A new non-destructive fatigue prediction model of the composite laminates is developed. The natural frequencies of fatigue-damaged laminates under extensional loading are related to the fatigue lift of the laminates by establishing the equivalent flexural stiffness reduction as a function of the elastic properties of sublaminates. The flexural stiffness is derived by relating the $90^{\circ}$-ply elastic modulus reduction, and using the laminate plate theory to the degraded elastic modulus and the intact elastic modulus of other laminate. The natural frequency reduction model, in which the dominant fatigue mode can be identified from the sensitivity scale factors of sublaminate elastic properties, provides natural frequency vs. fatigue cycle curves for the composite laminates. Vibration tests were also conducted on $[\textrm{90}_{2}\textrm{0}_{2}]_s$ carbon/epoxy laminates to verify the natural frequency reduction model. Correlations between the predictions of the model and experimental results are good.

A three node flat triangular element incorporating Layerwise Zig-Zag Theory(HZZT) is developed suitable for analyzing damped laminated composite structures. Using an interdependent kinematic relation, the higher order shear rotations are replaced by in-plane displacements, a transverse displacement and section rotations, which result in three translations and two rotations. Natural frequencies and modal loss factors of cantilevered laminated plates with embedded damping layers are calculated with the zig-zag triangular element and compared to the experimental results and MSC/NASTRAN results using a layered combination of plate and solid elements.

An active control of the vibration transmitted by longitudinal load in flight control system is investigated numerically. The flight control system is modeled as a finite, thin shell cylinder with constant thickness. A vibration source is generated by exterior monopole source. Distributed piezoelectric actuator is used to control of the vibration. Thin shell theory is used to formulate the numerical models. The amplitude of vibration at discrete location and power transmission are minimized by analytical optimization method. Genetic algorithm is used as numerical optimization method to search optimal actuator position and size which amplitude of vibration is minimized.

This paper deals with finite element analysis for free vibration and forced sine vibration of Ka- and Ku- bend antenna structures using MSC/PATRAN/NASTRAN. The structures are designed to satisfy minimum resonance frequency requirement in order to decouple the dynamic interaction of the satellite with the spacecraft bus structure. From the forced sinusoidal vibration, we have observed output acceleration versus input in X-,Y- and Z- direction, based on base excitation using large mass method. The results of finite elements analysis can be used as the reference data for the experimental test of satellite antenna, resulting in the reduction of cost and time by predicting and complementing experimental data.

This paper proposes a double cantilever sandwich-beam method for evaluating the frequency dependence of material dynamic characteristics. The flexural vibration of a double cantilever sandwich-beam specimen with a partially inserted rubber layer was studied using a finite element simulation in combination with the sine-sweep test. Quadratic relationships of dynamic elastic modulus and material loss factor of rubbers with frequency were quantitatively suggested employing the least square error method.

Since non-corrosive Fiber Reinforced Polymer(FRP) tendons have been in increasing use for underground and coastal structures constantly contacted with fresh water or sea water because of their superiority to metallic ones in corrosion-resistance, new non-metallic anchoring system for FRP tendons has been developed and investigated to verify the effectiveness of tendon force, which consist of mainly FRP pipes and Highly Expansive Mortar(HEM). The major factors considered in this experiment were expansive pressures of HEM during its hydration, sleeve lengths and types, and anchoring methods of tendon. New anchoring system were investigated from the pull-out tests. The pull-out procedures of the FRP tendons in the various pipe filled with HEM were analyzed and improved ideas were suggested to develop novel non-metallic anchoring system for FRP tendons The pull-out tests for the FRP tendon and new non-metallic anchoring system were conducted. The results show that non-metallic anchoring system for the FRP tendon has been more stablized due to the gradual expansive pressrure of HEM, as tims goes. Since tile lower stiffness of FRP pipes causes the weakness of anchoring force, it requires the increase of stiffness using a carbon fiber or an increased section area.

In the present study, AZ91Mg/$\textrm{Al}_2\textrm{O}_3$ short fiber+SiC particulates hybrid metal matrix composites(MMCs) were fabricated by squeeze casting method. Different particulate sizes of 45, 29 and $9\mu\textrm{m}$ were hybridized with 5% volume fraction to investigate the effect of SiC particulates size on microstructure, mechanical and thermal properties such as hardness, flexural strength, wear resistance and thermal expansion. Results show that the microstructure of the hybrid composites were quite satisfactory, namely revealing relatively uniform distribution of reinforcements. Some aggregation of SiC particulates caused by particle pushing was observed especially in the hybrid composites containing in fine particulates($9\mu\textrm{m}$). The hardness and flexural strength were improved by decreasing particulates size, whereas wear resistance improved by increasing particulates size because of large particulates restricting matrix wear from contacted stress. Regardless of particulates size, thermal expansion of composites was the same. This may be because the content of particulates was in all cases 5 volume fraction.1

