In order to reduce the emission of CO2 for solving the global warming issue, the operating temperature of thermal power plants is continuously increasing. Under the creep and creep-fatigue loading at elevated temperature, the effective lifetime of heat-resistant alloys such as Ni-base superalloy Alloy 617 which is expected to be used high temperature components of thermal power plants was found to decrease drastically. This is caused by the change in the crack propagation path from transgranular to intergranular, and thus, it is very important to quantitatively evaluate the acceleration mechanism of grain boundary cracking. In this study, an intermittent creep test was applied to Alloy 617 to continuously observe the change of microstructure by electron back-scatter diffraction (EBSD) analysis. It was found that vacancies accumulated around grain boundaries perpendicular to the applied uniaxial stress, and it was clearly seen that voids started to appear and accumulate around those grain boundaries in the early stage of the creep test. When the image quality (IQ) value of the damaged grain boundaries decreased to a critical value, grain boundary cracking started to occur at the grain boundaries.

In this study, an intermittent creep test was applied to the continuous observation of the change of the micro texture of SUS316LN and the initiation of intergranular cracking. It was found that the accumulation of dislocations along specific grain boundaries which were perpendicular to the direction of the applied uniaxial stress and the difference of the magnitude of plastic deformation between two nearby grains were the dominant factors of intergranular cracking. The large difference in the Schmid Factor between the nearby grains was attributed to the accumulation, and thus, the place where intergranular cracking started to occur. In addition, comparison experiments between SUS316L and SUS316LN were carried out to verify the improvement effect of material strength due to nitrogen doping. The relationship between nitrogen doping and Stacking Fault Energy (SFE) was briefly discussed.

In this study, the possibility of the application of gold thin films made by electroplating for bumps was investigated to improve the reliability of the TSV interconnection system. The variation of their crystallinity, in other words, the order of atom arrangement of grains and grain boundaries in electroplated gold thin films was investigated by changing their manufacturing conditions. It caused wide variation of mechanical and electrical properties of the films. By uniaxial tensile test of electroplated gold thin films, it was clarified that Young’s modulus and yield stress decreased with decreasing the volume ratio of low-crystallinity grain boundaries by increasing annealing temperature. In addition, fracture strain of the films annealed at temperatures higher than 300oC increased by about 2 times. Similarly, the EM (Electro Migration) resistance of the electroplated gold interconnections varied drastically depending on the volume ratio of porous grain boundaries and their crystallinity. The effective lifetime of the gold bumps was successfully predicted by considering both the crystallinity, and varied more than 10 times as a strong function of the crystallinity of grain boundaries in the fine bumps. Therefore, it is very important to control the crystallinity of the films in order to control the distribution of the mechanical properties and reliability of the electroplated gold thin films.

In the field of semiconductor devices, miniaturization of the device materials used in their internals makes it possible to increase the processing capacity per unit area, and reduce the size and power consumption of the device. At present, copper wiring with low electrical resistivity and high thermal conductivity has become the most common metal wiring in advanced semiconductor devices. However, the drastic decrease in the area of cross-section should increase the resistance of interconnections, and thus, Joule heat and signal delay. In addition, the local internal stress also increases due to the interaction of the nearby stress concentration fields, and it causes the decrease in the reliability of products. Furthermore, the atomic diffusion acceleration phenomenon called Electro Migration (EM) under high current density degrades the lifetime of interconnections. Anisotropic diffusion of atoms along grain boundaries in the metal causes voids, hillocks, and micro cracks, resulting in wire breakage and short-circuit defects that reduce product reliability. Therefore, it is essential to quantitatively evaluate the degradation of the quality of boundaries under operating conditions and to understand the dominant factors in order to assure product reliability. In this study, the effect of static and dynamic strains perpendicular to the grain boundary was analyzed by molecular dynamics to determine the dominant factors of grain boundary strength such as vacancies, dislocation density, and structural change due to local strains.

The electronic properties of graphene nanoribbons (GNRs) have a function of the ribbon width. It can vary from metallic-like ones to semiconductive-like ones when the width of single GNR is changed. Therefore, the novel structure of GNRs called dumbbell-shape GNR (DS-GNR) was proposed to achieve the development of highly sensitive, reliable, and deformable strain sensors. The DS-GNR consists of one long narrow GNR coalesced by two wide segments of GNRs at its both ends. The wide segments of DS-GNR possess the metallic-like electronic properties and the narrow segment of DS-GNR typifies the semiconductive-like electronic properties without uniaxial tensile strain. In this study, the strain-induced change of the electronic band structure of DS-GNR was analyzed by using the first-principles calculations. The range of the applied uniaxial tensile strain on DS-GNR was from 0% to 10%. When the length of the narrow segment of DS-GNR is longer than 4.3 nm, the effective bandgap located in the narrow segment changes obviously with the change of strain. The result indicates that the piezoresistive effect appear in the narrow segment, and thus high strain sensitivity of its resistivity can be applied to strain sensors.

