Bacterial cellulose (BC) synthesized by Acetobacter xylinum is one of the nano fiber materials. In this paper, the aggregation and dispersion behavior of C/C composite made with the BC and copper powders as a third constituent were considered. It is found that BC microfibril network can set copper powders into fine dispersion in the mBC-C/C composite. The tribological and electrical properties of Cu/mBC-C/C composite containing copper powder were also evaluated. From the experimental results, the mean value of the specific wear amount was at 10^-9 order, the dynamic friction coefficient was about 0.2 and the electrical resistivity was at 10^-4 order. Furthermore, the wear properties got worse due to the large amount of copper powder and the improvement in electrical conductivity was not enough. It is considered that it is necessary to find the optimum content of copper powder for the improvement of electrical conductivity in order to use for the conduction/friction material, for instance, brush for the DC motor.

The effect of fiber morphology on mechanical properties of thermoplastic composites reinforced by cellulose microfibers was investigated by multiscale numerical analysis. The homogenization theory was employed for scale coupling, and representative volume element (RVE) models with random fiber orientation was generated based on the random sequential adsorption (RSA) algorithm. The effects of fiber aspect ratio and aggregation on nonlinear mechanical properties were investigated. The elastic properties and maximum tensile stress were found to vary by 26.8% and 39.6%, depending on the fiber aspect ratio, and by 5.95% and 4.20%, depending on fiber aggregation.

Polypropylene (PP), a major thermoplastic resin, is widely used in compression molding and injection molding due to its excellent mechanical properties and recyclability. In general, talc, an inorganic mineral product, is widely used as a reinforcing filler in PP. Talc has excellent chemical stability, electrical insulation, and affinity with organic materials. However, PP has a high coefficient of linear expansion, making it difficult to use with the fused deposition modeling 3D printers that have become increasingly popular in recent years because of warping of the printed structures. On the other hand, cellulose nanofiber (CNF) is a plant fiber that has been degraded to the nanoscale and is expected to be used as a reinforcing filler for composite materials because of its superior specific stiffness and specific strength. It is expected to reduce environmental impact compared to conventional reinforcing fillers due to its reduced CO2 emissions and high recyclability. In addition, the high aspect ratio and low coefficient of linear expansion of CNF can be expected to reduce thermal deformation of composite materials. In this study, the mechanical properties of PP composites reinforced by talc and CNF fillers were tested by multiscale finite element analysis. The contents of talc and CNF were changed, and the effects of adding each were clarified.

In this paper, the fracture problem of a piezoelectric actuator consisting of a functionally graded piezoelectric material strip (FGPM strip) and a homogeneous layer by a transient thermal load combined with an electric load is considered. The FGPM strip contains a crack perpendicular to the interface. Material properties of the FGPM strip are assumed to be exponentially dependent on the distance from the interface. The thermo-electro-mechanical fields in the un-cracked laminate induced by the transient thermal load and the electric load are calculated. By using the superposition technique, the obtained normal stresses are used as the crack surface tractions with opposite sign to formulate the mixed boundary value problem. The integral transform techniques are employed to reduce the problem to the solution of a singular integral equation. The stress intensity factors are computed, and the results are presented for the various values of the nonhomogeneous and geometric parameters. We also focused on the crack contact phenomenon for the case of the pure electric load. Moreover, the effect of the difference between two kinds of the electric boundary conditions on the stress intensity factors under transient thermal load and the reduction of ones by the electric load would be discussed.

With the development expansion of environmental sensors in recent years, nanogenerators utilizing small amounts of mechanical energy in surrounding environment to generate electricity have been frequently studied. In order to convert mechanical energy into electrical energy more efficiently, it is necessary to fabricate single crystal ZnO nanostructures with specific crystal facet that exhibits piezoelectricity in the direction of applied strain. Since ZnO nanobelts have three pairs of crystal facets, controlling crystal growth can increase the size of specific crystal facet and their piezoelectricity is greater than that of ZnO nanowires, which is advantageous for power generation using piezoelectricity. ZnO nanobelts have been fabricated by chemical vapor deposition method, and we attempted to control the crystal growth by changing the heating temperature and pressure. Morphologies were observed by field emission scanning electron microscopy. Diffraction patterns were observed by transmission electron microscopy. ZnO nanobelts with the growth direction of [0001] and [0110] have been successfully fabricated in this research.

