This paper reports a development of space telescope mirror made by light and thermally stable CFRP. We first compare thermal stabilities of a mirror made by CFRP with a conventional that made by glass material. The superior point regarding the thermal stability of the CFRP mirror to the glass mirror is described. One of the most critical issues for CFRP mirror is the mirror-surface roughness deterioration induced by "fiber-print through". We made a prototype mirror consisting of only CFRP with a gel-coating on the mirror surface, addressing the issue. The gel-coated mirror-surface roughness was 20 nmRMS just after fabrication. Durability of the surface roughness under various hostile conditions is examined in the present study.

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It is well known that carbon nanofillers (CNFs) enhance the stiffness, electrical conductivity and thermal conductivity of polymers. Alignment of carbon nanofillers in polymer is expected to increase the performances in the aligned direction. Several papers have reported that applying AC electrical field to liquid suspension including CNFs make CNFs align in the electrical field direction. In this paper, the microscopic structure of carbon nanofiller/epoxy composites was controlled by using AC electrical field, i.e. carbon nanofillers were aligned unidirectionally in resin. The alignment of CNFs was in-situ observed during fabrication by using an optical microscope, and the effects of applied voltage, frequency and the weight fraction of CNFs on microscopic structure were investigated. Furthermore, thermal conductivity, electrical conductivity and mechanical properties of composites were measured. The results show that CNFs in uncured epoxy resin align in the AC field direction and form a chain-like network, and that the applied voltage and weight fraction affect the morphology of the chain-like network. Unidirectional alignment enhances the thermal and electrical conductivities, and affects mechanical properties.

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It is revealed that amorphous metals have many “unstable” atoms even at the equilibrium state, by local lattice instability analysis (LLIA) which discusses the positive definiteness of atomic elastic stiffness coefficients, B^α_ij. We have explored for relationships between the deformation and these unstable atoms in inhomogeneous or disordered structure. In the present study, we have discussed the changes in unstable atoms of det B^α_ij < 0 in four monatomic amorphous metals, Ni, Cu, Zr and Al, during uniaxial tension. First, we have separately evaluated the atomic stress on stable and unstable atoms. Unstable atoms feel hydrostatic compression in the amorphous Ni, Cu and Zr, while they feel hydrostatic tension in the Al at the initial state before loading. Under the uniaxial tension, it is considered from the comparison of stress components on each stable and unstable atoms that the local stress reduction occurs by the transition of stable → unstable in Ni, Cu and Zr, and unstable → stable in Al. Then we have picked up atoms that have actually switched between stable and unstable. Even at the equilibrium state, so many atoms switch their stabilities while the ratios of the negative and positive change nearly balance at each moment. Both positive and negative switching are activated by rises of the structural relaxation under the tension. Moreover, there is no difference in the stress between positive and negative switching atoms while constant detB^α_ij < 0 and detB^α_ij > 0 atoms showdifferent stress. We have concluded that the stress relaxation is not caused by a straightforward image of “stabilization” or “destabilization”, but by “shuffle of atomic arrangement” which involves positive and negative switching simultaneously. In fact, we have observed many incidences of positive and negative stability-switching at the locally deformed area.

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This paper presents an experimental investigation into the effects of water temperature and immersion times on the tensile strength degradation of plain-woven glass fiber reinforced plastics (GFRP) laminates. GFRP specimens were tested as-received and after hydrothermal aging in deionized water at 40 °C, 80 °C, 95 °C to evaluate their tensile properties. The strength and rupture strain had a tendency to decrease drastically in the early stages and to saturate toward certain strength with long-term aging, regardless of the water temperature. The fracture surfaces were examined by scanning electron microscopy (SEM) to study the fracture mechanisms of woven GFRP after hydrothermal aging. While the strength of the glass fiber decreased, the fracture surfaces of the E-glass fibers flattened, and the mirror zones on the fracture surfaces enlarged. Interfacial degradation was confirmed by fiber pull-out, and the debonded fibers showed no resin matrix adhesion to the fiber surfaces. These experimental results suggest that the degradation in the strength of woven GFRP is dominated by degradation of their fiber reinforcement and the fiber/matrix interface.