This paper describes flow and heat transfer characteristic of a pulsating flow in a curved rectangular duct. By miniaturization of electronic devices, high-density packaging of electronic equipment becomes a severe problem from the viewpoint of thermal management. To achieve an efficiently cooling, a new cooling technology that improves a cooling efficiency is required. However, due to the high-density packaging of electronic equipment, flow passages become narrower and higher pressure drop is caused. A Pulsating flow is drawn an attention as the new technology to solve these problems. As a verification of the applicability of pulsating flow, pulsating flow around heating elements mounted in a curved rectangular duct was investigated by numerical simulation. As a result, it is found that there is a relationship between heat transfer enhancement of the pulsating flow and a location of heating elements in the curved rectangular duct.

This study describes a next-generation heat transfer enhancement method of miniaturized heat exchangers by an application of pulsating flow. About recent cooling devices used in high-density packaging electronic equipment, both miniaturization and high heat exchange performance are required while decreasing pumping power. However, due to the miniaturization of the heat exchangers, the flow passages become narrower and higher pressure drop is caused. In order to avoid this problem, our study focuses on a pulsating flow. In this paper, against the result of the pulsating flow, a possibility of heat transfer enhancement by the pulsating water flow was investigated through the experiment. In the range of this report, it is found that the heat transfer enhancement by the pulsating flow can be confirmed regardless of the time-averaged Reynolds number. In addition, from the viewpoint of the cooling performance, we confirmed the possibility that the application of the pulsating flow can enhance heat transfer around the obstruction while decreasing the time-averaged supply flow rate.

This study aims to develop a novel water-cooled device that increases heat transfer performance while inhibiting the increase of pumping power for next-generation electronic equipment. We are especially focusing on a combination of ribs and pulsation flow that can be observed in blood flow in the living body. Our previous reports have shown this combination enhances heat trasnfer around the rib. The level of the heat transfer performance is dependent on the rib height. In addition, it was possible that the optimal rib height exist. On the other hand, the relationship between the heat transfer enancement and time-averaged Reynolds number shoud be investigated. In this report, we invistigated a effect of the Reynolds number on the level of the heat transfer enhancement by the combination of the rib and the pulsating flow through 3D-CFD analysis. It is found that the heat trasnfer enhancement by th epulsating flow can be confirmed regardles of the condition of the time-averaged Reynolds number. On the other hand, the change of the heat transfer efficiency is dependent on the time-averaged Reynolds number.

The Glass/Polycarbonate (G/PC) laminated safety glass, which is bonded by acrylic interlayer (ACIL), is often applied for the viewing port of the machine tools. The viewing port for the machine tools requires impact resistance, transparency, and solvent resistance. The G/PC laminated safety glass has excellent characteristics to satisfy above requirements. Recently, thinner structure and weight saving has been more required for the G/PC laminated safety glass. Impact absorption capacity of the G/PC laminated safety glass is influenced by the mechanical properties of ACIL. In this study, we focused on cellulose nanofibers (CNFs) that have high stiffness and strength. We investigated effects of concentration and aspect ratio of CNFs on tensile properties of ACIL with CNFs experimentally and analytically. Tensile tests were carried out to evaluate stress-strain (S-S) curves and effects of concentration and aspect ratio of CNFs on the hyper elastic properties of ACIL with CNFs was discussed. Finite element analysis (FEA) of hyper elastic properties of ACIL with CNFs was also conducted by using Digimat-FE software. Using three-dimensional representative volume element (RVE) models, effect of concentration and aspect ratio of CNFs on the hyper elastic properties of ACIL with CNFs were evaluated. As a result, the stress of ACIL containing CNFs with high aspect ratio obtained by tensile test was markedly increased in high strain region more than neat ACIL. On FEA, increasing CNF concentration showed increased stress of S-S curve. Also, effect of aspect ratio was remarkable at 5wt%.

