To fabricate thick nonporous surface layer on a closed-cell type aluminum foam (Shinko Wire Company, Ltd.: ALPORAS, relative density: 0.1, mean diameter of pore: φ4 mm) without causing the inside fracture, friction stir incremental forming (FSIF) and incremental hammering (IH) processes were combined. The cell walls at surface of the aluminum foam were folded by IH in the early stage of the process, and then the folded cell walls were stirred and joined by FSIF. The nonporous surface layer fabricated by the combination of IH and FSIF was approximately 1.6-4.0 times thicker than that fabricated by FSIF.

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In this study, we report the fabrication of high-strength aluminum (Al) matrix composites (AMCs) reinforced with in situ formed Al_4C_3 nanorods up to about 16 wt.%. Different contents (1,2 and 4 wt.%) of carbon nanotubes (CNTs) were used as the starting materials for the template reaction with Al matrix. Al-CNT powder mixtures were dispersed by a high energy ball milling process and then consolidated by spark plasma sintering and subsequent hot-extrusion. The microstructural and mechanical properties of Al_4C_3-reinforced composites were characterized. With 1 and 2 wt.% CNTs, homogeneous CNT dispersion was achieved and resulted in singly distributed 4 and 8 wt.% Al_4C_3 nanorods, respectively. However, with 4 wt.% CNTs, there existed CNT agglomerations in the powder mixture and it led to remained CNTs in the composite reinforced with about 16 wt.% Al_4C_3. Consequently, AMCs containing 8 wt.% Al_4C_3 showed highest tensile strength.

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In-situ observation and evaluation on the fracturing behavior of multi-walled carbon nanotubes (MWCNTs) reinforced powder metallurgy (PM) Al matrix composite materials was carried out by using tensile test equipment installed in scanning electron microscopy (SEM). Peeling and fracturing phenomena of MWCNT embedded hi Al matrix were obviously and directly observed hi this study. The peeling formation and resultant effect on tensile strength of the composites were examined. Through transition electron microscopy (TEM) characterizations, it was clarified that defective structures like inter-wall bridges cross-linked adjacent walls of MWCNTs. This structure was helpful to improve the inter-wall bonding conditions, and resulted in the effective load transfer between the walls and resultant peeling behaviors of MWCNTs. CNT/Al composites indicated a large improvement of strength compared to the monolithic pure Al material.

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Tribological properties of textured surface fabricated with discontinuous micro cutting process were investigated. An aluminum cast alloy (AC8A) disc was used for the specimen. The texturing process was carried out with a CNC machining center with a novel geometry of the cutting edge. The resulted surface morphology consisting from micro dimples having 200-300 μm of the diameter and 5-10 μm of the depth with controlled area fraction of 10 and 40 % and the milling cut finished top region. The tribological properties evaluated with a ring on disc type testing apparatus in lubricated condition showed that the friction coefficient of the textured surface was low and stable from the begining of the experiment. Dependence of the area fraction of the friction coefficient was also found. Further reduction of the friction coefficient was achieved on the textured surface having polished top region. It is concluded that the proposed discontinuous micro cutting process is effective means to fabricate micro texture for reduction and stabilization of the friction resistance.

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The present study describes role of soft intermetallic layer on friction properties of molybdenum disulfide penetrated chromium alloy steel in lubricated condition. Tin was used as the soft intermetallic layer and was coated with a micro shot peening on the various surface texture consisting from micro dimples. The coating thickness was approximately 1-2 μm. Molybdenum disulfide (MoS_2) was penetrated on the coated surface with a roller burnishing. The resulted surface morphology was relatively flat and consisted from tin and MoS_2. The tribological properties were evaluated with a 3 ball on disc type testing apparatus mated with chromium alloy (SUJ2) ball having flat contact surface. Results showed that the friction coefficient of the non-dimpled surface was low and stable.

