Design, Manufacturing and Applications of Composites 2012
Effect of Hot-Press Pressure on Mechanical Properties of Unidirectional Jute Spun Yarn Reinforced PLA
Natural fiber reinforced composites are carbon neutral materials and anticipated for alternative materials of GFRP. Most of them use biodegradable resin as matrix because biodegradable resin is made out of plants and has biodegradability. Recently, unidirectional reinforcement techniques of natural fibers have been developed for improvements of modulus and strength. Fatigue property of the unidirectional reinforced composites should be investigated to assure the structural integrity. In this paper, the effect of hot-press pressure on mechanical properties of unidirectional jute spun yarn reinforced polylactic acide (PLA) were investigated. Water-soluble PLA resin was used as matrix and jute spun yarn was used as reinforcement. Jute spun yarns were alkaline treated to make preforms. The molding temperature was 140°C and the molding pressures were 100kPa and 200kPa. Fiber volume fractions of composites pressed with 100kPa and 200kPa was 27%-44%. The quasi-static tensile tests and tension-tension fatigue tests were conducted. As a result, it was found that tensile and fatigue properties of composite were improved by using high molding pressure.
Evaluation of Thin Titanium Films—CFRP Fiber Metal Laminates for Composite Bolted Joints
Fiber1metal laminates that consist of carbon fiber composites and thin titanium films are applied to bolted joint to obtain better bearing strength and reliability. Tensile tests for bolted joints in quasi1isotoropic CFRP laminates [45/0/145/90]2S and the hybrid laminates with five thin titanium films inserted to the CFRP plates are conducted. It has been found that load drop point in load – displacement curve corresponds to damage onset in the plate. As for the CFRP plate the micro1buckling of the carbon fiber in 0° layer (fiber kinking) occurs first and then matrix shear cracking in adjacent layers induced by the kinking follows. The propagation of the matrix shear cracking, on the other hand, is found to be prevented by the titanium films in the hybrid laminates. With the titanium films inserted to form sandwich with inner 0° layer lower damage level is presented compared to the plate with the outer 0° layers are sandwiched by the films since the shear matrix cracking propagates from inside toward surface.
Debonding Behavior Characterization of Fiber Matrix Interface Using a Cruciform Model Composite with Multiple Fibers
A cruciform specimen with multiple fibers is used to evaluate the fiber/matrix interfacial tensile strength. The model composite contains thick fibers for the precise detection of the debonding initiation location. By arranging two fibers the influence of the adjoining fiber on a debonding behavior can be estimated. The fibers are aligned parallel each other and perpendicular to the loading direction. The effect of the interval between two fibers on the debonding behavior is observed. FEM analysis that has been carried out beforehand shows that the stress concentration at the inner pole of an interface becomes large as a fiber interval becomes small. However, it is experimentally observed that the debonding initiation occurs at the outer pole. Since this behavior is considered to be due to the cure shrinkage of resin, FE analysis in which thermal expansion is incorporated as chemical shrinkage was conducted.
Evaluation of Fiber/Matrix Interfacial Debonding Behavior Using a Partially Embedded Single Fiber
This paper examines fiber/matrix interfacial strength and growth behavior of the interfacial debonding with glass fiber and epoxy using a partially embedded single fiber. Test specimen with partially embedded single fiber in the resin is made by using the capillary action of the resin. By observing the cross section of a specimen with an optical microscope, it can be confirmed that the fiber is partially embedded in the resin. Interfacial debonding test is conducted by applying peeling force to the fiber to evaluate interfacial fracture toughness. By using the partially embedded single fiber fracture toughness is calculated from the load-displacement curve and the debonding growth length which is obtained by the experiments.