There is a global effort to realize the United Nations SDGs (Sustainable Development Goals) for a future that should be. In recent years, the problem of marine pollution caused by microplastics has attracted attention. As a measure against this, Chitin nanofibers (Chitin-NF), which is a renewable resource material, has begun to be studied for its application in various fields as a reinforcing material. In this study, we prepared a resin-based composite material using Chitin-NF, established the optimum composite ratio and optimum composite time, and evaluated the mechanical properties. Consider the effectiveness and future potential of Chitin-NF.In this method, 1 ml of slurry Chitin-NF was added to 1 g of base material PLA pellets using 1% acetic acid aqueous solution as a solvent to prepare a mixed solution, which was stirred by a magnetic stirrer. Then, the acetic acid aqueous solution was dried in a dry atmosphere furnace to prepare a composite material. As a test piece, Molded by injection molding machine. The molding conditions are an injection temperature of 205 °C and a mold temperature of about 60 °C.The following results were obtained in the fabrication and evaluation of composite resin materials using Chitin-NF. An attempt was made to use a magnetic stirrer and stirring for 1 h was the optimum time. It was confirmed that the maximum tensile stress in PLA/Chitin-NF composite material after stirring for 1 h was improved by 10%. The maximum bending stress of the composite was lower than that of the PLA alone. The Young's modulus reflected the effect of Chitin-NF and improved in all composite materials. However, the flexural modulus did not change much. However, it was confirmed that there was a proportional relationship with the stirring time.

Currently, 3D printers have a wide range of practical applications from the aerospace field to the medical field, and there are actual examples where 3D printers are already used for mass production of 10,000 parts in automobiles. As a result, it is possible to greatly reduce the manufacturing time and reduce costs. However, while there are expectations for commercialization that takes advantage of the 3D printer, there are many problems to be overcome. This is due to the existence of the laminating interface created by molding and the low strength of the resin material itself. As a result, it is difficult to shape and commercialize many resin products. So I focused on the FDM 3D printer. The FDM-3D printer is also characterized by being able to use ABS resin, which is a resin material with high strength and excellent versatility. Therefore, we considered the development of a new high-strength composite resin material that uses ABS resin that can be introduced into this FDM-3D printer as a base material and CNT as a reinforcing material. In addition, it was investigated whether it is possible to further improve the strength by combining the laminated interfaces that cause the decrease in the strength of the shaped article, and the synergistic effect with the new composite resin material. From this paper, it was confirmed that the tensile strength of the ABS / CNT composite material was improved by 10% in the filament state. In addition, it was confirmed that the tensile strength was improved by 70% and the bending stress was improved by 37% at the maximum by using a halogen spot heater to form the ABS filament. From these results, it was possible to confirm the effectiveness of compounding ABS resin and CNT and molding using a halogen spot heater.

The tensile properties of polypropylene (PP) composite systems filled with silica nanospheres having untreated surfaces were investigated with a focus on effects of the interface between hydrophobic PP matrix and originally hydrophilic inorganic nanofillers like surface of hydroxylated silica on their properties. The authors have fabricated the nano-composites, in which isolated nanoscopic colloidal silica primary particles without any surface modification using silane coupling agents could be dispersed through the breakdown of loose agglomerates of their colloidal spheres in PP matrix component. As the obtained results on the tensile properties of the silica/PP composite systems fabricated under conditions of silica volume fraction within a range from 0.008 to 0.030, the yield stress that was equivalent to the ultimate tensile strength, as well as the Young’s modulus, increased by filling silica in spite of no adhesion between dispersed hydrophilic silica fillers and PP matrix phase. At a small volume fraction of silica such as 0.021, a distinct increase in these two tensile properties was observed before encountering their decays at higher silica volume fraction. These results suggest a possibility that a toughening and a high-strengthening of PP can be achieved by filling small amounts of surface un-modified hydrophilic silica spherical fine particles in an isolated and uniformly dispersed state.

The aim of the present study is to elucidate the possibility of improvement of filler dispersibility of polymer composite by using hybridized hydrophilic silica nanofillers with carbon black (CB) particles. The experimental techniques of the fabrication method of polyolefin such as polypropylene (PP) composites were investigated on the basis of the strategy for the preparation of hybridized fillers of silica and CB having packing structure controlled as loosely as possible to enable easy peeling silica primary particle from CB to an isolated dispersed state at a blending stage with these polyolefin matrix composites. It was found from the tensile tests of the PP composites that remarkable increase stiffness and strength of PP could be achieved by filling hybridized silica nanoparticles with CB. Compared to the composite system with silica nanofillers alone, an improvement of silica filler dispersibility and an increase in the stiffness and strength of the composite system by filling hybridized silica nanoparticles with CB in the case of the PP composite system.