Japanese forest is expected as source of structure material, because trees planted in post war era have been grown up．In Japan, houses have been made by wood traditionally and wood is used as structural material such as pillar and beam. In order to use wood as a structural material, a joint is necessary. The shapes of these traditional joints are determined empirically and used without any analytical evaluation such as stress analysis. Therefore, stress analysis is necessary in order to use such joints efficiently. In our study, we estimate joint stress concentration factor of gooseneck joint under uniaxial tensile load analytically. Gooseneck joint is one of typical joint in japan and consist of male part and female part. In our previous study, we conducted a tensile test and measure the strain distribution of the joint by digital image correlation method (DIC) and FEM analysis. From these results, we proposed the formulae which give the stress concentration factors for male and female parts. In this study, we conducted tensile strength tests of goose-neck joint with varying the dimension parameter and estimating and tensile strength of the various shapes of the joint under uniaxial load. From the result, we examine the relation between the joint stress concentration factor and tensile strength of the joint for confirming the validity of using the joint concentration factor to evaluate the tensile stress of the joint.

The relationship between the shear strength of the metal-resin and the periodic structure of the metal surface was investigated. Femtosecond laser processing was applied to the Cr-plated carbon tool steel surface to form irregularities with a pitch of about 20 μm and a depth of about 10 μm, and a nano-scale fine periodic structure (so-called LIPSS) was formed on the top of the peaks. The epoxy resin was then placed in a mold and pressed by a heat press onto a metal plate. Then, the molded epoxy resin was pressed from the side with an indenter to measure the shear force, and the shear strength define as the maximum shear force. As a result, a positive correlation was observed between the shear strength and the opening valley angle of the micro-periodic structure, and a negative correlation was observed between the shear strength and the aspect ratio, which is the depth of the micro-periodic structure divided by the pitch.

In recent years, the use of multi-materials for weight reduction and performance improvement has become popular in a wide range of fields, from the automotives to the medical devices. In this study, we focused on silane coupling agents, which enable strong adhesion between organic and inorganic materials, and investigated the adhesion mechanism to metals by first-principles calculations. In particular, we compared the molecular structures of silane coupling agents and analyzed their effects on interfacial bond strength. As a result, it was found that the adhesion strength of GPS to aluminum was high, followed by MPS and APS, which was the lowest. The difference in stiffness and adhesive strength was due to deformation of the molecular structure, i.e., it was dominated in the balance between stretching and rotation of molecular structures.

Recently, fabrication of piezoelectric-particle-dispersed polymer composite materials using a 3D-printer has been attracting attention. By combining conventional thermoplastic polymer filaments with functional filaments containing piezoelectric ceramic particles, it is possible to add functions such as sensors, actuators, and energy harvesters to the structure, enabling the integrated fabrication of multifunctional devices. In this study, we investigate the enhancement of macroscopic piezoelectric properties of 3D-printed composites in the heterostructure of dual filaments with different piezoelectric particle content compared to the homostructure of single filaments, by numerical analysis and fabrication. Multi-scale analysis by the homogenization theory was applied to confirm the superiority of the heterostructure. Moreover, filaments with barium titanate particles were fabricated, and the relationship between piezoelectric properties and content ratio was clarified.

Magnetic sensors, angle sensors, energy harvesters, etc. have been developed using the transverse magnetoelectric(ME) constant, but in general, the transverse ME constant is one order of magnitude smaller than the longitudinal ME constant. Therefore, it is necessary to design and develop a heterostructure that is as effective as the longitudinal ME constant. In this study, multiscale optimal design was performed to find microscopic heterostructures that maximize the macroscopic ME effect. Asymptotic homogenization theory was employed in the scale coupling, and the microheterostructure was searched for by using the content ratio, arrangement, and polarization orientation of the constituent materials as design variables. As a result, in the case of barium titanium(BTO) for ferroelectric phase and cobalt ferrite(CFO) for ferromagnetic phase, the transverse ME constant a31 was 75.9 nNS/VC, which was a dramatic improvement over the conventional stacking structure.

This paper describes a fundamental discussion on stochastic mechanics of material for contribution on future sustainable society. From the viewpoint of sustainability, it is very important to reduce waste of materials and to use a natural material. In this case, a material property may be difficult to be well controlled compared to a conventional material, and therefore influence of this uncertainty or random variation should be considered in a design process of a structural product. For this problem, a concept of stochastic homogenization / multiscale stochastic stress analysis may contribute for evaluation of safety factor for the design. In this presentation, outline of a concept of the stochastic mechanics of materials and application of the stochastic homogenization of composites to the framework are introduced, and effectiveness of the presented approach will be discussed.

