This paper presents the analytical results of local - global interaction buckling of orthotropic I-shape compression members. Employing the equilibrium approach, the characteristic equation for local and global interaction buckling of I-shape compression member is derived. Using the derived equation, the buckling coefficients with respect to the ratio of length to width for the I-shape column are suggested as a graphical form. In addition, graphical forms of local, global and FEM results are presents, and they are compared with those in published document.

This paper presents the analytical investigation pertaining to the local buckling behavior of orthotropic open section thin-walled compression members with asymmetric edge stiffeners. In the analysis, 3 different cases of the second moment of inertia are considered to find the asymmetric edge stiffener effect on the local buckling strength. The analytical study results are presented in the graphical form so that the edge stiffener effects on the local buckling strength can be easily found.

This paper deals with the torsional buckling behavior of plain weave GFRP composite cylindrical shells having comparatively small length-to-diameter ratio. Boundary conditions corresponding to clamped ends and simply supported ends are considered. Torsional buckling loads and circumferential mode numbers according to the variation of shell length-to-radius ratio are conformed. To verify the availability of the theoretical results, comparison with the theoretical and experimental results are made.

This study is about the effect of braiding on the 2-D biaxial braided hollow composite(BD) compared with unidirectional hollow composite(UD). The specimens were made of T700S Carbon/Epoxy prepreg and T700S dried Carbon yarns. Fiber volume fraction of UD and BD was obtained experimentally and analytically. Fiber volume fraction of BD was derived based on unit cell of braiding yarn section. Bending test was executed to investigate the effect of braiding part. The result of experiment and analysis of fiber volume fraction has good agreement. Bending strength of BD is about 20% higher than that of UD.

Logarithmic electrical resistivity of the untreated or thin diameter carbon fiber composite increased suddenly to the infinity when the fiber fracture occurred by tensile electro-micromechanical test, whereas that of the ED or thick fiber composite increased relatively broadly up to the infinity. Electrical resistance of single-carbon fiber composite increased suddenly due to electrical disconnection by the fiber fracture in tensile electro-micromechanical test, whereas that of SFC increased stepwise due to the occurrence of the partial electrical contact with increasing the buckling or overlapping in compressive test. Electrical resistivity measurement can be very useful technique to evaluate interfacial properties and to monitor curing behavior of single-carbon fiber/epoxy composite under tensile/compressive loading.

The fiber reinforced composite materials is widely used in aircraft, space structures and robot arms because of high specific strength and high specific modulus. The on-line cure monitoring during the cure process of the composite materials has become an important research area for the better quality and productivity. In this paper, the dielectric circuit of the wheatstone bridge type for measuring the dissipation factor was designed and manufactured. Also, the dielectric sensor for the cure monitoring of the high temperature composites was developed. The residual thermal stresses of the dielectric sensor were analyzed by the finite element method and its dielectric characteristics under high temperature were evaluated. The on-line cure monitoring of the BMI resin was performed using the wheatstone bridge type circuit and developed high-temperature dielectric sensor.

The purpose of this paper is to determine the effect of the autoclave inner pressure rate, heat-up rate, tool round angle, Thickness of core, height of joggle on defects, and to minimize the defects of aircraft sandwich structure reinforced with honeycomb core occurred in autoclave processing. The results showed that the geometry of aircraft sandwich structure and tool such as tool round angle, Thickness of core, height of joggle, and the autoclave cure conditions such as inner pressure rate, heat up rate strongly affected the core movement, core wrinkle, bridge phenomenon of prepreg and depression of core that occurred in autoclave processing.

The effect of novel N-crotyl-N,N-dimethyl-4-methylanilinium hexafluroantimonate (CMH) curing agent on cure behavior and thermal properties of DGEBA epoxy cationic system was investigated. From DSC measurements of DGEBA/CMH system, it was shown that this system exhibits an excellent thermal latent characteristic in a given temperature and reveals complex cure behavior as indicated by multiple exotherms. The conversion and conversion rate of DGEBA/CMH system increased with increasing the concentration of initiator due to high activity of CMH. Viscoelastic properties during gel formation of DGEBA with CMH were investigated by rheological techniques under isothermal condition. The gel time obtained from the modulus crossover. point t(G')=G", was affected by high curing temperature and concentration of CMH, resulting in high degree of network formation in cationic polymerization. The thermal stabilities were discussed in terms of the activation energy for decomposition and thermal factors determined from TGA measurements.ents.

