佐藤 英一

High-temperature tensile deformation was performed using ODS ferritic steel, which has grain structure largely elongated and aligned in one direction, in the direction perpendicular to the grain axis. In the superplastic region II, two-dimensional grain boundary sliding (GBS) was achieved, in which the material did not shrink in the grain-axis direction and grain-boundary steps appeared only in the surface perpendicular to the grain axis. In this condition, a classical grain switching event was observed. Using kernel average misorientation maps drawn with SEMI EBSD, dominant deformation mechanisms and accommodation processes for GBS were examined in the different regions. Cooperative grain boundary sliding, in which only some of grain boundaries slide, was also observed.

The aim of this research is to evaluate high temperature damage of combustion chamber made of Cu-Cr-Zr alloy using eddy current testing (ECT) techniques based on AMR sensor. The cracks in a simulated combustion chamber can be detected by multi-frequency ECT technique. Also the relative conductivity of damaged copper alloy specimens both at room temperature during tensile testing and at high temperature of fatigue and creep testing were related to the applied damage with micro cracks.

打音検査や超音波検査のように振動を利用すると構造物の健全性を評価することができる。光ファイバセンサは電気センサの適用が困難であった極限環境下における構造体健全性評価を可能にすることが期待されている。近年、多機能、多重化可能、電磁波非干渉といった特長を有するファイバ・ブラッグ・グレーティング（FBG）による振動検出の研究が盛んに行われている。しかしこれまでのFBGセンサシステムは温度・ひずみ変動下で超音波を検出することが困難であった。我々はこの技術的障害を乗り越えるシステムを新たに開発した。この論文ではコンパクトで経済性に優れた数Hz～2 MHzの広帯域な振動検出が可能なFBGセンサシステムの開発過程を構成的アプローチに基づいて紹介する。

A structural health monitoring system using four fiber Bragg grating sensors (FBG sensors) was developed for solid rocket motor composite chambers. The system was designed to measure a large and fast strain change and to measure acoustic emissions (AE) simultaneously. The strain up to 1% and up to 100 kHz was considered. The system possesses two light sources; a newly developed four-band fiber ring laser and a broadband light source. Using the four-band fiber ring laser, the system can measure strain changes and AE simultaneously. Using the broadband light source, the system can measure high-speed strain changes. The strain sensitivities of FBG sensors obtained from the four-band fiber ring laser system agreed well with those obtained from a broadband light source system. A CFRP beam-bending test was conducted to confirm the possibility of simultaneous measurement of both strain and AE signals from a single FBG sensor. A strain gage and a piezoelectric AE sensor were used for reference. In the test, it was confirmed the strain change up to almost 1% was measured from the developed system. AE detection by an FBG sensor and a piezoelectric AE sensor, however, do have slight differences. The developed system will be applied to composite structures in aerospace engineering fields, such as Epsilon Launch Vehicle, which is under development by the Japan Aerospace Exploration Agency (JAXA).

Hypervelocity-impact experiments are performed on Sit): glass plates to investigate its damage process. The damage propagation behavior induced by a hypervelocity impact is observed using a high-speed video camera. The postmortem observations reveal that the damage structure of the impacted plates consists mainly of crater, internal failure zone, and radial cracks. The sequence of the damage formation and propagation during a hypervelocity-impact event is revealed using the images of the high-speed video camera. The propagation velocities of surface fracture show a nearly constant value regardless of impacting conditions. The propagation velocities of internal failure zone increase with decreasing target thickness. Hie formation of radial cracks is affected by the projectile kinetic energy nornialized by the target thickness. The radial crack velocities increase with increasing the normalized kinetic energy and approach asymptotically to the terminal velocity. (C) 2013 The Authors. Published by Elsevier Ltd.

A structural health monitoring system using multiple fiber Bragg grating sensors (FBG sensors) was developed. The system was designed to measure a large and fast strain change and to measure acoustic emissions (AE) simultaneously. The strain up to 1% and up to 100 kHz was considered. A multiple fiber ring laser was adopted as a light source, consisted of a multiple erbium-doped fiber amplifier (EDFA), an optical circulator, optical couplers, and FBG sensors. Its lasing wavelengths depended on strains loaded to FBG sensors. A CFRP beam-bending test was conducted to confirm the possibility of simultaneous measurement of both strain and AE signals from a single FBG sensor. In the test, signals from a conventional electric resistive strain gage and a piezoelectric AE sensor were revealed to be equivalent to those from the FBG sensor, respectively. The system will be applied to the development of composite structures in the aerospace field, such as Epsilon Launch Vehicle.

