Recently, porous aluminum has attracted special interest as a new functional material. However, the application of porous aluminum remains limited due to high-cost fabrication and low productivity. To overcome these problems, the authors proposed a new fabrication method by using friction stir processing (i. e. FSP route precursor method). In this study, at first, the precursors of ADC12 and A1050 were fabricated by FSP route individually and those precursors were welded by friction stir welding (FSW). Moreover, by foaming the welded precursor, ADC12-A1050 porous aluminum was manufactured. Based on the cross-sectional images and X-ray CT images, porosity and pore structures were examined. Although ADC12-A1050 bonded precursor tends to foam from the part of ADC12, ADC12-A1050 porous aluminum with high porosity and high circularity can be manufactured under proper forming conditions.

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Porous aluminum is expected to apply as multifunctional material in various industrial fields because of a very lightweight material with high energy absorptivity. In this study, by using friction stir processing (FSP) route, the porous aluminum/dense steel sandwich panel was manufactured. In the FSP route, both mixing a blowing agent into aluminum and bonding the aluminum precursor to dense steel plate can be conducted simultaneously. It was shown that the sandwich panel of porous aluminum/dense steel which have high interface strength with high porosity of 80% and comparatively good pore structure is successfully manufactured by optimizing the foaming condition.

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Porous aluminum is a multifunctional material with very lightweight and high energy absorptivity. In this study, the applicability of friction stir processing (FSP) route precursor method to the manufacture of near-net-shape porous aluminum component was discussed. Precursors fabricated by FSP route were foamed in a rectangular shape die, and it was shown that rectangular near-net-shape porous aluminum with a porosity of approximately 70% can be successfully manufactured under suitable foaming condition. The pore structure of near-net-shape porous aluminum was similar to those in commercially available porous aluminum.

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Porous aluminum is a multifunctional material with lightweight and high energy absorption properties. In this study, A1050-A6061 functionally graded porous aluminum was fabricated by friction stir processing (FSP) route. It is expected that both mixing a blowing agent into aluminum and bonding A1050 precursor to A6061 precursor can be conducted by FSP. It was shown that A1050-A6061 seamless functionally graded porous aluminum can be successfully fabricated at a holding temperature of 1003 K and at a holding time of 10 min.

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Closed-cell porous aluminum is a multifunctional material with both lightweight and high energy absorption properties. These properties are considered to be governed by morphology of pores of porous aluminum. In this study, compression test was conducted in the X-ray CT system and deformation process of pores was nondestructively observed during compression. It was shown that deformation process of individual pore can be observed in this system.

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Fast time-resolved measurement was carried out to detect photon emission (PE) during crack propagation in silica glass. The specimen was fractured by three-point bending at room temperature under 10^-4 Pa. The top and bottom surfaces of the specimen were coated with Au. Resistance of those surfaces was monitored to detect crack propagation in the specimen. Simultaneously, the PE was detected with photomultiplier tube. The PE around 650 nm increased and then gradually decreased during the crack propagation, while the strong the PE around 450 nm was observed at the beginning of the crack propagation. Moreover, both of the emissions started just before the onset of the crack propagation. It might be due to micro-cracks leading to a main crack propagation. The result suggests that a fracture precursor can be detected by monitoring the PE.

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Effect of mechanical milling conditions on hardness and constituent phase of pure titanium was investigated. The mechanical milling atmosphere and amounts of stearic acid, added as a process control agent (PCA), were varied. The hardness of mechanically milled (MMed) pure titanium powders in the air atmosphere was approximately 15 % higher than that in the argon atmosphere. The mean particle size of the MMed powders in the air atmosphere was smaller compared to that in the argon atmosphere. The MMed pure titanium powders produced by two different atmospheres had almost the same constituent phase. The MMed powders were consolidated into bulk materials by spark plasma sintering (SPS). The hardness of the SPS materials produced from the MMed powder in the air atmosphere was 13 % higher than that in the argon atmosphere. The oxygen content in the SPS materials significantly increased by the MM processing in the air atmosphere. Formation of β-Ti or ω-Ti was observed in the all SPSed materials. The products formed by phase transformation were not influenced by the heating rate and the hold time in SPS process. Vickers hardness of 881 HV was obtained for the SPSed material fabricated from 4 h of MM with 0.50 g of PCA in Ar atmosphere at 1073 K for 180 s with the heating rate of 2.33 K/s.