This study developed Fiber/Particle Hybrid MMCs and analyzed their mechanical properties. Using $\textrm{Al}_2\textrm{O}_3f$ and $\textrm{Al}_2\textrm{O}_3p$ with the fiber to particle ratio of 1:1, 1:3, 1:5 hybrid preform and MMCs are fabricated. For the analysis of the mechanical properties, three point bending tests were preformed for the preform and tensile test for the MMCs. The experimental results show that the hybrid MMCs can be successfully fabricated using the equipment of fiber preform fabrication system and squeeze casting method. And as the amount of particle in hybrid MMCs increases, the tensile strength, elastic modulus and the volume fraction of reinforcement increases.

A new 2-D braided textile metal matrix composite was developed and characterized. The constituent materials consist of PAN type carbon fiber as reinforcements and pure aluminum as matrices. The braided preforms of different braider yarn angles were fabricated. For a fixed bundle size of 12K, three braider yarn angles was selected: $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$. The braided preforms were infiltrated with pure Al by vacuum assisted squeeze casting. Through the investigation of melt pressing methods and the effects of process parameters such as applied pressure, and pouring temperature, the optimal process conditions were identified as follows: applied pressure of 60MPa, pouring temperature of $800^{\circ}C$. Using the measured geometric parameters, 3-D engineering constants of metal matrix composites have been determined from the elastic model, which utilizes the coordinate transformation and the averaging of stiffened and compliance constants based upon the volume of each reinforcement and matrix material.

The characteristics of smart skin for wireless LAN system under compression load are investigated. The smart skin structure is composed of 3 layers of face material and 2 layers of core material. Theoretical formula for determining buckling load is derived by Rayleigh-Ritz method and compared with experimental result. The maximum length of specimen that buckling does not occur is determined by only face material. In the experiment, if load supporting capability and the antenna property such as radiation pattern and reflection coefficient were examined.

In this paper. tile validity of work factor approach was investigated to determine compressive fracture toughness of unidirectional graphite/epoxy composites under hydrostatic pressure environment. The elastic work factor was determined under various pressures as a function of delamination length. It was found that elastic work factor was not affected by hydrostatic pressure.

An experimental research work for the fracture and notch strength of thick laminates has been performed to develop high quality composite notches for structural use. Thus, the multi-directional laminates are designed and compared to the baseline aluminum. The difference of notch strength caused by manufacturing techniques is also discussed. The notches of selected materials are evaluated by the static test and low-velocity impact test. Failure modes are also observed and assessed. Material design is evaluated by the FEA(finite element analysis) and confirmed by experiments. The successful results are obtained for thick composite notches, which shows higher strength than aluminum notches.

This paper presents an analytical investigation pertaining to the elastic buckling behavior of pultruded fiber reinforced plastic equal-leg angle members under concentric axial compression. The elastic local and global buckling (flexural, torsional, and flexural-torsional) analyses are conducted, respectively, and the analytical results are compared with the existing experimental results. The differences were more than 10%, and the experimental results were higher than the analytical results.

In this paper, the tension-compression fatigue test method and the fatigue life characteristics of carbon fabric/epoxy laminate coupon are presented. To avoid the buckling during the compression, a proper design for the test coupons is essential. The critical buckling loads for the coupons are calculated by assuming the coupons as columns under two types of fixed conditions. The first is that both ends of each coupon are perfectly clamped, the second is that both ends of each coupon are simply supported. The strain-load curves are obtained by compressing the representative coupons, on each surface of which a strain gage is attached. The buckling loads obtained from the tests are all between the two calculated critical buckling loads. All the coupons are broken by the compression during the fatigue tests. It is estimated to be the reason that the fatigue load causes delamination before the eventual failure of each coupon, and sequentially the micro-buckling in the delaminated region drives each coupon into fatigue failure during the compression. The S-N curve, the fatigue life characteristics of carbon fabric/epoxy is obtained.

In this research, damage initiation in singly oriented ply (SOP) FML under concentrated loading conditions was studied. The finite element method (FEM) base on the first order shear deformation theory is used for the analysis of fiber orientation effect on FML under concentrated loading conditions. The failure indices were calculated for the variation of fiber orientation and the results were compared with indentation experiments. The failure indices were well matched with damage initiation of SOP FML. Indentation results shows that the crack initiation of SOP FML is determined by stiffness induced by fiber orientation and tile penetration load of SOP FML are influenced by the deformation tendency and boundary conditions.