In recent years, increasing CO₂ emission has become a serious issue. In order to reduce CO₂ emissions, the weight of body such as vehicle has been reduced, so new lightweight and high strength materials are needed. Therefore, the purpose of this study is synthesis of a material with excellent mechanical properties. We focused on aluminum with high specific strength and nanocarbon with amazing mechanical properties. The normal casting process is difficult to fabricate a specimen because Aluminum and nanocarbon chemically react with each other, so it is an untapped study field. In this study, normal casting conditions are changed. Using Al powder as a base material, nanocarbon is highly dispersed by ultrasonic waves, and a nanocarbon/Al composite powder is cast at a temperature of 933[K] under a vacuum of about 1.5×10^-3[Pa] to fabricate a specimen, and evaluate mechanical property of material and analyze structure. The obtain main results as follows: from X-ray diffraction and FT-IR analysis, it was found that Aluminum chemically reacts with nanocarbon to produce Al₄C₃. Vickers hardness of specimen increased up about 26 % for 0.5 wt% CNT and about 19% for 2.0 wt% C₆₀ in comparison with the value of pure Aluminum specimen. Also tensile strength and flexural strength of nanocarbon/Al composite specimen decrease with the value of pure Aluminum specimen. These results show that it is necessary to search for conditions under which Al₄C₃ is not producted in order to impart the composite effect of nanocarbon. In the future, research will be conducted under different conditions to study the effectiveness of the development of nanocarbon/Al composite casting materials.

Carbon nanotubes (CNTs) are nanofibers with excellent mechanical properties and low specific gravity. In recent years, spinnable CNTs have been developed that can be spun into yarns. Research has been conducted on CNT composites using spun yarns as preform. However, excellent mechanical properties of CNTs have not been fully utilized due to defects in CNT, catalysts, left inside CNTs and disorder of CNT layers. For improving the mechanical properties of CNTs, annealing at high temperatures and thinning of CNT are effective. Annealing can reduce defects in CNTs. Thinning of CNT can increase the proportion of CNT layers that support load. Therefore, both treatments can be expected to improve tensile properties. In this study, the tensile properties of CNTs were investigated for large-diameter CNTs with a diameter of 40 nm and small-diameter CNTs with a diameter of 25 nm under the condition of as-produced and annealed. As a result, it was found that the reduction in diameter move attributed to the improvement of the tensile strength of CNTs than annealing in our case.

Polymer composites with high thermal conductivity offer new possibilities for thermal management in electric systems. The objective of this paper is to study the microstructural design for improvement of thermal conductivity of polymer composites with boron nitride (BN) and spherical particulate fillers (SP). Representative volume element (RVE) models of micro fillers were generated, and finite element analysis was performed to evaluate thermal conductivity of polymer composites by using Digimat-FE. The effect of volume fraction, aspect ratio and thermal conductivity of BN on the predicted thermal conductivity of BN/epoxy composites was discussed. In addition, experimental measurements of the thermal conductivity of the manufactured polymer composites with BN and SP were carried out by using a steady-state method. The results showed that thermal conductivity of epoxy composites with 10vol%BN and 20vol%SP and thermal conductivity of epoxy composites with 20vol%BN are nearly identical.

Thermal conductivity of polymer composites with micro filler has been investigated numerically and experimentally. The object of this study is to realize high thermal conductivity of polymer composites with alumina and boron nitride (BN) particles. Polymer composites with micro fillers were fabricated and experimental measurements of the thermal conductivity of the fabricated polymer composites were carried out by using steady-state method. Predicted thermal conductivity was obtained by finite element analysis using representative volume element (RVE) models and was compared with the experimental results. The results showed that increasing micro filler volume fraction lead to increase in thermal conductivity of the composites. The predictions for alumina/epoxy composites were lower than the experimental data. However, the predictions for BN/epoxy composites were higher than the experimental data. The predictions for BN/epoxy composites were higher than the predictions for alumina/epoxy composites when volume fraction of filler was same. Increasing void volume fraction lead to decrease in thermal conductivity of the composites. Decreasing void diameter lead to decrease in thermal conductivity of the composites.

CFRPs (Carbon fiber reinforced plastics) have been used in aerospace and automotive industries because of their light-weight and high-strength characteristics. Since various damages such as matrix cracking, fiber brake, and delamination are initiated in CFRPs, it is difficult to evaluate their sizes and locations non-destructively. The potential difference method is drawing attention as one of the appropriate non-destructive methods for CFRPs. However, the electric field analysis of CFRPs is difficult because the electric current flows only in the distributed carbon fibers and contacts between carbon fibers affect the electric resistance of CFRP. In the present research, direct-current electric potential field analyses were carried out using the finite element method and the current path was focused on. It was found from the analysis results that the electric resistance of CFRP is well correlated with the effective volume fraction of fibers.

