後藤 健

Stress–strain relations at different degrees of peak stress were investigated using loading–unloading tests to elucidate cumulative damage mechanisms of short fiber type C/SiC under tension. Damage observations revealed their crack length, number, and angle characteristics. Furthermore, stress–strain relations were estimated by expanding Basista's equations and by substituting measured damage characteristics into them, which revealed a nonlinear stress–strain relation. Cracks propagated in transverse fiber bundles without fiber fracture, connecting other cracks that had 75 ° – 90 ° orientation to the tensile axis. Stress–strain relations estimated qualitatively and quantitatively suggest that mixed mode I and mode II crack opening in transverse fiber bundles in the through-thickness plane caused the stress–strain nonlinear relations.

A cumulative damage mechanism for short fiber type C/SiC during shear loading– unloading testing was examined and quantified using Iosipescu specimens parallel in the in-plane and through-thickness plane, and by using modified fracture and damage mechanics theory referring to measured damage characteristics (crack length, number and angle). A nonlinear stress–strain relation was found for both specimens. Decrease in the apparent modulus was confirmed with increased peak stress, although permanent strain increased. Inelastic strain of the decomposed tensile direction derived from shear stress was greater than that of the compressive one. Cracks propa-gated perpendicularly to the tensile direction, intruding on the boundary of the transverse fibers and connecting to other cracks. The theoretical damage mechanics model succeeded to predict the stress–strain relation, proposing that the shear mechanical properties are predictable by measuring the damage characteristics.

This study investigated cumulative damage mechanisms of short fiber type C/SiC under compression. To measure mechanical properties (unloading modulus and permanent strain) before fracture, repeated loading-unloading tests were conducted using a strain gage. Damage was observed to assess characteristics of crack density, length, number, and propagation angle. Furthermore, relations between mechanical properties and damage characteristics were elucidated by application of Basista's equations and by substituting crack densities inferred from damage observations. Stress-strain relations revealed nonlinear behavior. The unloading modulus did not change, but the permanent strain increased. Cracks propagated mainly between fibers, without fiber fracture, connecting other cracks in the direction of orientation 0 deg to 30 deg to the compressive axis. We estimated permanent strain using Basista's equations and damage characteristics. Estimates roughly agreed with experiment results, suggesting that the permanent strain increase is attributable to closed crack sliding and friction caused by increased crack density.

We present an overview of the cryogenic system of the next-generation infrared observatory mission SPICA. One of the most critical requirements for the SPICA mission is to cool the whole science equipment, including the 2.5 m telescope, to below 8 K to reduce the thermal background and enable unprecedented sensitivity in the mid- and far-infrared region. Another requirement is to cool focal plane instruments to achieve superior sensitivity. We adopt the combination of effective radiative cooling and mechanical cryocoolers to accomplish the thermal requirements for SPICA. The radiative cooling system, which consists of a series of radiative shields, is designed to accommodate the telescope in the vertical configuration. We present thermal model analysis results that comply with the requirements to cool the telescope and focal plane instruments.

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. In molding of carbon fiber reinforced thermoplastics (CFRTP), resin impregnation behavior to fiber yarns is very important because higher viscosity of molten thermoplastics inhibits resin impregnation to the interspace among fibers. Resultant resin un-impregnation causes lower mechanical properties of CFRTP. The purpose of this study was to clarify the relation among molding method, molding conditions and resin impregnation to fiber bundles experimentally. In this study, CFRTPs using continuous carbon fiber yarn as a reinforcement and a thermoplastic polyimide which is excellent in heat resistance as a matrix resin were produced by Micro-Braiding, Film Stacking and Powder method. As a result, as the molding time increased, the impregnation ratio increased. The resin impregnation saturated in a certain molding time and the time was shorter the larger molding pressure. In addition, as the resin impregnation ratio increased, the mechanical properties also tended to increase.

