This study deals with the surface modification of raw powder to fabricate partially stabilized zirconia (PSZ)-pure titanium (Ti) composites via spark plasma sintering (SPS) technique. We tried to fabricate the PSZ-Ti composites with high fracture toughness and wear resistance via powder metallurgy technique. The composites, however, exhibited low fracture toughness due to the formation of brittle reaction products. The reaction products were formed because oxygen atoms in PSZ phase diffused into Ti phase during sintering. Hence, it is expected that the PSZ-Ti composites without no reaction products can be fabricated if the oxygen diffusion is suppressed. In this study, the technique of surface modification of raw powder using yttria is proposed to suppress the oxygen diffusion. The yttria coating is formed around Ti powder by Sol-Gel method, and the thickness and atomic concentration of the coating are evaluated using a scanning electron microscope and electron probe micro analyzer. Then, the PSZ-Ti composites are fabricated using modified Ti powder and PSZ powder via SPS, and the reaction products are investigated by X-ray diffraction analysis. As a result, the yttria coating formed by Sol-Gel method seems to be intact, and is evenly distributed around a Ti particle. The thickness of the coating is several micrometers. No reaction products are detected in the composites, irrespective of Ti volume fraction. Hence, it is expected that the composites exhibit high fracture toughness and wear resistance.

Glass fiber reinforced plastic (GFRP) is used for a variety of products in housing applications because GFRP is high specific strength material with waterproof, corrosion-resistant and dimensionally stable abilities. Cellulose nanofibers (CNF) have recently been attracted as a prospective material because of its high stiffness and high strength. In addition, CNF is an environmentally friendly material because CNF is extracted from plants. Therefore, CNF is expected to be alternative material for glass fiber.

In this study, a new technique is used to fabricate a hybrid preform composed of CNF and glass fiber; and the mechanical properties of epoxy-based composite materials using the hybrid preform were evaluated. A hybrid preform was fabricated by spraying CNF suspension on glass fiber non-woven fabric, resulting in highly densified web-like network structure that filled the gaps among glass fibers. Epoxy-based composite material was fabricated by a hand-layup method. Tensile tests were conducted to evaluate the tensile properties of composite materials.

An experiment was conducted to establish a test method to replace the high-pressure H₂ gas test for steel used in the hydrogen station. In this experiment, Continuous cathodically charge was adopted as the test method. All the tests were conducted at room temperature. The type of steel used was SCM435 steel. Two types of solution, 1 N NaOH + 3 g/L NH₄SCN and 3％ NaCl, were used, and the test was conducted at a constant potential and a constant current. The test was performed with displacement control, and the strain rate was adjusted to 5.0x¹⁰-5 s^-1. When continuous cathodic hydrogen charging is performed from the stress-stroke curve and fractured by the SSRT test, the relative elongation becomes shorter. In addition, the stress behavior of the constant potential test almost agrees with the current density of 600 A/m². The diffusible hydrogen content was higher in the constant-current test than in the constant-potential test, which is thought to be have an effect by the charge time. Moreover, the fracture surface after the test was observed using SEM. As a result, a quasi-cleavage surface was observed on the outer periphery of the fracture surface, while dimples near the center of the fracture surface.

For a structure design in consideration of hydrogen embrittlement, it is necessary to establish an analysis technique to simulate hydrogen-related crack propagation. However, crack propagation cannot be fully expressed by a conventional mechanical analysis, because of uncertainty of microscopic mechanisms of the hydrogen-related crack propagation. Therefore, an analysis of hydrogen embrittlement has been recognized to be difficult. In this study, we newly proposed a mechanism-based analysis model of crack propagation in consideration of hydrogen embrittlement through microstructure observations of a cracked material pre-charged with hydrogen gas. The fracture toughness test of Ni20Cr with hydrogen gas charging was performed, and the specimen was observed by electron channeling contrast imaging (ECCI) and electron backscattered diffraction (EBSD) technique in a scanning electron microscope. The entire fracture surface showed intergranular fracture, and the cracks propagated along grain boundaries. Small chinks along grain boundaries ahead a crack tip were observed, and deformation localization associated with the small chinks was observed in the grain on one side of the grain boundary. From the above facts, the following new model of crack propagation in hydrogen embrittlement of Ni20Cr was proposed; The crack propagation of some cracked materials with hydrogen gas charging occurs via repetition of the crack generation.

