In this paper we developed Composite-Smart-Structures(CSS) using sandwich structure composed of Glass/Epoxy laminates and Nomex honeycomb and microstrip antenna. Transmission/reflection theory shows that antenna performances can be improved due to multiple reflection by Glass/Epoxy facesheet, and honeycomb is used for air gap between antenna and facesheet. Stacked radiating patches are used for the wideband. Facesheet and honeycomb thicknesses are selected considering both wideband and high gain. Measured electrical performances show that CSS has wide bandwidth over $10\%$ and higher gain by 3.5dBi than initially designed antenna, and no doubt it has excellent mechanical performances by sandwich effect given by composite laminates and honeycomb core. The CSS concept can be extended to give a useful guide for manufacturers of structural body panels as well as antenna designers, promising innovative future communication technology.

About 175 vehicular bridges and 160 pedestrian bridges in service now, worldwide, are made of composites, completely of partially. In this paper, the status of this application is briefly explained.

Presented is a preliminary design concept of the carbon-glass hybrid composite rebars for the application in the construction field. A glass fiber rod with indentation is used for the core of the rebar. Carbon fibers are placed over the glass core by pultrusion. To increase the mechanical locking force and bonding surface, carbon filament windings are added in the hoop direction over the carbon face. Finite element analysis and test were conducted to evaluate the effective stiffness and strength of the rods. The results show that the effective axial stiffness of the rebar with indentation are about $50\%$ of the straight rebar.

In recent years, the deterioration of reinforced concrete structures has become a serious problem in civil engineering fields. This situation is mainly due to corrosion of steel reinforcing bars embedded in concrete. Recently, there has been a greatly increased demand for the use of FRP (fiber reinforced plastic) in civil engineering field due to their superior mechanical and physical properties. This paper presents an experimental study on the behavior of concrete bridge deck reinforced with FRP Box, FRP Plate, and FRP Re-bar. In tlIe study, mechanical properties of FRP Box, FRP Plate, GFRP Re-bar, and CFRP Grid have been investigated. Full scale one-way deck slab was tested under four point lateral load (equivalent to actual wheel load of DB-24 including impact). Load-deflection and load-strain data were collected through LVDT's and strain gages attached to the specimen.

A GFRP based composite blade was developed for a 750kW wind energy conversion system of type class I. The blade sectional geometry was designed to have a general shell-spar structure. The load cases specified in the IEC61400-1 international specification were considered. For withstanding all relevant extreme loads, the structural analysis for the complete blade was performed using a commercial FEM code. The static load carrying capacity, buckling stability, blade tip deflection and natural frequencies at various rotational speeds were evaluated to satisfy the strength requirements in accordance with the IEC61400-1 and GL Regulations. For designing a lightweight blade, the thickness and the lay-up pattern of the skin-foam sandwich structures were optimized iteratively using the DOT program T-bolts were used for joining the blade root and the hub, which were modeled using a 3D FE volume model. In order to confirm the safety of the root connection, the static stresses of the thick root laminate and the steel. bolts were predicted by taking account of the bolt pretension and the root bending moments. The calculated stresses were compared with the material strengths.

This paper describes method and procedure for DDT (Design Development Test) of composite wind turbine blade composites. The test type of DDT is bending test, such as cantilever beam, based on the rated wind speed of wind power generation system. DDT was carried out in order to compare with the result of FEM analysis, characterize structural stability, verify manufacturing process and review test method of full scale blade.

In order to speed up basic concept is to enhance high speed, curve limit speed, cross limit speed, acceleration/deceleration speed. It is important to optimal interface fundamental technology of vehicle, rail, electrical power, and signal system. Tilting train has advantage minimizing investment cost of infra railway system for increasing train limit speed in curve. the developed tilting train should be operated to commercial service speed 180Km/h of 200Km/h at KNR upgrade railroad. This paper proposed the basic model of system engineering for developing of tilting EMU (maximum operation speed : 180km/h) with speed-up of conventional railway system.

This paper suggested that the technical specification of tilting train EMU for speed up on existing lines. High speed strategy of existing lines are the modification of railway system which are made on cant, lengths of transition curves, the catenary system and train system. Tilting technology is more useful a strategy for speed increases on existing lines with low investment needed. We performed a feasibility study which is considered out real track conditions and designed propulsion and braking system of tilting EMU system.

Tilting trains could offer a low cost solution as they can be operated on existing track and attain higher speeds (as compared to conventional trains) thanks to a mechanism that tilts the vehicle body of the train when negotiating curves, thus giving it additional superelevation Also, the weight saving of the carbody structures of the tilting train is a significant problem to operate the tilting mechanism without failure and to minimize wear and tear on wheels and rails. Therefore, the TTX will be developed using hybrid design concept to match the challenging demands with respect to cost efficient lightweight design for carbody structures. Hybrid design helps to save production costs and to reduce the weight of carbodies.

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car made of composite material. The results of aerodynamic analysis for two leading car models, which one is expressed with lineal beauty and the other is with curvaceous beauty, are compared with each other and offer the proposal of modification for two models in order to decrease be drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

Through investing the criteria and evaluation for fire performance of interior components, this paper introduce the testing items and requirements for Flammability, Smoke density, and Toxicity properties of TTX(Tilting Train eXpress) interior parts. Next time, all trains including TTX will be occupied the components with superior fire-resistance and the sensing and monitoring system for fire in train.