A vibration measurement of a mechanical element in liquid hydrogen was conducted using a fiber Bragg grating (FBG) sensor. The monitored mechanical element was an 8-mm diameter stainless-steel rod connected to a bearing cartridge of a ball-bearing, which is an element of a liquid rocket engine. The rotation of the ball-bearing vibrates both the cartridge and the rod to be monitored. The vibration was measured during a rotational test where the test temperature and the maximum rotational speed were 26 K and 30,000 rpm, respectively. The FBG-sensor signals were recorded at the sampling frequency of 50 kHz. The vibration of the rod was measured successfully up to 25 kHz despite the root-mean-square level of the dynamic strain smaller than 10x10^-6. The frequency analysis revealed that the FBG-sensor signal corresponded well with the rotational speed of the ball bearing. The peak frequency agreed with the first-order frequency of the rotational speed of the ball-bearing. The experiment demonstrates that FBG sensors are available to mechanical measurements of liquid rocket engines during operational tests, and also seem to be useful for mechanical measurements of fuel cell cars and hydrogen engine cars.

Creep tests were conducted at low temperatures for ultrafine-grained aluminum (UFG Al) fabricated by accumulative roll bonding. The samples showed remarkable creep behavior with a stress exponent of about three, a grain-size exponent of almost zero, and a low apparent activation energy of 20 kJ/mol. This creep behavior is similar to that of low-temperature creep of coarsegrained (CG) Al, though UFG Al shows creep under stresses below its 0.2% proof stress while CG Al show it under stresses above that. © (2013) Trans Tech Publications, Switzerland.

It is understood that grains move by grain boundary sliding, and change their relationship to each other during superplastic deformation. Ideal two-dimensional observation of grain movements from the specimen surface is difficult even in the shear deformation because grains move three-dimensionally according to the stress distribution against the specimen surface. In this study, ODS steel with elongated grains aligned along one direction was deformed perpendicular to the aligned axis to achieve ideal two-dimensional grain movements. Surface height profiles with a laser microscope showed small amount of three-dimensional grain movements, while two-dimensional grain movements and rotations were appeared by observations before and after the deformation with SEM-EBSD. © (2013) Trans Tech Publications, Switzerland.

Creep tests were performed at less than 0.4 Tm (Tm is the melting temperature) for 99.999 99.57 and 99.52% aluminum with several grain sizes in the range of 50-330 μm. These Al materials show remarkable creep behavior with an apparent activation energy (Q) of 30kJ/mol a stress exponent of 4 and a grain-size exponent of zero and with a larger creep rate with increasing purity. These parameters resemble those of conventional dislocation creep which is rate-controlled by the usual diffusion processes except for the extra-low Q value. This means that a non-diffusional process affects the steady state deformation in this temperature region. Transmission electron microscopy revealed the development of a cell structure in the steady state and dislocations without any tangles in the cell interiors. Therefore because the ratecontrolling process could not occur inside of the cells dislocation annihilation occurred through cross slip around the cell walls. According to these creep parameters and microstructural observations the observed creep region is suggested to be a new creep region occurring through a non-diffusional process within the existing deformation mechanism map of Al at less than 0.4 Tm. © 2013 The Japan Society for Technology of Plasticity.

Combined compression torsion tests were performed on the thermal-treated and as-machined silicon nitride ceramics to investigate their fracture behavior under multiaxial stress states. The thermal-treated samples showed considerable high strength and low anisotropy to the grinding direction in flexure tests compared to the as-machined samples. Under combined compression and torsion stress states, the thermal-treated samples showed considerably higher tensile strength than that of as-machined samples at low compressive stress states and weakening with increasing compression stress. The as-machined samples showed little decrease in tensile strength with increasing compression stress and comparable tensile strength with the thermal-treated samples under a highly compressive stress state. The behavior of thermal-treated samples were well described by the statistical theory of multiaxial fracture for volume-distributed flaws combined with a mixed-mode fracture criterion with the shear sensitivity constant of 1.75 and 1.65 for Shetty's criterion and the ellipsoidal criterion, respectively. (C) 2011 Elsevier Ltd. All rights reserved.