High temperature cure characteristics of polyester resin systems were investigated by isothermal and dynamic differential scanning calorimetries. During isothermal scanning, the experimental procedure was modified to reduce the initial Boss of heat. no kinetic equation from the isothermal experiment was compared with that from the dynamic experiment.

The properties of thermosetting resins are dependent on the degree of cure and consolidation quality. Since the consolidation process of thermosetting resin matrix fiber composites is much dependent on the viscosity of resin in the composites, in this study, the dissipation factor which is a function of viscosity was measured by the newly developed Lacomtech dielectrometry apparatus and sensors. Using the measured dissipation factors, the relationship between the dissipation factor and degree of cure with respect to environmental temperature was investigated.

A decoupled thermo-~lezoelectric-mechanical model of composite laminates with surface bonded piezoelectric actuators, subjected to externally applied load, temperature change load, electric field load is developed. The governing differential equations are obtained by applying the principle of free energy and variational techniques. A higher order zigzag theory displacement field is employed to accurately capture the transverse shear and normal effects in laminated composite plates of arbitrary thickness.

The effect of punching density on the mechanical and thermal properties of nonwoven needle-punched carbon/phenol composite was studied. The carbonized preforms were farmed into composites with phenol resin. The interlaminar shear, tensile and flexural strengths were increased with increasing punching density. However, excessive punching density decreased interlaminar shear and tensile strengths. Erosion rate of carbon/phenol composite was decreased with increasing punching density

Thermal deformation behavior has been investigated for unsymmetric laminates composed of various kinds of material layers, such as stainless steel, aluminum, carbon/epoxy or glass/epoxy. The thermal deformations of unsymmetric laminates were predicted using the classical lamination theory and compared with those obtained from experimental measurement. In the case of unsymmetric laminate composed of stainless steel and aluminum layer, the experimental results were agreed well with the values predicted. But in the case of unsymmetric laminate composed of fiber composite layers, there was a considerable difference of thermal deformation between the prediction and experimental measurement, which may be from the change of material properties of fiber composite layers for temperature variation.

The fabrication process and analysis of thermal properties of 50~76vo1% SiCp/Al metal matrix composites(MMCs) for heatsink materials in electronic packaging were investigated. The 50~76vo1% SiCp/Al MMCs fabricated by pressure infiltration casting process showed that thermal conductivities were 85~170W/mK and coefficient of thermal expansion(CTE) were ranged 10~6ppm1k. Specially, the thermal conductivity and CTE of 71vo1%SiCp/Al MMCs were ranged 115~156W/mK and 6~7ppm/K. respectively, which showed a improved thermal properties than the conventional electronic packaging materials such as ceramics and metals.

This research addresses study on thermal residual stress of a composite patch repair of the edge cracked aluminium panel of aging aircraft. Composite patch repair is an efficient and economical technique to improve the damage tolerance of cracked metallic structures. These are thermal residual stresses due to the mismatch of coefficient of thermal expansion, and these are affected by the curing cycle of patch specimen. In this study, three curing cycles were selected for F.E. analysis. This study features the effect on composite patch and aluminum by thermal residual stress during crack propagation in aluminum plate.

This study was performed to investigate the material behavior of hybrid thermoplastic composites contained glass fiber and calcium carbonate. The composite was prepared with each combination ratio of calcium carbonate, and the content of glass fiber was fixed with 10% by weight. In order to investigate the material behavior for various combination ratio, tension test, flexural test, and impact test were performed. Microscopic observation were conducted to examine the fractured surface of specimen for tension test. And the material behavior of the hybrid thermoplastic composite immersed in salt water with definite time was investigated.

In this study, the optimal condition of surface treatment for aluminum panel was determined by measuring the contact angle and T-peel strength. The contact angle was measured for various mixture ratios of acetylene gas and nitrogen gas. The mixture (acetylene gas to nitrogen gas) ratios used were 1:9, 3:7, 5:5, 7:3, and 9:1. The contact angle was also measured as a function of time of surface treatment. The results showed that the contact angle was a minimum for mixture ratio of 5:5. T-peel strength was a maximum for the treatment time of 30 second.

This study investigates the effect of surface treatment on the shear strength between aluminum panel and composite plate. The aluminum panel was surface-treated by DC Plasma and the composite Plate was surface-treated by ion beam. Lap shear test and T-peel test were performed to determine the shear strength and T-peel strength. Results showed that the shear strength of surface-treated case was 2.5 times higher than that of untreated case. The T-peel strength of treated case was more than 5 times higher than that of untreated case. SEM examination showed that the strength increase of surface-treated case was due to the more spread of epoxy to the panel.