Ballistic Performance Prediction of Three-Layered Thermoplastic Laminates
This paper presents semi-empirical expressions for predicting the ballistic performance of three-layered thermoplastic laminates made up of polycarbonate (PC) and polymethyl methacrylate (PMMA) in closed forms, and also to verify the predictions by a series of ballistic impact tests. In the analysis, a normal impact of a steel ball projectile impinging on and passing through a three-layered laminate is described using an energy balance equation, from which semi-empirical expressions for predicting the residual velocity and the ballistic limit velocity are derived in the closed forms. The expression for the ballistic limit velocity thus obtained includes those of individual plates composing the laminate and interface coefficients depending on the layer structure and the bonding conditions between two adjacent plates. The predictions are verified by a series of ballistic impact tests carried out on the four kinds of three-layered laminates, and the effects of the stacking sequences and interfacial bonding conditions on the ballistic performance are examined
Temperature Effect on Delamination Detection Method in CFRP Laminates Using Mode Conversions of Lamb Waves
The authors have developped a built-in ultrasonic propagation system consisting of macro fiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. When two MFCs on both surfaces of the laminate are actuated in sychronization and two FBGs receive the propagated waves simultaneously, multiple modes of broadband Lamb waves can be propagated in the laminate and types of all the modes can be identified. Therefore, a new detection method of delamination in laminates could be established based on the dispersion change caused by the mode conversions at the delamination edges. However, since the dispersion is also affected by the temperature change, it is important to compensate the temperature effect on this detection method. Hence, we conducted experiments for CFRP quasi-isotropic laminates with an artificial delamination at various temperatures in a thermostatic chamber, in order to evaluate the temperature effect on the dispersion of anti-symmetric (A) modes. The obtained results indicated that the environmental temperature can be estimated from the change in the time of flight of A0 mode, and it can be used to compensate the temperature effect on the change in the dipersion slope of A1 mode. Therefore, we will be able to evaluate the delamination length in CFRP laminates with temperature compensation. Furtheremore, we evaluated the main reason of the temperature effect with FEM analysis through changes in properties of laminates, adhesive layer, and MFC actuators.
Processing and Testing of Basalt/Wood Fibre Reinforced Recycled Plastic Composite Materials
In this study, wood/recycled plastic composite material (WRPCM) was first fabricated with the post-consumer high density polyethylene (HDPE) and wood flour using a single-screw extruder. To improve the interfacial adhesion between the wood fibre and the HDPE, alkaline, silane and maleic anhydride modified polypropylene (MAPP) were used as modifiers to treat wood fibre and the results are presented. The effects of wood fibre length, weight fraction and surface treatment on the mechanical properties of WRCP were investigated and presented. Fracture surfaces of tested WRPCM were examined and the fracture mechanism of WRPCM was also analyzed in this paper. Test results indicated that WRCP with wood fibre simultaneously treated by alkaline, silane and MAPP possesses improved mechanical properties as compared with the baseline. The content of wood fibre would affect the flexural strength and modulus of WPCM. In general, the mechanical properties of WRPCM are relatively low and may not be adequate for any structural applications. To improve the mechanical performances, continuous fibres would have to be used for reinforcement. Processing and testing results are presented and discussed.
Development of Underground Composite Pipes Having Health Monitoring Functions
In this paper, carbon blacks (CB) and charcoal powders (CP) were used as conductive fillers for fabricating conductive polymer composites. Those carbon fillers were dispersed into high density polyethylene (HDPE) by a melt compounding method using a twin screw extruder. The resulting composite with pellet shape was used to produce specimens for the evaluation of their electrical properties. The electrical properties of the polymer composite were evaluated by the four-point probe array method following JIS K 7194. The HDPE/CB/CP composites showed low volume resistivity when the filler contents were 9 wt% of CB and 20 wt% of CP, which indicated sufficient dispersion of CB and CP within HDPE to form a conductive network. In order to observe the dispersion state of fillers in the HDPE/CB/CP composites, 3-D computed tomography (CT) was used. In addition, the tensile properties of the HDPE/CB/CP composites were also measured to verify the reinforcement effect by carbon fillers. Furthermore, HDPE/CB/CP composite pipes were fabricated and their electrical properties were investigated by the four-point probe array method.
Evaluation for Vibrational Characteristics of CFRP Wind Turbine Blade
In the recent years, CFRP was recognized as the main material for fabricating large scale wind turbine blades. However, there is some likelihood of damage occuring in the thickness direction of CFRP laminates caused by impact loads because there are no fibers. If the bending and compressive loads are applied to the damaged area, the buckling and the compression failure easily arise. So, it is desirable to evaluate interior damage with a non-destructive method. In this paper, the vibration characteristics of the CFRP wind turbine blades were evaluated by using an impulse hammer test. The natural frequencies and the damping ratios of the CFRP wind turbine blades were measured and their vibration mode shapes were obtained from modal analysis software. Furthermore, the experimental results were compared with numerical ones obtained by FEM.