A new advanced ceramic thruster made of monolithic silicon nitride ceramics was developed for the planetary exploration spacecraft AKATSUKI (PLANET-C) at Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). To ensure its operation onboard the spacecraft, the reliability of the ceramic thruster against micrometeoroid hypervelocity impact has been investigated. Silicon nitride plates were impacted by spheres of stainless-steel and other materials with 0.2-0.8-mm diameters in the velocity range up to 8.0 km/s using a two-stage light-gas gun. Using crater depth data under various impact conditions, the penetration equation of silicon nitride was determined. The impacted samples showed fracture patterns of three types: cratering, cratering with spallation, and perforation. These fracture patterns were well categorized by the multiple forms of the penetration equation. (C) 2011 Elsevier Ltd. All rights reserved.

In the construction of a space radio telescope, it is essential to use materials with a low noise factor and high mechanical robustness for the antenna surface. We present the results of measurements of the reflection performance of two candidates for antenna surface materials for use in a radio telescope installed in a new millimeter-wave astronomical satellite, ASTRO-G. To estimate the amount of degradation caused by fluctuations in the thermal environment in the projected orbit of the satellite, a thermal cycle test was carried out for two candidates, namely, copper foil carbon fiber reinforced plastic (CFRP) and aluminum-coated CFRP. At certain points during the thermal cycle test, the reflection loss of the surfaces was measured precisely by using a radiometer in the 41-45 GHz band. In both candidates, cracks appeared on the surface after the thermal cycle test, where the number density of the cracks increased as the thermal cycle progressed. The reflection loss also increased in proportion to the number density of the cracks. Nevertheless, the loss of the copper foil surface met the requirements of ASTRO-G at the end of the equivalent life, whereas that of the aluminum-coated surface exceeded the maximal value in the requirement even before the end of the cycle.

A simultaneous measurement system for strain and acoustic emission signals (AE signals) was developed for one fiber Bragg grating sensor (FBG sensor) using a fiber ring laser. The system consists of an erbium-doped fiber amplifier (EDFA), an optical circulator, optical couplers, photo detectors and an FBG sensor. A CFRP beam bending test was carried out to confirm the possibility of simultaneous measurement of both strain and AE signals from a single FBG sensor. In the test, signals from a conventional electric resistive strain gage and piezo-electric AE sensors were compared to those from the FBG sensor. Those were equivalent each other, and the simultaneous measurement of strain and AE signals using the newly developed system was verified.

A single microparticle launching method is described to simulate the hypervelocity impacts of micrometeoroids and microdebris on space structures at the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency. A microparticle placed in a sabot with slits is accelerated using a rifled two-stage light-gas gun. The centrifugal force provided by the rifling in the launch tube separates the sabot. The sabot-separation distance and the impact-point deviation are strongly affected by the combination of the sabot diameter and the bore diameter, and by the projectile diameter. Using this method, spherical projectiles of 1.0-0.1 mm diameter were launched at up to 7 km/s. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3498896]

Creep behavior was investigated carefully for typical face-centered cubic (fee) metals, i e, high purity Al, Cu, and Pb, below 0 3T(m), where T(m) is the melting temperature. All samples showed marked creep behavior at such low temperatures, with an apparent activation energy of 15-30 kJ mol(-1), a stress exponent of 2-5 and a grain size exponent of 0. These results show a new creep region that has not appeared in deformation mechanism maps of pure fcc metals (C) 2010 Acta Materialia Inc Published by Elsevier Ltd All rights reserved.