Weight reduction of the carbody is of great concern in developing high speed tilting train. Currently the composite materials are widely applied to the carbody structure due to their excellent material properties such as high specific strength and stiffness characteristics. In this paper, finite element analysis was conducted to design sandwich structures of composite carbody of the Korean Tilting Train eXpress(TTX). Several load tests on the carbody according to JIS E 7105, such as static vertical, compressive and torsional load tests was performed by finite element analysis, and the structural safety of composite carbody structure was verified.

Testing methods for mechanical properties of the advanced composites were introduced. The mechanical properties, such as tensile properties, compressive properties, in-plane shear properties, flexural properties, and interlaminar shear properties, were evaluated along the warp and the fill directions. The CF3327 of the carbon fabric, the HG1581 of the glass fabric, and the HK285 of the aramid fabric were considered as reinforcements. Epoxy and phenolic resin were used as resin. The experimental results obtained in this study would be applicable in the design and structural analysis for the manufacture of the carbody of the tilting train.

Phenolin resin, prepared form phenol and formaldehyde, is one of the oldest thermosetting resins available. Phenolic resins are cured via condensation polymerization with evolution of water, which in molding process is a big problem. The use of phenolic resins in glass fiber composites is growing, primarily due to their low flame spread, low smoke generation and low smoke toxicity properties. SMC of phenolics has been rearched since the 1986. The technology challenge was to match resin viscosity, handling and cure with those for the polyester SMC to avoid any special processing for fabricators and end users. Phenolic SMC was chosen because of the ease of molding to the required shape with light- weight, thin wall structure and with excellent fire protection.

According to the change of industry structure, design is the key element to accelerate enhance the value of railway industry as they core competence factors for productive and superiority its level. It is important utilizing materials to embody new train aesthetics and build high technologies. Consequently, apply properties of composite with design formative attribute also functional usability and technology system.

In this study, a hybrid composite journal bearing composed of carbon fiber reinforced phenolic composite liner and metal backing was manufactured to solve the seizure problem of metallic journal bearing materials because the carbon fiber has self-lubricating ability and the phenolic resin has thermal resistance characteristics. To estimate the wear resistance of carbon fiber phenolic composite, wear tests were performed at several pressures and velocities. The oil absorption characteristics, coefficient of thermal expansion, strength and stiffness of the composite were also tested. Using the measured stiffness values, the thermal residual stresses in the composite were calculated to check the reliability of the composite journal bearing.

An investigation was performed to study the impact damage of the laminated composite plates caused by a low- velocity foreign object with multi-scale modeling based on the concepts of Direct Numerical Simulation (DNS)[4]. In the micro-scale part, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. A micro-scalemodel was developed for predicting the initiation of the damage and the extent of the final damage as a function of material properties, laminate configuration and the impactor's mass, etc. Anda macro-scale model was developed for description of global dynamic behavior. The connection betweenmicroscopic and macroscopic is implemented by the tied interface constraints of LS-DYNA contact card. A transient dynamic finite element analysis was adopted for calculating the contact force history and the stresses and strains inside the composites during impact resulting from a point-nose impactor. The low-velocity impact events such as contact force, deformation, etc. are simulated in the macroscopic sense and the impact damages, fiber-breakage, matrix cracking and delamination etc. are examined in the microscopic sense.

A composite-aluminum hybrid joint of composite external fuel tank of an aircraft has been analyzed by a 3-dimensional finite element method. Curvature and contact of the joint structure were considered in the analysis. Yamada-Sun failure criteria was utilized for the failure evaluation. A finite element program ABAQUS was used for the nonlinear contact analysis. The joint structure was predicted to be safe in both the test and analysis.

Traditionally aluminum alloy have been used in manufacturing of aircraft structures, and semi-monocoque structural concept have been mainly applied in structural design of fuselage and wing. However, recently monocoque structural concept is applied in many small-size aircraft structures manufactured with composite materials. In such case appling monocoque structural concept, in initial conceptual design stage on wing, it is not easy to analyze shear flow using classical shear flow analytical method because composite skin structure can support span-wise tension/compression stress as well as sectional shear stress. In this study, an extended shear-flow analytical method to apply to composite monocoque structural concept was developed through extending the classical shear-flow analytical method.

The rotor drive system in rotor-craft carries out power transmission from powerplant to rotors and the drive shafts are fallen into misaligned condition by the vibration of engine and shafts and the deformation of supporting structures. The high performance flexible coupling accommodates these misalignments of drive shafts. In this study, we compare the performance of the metalic flexible coupling with the composite flexible coupling through analytic method to develop the high performance flexible coupling used in the rotor drive system of UAV tilt-rotor.

The aeroelastic stability analysis of composite bearingless rotors is investigated using a large deflection beam theory in hover. The bearingless rotor configuration consists of a single flexbeam with a wrap-around type torque tube and the pitch links located at the leading edge and trailing edge of the torque tube root. For the analysis of composite bearingless rotors, flexbeam is assumed to be a rectangular section made of laminate. Two-dimensional quasi-steady strip theory and Loewy's aerodynamic theory with the lift deficiency function are used for unsteady aerodynamic computation. The finite element equations of motion for beams are obtained using Hamilton's principle. Numerical results of selected bearingless rotor configurations are obtained for the lay-up of laminae in the flexbeam and pitch links location.