Poly(lactic acid) (PLA) is degraded to nontoxic lactic acid through non-enzymatic hydrolytic degradation. Thus, the foreign body reaction during PLA degradation is mild. PLA has attracted much attention as a material of bioabsorbable bone fixation screw which is used for fracture treatment. The purpose of this study is simplify a molding method of screw made from extrusion drawn PLA. PLA screws were prepared by three different molding methods : molding method A ; casting, molding method B ; extrusion drawing and forging, molding method C ; the draw screw molding. In molding method C, the draw screw molding was proposed for simultaneous with extrusion drawing and thread molding. Mechanical properties of PLA screw were investigated by shear and torsion tests. As a result, PLA screws could be molded by all molding method. The molding time of molding method C was shortened by about 30 minutes per molding compared to molding method B. As results of shear and torsion test, screws of molding method A was more ductile than molding method B and C. On the other hand, shear strengthes of molding method B and C were higher than molding method A. In comparison of molding method B and C, the shear strength of molding method C was slightly higher than molding method B. And, the torsional strength of molding method C was slightly lower than molding method B. Those results might be due to molecular orientation by extrusion drawing and subsequent disorder of orientation during forging.

Although a Fresnel’s fiber optic sensor is very useful to monitor cure process of CFRP in real time, some voids remain in resin rich region around the sensor tip and reflected lights from them may affect measurement accuracy. The effect of lights from the voids on the accuracy could be reduced by appropriate filtering method, however the lights provide information of voids forming during molding. In the present study, we observed reflected light spectrum obtained by the Fresnel’s sensor embedded in CFRP prepreg during hot-press molding. The results showed that the voids disappeared when resin melted but formed again when the degree-of-cure became about 0.6 because the increased viscosity of resin resulted in the voids trapping on the boundary between fibers and resin.

In this paper, in order to investigate the mechanical property of V-shape carbon fiber reinforced thermoplastics (CFRTP), four point bending tests were conducted. The test was carried out using similar testing tool to ASTM D 6415. Also, step-by-step four point bending test with acoustic emission (AE) measurement were performed and the damage process were characterized. CFRTP plates were molded with a bending-type V-shape mold which has angle 90°. CFRTP studied was plain woven carbon fabric reinforced polyamide 6 (PA6). Pre-consolidated laminates were preheated above melting temperature of PA6 in a hot press machine, and then pressed after transferred to the V-shape mold. As a result, the molding temperature 250 °C specimen indicated maximum interlaminar tensile strength about 44 MPa. Also, the difference between damage process and modes occurred with change of molding temperature. The critical damages of 200 °C specimen was weft fiber yarn cracks and 250 °C specimen was interfacial peeling between weft fiber yarn and warp fiber yarn.

The discontinuous fiber CFRP formed by press forming has a problem in that there is an unimpregnated part where the resin is not sufficiently impregnated in the carbon fiber at the stage of the intermediate base material before forming, which causes voids in the product. It has become. In this study, we propose a new detection method based on the thermal diffusivity distribution in the thickness direction using line heating as a method for detecting the non-impregnated part at the stage of the intermediate substrate. In this paper, we report the validation of the thermal diffusivity measurement using standard samples, and the results of applying and comparing this method to impregnated and unimpregnated CFRP before molding.

In this study, the mode I delamination fracture toughness of CFRTP laminates molded by FDM type 3D printer was evaluated by DCB test. This CFRTP obtained in the present study was compared with the result of 0° material in which the fiber orientation angle was not changed, and it was considered how the difference in the fiber orientation angle of the CFRTP laminated material affects the toughness value around the interface of the laminates. The appearance of the fracture surface of the test pieces was observed by SEM. As a result, it was found that the interlaminar fracture toughness value of the CFRTP laminates with different fiber orientation angles formed by 3D printer this time is low. As a result of SEM observation, a rough fracture surface was observed at the place where the toughness value increased, and a smooth fracture surface was observed at the place where the toughness value decreased, which is one of the reasons for the result.

In the present study, interlayer strength of Carbon fiber reinforced plastic (CFRP) is evaluated by using laser ultrasonic waves and a wave propagation analysis. The laser spallation technique of various laser irradiation has been used to induce interlayer delamination of specimens. The interlayer stress is estimated by an inverse analysis using the displacement at a back surface of a specimen and the impulse response calculated by a finite element analysis. In addition, interfacial strength between carbon fiber and matrix resin in CFRP laminates is evaluated by the homogenization theory. In order to estimate the interfacial strength, macroscopic stress at the place where fiber/matrix interfacial failure occurred is calculated by the inverse analysis using a finite element method, and localized analysis by a homogenization method is performed to evaluate the interfacial stress between fiber and matrix.