This paper includes the concept of polymer-lined composite tank, design method, and verification results of prototype tanks. At first the outline of polymer-lined composite tank, their benefits, and overview of fabrication process are shown. This also includes a comparison with the previously developed metal-lined composite tank. Next, the design method based on not only stress and strain but fracture mechanics is shown. Fracture-mechanical evaluation is important to prevent delamination of composite or exfoliation of metal parts. Some example of choice for metal material is also shown. At last the results of the tests for three prototype tanks and other trial tanks are shown. Their failure modes are evaluated and prevent method for each failure is described. As the final result, the third prototype tank passed a proof pressurized test and repeated pressurized tests for MEOP. The test data were fine and any delamination, exfoliation or H2 gas leak was never detected. This concludes the completion of polymer-lined composite liquid hydrogen tank for Reusable Vehicle Test. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

ISAS/JAXA is now planning to adopt a thruster made of monolithic silicon nitride (SN282 manufactured by Kyocera Co.) onto a Venus exploration probe, PLANET-C, in replacement of conventional niobium heat-resistant alloy. Silicon nitride is still brittle and requires precise analysis on multiaxial thermal stresses induced during firing, though it has high toughness among other structural ceramics. This study evaluated quasi-static fracture characteristics of SN282 considering the surface conditions through compression-torsion biaxial fracture tests as well as the conventional four-point-bending tests. The samples were applied to the mechanical tests either as-ground or after annealing at 1300 degrees C in air for 1 h, which formed an oxidation layer of more than 250nm on the specimen surface. Symmetry four-point-bending tests showed that annealing improves flexure strength and reduce the difference caused by grinding directions. Biaxial stress fracture tests showed the high compressive stress makes the influence of facial crack insensitive.

Acoustic emission during a pressure proof test of a CFRP pressure vessel was measured using an FBG sensor, as well as a conventional piezoelectric sensor for reference. Part of an FBG-inscribed optical fiber other than the grating section was affixed to the vessel so that the Bragg wavelength of the FBG was not affected by the strain applied to the vessel. The FBG sensor showed resonant characteristics and could detect AE continuously throughout the test where the maximum strain reached 1 %. Acoustic emission detected by the FBG sensor exhibited a cumulative behavior similar to that detected by the piezoelectric sensor. The FBG sensor was demonstrated to have comparable AE detection capability to conventional piezoelectric sensors.

The deformation behaviour of high-purity aluminium at low temperatures was investigated in order to re-examine Ashby-type deformation mechanism map. All specimens with different purities showed significant creep below room temperature. Under the same stress and temperature, the steady-state creep rate increased with increasing purity of the material. They showed stress exponents around 5.0 and apparent activation energies around 20 kJ/mol at temperatures below about 400 K, and 4.0 and 70-80 kJ/mol at temperatures above that temperature. The grain size had no effect in the low temperature region. From the microstructural observation, secondary slip system was observed. These features imply that pure aluminium deforms in the different mode from the ambient temperature creep of h.c.p. metals which has similar activation energy.

Even at ambient temperature or less, below their 0.2% proof stresses all hexagonal close-packed metals and alloys show creep behaviour because they have dislocation arrays lying on a single slip system with no tangled dislocation inside each grain. In this case, lattice dislocations move without obstacles and pile-up in front of a grain boundary. Then these dislocations must be accommodated at the grain boundary to continue creep deformation. Atomic force microscopy revealed the occurrence of grain boundary sliding (GBS) in the ambient-temperature creep region. Lattice rotation of 5 degrees was observed near grain boundaries by electron backscatter diffraction pattern analyses. Because of an extra low apparent activation energy of 20 kJ/mol, conventional diffusion processes are not activated. To accommodate these piled-up dislocations without diffusion processes, lattice dislocations must be absorbed by grain boundaries through a slip-induced GBS mechanism.

Hexagonal close-packed metals and alloys show significant creep behavior with extremely low activation energies at and below ambient temperature even below their 0.2% proof stresses. It is caused by straightly-aligned dislocation arrays in a single slip system without any dislocation cuttings. These dislocation arrays should, then, pile up at grain boundary (GB) because of violation of von Mises' condition in H.C.P. structure. The piled-up dislocations have to be accommodated by GB sliding. Electron back scatter diffraction (EBSD) analyses and atomic force microscope (AFM) observations were performed to reveal the mechanism of GB sliding below ambient temperature in H.C.P. metals as an accommodation mechanism of ambient temperature creep. EBSD analyses revealed that crystal lattice rotated near GB, which indicates the pile up of lattice dislocations at GB. AFM observation showed a step caused by GB sliding. GB sliding below ambient temperature in H.C.P. metals are considered to compensate the incompatibility between neighboring grains by dislocation slip, which is called slip induced GB sliding.