In this study, we show the relation of corrosion thinning threaded parts to hydrogen penetration behavior. Specimens are bolts and nuts, that were actually used as threaded parts for sprinkler pipes in the Kashima Seaside Industrial Area. Corrosion studies typically were done with electrochemical measurement systems. Polarization and corrosion rate measurement was done, TDA (Temperature Desorption Analysis) was also used to measure the hydrogen evolution rate. For these reasons, hydrogen generation is dominant in the bolts on the inside of the externally exposed threaded parts, and corrosion of the outer surface of the member and the outer surface of the nut proceeds. Corrosion potential does not change with the bolts and nuts of the thinning threaded parts that have undergone corrosion. The corrosion potential is not a factor that causes the nut to corrode preferentially. There is no relationship between hydrogen penetration and the corrosion potential.

The operating temperature of advanced thermal power plants is increasing continuously to improve their thermal efficiency to reduce the emission of CO2. Under the creep and creep-fatigue conditions at elevated temperature, however, the effective lifetime of heat-resistant alloy such as Ni-base Alloy 617 which has high strength and good corrosion resistance at about 750oC was found to decrease drastically. Main reason for this short lifetime is attributed to the change in the crack initiation and propagation paths from trasgranular one to intergranular one. It is, therefore, important to clarify the criteria of the grain boundary cracking quantitatively. In this study, electron back-scatter diffraction (EBSD) was applied to the analysis of the degradation process of the quality of grain boundaries in the alloy. The change in the crystallinity of grains and grain boundaries were continuously monitored during creep and creep-fatigue tests. It was found that accumulation of vacancies and dislocations degrades the crystallinity of grain boundaries and thus, their strength. The accumulation occurred around the specific grain boundaries which consisted of grains with large difference of Schmid factor and initial crystallinity which was defined by image quality (IQ) value obtained from the EBSD analysis.

Thermal power generation is required to be highly efficient due to concerns such as environment and energy problems. In order to improve the efficiency, it is essential to increase operating temperature. In addition, since thermal power generation is expected to control its output to be coexistent with renewable energies, not only creep but also creep-fatigue load is applied to its component because it is required to assure the safe and stable energy supply under random output of the renewable energies. For non-destructive inspection of actual plants, it is indispensable to develop a new technology for observing the degradation of materials used under the harsh conditions in the atmosphere. In this research, the reflection spectrum of the visible light was applied to the observation of micro texture and precipitates with different compositions in Ni-base superalloy (Alloy 617). A creep-fatigue test was applied to a small specimen of Alloy 617, and the reflectance spectrum was measured by irradiating white light on the as-received and damaged specimens. Under the creep-fatigue load, fine intergranular cracks appeared around the center region of the specimen before the final fracture. It was confirmed that the surface roughness in the damaged area increased and the growth of the surface oxide was observed by the spectrum analysis. In addition, the distributions of fine carbides and nitrides were successfully visualized by the spectrum analysis.

La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ(LSCF), which is a mixed conductive oxide, is expected to be used in the air electrode of oxygen separation membranes and solid oxide fuel cells. For use in such products, it is necessary to improve the oxygen ion conductivity of the material. Therefore, the aim of this paper is to develop a method to improve the oxygen ion conductivity of LSCF. Mechanical stress is applied to the material to improve the oxygen ion conductivity. In this paper, in order to evaluate only oxygen ion conduction, it was combined with yttria−stabilized zirconia(8YSZ), which has only oxygen ion conductivity. A multi-layered specimen was made, and the conductivity was measured while stress was applied. By continuing this study, the influence of stress on the oxygen ion conductivity of LSCF can be clarified.

Polycrystalline materials in nano-scale have been found to show the drastic variation of both mechanical and electrical properties strongly depending on the quality of grain boundaries. As for the electroplated copper thin-film interconnections applied to the semiconductor devices, the reliability of the fine interconnections should vary depending on the order of the atom arrangement around grain boundaries. In this research, in order to clarify the effect of the mismatch in the crystallographic orientation between two grains, of which a grain boundary inbetween is consisted, on the strength of the grain boundary, molecular dynamics analysis was applied to the deformation analysis of the bi-crystal structures with various combinations of crystallographic orientations. It was found that the effective strength and fracture mode of bicrystal structures varied drastically depending on the combination of the crystallographic orientations of the two grains in the bicrystal structures.

In this study, a shape-memory polymer (SMP) with large deformability and high biodegradability was developed. We made biodegradable shape-memory polymers by blending two polymers, poly(L-lactide) (PLLA) and copolymers composed of _{D, L-}lactide and ε-caprolactone (PLCL). We attempted to improve the mechanical properties of the SMP by chemically combining the PLLA and PLCL using isocyanate. It is known that mechanical properties could be significantly improved by chemically linking two different types of molecular chains, occasionally resulting in microphase separation, which could not be realized by simply blending (i.e. not chemically linked) polymers. We used isocyanate to bond the molecular ends of hydroxyl groups of PLLA and PLCL to prepare the shape-memory polymer with a high molecular weight and high mechanical properties (PU(PLCL/PLLA)).