Impact-Damage Detection Available for a Check Maintenance for CFRP Airplanes by Selective Resistive Heating
Impact loads initiate damages of several forms such as an indentation, fiber breakage, matrix cracking, and delamination cracking in carbon fiber reinforced polymer (CFRP). In this study, rapid diagnosis, which can finish inspecting the whole aircraft structure within an hour during refueling, was developed for composite aircraft. The proposed method consists of two steps; the first target for detection is indentation in the whole structure, and the second one is delamination cracking. After an indentation is detected in the first step, you only have to inspect limited area around the indentation for delamination inspection. Therefore, you can make use of an indentation as a marker of impact damage and can save inspection time and money even if large CFRP components are inspected. In the first step for indentation detection, indentation increases fiber–fiber contact at the interlaminar interface and electrical conductivity. Consequently, electrical current applied to the material will concentrate around the indentation, and lead to selective and intense resistive heating. This temperature increase can be observed by thermography or detected as a change in electrical resistance caused by the temperature difference. In the second step, delamination around an indentation can be detected without sampling the data from intact structures using statistical treatment. Moreover false diagnoses from changes in electrical resistance caused by damage to the electrical contacts at the electrodes can be prevented.
Study on Approximation of Thermal Deformation for Constraint on Stacking Sequence Optimization
This paper discusses optimum design of a stiffened composite panel, which is used in aerospace structures. Anisotropic thermal expansion coefficients of the composite laminates causes complicated deformation of the panel after the curing. In previous researches, stacking sequence optimizations were performed without considering thermal deformation: a response surface was used to obtain an objective function, and lamination parameters were sued as variables for the response surface of the objective function such as buckling load. However, the thermal deformation must be considered as a constraint factor for actual composite structures. In the present study, therefore, thermal deformation is dealt with as a constraint for a stacking sequence optimization problem. Three surrogate models of the thermal deformation are discussed here: a conventional method using lamination parameters; a new method using thermal coefficients; a modified new method As a result, the modified new method is shown to be effective for the surrogate model.
A Numerical Study on Failure Strength of CFRP Laminates with Impact Damage
Compression behavior and failure mechanism of impact damged composite laminates are numerically discussed by using finite element method to explain the compression strength reduction due to barely-visible-damage (CAI). Impact damage is modeled as a double-spiral-shape damage consisting of delaminations and matrix cracks. The numerical results considering geometrical nonlinearity and cantact condition show that buckling of the entire damage area causes a rapid increase of the energy release rate and the compressive stress beside damage area. The failure load is investigated through energy release rate distribution along the delamination front and the stress concentration at the side of the buckled portion. The failure problem is discussed through parametric study of the material properties.
An Experimental Study on Self-resistance Welding of CFRTP
In this study, a new welding method which utilizes conductivity of CFRTP (Carbon fiber reinforced thermoplastic) is proposed. Electrical current is applied through the CFRTP single-lap joints in thickness direction. Since resistance of joining surface is the highest in the current path, the joining surface is preferentially heated by Joule heating. In this study, spot welding and surface welding were conducted. By applying constant voltage of 5.0V or ,10.3V, the joint-surfaces were heated above melting temperature, Tm of the material and were welded. In order to evaluate lap-shear strength (LSS) of welded joints, tensile lap-shear tests were conducted. As a result, the tensile lap-shear true stress of spot welding is 31.0MPa and LSS of surface welding is 22.0MPa. These strengths were comparable to those that were welded by traditional resistance welding. It is also found that LSS is changed with welding pressure of joint parts.