<p>天文衛星や地球観測衛星ではより大型で高精度な構造物が必要とされている．このような構造を構築するためには，軽量で弾性率が大きく熱膨張係数が小さい材料が必要である．熱膨張係数の小さい材料としては炭素や石英があり，各種の人工衛星の高精度構造にはこれらを利用した構造要素とその複合材料が活用されている．本稿では，電波天文衛星ASTRO-G（2011年中止）向け大型展開アンテナにおける各種高精度構造要素の構成素材に関する開発において発生した技術課題を発端として，筆者らが取り組んでいる将来のASTRO-Gのような大型アンテナをはじめとする高精度構造への適用を目指した材料および構造要素の開発に関する基礎的研究について紹介する．</p>

The oxidation behavior and oxidation mechanisms of monolithic ZrB2 and particulate-ZrB2 matrix composites were reviewed. Dispersion of SiC particles into ZrB2 was found to be an effective way to prevent extensive oxidation. However, the formation of a SiC-depleted layer can become a critical problem because it can lead to spallation and delamination of the protective surface layer. The addition of ZrC in conjunction with rapid heating to temperatures higher than 2000 °C effectively reduced the porosity of the SiC-depleted layer. The formation of a dense surface layer was attributed to large volumetric expansion during the conversion from ZrC to ZrO2. The effect of the ZrC addition depended on the temperature, heating rate, and composition. This review showed that material design for specific applications is required for high-temperature applications to maximize the oxidation resistance of ZSZ composites.

We describe the fabrication of in-plane randomly oriented short carbon fiber-dispersed ZrB2-SiC (Csf/ZS) and ZrB2-SiC-ZrC (Csf/ZSZ) matrix composites with different slurry compositions using Si-melt infiltration (Si-MI). We also carried out microstructural observations, measurements of thermal conductivity, and oxyhydrogen torch oxidation tests. Microstructural characterization indicates that carbon fibers exist in the form of bundles, and these bundles are disconnected from each other. We also identify the formation of a eutectic ZrSi2 phase in the Csf/ZSZ composites during processing. The thermal conductivity of the Csf/ZSZ composites is found to be independent of the composition of the slurry and is strongly affected by the presence of the carbon fiber bundles. Post-oxidation analysis shows that the heterogeneous microstructure of the samples causes non-uniform surface oxidation. The formation of ZrO2 and SiO2, as well as of sintered monolithic ZrB2-SiC-ZrC (ZSZ) composites, was also identified. The thickness of the oxidized area in the unreacted regions of the Csf/ZSZ composites is found to be analogous to those observed in Csf/SiC and Csf/ZS composites, albeit thinner. Si and the Si-ZrSi2 eutectic phase melt during heating and they move toward the outside of specimens in oxyhydrogen torch conditions, which is a unique phenomenon never observed before in related systems.

The oxidation behavior of four ZrB2-SiC-ZrC compositions with varying ZrC contents (20, 34, 50, and 64 vol.%) was compared to that of ZrB2-SiC. The ceramics were oxidized at 1700 °C in an oxygen-hydrogen torch environment. The liquid oxide on the ZrB2-SiC sample came off from the surface under such an environment. In contrast, the all ZrB2-SiC-ZrC samples maintained the convex oxide on the surface, which consisted of ZrO2 and SiO2. The convex oxide of ZSZ with higher ZrC content was thicker, with the exception of ZrB2-SiC-64vol.%ZrC sample. The ZrB2-SiC-64vol.%ZrC sample formed a ZrO2-rich layer, which was clearly denser than the ZrO2-SiO2. This densification was caused by ZrO2-sintering, and it was specific behavior under the dynamic pressure.

We present an overview of the thermal and mechanical design of the Payload Module (PLM) of the next-generation infrared astronomy mission Space Infrared Telescope for Cosmology and Astrophysics (SPICA). The primary design goal of PLM is to cool the whole science assembly including a 2.5 m telescope and focal-plane instruments below 8 K. SPICA is thereby expected to have very low background conditions so that it can achieve unprecedented sensitivity in the mid- and far-infrared. PLM also provides the instruments with the 4.8 K and 1.8 K stages to cool their detectors. The SPICA cryogenic system combines passive, effective radiative cooling by multiple thermal shields and active cooling by a series of mechanical cryocoolers. The mechanical cryocoolers are required to provide 40 mW cooling power at 4.8 K and 10 mW at 1.8 K at End-of-Life (EoL). End-to-end performance of the SPICA cryocooler-chain from 300 K to 50 mK was demonstrated under the framework of the ESA CryoChain Core Technology Program (CC-CTP). In this paper, we focus on the recent progress of the thermal and mechanical design of SPICA PLM which is based on the SPICA mission proposal to ESA(1).*