Nickel-based superalloys are used as blade materials for aircraft jet engines. Recently, ceramic composites are developed to improve heat resistance and reduce weight. However, further cost reduction is desired. In this study, we focused on the nacreous layer of red abalone and investigated the stress-strain curve and fracture characteristics. It was found that the slip deformation and zig-zag-like crack propagation path between the thin-plate layers that constitute the nacreous layer exhibit nonlinear deformation behavior and high ductility. It was modeled by brick and finite element analysis was carried out. The analysis results faithfully simulate the actual deformation and fracture behavior. In the future, the geometry and material constants of the model will be optimized to propose advanced material.

Titanium alloys are widely used in industry because of their excellent mechanical properties, but their applications are limited due to their poor wear resistance. In this study, we attempted to improve the surface hardness of titanium alloys by applying an atomic rearrangement technique using high-frequency current application. Vickers hardness tests were conducted after the application of high-frequency current, and the surface Vickers hardness was improved by 8.2% at the maximum. Dislocation density was measured using an X-ray diffraction method to evaluate the microstructural change, and an increase in the dislocation density of the α-phase was confirmed. These results suggest that high-frequency current treatment is effective in improving the wear resistance of titanium alloys.

The design life of artificial joints is 10 to 20 years and in an aging society, improvements in durability are expected. Therefore, as a method for improving fatigue characteristics, the authors have expected the effect of shot peening and reported that the fatigue properties of the Co-Cr alloy, which used as an artificial joint material, treated with Shot peening (SP) are significantly improved. In addition, mass finishing (MF) was applied to smooth the surface of the shot-peened Co-Cr alloy. It was confirmed that the high-performance layer obtained by the SP remained and was maintained. However, the wear properties using this method have not been verified.

In this study, we measure the friction coefficient and wear volume of the Co-Cr alloy surface that has undergone MF after SP and observe the wear marks. In addition, the wear characteristics and mechanism were examined from the viewpoint of the hardness characteristics affected by SP and MF. It was clarified that it is possible to improve the wear characteristics of Co-Cr alloy by applying MF after SP.

In recent years, the demand for implants has increased in the orthopedic field due to the aging of the population. Among them, Ti-6Al-4V alloy is very often used. However, its high Young's modulus and cytotoxicity are regarded as problems. Therefore, we are focusing on titanium and tantalum, which are highly corrosion-resistant elements, and are developing Ti-Ta alloy, which is a β-type titanium alloy that exhibits low Young's modulus and low cytotoxicity. Furthermore, from the viewpoint of safety and durability, both high strength and low elasticity and excellent fatigue characteristics are required. In this study, we identified the microstructure and crystal structure of 4-types of heat-treated Ti-Ta alloys. In addition, torsional fatigue and plane bending fatigue tests were performed. By comparing these results, we investigated the relationship between structure and fatigue characteristics. From SEM and TEM observation, EBSD and EDS results, it was found that Tantaulum was dissolved in the β-Ti matrix in any heat treatment conditions. Furthermore, α-Ti was deposited at the grain boundaries by 500℃ aging. It was also found that the average crystal grain size increased due to the increase in the solution temperature and the aging treatment. Then, the torsional fatigue characteristics improved as the crystal grain size became smaller. The plane bending fatigue characteristics were improved by strengthening precipitation with α-Ti.

Knee joint diseases have been increasing in recent years due to the aging of society and the increase in the sports population. Knee braces used in treatment play a role in immobilizing and stabilizing the knee joint and reducing the direct burden on the knee joint. Therefore, the development of knee braces using CFRP material by fused deposition modeling (FDM), one of the additive manufacturing (AM) methods, is expected. The application and development of CFRP for knee orthoses requires safe design that considers the weakest points in terms of the shape of the various parts used in the orthoses and the walking motion. However, the mechanical properties of CFRP materials using FDM have not been clarified. In this study, the effects of carbon fiber content and orientation on the flexural strength of FDM-molded CFRP were investigated. 4-point flexural strength tests revealed that the carbon fiber layer was distributed throughout the entire structure, and that the higher the fiber content, the higher the strength. Therefore, it is suggested that an even arrangement of the fiber and resin layers increases the bending strength.