This paper reports creep tests on three kinds of polycrystalline hexagonal close-packed metals, i.e. commercially pure titanium, pure magnesium, and pure zinc, in the vicinity of ambient temperature even below their 0.2% proof stresses. These materials showed significant steady state creep rates around 10-9 s(-1) and had stress exponents of about 3.0. Arrhenius plots in the vicinity of ambient temperature indicate extremely low apparent activation energies. Q, of about 20 kJ/mol, which is at least one-fourth of the Q of dislocation-core diffusion. Ambient-temperature creep also has a grain-size effect with an exponent of 1.0. These parameters indicate that ambient-temperature creep is a new creep deformation mechanism in h.c.p. materials. [doi:10.2320/matertrans.M2009223]

Intragranular deformation mechanisms were investigated for ambient-temperature creep of pure hexagonal close-packed (h.c.p.) metals. i.e. commercially pure titanium, pure magnesium and pure zinc, by transmission electron microscopy and electron back-scatter diffract ion pattern mapping analysis. First, straightly aligned dislocation arrays were observed in all of the specimens. Second, although the Burgers vectors of (a) and several slip systems were observed, only one slip system was activated inside of each grain. Third, the deformation twins that form during creep hinder creep strain. Therefore, the dominant intragranular deformation mechanism of ambient-temperature, creep is a planner slip of dislocations inside of a grain. [doi: 10.2320/matertrans.M2009224]

The suppressing effect of ambient-temperature creep of CP-Ti by cold-rolling was reported. Annealed plates of CP-Ti grade 2 were cold-rolled with thickness reductions, and then creep tests under the applied stresses of 0.6-0-9 sigma(0.2) were performed at ambient temperature. With increasing the thickness reduction, the twin, dislocation density and sigma(0.2) were found to increase. At the same time, the steady-state creep rates under the applied stress for constant sigma/sigma(0.2) were decreased. The cold-rolled sample with 20% thickness reduction was then annealed at 813 K for 2400 s to decrease only the dislocation density. After the annealing, the steady-state creep rate remained constant, suggesting that the reduction of the steady-state creep is associated with the increasing twin density. (C) 2008 Elsevier B.V. All rights reserved.

The role of grain boundaries (GBs) for ambient-temperature creep of h.c.p. metals was investigated using pure Zn with several grain sizes. To reveal the relaxation mechanism of ambient-temperature creep, scanning electron microscopy and atomic force microscopy were performed to evaluate the amount of grain boundary sliding. Grain orientation variations were then measured using electron backscatter diffraction to investigate a lattice rotation after ambient-temperature creep. The results obtained by these experiments are as follows: (I) Strong grain size dependency, i.e. larger grain size showed lower total true strain. This is different from high temperature dislocation creep. (2) Grain boundary steps of a few tenths of a micrometer gave evidence of grain boundary sliding during ambient-temperature creep. (3) Lattice rotation of a few degrees was observed near GBs, which indicates that dislocations piled up at GBs. (4) Grain boundary sliding is considered as accommodation process of piled-up dislocations with an apparent activation energy of 18 kJ/mol. (C) 2008 Elsevier B.V. All rights reserved.

An adhesive bonding structure around a metallic mouthpiece of a cryogenic composite tank was analyzed with fracture mechanics. The energy release rate was formulated analytically by considering difference in strain energies in tension and bending before and after crack growth based on a simplified mathematical model. The analytical results were compared by finite element method calculations for five example tanks; there was a fairly good match between the analytical and numerical results. This analysis provides a guideline for the initial optimal design of a cryogenic composite tank based on fracture mechanics.