Performance of Vacuum Insulation Panel (VIP)—Foam Composite as Exterior Insulation: Observations from a Pilot Field Study in Yukon
Although still virtually unknown in the construction industry, vacuum insulation panels (VIPs) have thermal resistance values up to 10 times or more greater than those of conventional thermal insulation materials. However, VIPs are slowly but steadily gaining recognition for their potential use in the building envelope construction. In Canada, the potential to apply VIPs in the building construction industry is estimated to be enormous, particularly with the introduction of the new 2011 National Energy Code of Canada for Buildings (NECB) that aims to achieve 25% less energy use in buildings than the energy code requirements set in 1997. Quite naturally, VIPs can play a major role in Canadian buildings to meet the new requirements of the 2011 NECB. However, lack of long-term performance credentials and various constructability issues are perceived to be the major barriers for mass application of VIPs in the Canadian construction industry. Yukon, located in Northern Canada, is known for its sub-arctic weather, and because of its climate, thermal insulation plays a very important role in building envelope construction in this region. Use of high performance, lightweight and thin VIPs in northern buildings is potentially an attractive option for the construction industry because of its high insulation value per unit of thickness, and low material volume. Regional stakeholders and researchers collaborated to retrofit a portion of the exterior of an institutional building in Yukon with a vacuum insulation panel - polystyrene foam composite. This paper outlines the construction details, challenges, and instrumentation used for long-term performance monitoring of this VIP-foam composite wall system. Critical analysis of selected thermal performance data from the first winter of use are presented in this paper. Field performance of the VIPs is compared with the laboratory measured data. It is hoped that application of a VIP – polystyrene foam composite in this project will lead the way to eventual mass application of VIPs in building envelope construction, and enhance energy efficiency in buildings located in extreme cold climates.
Thermal Conductivity of Unidirectional Pitch Based Carbon Fiber Reinforced Aluminum Composites by Low-Pressure Infiltration Process
Fabrication of Cellulose Nanofiber Aerogels by Freeze-Drying Using Water as Dispersion Medium
This study describes a method to produce cellulose aerogels by freezing nanofiber aqueous suspensions and sublimating the water phase to obtain a lightweight porous structure. As the formation of water crystallites is highly dependent on the freezing speed, various methods were attempted to obtain homogeneously distributed microscopic pores in order to preserve the macroscopic mechanical integrity of the aerogel, i.e., a structure free of big size pores or cracks. The interconnection among the nanofibers is accomplished solely by hydrogen bonds. The scanning electron microscopy revealed the structural similarities with bacterial cellulose, an interconnected web-like network of nanofibers. Open cell structure aerogels were completely impregnated with epoxy resin using a vacuum assisted resin transfer molding (VARTM) to fabricate composites. The present protocol to obtain aerogels relies only on water, without the use of any chemicals, thus being an environmentally friendly process.
Mechanical Properties of Hemp Textile Composites Made by VaRTM Method
In this study, we aimed to improve the strength of textile composites by applying surface treatment on natural fibers. Natural fibers used were flax and hemp, and the matrix was an epoxy acrylate resin. The flax fiber textile was treated with acetone, laundry detergent and aqueous solution of sodium hydroxide, because water repellent substances were adhered to the fibers. Hemp fiber textile was chemically-treated with aqueous solution of sodium hydroxide or coated by PVA (polyvinyl alcohol). Natural fiber textile composites were made by a VaRTM (Vacuum assisted Resin Transfer Molding) method. The most effective washing process was alkali-treatment with an aqueous solution of sodium hydroxide. The alkali-treated flax fiber composite had its tensile strength improved by 19.7% and bending strength by 12.8%, relative to the untreated fiber composite. However, the tensile and bending strengths of alkali-treated hemp fiber composite were reduced. In addition, the strength of PVA coated hemp fiber composites was also reduced. The effect of PVA coating was examined by using a micro-droplet method. Interfacial shear strength of PVA-coated hemp fiber was reduced compared to that of untreated hemp fiber. In addition, the interfacial shear strength was reduced with increasing PVA conte
Effect of Surface Modification on Mechanical Properties of Bamboo Fiber Reinforced Composites Made by VaRTM
In this study, bamboo fiber reinforced composites were prepared by using VaRTM (Vacuum assisted Resin Transfer Molding) method. Several chemical treatments for bamboo fibers were applied to improve the interfacial adhesion between fiber and resin. Bamboo fiber surface was modified by chemical processing; namely alkali treatment and bleaching treatment. As a result of increased resin bonding area, the interfacial adhesion seems to be increased. In addition, the surface impurities which might act as defects have been removed after the chemical processing. We found that, compared to composites of untreated bamboo fiber, the strength of composites reinforced by alkali-treated bamboo fiber increased by 35.3%, that of bleaching-treated bamboo fiber was 37.9%, and that of composites subjected to both surface treatments was increased by 36.9%. According to FTIR results, the disappearance of peaks assigned to lignin in the treated fiber is believed to be due to the removal of lignin after the chemical treatments. It was also found that lignin can be removed by chemical processing.