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A large number of tiny particles, which is less than 200 µm in diameter, hit the specimen simultaneously for the surface modification in Fine Particle Peening (FPP) treatments. For the fatigue resistance, it is important to induce the higher compressive stress at the surface. In FPP treatment, the induced compressive residual stress is influenced by many parameters such as material properties, particle size, nozzle distance, air pressure and so on. We focused on the material hardness and investigated the effect of hardness ratio between a shot particle and a specimen on the plastic dissipation energy and the compressive residual stress in the specimen. FPP treatment is very complex and it is quite difficult to observe the local phenomena in experiments. Thus, numerical simulations were employed in this study. The obtained results show that the hardness ratio is the dominant parameter for the plastic dissipation in the specimen. As the hardness ratio increases, the kinetic energy of shot particles effectively transfers into the plastic dissipation in the specimen and the higher compressive residual stress is induced in the specimen.

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We measured residual stress relaxation in epoxy-based CFRP laminates and cyanate-based CFRP laminates. We estimated the residual stress in symmetric cross-ply laminates by measuring the curvature of unsymmetric cross-ply laminates and investigated the relaxation of the residual stress by measuring the curvature of unbalanced laminates in a nitrogen environment. Our experimental results demonstrated that the residual stress in both kinds of laminate can decay by approximately 15% after 500 hours at 40°C. The stress relaxation can be modeled by the power law model. Viscoelastic parameters were obtained by a quasi-static tensile test to predict stress relaxation. The validity of the prediction is discussed.

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This paper suggests a theoretical model to estimate Young's modulus of green composites reinforced by natural fiber twisted yarns considering a migration structure. First, we made fully green composites using biodegradable resins and ramie twisted yarns to develop a biodegradable material, and then investigated the effect of yarn twist on mechanical properties of green composites. Next, the migration structure of twisted yarn was taken into account and the relation between twist angle and Young's modulus was discussed by proposing a new reduced stiffness for twisted yarn, in which a twisted yarn was regarded as an orthotropic material with an off-axis angle. The proposed reduced stiffness was verified through comparison between theoretical and experimental results.

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Many kinds of optical glass devices are needed in various fields such as optics, biotechnology, medical care and so on. If an optical device such as an aspheric lens does not have a simple shape, and/or its size is micro-/nanometer scale, press molding should be carried out at a higher temperature than the glass transition temperature (T_g) to reduce cost and increase productivity. However, the most suitable conditions for glass molding are generally determined by performing many experiments. Consequently, it is useful to be able to predict the most suitable molding condition by numerical simulation. Press molding experiments and numerical simulation using finite element analysis, in relation to micro press molding of the borosilicate glasses Pyrex and D263, were carried out. Thermo-viscoelastic properties of the glasses were estimated using unidirectional compression creep testing according to traditional thermo-viscoelastic theory. Glass micro press molding was carried out with a glassy carbon die with a line and space pattern machined by a dicing saw. The optimum molding temperatures for accurate transcription of the die profile to the glass were investigated. Numerical simulation of micro press molding of the glass was carried out by the finite element method using universal FEM code (ANSYS ver.11.0). Experimental and numerical simulation results for the cross-section shape and the height of the groove profile were in approximate agreement.

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Effects of multiple overloads and hydrogen on high cycle fatigue limit was examined to establish a criterion which assesses whether hydrogen utilization machines can be used after large earthquakes. Test materials were SUS304 and SUS316L. The test environments were 0.6MPa hydrogen gas and air. Hydrogen pre-charged specimen was used for in-hydrogen gas test. The reduction of fatigue strength was caused by overloads in both materials. The cause of the reduction was small cracks formed by overloads. In SUS304, the reduction of fatigue limit was enhanced by hydrogen since propagation of small cracks during overloads was accelerated due to hydrogen. In SUS316L, there was no reduction of fatigue limit due to hydrogen. Maximum overload amplitude which caused no reduction of fatigue limit was 0.5σ0.2 for SUS304 and 0.75σ0.2 for SUS316L. These values were regarded as the upper limits of overload amplitude below which the continuous use of components are allowed after earthquakes.