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The present study describes friction properties of polymer overlay containing molybdenum disulfide (MoS_2) fine particles formed on the aluminum cast alloy (AC8A) surface in lubricated condition. The material of the polymer overlay was poly amide imide and fabricated on the micro dimpled surface using a spin coating process. The overlay thickness was approximately 10 μm and the various overlay containing 0, 10, 20 and 30wt. % MoS_2 were prepared. The friction properties evaluated with a 3 ball on disc type testing apparatus showed that the friction coefficient of the overlay containing 20 and 30% MoS_2 was low and stable at the beginning of the experiment without the peeling off. A micro indentation was applied to evaluate the mechanical properties of the overlay and showed the stiffness increased with the increase of the MoS_2 content. Effect of the mechanical properties on the friction properties was discussed.

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Carbon fiber reinforced plastic (CFRP) is potentially applicable to precision structures such as antenna reflectors and mirrors for space telescopes due to its thermal stability and high specific stiffness. CFRP mirrors consist of honeycomb core and thin CFRP skins have both low areal density and dimensional stability, however, honeycomb-shaped dimples was observed on the surface sheet with temperature change. In this study, we fabricated double-core structure sandwiches which have foam layer between skin and honeycomb core in order to prevent from dimple appearing and evaluated its surface accuracy. As the result, inserted foam layer could be effective material in the suppression of the dimple. In addition, we simulated surface deformations of these sandwich panels using finite element analysis.

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Tensile tests were performed using plate specimens of self-reinforced polyethylene (SRPE) with short ultra-high molecular weight polyethylene (UHMWPE) fibers. The effect of fiber length on the properties was investigated. The specimens were made by hot-pressing the stacked HDPE films with short UHMWPE fibers distributed between each film at high temperature. The SRPE specimens showed much larger elastic modulus and tensile strength than monolithic HDPE specimens while their fracture took place at smaller strain than the monolithic HDPE specimens. Focusing on the effect of UHMWPE fibers, the specimens reinforced with longer fibers of 120 μm showed larger elastic modulus and tensile strength than those reinforced with shorter fibers of 60 μm. It was considered that the difference was attributed to the shearing force between fibers and matrix or pull-out force of fibers during tension taking into consideration the feet that lots of pulled-out fibers were observed on the fracture surface.

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Puncture impact tests of injection molded glass reinforced polypropylene with and without elastomer were conducted at temperatures of 23℃ and -30℃ to compare and quantify the effects of elastomer addition and residual glass fiber length on material impact energy absorption. The addition of elastomer resulted in a significant increase in the impact energy absorption at 23℃, but had little effect at -30℃. The residual fiber length dramatically influenced the impact energy absorption for the glass fiber reinforced polypropylene without elastomer addition. At -30℃, glass fiber reinforced polypropylene without elastomer and with residual glass fiber lengths of greater than 3 mm achieves equivalent impact energy absorption as the elastomer modified glass fiber reinforced polypropylene with similar glass fiber length.

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An effect of compressive loads on the out-of-plane fatigue properties of thick CFRP laminates with the toughened interlaminar layers was investigated. The unidirectional [O_<88>] and quasi-isotropic [45/0/-45/90]_<11s> laminates were fabricated using T800S/3900-2B prepreg. This prepreg is constituted of a fiber layer and an interlaminar toughened layer in which polyamide particles are dispersed uniformly. The spool shaped specimens which were machined from the thick laminates were loaded in the out-of-plane direction of the specimen. The fatigue tests were performed at three types of stress ratios of R= 0.1, -1 and -3. As the results of the fatigue tests, it was conformed that the fatigue life was reduced with the compressive load under same maximum stress. In addition, the effect of the stress ratio on the fatigue life was dependent on the laminate configuration. When the cyclic loading at R= -3 were applied in the unidirectional specimen, the shear fracture mode was observed in the high-cycle region.

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Carbon fiber reinforced plastics (CFRP) is now widely used in aerospace structural applications, particularly in industry, due to their high specific strength and stiffness characteristics. If curing conditions in CFRP laminate are not within the specified tolerances, voids may be formed in matrix and result in significant reductions in matrix dominated strength such as transverse tension, flexure and shear. In this study, tests were performed for more detailed understanding about the effect of voids on matrix dominated strengths using the specimen with intentionally included voids. Transverse strength test and short beam strength test was performed. These specimens were observed by X-ray computed tomography (CT) to understand the relationship voids and strength reduction.