This study aimed to evaluate the effect of the elastic modulus gradient on the osteoclastic metabolic behavior on the functional gradient substrates prepared by welding PLA and PCL. First, the elastic modulus distribution of the substrates with the elastic modulus gradient in the depth-direction were directly evaluated and verified by the tensile and indentation tests. Then, the osteoclasts were cultured on the PLA-side surface of the PCL/PLA functional gradient substrates. The osteoclastic metabolic behavior was evaluated by the ATR method using a FT-IR. As a result, it was confirmed that the elastic modulus of the PCL/PLA functional gradient substrates decreased from the PLA side to the PCL side. This indicates that the functional gradient substrates have the elastic modulus gradient successfully. The FT-IR measurement revealed that the osteoclastic dissolution rate of the substrates increased with the increase of the culture period until 4 weeks, and then decreased at the 5th week. This indicates that the elastic modulus gradient in the depth direction could control the osteoclastic metabolic behavior.

The supraspinatus tendon (SSPT) is a tendon connected the supraspinatus muscle to the greater tuberosity of the glenohumeral joint and acts during shoulder abduction. The SSPT is known to be the most frequently injured tendon in the rotator cuff, and repetitive movements and age-related muscle weakness are the most common causes of injury. The mechanical properties of the SSPT are important not only for the diagnosis of damaged tendons, but also for the evaluation after rotator cuff repair. The aim of this study was to evaluate the stiffness of the SSPT in vivo by shoulder abduction and muscle contraction using ultrasound elastography. This study showed that the stiffness of each part of the SSPT decreased as the shoulder abduction angle increased.

The Anterior oblique ligament (AOL) of the ulnar collateral ligament (UCL) attaches to the inferior aspect of the medial epicondyle of the humerus and the coronoid process of the ulna, and has an important role in life and exercise by inhibiting flexion and valgus of the elbow. Understanding the mechanical function of the UCL in vivo is important for the diagnosis and prevention of elbow injuries caused by baseball and other sports. In this study, we aimed to measure the stiffness of the AOL during changes in elbow flexion angle and pronation and supination using ultrasound elastography. The stiffness of the AOL decreased with increasing elbow flexion angle in all conditions, and was less affected by pronation and supination compared to the intermediate position at the same elbow flexion angle.

In this study, we developed a knee simulation model considering the attachment area of the knee joint cruciate ligament bundles. 3D geometry extraction of the femur, tibia, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) from CT images of the knee joint. In addition, the stress-strain curves of ligaments were derived from uniaxial tensile tests. A finite element analysis model of the knee joint was created based on the above conditions. The state of ligament bundle attachment was reproduced by dividing the attachment area of the ACL and PCL to the femur and tibia. As a result, although the behavior of the ligament during compression remained to be an issue, similar tendencies to those of ligament desmotomy studies were obtained.

In recent years, a regenerative therapy method using human iPS cell-derived myocardial cells (hiPS-CM) has attracted attention. In the future, large-scale myocardial three-dimensional structures that apply tissue engineering technology are expected. In this study, we developed a three-dimensional structure with a pump function by the self-beating power of hiPS-CM. Then, the deformation behavior of the 3D hiPS-CM structure associated with self-pulsation was examined. The pulsatile behavior of hiPS-CM was quantitatively evaluated by using a high-speed optical measurement system with the digital image correlation method. Then, the experimental strain data was used to construct the stress-strain response with use of a theoretical active stress model originally developed by Guccione et al. A theoretical constitutive model was also developed by combining the Guccione's active stress model and the viscoelastic Maxwell model. As a result, this theoretical model stress-strain behavior showed a good agreement with the combination model of experimental strain and theoretical stress.

We considered the axisymmetric indentation of poroelastic multi-coating bonded to poroelastic substrate indented by a rigid flat-ended cylindrical indenter. The approach that expressed poroelastic solutions in term of two displacement functions and the transfer matrix method which can formulate the effect of multi-layer composite were applied in this study. Furthermore, we adopted the analytic method that using Laplace-Hankel transform and expressing the normal contact stress at the surface layer as an appropriate series with a Chebyshev orthogonal polynomial to reduce dual integral equations to an infinite system of simultaneous equations in Laplace transform domain. The numerical results of time-dependent axial displacement of rigid cylindrical indenter were presented by performing numerical inverse Laplace transform. The results of axial displacement for one-layer bonded to rigid impervious substrate given by this study were good agreement with previously reported results.