The initial oxidation behavior of ZrB2-SiC-ZrC (ZSZ) composites above 2000 degrees C after the initial similar to 5-10 s was examined by an electric heating system. The morphology of the oxide layer was shown to depend on the ZrC content. Volume expansion during the conversion of ZrC to ZrO2 contributed to the morphology of the surface oxide layer. Above 2000 degrees C, the ZSZ composite with the highest ZrC amount had the lowest oxide layer thickness. This study clearly showed the efficacy of ZrC as an additive to significantly alter the oxide layer morphology relative to that observed for ZrB2-SiC composites tested under the same condition. (C) 2017 Elsevier B.V. All rights reserved.

Short and plain-woven continuous carbon fiber-reinforced ZrB2-SiC-ZrC (Csf/ZSZ and Cpw/ZSZ) matrix composites were fabricated by a Si melt-infiltration process for application to thermal protection systems (TPSs). The fracture toughness of both composites was improved compared to those of ZSZ ceramics. The effects of the thermal properties, volume fraction, and architecture of the carbon fibers on the oxidation behaviors of the composites were also examined by oxyhydrogen torch testing. The experimental results showed that the oxidation of both composites significantly depended on the microstructural parameters and properties of the constituent materials. In particular, the high thermal conductivity of the Csf/ZSZ composite was important in preventing local increases in temperature and material consumption. In the present study, the starting material, volume fraction, and architecture of carbon fibers were identified as important parameters for the development of TPS materials.

The oxidation behaviour of four compositions of ZrB2-SiC-ZrC and one composition of ZrB2-SiC were studied at 1700 degrees C in air and under low oxygen partial pressure. Volatility diagrams for ZrB2-SiC-ZrC and ZrB2-SiC were used to thermodynamically elucidate the oxidation mechanisms. SiO2 and ZrO2 layers formed on the surfaces of ZrB2-SiC-ZrC and ZrB2-SiC oxidized at 1700 degrees C. A SiC-depleted layer only formed on the surface of the ZrB2-SiC oxidized under low oxygen partial pressure. The oxide layer thickened with increasing ZrC volume content during oxidation in air and under low oxygen partial pressure. The ZrB2-SiC-ZrC oxide surface exploded in air when the ZrC volume content was more than 50%. Under low oxygen partial pressure, the oxide surfaces of all the ZrB2-SiC-ZrC specimens bubbled. (C) 2016 Published by Elsevier Ltd.

日本複合材料学会

Very lightweight mirror will be required in the near future for both astronomical and earth science/observation missions. Silicon carbide is becoming one of the major materials applied especially to large and/or light space-borne optics, such as Herschel, GAIA, and SPICA. On the other hand, the technology of highly accurate optical measurement of large telescopes, especially in visible wavelength or cryogenic circumstances is also indispensable to realize such space-borne telescopes and hence the successful missions. We have manufactured a very lightweight Φ=800mm mirror made of carbon reinforced silicon carbide composite that can be used to evaluate the homogeneity of the mirror substrate and to master and establish the ground testing method and techniques by assembling it as the primary mirror into an optical system. All other parts of the optics model are also made of the same material as the primary mirror. The composite material was assumed to be homogeneous from the mechanical tests of samples cut out from the various areas of the 800mm mirror green-body and the cryogenic optical measurement of the mirror surface deformation of a 160mm sample mirror that is also made from the same green-body as the 800mm mirror. The circumstance and condition of the optical testing facility has been confirmed to be capable for the highly precise optical measurements of large optical systems of horizontal light axis configuration. Stitching measurement method and the algorithm for analysis of the measurement is also under study.