Interfacial and microfailure properties of carbon liber/bismaleimide (BMI) composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Since BMI is rather difficult matrix to apply for the conventional fragmentation test because of its too low elongation and too brittle and high modulus properties, dual matrix composite system was applied. After carbon fiber/BMI composite was prepared for rod shape by controlling differing curing stage, composites rod was embedded in toughened epoxy as outer matrix. The typical microfailure modes including fiber break, matrix cracking, and interlayer failure were observed during tensile testing, whereas the diagonal slippage in fiber ends was observed during compressive test. On the other hand, AE amplitudes of BMI matrix fracture were higher than carbon fiber tincture under tensile test because BMI matrix has very brittle and high modulus. The waveform of signals coming from BMI matrix fractures was consistent with AE amplitude result under tensile tests.

Square tubes used for vehicle structure components have an important role on keeping its stiffness and preserving occupant safety in vehicle collision and rollover in which it experience axial collapse, bending collapse or both. Bending collapse, which absorbs kinetic energy of the impact and retains a survival space for the occupant, is a dominant failure mode in oblique collision and rollover. Thus, in this paper, the bending collapse characteristics such as the maximum bending moment and energy absorption capacity of the square tube replaced by light-weight material were evaluated and presented. The bending test of cantilever tubes which were fabricated with aluminum, GFRP and aluminum/ GFRP hybrid by co-curing process was performed. Then the maximum bending moment and the energy absorption capacity from the moment-angle curve were evaluated. Based on the test results, it was found that aluminum/ GFRP hybrid tube can show better specific energy absorption capacity compared to the pure aluminum or GFRP tube and can convert unstable collapse mode which may occur in pure GFRP tube to stable collapse mode like a aluminum tube in which plastic hinge is developed.

흑연분말, 카본블랙, 탄소섬유분말을 첨가제로 한 저밀도 2-D 탄소/탄소 복합재의 밀도 및 기 기공도에 피치는 영향과 ILSS, 굽힘강도 및 충격에너지와 같은 기계적 물성과의 상관관계에 대하여 연구하였다. 흑연분말을 약 9 vol.% 첨가한 경우 가장 큰 ILSS값과 굽힘강도 및 충격에너지 흡수 거동을 나타내었는데, 특히 흑연의 함량이 증가함에 따라 puncture mode로의 충격 거동을 나타내 띠 많은 충격에너지를 흡수하였고, 인성이 상당히 증가하였다 카본블랙이 첨가된 경우에는, 약 3 vol.%에서 ILSS 값이 증가하였으나 큰 개선을 보이지 못하였으며, 굽힘강도는 감소하였다. 탄소섬유분말의 첨가량이 증가함에 따라 층간분리에 의해 밀도가 현저히 감소하여 ILSS 및 굽힘강도의 감소를 보였다.

저속 충격을 받은 복합재로 만들어진 두꺼운 압력용기의 파괴모드와 손상 상태에 대하여 조사하여 이를 정량적으로 나타내는 것이 본 연구의 관심이다. 본 논문에 사용된 시편은 압력용기의 중앙을 길이 305mm로 잘른 원통형 ring모양이다. 충격자는 직경이 25.4mm와 12.7mm인 반구형 2종류와 모서리의 직경이 1mm인 원추형 1종류로 무게는 3.9kg이며 자유낙하 높이는 20mm에서 200mm로 종류에 따라 간격을 달리했다. 실험 장치로는 실린더가 충격에 흔들리지 않도록 고정하는 받침대와 자유낙하 하는 impactor 이며 impactor의 윗면에 한 개의 가속도 게이지를 설치했으며 밑면에 90도 간격으로 4군에 스트레인 게이지를 붙여 충격에너지, 최대 충격력, contact radius를 측정하고 시험후 시편은 방사선 촬영을 하여 충격자의 종류에 따라 손상의 정도가 어떻게 다른지를 파악했다. Herzian이론을 사용하여 contact radius를 구하고 측정된 자료와 비교 검토하였다. Contact radius 값은 충격자의 직경이 클수록 큰 것을 알수 있고 실험치 값은 이론치 값 보다 큰데 이는 실제 연소관의 기계적 성질의 값이 계산치 보다 적은 것이 원인이다. 직경이 25.4mm인 반구형의 충격자는 직경이 12.7mm인 반구형의 충격자에 비하여 내부에 delamination크기가 컸다. 가속도의 값은 높이에 따라 선형적으로 변하고 충격자의 모양이 둔탁할수록 가속도 값이 커지는 것을 알 수 있다.