In this paper, geometrically non-linear finite element analyses were performed to study the mechanical behavior of the material system of the envelope of stratospheric airships. The microstructure of the load­bearing plain weave layer was identified and modeled. The Updated Lagrangian formulation was employed to consider the geometric non-linearity as well as the induced structural non-linearity for the fiber tows. The stress-strain behavior was predicted and the effective elastic modulus was calculated by numerical experiments. It was found the non-linear stress-strain curves were largely different from those by linear analysis with much higher non-linear elastic moduli. The difference was more distinguishable when the tow waviness was smaller.

A cyclocopter with the cycloidal blades system can be the type of UAV which can combine the high-speed characteristics of the conventional airplane with the low-speed characteristics of the helicopter. The cycloidal blades system, which can be described as a horizontal rotary wing, offers powerful thrust levels, and a unique ability to change the direction of the thrust almost instantly. Rotor blades are designed to withstand tremendous transverse centrifugal loadings, and responding to a number of aerodynamic harmonic vibratory forcing frequencies. To reduce the weight and increase the strength, the blades are made of composite materials. The blades consist of the skin, spar, and trailing stiffener. In this study, static and dynamic behaviors of cyclocopter rotor blades are analyzed by using MSC/NASTRAN.

변형률과 파손신호를 동시에 계측하기 위하여 이중복조기를 갖는 광섬유 브래그 격자센서시스템을 제안하였다. 이중복조기는 가변 패브리-페로 필터를 사용하여 변형률과 같이 변화가 큰 저주파신호를 측정하는 복조기와 수동 마흐-젠더 간섭계를 사용하여 파손신호나 충격신호와 같이 미세한 크기의 고주파 신호를 측정하는 복조기로 구성된다. 제안된 광섬유 브래그 격자센서시스템을 이용하여 인장하중을 받는 직교적층 복합재 구조물의 변형률과 파손신호를 동시에 계측할 수 있었다. 하나의 광섬유브래그격자센서로 측정한 변형률과 파손신호를 분석한 결과, 복합재 시편의 90도 층에서 모재균열이 발생할 때 급격한 변형률 변이가 유발되고, 최대 수백킬로헤르쯔에 이르는 주파수 성분을 가진 진동신호가 발생함을 알 수 있었다.

Impact location monitoring is one of the major concerns of the smart health monitoring. For this application, multipoint ultrasonic sensors are to be employed. In this study, a multiplexed FBG sensor system with wide dynamic range was proposed and stabilization controlling system was also developed for the maintenance of maximum sensitivity of sensors. For the intensity demodulation system of FBG sensors, Fabry-Perot tunable filter(FP-TF) with 23.8nm FSR(free spectral range) was used, which behaves as two separate filters between $1530 \~ 1560$ nm range. Two FBG sensors were attached on the bottom side of the graphite/epoxy composite beam specimen, and low velocity impact tests were performed to detect the one-dimensional impact locations. Impact locations were calculated by the arrival time differences of the impact longitudinal waves acquired by the two FBGs. As a result, multiplexed in-line FBG sensors could detect the moment of impact precisely and found the impact locations with the average error of 1.32mm.

In this paper, a new structural health monitoring technique for composite laminates through the use of embedded fiber Bragg grating (FBG) sensors is presented. The method traces the ply stress states of a laminate and compares them with failure criteria during the service time of structures. The ply stress state of every ply composing the composite laminate can be obtained using classical lamination theory by embedded FBG sensors in the laminate. Graphite/epoxy laminate specimens, embedded with three FBG sensors, were fabricated. Tension tests were performed to evaluate the ply stress states tracing technique. Experimental results show that laminates experience fracture when the ply stress states are over the boundaries of failure criteria. In this method, critical damage can be detected by the ply stress states which are close to the boundaries of the failure criteria.

Using the embedded optical fiber sensor of totally-reflected extrinsic Fabry-Perot interferometer(TR-EFPI), longitudinal strains(Ex) of the core and skin layers in glass fiber reinforced plastic(GFRP) cross-ply composite laminates have been measured. Transmission optical microscopy was employed to study the damage formation around the TR-EFPI sensor. It was observed that values of ex in the interior of the skin layer and the core layer measured by embedded TR-EFPI sensor was significantly higher than that of the specimen surface measured by strain gauges. The experimental results agreed well with those from finite element analysis on the basis of uniform stress model. Large strains in the core layer led to the occurrence of transverse cracks which drastically reduced the strain at failure of optical fiber sensor embedded in the core layer.

In this paper, a Fiber Bragg Grating (FBG) sensor system for smart structures is described. FBGs are well-suited for long term and extremely severe experiments, where traditional strain gauges fail. In the system, a reflect wave-length measurement method which employs a tunable light source to find out the center wave-length of FBG sensor is used. We applied the FBG system to composite repairing structures and beam column joint of building structure. We also applied the system to nuclear energy power plant for structural integrity test to measure the displacement of the structure under designed pressure and to check the elasticity of the structure by measuring the residual strain. The system works very well and it is expected that it can be used for a real-time strain, temperature and vibration detectors as parts of smart structures.