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact force is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. The distribution of delamination along the thickness direction of curved laminates are also different from that of flat plates. Delamination was distributed rather even]y at each interface along the thickness direction of curved laminates. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.

The impact response and damage of CLAS panel was investigated experimentally. The facesheet material used was RO4003 woven-glass hydrocarbon/ceramic and the core material was Nomex honeycomb with a cell size of 3.2mm and a density of 96 kg/$\textrm{m}^{3}$. The shield plane used was RO4003 and 2024-T3 aluminum. Static indentation and impact test was conducted to characterize the type and extent of the damage observed in two CLAS panels, and the performance of antenna used in a wireless LAN system. Correlation of peak contact force, residual indentation and the delamination area shows impact damage of the panel with an aluminum shield plane is larger than that of the panel with RO4003 shield plane, although tile former is more penetration resistant. The damage was observed by naked eye, ultrasonic inspection and cross sectioning. The shape and size of delamination was estimated by ultrasonic inspection, and the area of delamination linearly increases as impact energy increases. The performance of impact damaged antenna was estimated by measuring return loss and radiation pattern.

Impact behaviors of Aluminum Honeycombs Sandwich Panel(AHSP) by drop weight test were investigated. Two types of specimens with 1/2" and 1/4" cell size were tested by two impactors which are weight of $5.25\textrm{kg}_{\textrm{f}}$ and $11.9\textrm{kg}_{\textrm{f}}$. Parametric studies were achieved including the impactor weight and impact sites which consist face, long-edge, short-edge, and point of the specimen. Face one of impact sites was the strongest and short-edge one of impact sites was the weakest. The damaged area of AHSP was enlarged with the increase of impactor weight that is equal to impact energy. After 3 point bending test, fracture modes of AHSP were analyzed with AE counts. Lower facesheet was fractured in the long-edge direction and then separated between facesheet and core. In the short-edge direction after core wrinkled, lower facesheet tear occurred. Impact behavior by FE analysis were increased localized damage in fast velocity because the faster velocity of the impact was, the smaller the stress of core was. Consequently, impactor weight had an effect on widely damaged area, while the impact velocity was caused on the localized damaged area.aged area.

In this study, the tensile and compressive tests of glass fiber epoxy composites were performed to measure the strength variation with respect to strain rates of 1-200 $\textrm{sec}^{-1}$. In addition, tensile and compressive tests of 50-200 $\textrm{sec}^{-1}$ strain rates were conducted at a low temperature ($-60^{\circ}C$) to investigate the effects of temperature on the strength variation. From the test results, it was found that the tensile and compressive strengths increased about 100% and 70%, respectively, at the strain rates of 10-100 $\textrm{sec}^{-1}$ compared to the quasi-static strengths while the strengths were little affected by the environmental temperature variation.

Drop weight impact tests were performed to investigate the impact behavior of carbon fiber/epoxy composite laminates reinforced by short fibers and other interleaving materials. Characterization techniques, such as cross-sectional fractography and scanning acoustic microscopy, were employed quantitatively to assess the internal damage of some composite laminates. Scanning electron microscopy was used to observe impact damage and fracture modes on specimen fracture surfaces. The results show that composite laminates experience various types of fracture; delamination, intra-ply cracking, matrix cracking and fiber breakage depending on the interlayer materials. Among the composite laminates tested in this study, the composites reinforced by Zylon fibers showed very good impact damage resistance with medium level of damage, while the composites interleaved by poly(ethylene-co-acrylic acid) (PEEA) film is expected to deteriorate the bulk strength due to the reduction of fiber volume fraction, even though the damaged area is significantly reduced.

Structural polymer composites are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. A recent methodology for the damage repair of polymer composites using the self-healing technique is reported. The polymerization of the healing agent is triggered by contact with an embedded catalyst, being necessary to damage repair of polymer composites. For this purpose, the self-healing concept is introduced and the manufacturing process of microcapsule with the healing agent is briefly described. The polymerization between the healing agent and the catalyst is verified by the use of ESEM and IR spectroscopy. Finally the efficiency of the self-healing technique is investigated by measuring the critical load of TDCB specimen.

Composite materials have been applied widely in interior panels of buildings and transport vehicles. Recently good fire performance and weight reduction are key issues in the fields. In the present study we investigated effects of processing parameters on the performance of honeycomb sandwich panels, especially peel strength of the panel and fire performance. The processing parameters considered were types of matrix resin, resin contents, panel cure conditions, and surface painting process conditions. The results showed that the higher resin content provides the better peel strength. Controled cure steps are also needed to obtain good pee] strength. Paint processing parameters including base putty thickness and paint drying conditions and paint thickness are important to obtain good paint adhesion and good fire performance.