Recently, composite material which has much excellent mechanical characteristics has been applied in many industries. However, it has a brittle characteristic under impact condition and its invisible characteristics of the damaged area has been the motivation of many engineers investigation. The modified failure criterion is implemented to predict the failure behavior of the composite plate subjected to low velocity impact using commercial finite element analysis code, ABAQUS-Ver. 5.8. The new criterion is in good agreement with experimental results and can predict the failure behavior of the composite plate subjected to low velocity impact more accurately.

Recently, applications of integrated large composite structures have been attempted to many structures of vehicles. To improve the cost performance and reliability of the integrated composite structures, it is necessary to judge structural integrity of the composite structures. For the judgement, we need fracture simulation techniques for composite structures. Many researches oil the fracture simulation method using FEM have been reported by now. Most of the researches carried out simulations considering only matrix cracking and fiber breaking as fracture modes, and did not consider delamination. Several papers have reported the delamination simulation, but all these reports require three-dimensional elements or quasi three- dimensional elements for FEM analysis. Among fracture mechanisms of composite laminates, delamination is the most important factor because it causes stiffness degradation in composite structures. It is known that onset and propagation of delamination are dominated by the strain energy release rate and interfacial moment. In this study, laminated composite has been described by using 3 dimensional finite elements. Then impact behavior of the laminated composite is simulated using FEM(ABAQUS/Explicit) with progressive failure mechanism. These results are compared with experimental results.

Impact tester was build up to evaluate the characterization of CFRP laminate plates under the low velocity impact. The tests were conducted on several laminates of different ply orientation A system was budded for the impact strength of CFRP laminates in consideration of stress wave propagation theory using drop-weight impact tester as one of impact test. Results indicate that absorbed energy of quasi-isotropic specimen having four interfaces is higher than that of orthotropic laminates with two interfaces. Also the damage area was measured with ultrasonic C-scanner on some samples. In the specimens the relationship was linear between damaged area and absorbed energy to some degree. Absorbed energy in the specimen that ply number, interface number and fiber stacking sequences is same but having hybrid is higher than that of orthotropic laminates without hybrid.

The Interlaminar fracture behavior of hybrid composite with non-woven carbon tissue was investigated under Mode I (DCB) and Mode II (ENF) loading condition. Hybrid composites were manufactured by means of inserting a non-woven tissue between prepreg layers. Two kinds of specimens were prepared from [0]$_{24}$ and [$0_{12}/0_{12}$]. Where, the symbol "/" means that a non-woven carbon tissue was located at 0/0 mid-plane of the specimen. The interlaminar fracture toughness of hybrid composites was compared with that of CFRP. The fracture surfaces of the specimens were observed using optical microscope and SEM, and the failure mechanism was discussed. The hybrid laminates, which are made by inserting non-woven carbon tissue between layers, were shown to be effective to remarkably improve Mode II fracture toughness.toughness.

The development of high-strength fibers such as boron/epoxy and carbon/epoxy and adhesives has made it possible to repair cracked metallic plates by bonding reinforcing patches to the plate over the crack. In this study, aluminum 6061-T6 alloy plates with the high strength are applied to specimens with a cracked bolt hole to study the effect of diverse patch materials on the fatigue behavior of this structure. Additionally, the observation of the effort of different patch sizes on the specimen was performed. The results shows that the patch repair can improve the static strength by about 17% and the fatigue life by 200% compared with non-repaired case. And it was also revealed that the patching method along to crack growth direction is mort efficient in cost and weight reduction.

The characteristics of fatigue life distribution for Carbon/epoxy composite laminates was investigated under tension-tension loading(R=0.1). The statistical nature of the fatigue life of the composite materials was analyzed by Weibull, normal, lognormal distributions As a result, it was observed that the correlation between the experimental results and the theoretical predictions for the fatigue life is good. The distribution of the static ultimate strength has the characteristic of lognormal distribution and distribution of the fatigue life has characteristics of the weibull distribution.