Hexagonal close-packed metals and alloys show significant creep behavior at ambient temperature, even below their 0.2% proof stresses. That creep behavior arises from straightly aligned dislocation arrays in a single slip system without any dislocation cuttings. These dislocation arrays pile up at grain boundary (GB) because of violation of von Mises' condition. Therefore, GB sliding must accommodate the piled-up dislocations. In this study, electron back scatter diffraction (EBSD) analyses and atomic force microscope (AFM) observations revealed an accommodation mechanism in ambient temperature creep region. Lattice rotation occurred near GB during creep, as revealed by EBSD analyses, indicating the pile up of lattice dislocations there. GB sliding during creep was revealed by AFM observations.

A new ceramic thruster for an interplanetary probe is currently under development. Monolithic silicon nitride (Si₃N₄) , which has good heat resistance and high fracture toughness among conventional structural ceramics, is a promising material for a high performance thruster. However ceramics are brittle compared to metallic materials. In order to evaluate reliability of the ceramic thruster as a space-use component, fracture behavior against micrometeoroid impacts was investigated. First the risk probability of the meteoroid impacts which may occur during a mission was estimated based on impact energy which may cause failure of the material. Second, damage of the silicon nitride ceramics by a possible micrometeoroid impact was investigated experimentally. Hypervelocity impact tests were carried out on the silicon nitride ceramic samples with a two-stage light-gas gun. Impacts at various velocities ranging from 1.0 km/s up to 4.5 km/s brought about three types of failure. However no shattering occurred by the hypervelocity impact with a possible energy. The experimental results together with the risk evaluation considering the flight mission conditions show that the Si₃N₄ ceramic thruster for the interplanetary probe would have no serious problems caused by a meteoroid impact during the flight mission even with local damage.

A new advanced ceramic thruster made of monolithic silicon nitride (Si(3)N(4)) is under development for the next interplanetary probe of PLANET-C Venus exploration mission in Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). In order for secure operation of a spacecraft with a ceramic component onboard a real mission, the reliability against micrometeoroid impacts on the ceramic component has to be investigated in addition to the quasi-static mechanical and thermal analyses and verifications. First, the risk probability of the micrometeoroid impacts was evaluated by using an interplanetary flux model, and the risk evaluation in terms of impact energy was proposed by combining the velocity distribution with the flux model. The probability of impacts on the ceramic thruster during the mission was estimated with this model. Second, hypervelocity impact tests were performed with a two-stage light-gas gun. Three types of failure were observed: one was only a crater formed on the impact surface. Another type was crater formation on the front-face and spall fracture on the back-face and in the last type a perforation was formed in addition to cratering and spalling. The samples did not either shatter or breakdown for the impact energies tested in this study. The impact failure morphology observed in this study showed dependency on the plate thicknesses and the projectile kinetic energy. The energy-based risk evaluation together with the series of the hypervelocity impact tests indicated that the silicon nitride ceramic thruster onboard the interplanetary probe would have only a local damage and survive during the mission term. (C) 2008 Elsevier Ltd. All rights reserved.

This paper includes everything which is necessary to make a polymer-lined cryogenic composite tank, i.e. concept, design method, manufacturing process, and recent results of tests. They are also the history of development of the tank in our Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS/JAXA). At first the concept and production method of the tank is explained. In the production process it is the key that whole liner is formed at one time by use of heat melt bonding. Next the design method based on fracture mechanics is derived. Here an analytical solution of energy release rate for the bonding structure is formulated by considering difference in strain energies in tension and bending before and after crack growth based on a simplified mathematical model. In addition to this derivation, comparison with numerical results and one design optimization sample are also shown. After that the results of tests for actual tank is shown and current status of the tank is discussed. At last conclusion is shown.

Adhesive bonding structure around a metalic mouthpiece of a cryogenic composite tank was analyzed based on fracture mechanics. Energy release rate was analytically formulated considering difference in strain energies in tension and bending between before and after the crack growth based on a simplified mathematical model. The analytical results were compared with the calculated results by finite element method for five example tanks; they revealed fairly good match. This analysis gives a guideline of the initial optimal design of a cryogenic composite tank based on fracture mechanics.