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PbTiO₃ and Pb(Zr,Ti)O₃, have been applied to various actuators and sensors due to their high piezoelectric and dielectric properties. However, the usage of lead-based materials is prohibited by Restriction of Hazardous Substances. In this study, a new biocompatible MgSiO₃ thin film is generated on the Au/SrTiO₃(110) substrate, which is determined on basis of our three-scale analyses, by using the radio-frequency magnetron sputtering method. The crystallographic orientation of thin film was measured by using X-ray diffractometer and the displacement-voltage curves were measured by using the ferroelectric character evaluation system, respectively. An optimum condition, which leads to the highest piezoelectric property, is determined through the experimental design algorithm and the analysis of variance table schemes. The peak of MgSiO₃(111) crystal was obtained and its intensity increased with the substrate and the post-annealing temperatures. MgSiO₃ thin films showed good piezoelectric properties, because they yielded the typical butterfly-type hysteresis curves. Additionally, the substrate temperature was significant at 1% level for piezoelectric strain constant d₃₃. Optimum generating condition was obtained as T_s= 300 °C, T_a= 650 °C and f_O2= 3.0 sccm, and its piezoelectric strain constant was d₃₃= 346.7 pm/V, which was higher than the values of the existing piezoelectric BaTiO₃.

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In high-temperature gas-cooled reactors that use helium gas as a coolant, impurities in the helium coolant, such as H₂, H₂O, CO and CH₄ molecules, react with the component materials of the reactors such as its heat transfer tubes. Theses reactions degrade the mechanical properties and shorten the lifetime of the components. In this study, tight-binding quantum chemical molecular dynamics simulations were employed to understand the chemical reactions caused by impurities (CH₄ and O₂) on Ni-Cr alloy surfaces. The molecules of the impurities were dissociated on the surface and dissociated oxygen and carbon atoms preferentially bonded with chromium atoms. Cr-C bonds were maintained during the simulation and consequently, chromium atoms were trapped by carbon atoms after the formation of Cr-C bonds. This result suggests that the carburized chromium atoms do not contribute significantly to the formation of oxide films because of the strong affinity of carbon for chromium. It is concluded, therefore, that the characteristics of the oxide film formed on the Ni-Cr alloy surface in a helium coolant are significantly affected by the chemical composition of the impurities in the coolant.

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Ultrasonic flaw detection and sizing is an important issue for ensuring structural reliability of industrial plants. The ultrasonic phased array technique is one of the most effective tools for visualizing the flaws in structural components. It is important to enhance the spatial resolution of phased array images to clearly visualize flaws; however, the spatial resolution of phased array images needs more research. A high spatial resolution phased array probe was designed as the first stage of this study. To investigate the spatial resolution of the phased array probe, acoustic analysis was conducted utilizing the Rayleigh-Sommerfeld Integral. The spatial resolution was investigated by changing the total aperture of the probe. As a result, the large-aperture phased array probe achieved high spatial resolution. Next, ultrasonic testing was simulated by the finite differential method using conventional and specially designed phased array probes. For the conventional probe, the flaw could be visualized but the shape was not clear enough. On the other hand, for the specially designed large-aperture probe, extensive noise appeared in the image and the flaws could not be visualized. Because of mode conversion, Rayleigh waves are generated at the contact surface between the transducer and testing material. The amplitude of Rayleigh waves are much higher than the diffraction echoes, hence the Rayleigh waves disturb the visualized image at the near field of the probe. Consequently a new technique for flaw visualization at the near field of the phased array probe was developed by eliminating detrimental waves. As a result the flaws could be clearly visualized using this technique.

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In this study, the creep behavior of angle-ply CFRP laminates subjected to an in-plane uniaxial load at an elevated temperature is analyzed based on the time-dependent homogenization theory developed by the present authors. For this, a multi-scale simulation method applicable to the creep analysis of CFRP laminates is described using the time-dependent homogenization theory. To confirm the validity of the method, the creep analysis of a unidirectional carbon fiber/epoxy laminate at an elevated temperature is firstly performed using the method. Comparison between the analysis results and experimental data reveals that the present method accurately predicts the creep behavior of unidirectional CFRP laminates. Then, the present method is applied to the creep analysis of three kinds of angle-ply carbon fiber/epoxy laminates, i.e. [±30°] , [±45°] and [±60°] , subjected to an in-plane uniaxial load at an elevated temperature. The results obtained agree well with experimental data for all of the laminates, showing that the present method can be successfully applied to the creep analysis of angle-ply CFRP laminates.

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A Galerkin-type new meshfree formulation for large deformation analysis of elastic and viscoelastic bodies with a quasi-implicit time advancing scheme was proposed. The proposed method uses floating stress-points for the domain integration instead of background cell integration or nodal integration. The nodes and stress-points are initially arranged in the domain in a similar way of finite elements with coarseness and fineness. The number of stress-points is set greater than that of the nodes so that zero-energy modes don't arise unlike nodal integration methods without stabilization. Shape functions and their derivatives at each stress-points are defined by moving least squares (MLS) approximation with variable support radii and are updated in every time steps. A scaling-typed integration correction was introduced for the satisfaction of integration constraints. A patch test and beam bending analyses were performed to verify and evaluate the accuracy of the proposed method. Additionally, a press forming-like analysis that is difficult to be analysed with finite element methods without adaptive meshing technique was performed and successfully converged.