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In this study, we synthesized cup-stacked carbon nanotubes (CSCNT) supported platinum nanoparticles (PtNPs) using liquid phase plasma treatment, and morphology, particle size distribution and supported amount of the PtNPs supported onto the CSCNT were investigated. PtNPs were supported onto the CSCNT surfaces using liquid phase plasma treatment after adsorption of Pt precursor onto the CSCNT surfaces. First, observation of the CSCNT surfaces with field-emission transmission electron microscopy (FETEM) were conducted to examine the morphology of the PtNPs supported onto the CSCNT surfaces. PtNPs were well anchored and uniformly dispersed on the CSCNT surfaces without any dispersion stabilizer due to an exposure of the dangling bonds of graphene sheet which has high chemical reaction field. Moreover, the PtNPs size distribution of the CSCNT supported PtNPs were investigated with FETEM images of the CSCNT surfaces. The average size of PtNPs supported onto the CSCNT surfaces was about 2.2 nm, which was smaller than the PtNPs of conventional electrode catalysts for PEFC (3〜5 nm). Thermogravimetric analysis (TGA) of the CSCNT supported PtNPs were performed to investigate the supported amount of Pt of the CSCNT supported PtNPs. The supported amount of Pt was about 14.7 wt%, which was smaller than the PtNPs of conventional electrode catalysts for PEFC (50〜60 wt%).

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Magnesium-calcium alloy-based composites reinforced with vapor grown carbon fibers (VGCFs) are supposed to possess satisfactory high-temperature applications. However, poor wettability of magnesium with carbon fiber is a technical problem encountered in fabrication of the composites. In order to cover the wetting problem, wetting behavior of magnesium alloys on graphite sheet, pure nickel, and nickel coated graphite sheet were investigated using sessile drop method. The graphite was non-wetting by both Mg-5Al alloy and Mg-5Al-3Ca alloy with contact angles about 120°. The droplet of magnesium alloys on nickel plate spread rapidly. Contact angle of Mg-5Al-3Ca alloy decreased from about 94° to 43°. Wettability of magnesium alloys on nickel coated graphite sheet was improved through the dissolution of nickel into the liquid magnesium alloy. Calcium addition showed negative effect on contact angle of nickel substrate, and also slightly hindered the spread of magnesium alloy droplet on nickel coated graphite sheet.

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The electric power generation properties of lead zirconate titanate (PZT) ceramic have been studied under various cyclic loading conditions. The maximum voltage increases with an increase in the frequency under the triangular and sinusoidal wave modes, whereas the voltage decreases with an increase in the frequency for the square wave mode. The maximum electric voltage for all wave mode is saturated at around 15Hz, namely, the electric voltage for the three wave modes is almost constant even if the frequency increases by more than 15Hz. The maximum electric voltage increases with an increase in the frequency under the triangular and sinusoidal wave modes, because of the high kinetic energy. For the square wave mode especially at high frequency, a low electric voltage is obtained, which is caused by the switching back of the electric generation arising from rapid loading speed.

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This paper proposes an easy-to-use torsion test method for bioceramics in artificial bone application, because the artificial bones were sometimes broken in torsion in clinical courses and an international standard of torsion test has been needed to guarantee durability of the bioceramics. The dimensions of specimens were 8 mm in diameter, 20 mm in gage and 10 mm square in grip. The samples were chalk, 3 types of porous hydroxyapatites (porosity = 75% or 50%), and porous and dense hydroxyapatite / tri-calcium phosphate composites (porosity = 35% or 0%). The specimen was set in an opening torque measuring device for PET bottles, attached with cylindrical jigs to grip it. Torque was given by hands, with a special attention paid not to cause bending moment and axial load to the specimen. Except for dense hydroxyapatite / tri-calcium phosphate composite, most of samples were fractured in torsion at the gage, leaving spiral fracture surfaces. The torsion strength of the bioceramics ranged from several MPa to several tens MPa.