An ultrasonic inspection method for a graphite ingot was developed to detect internal planar flaws that are oriented in various directions; this method is necessary to perform quality assurance of throat inserts of solid rocket motors. Major problems that are unique to this graphite inspection were solved. An ultrasonic beam in graphite shows uneven propagation behavior both within and among individual ingots. That individual unevenness engenders variation in echo heights of flat-bottomed holes, which can be compensated through two-dimensional scanning accompanying a change in incident angles of two directions. This scanning procedure is therefore necessary to detect internal planar flaws that orient in various directions. The unevenness among ingots can be compensated by measuring the wave velocity and attenuation coefficient in the test block itself before inspection. A test block including artificial internal flaws was fabricated and inspected using the developed method. It was then sliced into several thin disks. The sliced disks were inspected using the conventional ultrasonic testing method using a normal beam technique. The two methods detected identical flaws, thereby validating the developed method. The technique described here has been enacted as JIS Z 2356 under the title, "Method of automatic ultrasonic inspection for graphite ingot".

Closed-cell Al-Mg alloy (A5052) foams are produced through accumulative roll-bonding (ARB) process. The preform plate containing uniform titanium hydride (TiH2) particles is manufactured after six ARB cycles. Macroscopic porosity is as large as 47% in the condition of infrared heating at 913 K. Compressive tests are carried out in the condition of different loading axes. Yield stress in the normal direction (ND) was lower than other loading directions. Anisotropic deformation behavior is due to the anisotropic cell morphology which was induced during the ARB process. (c) 2006 Elsevier B.V. All rights reserved.

Institute of Space and Astronautical Science (ISAS/JAXA) in collaboration with Nlitsubishi Heavy Industries (MHI) has developed fuel and gas tanks for reaction control system and orbital control systern of satellites; A tank is fabricated through welding of two thin, hemi-spherical or conical parts, which are fabricated by superplastic blow forming. Mass-productivity is not an important factor but the forming precision and flexibility in the process are important for this application. ISAS and MHI, therefore, developed a new blow-forming technique, which has high flexibility in terms of tank size because it requires a furnace but not a hot-press machine. Some typical propulsion tanks fabricated through this process are presented.

A new application of superplasticity has been developed in the field of porous metals. Porous metals manufactured through a liquid-state foaming process often include large pores and inhomogeneous pore distribution which decrease in the mechanical properties. A solid-state foaming process enables to suppress the collapse and coalescence of pores, but high porosity is not achieved due to the large flow stress. Superplastic flow during the solid-state foaming is effective to accelerate the foaming rate and to increase the porosity, Superplastic 5083 aluminum alloy sheets are used as a starting material for manufacturing of porous aluminum. A preform plate containing titanium hydride particles as a foaming agent is produced through roll-bonding processing. Porous aluminum with small pores and relatively high porosity is manufactured through superplastic foaming process. A thin sandwich panel with a porous aluminum core and porous bulge structures can be manufactured by utilizing the superplastic flow. This technique of superplastic forming and foaming (SPFF) processing has a potential for near net-shape forming as well as evaluation of the solid-state foaming of porous metals.

Metals with a hexagonal closed packed (HCP) structure show creep behavior at ambient temperature. Features of this phenomenon are: (1) it appears in all and only HCP structure metals and alloys; (2) dislocations are contributing; and (3) it shows very low apparent activation energy (ca. 10 kJ/mol). Transmission electron microscope (TEM) observation was conducted on crept specimens of commercially pure Ti (CP-Ti), pure Mg, and Zn. Results showed no dislocation tangle. The dislocation arrays were aligned straightly inside the grain. The dislocation array consisted of one dislocation type. One slip system was activated in the ambient temperature creep condition. Therefore, it was considered that work hardening does not occur, and that creep deformation continued.

Lightweight metallic foams are an attractive material having excellent energy absorption and acoustic damping. The density of magnesium is the smallest among structural metallic materials, and is about two third of the density of aluminum. It is, however, difficult to produce magnesium foams by conventional process because of their chemical activity. This paper provides a novel manufacturing process of magnesium foams. Accumulative diffusion-bonding process can produce a magnesium matrix composite (preform) containing titanium hydride (TiH2) particles as a blowing agent. Foaming tests of three magnesium alloys, AZ31, AZ91 and ZA146, revealed that low solidus temperature is effective to produce fine cell morphology. Chemical composition is significantly important to optimize the cell morphology of magnesium foams.