A CPGFRP(Carbon Powder Glass Fiber Reinforced Plastics) sensor was fabricated for fine crack detection of structures. The electrical resistance of the sensor was measured on condition of various composition of carbon powders and thickness of bundle of glass fibers. The resistance was decreased as the increase of the content of carbon powders and the TEX of the glass fibers. In the case of loading on CPGFRP sensor, because inner crack was propagated, the part of percolation structures was disconnected. The sensor is superior to carbon fiber for the detecting ability of fine crack.

Two-way shape memory effect(TWSME) under residual stresses are considered in the present study. The structure using two-way shape memory effect concept returns to its initial shape by increasing or decreasing temperature under the initially given residual stress. In the present study, we use a thermo-mechanical constitutive equation of SMA and laminated composite beam are considered as simple morphing structural components which are based on large deformable 2D composite beam theory. Numerical results of fully coupled SMA-composite structures are presented.

In this paper, active shape control of composite structure actuated by shape memory alloy (SMA) wires is presented. Hybrid composite structure was established by attaching SMA actuators on the surfaces of graphite/epoxy composite beam using bolt-joint connectors. SMA actuators were activated by phase transformation, which induced by temperature rising over austenite finish temperatures. In this paper, electrical resistive heating was applied to the hybrid composite structures to activate the SMA actuators. For faster and more accurate shape or deflection control of the hybrid composite structure, PID feedback controller was designed from numerical simulations and experimentally applied to the SMA actuators.

The object of this study is to design the Radar Absorbing Structures (RAS) having sandwich structures in the X-band $(8.2\~12.4GHz)$ frequencies. Glass fabric/epoxy composites containing conductive carbon blacks and carbon fabric/epoxy composites were used for the face sheets. Polyurethane (PU) foams containing multi­walled carbon nanotube (MWNT) were used for the core. Their permittivities in the X-band were measured using the transmission line technique. The reflection loss characteristics for multi-layered sandwich structures were calculated using the theory of transmission and reflection in a multi-layered medium. Three kinds of specimens were fabricated and their reflection losses in the X-band were measured using the free space technique. Experimental results were in good agreements with simulated ones in 10dB absorbing bandwidth.

Conventional piezoelectric lead-zirconate-titanate (PZT) senor has high sensitivity, but it is very brittle. Recently polymer films such as polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride­trifluoroethylene) (P(VDF-TrFE)) copolymer have been used as a sensor. The advantages of polymer sensor are the flexibility and mechanical toughness. Simple process and possible several shapes are also additional advantages. Polymer sensor can be directly embedded in a structure. In this study, nondestructive damage sensitivity of single basalt fiber/epoxy composites was investigated with sensor type and thermal damage using AE and oscilloscope. And AE waveform for epoxy matrix with various damage types was compared to each other. The damage sensitivity of two polymer sensors was rather lower than that of PZT sensor. The damage sensitivity of PVDF sensor did not decrease until thermal damage temperature at $80^{\circ}C$ and they decreased significantly at $110^{\circ}C$ However, the damage sensitivity of P(VDF-TrFE) sensor at $110^{\circ}C$ was almost same in no damage sensor. For both top and side impacts, the difference in arrival time increased with increasing internal and surface damage density of epoxy matrix.

As fiber reinforced composite materials are widely used in aircraft, space structures and robot arms, the study on the non-destructive testing methods of the composite materials has become an important research area for improving their reliability and safety. In this paper, the AE signal analyzer with the resonance circuit to extract the specified frequency of the acoustic emission signal were designed and fabricated. The noise levels of the fabricated AE signal analyzer by the disturbance such as impact or mechanical vibration had a very small value comparable to those of the conventional AE signal analyzer. Also, the crack detection capabilities of the fabricated AE signal analyzer under the static and dynamic tensile test were evaluated and compared with the conventional AE signal analyzer.

Fiber reinforced plastic material should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. Generally, ultrasonic technique is widely used to evaluate FRP. In conventional ultrasonic techniques, transducer should be contacted on FRP. However, conventional contacting method could not be applied in fabrication process and novel non-contact evaluating technique was required. Laser-based ultrasonic technique was tried to evaluate FRP plate. Laser-based ultrasonic waves propagated on CFRP were received with various transducers such as accelerometer and AE sensor in order to evaluated the properties of waves due to the variation of frequency. Velocities of laser-based ultrasonic waves were evaluated for various fiber orientation.

Graphite reinforced conductive polymer composites were fabricated by the compression molding technique. Graphite powder (conductive filler) was mixed with an epoxy resin to impart electrical property in composites. The ratio of graphite powder was varied to investigate electrical property of cured conductive composites. In this study, graphite filled conductive polymer composites with high filler loadings$(>60wt.\%)$ were manufactured to accomplish high electrical conductivity(> 100S/cm). Graphite powder increase electrical conductivity of composites by direct physical contact between particles. While high filler loadings are needed to attain good electrical property, the composites becomes brittle. So the ratio of filler to epoxy was varied to optimize of cured composites. The optimum molding pressure according to filler was proposed experimentally.