Development of Instant and Low Cost Joint for CFRP Laminate by Modified Self Piercing Rivet
A modified self-piercing rivet (SPR) has been proposed to mechanically fasten CFRP laminates. The modified SPR consists of a rivet body and two flat washers. The two flat washers were used to suppress delamination in the CFRP laminates at the point of piercing. The advantages of the modified SPR for fastening CFRP laminates are instantaneous process time and low cost. Any pretreatments such as surface treatments or hole drilling are not required. In this study, the viability of the modified SPR for a quasi-isotropic CFRP laminate was investigated by tensile and fatigue tests on the single lap joints. The experimental results showed that the tensile strength of a modified SPR joint was slightly higher than a bolted joint. In tension-tension fatigue tests, a fatigue limit at Nf=107 cycles was about 50 % of the tensile joint strength. Experimental results showed that the modified SPR was one of the promising fasteners for future mass-production CFRP automobiles.
Development of Green Nanocomposites Reinforced by Cellulose Nanofibers from Waste Newspaper
Nano-scale cellulose fibers have shown much greater potential to improve mechanical properties in water soluble polymer than micro-scale cellulose. The objective of this study was to extract the crystalline cellulose from waste newspaper as one of the cellulosic sources. Newspaper was treated chemically and physically in order to extract individualized crystalline cellulose. Acid hydrolysis and mechanical extraction treatments resulted in crystalline cellulose with diameter mostly between 10-40 nm. The reinforcing effect of obtained crystalline cellulose was investigated by composing with starch-based biodegradable resin. Celish®-reinforced composites were used as reference to newspaper crystalline cellulose-reinforced composites in mechanical properties test. The results showed the increase in mechanical properties of reinforced composites for both composites. However, Celish®-reinforced composites showed much greater enhancement than newspaper crystalline cellulose-reinforced composites. For example, the maximum tensile strength of Celish®-reinforced composites at a fiber load of 20% was 29.8 MPa, which is 3.7 times higher than neat starch. Meanwhile, the newspaper crystalline cellulose-reinforced composites at a fiber load of 20% recorded tensile strength of 12.6 MPa, which is 1.6 times higher than neat samples.
Strength Evaluation of Quasi Isotropic Green Composite Laminates Reinforced by Bamboo Fiber
In recent years, bamboo fiber obtained by a steam explosion method has shown great performance as reinforcement in polymer based composites. In this study, steam exploded bamboo (SEB) fiber was used as the reinforcing phase in cross ply and quasi isotropic SEB/polylactic acid (PLA) laminates with different stacking sequences. The stacking sequences employed in this study were (0/90)s, (90/0)s, (0/+45/90)s, and (90/+45/0)s. Their tensile strength was characterized as a function of fiber content. Results for cross ply laminates indicated that cross ply (0/90)s and (90/0)s with 63wt.% fibers, increased the tensile strength of the composites, to approximately 6.74 and 7.2 times higher than that of neat PLA resin, respectively. In the other case, quasi isotropic laminates (0/+45/90)s with 53wt.% fibers and (90/+45/0)s with 40wt.% fibers, showed increase in tensile strength of the composites, to approximately 3.4 and 3 times at that produced by pristine PLA, respectively. Simple analysis of back-out factor for cross ply laminates was investigated. Morphological analysis was also carried out to observe fiber pull out of the composites using a digital microscope and SEM to evaluate the interfacial bonding between fiber and resin.