This study investigated the effect of vacuum ultraviolet (VUV) light irradiation on the thermal fusion bonding strength of carbon fiber/thermosetting polyimide composite laminates (CF/PI) at high temperatures. Thermoplastic polyimide (TPI) film was used as a hot-melt adhesive. The adherend (CF/PI) surfaces were irradiated by the VUV light (172nm) for 4min in a low oxygen atmosphere (0.2±0.1%), followed by the thermal bonding of two CF/PI specimens with TPI film adhesive under 320°C. The bonding shear strengths was from 19.4MPa to 21.0MPa at 150, and 200°C through the VUV light irradiation process. The strength data of the specimens irradiated with VUV light on the surface of the adherend (CF / PI) were significantly scattered.

Carbon fiber reinforced thermoplastics (CFRTPs), which have excellent specific strength and specific rigidity, are used with metallic materials such as aluminum (Al) alloys. Therefore, there is a demand for a technique for bonding metal and CFRTP. The purpose of this study is to evaluate the effect of the nanostructure of the interface on the strength in the joining of Al alloys and CFRTP laminates with PEEK as matrix resin. In the experiment, nanostructures were fabricated on the Al alloy surface by anodizing and etching treatments. After that, they were joined using a hot press and the tensile shear tests were performed. The shear strength of A5052 and CF/PEEK was 12.4 MPa. As a result of the fracture surface observation, it is due to the anchor effect of the resin impregnated into the nanostructure. From these results, it was found that the micropores with a diameter of approximately 1 μm are effective for joining with CF/PEEK. The shear strength of the joint between A2024 or A7075 and CF/PEEK was 2.41 and 2.82 MPa, respectively. This is probably because the nanostructure had a very small shape and was not impregnated with resin. Therefore, it is necessary to investigate suitable nanostructure fabrication conditions for these Al alloys.

Matrix cracking in CFRP laminates results in the mechanical property degradation of the material such as stiffness reduction, the existence of residual strains, etc. Usually, the damage parameters used for matrix cracking are stiffness reduction, Poisson’s ratio reduction and the change in thermal expansion coefficients. In this study, a damage parameter, the existence of residual strains, is experimentally and analytically investigated for CFRP [0/75₆]_s laminates. Due to very small residual strains at the unloading condition, the residual strains have also been measured at other different stress levels for laminates with different crack densities and are compared with theoretical predictions. Laminates’ time-dependent viscoelasticity behavior of the residual strains is also considered so that only residual strains due to the occurrence of matrix cracks can be accurately measured. The experimental results of the residual strains are in reasonably good agreement with the theoretical predictions.

In this paper, we evaluated transverse crack propagation and accumulation of CFRP laminates with kidney-shape carbon fibers by experimental and computational micromechanics. We investigated the effect of a cross-sectional shape of carbon fibers on the transverse crack density by the tensile tests of cross-ply laminates with round-shape and kidney-shape carbon fibers. We temporarily interrupted the tests and measured the crack density by replica method when the tensile strain reached specific values. Experimental results showed that the CFRP laminates with kidney-shape carbon fibers have a smaller increasing rate and larger variation of the crack density than those with round-shape carbon fibers. In order to consider the difference in crack propagation depending on the fiber cross-sectional shape, we carried out elastic-plastic damage analysis by finite element analysis. In the CFRP model with round-shape carbon fibers, the major failure mode is damages on fiber/matrix interface. On the other hand, the major failure mode of the CFRP model with kidney-shape carbon fibers is damages on matrix resin. The simulation results agreed well with experimental results about the increasing rate and the variation of the crack density.

In this study, multi-scale analysis was carried out by designing a porous cement paste model, and a mortar model using glass spheres as fine aggregates. The tensile simulation of porous cement paste model was conducted by RVE model that reflects the distribution of pore size in a cement specimen. It was shown that the elastic modulus and strength of cement have a linear relationship with porosity. The finite element model of cylindrical samples was then created to simulate the splitting tensile test. For the cylindrical mortar model, spatial variation of the physical properties due to the porosity distribution in cement was reflected. When cement had a distribution of physical properties, the strength of the cement model was similar to that of mortar model as it was observed from the experiment, whereas the strength of the cement model was higher by 20 % if uniform physical properties were used for cement matrix. It was confirmed that our simulation well corresponded to the experimental result of at the ages of 28 days. In addition, the decrease in the strength, which would be expected for further aging mortar, can be also modeled by the porous layer at glass-cement interface, representing the Interfacial Transition Zone.