In this paper, the solution of two dimensional deflection of circular wavy elastica beam was obtained for one end clamped boundary and concentrated load condition. The beam was regarded as a linear elastic material. Wavy shape was described as a combination of half-circular arc smoothly connected each other with constant curvature of all the same magnitude and alternative sign. Also load direction was taken into account. As a result, the solution was expressed in terms of a series of integral equations. While we found the exact solutions and expressed them in terms of elliptic integrals, the recursive ignition formulae about the displacement and arc length at each segment of circular section were obtained. Algorithm of determining unknown parameters was established and the profile curve of deflected beam was shown compared with initial shape.

In this work, we investigate the toughening mechanism of the rubber-modified epoxy resin. The fracture toughness($K_{IC}$) is measured using CT specimens for three kinds of rubber-modified epoxy resin with different rubber content. The damage zone and rubber particles around a crack tip of a damaged specimen just before fracture are observed by a polarization microscope and an atomic force microscope(AFM). Both the fracture energy($G_{IC}$) and the size of damage zone increase with the rubber content below l5wt%. The size of the rubber particles can be qualitatively correlated with the $G_{IC}$ and the size of damage zone. The cavitation of the rubber particles inside the damage zone is observed, which is expected to be main toughening mechanism by rubber particles. the stress which causes the cavitation of rubber particles is estimated by the Dugdale model.

Dielectrometry has been used to monitor the cure of epoxy resin using composite matrix. In this investigation, physical properties of the mixture of epoxy resin(LY564), bisphenol A type, and cycloaliphatic hardener(HY 2954) were observed. Activation energy at maximum tan $\delta$ and gelation point was determined during isothermal scanning. From IonViscosity data, it was found that vitrification peak after gelation was appeared on slow heating rate. It was also measured that the duration time for full cure was necessary and it was about 24 hr at $145^{\circ}C$. Therefore, epoxy resin used in this research is required the extended time for full cure.

A higher order zig-zag plate theory is developed to refine accurately predict fully coupled of the mechanical, thermal, and electric behaviors. Both the displacement and temperature fields through the thickness are constructed by superimposing linear zig-zag field to the smooth globally cubic varying field. Smooth parabolic distribution through the thickness is assumed in the transverse deflection in order to consider transverse normal deformation. Linear zig-zag form is adopted in the electric field. The layer-dependent degrees of freedom of displacement and temperature fields are expressed in terms of reference primary degrees of freedom by applying interface continuity conditions as well as bounding surface conditions of transverse shear stresses and transverse heat flux The numerical examples of coupled and uncoupled analysis are demonstrated the accuracy and efficiency of the present theory. The present theory is suitable for the predictions of fully coupled behaviors of thick smart composite plate under mechanical, thermal, and electric loadings.

The investigation of cure kinetics and morphology studies on DGEBA/PEI/Anhydride system were performed by differential scanning calorimetry and scanning electron microscopy. Autocatalystic kinetics model was applied by isothermal scan test. Ozawa method and Kissinger method was applied by temperature scan. Activation energy was 95kJ/mol for neat DGEBA/NMA, 120kJ/mol for DGEBA/PEI(10p.h.r.)/NMA. The generation of secondary phase of PEI was observed and its size was grown up by increasing contents of PEI.

The objective of this research is to develop hybridized yarns for thermoplastic composites, and to examine tile effect of cooling rate on mechanical properties of the composites. The co-braided yarn utilizing carbon fibers as reinforcements and Nylon 66 fibers as matrix materials has been fabricated. Thermoplastic composites have been manufactured by the hot-press forming process. For the processing conditions, cooling rates of $-2.5^{\circ}C$/min and $-60^{\circ}C$/min have been considered. Three-point bending test and losipescu shear test were performed to investigate the effect of the cooling rate and the surface treatment of carbon fibers. SEM photographs were used to investigate the fracture surfaces of the tested samples. The cooling rate of $-60^{\circ}C$/min resulted in the higher strength and elastic modulus for bending and shear tests. The composites of the epoxy-sized carbon fibers showed the lowest strength due to the degradation of the sizing material during the thermoforming process.

LIPCA (LIghtweight Piezo-composite Curved Actuator) is an actuator device which is lighter than other conventional piezoelectric ceramic type actuator. LIPCA is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. LIPCA has curved shape like a typical THUNDER (thin-layer composite unimorph feroelectric driver and sensor), but it is lighter an than THUNDER. Since the curved shape of LIPCA is from the thermal deformation during the manufacturing process of unsymmetrically laminated lay-up structure, an analysis for the thermal deformation and residual stresses induced during the manufacturing process is very important for an optimal design to increase the performance of LIPCA. To investigate the thermal deformation behavior and the induced residual stresses of LIPCA at room temperature, the curvatures of LIPCA were measured and compared with those predicted from the analysis using the classical lamination theory. A methodology is being studied to find an optimal stacking sequence and geometry of LIPCA to have larger specific actuating displacement and higher force. The residual stresses induced during the cooling process of the piezo-composite actuators have been calculated. A lay-up geometry for the PZT ceramic layer to have compression stress in the geometrical principal direction has been designed.