ZrB₂&ndash;SiC&ndash;ZrC (ZSZ) ternary composites of four differing compositions were fabricated by spark plasma sintering (SPS). The effect of the ZrB₂/ZrC ratio on the oxidation behavior was examined by thermogravimetric (TG) analysis and microstructural observations. In addition, in-situ observation above 1500&deg;C was performed using a high-temperature observation system (HTOS). ZSZ composites with high ZrC contents were fully oxidized at temperatures below 1500&deg;C. However, ZSZ composites with low ZrC contents formed protective oxide layers during heat exposure. These layers protected the unreacted regions from further oxidation. Island nucleation was successfully observed on the surface oxide layer at 1500&deg;C using the HTOS. The nucleation of islands strongly depended on the ZSZ composition. The difference in oxidation behavior originated from the concentration and interparticle distance of the ZrC in the as-sintered compacts.

Aligned multi-walled carbon nanotube (CNT) sheets produced from aligned CNT arrays were used to develop high volume fraction CNT/epoxy composites. Stretching and pressing techniques were applied during CNT sheet processing to straighten the wavy CNTs and to enhance the dense packing of CNTs in the sheets. Raman spectra measurements showed better CNT alignment in the CNT sheets and the composites after stretching and pressing. Aligned CNT/epoxy composites with CNT volume fraction up to 63.4% were developed using hot-melt prepreg processing with a vacuum-assisted system. Stretching and pressing of the CNT sheets enhanced the mechanical properties of high volume fraction CNT/epoxy composites considerably. Stretching and pressing increased tensile strength of the composites by 32% and elastic modulus of the composites by 27%. Applying stretching and pressing is effective for production of superior CNT sheets with high alignment and dense packing of CNTs, thereby supporting the development of high-performance CNT composites. (C) 2015 Elsevier Ltd. All rights reserved.

We present the new design of the cryogenic system of the next-generation infrared astronomy mission SPICA under the new framework. The new design employs the V-groove design for radiators, making the best use of the Planck heritage. The new design is based on the ESA-JAXA CDF study (NG-CryoIRTel, CDF-152(A)) with a 2 m telescope, and we modified the CDF design to accommodate the 2.5 m telescope to meet the science requirements of SPICA. The basic design concept of the SPICA cryogenic system is to cool the Science Instrument Assembly (SIA, which is the combination of the telescope and focal-plane instruments) below 8K by the combination of the radiative cooling system and mechanical cryocoolers without any cryogen.

A solid-state drawing and winding process was done to create thin aligned carbon nanotube (CNT) sheets from CNT arrays. However, waviness and poor packing of CNTs in the sheets are two main weaknesses restricting their reinforcing efficiency in composites. This report proposes a simple press-drawing technique to reduce wavy CNTs and to enhance dense packing of CNTs in the sheets. Non-pressed and pressed CNT/epoxy composites were developed using prepreg processing with a vacuum-assisted system. Effects of pressing on the mechanical properties of the aligned CNT sheets and CNT/epoxy composites were examined. Pressing with distributed loads of 147, 221, and 294N/m showed a substantial increase in the tensile strength and the elastic modulus of the aligned CNT sheets and their composites. The CNT sheets under a press load of 221N/m exhibited the best mechanical properties found in this study. With a press load of 221N/m, the pressed CNT sheet and its composite, respectively, enhanced the tensile strength by 139.1 and 141.9%, and the elastic modulus by 489 and 77.6% when compared with non-pressed ones. The pressed CNT/epoxy composites achieved high tensile strength (526.2MPa) and elastic modulus (100.2GPa). Results show that press-drawing is an important step to produce superior CNT sheets for development of high-performance CNT composites.

Drawing, winding, and pressing techniques were used to produce horizontally aligned carbon nanotube (CNT) sheets from free-standing vertically aligned CNT arrays. The aligned CNT sheets were used to develop aligned CNT/epoxy composites through hot-melt prepreg processing with a vacuum-assisted system. Effects of CNT diameter change on the mechanical properties of aligned CNT sheets and their composites were examined. The reduction of the CNT diameter considerably increased the mechanical properties of the aligned CNT sheets and their composites. The decrease of the CNT diameter along with pressing CNT sheets drastically enhanced the mechanical properties of the CNT sheets and CNT/epoxy composites. Raman spectra measurements showed improvement of the CNT alignment in the pressed CNT/epoxy composites. Research results suggest that aligned CNT/epoxy composites with high strength and stiffness are producible using aligned CNT sheets with smaller-diameter CNTs. (C) 2015 Elsevier Ltd. All rights reserved.