In this study, a technique for monitoring of fatigue damage of composite laminates by measuring the stiffness change using embedded intensity-based optical fiber sensors was investigated. Firstly, the underlying measurement principle and structure of intensity-based sensors and then a simple stiffness conversion process was explained. The monitoring technique was evaluated by fatigue tests of composite laminates with an embedded intensity-based sensor. From the test results, the response of the intensity-based sensor showed good correlation with that of surface mounted extensometer. Therefore, it can be concluded that the intensity-based sensors have good potential for the monitoring of fatigue damage of composite structures under fatigue loading. In addition, it could be confirmed that the intensity-based sensors have higher resistance to fatigue than the commercial electrical strain gauge.

The objective of this research is to develop real-time failure detection techniques for damage assessment of composite materials using optical fiber sensors. Signals from matrix cracking or fiber fracture in composite laminates are treated by signal processing unit in real-time. This paper describes the implementation of time-frequency analysis such as the Short Time Fourier Transform(STFT) to determine the time of occurrence of failure. In order to verify the performance of the optical fiber sensor for stress wave detection, we performed pencil break test with EFPI sensor and compared it with that of PZT. The EFPI sensor was embedded in composite beam to sense the failure signals and a tensile test was performed. The signals of the fiber optic sensor when damage occurred were characterized using STFT and wavelet transform. Failure detection system detected the moment of failure accurately and showed good sensitivity with the infinitesimal failure signal.

A numerical method fur performance evaluation of LIPCA is proposed using a finite element method. Fully coupled formulations for piezo-electric material are introduced and eight-node incompatible element is used. After verifying the developed code, the behaviors of LIPCA and $THUNDER^{TM}$ are investigated.

It has many variables and factors to design the friction materials for automotive brake pads. In this study, the friction and wear characteristics of automotive blake pads have been studied using 1:l full size dynamo meter. Using conventional manners, it takes a great of time and efforts to know that it affects the each raw materials for friction characteristics. For the purpose of examining the effect of each major raw materials, we used the more convenient Taguchi L9 ($3^4$) orthogonal matrix and 1/5 scale dynamo machine for evaluation of the friction characteristics of composite brake pads.

This paper presents the thermoelastic analysis and 3-D failure analysis of the carbon/carbon brake disk. The mechanical properties of the carbon/carbon brake disk were measured for both in-plane and out of plane directions. The mechanical properties were used as the input of the thermoelastic analysis and 3-D stress analysis for the brake disk. The gap between rotor clip and clip retainer was an important parameter in the loading transfer mechanism of the rotor. The change of gap was considered separating the mechanical deformation and thermal deformation. Because the rotor clip and clip retainers were not contacted, the clip retainers and rivets were excluded from the rotor analysis model. The disk was modeled by using the cyclic symmetry condition and the contact problem between the rotor disk and rotor clip was considered. From the results of the 3-D stress analysis, the stress concentration at the key hole of the brake disk was confirmed.

In author's previous paper, a finite element algorithm was presented to calculate the buckling and crippling stresses of composite laminated stringers. In this study, for the validation of the finite element analysis, Z-section composite stringers of different lengths and flange-widths were tested in axial compression. The stacking sequence of graphite/epoxy is [$\pm$45/0/90]s. Strain gages were attached to each specimen to get the strain response. Deflection and end-shortening were obtained by a displacement transducer. The buckling and crippling loads are determined from the strain response, load vs. end-shortening curves, and load vs. out-of-plane deflection curves. Comparison between finite element and experimental results shows good agreement in the buckling, local buckling, and crippling stresses.

In this paper, a finite element structural analysis for thin-walled open-section composite beams with elastic couplings has been performed. The analysis includes the effects of transverse shear across beam sections, torsion warping and constrained warping. Reissner's semi-complementary energy functional is used to obtain the beam st illness coefficients The bending and torsion related warpings and the shear correct ion factors are obtained as part of the analysis. The resulting theory describes the beam kinematics in terms of the axial, flap and lag bending, flap and lag shear, torsion and torsion-warping deformations. The static response has been validated against finite element predict ions, closed form solutions, and experimental data for rectangular sol id and I-beams with elastic couplings. The free vibration results are also compared with available literature.

로켓엔진에서 노즐은 추력을 발생하고, 단위 면적당 열 전달이 최대가 되는 곳으로 구조적으로 가장 취약한 부분이다. 이런 가혹한 조건에서 사용되어질 수 있는 4D 탄소/탄소 복합재를 제조하였으며. 초밀도화시, 탄화압력은 100bar 와 900bar 에서 각각 시행되었다. 만들어진 시편의 밀도는 1.5~l.9g/$cm^3$ 이었다. 실제 로켓을 모사할 수 있는 지상연소시험을 통해 밀도에 따른 삭마율을 계산한 결과, 밀도가 높을수록 삭마율은 감소하였다. 또한 3-point bending test를 통해 굽힘강도(flexural strength)를 측정하였으며, 굽힘강도를 개선시켜주었다.