Self-Sensing TFDR for Damage Detection of CFRP Structures
Carbon fiber reinforced polymer (CFRP) composites have higher specific strength and specific stiffness than conventional metallic materials. The CFRP structures, however, are easily damaged by impact loading. It is quite difficult to detect damage of the impact loading by visual inspection. In the present paper, self-sensing Time–Frequency–Domain Reflectometry (TFDR) is proposed as a damage detection method for large CFRP structures. The TFDR uses a set of high-frequency burst signals. From the time span between the input signal and the reflected signal, the location of the damage is identified. By using the several signals of different frequencies, other information can be measured. This is the advantage of the frequency domain Reflectometry. TFDR uses both methods to locate the damage and dimension of the damage. The effect of micro structure of CFRP is investigated for the Finite Difference Time Domain (FDTD) analysis. Microstructures of CFRP of fiber direction and transverse direction are modeled and FDTD analyses are performed to check the limitation of the orthotropic homogeneous approximation of CFRP. As a result, CFRP may be considered as an orthotropic homogenous conductor when the electromagnetic wavelength is longer than 25 times of averaged CFRP microstructure. The electrical analyses showed that the TFDR was applicable to detect damage location and size of CFRP structures.
Parametric Numerical Study of Crack Restriction Effect in Thin-Ply CFRP Laminate
We built meso-scopic numerical simulation models in order to evaluate the effect of ply-thickness on the propagation behavior of transverse crack. The randomness of fiber distribution, elasto-plasticity of matrix, and interfacial strength between fiber and matrix were considered in the model. In the numerical simulation, the transverse crack drastically propagated less than 1.0% strain in the 160 μm- and 80 μm-thick ply laminates. On the other hand, intraply transverse crack penetration was not caused up to 1.5% strain, and crack gradually propagated in the 40 μm-thick layer. Therefore, it was theoretically found that crack propagation was restricted in 40 μm-thick layer. This crack restriction effect is presumably caused by some structural factor, especially the existence of neighboring 0o layers. In addition, matrix property and interfacial property between fiber and matrix are candidates for the factor of crack restriction effect in thin ply laminates. In order to clarify what the most effective factor on crack propagation behavior, we introduce the parametric study varying (i) matrix property, (ii) interface property between fiber and matrix, and (iii) ply thickness.
Resin Flow Monitoring for VaRTM by an Approach Integrating Electrical Measurements and Numerical Simulation
Vacuum assisted Resin Transfer Molding (VaRTM) is widely used for molding of composite structures. However, ensuring complete impregnation of the resin into fiber materials is difficult and it sometimes causes the formation of un-impregnated regions, called dry spots. Due to the poor quality of a VaRTM process, its application is currently limited. Therefore, monitoring of the resin flow during the process is necessary to predict and prevent the formation of dry spots. This paper presents a method to observe resin impregnation in a VaRTM process without embedding sensors into composite structures. Planar-shaped sensor electrodes arranged on a molding tool are used to measure electrical capacitance values from pairs of the electrodes. These measurements are combined with the numerical simulations of a VaRTM process to estimate the state of the resin impregnation. This method is based on the ensemble Kalman filter (EnKF), known as a sequential data assimilation technique. The proposed method was examined by a numerical experiment. In the numerical experiment, the resin-impregnated region and the permeability distribution of a fiber preform were estimated concurrently and it was confirmed that the decrease of flow velocity in a low permeability region could be estimated.
Development of Golf Shafts with Vibration Damping
Liquid crystal polymer fiber reinforced plastics is applied to golf shaft. The vibration test of cantilever is carried out to reveal the differece of damping performance between CFRP and LCP-FRP golf shaft. From the result of this vibration test, LCP fiber has high damping properties. Next the paper presents effect of location of high damping material on damping performance. The damping ratio of golf shaft has been investigated by varying the location of high damping sheet from the fixed end of the structure.
