A plastic flow joining method for fixing cold bars with a hot plate, “indentation joining”, is proposed, and the optimum conditions of the proposed joining method for AA6061 aluminum bar and plate are examined by experiment and finite element simulation. In the developed plastic flow joining method, the cold bar is indented into the hot plate to pierce the plate without lubrication on a press. It is expected that the newly created surface of the hot plate will cause seizure and a high joining strength may be attained. After cooling of the plate, thermal shrinkage of the plate may assist to clamp the bar strongly. The attained shear bonding stress of the aluminum bar·plate is approximately 40% of the shear strength of the plate material. The bonding mechanism is discussed from the viewpoints of seizure of the plate and clamping force associated with the process. In the case of indentation temperature of 300 °C, about 80% of the bonding strength is due to seizure during indentation of the bar and about 20% of the bonding strength is due to clamping force after cooling of the plate.

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Amorphous carbon film (a-C:H) applications, such as hard disks, require films with nanometer thicknesses. In an indentation test, the obtained hardness values of these films are affected by substrates. On the indentation tests, we studied the effect of substrate hardness on films less than 200 nm in thickness. a-C:H and Si doped a-C:H (a-C:Si:H) films were deposited by electron cyclotron resonance plasma chemical vapor deposition onto aluminum (Al) and silicon (Si) substrates. The film thicknesses were approximately 140 nm. The hardnesses of the a-C:H film and substrates were obtained using a high-resolution indentation tester (pico-dentor) with a Vickers tip whose depth resolution was 0.04 nm. Maximum indentation loads were varied from 0.01 to 0.5 mN. The Martens hardnesses of films on the Al and Si substrates were 600 and 7000 N/mm², respectively. On the a-C:Si:H film deposited on the Al substrate, the hardnesses increased from 1600 to 3900 N/mm² with decreasing indentation load. The hardnesses of the films deposited on the Si substrate decreased from 5300 to 3500 N/mm² when the maximum indentation loads were reduced. The effect of the substrates increased with the maximum load increasing. From these findings, the actual hardness value was determined to be 3600 N/mm². These results indicate that the high-resolution indentation test achieved hardness estimations for nanometer-thick films with certain hardnesses.

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In this study, the photocatalytic activity of annealed TiN powders and films were examined to clarify the influence of annealing temperature and pressure on the photocatalytic properties under UV and visible light irradiation. TiN films were deposited on stainless steel and quartz substrates by DC magnetron sputtering, and annealed TiN powders were used as a reference material to confirm the effectiveness of TiN oxidation. TiN powders which were annealed at 873-1173K, showed obvious photocatalytic activity, under both UV and visible light irradiation. However, annealed TiN films on the stainless steel substrate showed low photocatalytic activity except for those annealed at 823K and 1.0kPa. This is because film annealed above 923 K consisted of a dominant rutile phase, and the film annealed at 1023K delaminated from the stainless substrate. For the quartz substrate, the dominant phase of the films annealed at 823 and 923 K was anatase, and all films remained completely on the substrate after annealing. In particular, the film which was annealed at 923K and 1.0kPa showed high photocatalytic activity both under UV and visible light irradiation. Thus, good photocatalytic activity can be obtained by annealing TiN with an appropriate temperature, pressure and substrate material.

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A number of special blanking processes are available for producing fine cut edges and blanking with a negative clearance is one of them. The aim of this study is to elucidate the mechanism of precision blanking with a negative clearance by using finite element method. Experiments were performed for two kinds of aluminum sheets over a wide range of clearances between -30 and 20 percent of the sheet thickness. Fine blanked products with no fractured zone were obtained in the case with negatively large clearances, while fractured zone appeared on the cut edge by conventional blanking. Corresponding simulations were carried out by using the Ayada's and the Jeong's criterion to predict ductile fracture initiation. Numerical results with both criteria agreed well with the experimental results except a few cases accompanied by secondary shear. The difference in blanking mechanism between the positive and the negative clearance blanking was explained by the variation of the damage value; it reached the threshold value for positive clearances, while it was kept low and never exceeded the threshold for negatively large clearances.

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The ultrasonic testing (UT) of an austenitic steel with welds is difficult due to the acoustic anisotropy and local heterogeneity. The ultrasonic wave in the austenitic steel is skewed along crystallographic directions and scattered by weld boundaries. For reliable UT, a straightforward simulation tool to predict the wave propagation is desired. Here a combined method of elastodynamic finite integration technique (EFIT) and digital image processing is developed as a wave simulation tool for UT. The EFIT is a grid-based explicit numerical method and easily treats different boundary conditions which are essential to model wave propagation in heterogeneous materials. In this study, the EFIT formulation in anisotropic and heterogeneous materials is briefly described and an example of a two dimensional simulation of a phased array UT in an austenitic steel bar is demonstrated. In our simulation, a picture of the surface of the steel bar with a V-groove weld is scanned and fed into the image based EFIT modeling.