Although extensive efforts have been devoted to the optimal design of composite laminated plates in recent years, some practical issues still need further research. One of them is the handling of the uncertainties in material properties, which were ignored in most researches in the past. In this paper, the convex modeling is used in calculating the failure criterion, given as constraint, to consider the uncertain material properties in the thickness optimization. Numerical results show that the optimal thickness increases when the uncertainties of elastic moduli considered, which shows such uncertainties should not be ignored for safe and reliable designs.

Finite element model based on the Naghdi's shell theory in the general tensor-based form is formulated in the present study. Partial mixed variational functional for assumed strain is formulated in order to avoid the severe locking troubles known as transverse shear and membrane locking. The proposed assumed strain element in general tensor Naghdi's shell model provides very accurate solutions for thin shells in benchmark problems. In additions, linear elastic constitutive equations are given in the general curvilinear coordinate system including anisotropic layered structures. Thus laminated composited shell structures are easily analyzed in the present formulation.

This paper predicted the equivalent stiffness of spatially reinforced composites (SRC) using the volume average of a fiber rod and matrix stiffness, and the strength of SRC using the stiffness reduction and the modified Tsai-Wu composite failure theory. Those equivalent engineering constants are used to analyze the mechanical behavior and the failure of SRC structures. Because the distribution of equivalent engineering constants is varying with the change in SRC shape, we made a program that predicts engineering constants of SRC. Both 3-D and 4-D SRC show the smallest tensile modulus and the largest shear modulus at the maximum rotated direction from each rod. Also the strength properties show the same tendency.

A new textile metal matrix composite fur electronic packaging was developed and characterized. The thermal management materials consist of a plain woven carbon fabric as reinforcement and pure aluminum as matrix. The finite element method has been utilized in the analysis of thermal stress between the constituent components of packaging. The prototype part was manufactured by the liquid pressurizing method. The composite has CTE values of 4 to $5{\times}10^{-6}\;^{\circ}C^{-1}$10 in the range of $25^{\circ}C$ ~ 175$^{\circ}C$, resulting in good agreement with electronic materials such as Si and GaAs.

Cyclocopter is air vehicle to vertically take-off and land like a helicopter. This is an efficient and quiet means of being able to direct thrust compared to a helicopter. The rotor consists of several blades rotating about a horizontal axis perpendicular to the direction of normal flight. The direction of blade span is parallel to rotating axis and both end roots are connected to the hub to resist centrifugal force and to transmit the power. The pitch of the individual blades to the tangent of the circle of the blade's path is varied cyclically to gain thrust. In the paper, the design and manufactures of cyclocopter rotor blades are presented. Stress at the roots of cyclocopter blades is great due to centrifugal and aerodynamic forces and aeroelastic instabilities appear. The blades consist of main spar, front spar, polyurethan foam, weight, and skin and spars and skin are made of glass/epoxy composite.

In this study, experimental verification of performance of flat speaker has been conducted. The piezofilm (PVDF) actuator has been designed to prevent the distortion of sound and make the frequency response of radiated sound flat. The electrode pattern of piezofilm actuator is optimized to satisfy the design objective. The formulation of design method is based on the coupled finite element and boundary element method and electrode pattern is optimized by genetic algorithm. The flat speaker with optimized piezofilm actuator has been manufactured. The sound pressure level at the distance of 50cm is measured using microphone and compared with the result of numerical simulation.

Microstrip antenna for SAR applications is designed with microwave composite laminates and Nomex honeycomb cores, which becomes an aircraft's structural panel. This study demonstrated fabrication, design procedures and structural and electrical performances of complex antenna system presented. For validating structural rigidity, 3-point bending test is performed, and simulation results for the complex antenna array are compared with measurements for its electrical performance. The results show that this antenna system can be applied in dual polarized synthetic aperture radar and has a good flexural stiffness with comparison of previous sandwich constructions.

Compared with existing construction materials, ACM(Advanced Composites Material) possesses many advantage such as light-weight, high-strength, corrosion resistant properties, etc. In this study, utilizing those advantages of ACM, composite skin and comer plate for protection of concrete port structure are developed. Detailed procedure fur analysis, design and fabrication along with site installation for demonstration project are described. It is also demonstrated that pultrusion process for comer plate and VARTM process for composite skin are promising fabrication methods fer future civil infrastructure application.