Despite of the excellent properties of carbon nanofiber, The properties of carbon nanofiber filled polymer composites were not increased largely. The reason is that it is still difficult to ensure the uniform dispersion of carbon nanofiber in a polymer matrix. In this study, For improvement properties of carbon nanofiber filled epoxy composites, the effect of dispersion was investigated. The compounds were prepared by two methods, solution blending and mechanical mixing. Mixing of solution blending method was used using ultrasonic. Dispersion of carbon nanofiber was observed by optical microscope and scanning electron microscope (SEM). UV adsorption and turbidity measured by UV spectrometer was used for the comparison of dispersion of carbon nanofiber.

This paper presents a study on the permittivities of the carbon black/epoxy composite at microwave frequency. The measurements were performed at the frequency band of $1 GHz\~18GHz$. The results show that the complex permittivities of composites depend strongly on the natures and concentrations of the carbon black dispersion. The frequency spectrums of dielectric constants and ac conductivities of composites show the good conformities with descriptions of the percolation theory. The carbon black concentration dependencies do not have conformities with the descriptions of percolation theory and there is no peculiar concentration like percolation threshold, on that concentration, the conductivity of composite jumps up. A new scheme, that is a branch of Lichtenecker-Rother formula, is proposed to obtain a mixing law to describe the complex permittivities of the composites as function frequency and concentration of carbon black.

In these days, composite materials are applied to the military field like parts of air crafts, rockets, ammunitions and so on. As high pressure is loaded on the composite body, however, cracks or delamination phenomena can be occurred between layers of laminate. These cracks or delamination usually cause a deterioration of mechanical properties under the complicated loads. In this study, methods for improvement of the inter-laminar bonding strength of thick carbon/epoxy composite structures are suggested and discussed in terms of segment bending test.

Carbon nanotube is a geometrical frame-like structure and the primary bonds between two nearest-neighboring atoms act like beam members, whereas an individual atom acts as the joint of the related beam members. The sectional property parameters of these beam members are obtained from molecular mechanics. Computations of the elastic deformation of single-walled carbon nanotubes reveal that the Young's moduli of carbon nanotubes vary with the tube diameter and are affected by their helicity. With increasing tube diameter, the Young's moduli of carbon nanotubes approach the Young's modulus of graphite.

We fabricated MWNT-added glass fabric/epoxy composites. We observed the distribution of MWNTs in the composites using scanning electron microscopy and conformed that most of MWNTs exist in matrix rich region and interface between yams in warp and fill directions. We also investigated the change of permittivities with MWNT concentrations. Only $1wt\%$ MWNTs leads to high permittivity and electromagnetic waves are impossible to be transmitted to more than $3wt\%$ MWNT-added composites, which means the characteristics of these composites are comparable to those of metals or carbon fiber-reinforced composites.

In this study, the effect of laminate thickness on the compressive behaviour of composite materials was investigated through systematic experimental work using the stacking sequences, [04]ns, [45/0/-45/90]ns and [45n/0n/-45n/90n]s (n = 2 to 8). The stacking sequence effects on failure strength of multidirectional laminates were examined. For this purpose, two different scaling techniques were used; (1) ply-level technique [45n/0n/-45n/90n]s and (2) sub laminate level technique [45/0/-45/90]ns. An apparent thickness effect existed in the lay-up with blocked plies, i.e. unidirectional specimens $([0_4]ns)$ and ply-level scaled multidirectional specimens ([45n/0n/-45n/90n]s). From the investigation of the stacking sequence effect, the strength values obtained from the sub laminate level scaled specimens were slightly higher than those obtained from the ply level scaled specimens. The measured failure strengths were compared with the predicted values

In this work, the carbon fabric reinforced phenolic composite is applied for heavy-duty journal bearings. The through thickness compressive strength (TTCS), which is one of the most important characteristics for the bearing material, is measured and analyzed with respect to the stacking sequence and composite thickness. Also, the coefficient of thermal expansion (CTE) and thermal conductivity of the composite in the thickness direction were measured with respect to stacking sequence.

In this work, the effect of chemical treatments on surface properties of SiC was investigated in mechanical interfacial properties of carbon fibers-reinforced composites. The surface properties of the SiC were determined by acid/base values and contact angles. The thermal stabilities of carbon fibers-reinforced composites were investigated by thermogravimetric analysis (TGA). Also, the mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical strain energy release rate mode II $(G_{IIC})$ measurements. As a result, tile acidically treated SiC (A-SiC) had higher acid value than that of untreated SiC (V-SiC) or basically treated SiC (B-SiC). According to the contact angle measurements, it was observed that chemical treatments led to an increase of surface free energy of the SiC surfaces, mainly due to the increase of the specific (polar) component. The mechanical interfacial properties of the composites, including ILSS and $(G_{IIC})$, had been improved in the specimens treated by chemical solutions. These results were explained that good wetting played an important role in improving the degree of adhesion at interfaces between SiC and epoxy resin matrix.

A thermal model of carbon spun yam is presented. The unit cell of spun carbon yam is divided into a number of volume elements and the local material properties have been given to each element. By using Finite Difference Method (FDM), temperature distribution in the unit cell can be obtained. Effective thermal conductivity of the spun carbon yam unit cell is calculated using the temperature distribution and thermal conductivities of local elements.