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Through intensive analysis of the tensile stress-strain curves of a variety of steel sheets over a wide range of strain rates on the order of 10^-2 ∼10³ s^-1 obtained by using the Sensing Block Type High Speed Material Testing System, it was confirmed that the newly-partially extended constitutive model (Tanimura-Mimura Model) is useful to simulate the dynamic stress-strain curves for the entire range of deformation reaching as far as fracture over the wide strain rate range, as long as the quasi-static stress-strain curve of the material concerned is only known in advance. Dynamic tensile properties, over the wide strain rate range and the entire strain region reaching the true fracture strain, of ten kinds of aluminum alloys, which compose of a wide strength level from a commercial pure aluminum to the extra super duralumin are systematically studied. It was cleared that the aluminum alloys belonging to the one group exhibit the positive strain rate sensitivity and the aluminum alloys belonging to another group exhibit the negative sensitivity or almost non sensitivity. It was found that the values of the true fracture strain ε_f are substantially not affected by the strain rates, for all the tested aluminum alloys, and are closely related to the values of the tensile strength σ_B whose values are obtained by the quasi-static nominal tensile stress-strain curves.

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Fatigue crack growth behavior of AZ61 magnesium alloy was investigated in low humidity (55% relative humidity) and 3.5% NaCl spray environments under various stress ratios. Fatigue crack growth rates became higher with increasing load ratio for both environments. However, the results of fatigue crack growth test under 3.5% NaCl spray environment showed lower fatigue crack propagation rate compared to those in low humidity environment for all stress ratios. The difference in crack growth rate was resulted from the different crack closure behavior. The crack growth curves arranged by ΔK_eff merged to one curve regardless of stress ratio. In order to investigate the higher crack growth resistance in 3.5% NaCl spray environment, fracture surface observation was carried out using a scanning electron microscope. Fracture surface of the specimen tested in 3.5% NaCl environment was fully corroded. However, no corrosion was observed for the specimen tested in low humidity environment. The corrosion products on the fracture surface could induce higher crack closure point. This might lead to the higher crack growth resistance observed for the specimen tested in 3.5% NaCl spray environment.

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In this study, for prediction of free surface roughening behavior with a simple model, we focus on finite element (FE) modeling considering microscopic material inhomogeneity due to different flow stresses for each crystal grain. For this purpose, an evaluation method of microscopic material inhomogeneity using the micro Vickers hardness distribution was proposed and discussed. It was found that decreasing the ratio of the average impression size to the average grain size is necessary to express the microscopic material inhomogeneity appropriately using the hardness distribution. The flow stress-strain curve of the inhomogeneous FE model was in good agreement with those of the conventional homogeneous FE model and the experiment. Therefore, the deformation response of FE simulation considering microscopic material inhomogeneity presents a real response macroscopically. The free surface roughening obtained from FE model considering microscopic material inhomogeneity is closer to the experimental result of the plane strain bending test with decreasing indentation load in the hardness test for evaluating the microscopic inhomogeneity of the material.

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Ti and its alloys have been widely used for various industrial and medical applications because of their excellent characteristics of low density, high strength, high corrosion resistance and high biocompatibility. However, it is not easy to produce the complicated shape and precise parts because of their poor workability. Therefore, the advanced powder processing techniques such as Metal Injection Molding (MIM) are hoped to be a suitable technique for fabricating complex shaped Ti or its alloy parts with low cost. In this paper, various high performance Ti alloy materials such as Ti-6Al-4V added Mo or Fe or Cr have been developed by MIM process. The effect of powder type and sintering conditions on the microstructures, relative density and mechanical properties of injection molded compacts were investigated. Also the oxygen and carbon contents were checked in detail for obtaining high performance properties as same as the wrought materials. Eventually, more than 1000MPa of strength and 15% of elongation were achieved with MIM process.

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Nanoporous carbon materials for use as hydrogen storage materials were fabricated from rice husks. Rice husks from agricultural waste changed to porous carbon materials by heat treating and KOH activation. The specific surface area of the porous carbon materials increased from 11 to 2061 m²/g as the KOH weight ratio increased. The pore volume of the materials also increased from 0.01 to 0.88 cm³/g by KOH activation. The pore sizes of the activated porous carbon materials were distributed around 0.6 and 1.2 nm at micro-pore ranges. These results suggested porous carbon material have micro-pore structure. The hydrogen storage capacity of the porous carbon materials showed a 0.62 wt.% at 298 K under 12 MPa. The fabrication of hydrogen storage materials from agricultural waste rice husks was achieved. The results indicate that porous carbon materials synthesized from rice husks have micro-pore structures which influence their hydrogen storage capabilities.