Thermoelastic stress analysis is a non-contact measurement method that can evaluate the stress distribution on the surface of objects. However, it does not work well for rubbers because not only the thermoelastic effect but also the entropic effect and the viscous dissipation effect influence the temperature variation. This study focuses on determining the quantitative relationship between the temperature variation and these three effects of rubber dumbbell specimen subjected to cyclic tension. A thermo-mechanical model was utilized to simulate the temperature variation under different loading conditions, and the simulation result was compared to the experimental result obtained from the thermographic measurement.

In order to construct soft actuater, to know the deformation behavior of hyperelastic materials such as rubber is important. It is necessary to obtain parameters of energy functions, which are determined by using the experimental data. Not only uniaxial elongation test data, but also biaxial and simple shear data should be requailed. But, biaxial and simple shear test are difficult. Therefore, in this study, a equipment, which makes indentation of a thin disc specimen, is constructed. The uniaxial, biaxial and simple shear data can be obtained by the present equipment at one time. The parameters of various energy functions are identified by minimizing the mean square of the difference between the experimental results and the simulation results, which are calculated by the finite element method.

Rubber is widely utilized in industries. However, material properties vary significantly depending on recipe and mixing / curing conditions. When conducting researches on mechanics of rubbers such as deformation, fracture and tribology, mechanical properties of the material being used in the research should be always examined. This is actually troublesome and causes difficulties in sharing results between researchers. Technical Section (A-TS03-29) in Materials and Mechanics Division of JSME proposed to establish a standard specimen with simplifying recipe and production method in order to share and promote researches on mechanics of rubbers. A standard Styrene-butadiene rubber specimen was made under a simple and open recipe and production method. The specimen was distributed in the members of Technical Section and its material properties were measured. This report provides the analysis results of uniaxial tensile results and application of identified constitutive parameters.

A thin elastic object frequently exhibits various pattern formations, such as wrinkles, facets, and loops, under twisting deformation. In the present study, we conduct experimental and numerical analysis for twist deformation of elastic ribbons with various boundary conditions. A sequential pattern transition has been observed from helicoid to local loop through triangular facets in the traction boundary condition. We also observed small oscillations in torque during the development of facets. Isogeometric analysis based on St.Venant-Kirchhoff hyperelastic material reproduced the experimental results.

To elucidate the static and dynamic behaviors of mechanical metamaterials, we mechanistically constructed a metamaterial structure using bars, discs, springs, and bolts, and conducted in-situ tensile experiments. We found that the system undergoes multiple structural transformations by an imposed strain. We inferred that the multi-stability and bifurcation play an important role in non-linear mechanics of mechanical metamaterials.

Elastomeric gels are soft-elastic materials consisting of a three-dimensional cross-linked polymer network and liquid filling the space among such network. To take advantage of the swelling-deformation behavior of elastomeric gel and explore its possibility for applications in engineering as a structural member, the effect of concentration of ion in the solution on the deformation behavior of gel should be clarified, especially when the gel is loaded inside the solution. In this study, we at first proposed a nonaffine model for the elastomeric gel to account for the change of the entangling structure of polymer chains during the swelling-deformation process, in which the change of the number of polymer chains per unit volume N is depending on the first invariant of right Cauchy-Green deformation tensor I₁. And then, the simple tensional deformation behavior of gel is calculated when the gel is loaded inside the solution with different concentration of ion. The results show that the nonaffine model can reproduce the experimental results very well. Moreover, the high concentration of ion leads to the high deformation resistance.

Hydrogel, a soft and wet functional material with excellent swelling and ductility, have expected to be used as a biomaterial because of its biocompatibility. While most biological tissues exhibit anisotropy of physical properties, hydrogels are isotropic materials. This paper reports the effect of the high elongation process on the anisotropy of mechanical properties and morphologies of CMC/PAA hydrogels prepared by visible light-induced polymerization. As a result, the tensile strength of hydrogels changes with elongation direction and shape-fixing temperature in the elongation process, and the pores expand to the elongation direction.

