Due to their high specific surface area and measurable change in conductance according to the chemical environment changes, carbon nanotubes (CNTs) have been proved to be an ideal material for next generation of gas sensor. However, before CNTs-based sensor can become a candidate for commercial implementation, there are still challenges including mass production of sensor arrays and improvement of sensor reproducibility. In this research, a high sensitivity CNT sheet-based gas sensor was fabricated, which can push forward the commercialization of CNT-based sensor. By controlling the reaction conditions during chemical vapor deposition (CVD) process, a spinnable CNT array was synthesized reproducibly. The CNT sheets were drawn from a sidewall of spinnable CNT array. CNT sheets were directly fixed onto Au electrodes and were heated up to 300°C for 2 h to oxidize amorphous carbon. Gas detection toward hydrogen gas was operated in a quartz tube chamber. With the change of gas concentration, the change in sensor resistances as response and recovery behavior was measured using a programmable electrometer. A sensitivity of 5% for 4% H₂ was achieved at 200°C for pure CNT sheet and a sensitivity of 2.5% towards H₂ gas at room temperature was achieved by Pd functionalization.

Stress migration (SM) is a promising technique for fabricating micro/nano materials due to its mass productivity, simple processing, and high purity of the fabricated materials. When a passivated metallic sample is heated, thermal stress would generate and stress gradients would happen, driving atoms to migrate to low stress positions and form into micro/nano materials. However, these materials usually form in random distribution and uncontrollable sizes, limiting their further application. In this study, a controllable fabricating method of Al micro wires utilizing SM with artificial holes is proposed. Through this method, micro wires with desired diameters at predetermined positions are able to be fabricated.

The possibility for development of thin-filmed magnesium alloy was investigated in this study. A file with a thickness of ~ 30 μm was successfully produced by controlling of initial microstructure, rolling temperature and applied strain. This thin-filmed magnesium alloy had a strong basal texture due to wrought process, i.e., the rolling; however, the mechanical properties, such as hardness and damping capacity, were superior to those of pure magnesium. This result is expected to open doors to the development of functional magnesium alloys having good mechanical properties.

Transparent conductive films (TCFs) are widely used in various electronic devices. In addition, due to the excellent transparency (T=97.7%) and electrical conductivity by the effect of sp2 hybridized orbital, using graphene for the materials of TCFs is ideal. Typical method for manufacturing graphene TCFs is chemical vapor deposition (CVD) method. However, CVD method takes a high cost. On the other hand, liquid phase exfoliation (LPE) is the method for obtaining thin-layer graphene by peeling graphite in the organic solvent. In the LPE, method of making graphite oxide and peeling graphite is often used, but this method has problem that falling down conductivity due to structural defect in graphene. In this study, we used pressure homogenizer to obtain thin-layer graphene without using chemical treatment. Then, we made TCFs by using thin-layer graphene and evaluated some characteristics. Finally, we investigated transmittance and sheet resistance of the TCFs.

Polyimide/Fe/Mg/Ti thin films were produced with the resistance heating of vacuum deposition for absorbing and desorbing hydrogen using Mg hydride for making a hydrogen storage system. The thickness of Mg was 10000 nm and the amount of Fe was about 4 at.% in the samples. There were five kinds of thickness of Ti, 15, 50, 200, 500, 1000 nm. From the results of XRD the samples that were 15 nm, 50 nm, 200 nm thickness of Ti made the Mg hydride under 2.5 MPa and even 200°C hydrogenation conditions. Ti in the hydrogenation of Mg might play the role of a catalyst for improving hydrogen absorption properties of Mg. It resulted that TiO₂ formed at the surface of the samples promoted a hydrogen dissociation into atoms. And also thinning of Mg layer facilitated crystalizing MgH₂. The samples that absorbed hydrogen desorbed hydrogen at 235 - 280°C and the temperature is less 140 - 185°C than that of commercial MgH₂ powder. It might be that laminated Fe underneath Mg layer reduced the desorption temperature of hydrogen.

Transparent polycrystalline alumina (TPA) was able to be fabricated by two-step pulsed electric current sintering (TS-PECS). In order to produce a large TPA sample, controlling the temperature distribution across the sample-die-punch system is very important. In this study, the large polycrystalline Al₂O₃ samples, such as Φ30 mm in diameter, were fabricated by TS-PECS with various conditions. As well, the heterogeneity of grain size and optical transmittance of Al₂O₃ samples were investigated. Both the sintering temperature and the heating rate for Φ30-mm TPA sample should be lower than those for Φ15-mm one. The heterogeneity of Φ30-mm samples was also more serious than the smaller samples. The heterogeneity in the samples, especially in large samples, may be caused by the heterogeneity of temperature distribution during PECS process.

