cycles, crack tended to propagate along the strain concentrated area. Additionally, local cyclic strain hardening was confirmed by micro vickers hardness test at the strain concentrated area with dense slip band.

The previous study shows the adhesive strength can be expressed as a constant value of the critical ISSF (Intensity of Singular Stress Field) for butt joints. This study deals with the scarf joint considering two ISSFs corresponding to two distinct singular stress fields. How to evaluate the scarf joint strength is described in comparison with the lap joint having similar two ISSFs. The debonding strength for scarf joints and lap joints can be predicted by the critical ISSF K_σc,λ1 the singular stress σ_θc(10μm).

In this paper, the intensity of singular stress field (ISSF) is focused and newly analyzed for the stepped-lap joint, and the adhesive strength is considered in terms of the ISSF. In this problem, it is necessary to analyze the two different singular stress fields at the interface end point A and each interface corner point B_i (i=1,2…Ns-1, Ns=the number of steps) on the adhesive surface. In order to investigate the effect of the number of steps Ns on the ISSF of the stepped lap joint, four models with different numbers of steps are calculated. By comparing the stress distributions, it is found that the ISSF at point A is larger than that at point B_i. Moreover, it is also shown that the ISSF at point A decreases with increasing of step number Ns, but there is almost no change of the ISSF at points B_i.

In this paper, a convenient evaluation of an intensity of singular stress field (ISSF) at an interface corner in a single lap joint (SLJ) with a fillet is examined. The analytical method is focused on the ratio of the stress values at the interface corner obtained by applying the finite element method (FEM) to the SLJ model and the reference model which are subdivided by the same mesh pattern. It is shown that the square-shaped inclusions in the infinite plate under the bi-axial uniform stress and the pure shear stress can be analyzed by the reciprocal work contour integral method and are suitable for the reference model. The numerical simulations are performed on the SLJs with the fillet. It is confirmed that the ISSF for the SLJ can be evaluated conveniently and accurately by comparing the asymptotic solution with the FEM stress distributions.

Failure of butt joints generally occurs at the interface edge due to the singular stress. In this study, to reduce the intensity of singular stress field (ISSF) at the interface end of a jointed round bar, the butt joint specimen with circumferential notch near the adhesive layer is used. The variation of the ISSF due to the interaction effect between the notch and the interface is investigated by the finite element analysis. The calculations show that as the adhesive layer thickness decreases, the ISSF at the interface end of the notched butt joint specimen decreases. When the adhesive layer thickness is 1mm, the ISSF of the notched butt joint specimen is reduced to half that of the unnotched specimen. In the case the adhesive layer thickness is less than 0.3mm, the compressive stress occurs at the interface end and maximum tensile stress occurs inside the butt joint. This indicates that the fracture strength of the butt joint can be improved.

A hybrid polyvinyl alcohol/poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PVA/PEDOT:PSS) hydrogel electrode with 3D interpenetrated network structure is prepared by the freeze-thaw crosslinking and solution immersion method. Due to the strong intermolecular force between PVA and PEDOT:PSS, coupling with the use of liquid phase mixing, this hybrid hydrogel electrode shows uniform interconnectivity and robust mechanical properties. The all-solid flexible supercapacitor prepared based on this composite electrode exhibits excellent mechanical durability as well as excellent electrochemical performance.

Mechanical stress is being increasingly recognized as one of the factors that significantly affect the fundamental properties of the materials for solid state electrochemical devices, including batteries. However, the influence of stress has not been precisely understood because it is challenging to experimentally and quantitatively evaluate the relationship between the stress and the material properties. Here, we developed an experimental method to quantify the influence of stress on the chemical potential in a material and successfully evaluated the stress-induced Li chemical potential (μ_Li) modulation in a conventional battery electrode material, LiCoO₂ (LCO). Our results suggested that the stress-induced μ_Li modulation in LCO was anisotropic because of its anisotropic chemical expansivity. As well as LCO, many other electrode materials exhibit the anisotropic chemical expansivity, and they are subjected to highly anisotropic stress in the practical electrochemical devices. Thus, the findings in this study can provide valuable information for the design and development of the solid state electrochemical devices.

In this paper, we study the prediction of behavior using proper orthogonal decomposition (POD) to oxygen potential in a solid oxide fuel cell (SOFC). Transient electro-chemical potential analyses of the SOFC with some fuel mass inflow and temperature as input parameters are performed and oxygen potentials that changes over time are obtained. POD is applied to the data matrix of oxygen potentials and a reduced model that extracts the dominant mode is created. Then, by using function approximation for the reduced model, a surrogate model is developed to predict the efficient behavior of the oxygen potential in SOFC under different conditions. To validate the surrogate model, we compare the result of surrogate model with the one of electro-chemical potential analysis under arbitrary condition, in which hydrogen pressure and temperature are distributed in SOFC under this condition.

Shape determination based on optimization methods is attracting attention in designing of structures. Optimization methods can be classified into size optimization, shape optimization, and topology optimization. In these methods, the design domain is limited in advance and the degree of design freedom is limited. Conversely, biological growth is an example of optimization in nature. An organism repeatedly develops their structure by optimization in response to the environment. In this study, we propose a new optimization method based on biological growth process using the transfer matrix method. In addition, the method will be verified by comparing with the results of several analyses of the plane cantilever design problem.

We developed a theoretical model to calculate the bending-torsional vibration modes for branched structures like trees or plants. By considering the equation of motions and the boundary conditions, we obtained fundamental frequencies and amplitudes. As we compared the theoretical results with experiments, we confirmed reasonable agreement with each other. We also found an abnormal feature that two different eigen modes have similar modal shapes with different frequencies.