Structures smaller than submillimeter scale can be easily deformed by capillarity, but it is difficult to predict because the capillary-induced deformation is usually unstable phenomena. In this study, a simple experiment was proposed to characterize the capillary-induced coalescence of thin tall structures. Multiple parallel plates separated by small gaps and fixed at their bottom ends were lowered into a liquid to generate their bending deformation by a liquid bridge formed between them. It was revealed that the plates do not coalesce simultaneously, but in a sequence starting from the plate pairs with the smallest gap. These plates after the contact can be regarded to be a single plate with the increased thickness. An analytical model was established to predict the bending deformation of the plates based on the minimum potential energy. The effectiveness of the model was confirmed by accurately predicting the sequence of coalescence in multiple plates.

Soft robots employing soft polymer materials such as gels and elastomers have various advantages such as compact, lightweight, and silent motion. Recently, biomimetic structures driven by pneumatic control have been attracting attention though various driving sources have been proposed. In this study, we have fabricated auxetic channel structure in elastomer using 3D printer and aimed to develop a novel wearable device with liquid metal inflow, and cylinder-shaped soft robot with an armored (exoskeleton-like) auxetic structure with a negative poisson's ratio that placed around bellows-typed tube. We have investigated the structural variability and walking performance of the armored cylinder structure.

Active matter is a materials and objects that have autonomous motion mechanisms and interact with each other. For example, animals, living cells, and bacteria are classified as active matter. The dynamic performance of various animals and insects that walk and propel themselves on the water surface is mainly related to the surface tension.

In this study, the elastomeric film containing liquid metal was floated on the water surface, and the Marangoni propulsion induced by near-infrared light (NIR) irradiation was verified by kinetic analysis.

In this study, we investigate the helix formation mechanism of cucumber tendrils using elasticity theory on Riemannian manifolds and the Material Point Method (MPM). During growth, cucumber grows an organ called a tendril, which forms a characteristic helical structure. This helical structure is expected to be applied to biomimetic technology such as torsion-free spring design, but its formation mechanism has not been clarified yet. We developed a mechanical model that takes into account the original geometry and internal organization of the tendril as well as its contact with the support. We then applied non-uniform axial contraction to the internal part of the tendril and performed a quasi-static dynamics analysis using the finite element method to confirm the formation of spiral and inverted helical structures.

Tree branches are deformed with large deflection under mechanical loads such as wind, rain and snow weight, and also deformed by own weights including fruits. Stress and strain distribution characteristics under loading are important information to evaluate the mechanical strength of tree branch formations. In this study, a numerical analysis method of large bending deformation was proposed and used for evaluating the deformation behavior of branch focusing on the base angle and diameter changes. The branch model was created as a curved cantilever of tapered shape with a constant elastic modulus. As the simulation results, the large bending deformation for downward under the distributed load condition reduced the bending moment applied at the base end of branch model. And the base angle for upward directions made severe bending strain on the tip side. This simulation was available to estimate the large deflection geometries of cantilever and could be used to predict the failure location on the tree branch.

Plant materials sometimes have high mechanical strength in its outer structure which is derived from the cell wall at the microscopic level. Since the deposition of the cell wall is thought to be induced by the microtubule alignment inside cells, it is important to know the microtubule dynamics from the viewpoints of both plant and materials sciences. To investigate the microtubule dynamics in silico, we constructed an agent-based model of microtubule that simulates the growth and shrinkage of microtubules with microtubule-microtubule interactions. In addition to this initial setup, we further considered the condition of the edge-catastrophe that microtubule is to shrink when it hits the edge of the geometry, or the condition of the tension-catastrophe that cell surface tension induces the shrinkage. By introducing these conditions to our model, we aim to elucidate how the ring-like microtubules are formed during plant zygote development. Our formulation suggests a control parameter of the orientation order from the collective behavior of microtubules. It would greatly help to test some hypotheses on the microtubule ring formation that have been experimentally difficult to investigate.

Plant roots have three-dimensional branching structure to mechanically support the above-ground portion of the plant. In addition, it is probable that each root forms an optimal morphology for the environment in which it is placed. If we can identify and analyse this three-dimensional morphology and physical properties such as rigidity and stress profile, it would be possible to propose new materials that take advantage of the branching structure. However, since it is difficult to evaluate the three-dimensional morphology of root systems in soil, we intend to capture and quantify the morphology using hydroponics. In this study, we present the results of image analysis of root morphology in 2D images we have been working on, as well as a 3D stereo imaging method and a 3D morphology reconstruction method using the direct linear transformation method (DLT).