In this study, we introduced out-of-plane low-speed impact damage for continuous carbon fiber reinforced thermoplastics (Continuous CFRTP) pseudo-isotropic laminates formed by a fused deposition modeling (FDM) type 3D printer, In addition to quantitatively evaluating the impact properties, the appearance of damage in the specimen was observed in detail using X-ray CT and an optical microscope , and the post-impact compressive strength was evaluated In addition to damage to the laminated composite material , damage patterns peculiar to 3D printer moldings could be confirmed.

Damage behavior of self-healing spread carbon fiber (SCF)/epoxy (EP) laminates was investigated in this study. A UV fluorescent dye was mixed to a healing agent within microcapsules to observe damage behavior of SCF/EP laminates visually. The apparent interlaminar shear strength and the healing efficiency of the laminates were evaluated by short beam shear testing. After the testing, a damaged area was observed by optical microscope under UV light source. It could be visually observed under UV light source that the healing agents released from broken microcapsules into crack plane, and the cracks propagated through microcapsules. The results also showed that the damage behavior can affect the apparent interlaminar shear strength and the healing efficiency of the laminates.

In this study, interim stopping tensile fatigue tests with acoustic emission (AE) measurement were performed on unidirectional carbon fiber reinforced plastic (CFRP) laminates with a notch. The relationship between splitting behavior and associated AE behavior were characterized. Then, tensile fatigue tests with AE measurement were carried out on CFRP laminates without a notch, and the damage and AE behaviors with and without a notch were compared. Consequently, splitting occurred along the fiber direction from the tip of a notch in a specimen with a notch and the AE behavior reflected the splitting developing behavior. We discussed the AE behavior based on the experimental results about splitting behavior, and the relationship between the AE and the fatigue damage behaviors in unidirectional CFRP laminate was clarified. From this relationship, it is possible to predict the damage type by comprehensively evaluating the frequency characteristics and each parameter of AE waves. The AE waves from splitting occurrence and progress were also identified.

In order to clarify the long-term durability of CFRP strands, tensile and fatigue tests at room and elevated temperatures were conducted. Firstly, tensile tests were performed under several temperature conditions from 23 to 250 ℃. The results showed that ultimate tensile strength of CFRP strands are dependent on temperature and superior to conventional steel materials. Secondly, fatigue properties at room temperature were examined and plotted on Haigh diagram. It is observed that CFRP strands have higher fatigue resistance than conventional steel wire rope used in prestressed concrete. In addition, a new data processing method was proposed to evaluate fatigue damage in CFRP strands. In this method, the phase angle between stress and strain is a significant factor that indicates damage in composites. It was shown that the fatigue mode changes around 10,000 cycles and the rapture is likely to occur before phase differences reach at the maximum value. Lastly, fatigue tests at 200 ℃ were conducted. The results showed that CFRP strands become sensitive to mean stress at elevated temperature.

Plate-shaped talc particles are very attractive as inorganic fillers for polymer composites. Polypropylene (PP) compounded with talc particles has been used widely for automobile plastic parts. However, though the stiffness and strength of talc/PP composites are increased, the elongation at the break of talc/PP composites is greatly decreased, compared to that of neat PP. Decrea、sing the elongation at the break of those composites is strongly influenced by the shape of talc particles. Talc has a layered structure which is regularly piled up in silicate and magnesia layers. In this study, shape-controlled talc particles were manufactured by using a high-pressure water jet apparatus and shape-controlled talc particles were compounded with PP by using an extruder. The thickness of the talc particles in PP was measured by observation of the fracture surface of injection molding specimens of talc/PP composites with a scanning electron microscope (SEM). The distribution of measured thickness of talc particles was evaluated by using particle size distribution analysis software Mac-View. The plate size of talc particles was also measured by the laser scattering distribution analyzer. Effects of mean thickness, thickness distribution and plate size of talc particles on tensile properties of composites were discussed.

The resonance scattering theory of elastic waves in a cylinder with a spring interface between the matrix and the cylinder is theoretically investigated. The analysis shows that the resonance scattering theory is applicable not only to the model with a perfectly bonded cylinder-matrix interface but also to the model with a spring interface. The resonance scattering theory for a cylinder with a spring interface is an extension of the previous analysis, since the boundary condition for perfect bond is the limit of the spring stiffness at infinity. In addition, backscattered waves from the steel cylinder press-fitted into the aluminum alloy were measured. The interfacial stiffness was estimated by comparing the experimentally obtained amplitude spectrum with the results of the numerical analysis. It was confirmed that the spring interface adequately models the resonance wave scattering of the specimen.