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Aluminium (Al) based composites containing vapor-grown carbon fibers (VGCF) and carbon nanotubes (CNT) are fabricated by spark plasma sintering (SPS) in this paper. The thermal conductivity of the composite is three times higher than that of Al material. The composite materials will be able to use as a radiation fin of a heat exchanger and a heatsink. To apply the composites to real used conditions, the strength at several temperatures of the composites should be clarified experimentally. In this paper, therefore, pure tensile tests are conducted to clarify strength of the composites at several temperatures. According to the experimental result, the composite has the different thermal effect on the strength from pure Al. And then the interfacial strength between the fibers and the matrix is improved at high temperature.

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Two kinds of the alumina composites made with chemical-vapor-deposition (CVD) -grown MWCNTs and thermal annealed version of this MWCNTs type that have highly crystalline layers and higher flexural rigidity were prepared to investigate the effects of such properties of the MWCNTs on the mechanical and electrical properties of the composites. SEM observations on the fracture surface demonstrated that no severe phase segregation was observed for the composites prepared by using the thermal annealed MWCNTs, whereas the CVD-grown MWCNTs revealed an inhomogeneous structure. The experimental results have shown that lower percolation threshold and higher electrical conductivity were observed for the thermal annealed MWCNT/alumina composites, presumably owing to the good dispersibility of the MWCNTs in the matrix. However no apparent change in the mechanical properties have been found in the two types of MWCNTs. TEM observation suggested that both types of MWCNTs, rather than pulling out from the alumina matrix, broke in the “sword-in-sheath” and “clean break” manner during crack opening in the composite. The present study implies that the use of MWCNTs having higher flexural rigidity leads to better MWCNTs dispersibility in the composites, and it should be critically important to prevent the rupture in MWCNTs.

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The mechanical properties of the clustered shrinkage pores in high-pressure die cast aluminum alloy ADC12 were evaluated through the serial sectioning experiment and the image-based finite element analyses. We have investigated the effect of pores on the fatigue strength, and found a mechanical significance of the clustered shrinkage pores, which considerably undermines the fatigue strength of die cast aluminum alloys. In this study, we constructed twenty three unit cell models for the homogenization analysis based on the three-dimensional image of a clustered shrinkage pore. From the homogenization analysis and uniaxial extension analysis, we obtained the equivalent elastic constants and the micro stress concentration factor as a function with respect to the porosity volume fraction.

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Plastic deformation energy is transformed into heat in about 90 percent. If heat generation by plastic deformation of work metal is applied to its temperature rising, deformation resistance can be reduced. We propose a new cold stamping technology characterized by using a die which has low thermal conductivity to apply heat generation by plastic deformation to uniform temperature rising of work metal. Our aim in this study is to achieve ecological and technical advantages such as energy saving, high formability and high form accuracy. In this report, the effect of die materials and deformation rate on deformation load was examined by compression tests on TW340 and SUS304. The following results were obtained: 1) Deformation load on TW340 and SUS304 using ZrO₂ for the die is lower than using SKD11 for the die to make efficient use of heat generation by plastic deformation. 2) Deformation rate has optimum value related to thermometric conductivity of work metal.

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This study aims to evaluate position and size of corrosion on a steel plate using low-frequency So mode Lamb waves. Dome-shaped artificial defects with diameter of 4 mm to 30 mm and depth of 2.7 mm to 5.1 mm on 6-mm-thick carbon steel plate were machined. Low-frequency So mode lamb wave whose amplitude profile along thickness of a plate has almost uniform was generated by striking a distal plane of a plate with a rectangular type longitudinal PZT transmitter. We can detect the defect with 4 mm diameter and 2.7 mm depth and also detect aligned defects with separation distance of 100 mm individually. Distance to the defects from the transmitter could be estimated from arrival times of reflected wave by the defects and calculated velocity of So mode lamb wave. Wave amplitude reflected by the defects that was normalized by amplitude of wave reflected by an opposite edge to incident point was almost proportional to cross-sectional area of the defects

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The major problem for forging of magnesium alloy is the lack of process ductility at the low temperature. The Mg₉₆Zn₂Y₂ is a high strength magnesium alloy material developed by Mr. Kawamura in Japan. Mg₉₆Zn₂Y₂, a newly developed high strength magnesium alloy material is expected as forged parts of the automobile and materials for aerospace applications. It is necessary to clarify forging process characteristics of this material. The purpose of the present study is to examine increasing of ductility of forging process for the Mg₉₆Zn₂Y₂ material. For this purpose, cylinder upsetting tests were performed by this method of two stages. In addition, the deformation resistance and ductility of the material were examined. The two stages forging process is effective for an increase of ductility of the material.