To elucidate the pull-out mechanisms of plant roots from soil, we conducted tensile experiments of model root structure fabricated with 3D printers. We found that the maximum pull-out force is dependent on the branch angle and the bending stiffness of the roots. We inferred that the motion and deformation of the root inside the soil plays an essential role in determining the maximum pull-out force.

Crack nucleation and propagation in SrTiO₃ single crystal were observed at the atomic level by in situ scanning transmission electron microscopy (STEM) loading experiment with a MEMS loading device. It was found that a crack initiated from the bottom of a notch and propagated along the {110} plane. The fracture toughness for the {110} crack was estimated to be K_IC=1.4MPam_1/2 based on the measured crack opening displacement. In addition, an atomic structure model of the {110} fracture surface was constructed based on the experimental observations, and first-principles calculations showed that its cleavage energy was γ=3.8Jm^-2. From the relationship of K_IC=(2γE)_1/2 (E: Young’s modulus), the fracture toughness is estimated to be =1.4MPam, which agrees well with the experimental value.

Lap joints were prepared using epoxy adhesive and aluminum plates, and the properties of high-temperature strength were studied. Tensile test and aging test were performed at high temperature. The effects of test temperature were systematically investigated. The obtained conclusions were following. When the specimen was exposed at temperature of 135℃, the strength decreased significantly. The adhesive changed its chemical structure by oxidation. The relationship between test temperature and tensile strength could be expressed using the Arrhenius equation.

In recent years, multi-material design has been applied in many industries. Among various methods of joining dissimilar materials, adhesive bonding has the advantage of being able to combine materials with dissimilar properties and relatively low weight. The strength of the adhesive structure is not only influenced by material properties but also structural factors such as thickness of adhesive layer. As a result, A co-design process including both material and structural factors is necessary. Experiments using pipe specimens with inclined surfaces bonded by epoxy adhesive were performed, whereby multiaxial stress states were realized simply by conducting a uniaxial tensile test. The failure function of the epoxy adhesive, expressed by the mean stress and octahedral shear stress, was then obtained from the experimental data and compared with that of acrylic adhesive previously reported in the literature reflecting material factors. The obtained failure functions of both adhesives were then applied to the shape optimization of the adhesive layer under different loading conditions. The optimization object is the strengthening of jointed structures reflecting structural factors. The optimal shape for different loading conditions differed for the different adhesives because of the driving force generated by the applied stress. The final shapes were thus optimized numerically to attain the highest mechanical integrity of the adhesive layer and found to be strongly dependent on the initial shapes before optimization.

In an adhesive joint under certain conditions, the adhesive joint strength is larger than the bulk adhesive strength. In this study, the fracture of adhesive joints by using the elastic-plastic behavior is considered. Then, the validity of evaluating the adhesive strength by two ISSFs based on the elastic analysis is discussed. Even when the butt joint strength is larger than the bulk adhesive strength, the small-scale yielding is occurred. Therefore, it is shown that the ISSF strength evaluation method is appropriate.

In this study, the intensities of the singular stress field (ISSFs) at the interface corner and interface edge in 3D BJ models with similar/dissimilar adherends are calculated by changing the adhesive layer thicknesses by the proportional method. The differences between the ISSFs for the 3D BJ models with similar/dissimilar adherends are discussed. The ISSF for the BJ with dissimilar adherends is larger than that for the BJ with similar adherends. The differences between the ISSFs for the 3D BJ models with similar/dissimilar adherends increase as the adhesive layer thickness decreases. When the adhesive layer thickness is 0.05 mm, the ISSF at the interface corner in the BJ with dissimilar adherends is about 1.7 as large as that for the BJ with similar adherends. Then, the remarkable differences between the singular stresses at the interface corner and along the interface edge in the BJ with dissimilar adherends are found.

The rolls are classified into two types; one is a single-solid roll, and the other is a shrink-fitted sleeve roll consisting of a sleeve and a shaft. Regarding the shrink-fitted sleeve roll, the interfacial creep sometimes appears between the shaft and the shrink-fitted sleeve. In previous studies, the numerical simulation was performed to realize the interfacial slip.

However, there are no empirical studies on interfacial slip or studies on the inner surface stress of the sleeve caused by sleeve slip under actual rolling conditions. Therefore, in this paper, we perform a verification test of interfacial slip using the miniature rolling mill shown in Fig.1 (b), reproduce this interfacial slip experimentally, and consider the relationship between the damage caused and the amount of slip. In addition, for the shrink-fitted bimetallic roll of an actual rolling mill (Fig.1 (a)), the inner surface stress of the sleeve caused by sleeve slip under actual rolling conditions is obtained by numerical simulation, and its effect on fatigue fracture is clarified.