Two different diene monomers [dicyclopentadiene (DCPD) and 5-ethylidene-2-norbomene (ENB)] as self­healing agent for polymeric composites were microencapsuled by in-situ polymerization of urea and formaldehyde. The healing agents were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Exothermic reaction and glass transition temperature from DSC and storage modulus (G') and tan $\delta$ from DMA curves were analyzed for the samples cured for 5 min and 24 h in the presence of different amounts of catalyst. Micorcapsules were successfully formed for both diene monomers. Microcapsules containing the healing agent were manufactured and its thermal properties were characterized by thermo gravimetric analysis (TGA). Optical microscope (OM) and particle size analyzer (PSA) were employed to observe morphology and size distribution of microcapsules, respectively. Comparison of the two self-healing agents and their microcapsules with the two was made in this study.

In this paper, compressive characteristics of carbon fabric skin with polymeric foam core sandwich structure were investigated by FE analyses and compressive tests of polyurethane foam were also conducted with respect to temperature changes, which were determined by curing processes of epoxy or polyester resin to obtain mechanical behaviour of polyurethane foam. FE analyses indicated variation of parameters with respect to manufacturing pressure, which have comparatively massive effect upon mechanical properties of sandwich structures, i.e. wavelength as well as crimp angle of carbon fabric

This paper aims to investigate the micro-mechanical behaviour of tow geometry with forming pressures and densities of foams during the curing process of plain weave carbon fibre fabric prepregs onto polymer foams. In order to find out and compare deformation patterns between different forming conditions, tow parameters such as amplitude and crimp angle etc. are investigated. From the observation results, geometric difference in the tow architecture with respect to forming conditions and foam characteristics were found. To observe the micro-deformation of the fabric structure, appropriate specimens from carbon fibre-foam sandwich structures are sectioned and observed under the microscope.

A numerical method is presented to determine the characteristic lengths for the failure analysis of composite joints without characteristic length tests. In the conventional methods, compressive characteristic length was determined from the result of a combined bearing test and finite element analysis. The present study, however, shows that the same compressive characteristic length can be obtained by numerical calculation without the bearing test. A new method to define the tensile characteristic length is also introduced so that the tensile characteristic length is numerically determined without the tensile test. Failure loads based on the numerically calculated characteristic lengths are validated by the test results for composite joints

Mechanical behavior of a fuel stack was studied using an orthotropic material model. The fuel stack is essentially composed of a bipolar plate (BP), a gasket, an end plate, a membrane electrolyte assembly (MEA), and a gas diffusion layer (GDL). Each component is fastened with a suitable pressure. It is important to maintain a suitable contact pressure distribution of BP, because it influences the power efficiency of the fuel cell stack. When it is exposed to high temperature, its behavior must be stable. Hence, we performed stress analysis at high temperature as well as at room temperature. At high temperature, the contact pressure distribution becomes poor. Many patents have shown that using an elastomer can overcome this phenomena. Its effect was also studied. By using an elastomer, we found a good contact pressure distribution at high temperature as well as at room temperature.

We study the fracture behavior of the lumbar No.4 and No.5 vertebra subjected to posteroanterior (PA) forces, a three dimensional finite element method (FEM). The lumbar spine was modeled 3-dimensionally using commercial software based on the principle of convert stacked two dimensional CT scan images into three dimensional shapes. Determination of the boundary conditions corresponding to actual surgical conditions was not easy, so that the simplified spine beam analyses were performed. The results were used in three dimensional finite element (FE) analysis. This FE analysis, indicates that the fracture loads of the lumbar No.4 and No.5 vertebra are respectively 1550 N and 1500 N. These fracture loads are for static loading, but in actual conditions the load on the lumbar spine varies dynamically. We found that the fracture load of lumbar No.4 vertebra is larger than that of lumbar No.5 vertebra, as a result of the total stress difference by the moment.

The cure kinetics of blends of epoxy(tetraglycidyl-4,4'-diaminodiphenylmethane ; TGDDM)/curing agent(diaminodiphenyl sulfone ; DDS) resin with amine terminated polyetherimide-CTBN-amine terminated polyetherimide triblock copolymer(ABA) were studied using differential scanning calorimetry under isothermal conditions to determine the reaction parameters such as activation energy and reaction constants. By increasing the amount of ABA in the blends, the final cure conversion was decreased. Lower values of the final cure conversions in the epoxy/ABA blends indicated that ABA hinders the cure reaction between the epoxy and curing agents. 1be value of the reaction order, m, for the initial autocatlytic reaction was not affected by blending ABA with epoxy resin, and the value was approximately 1.0. The value of n for the nth order component in the autocatalytic analysis was increased by increasing the amount of ABA in the blends, and the value increased from 2.0-3.4. A diffusion controlled reaction was observed as the cure conversion increased and the rate equation was successfully analyzed by incorporating the diffusion control term for the epoxy/DDS/ABA blends.

The effects of short fiber and particle hybrid reinforcement on fatigue crack propagation behaviors in aluminum matrix composites have been investigated. Single and hybrid reinforced 6061 aluminum containing same 20 $Al_2O_3\;volume\%$ with four different constituent ratios of short fibers and particles were prepared by squeeze casting method and tested to check the near-threshold and stable crack growth behavior. The fatigue threshold of the composites increased with portion of particle contents and showed the improved crack resistance especially in low stress intensity range. Addition of particle instead of short fiber also increased fracture toughness due to increase of inter-reinforcement distance. These increase in both fatigue threshold and fracture toughness eventually affected the fatigue crack growth behavior such that the crack growth curve shift low to high stress intensity factor value. Overall experimental results were shown that particle reinforcement was enhanced the fatigue crack resistance over the whole stress intensity factor range.