Recent days composite bridge deck is gaining attraction due to many advantages such as light weight, high strength, corrosion resistance, and high durability. In this study, composite sandwich deck models of hat, box, and triangular section type were fabricated by VARTM process. For those models, three point flexural test was carried out both in strong and weak axis. The experimental results are compared with each other to determine efficient section type. Also finite element analysis was performed to verify analysis model. It is demonstrated that the results of numerical analysis agree well with experimental results.

A post-tensioned reinforced concrete slab bridge is analyzed by specially orthotropic laminate theory. Symmetrically reinforced slab with tension and compression steel is considered for convenience of analysis. Each longitudinal and transverse steel layer is regarded as a lamina, and material constants of each lamina is calculated by the use of the rule of mixture. This bridge is under uniformly distributed vertical loads, and axial loads and end moments due to post-tensioning. In this paper, finite difference method is used for numerical analysis of this bridge. Theory and analysis method of specially orthotropic laminate plates used in this paper can be used for design of new bridges, and maintenance and repair of old bridges.

A post-tensioned steel plate girder bridge with cross-beams is analyzed by specially orthotropic laminate theory. The cross-sections of both girders and cross-beams are WF types. The result is compared with that of the beam theory. This bridge with simple support is under uniformly distributed vertical load, and axial loads and moment due to post-tension. In this paper, finite difference method for numerical analysis of simple supported bridge is developed. Relatively exact solution is obtained even with small number of meshes. Theory and analysis method of specially orthotropic laminate plates used in this paper can be used in design of new bridges, and maintenance and repair of old bridges.

In the present work, a linear static analysis is presented for thin-walled prismatic box-beams made of generally anisotropic materials. A mixed beam theory has been used to model and carry out the analysis. Three different constitutive relations are assessed into the beam formulation. Simple layup cases having symmetric or anti-symmetric configuration have been chosen and tested to clearly show the effects of elastic couplings of the beam. Both 2D and 3D finite element structural analysis using the MSC/NASTRAN has been performed to validate the current analytical results. Results show that appropriate assumptions for the constitutive equations are important and prerequisite for the accurate prediction of beam stiffness constants and also for the beam behavior.

Shape memory alloy (SMA) has demonstrated its potentials for various smart structure applications. SMA wires undergo a reversible phase transformation from martensite to austenite as temperature increases. This transformation leads to shape recovery and associated recovery strains. If SMA actuators are embedded off the neutral surface and are oriented in arbitrary angles with respect to a beam axis, then the beam bends and twists due to the coupling effects of recovery strains activated. In this study, the bending and twisting of a SMA/Composite beam were controlled by both electric resistive heating and passive elastic tailoring. 3-dimensional finite element formulations were derived and validated to analyze the responses of the SMA/Composite beam. Numerical results show that the shape of the SMA/Composite beam can be controlled by judicious choices of control temperatures, SMA angles, and elastic tailoring.

The layup optimization by genetic algorithm (GA) for the strength of laminated composites with free-edge is presented. For the calculation of interlaminar stresses of composite laminates with free edges, extended Kantorovich method is applied. In the formulation of GA, repair strategy is adopted for the satisfaction of given constraints. In order to consider the bounded uncertainty of material properties, convex modeling is used. Results of GA optimization with scattered properties are compared with those of optimization with nominal properties. The GA combined with convex modeling can work as a practical tool for light weight design of laminated composite structures since uncertainties are always encountered in composite materials.

A combined finite element and experimental study based on the characteristic length method is performed to investigate the strength and behavior of the pin joint in composite control rod. The failure is estimated by the Yamada-Sun and Tsai-Wu criteria on the characteristic curve. The gap elements are used to simulate the contact between the pin and the composite fitting with hole. The accuracy and applicability of the method are validated by the joint tests. All the specimens were failed in the bearing mode in the test and finite element analysis, and good agreement was found between the predicted and test results on the joint strength of composite control rod.

A two-dimensional progressive failure analysis method is presented for the strength characterization of the composite joints under pin loading. The eight-nodes laminated she]1 element is utilized based on the updated Lagrangian formulation. The criteria by Yamada-Sun, Tsai-Wu, and the maximum stress are used for the failure estimation. The stiffness of failed layer is degraded by the complete unloading method. No factor depending on test is included in the finite element analysis except for the material strength and stiffness. Total 20 plate specimens with and without hole are tested to validate the finite element prediction. The Tsai-Wu failure criterion most conservatively estimates the strength of laminate, and the maximum stress criterion yields the highest strength because it does not consider the coupling of the failure modes. The strength by Yamada-Sun method neglecting the matrix failure effect are located between other two methods and shows best agreement with test result for laminate with hole.