Ultrasonic pulse-echo methods with a buffer rod are expected to be effective means for high temperature measurements of materials and online monitoring in materials processing where the use of conventional ultrasonic sensors are restricted. For practical application of such buffer rod method, it has often been required to employ a thin and long buffer rod because such thinner rods could be useful for measurements with high spatial resolution at a narrow region. In this work, a tapered buffer rod with a small probing tip has been designed. The influences of the tip diameter, taper angle and frequency of tapered polymer buffer rods on its signal-to-noise ratio (SNR) are systematically examined by a finite element method. An appropriate geometrical shape of a tapered buffer rod with higher SNR is then determined.

If the electromagnetic acoustic transducer (EMAT) is used directly to inspect a high temperature pipe, the EMAT becomes too hot. That’s why it is to difficult to use. Therefore, an ultrasonic sensor system with a long waveguide was developed to keep a sensor part at normal temperature. As a previous study, two types of waveguide were studied to use two types of ultrasonic guided wave. In this report, two types of ultrasonic wave sources are used to propagate two types of guided waves into a pipe. Next, the evaluation results of flaw detection are described.

Bellows pipes are piping joints with bellows structure, and they are excellent in elasticity, airtightness, and spring characteristics. It has been used to connect equipment piping in power plants and industrial plants, and exhaust pipes for transportation equipment. On the other hand, the thickness of the bellows is extremely thin compared to that of conventional pipes, and fatigue cracks and corrosion thinning lead to rapid damage propagation. Therefore, it is expected that the Guided wave inspection method and acoustic emission (AE) method will be used for screening and condition monitoring as the nondestructive inspection. However, the characteristics of elastic waves propagating through bellows have not been shown in the previous studies. In this study, the characteristics of elastic waves propagating in the bellows are evaluated. Artificial AE signals were excited to the bellows by a pulsed YAG laser, and time-frequency analysis of the detected AE signals were performed using the wavelet transform. As a result, it was classified into L (0, 1) mode and F (1, 1) mode as cylindrical wave mode of the approximate pipe. In addition, the relationship between the cylindrical modes and the circumferential waveform distribution of the bellows was investigated, and it was found that the intensity of the F (1,1) mode changed depending on the detection position in the circumferential direction, and that the characteristics of the mode were close to the characteristics of the elastic wave propagating through the pipe.

We conduct a direct observation on propagation of transverse wave in colloidal suspension by confocal microscopy technique. Frame rate of the conventional microscopy technique was 30-40 frames/s, and particle motions at high frequencies could not be observed. However, using a periodic motion of the suspension, we succeeded to observe the motion of particles at 1,600 Hz. Displacement of the colloidal particles are synchronized with the excitation but the amplitude decays monotonically with respect to the distance from the excitation point. Fourier transformation of the damped oscillation revealed the propagation of transverse wave in the colloidal suspension.

In the early stage of deposition of metallic films, island-like clusters are formed on the substrate. As the deposition proceeds, the clusters grow, contact each other, and form a continuous film. This morphological transition is expected to be affected by the experimental conditions such as the substrate temperature. However, the morphological transition is difficult to observe during the deposition. In this study, we developed a method for observing the transition of a metallic thin film on a heated substrate by using the piezoelectric resonance. By using this method, we observed the morphological transition of Pd films on silica glass substrates at high temperatures. As a result, it was found that the timing of the transition depends on the substrate temperature. It was also suggested that the differences in the transition originate from the difference in the cluster size at high temperatures.

When a Lamb wave electromagnetic transducer(EMAT) is used to detect different types of defects, any different types of electromagnetic induction coils and magnets are needed to change modes. This study is examined whether it is possible to improve the function of Lamb wave EMAT by combining the same Lamb wave EMAT and a magnetic field concentrator with a different structure.

At present, small-diameter metal tubes mainly are inspected an optical endoscope, or eddy current examination. However, due to the limited space of small diameter pipes, there are various difficulties in such inspection systems. Therefore, in this study, the guided wave of wholly vibrates in the direction of tube thickness is selected through modal analysis. Based on this, a unidirectional EMAT based on interference principle is developed to replace the EMAT for optimum inspection, and the non-destructive inspection of scratches in the circumferential direction of small-diameter metal tubes is carried out. If indicated that the modal analysis results coincidence with a experimental result by circumferential scratch.