Molecular weights were measured by the high performance liquid chromatography (HPLC). The molecular weight was increased by chemically bonding the two polymers, PLCL and PLLA. PU(PLCL/PLLA) successfully exhibited shape-memory behavior at 80°C. The shape-recovery ratio was measured by tensile testing and calculated through the applied mechanical strains and the recovered strains measured by the thermal mechanical analyzer (TMA). In fact, the ratio was improved by 14% as compared with our previous sample (the blend of PLCL/PLA). Additionally, it was confirmed that the maximum strain and the maximum stress were 2.5 and 4.4 times higher, respectively than those of the PLCL/PLA blend.

It has been reported that macromolecular contrast agents could be uptaken selectively by lymphatic vessels through subcutaneous injection to perform high-resolution imaging of the lymphatic system. This is because particles larger than 3 nm in diameter can be drained by lymphatic vessels, but are difficult to penetrate through venular endothelia, resulting in selective lymphatic drainage. Particles smaller than 10 nm in diameter would be uptaken by vessels and filtrated in a kidney for the final excretion. Therefore, fabricating contrast agents with 3–10 nm in size could be a major pathway to address this problem.

Previously, we fabricated MRI contrast agents of a few nanometers in diameter with the condensation of gadolinium complexes and ND particles (Gd-DTPA-ND). The primary particles of these contrast agents possessed a diameter of approximately 5 nm, which was considered to be an adequate size for contrast agents to be selectively uptaken by the lymphatic vessels before the excretion in a kidney. However, these particles could form tight aggregations in water, resulting in micro-scale aggregates. The aggregates were too large to be well uptaken and excreted, and the agents could not be used for lymphatic imaging. In this work, the dispersity of the Gd-DTPA-ND particles was analyzed, which was improved by employing ND particles with abundant hydrophilic carboxyl groups on their surface by a pre-oxidation step (CND). The surface carboxyl groups of the CND particles are expected to introduce negative charge on the particles’ surface, inducing the electrostatic repulsion that enables the gadolinium-complexed particles (Gd-DTPA-CND) to disperse in aqueous solution.

The dispersity of the fabricated Gd-DTPA-CND particles in distilled water was evaluated by the transmission electron microscopy (TEM). TEM results revealed that Gd-DTPA-CND particles possessed a hydrodynamic diameter of around 4–5 nm, which did not form aggregation, suggesting the improved dispersity in distilled water. Furthermore, the T-1 weighted images of the Gd-DTPA-CND particles in distilled water presented strong contrast, confirming the high MRI visibility of the particles. The new Gd-DTPA-CND particles were, therefore, expected as excellent MRI contrast agents for the achievement of the selective MR imaging of the lymphatic system.

Turbine blades are deformed and cracked during operation due to stresses caused by centrifugal force and bending force. In order to prevent possible failure, it is important to predict the remaining lifetime based on the estimation of the inelastic strains in the entire region. Nondestructive detection of the cracks in the blade is possible, but it is necessary to evaluate the residual lifetime before the cracking due to its higher crack growth rate. The authors have proposed a method to estimate three-dimensional inelastic strains by the inverse analysis using the contour changes of the blade. This method makes it possible to estimate inner inelastic strains for whole structure even when only the displacements at the corner of the blade are measurable. In this study, numerical simulations using a simple FEM model were carried out to prove the effectiveness of the proposed method. As a result, it was possible to estimate inelastic strains with relatively high accuracy by the iterative calculation based on this method.

In steel products, the tensile strength and fatigue limit characteristics may be degraded by a punching process, and the extent of the decrease differs depending on the steel type. During static tensile loading, unstable brittle fractures can occur in the area of elastic deformation despite ductile materials. A crack along with the place with the highest shear stress first initiates when tensile loading is applied to the punched material. Furthermore, this crack initiated when a load of about two thirds of the tensile strength is applied, which is considered to charge in the tensile strength characteristics of the punched material. In the case of drill holed materials, the shear crack does not initiate. Therefore, the cause of the shear crack is considered to be in the shear-affected-zone (SAZ) by the punching process. In this study, observation of the SAZ and intermittence tensile tests were conducted on dual phase steel and precipitation harden steel to compare the two tests quantitatively. It was shown that plastic strain in the SAZ might be the cause of deterioration of the strength characteristics.