The pitch difference nut can be used in automobiles and other industries to improve anti-loosening and fatigue strength with low cost. In this paper, based on the suitable pitch difference α experimentally obtained previously for JIS M12 and M16, the suitable pitch difference is discussed for other bolt nominal diameters. Here, the overlap thread length is calculated from the suitable α obtained for M12. Then, the same value of is assumed to estimate the suitable α for other diameters. The validity of this theory is confirmed through calculating the prevailing torque for other diameter by applying FEM analysis.

In resistance spot welding of Fe-Al dissimilar materials, it is known that intermetallic compounds are formed at the joining interface, and as these compounds thicken, joining strength in the peeling direction decreases. the formation of intermetallic compounds must be suppressed in order to improve joint strength, and one of the control methods is to control the temperature field. Therefore, In this study was to improve joining strength by controlling the temperature field. To control the temperature field, we focused on the current path, make a hole in a polyimide film, known as an insulator, and performed welding with the polyimide film between the electrode and the plate. As a result, it was found that controlling the current path between the Al and the electrode was effective in improving joining strength in the peeling direction. In addition, it was found to affect the formation state of intermetallic compounds, which is a joint property, and the properties of melting zone.

The 90° peel test has been commonly used to evaluate interfacial strength of rubber/metal dissimilar materials joint. However, peel strength obtained with this testing method might be affected by peel angle between metal and rubber, mechanical properties of the rubber and specimen geometry. In this study, a peel test was conducted by applying a shear force to induce delamination at interface between rubber and metal. In the present study, shear force peel test was carried out with different tool height (distance from the interface) and its effect on shear strength was investigated. In case of higher tool height, bending moment working on rubber became large and resulted in occurrence of normal stress at the interface to induce delamination. In case of that tool height was low, normal stress acting at the interface became relatively low, then crack was initiated and propagated inside rubber but not delamination occurred at the interface.

Carbon nanotube (CNT) is tubular nanofibers made of cylindrical graphene sheets. CNT is thought to have higher tensile strength and elastic modulus than those of conventional carbon fibers. Its ideal mechanical properties are estimated to be about 1 TPa for Young's modulus and 10 GPa or more for tensile strength. However, intrinsic excellent mechanical properties of CNTs have not been fully utilized owing to defects of graphene, catalysts left in the core of CNTs and kinks of graphene layers. Decreasing the diameter of CNT and annealing of CNT at high temperature are thought to be useful to improve the tensile properties of CNT. In this study, we investigated the effects of annealing and diameter of CNTs on the tensile properties of CNTs by conducting tensile tests of as-produced and annealed CNT untwisted yarns.

CNT spun yarn is expected to be used for high-strength wire rods, but at present, it does not reach the mechanical strength of carbon fiber, which has already been put into practical use. Recently, it has been proposed that an electric heating method with tension is effective as a method of increasing the strength of CNT spun yarn. In this study, in order to make this method more practical, we introduced a new process to increase the density by passing the CNT spun yarn over ethanol absorbent cotton before heating. By introducing this process, we succeeded in stabilizing the high-temperature heat treatment (3000 K) and succeeded in significantly increasing the strength to a maximum tensile rupture stress of 2.61 GPa (untreated: 1.31 GPa).

In this study, we design novel stable wavy graphene sheets (GSs) using a technique based on origami and kirigami to control the exchange of carbon atoms and generate appropriate disclinations. The impact characteristics of these GSs are evaluated using molecular dynamics (MD) simulation, and the accuracy of the simulation results is verified via a theoretical analysis based on continuum mechanics. In the impact tests, the C60 fullerene is employed as an impactor, and the effects of the different shapes of wavy GSs with different disclinations, different impact sites on the curved surface, and different impact velocities are examined to investigate the impact characteristics of the wavy GSs. We find that the newly designed wavy GSs increasingly resist the kinetic energy (KE) of the impactor as the disclination density is increased, and the estimated KE propagation patterns are significantly different from that of the ideal GS. Based on their enhanced performance in the impact tests, the wavy GSs possess excellent impact behavior, which should facilitate their potential application as high-impact-resistant components in advanced nanoelectromechanical systems.