The infrared space telescope SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a next-generation astronomical project of the Japan Aerospace Exploration Agency, which features a 3 m class and 6 K cryogenically cooled space telescope. This paper outlines the current status for the preliminary structural design of the SPICA payload module. Dedicated studies were conducted for key technologies to enhance the design accuracy of the SPICA cryogenic assembly and mitigate the development risk. One of the results is described for the concept of the on-orbit truss separation mechanisms, which aim to both reduce the heat load from the main truss assembly and isolate the microvibration by changing the natural frequency of the spacecraft. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Biodegradable composites based on poly(butylene succinate) (PBS) and unidirectional plain jute fabrics have been developed. These composites were fabricated by compression molding of sandwiching 4-7 jute fabric layers between five and eight layers of PBS sheets. Surface modification of the jute fabric by alkali and combined alkali-silane treatments was investigated. The effects of surface modification on the mechanical and thermal properties of jute fabric/PBS biodegradable composites were studied. The mechanical properties of surface-treated jute fabric/PBS biodegradable composites were significantly higher than those of untreated ones. Compared with the alkali treatment, the combined alkali-silane treatment showed higher mechanical properties of the jute fabric/PBS biodegradable composites. The alkali-silane-treated jute fabric/PBS biodegradable laminated composite with six reinforced fabric layers (47.5 wt.%) achieved the best mechanical properties in this study, which showed an increase in tensile strength by 16.4%, tensile modulus by 10.8%, flexural strength by 24.2%, and flexural modulus by 21.9% compared with those of untreated one. Fractured surface morphologies of tensile specimens exhibited an improvement of interfacial fiber-matrix adhesion in the PBS biodegradable composites reinforced with surface-treated jute fabric. Thermal stability of the jute fabric/PBS biodegradable composites was remarkably to be intermediate between the PBS resin and the jute fabric. Surface-treated jute fabric/PBS biodegradable composites having good interfacial fiber-matrix adhesion resulted in stable composites with better thermal stability than that of untreated ones.

An attempt was made to apply carbon fiber reinforced three-dimensional composites (3D-CF) to a high speed rotation disk aiming at enhancing the burst tip speed of the disk by placing reinforcements in three directions r, θ and z of the cylindrical coordinate. It was shown by finite element calculations that 3D-CF is advantageous for high speed rotation due to capability of fabricating a disk having low outer to inner radius ratio (Dr), 0.5 or below. Thus, 3D-fabrics for a prototype rotor with Dr of 0.14 were produced, and three specific methods for joining the 3D-CF to a hub were designed and evaluated by spin test.

Carbon fiber reinforced plastics (CFRPs) often used in precise structures of satellite systems for examples, optical benches and high gain antennas, since their coefficient of thermal expansion (CTE) can design almost zero by controlling laminate sequence. Within usage on orbit, satellite structures exposed severe thermal cycle loading between -170°C to 120°C. CTE and Young's modulus change of CFRP by thermal cycle loading were precisely investigated to understand the damage mechanism of CFRP. By thermal cycle loading Young's modulus of CFRP were degraded up to 6% from its original value, however, CTE changes of CFRP laminates by thermal cycles were slight. Damages related to the Young's modulus change were discussed by experimental observations.