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This paper proposes the modification of the Sneddon's solution in a wide range of ν from 0 to 0.5 through the numerical analysis on the unloading behavior of a simulated conical nanoindentation with a finite element method. As a result of the modification, the coefficient of linearity between the indentation elastic parameter k_e and Young's modulus E is empirically given as a function of v and the inclined face angle of the indenter, β, where k_e is defined as k_e≡P/h^2 with the indentation load P and penetration depth of the indenter h. According to the linear relationship between k_e and E, it is found that elastic rebound during unloading of a nanoindentation is uniquely characterized by a representative indentation elastic modulus E^* defined in terms of E, ν and β, and that the value of E^* can be evaluated from the P-h relationship with k_e and β. For an isotropic elastoplastic solid, the indentation unloading parameter k_2 defined as k_2≡P/(h-h_r)^2 for a residual depth h_r is different from k_e even though a linearly elastic solid with k_e and elastoplastic solid with k_2 have a common E^*. In order to evaluate E^* of an elastoplastic solid, the corresponding k_e is estimated from k_2 with an empirical equation as a function of the relative residual depth ξ defined as ξ≡h_r/h_<max> for the maximum penetration depth h_<max>. A nanoindentation experiment confirmed the validity of the numerical analysis for evaluating the elastic modulus

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Tensile test of Indium Tin Oxide (ITO) deposited on polyerhylene naphthalate (PEN) films used in solar cells were carried out. It was found from tensile tests that many AE signals were detected in ITO films. On the other hand, the electric resistance of ITO + PEN film was also measured later than first AE signal during tensile tests. In order to identify AE sources, in-situ observation of specimen and measurement of electricity resistance were also carried out. It was demonstrated that AE behavior shows good agreement with the cracking behavior in ITO. In addition to it, AE monitoring could be detected damages in ITO under mechanical strain earlier than were measurement of electricity resistance. Consequently, it was suggested that AE technique was extremely effective technique for damage detection and evaluating the damage accumulation process in films used in solar cells.

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Mg_2Si (Magnesium silicide) has been expected as the materials used for thermoelectric (TE) technologies due to lightweight, abundance of its constituent elements and its non-toxicity. Because TE conversion devices are subjected to various thermo-mechanical loadings during operation, evaluation of the mechanical properties of Mg_2Si is necessary for designing reliable TE modules. Furthermore, Mg_2Si is used at 600℃ in the view of thermoelectric properties, however, the effect of heat exposure at 600 ℃ on the mechanical properties of Mg_2Si has not been sufficiently investigated. In the present study, therefore, mechanical properties of Mg_2Si after heat exposure at 600 ℃ were evaluated. The effect of holding time on the strength was also investigated. The specimen was cut from an as-sintered pellet and was polished and heated in Ar atmosphere at 600 ℃ for 100 h, 250 h, respectively. The four-point bending test was carried out on as-sintered and heat-exposed specimens to obtain bending strength at room temperature. The as-sintered specimen showed bending strength of 48 MPa on average. In case of 100 h heat-exposed specimen, the bending strength was almost equal to that of as-fabricated specimen. However, it increased after the heat exposure for 250 h up to about 90 MPa. The fracture surface observations revealed that the increase in strength is attributed to slight oxidation on the surface.

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ZrB_2-SiC-ZrC(ZSZ) is known as one of ultra-high temperature ceramics (UHTCs) composite materials. In this study, four different composition of the ZSZ and ZrB_2-SiC were fabricated by spark plasma sintering. The specimens were oxidized at 1700℃ for 10 min in two different oxygen partial pressure. After the oxidation tests, SiO_2 and ZrO_2 were formed on the surface of both ZSZs and ZrB_2-SiC. In addition, unoxidized region still remained under these oxides. In case of the ZSZ, thickness of oxidized layer increased with ZrC volume content. After oxidation test under low oxygen partial pressure, porous layer was observed in the ZrB_2-SiC, but no such layer was observed in the ZSZs. Since the porous layer is brittle and low strength, the ZSZ has an advantage in the mechanical properties after oxidation. In order to validate the advantage of the ZSZ, the oxidation behavior was thermodynamically analyzed using volatility diagrams.

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