Due to intrinsic load eccentricity, severe peel stress concentration occurs at both ends of the single-lap joint. To avoid load eccentricity as well as the singular tensile peel stress in the joint interface, composite wavy-lap joint is proposed. In this paper, refined 3-D stress analysis of wavy-lap joint is performed by finite element method using parallel mutifrontal solver. Analysis results show that the singular tensile peel stress concentration is totally avoided in wavy-lap joint, and that loads are more evenly transferred over the length of the joint. Therefore, the strength of wavy-lap joint is significantly higher than that of conventional single-lap joint. And it is believed that even higher strengths can be obtained by optimizing the new design configuration.

The co-cured Joining method, which is regarded as an adhesively bonded Joining method, is an efficient joining technique because both curing and bonding processes for the composite structures can be achieved simultaneously. It requires neither surface treatment onto the composite adherend nor an additional adhesive joining process because the excess resin, which is extracted from composite materials during consolidation, accomplishes the co-cured Joining process. Since the adhesive of the co-cured joint is the same material as the resin of the composite adherend, the analysis and design of the co-cured joint for composite structures are simpler than those of an adhesively bonded joint, which uses an additional adhesive. In this paper, effects of the manufacturing parameters, namely surface roughness, stacking sequence of the composite adherend, and manufacturing pressure in the autoclave during curing process, on the tensile load bearing capacity of the co-cured single lap joint will be experimentally investigated.

When the preform is composed of more than two layers with different in-plane permeability in resin transfer molding, effective average permeability should be determined for the flow analysis in the mold. The most frequently used averaging scheme is the weighted average scheme, but it does not account for the transverse flow between adjacent layers. A new averaging scheme is proposed predicting the effective permeability of the multi-layered preform, which accounts for the transverse flow effect. The new scheme is verified by measuring the effective permeability of the multi-layered preforms and the difference in each flow front position.

Glass fiber reinforced plastic(CFHP) tent pole fabricated by the pultrusion process with unidirectional glass fiber is two times as heavy as aluminum tent pole owing to the low specific modulus The first objective of this research is the design the high strength and light weight tent pole compete with. the second is the develope glass fiber carbon fiber hybrid tent pole pultrusion process. the third is the evaluate the mechanical properties of the hybrid tent pole compare to these of the duralumin tent pole.

The squeeze infiltration process is potentially of considerable industrial importance. The performance enhancements resulting from incorporation of short alumina fiber into aluminum are well documented. These are particularly significant for certain automobile components. But the solidification process gets complicated with manufacturing parameters and factors for porosity formation do not fully understand yet. In this study porosity defects were observed under several infiltrating conditions ; a kind of matrix, an initial temperature of melt, and a volume fraction of reinforcement. The desimetry and the microscopic image analysis were done to measure the amount of porosity. A correlation between manufacturing parameters and defects was investigated through these.

Resin transfer molding process has been widely used in the automobile industry, because the product with large area can be manufactured easily and the cost for the manufacturing is lower than that of compression molding and hand lay up method. Since RTM process is suitable for large bus housing panels, in this work, the composite housing panel was manufactured by RTM process and the mechanical properties, surface quality and the condition of manufacturing process were studied.

The purpose of this study is the design of composite shaft which is wound by Filament Winding method. Classical laminated plate theory was used for analyzing the stress, and for structure design. The diameter and thickness of composite shaft were calculated by this theory. The result that if tensile stress was zero, torsion stress was a certain value below 0.4(diameter rate) and torsion strength was the highest value on $45^{\circ}C$(winding angle). In case of $90^{\circ}C$(winding angle), we have to consider the torsional monent when the composites shaft was load.

A manufacturing process of composite pressure vessel was studied. The vessel was fabricated using the filament winding process. It is utilized as a container of high pressure Helium gas which propels a rocket fuel and an oxidizer. The layup patterns were determined based on the lamination theory. 3-axis controlled filament winding machine was developed to realize the patterns. The vessel was successfully fabricated using the developed machine. And the hydraulic pressure test was performed to measure an applied pressure-strain relations on the composite vessel.