Filament Winding Process is a comparatively simple operation in which continuous reinforcements in the form of roving are wound over a rotating mandrel. And now well established as a versatile method for storage tanks and pipe for the chemical and other industries . In this study, tensile strength of a filament wound ring specimens were evaluated by split disk test fixture and dress disk test fixture , The results obtained from experiments were compared with the theoretical values obtained by the rule of mixtures. And the purpose of this paper is the suggestion of an appropriate test method for the evaluation of tensile properties of filament wound structures .The tensile strength of a ring specimen tested by the dress disk test showed better agreement with the theoretical values than of a ring specimen tested by the split disk test because the stress concentration in edges of a split disk test fixture is more severe than that of dress disk test fixture. The results showed that the tensile strength of a ring specimen was influenced by the geometry of test fixture, the continuity of fibers, fiber-tension, fiber-end and stress concentration in specimen.

Processing parameters of filament winding were investigated by using design of experiment. To understand 4 main effects(fiber tension, impregnation pressure, processing rate, and temperature) and 3 interactions, $L_{27}(3^{13})$ orthogonal array table was adopted. The used materials were carbon fiber and epoxy resin. Split disk test and short-beam test, which are the general test methods for filament wound composite material, were selected as evaluation methods for a filament would part. The optimal processing parameters for the filament winding were easily found through the analysis of variance of the experimental results.

For the production of high strength constructional glass reinforced plastics and various composite materials continuous glass fibers of high strength and increased modulus of elasticity are used. As is known, the glasses with highest strength were obtained in magnesia alumosilicate and magnesia lime-alumosilicate systems when introducing oxides of titanium and zirconium, boric anhydride, etc. in some cases. The experimental investigations have shown that some glass compositions are characterized by the ratio viscosity/crystallization which is favourable for glass fiber drawing process that permits the attainment of high strength level at the conditions of high temperature glass melting and formation.

The adhesive bonded single-lap joint is due to its intrinsic load eccentricity problem, severe peel stresses concentration occur at both end of the joint. In this paper, new lap-joint is designed to avoid the singular peel stress, and to compare the stresses of the middle adhesive layer between the single-lap joint and the wavy-lap joint. Two adherend lay-up, i.e., [90/0/90/0]$_{2s}$ and [0/90/0/90]$_{2s}$ were consider in the study.

A method of calculating the natural frequency corresponding to the modes of vibration of beams and tower structures, with irregular cross sections and with arbitrary boundary conditions was developed and reported by Kim, D. H. in 1974. In this paper, the result of application of this method to the three span continuous reinforced concrete bridge with elastic intermediate supports is presented. Such bridge represents either concrete or sandwich type three span bridge on polymeric supports for passive control or on actuators for active control The concrete slab is considered as a special orthotropic plate. The influence of the modulus of the foundation and $D_{22}$, $D_{12}$, $D_{66}$ stiffnesses on the natural frequency is thoroughly studied.

Modal damping characteristics of the flexural vibration of a sandwich beam with paaially inserted viscoelastic layer have been quantitatively studied using the finite element analysis in combination with an experiment. Antisymmetric mode shapes of the flexural vibration were visualized by the holographic interferometry and agreed with those calculated by the finite element simulation. Effects of the length and thickness of partial viscoelastic layers on the system loss factor($\mu$) and resonant frequency($\omega$) were considerably latge at both symmetric and antisymmetric modes of the sandwich beam.

The active vibration control of laminated composite shell has been performed with the optimized sensor/actuator system. PVDF film is used fur the material of sensor/actuator. Finite element method is utilized to model the whole structure including the piezoelectric sensor/actuator system, The distributed selective modal sensor/actuator system is established to prevent the adverse effect of spillover. In the finite element discretization process, the nine-node shell element with five nodal degrees of freedoms is used. Electrode patterns and lamination angles of sensor/actuator are optimized using genetic algorithm. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator profiles are optimized for the first and the second modes suppression of singly curved cantilevered composite shell structure. Discrete LQG method is used as a control law. The real time vibration control with profile optimized sensor/actuator system has been performed. Experimental result shows successful performance of the integrated structure for the active vibration control.