We focused on dynamic strain aging that can effectively raise the non-propagation limit of a fatigue crack. However, in the supersaturated carbon steel, carbides are formed at high temperature over time, and the content of solute carbon is decreased, thereby reducing the contribution of strain aging and the non-propagation limit of a fatigue crack. From these results we confirmed that increasing the test time with decrease of the frequency produced the deterioration of the fatigue characteristics. In addition, we propose the method to predict the frequency dependence of the fatigue characteristics by a simpler hardness test as an alternative test of a fatigue test. In the fatigue test using Fe-0.016C-1.0Si alloy, it was found that the fatigue strength at a frequency of 30 Hz is higher than the fatigue strength at a frequency of 10 Hz. Next, when Fe-0.016C-1.0Si alloy was pre-strained at 8 % and a hardness test was conducted at 433 K, the hardness increased until 2 hours from the start of the test. In the 0 and 4 % pre-strained materials of the previous research, the hardness starts to decrease 24 hours and 6 hours after the start of the test respectively. From this result, it was found that the time when the hardness starts to decrease is faster as the pre-strain is larger.

To investigate the initiation and propagation processes of internal fatigue crack in high strength metallic materials, high resolution and non-destructive observation technique was proposed. The opening and closing behaviors of fatigue cracks in Ti-6Al-4V, and the non-metallic inclusions in SNCM439, which are regarded as a potential crack initiation site, were observed by synchrotron radiation CT (SR-CT) at SPring-8. To ensure a sufficient X ray transmission, fatigue specimens with a small diameter were designed, and a tensile loading jig was newly developed to measure the CTOD during SR-CT. In Ti-6Al-4V, micro CT and nano CT with a resolution around 1 μm and 200 nm, respectively, were used to observe internal cracks. As a result, it was clarified that surface cracks and internal cracks showed different behaviors. The crack tip of surface cracks had a sharp shape and the CTOD was changed by the tensile load. On the other hand, the shape of crack tips of internal cracks was blunted, and the tensile load did not affect CTOD. This crack blunting was explained by the vacuum-like environment around the internal crack. In SNCM439, small non-metallic inclusions with the size around 8 μm in diameter were clearly observed. Accordingly, it is expected that we can observe the initiation and propagation of internal cracks in high strength steel by repeating fatigue tests and SR-CT alternately.

In recent years, it has been revealed that in high strength steel, fracture occurs from non-metallic inclusions inside of the material in the very high cycle region. However, because of the difficulty in directly observing the internal fatigue process, its mechanism is still unknown. Subsequently efforts are being made for better understanding of fatigue crack initiation and propagation. In this study, we have tried to estimate life in this subsurface fatigue region using crack growth rates measured in a vacuum environment and compare it with actual life found out in subsurface fractures in fatigue test to better understand fatigue crack properties.

In this study, we conduct isogeometric analysis to obtain the internal stress field around wedge disclination. Our formulation is based on the continuous theory of disclinations developed by Yavari and Goriely. In this framework, distributed disclinations are identified as the curvature tensor in a Riemann manifold. Riemann metric in the manifold is determined by using Cartan structural equation in differential geometry. Elastic deformation is obtained so as to minimize the strain energy functional by numerically solving weak form of nonlinear stress equilibrium equation. The distribution of the second Piola-Kirchhoff stress tensor around the disclination, which is obtained by the numerical analysis, agreed qualitatively well with the previous study reported by Lazar.

External force on the skin surface consists of pressure and shear force. To reduce the resistance to shear force on the skin surface, a gel-like material layer such as synthetic rubber is added on the polyurethane foam layer. It is important to reduce the resistance for bony prominences which deforms not only the gel-like material layer but also the polyurethane foam layer. The aim of this study was to evaluate the relationship between the shear force and shear displacement under loading conditions of fully-reversed cyclic shear displacement with various constant compressive displacements using a half-cylinder. Shear modulus was estimated by formulating an equation of the balance of shear force for a nonuniformly deformed synthetic rubber layer. A block of polyurethane foam was also deformed by a half-cylinder and was recorded on video under microscope. The digital image correlation analysis was conducted to obtain the strain distribution. Mean slopes of the shear force-displacement relationship were 0.46-0.63 N/mm and the corresponding shear modulus were 1.7-3.4 kPa, which were larger than the values of the cases of uniform shear deformation. The normal strain component in the direction of compression was concentrated near the half-cylinder which occurred due to the buckling of open cells of the foam. The proposed estimation method of shear modulus may lead to a better design of multi-layered mattress.