The pultruded structural shapes are usually composed of thin-walled plate elements. Because the composite material has relatively low elastic moduli, the design of pultruded compression members may not be governed by the material strength limit state but by the stability limit state such as the local buckling or the global buckling. Therefore, the stability limit state must be checked to design pultruded columns. In this research, the local buckling analysis of pultruded I-shape column was conducted for various composite materials using the closed-form solution. To establish the design guidelines for the local buckling of pultruded I-shape compression members, the simplified form of equation to find the local buckling coefficient of pultruded I-shape column was proposed as a function of mechanical properties and the width ratio of plate components using the results obtainde by the closed-form solution. In order to verify the validity of proposed solution, the results obtained by the proposed approximate solution were compared with those of the closed-form solution and the experimental results.

For the bolted joint of the composite structure, quasi-isotropic stacking is generally used to increase the bearing strength. For the bolted joint of uni-directional composite, the fatigue life limit of the bolted joint can be improved by applying clamping force though the static strength is still very low. In this paper, the static and fatigue characteristics of hybrid joint are investigated which can overcome the disadvantage of the bolted joint of uni-directional composite under static loading by applying adhesive joining. The experimental result shows that the static strength and fatigue life can be improved by applying clamping force to the hybrid joint and the hybrid joint is a good solution for the efficiency of the composite structures.

The fracture characteristics of unidirectional composite single-lap bonded joints were investigated experimentally and numerically. The effects of bonding method, surface roughness, bondline thickness and the existence of fillet on the failure characteristics and strength of bonded single-lap joints were evaluated experimentally. The failure process, failure mode and the behavior of load-displacement curve was apparently different according to bonding method. The failure load of the specimen co-cured without adhesive was definitely superior to other types of specimens but the specimens co-cured with adhesive film had a less strength than secondary bonded specimens. In the secondary bonded specimens, the lower value of surface roughness and existence of fillet improved the strength of specimens. The strain energy release rates calculated by geometric nonlinear finite element analyses and Virtual Crack Closure Technique for the secondary bonded specimens considering the three types of initial cracks - comer crack, edge crack and delamination crack - were consistent with the test results.

High strain-rate deformation behavior of NiAl/Ni micro-laminated composites was characterized by split hopkins on pressure bar(SHPB). When the strain rate increased, the compressive stress of micro-laminated composites were increased a little. When the intermetallic volume fraction increased, the compressive stress of micro-laminated composites increased linearly irrespective of strain rate. Absorbed energy during the quasi-static and SHPB tests was calculated from the integrated area of stress-strain curve. Absorbed energy of micro-laminated composites deviated from the linearity in terms of the intermetallic volume fraction but merged to the value of intermetallic as the strain rate increased. This was due to high tendency of intermetallic layer for the localization of shear deformation at high strain rate. Microstructure showing adibatic shear band(ASB) confirmed that the shear strain calculated from the misalignment angle of each layer increased and ASB width decreased when the intermetallic volume fraction. Simulation test impacted by tungsten heavy alloy cylinder resulted that the absorbed energies multiplied by damaged volume of micro-laminated composites were decreased as the intermetallic volume fraction increased. Fracture mode were changed from delamination to single fracture when the intermetallic volume fraction and this results were good matched with previous results[l] obtained from the fracture tests.

An analytical study was conducted to characterize the fatigue crack growth behavior of pre-cracked aluminum plates repaired with asymmetric bonded composite patch. For single-sided repairs, due to the asymmetry and the presence of out-of-plane bending, crack front shape would become skewed curvilinear started from a uniform through-crack profile, as observed from previous studies. In this study, the fatigue analysis of single-sided repairs considering crack front shape development was conducted by implementing three-dimensional successive finite element method coupled with linear elastic fracture mechanics (LEFM) concept, which enables the growing crack front to be directly traced and modeled in a step by step way. Through conducting present analysis technique, crack path of the patched plate as well as the fatigue life was evaluated with sufficient accuracy. The analytical predictions of both the crack front shape evolution and the fatigue life were in good agreement with the experimental observations.

When MWK (Multiaxial Warp Knitted Fabric) composites are applied for the structures, the connections of each component using mechanical fastening is needed. The local contact between the bolted joint and the composite laminates may induce high stress concentration or breakdown in the laminates for the mechanical joints. There for, it is strongly required to study the characteristics of mechanically joints of MWK composite laminates. In this study, stress analysis near the hole boundary of MWK composite laminate is conducted with various geometric factors under different loadings. In the case of multi-pin loaded MWK composite laminates, the results show that the types of loadings and geometric factors of mechanical joints have a significant influence on the joint performances.

Emphasis has been placed on thin plate fabrication of plain woven carbon fabric reinforced Al matrix composites using liquid pressing process. The composite has potential applications for PDP rear plate. The process is to use the low pressure for infiltration of Al melt into plain woven carbon fabric as the Al melt is pressurized directly. The minimum pressure required for the infiltration was calculated from force balance equation, permeability measurements and compaction behavior of carbon fiber. Also, the melting temperature and the holding time have been optimized. In order to measure coefficient of thermal expansion (CTE) of the composites, the thermal strain measurement using strain gage was performed and the thermal conductivity of the composites was measured using laser flash method. The constituent materials of the composite are PAN type carbon fibers as reinforcements and 6061 Al alloys as matrices.