Astro-H is the Japanese X-ray astronomy satellite to be launched in 2015. The Soft X-ray Spectrometer (SXS) on board Astro-H is a high energy resolution spectrometer utilizing an X-ray micro-calorimeter array, which is operated at 50 mK by the ADR with the 30 liter superfluid liquid helium. The mechanical cryocoolers, 4K-class Joule Thomson UT) cooler and 20 K-class double-staged Stirling (2ST) cooler, are key components of the SXS cooling system to extend the lifetime of LHe cryogen beyond 3 years as required. Higher reliability was therefore investigated with higher cooling capability based on the heritage of existing cryocoolers. As the task of assessing further reliability dealt with the pipe-choking phenomena by contaminant solidification of the on-orbit SMILES JT cryocooler, outgassing from materials and component parts used in the cryocoolers was measured quantitatively to verify the suppression of carbon dioxide gas by their storage process and predict the total accumulated carbon dioxide for long-term operation. A continuous running test to verify lifetime using the engineering model (EM) of the 4 K-JT cooler is underway, having operated for a total of 720 days as of June 2013 and showing no remarkable change in cooling performance. During the current development phase, prototype models (PM) of the cryocoolers were installed to the test SXS dewar (EM) to verify the overall cooling performance from room temperature to 50 mK. During the EM dewar test, the requirement to reduce the transmitted vibration from the 2ST cooler compressor was recognized as mitigating the thermal instability of the SXS microcalorimeter at 50 mK. (C) 2014 Elsevier Ltd. All rights reserved.

Composites based on epoxy resin and differently aligned multi-walled carbon nanotube (MWCNT) sheets have been developed using hot-melt prepreg processing. Aligned MWCNT sheets were produced from MWCNT arrays using the drawing and winding technique. Wavy MWCNTs in the sheets have limited reinforcement efficiency in the composites. Therefore, mechanical stretching of the MWCNT sheets and their prepregs was conducted for this study. Mechanical stretching of the MWCNT sheets and hot stretching of the MWCNT/epoxy prepregs markedly improved the mechanical properties of the composites. The improved mechanical properties of stretched composites derived from the increased MWCNT volume fraction and the reduced MWCNT waviness caused by stretching. With a 3% stretch ratio, the MWCNT/epoxy composites achieved their best mechanical properties in this study. Although hot stretching of the prepregs increased the tensile strength and modulus of the composites considerably, its efficiency was lower than that of stretching the MWCNT sheets. (C) 2014 Elsevier Ltd. All rights reserved.

In order to achieve a sufficiently high volume fraction and the preferred alignment of long carbon nanotubes (CNTs), CNT spun yarns were used as preforms for fabricating epoxy-based composite materials with excellent mechanical properties using the pultrusion technique. Epoxy resin was well impregnated into the preforms, resulting in better load transfer from the resin to the CNTs. By using CNT spun yarn as the preform, the Young's modulus and tensile strength were improved by up to 15 times and 7 times over those of the epoxy resin, respectively. SEM observation suggested that the dominant fracture mode of the composite was fiber breakage of the CNTs. (C) 2014 Elsevier Ltd. All rights reserved.

The infrared space telescope SPICA, Space Infrared Telescope for Cosmology and Astrophysics, is a next-generation astronomical project of the Japanese Aerospace Exploration Agency (JAXA), which features a 3m-class and 6K cryogenically- cooled space telescope. This paper outlines the current status for the preliminary structural design of the SPICA payload module. Dedicated studies were conducted for key technologies to enhance the design accuracy of the SPICA cryogenic assembly and mitigate the development risk. One of the results is described in this paper for the concept of the on-orbit truss separation mechanisms, which aim to both reduce the heat load from the main truss assembly and isolate the micro-vibration by changing the natural frequency of the spacecraft.

Sandwich structures made of carbon fiber reinforced plastics (CFRPs) have excellent characteristics such as lightweight, high stiffness, and low coefficient of thermal expansion. Therefore, CFRP is one of attractive candidates as structural material in aerospace field. Today, the use of satellite at high temperature environment such as exploration in Venus, etc., is under schedule. However, the heat resistance of resin used for current CFRP sandwich panels is pretty low. The objective of this study is to evaluate high-temperature property of newly developed sandwich panels. In the present study, polyimide and polyamide-imide resins with high thermal resistance were used for the matrix of both skin and core of heat-resistant CFRPs. The polyimide CFRP (PI) and polyamide-imide CFRP (PAI) were used for the skin materials. For core materials, in addition to PI and PAI CFRPs, diffusion-bonded aluminum honeycomb core (AL) was also used; the combinations of skin/core examined here are PAI/PAI, PI /AL and PI/PAI. To evaluate the characteristics of sandwich panels, a flatwise tensile test was performed at both room temperature and high temperature, 200?. At room temperature, an epoxy adhesive was used for the bonding between the specimen and the test fixture, and a polyimide adhesive was used for high temperature test. The highest flatwise tensile strength was realized by PI/ PAI sandwich panels. On the other hand, PI/AL sandwich panel showed the lowest strength. According to microscopic observation, it was confirmed that, for low strength specimens, the bonding between skin and core was insufficient. In addition, it was confirmed that the PI/AL panel could maintain the flatwise tensile strength up to high temperature of 200?.