A Confocal Laser Scanning Microscope (CLSM) is applied to determine three-dimensional fiber orientation states in injection-molded short fiber composites. Since the CLSM optically sections the composites, more than two planes either on or below the surface of composites can be obtained. Therefore, three dimensional fiber orientation states are determined without destruction. To predict the orientation states, velocity and temperature fields are calculated by using a hybrid FEM/FDM method. The change of orientation state during packing stage is also considered by employing a compressible Hele-Shaw model. The predicted orientation states show good agreement with measured ones. However, some differences are found at the end of cavity. They may result from other effects, which are not considered in the numerical analysis.

In this work, virtual material characterization of 3D orthogonal woven composites is performed to predict the elastic properties by a full scale FEA. To model the complex geometry of 3D orthogonal woven composites, an accurate unit structure is first prepared. The unit structure includes warp yarns, filler yarns, stuffer yams and resin regions and reveals the geometrical characteristics. For this virtual experiments by using finite element analysis, parallel multifrontal solver is utilized and the computed elastic properties are compared to available experimental results and the other analytical results. It is founded that a good agreement between material properties obtained from virtual characterization and experimental results. Using the method of this virtual material characterization, the effects of inconsistent filler yarn distribution on the in-plane shear modulus and filler yarn waviness on the transverse Young's modulus are investigated. Especially, the stiffness knockdown of 3D woven composite structures is simulated by virtual characterization. Considering these results, the virtual material characterization of composite materials can be used for designing the 3D complex composite structures and may supplement the actual experiments.

Electronic Speckle Pattern Interferometry(ESPI) is one of optical technique to measure displacement precisely, uses CCD camera to show result image in real time. General ESPI system measures in-plane or out-of-plane displacement. Shearography is one of electronic speckle pattern interferometric methods which allow full-field observation of surface displacement derivatives and it is robust in vibration. The shearography provides non-contacting technique of evaluating defects nondestructively. In this study, the shearography was used to evaluate defects in Carbon Fiber Reinforced Plastic(CFRP). Various sizes of artificial defects were embedded in various depths of woven CFRP plate. Effects due to the variation of size and depth of defects were evaluated in this study.

태핑 검사법을 이용한 복합재료 구조물의 손상검사 과정을 수치해석을 이용하여 모사하였다. 타격체에 의한 태핑을 모사하기 위해 동적접촉 알고리듬을 이용한 유한요소법을 이용하였다. 손상의 유무를 판별하는데 사용되는 척도로서 타격체와 구조물의 접촉하중의 시간이력을 계산하였다. 손상이 없는 복합재료 평판과 층간 분리 손상이 있는 복합재료 평판에 대한 해석을 통하여 접촉특성의 변화를 고찰하였다. 또한 태핑 검사법의 민감도에 대한 해석도 수행하였다.

The on-line cure monitoring during the cure process of composite materials is important for better quality and productivity. The dielectric sensor for cure monitoring consists of base film and electrodes. Because the characteristic of dielectric sensor for the on-line cure monitoring is dependent on the base material, width and number of electrode, etc, the dielectric sensor should be standardized. And the selection of base film material of sensor is very important. In order to prevent the measuring errors generated from the increase of environmental temperature, the base film material should have stable dielectric constant with respect to environmental temperature. In this study, the newly developed dielectric sensor for cure monitoring was designed and the dissipation factor which is function of degree of cure was measured using the sensor. The relationship between the dissipation factor and degree of cure with respect to environmental temperature was investigated.

Adaptive analysis of multilayered composite and sandwich plates is carried out. The adaptive analysis is based on a finite element error form, which measures the difference between the through-the-thickness distribution of finite element displacement and the actual displacement. The region where the error-measure exceeds the prescribed admitted error value, the finite element mesh locally refined in the thickness direction using the mesh superposition technique. Several numerical tests are conducted to validate the effectiveness of the current approach for adaptive analysis of laminated plates.

Satellite system experiences severe mechanical loads during the launch period. Therefore, positive margin of safety of the satellite system must be demonstrated for every possible mechanical loading condition during the launch period. This paper presents modal and stress analysis result due to quasi-static loads for the satellite antenna system. The failure tendency for the sandwich construction of the satellite antenna system has been studied with various lamination angles of unidirectional prepreg.

In this study, efforts were made to understand the propagation of electromagnetic wave through the foam core sandwich structure by the analytical model. Foam core sandwich structure is composed of glass/epoxy composite skins and foam core. Transmittance and reflectance of the arbitrary linearly polarized incident TEM waves through the unidirectional composites, foam and foam core sandwich structures were determined as functions of thickness, fiber orientation of composites, incident angle and polarization angle by the analytical model. From the results of the analysis, the general tendency of transmittance and reflectance of electromagnetic wave through composites, foam and foam core sandwich structures was obtained.