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When grown on the surface of carbon fiber, vertically aligned arrays of ZnO nanowires have been shown to increase the interfacial shear strength without decreasing the in-plane properties of the composite. Analysis of the failure surface indicates that the ZnO debonds from the carbon fiber which combined with the higher interfacial shear strength, indicates that the ZnO more strongly adheres to the carbon surface than epoxy adheres to the carbon surface. Previous work was unable to identify the specific chemical interaction that enhanced the ZnO — carbon fiber interface, however it hypothesized that the presence carboxylic acid groups on the fiber were responsible. In this study an aramid fiber is used to elucidate the surface interaction since it can be produced with no carboxylic acid or with these groups through functionalization. The model fiber demonstrates that only fibers with carboxylic acid groups experience increased interfacial strength from the ZnO nanowires. The interaction between ZnO and carboxylic acid groups is verified to be critical to the enhancement of the interfacial strength in carbon fiber — ZnO nanowire — epoxy composites.

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This paper deals with fabrication and strength evaluation of biocompatible composites consisting of hydroxyapatite (HAp), partially stabilized zirconia (PSZ) and pure titanium (Ti). The biocompatible composites of HAp-Ti and PSZ-Ti were fabricated by a hot pressing method of powder metallurgy. In these composites, a volume ratio of HAp, PSZ and Ti was changed. Four-point bending tests and Vickers hardness tests of the HAp-Ti and PSZ-Ti composites were performed to determine the Young's modulus, bending strength and Vickers hardness, respectively. These properties were characterized as a function of Ti volume fraction. In both composites, the Young's modulus and Vickers hardness were higher than the prediction of the rule of mixture. The bending strength was improved by dispersing the Ti phase into HAp phase in the HAp-Ti composites and decreased with increasing Ti content in the PSZ-Ti composites. To discuss these results from a viewpoint of reaction products, the components of raw powders and sintered composites were investigated by X-ray diffraction analysis. It is concluded that oxide of titanium and other reaction products were created after sintering and they affected the mechanical performances of the composites.

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The application of microwave reflectometry was studied for nondestructive detection of glass fiber reinforced plastic (GFRP) laminates. The specimens having different kinds of defects and dimensions were prepared. The change of the microwave signals was measured by scanning the specimens with a K band waveguide sensor which can propagate microwaves from 18 to 26 GHz. The influence of the frequency of microwaves and the thickness of the laminates on measurement sensitivity was investigated. As a result, it was shown that the defects of more than 0.2 mm thickness in the GFRP laminate can be detected. The stable measurement results were obtained at lower frequency though measurement sensitivity for small defects was better at the higher frequency. It is necessary to select the suitable frequency for the measurement objectives because the interference due to the reflection waves from the top and bottom surfaces of the measurement objectives is caused depending on the objective and defect dimensions. In addition, it was shown that the defect of an aluminum film can be detected within the GFRP laminates of 30 mm thickness.

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Rotating bending fatigue tests on AZ31 and AZ61 wrought magnesium alloys were carried out in order to investigate the effects of specimen surface texture and the humidity environment of experiment. Specimen surface texture was varied by using an emery paper of a different roughness or by buff polishing to mirrored surface in final finish of specimen surface treatment. The conditions of environment in which fatigue tests were conducted were the laboratory's air, the dry air, the humid air and the water. As a result, the fatigue life of a specimen with a rough surface was shorter than that with a smooth surface. But the fatigue life of a specimen with mirrored surface was shorter than that with a little rougher surface by an emery polishing. It is attributed to that the effect of work-hardened layer on the fatigue life exists. And then the fatigue life is predicted by the √area parameter model in which a depth of surface roughness is regarded as a size of defect. The effect of surface roughness was more apparent in the case that a specimen is polished in the circumferential direction which is parallel to the crack propagation direction compared with the case that a specimen is polished in the axial direction. The fatigue strength in the region of a long fatigue life in water was smaller than that in the other environments; however this feature is not so apparent in the region of the short life. Except for in the water environment, the fatigue life became shorter in the descending order of the dry air, the laboratory's air and the humid air.

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