Fiber-reinforced self-healing ceramic exhibits the competition between crack propagation and crack self-healing. The purpose of this study is to clarify the competition behavior in Alumina matrix/ SiC interface/ Alumina fibers composite under the accumulated damage. The creep test is performed for evaluate of accumulated damage, and the creep text was conducted at 1000°C and 1200°C. The creep strength at 1000°C was determined to be 137 MPa, because the creep rate reached to 0 after 300 h. As the creep strength is much higher than the crack imitation strength (= 67 MPa), the present authors found that the competition between crack propagation and crack self-healing occurs at 1000°C.

CMCs used poly-organoborosilazane's interphase technique between carbon fiber or SiC fiber and SiC matrix have been investigated. Characteristic of interphase treatment technique is wet process and the interphase is fabricated by simple process. And so this process have made the forming interphase speedy and low cost. Poly-organoborosilazane was synthesized by co-ammonolysis of organochlorosilane and borontrichloride with controlling composition and molecular structure. C/SiC composite was fabricated by PIP method with polycarbosilane. C/SiC by poly-organoborosilazane's interface technique showed 400MPa of flexural strength. In case of SiC/SiC , we can get similar consequence to C/SiC.

The aim of this study is to make transparent conductive glass by using carbon nanofibers (CNFs). The percolation paths of CNFs in the glass matrix composite was designed with silica glass particles coated with CNFs, which are made by layer by layer technique. We have found that material design with the layer by layer technique decreases the critical volume fraction of CNFs for the percolation, which is detected by the steep increase in electrical conductivity as a function of CNFs' volume fraction. The glass composite shows relatively high optical transparency at that CNFs' volume fraction.

The thermal shock fracture behavior of alumina ceramics was characterized by Disc-on-Rod test, which was developed by the authors. Thin disc specimen was uniformly heated to high temperature and the center region of specimen was quenched by means of contacting with the cool metal rod. Then, the center of disc specimen was subjected to the biaxial tensile stress. The temperature distribution of specimen was measured by a high speed infrared camera and used for the determination of transient thermal stress field by the finite element analysis. Furthermore, microfracture process was characterized by AE measurement. In order to obtain various thermal stress ratio, elliptical specimens, as well as circular specimens, were prepared. Consequently, experimental technique for evaluating thermal shock behavior under various stress ratio has been developed.

In-situ observation during heating and cooling was carried out in order to understand damage evolution behavior of environmental barrier coating system at high temperature. In addition, in-plane deformation was measured using digital image correlation (DIC) technique. Quality of acquired image was not changed up to 1200°C. The results of strain distribution measurement showed that HTOS could measure in-plane average strains up to 1200°C.

C/ZrB₂-SiC-ZrC (C/ZSZ) composite is one of the candidate materials for thermal protection systems of aerospace application. This heat-resistant material indicates excellent ablation resistance at high temperature above 1700°C. In the present study, C/ZSZ and C/ZrB₂-SiC were fabricated by melt infiltration of Si. ZSZ, ZrB₂-SiC and ZrC-SiC were also prepared by spark plasma sintering (SPS) to compare with C/ZSZ. Oxidation behavior and ablation properties of C/ZSZ at 1700°C were investigated by oxyhydrogen torch testko in air atmosphere at 1700°C for 600 s. After the ablation test, the cross-section was observed using SEM-EDS. The experimental results showed that C/ZSZ has excellent recession resistance compared with C/ZrB₂-SiC. The ZSZ matrix of heated surface converted into a ZrO₂-SiO₂ layer. As the increase of ZrC content in matrix, the recession resistance of ZrO₂-SiO₂ layer was improved. ZrO₂-SiO₂ layer of C/ZSZ protected the carbon fiber bundle from ablation effectively and contributed to high recession resistance under dynamic pressure.

Melt infiltration (MI) method is a practical process to fabricate dense SiCf/SiC composites in a short time. In our previous works, dense SiCf/SiC compositeswith excellent mechanical properties were fabricated by melt infiltration (MI) process using Si-16at%Ti alloy. In this study, wet oxidation behavior of Si-TiSi₂ eutectic matrix in the SiC fiber-reinforced composites and monolithic TiSi₂ were evaluated. Oxide layer consisting of TiO₂ and SiO₂ was formed on monolithic TiSi₂ after oxidation. On the other hand, SiO₂ was produced in the eutectic matrix after oxidation, and the matrix showed superior oxidation resistance similar to the Si. These results were explained based on Gibbs energy change of oxidation reaction.