Trees in nature have many branches so that the leaves growing at the ends of the branches can receive a sufficient amount of sunlight. Furthermore, it is presumed that the tree branch autonomously forms a mechanically optimal structure in order to distribute stress almost uniformly over the branch. Reaction wood is one of the primary organs that seems to contribute to the realization of such a mechanically optimal structure. It is abnormal woody portion that develops at the base of the branches in response to gravity and the growth environment inducing mechanical stresses in the tree. The position where the reaction wood is formed depends on the tree species. In general, conifers have compression wood just below the base of the branches, and the broad-leaf trees have tension wood right above the base. To obtain a better understanding of the tree’s structural optimization mechanism, we have theoretically scrutinized the correlation between the spatial distribution of reaction-wood-related material parameters (mass density, Young’s modulus, etc.) and the mechanical response (bending stress, deflection curve, etc.) of the branches. In particular, we have explored the effect of the positional difference in the formation of reaction wood on the loading condition that suffices to realize uniform stress distribution.

Fruit tree branches are deformed with large deflection under mechanical loads such as wind, rain and snow weight, and deformed by fruit weights. The bending stress and strain under deformation are important to evaluate the mechanical strength of long-shaped beam structures. The bending deformation of the beam structure is determined by configuration of applied loads which include amount and location. A bending deformation analysis for tree branch was conducted focusing on the base angle and diameter of the branch in this study. The numerical analysis models were created as the cantilever of tapered shape with a constant elastic modulus. As a simulation result, the large bending deformation for downward reduced the bending moment applied at the base end of branch model. And the base angle for the upward direction made severe bending strain at the base side. The bending deformation simulation was available to estimate the strength of branch geometries and predict the failure location on the branch.

Present study concerns the functional fatigue due to the cycles of superelasticity in shape memory alloy. When superelasticity is repeated for large number of cycles, the functional fatigue would be observed as the accumulation of residual strain. As a result, the extent of superelastic strain decreases with increasing the number of cycles. First, present study found that as cold-drawn wire of Nickel Titanium alloy (50.6 at.% Ni) exhibits superelasticity after the heat treatment at 500℃ for a few ten seconds. We shall call this flash heating “short time aging”. Next, it was also found that the short time aged sample showed smaller amount of residual strain after the repetition of superelasticity. The amount of residual strain decreased with decreasing the period of aging.

In this study, we investigated the optimal conditions for achieving higher response of Ni-Ti based shape memory alloy (SMA) wire actuator. High speed driving of SMA actuators have been said to be difficult because their deformation speeds depend on temperature change; especially, cooling speed is important factor, and many studies focus on it. We had developed a method for improving the response of SMA actuators by adding DC bias to the input voltage signal. As opposed to the methods for improving cooling performance, this method has the advantage in non-necessity of external devices. In order to examine the optimum conditions, we connected SMA actuator and spring in series and conducted experiments of changing DC biases voltage applied to the single frequency input. From the result of experiments, we found that response of SMA actuator changed depending on the displacements, and the maximum response was obtained when the strain was 4.51 % in 200 Hz input signal.

Shape memory polymers (SMPs) are one of the shape memory materials that have attracted attention in recent years, and can be formed into arbitrary shapes by FDM 3D printers. Since the printed SMP is formed while being strained, it deforms due to change in the elastic modulus by heating. The purpose of this study is to develop an actuator that operates with temperature change by combining SMPs with different glass transition temperatures (T_g) formed by an FDM 3D printer. The results obtained are summarized as follows. （1）The deformation behavior of an actuator that combines two SMPs with different T_g shows two-step behavior because the deformation occurs near each T_g. However, the way of deformation differs depending on the thickness of the printed SMP, and the actuator continues to deform even above the T_g region. （2） The printed SMP deforms little around T_g, and deforms significantly at temperatures above the T_g region, and stops deforming after reaching a certain temperature.

Polyurethane shape memory polymers (SMPs) are currently being applied in a various fields. SMP has two characteristics such as shape fixity and shape recovery due to temperature changes. Using these properties, SMP can be obtained large recovery stress under constant strain in heating after deformed by cooling. In this study, using the recovery stress, a functionally graded SMP foam (FGSMPF) was fabricated to develop a novel actuator by stacking SMPFs with different glass transition temperatures. Shape recovery test was conducted and two-step behavior of FGSMPF was investigated.

Ti-Ni SMA, which is currently in practical use as a shape memory alloy (SMA). We can be controled the shape recovery temperature by changing the concentrations of Ti and Ni^1),2). However, Ti-Ni SMA does not show shape recovery effect in the temperature range over 100 ℃^2),3). Therefore, Zr-Cu SMA is mentioned as a high-temperature shape memory alloy that is driven in a high-temperature range exceeding 100 ℃. However, with Zr-Cu binary, the shape recovery temperature cannot be controlled even if the concentrations of Zr and Cu are changed. It has been reported that Zr-Cu SMA may be able to control the shape recovery temperature by adding the third element^6),7). However, there is little knowledge about the mechanical properties and shape recovery properties when the third element is added to the Zr-Cu alloy. Therefore, the purpose of this study is to investigate compressive deformation and shape memory behavior. Futhermore, the martensitic transformation temperature is measured by the DSC test to investigate the correspondence with the shape recovery behavior. As a result, the Zr-Cu alloy tends to retain residual strain even with a small load by adding Al.