This paper predicted the thermal conductivity of spatially reinforced composites(SRC) by applying the volume averaging method and the thermal resistance method. The former method employs existing micro-mechanical theories and conventional transformation rules to constitute relations for the unit cells of the composites and the latter one uses the analogy between the diffusion of heat and electrical charge. To verify the theoretical prediction, the thermal conductivity of 4-D(dimensional) SRC was examined experimentally. The comparison of the numerical results with those measured by the experiment showed good agreement.

In this paper, we present the simultaneous measurement of the fabricaition strain and temperature during and after cure of unsymmetric composite laminate uising fiber optic sensors. Fiber Bragg grating/extrinsic Fabry-Perot interferometric (FBG/EFPl) hybrid sensors are used to measure those measurands. The characteristic matrix of sensor is analytically derived and measurements can be done without sensor calibration. A wavelength-swept fiber laser is utilized as a light source. FBG/EFPI sensors are embedded in a graphite/epoxy unsymmetric cross-ply composite laminate at different direction and different location. We perform the real time measurement of fabrication strains and temperatures at two points of the composite laminate during cure process in an autoclave. Also, the thermal strains and temperatures of the fabricated laminate are measured in thermal chamber. Through these experiments, we can provide a basis for the efficient smart processing of composite and know the thermal behavior of unsymmetric cross-ply composite laminate.

Recently, based on the smart structure concept, optical fiber sensors have been increasingly applied to monitor the various engineering and civil structural components. Repairs based on adhesively bonded fiber reinforce composite patches are more structurally efficient and much less damaging to the parent structure than standard repairs based on mechanically fastened metallic patches. As a result of the high reinforcing efficiency of bonded patches fatigue cracks can be successfully repaired. However, when such repairs are applied to primary structures, it is needed to demonstrate that its loss can be immediately detected. This approach is based on the "smart patch" concept in which the patch system monitors its own health. The objective of this study is to evaluate the potentiality of application of transmission-type extrinsic Fabry-Perot optical fiber sensor (TEFPI) to the monitoring of crack growth behavior of composite patch repaired structures. The sensing system of TEFPI and the data reduction principle for the detection of crack detection are presented. Finally, experimental results from the tests of center-cracked-tension aluminum specimens repaired with bonded composite patch is presented and discussed.

An intensity-based optical fiber vibration sensor is applied to detect and evaluate damages and fiber failure of composites. The optical fiber vibration sensor is constructed by placing two cleaved fiber end, one of which is cantilevered in a hollow glass tube. The movement of the cantilevered section lags behind the rest of the sensor in response to an applied vibration and the amount of light coupled between the two fibers is thereby modulated. Vibration characteristics of the optical fiber vibration sensor are investigated. Surface mounted optical fiber vibration sensor is used in tensile and indentation test. Experimental results show that the optical fiber sensor can detect damages and fiber failure of composites correctly.

The contact resistivity was correlated with IFSS and microfailure modes in conductive fiber/cement composites electro-pullout and AE. As IFSS increased, the number of AE signals increased and the contact resistivity increased latter to the infinity. In dual matrix composite (DMC) test and AE, the number of signals with high amplitude and energy in g]ass fiber composite is significantly larger than that of no-fiber composite. Many vertical and diagonal cracks were observed in glass fiber and no-fiber composite under tensile test, respectively. Electro-micromechanical technique and AE can be used efficiently for sensitive nondestructive (NDT) evaluation and to detect microfailure mechanisms in various conductive fibers reinforced brittle and nontransparent cement composites.

The changes of interfacial properties and microfailure degradation mechanisms of bioabsorbable composites with hydrolysis were investigated using micromechanical test and acoustic emission (AE). As hydrolysis time increased, the tensile strength, the modulus and the elongation of PEA and bioactive glass fibers decreased, whereas those of chitosan fiber changed little. Interfacial shear strength (IFSS) of bioactive glass fiber/poly-L-lactide (PLLA) composite was significantly higher than that two other systems. The decreasing rate of IFSS was the fastest in bioactive glass fiber/PLLA composite, whereas that of chitosan fiber/PLLA composite was the slowest. With increasing hydrolysis time, distribution of AE amplitude was narrow, and AE energy decreased gradually.

When compared to other composite materials such as FRP and MMC, hybrid composite material is more attractive one due to the high specific strength and the resistance to fatigue. However, the fracture mechanism of hybrid composite material is extremely complicated because of the bonding structure of metals and FRP. Recently, nondestructive technique has been used to evaluate the fracture mechanism of these composite materials. In this study, AE technique has been used to clarify the fracture mechanism and the degree of damage for Al 7075/CFRP hybrid composite material. It was found that AE event, energy and amplitude among AE parameters were effective to evaluate fracture process of Al 7075/CFRP composite material. In addition, the relationship between the AE signal and the characteristics of failure surface using optical microscope was discussed.