Author's previous works revealed that tensile strength of C/C especially enhances up at 2773K. In order to reveal the mechanisms of the remarkable enhancing tensile strength at 2773K, mechanical properties of the C/C subjected to different heat treatment temperatures and to pre-creep deformation were examined. A course of discussion lead to a conclusion that creep deformation of fiber is a main source of the strength enhancement.

Fiber-matrix interface mechanical properties are the key design point for the composites, however, methodology for evaluating interface properties of C/Cs are not still well established. In this study, capability of the fiber bundle push-out method was demonstrated as a measurement technique of fiber-matrix interfacial mechanical properties of various C/Cs. First, to carefully determine the experimental conditions to give proper interface mechanical properties, the influences of a radius of an indenter and the thickness of specimens on the measured results were examined. From the experimental result, interface debonding stress, τ_d, and sliding stress, τ_s, could be obtained as a constant value independent from specimen thickness as long as tested using the same indenter size and the proper specimen thicknesses of < 400 µm. However, absolute value of especially τ_d showed dependence of on indenter size. This was shown to be the limitation of this method that τ_d obtained from this method cannot be treated as a quantitative value. To demonstrate the capability of the method, the change of fiber-matrix interface mechanical properties of C/Cs on the type of fibers and final heat treatment temperature. τ_d decreased with the heat treatment temperature in both C/Cs with pitch based carbon fibers, K633 and K321 and C/Cs reinforced with a carbon fiber with higher heat treatment temperature gave lower τ_d at the same heat treatment temperature. Main reason for the degradation of τ_d up to 2273K was attributed to the enlargement of debonding area at fiber-matrix interface. Degradation of τ_d was enhanced at the temperature range of > 2273 K by the structure change of the interface from the graphitization of matrices. Finally, The fiber bundle push-out method was proved to be a strong tool to investigate fiber-matrix interface mechanical properties of C/Cs.

Carbon fiber reinforced carbon matrix composites (C/C) are promising in the aerospace fields. Characteristics of the interface between carbon fiber and carbon matrix are required to estimate the C/C strength. Therefore, Pyrolytic graphite (PG) and isotropic graphite were adopted as a model of carbon fibers, and phenolic resin was used as the matrix for this fundamental study to sort out the factors of bonding interface in C/C. The graphite plates were joined with the phenolic resin. One of the joined planes of the crystal orientation of the PG was parallel to the graphite base plane (P/P) and the other was vertical (V/V). Isotropic graphite was also joined (I/I). The resin was carbonized at 1773K, and the samples were heat treated at high temperatures up to 3173 K. In this paper, the bonding strengths of these specimens were determined by specially designed shear load test. The experimental results by this method were discussed in terms of thermal and crystalline conditions. Crystal structure and orientation of the bonding layer were observed by transmission electron microscope (TEM).

Gas leakage through C/Cs was examined for the application of C/Cs to a combustion chamber of an ATR engine. Because C/Cs have many cracks and pores, gas easily leaks through the deffects. To predict and prevent this gas flow through the C/Cs, the leakage rates were measured as a function of pressure, and gas flow paths were identified by microscopic observations of C/Cs. On the basis of these results, gas flow models through C/Cs were proposed for unidirectionally (1D), 2-dimensionally (2D), and 3-dimensionally (3D) reinforced C/Cs. For the 1D- and 3D-C/C, the viscous flow models were found to be effective, and the labyrinth seal model was useful for 2D-Bare. Then, various methods for the prevention of the gas leakage through C/Cs were investigated. To this end, the combination of Si infiltration, sol-gel treatment, and glass coating over the surface was shown to significantly reduce leak rate, and to be sufficient for combustion chamber application.