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Tailor welded blanks with two different materials (SPCC-SPFC980Y) were V bent by laser forming which is a bending method with thermal stress induced by rapid heating by means of laser irradiation, and it is suitable for bending of large spring back sheets since spring back is not affected. Forming conditions for SPCC part and SPFC980Y part were changed. A 50W CW YAG laser was employed with laser scanning number of 10 and defocus length of 25mm. When same laser power (38W) was employed for SPCC and SPFC980Y parts, bending angle of SPCC part was greater than that of SPFC980Y part. However, when laser power was 40W for SPFC980Y part and 36W for SPCC part, the bending angle of both parts were almost same and this means constant bending angle was obtained by controlling the laser power. Uniform bending angle was also obtained by controlling the laser scanning velocity as well as the laser power.

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In this study, water-soluble biodegradable resin was introduced as a coating agent to improve the interfacial strength and then to fabricate a high-performance green composite with polylactic acid (PLA) and hemp yarn. Dip coating was carried out for hemp yarn and the green composites were fabricated by hot processing. The coated green composite achieves a high tensile strength of 117 MPa even though the fiber volume fraction is less than 30%. Interfacial shear strength (IFSS) was measured by a single fiber pull-out test, and the effect of water-soluble resin on the tensile properties of the composites was evaluated. As a result, when using coated natural bundles, the IFSS value is smaller than when using noncoated natural bundles. On the basis of observations of the fractured surface of composites and initial yarns using a scanning electron microscope (SEM), the effect of the impregnation of water-soluble resin into the natural bundles on the tensile strength is discussed in detail. It is found that water-soluble resin is effective in improving the mechanical properties of the composite, although the interfacial strength between PLA and water-soluble resin was decreased, and as a result, the tensile strength of green composites increases by almost 20%.

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Biaxial tensile tests of austenitic stainless steel sheet (SUS304) 0.2mm thick have been carried out using cruciform specimens. The specimens are loaded under linear stress paths in a servo-controlled biaxial tensile testing machine. Plastic orthotropy remained coaxial with the principal stresses throughout every experiment. The successive contours of plastic work in biaxial stress space changed their shapes progressively, exemplifying differential work hardening. The geometry of the entire family of the work contours and the directions of plastic strain rates have been precisely measured and compared with those calculated using conventional yield functions. Yld2000-2d [Barlat, F., Brem, J.C., Yoon, J.W., Chung, K., Dick, R.E., Lege, D.J., Pourboghrat, F., Choi, S.H. and Chu, E., International Journal of Plasticity, Vol. 19, (2003), pp. 1297-1319.] with an exponent of 6 was capable of reproducing the general trends of the work contours and the directions of plastic strain rates with good accuracy. Furthermore, in order to quantitatively evaluate the Bauschinger effect of the test material, in-plane tension/compression tests are conducted. It was found that the non-dimensional (σ /σ_u) - Δε /(σ_u/ E) curves measured during unloading almost fall on a single curve and are not affected by the amount of pre-strain, where σ is the current stress during unloading, σ_u is the stress immediately before unloading, Δε (< 0) is the total strain increment during unloading.

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We examined whether surface flaw on wire rods grow or are removed during drawing by finite element method (FEM) analysis and experiments. The deformation behavior of V-shaped, concave, and U-shaped transversal flaws were observed upon repeated drawing. We clarified the conditions under which these transversal flaws are removed in order to achieve a surface condition similar to that of the area without flaw. The effects of the angle, width and depth of surface flaw on their removability were also clarified.

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With the development of advanced medical treatment, the demand for fine tubes in the medical field is now very high. The technology employed must enable the production of tubes with various features, such as the following four; small size, high quality, high functionality, and low processing cost. In the soft metal mandrel drawing, that is, drawing with a flexible mandrel, is a good method of fine tubes with high drawability; however, this is not appropriate for the fabrication of long tubes because of the difficulty in the complete removal of the mandrel from the tube. Then We proposed new drawing methods using fluid such as water for mandrel. Fluid mandrel drawing with water is the most appropriate for fabricating tube products, because water is more easily removed from the tube surface than oil.

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Soldering and anisotropic conductive adhesives (ACAs) are widely used for assembling electronic devices with narrow-pitch terminals. Solder bump methods need a number of processes, while interconnects of ACAs are less reliable. The purpose of this study is to develop a novel assembling method. The Self-organization assembly method using active resin containing solder fillers may allow reliable interconnects by simple process. The focus of this paper is on the movement of fillers, one of the fundamental processes of the Self-organization assembly method. In-situ observations on the behavior of 40 µmφ molten fillers in the resin revealed irregular movement of the fillers at a velocity of several µm/s. Numerical analysis, using improved volume of fluid method, indicated that even 10% difference of interfacial energy between half sides of a 40 µmφ filler could move the filler at the velocity of several mm/s. The inhomogeneous distribution of the interfacial energy is thought to be caused by the remaining surfactant elements.

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