Fiber placement system (FPS) carries out an advanced composites process which orients high strength reinforcing fibers in specific directions. The process includes wet winding, thermoset tape winding, thermoset prepreg placement and thermoplastic prepreg placement. FPS have the advantage of tape laying and filament winding with computer control and software. Using FPS can reduce costs, cycle times, structural weight, and handwork/rework when manufacturing composite parts. The sleeve extension is a part of the helicopter rotator systems. In this study, The sleeve extension composites were manufactured using FPS and tensile properties of this composites were characterized using universal testing machine(UTM).

This paper contains the tension-tension, the tension-tension bearing and the tension-tension steel bolt joint fatigue characteristics of glass fabric/phenol composite laminates. The experimental results show that the bearing and the steel bolt joint fatigue characteristics of the material is so excellent compared with the simple tension fatigue characteristics, that there are no needs of additional strengthening for mechanical joint parts when the parts are properly designed.

This study focused on the introduction of the self-healing technique for polymeric composites and evaluated the healing efficiency through the interlainar fracture toughness tests. The DCPD and ENB were used for a healing agent and the Grubbs' catalyst as a catalyst. The healing efficiency was evaluated by the use of mode I and the mode n fracture toughnesses. According to the results, the DCPD-ENB mixture with a suitable ratio revealed better healing efficiency than DCPD only.

In this study, bond strengths for the self-healing agents were evaluated through the modified lap shear test in order to suggest the optimal healing conditions for the repair of polymeric composites. The healing agents of DCPD, ENB, and their mixtures were activated with Grubbs' catalysts. According to the results, the mixture of DCPD and ENB gave better opportunity than DCPD only due to the rapid acivation with catalyst in view of the economic and practical use.

Aircraft composite structure with honeycomb core experiences core crush problem in manufacturing. To prevent core crush additional processes are needed such as core stabilization and prepreg material tie-down and this is the cause of increasing cost. Recent study shows that high friction prepreg prevent core crush without additional process. This paper presents the analysis of high frictional material which attracts lots of interests through physical property, mechanical property and microscopic morphology and the cause of friction.

In this paper, the fracture strength of the surface damaged laminates was predicted by applying the fracture strengths of the unflawed and flawed laminates. For prediction, the theoretical equation about the fracture strength of laminates was simplified applying classical laminate theory and was applied to the surface damaged laminates. Lagace's and Tsai's experimental data were used for verifying the theoretical equation. Moreover, to verify the theoretical prediction, an experiment was performed. Surface unflawed laminate and flawed laminates were fabricated and the experiments were made and these results were compared with theoretical predictions. The specimens' fiber direction was same to the tensile direction and the theoretical predictions and the experimental results were showed good agreement. Therefore, by this equation, the fracture strength of structures made of composites will be able to be predicted when the surface of the structures was damaged.

Thermal postbuckling and vibration analyses of functionally graded plates (FG plates) are performed. The nonlinear finite element equation based on the first-order shear deformation plate theory is formulated for the FG plate. The von Karman strain-displacement relation is used to account for the thermal large deflection. The incremental method considering the effect of the initial deflection and the initial stress is adopted for temperature-dependent material properties of functionally graded materials. The numerical result shows characteristics of the thermal postbuckling and vibration of FG plates in the pre- and post- buckled regions.

After we experiment one direction fiber reinforced composites$(\theta\;=\;0^{\circ},\;J=1)$ to the X direction$(\theta\;=\;0^{\circ},\;J=1)$, we can say that fiber orientation efficiency and fiber orientation angle efficiency become lower. It is because the more the fabric is orientated in a equal direction with one direction fiber floor the more the load given from the exterior becomes shear rather than tension, even though one direction fiber floor gets the most of the exterior power. when fiber content ration is $10wt\%$, the fiber reinforcement efficiency of J=0.3 is similar with the fiber reinforcement efficiency of $\theta=30^{\circ}$ We also found that the fiber reinforcement efficiency of J=0.2 is similar with the fiber reinforcement efficiency of $\theta=20^{\circ}$ in case of $20wt\%$.

The characteristics of the buckling analysis module for stiffened composite structures were studied in this paper. Composite stiffened structures have geometrical asymmetry and material properties asymmetry. Due to these reason, postbuckling analysis was essential and the characteristics of postbuckling analysis modules for ABAQUS were researched. Static analysis module was considered. By considering the material nonlinearity, progressive failure mechanism was applied and buckling strength was estimated

In case of Resin Transfer Molding(RTM) process, 'race-track' effects and non-uniform fiber volume fraction may cause undesirable resin flow pattern and thus result in dry spots, which affect the mechanical properties of the finished parts. In this study, a real time RTM control strategy to prevent these unfavorable effects is proposed. The control strategy consists of two 'stages' depending on the extent the resin front has reached. Through numerical simulations and experiments, the validity of the proposed scheme is demonstrated. The results show that the proposed scheme is effective in reducing the void formation during RTM mold filling.