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A roll caster for making the five layers clad strip was devised. In this process, three twin roll casters were set at the vertical tandem position. This vertical type tandem twin roll caster was assembled. Five layers clad strip can be cast directly from the molten metals by the vertical type tandem twin roll caster. First layer was cast by the first caster (upper caster). Second layers were cast by the second caster (mid caster). Third layers were cast by the third caster (lower caster). Procedure of casting to make five layers clad strip is as below. First layer was cast by first caster. This layer was drawn into second caster. When first layer went into the roll-bite of the second caster, the molten metal of second layers was poured to second caster. This three layers clad strip was drawn into third caster. When this three layers clad strip went into the roll-bite of the second caster, the melting of third layers was poured to third caster. In this study, two kinds of five layers clad strips were tried by this caster. One of 3003 aluminum alloy was used for first and second layers, and 4045 aluminum alloy was used for third layers. The other of 3003 aluminum alloy was used for first layer, and AC4C aluminum alloy was used for second layers, and 4045 aluminum alloy was used for third layers. Two kinds of five layers clad strips could be cast by this caster. The interfaces of five layers clad strips were clear and flat.

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A single roll caster equipped with a scraper (SRCES) was devised in order to improve the free solidified surface. The scraper contacted to the free solidified surface at the constant force. The some amount of semisolid layer on the solid layer was removed and the surface became flat. The scraper was made from the mild steel plate. The mild steel plate was covered by the insulator paper to prevent the cooling of the melt. The melt pool was made on the roll by the side dam plates, back dam plate and the scraper. Therefore, a tip or a nozzle was not needed. In this study, AA6022 and AA5182 aluminum alloy were cast by SRCES. The scraped surface condition of the strip cast by SRCES was investigated. The free solidified surface was flat. The as-cast strip could be cold rolling. The free solidified surface could be cold-rolled and the roughness was reduced. The mechanical properties of cast strip were investigated by the 180 degrees bending test. There was no difference between the roll contact surface and the free solidified surface after cold rolling. This result showed that the free solidified surface could be improved up to the roll contact surface by the scraper and cold rolling. Furthermore, in this study, the scraper was applied to a twin roll caster. The aluminum alloy clad strip was cast by twin roll caster equipped with a scraper. Interface of the clad strip was connected and clear.

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This study was aimed at investigating of Casting of hypereutectic Al-Si alloy strip by a vertical type twin roll caster. Hypereutectic Al-Si alloy has some useful advantages i.e., low thermal expansion, better thermal conductivity and wear registrant. Recently, the plate of hypereutectic Al-Si alloy which thickness is thinner than 1mm, is demanded. The hypereutectic Al-Si is hard and brittle. Therefore, only the many times of hot rolling was useful process to make thin plate. In the present study, the roll casting of Al-25%Si strip was tried by a vertical type high speed twin roll caster from the point of energy saving. The twin roll size of the roll was φ300×W100. Roll-load was set low enough to prevent the sticking of the strip. The roll speed was operated at 20m/min and 40m/min. The solidification length was 100mm. The Al-25%Si strip, which thickness was about 1.7mm, was cast directly from the molten metal. The primary Si was not dispersed uniformly. The eutectic Si became fine and globular. The roll cast Al-25%Si was expected superior ductility.

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In this study, we try to reveal the relationship between the plastic deformation and the microscopic crystal misorientation evolution by using the homogenized finite element (FE) procedure with the proposed crystal plasticity constitutive equation. Since plastic deformation of polycrystal sheet metal is greatly affected by its initial and plastic deformed textures, multi-scale FE analysis based on homogenization theory with considering micro polycrystal morphology is required. We formulated a new crystal plasticity constitutive equation to introduce not only the effect of crystal orientation distribution, but also the size of crystal grain and/or the effect of crystal grain boundary for the micro FE analysis. The hardening evolution equation based on strain gradient theory was modified to consider curvature of crystal orientation by using crystallographic misorientation theory. We employed two-scale structure, such as a microscopic polycrystal structure and a macroscopic elastic/plastic continuum. Our analysis code predicts the plastic deformation of polycrystal metal in macro-scale, and simultaneously crystal texture and misorientation evolutions in the micro-scale. The crystallographic misorientation evolution induced by the plastic deformation of polycrystal aluminum alloy was investigated by using the multi-scale FE analysis with new proposed hardening evolution equation. We confirmed the availability of our analysis code employing the new constitutive equation through the comparison with numerical and experimental results of uniaxial tensile problem.

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In this paper, the energy absorption capacity for circular tubes with corrugated surface is studied based on the numerical analysis, FEM. The axial compressive behaviour for circular tubes with corrugated surface behaves more stable and efficient as compared with that for standard tubes. A simple and predictable method of energy absorption capacity for circular tubes with corrugated surface is needed for designing the tubes as impact energy absorption devices for vehicles. In this study, effects of strain hardening and tube geometries on the radius of curvature for each wrinkle observed in a tube are discussed. Also, based on the numerical results, a simple and approximate method for estimating the average compressive load in axial direction and the axial crushing distance is developed, and the validity of the approximation is checked by comparing the prediction with numerical and experimental results.