Increased use of Carbon/Carbon composites (C/Cs) has necessitated fabrication of complex structures made of the C/Cs. Several techniques can be applied to form complex C/C structures. Joining technique, mechanical and chemical joint, was often required for build up structures with various complex shapes and/or large structures. In the present study, we focused on chemical bonding, where high temperature capability as well as high bonding strength was key issue. For exploring suitable bonding technique for C/Cs, carbon and SiC bonding techniques were at first discussed in detail, and a new bonding technique, the hybrid bonding, was proposed. This method was shown to overcome difficulties found in the carbon and SiC bonds; the hybrid bonding was found to simultaneously possess high strength and easy process ability. Then, the strength of carbon bonding and hybrid bonding were compared at elevated temperatures, and the mechanisms yielding high strength of the hybrid bonding was discussed. Finally, these techniques were applied to 3D-C/C specimens to secure availability of this bonding to 3D-C/Cs. However, it was suggested that 3D-C/C bonding technique need much further efforts for reducing the high thermal mismatch strain induced by fiber bundle orientation distribution at the bonding surfaces of 3D-C/Cs.

The thermal design for BepiColombo MMO (Mercury Magnetospheric Orbiter) is shown. A heat shield protects common and scientific instruments against harsh environment, i.e. solar flux of up to 10 solar constants and infrared radiation from the Mercury. The heat shield temperature is controlled passively by second surface mirrors (SSMs), and is less than 200 degrees centigrade. The temperatures of instruments, tank, and battery are controlled with in their allowable limit by thermal standoffs. Materials for antennas, booms and multi-layer insulations (MLIs) are under development. Because MMO is spin-stabilized spacecraft, MMO requires the sun-shield and the radiator-shield in the cruise phase (Earth to Mercury) in which MMO is 3-axis stabilized, to avoid the exposure to the direct solar flux.

Feasibility studies were carried out regarding the application of carbon/carbon (C/C) composites to a turbine disk and heat exchangers for an engine used in a future space vehicle. In these applications, the maximum temperature is estimated to be about 1500degreesC. In order to overcome this high temperature, attempts were made to apply three-dimensionally reinforced C/C composites to both the structures. The most serious problem encountered in the application to the turbine disk was losing fragments of the material located near the outer periphery of the disk due to strong centrifugal force, which induced severe vibration due to rotational unbalance. The heat exchangers have complex shapes in order to realize a large heat exchanging area, so that joined structures were explored. In this application, our main effort has been focused on finding structures requiring minimum joining strength and materials with the lowest gas leakage.

Fracture behavior of three-dimensional reinforced C/C disk was investigated to establish design criteria for high temperature turbine disk. Fly-out objects were detected from the rotation speed of 3000 r.p.m and the vibration amplitude increased with increase of rotation speed. The observation of the surface after high speed rotation revealed that the object flown-out from the disk was θ-directional fiber bundles. The vibration increasing behavior was predicted with simplified model and the result agreed well in tendency.

Increased use of Carbon/Carbon (C/C) composites necessitates fabrication of complex structures, which require high temperature secondary bonding. Secondary bonding of C/C interfaces provides design flexibility and also alleviates complicated fabrication problems. In this study, resin-carbonizaition process was applied for the bonding of C/C composites. In this process, C/C composites were bonded with phenolic resin and the cured resin was then heat-treated to carbonize. Bonding strength of thus bonded layers was evaluated by a double-ends-notched method at elevated temperatures up to 2000℃ in vacuum. The results revealed that bonding-strength increase with increasing temperature. Since strength of graphite is known to be affected by absorbed gas, out gas test was also performed. Absorbed gas is shown to lower bonding strength. Therefore it is concluded that this effect was shown to be one of major factors for the strength enhancement at elevated temperatures.