Thermopiezoelastic snap-through phenomena of piezolaminated plates are numerically investigated by applying a cylindrical arc-length scheme to Newton-Raphson method. Based on the layerwise displacement theory and von-Karman strain-displacement relationships, nonlinear finite element formulations are derived for thermopiezoelastic composite plates. From the static and dynamic viewpoint, nonlinear thermopiezoelastic behavior and vibration characteristics are studied for symmetric and eccentric structural models with various piezoelectric actuation modes. Present results show the possibility to enhance the performance of thermal structures using piezoelectric actuators and report new phenomena, namely thermopiezoelastic snapping, induced by the excessive piezoelectric actuation in the active suppression of thermally buckled large deflection of piezolaminated plates.

FBGs have been extensively used as strain sensors or temperature sensors in a variety of applications related to composites because of embedding ability, small size and multiplexing capability. We inspected embedding environments inside composites with optical fiber by microscope analysis and birefringence characteristics of FBG embedded into textile composite laminate by cure monitoring using a high power WSFL. The cure monitoring of the cases with the striped FBG and the recoated FBG provided comprehensive understandings about the birefringence effect induced by the transverse stress. And these results allowed to consider a recoating method as an important tool to relieve birefringence.

Modern aircraft composite structures are designed using a damage tolerance philosophy. This design philosophy envisions sufficient strength and structural integrity of the aircraft to sustain major damage and to avoid catastrophic failure. The only reasonable way to treat on the same basis all the conditions and uncertainties participating in the design of damage tolerant composite aircraft structures is to use the probability-based approach. Therefore, the model has been developed to assess the probability of structural failure (POSF) and associated risk taking into account the random mechanical loads, random temperature-humidity conditions, conditions causing damages, as well as structural strength variations due to intrinsic strength scatter, manufacturing defects, operational damages, temperature-humidity conditions. The model enables engineers to establish the relationship between static/residual strength safety margins, production quality control requirements, in-service inspection resolution and criteria, and POSF. This make possible to estimate the cost associated with the mentioned factors and to use this cost as overall criterion. The methodology has been programmed into software.

To overcome problems of excavation technology far repairing or replacing underground buried pipes which are worn out or damaged, various trenchless repair-reinforcement technologies have been invented. But these trenchless technologies also have many problems in the aspect of economy and convenience of operation. In this research, the repair-reinforcement process using RTM (Resin Transfer Molding) which can solve problems of present trenchless technologies was developed. The resin wetting and void removal during RTM process to form large composite structures inside of buried pipes were experimentally investigated. From the experiment, it was found that the new technology had advantage over conventional methods by employing appropriate process parameters and void removal vents.

In order to commercialize the low cost composite fabrication technology in the area of domestic aerospace structure field, Resin Transfer Molding process has been considered as an alternative process to replace the high cost autoclave technology. The end part for the development of RTM process is the control rod of flight control system of aircraft. A braided preform was triaxially designed to improve the dimensional stability and mechanical property in the direction of external loads. Through the flow analysis using CVFEM, the resin filling time was calculated and the resin injection method was determined. The results of the flow analysis were directly applied to RTM mold design. The control rod was successfully manufactured by RTM process using internal pressure. The length and outer diameter of the manufactured part are 1148mm and 32mm, respectively.

The composite composed of glass fabric and BMI resin was fabricated using resin transfer molding(RTM) process. it will be used as a supporting plate of transformer coil for high speed train. To develop a RTM process, permeability of preform was measured and resin properties like a viscosity and gellation time were checked. A resin pre-heating system and a mold system were also designed and developed. Using a vacuum-assisted RTM process, the composite supporting plate was successfully fabricated.

The objective of this work was to characterize mechanical properties of thermoplastic composites for various forming condition in compression molding. Randomly oriented long glass fiber reinforced polypropylene(PP) was used in the work. The composite materials contained 20%, 30%, and 40% glass fiber by weight. Compression molding was conducted to make the test specimen. Dimensional stability was measured on each forming condition with the spring-forward angle. Tensile test was conducted to characterize mechanical properties of formed parts in various forming conditions.

Injection molding is a very important industrial process for the manufacturing of plastics objects. During an injection molding process of composites, the fiber-matrix separation and fiber orientation are caused by the flow of molten polymer/fiber mixture. As a result, the product tends to be nonhomogeneous and anisotropic. Hence, it is very important to clarify the relations between separation· orientation and injection molding conditions. So far, there is no research on the measurement of fiber orientation using image processing. In this study, the effects of fiber content ratio and molding condition on the fiber orientation-angle distributions are studied experimentally. Using the image processing method, the fiber orientation distribution of weld-line parts in injection-molded products is assessed. And the effects of fiber content and injection molding conditions on the fiber orientation functions are also discussed