The thermal deformation of double cantilever specimen with support structures made from Ni-base alloy, Inconel 718, fabricated by selective laser melting (SLM) was estimated by thermos-elastic-plastic finite element method. The temperature dependent physical properties, coefficient of thermal elongation, Young modulus, and two-linear-line hardening law, were considered in the numerical analysis. The estimated deformation values were compared with the experimentally fabricated double cantilever specimens' dimensions. The difference of estimated values and measured values were around 1%, though the layer compilation process of SLM was not considered in the analysis.

It is investigated by numerical simulation that the effect of support structure shape on the residual stress and thermal deformation after the selective laser melting process for Ni-base alloy. The analyzed models were double cantilever models with comb type support structure under the thin plate and triangular prism on the tips. The comb width was varied. The models were virtually cooled from 1240°C down to 100°C. And the bottom of support structure was detached from the base-plate. The equivalent stress showed that the residual stress was not generated in comb support structure but the triangle prism part. The tip of the triangle prism part had the maximum equivalent stress, which suggests that the detachment of support structure begins from the tip. The deformation after the detachment of from the base-plate revealed the cantilever with fat comb had relatively smaller spring-back and flat surface. The cantilever without support structure showed large spring-back.

Accidents due to fatigue of bolted joints frequently occur. In fatigue characteristics of bolts made of high strength steel alloy, it is well-known that the mean stress which is applied on the bolt as clamping force does not have an influence on the fatigue strength. But an influence of the mean stress on fatigue strength for bolt made of non-ferrous materials has not been investigated yet. In this study, fatigue test for a bolted joint made of aluminum alloy A5056 were conducted to investigate the influence of mean stress on fatigue strength. The result showed that fatigue strengths for A5056 bolts decreased with an increase in the mean stress. It is considered as one of the causes that fatigue fracture origins were different in A5056 bolt. And fatigue fracture origins tended to be affected by stress amplitude.

The purpose of this study is to investigate the tribological properties of plants-derived polyamide 11 (PA11) biomass composites against microstructures on the metal counterpart fabricated by femtosecond laser in order to control the tribological properties of plants-derived polymeric materials. Hemp fiber (HF) reinforced plants-derived PA11 biomass composites pin were used as test specimens. These biomass composites were extruded by a twin screw extruder and injection-molded. Surface microstructures on SUS304 were fabricated by femtosecond laser. This SUS304 with microstructures using femtosecond laser was used as counterparts. Tribological properties were measured by a pin-on-plate type reciprocating-sliding wear tester under oil lubrication conditions. It was found that the frictional properties differs according to with or without microstructures on SUS304. The frictional coefficient of HF/PA11 biomass composites against textured was higher than that of non-textured.

To develop the new tribomaterials for mechanical sliding parts with sufficient balance of mechanical and tribological properties, the effect of addition of high density polyethylene (HDPE) on the tribological properties of vapor grown carbon nanofiber (VGCF-X) filled polyamide 6 (PA6) composites was investigated. Five different processing sequences were attempted for preparing of the ternary composites (VGCF-X/PA6/HDPE). These ternary composites were melt-mixed by a twin screw extruder and injection-molded. Tribological properties were measured by a ring-on-plate type sliding wear tester under dry condition. It was found that the tribological properties of VGCF-X/PA6 composites improve with the addition of HDPE and slightly change in according with the processing sequence of ternary composites (VGCF/PA6/HDPE).

The electrodeposition process of multilayered nanocrystalline nickel/iron alloy was investigated using an electrolytic bath mainly composed of ferric chloride and nickel sulfamate, to develop high strength and multifunctional materials for micro-electro-mechanical- systems (MEMS). The specimens obtained by electrodeposition at current density less than 2.0 mA/mm² had iron-rich chemical composition. The nickel contents of electrodeposited specimens increased with increasing current density during electrodeposition. The multilayered nickel/iron alloy specimens were obtained by changing current density from 3.0 mA/mm² to 2.0 mA/mm² at predetermined intervals. The hardness of multilayered nickel/iron alloy specimens was increased with increasing thickness of specimens. Moreover, the hardness of multilayered nickel/iron alloy specimens was dependent on indentation load. The hardness increased with increasing indentation load for each specimen with different alloy layer thickness. From obtained results, the optimum multilayered structure of nickel/iron alloy was discussed.