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Strips are produced in steel, plastic and paper making industries and the strip is a primitive structure. Lateral movement problems cause low productivity in continuous strip processing lines. Now most these problems are solved experimentally only. Development of realistic, robust and speedy simulation methods for these problems is required. In this paper, we propose a large deflection strip model to simulate the running strip on rolls. The new model is a basic one, which is defined on approximated curvilinear coordinate systems along the strip deflection and includes in-plane bending. We confirmed that numerical simulation results from the new method correspond with conventional results from the large deflection plate model.

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There is a phased array technique which makes use of flaw echoes, measured by every two-element combination as a pulser and a receiver, to synthesize high amplitude beams for any arbitrary angle and/or focal depth. Using this full waveform sampling and processing (FSAP) technique, we show a flaw reconstruction method for the angle beam phased array ultrasonic testing. In the case of the angle beam testing, it is necessary to estimate a beam path from a wedge to a specimen appropriately and to consider the mode conversion at the wedge-specimen interface. The main feature of our method is the use of processed wave data, called “scattering amplitude”, which is extracted from each flaw echo. First, the basic principle of the reconstruction method is described and then some flaw reconstructions are demonstrated. The resolution of the flaw images and the accuracy of flaw sizing can be improved by means of the scattering amplitude.

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In this study, transverse crack initiation in cross-ply CFRP laminates under fatigue loading was evaluated focusing on the transverse crack growth and saturation. The number of cycles that a transverse crack initiates was predicted by the analytical model on the basis of the modified Paris law. In addition, the lower threshold of the transverse crack formation was researched by a modified Paris-law, and the fatigue limit of the transverse crack initiation was evaluated by calculating the stress applied in 90° layer where the increase of the transverse cracks was saturated. Moreover, transverse crack was observed by using scanning electron microscope (SEM) in order to investigate the mechanism of transverse crack initiation. As the results, the analytical results for predicting the transverse crack initiation showed good agreement with the experimental results. Moreover, it was shown that the lower threshold of the transverse crack formation existed, and that the stress applied in 90° layer at saturation state was almost equivalent to the fatigue limit of the transverse crack initiation from the experimental results. From the observation with SEM, it was found that the initiation of the transverse crack under fatigue loading depended on the interface property between fiber and matrix.

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Appendix E-9, “Elastic-Plastic Fracture Mechanics Evaluation,” in the JSME Rules on Fitness-for-Service for Nuclear Power Plants (Codes for Nuclear Power Generation Facilities) uses the load multiplier Z-factor that is applied to elastic-plastic fracture mechanics evaluation for a pipe circumferential flaw of austenitic stainless steel piping and ferritic steel piping. The Z-factor is defined as the ratio of the limit load to the load at tearing instability. Here, the Z-factor of the current JSME Rules on Fitness-for-Service for Nuclear Power Plants was developed for a through-wall pipe circumferential flaw with the angle of 60°. In Code Case JSME S NA-CC-002, ”Alternative Rule of Criteria on Allowable Flaw Angle for Circumferential Crack” published in 2005, the Z-factor equations are applicable to a circumferential surface flaw including the angle of greater than 60°, but the Z-factor equations of the Code Case were conservatively formulated as upper-bounded those Z-factors for through-wall pipe circumferential cracks including the angle of greater than 60°. However, the original purpose of the Code Case was to eliminate the limitation of flaw angle and evaluate non-through-wall flaws. Accordingly, Z-factors for non-through-wall flaws should be developed to have the consistency. Therefore, Z-factor equations of austenitic stainless steel piping and ferritic steel piping have been developed for non-through-wall flaws.

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To prevent stress corrosion cracking (SCC) initiation at the inner surface of the butt-welding region of a small-diameter pipe, a residual stress improvement method has been developed. In this method, the local expansion process is applied to the butt-welding region with ice plugs. During the local expansion process, tensile yielding is generated in the butt-welding region. The tensile yielding generated at the inner surface is larger than that of the outer one. After this process is applied, compressive residual stress can be introduced at the inner surface due to larger tensile yielding. In this study, residual stresses at the inner surface of the butt-welding region were measured, and SCC initiation tests in the accelerated environment (in boiling 42% Magnesium Chloride) were performed. The measured residual stresses and the results of SCC initiation tests proved this method effectively reduces residual stresses and prevents SCC initiation.

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