Use of a Lightning Protection Shield for Composite Airplanes as a Load Sensor
A rapid diagnosis method for composite aircraft is required. In this study, a new inspection method using a lightning protection shield (LPS) as a load sensor and its wiring is proposed. The load sensor consists of upper layer and lower layer composed of an electrical circuit which has many pressure-sensitive elastomer pills in it. The upper layer is a copper mesh sheet acting as a LPS. The lower layer consists of two kinds of wires. One is high–electrical-resistance nichrome, and another is low–resistance copper. The pressure-sensitive pill changes from an electrical insulator into a conductor when it is compressed. When an impact load is applied to the sensor, the pressure-sensitive pill gives a new electrical path between the two layers at the load point. During the operation of the load sensor, a unidirectional gradient of electrical potential is applied to the lower layer. When a new electrical path is formed between the two layers by the load, potential of the upper layer comes to be equal to that of the indented part of the lower layer. Consequently, measuring the potential of the upper layer provides the X coordinate of the load point. After the X coordinate is acquired, the orthogonal potential gradient is applied to the lower layer to measure the Y coordinate. These XY coordinates can be evaluated within a few milliseconds. In addition, it comes possible to estimate the peak value of the load by measuring the electrical resistance of the pressure–sensitive pill
Development of Fiber Tow Spreading System for Thin Fiber Reinforced Materials
In order to expand the application of fiber reinforcement as light-weight material it is important to spread the fiber tow in thin geometry. There are various methodologies to spread the fiber tow, however, the spread fiber tow was sometimes not uniform and its cost was very high. In this study we have developed the fiber tow spreading system to obtain the uniform thin fiber tow, and have applied this developed system to fabricate thin fiber tow reinforced adhesive tapes. In this developed system the mechanical load was applied to the fiber tow through the plate with arc-shape edge. By using this system we tried to spread the UHMWPE fiber and aramid fiber.
Process Monitoring of CNT Composites by Optical Fibers
CNT composites are promising materials due to the high-functions of electricity and damage resistance. In order to develop quality of CNT composites, it is necessary to improve dispersion of CNT because large CNT clusters grow easily. However, it is difficult to monitor growth of CNT clusters during molding. In the present paper, we proposed a new sensing method for the purpose by employing a refractive index measurement using an embedded optical fiber. This method utilized interference signals between Fresnel reflection from the distal end and Rayleigh scattering at the clusters. Only scattering lights, which include information of CNT clusters, can be obtained from the measured signals. From the experimental results, it appeared that the measured signals fluctuated largely when 0.077wt% of CNT exists in the resin. The amplitude of fluctuation of CNT composites was much larger than the carbon-black composites. It might be considered that the amplitude of fluctuation depend on the cluster size of fillers in composites.
Process Monitoring of Hot-Press Molding of FRP Laminates by Fiber-Optic Index Sensor
We have developed a measurement method of refractive index for monitoring degree of cure of resin. The present paper describes the application of fiber optic refractive-index sensor on hot-press molding of GFRP laminates. From the experimental results, it appeared that the transverse molding pressure to optical fibers did not affect the optical loss. The increase of optical power resulted from reflection light between air and resin flow closing to the sensor. It was found that the cure process of FRP laminates during hot-press molding could be monitored by this method after the sensor edge was filled with resin. During gelation of resin, it could be seen that large fluctuation existed in the sensor signal due to scattering from micro air-voids in resin. The fluctuation disappeared within 20 minutes because the voids were vacuumed completely. The trend of index curve turned from decrease to increase because of proceeding of cure reaction and then became constant when cure reaction finished. From the experimental results, it was found that the embedded refractive index sensor could detect resin flow and void vacuuming as well as degree of cure.
Cure Monitoring of FRP by FBG and Refractive-Index Sensors
In the present study, we propose a system for monitoring cure process of FRP prepregs during hot-press molding using dual light sources, FBG sensors and refractive-index measurement. The optical system is composed of a 1310 nm narrow-band FP-LD light, a 1510nm broad-band SLD light, 1300/1500 WDM couplers, a spectrum recorder and an optical power meter. The FBG sensors have a distal end at which Fresnel’s reflection between glass and resin occurs. The reflected 1310nm light form the distal end and the FBG reflection (about 1550nm) were divided into two individual paths by a WDM coupler. The power of 1310nm light was measured by an optical power meter and used for calculating refractive index of matrix resin. Spectra of the FBG light were recorded by a spectrum analyzer. In this study, GFRP prepregs were used for the experiments. From the results in the present paper, it was found that the our monitoring system monitor both cure index and strain during molding quantitatively. In addition, it apperaed that the system can be used for monitoring existence of air voids.
Study on Dynamic Response of Fiber-Reinforced Plastic Float for Light Seaplane
The Japanese marine area is the sixth largest in the world at about 4,470,000 km2. Therefore, it is becoming necessary to establish appropriate means of transportation other than ships in order to utilize the area efficiently. In this respect, ultralight seaplanes are attracting attention from the viewpoint of protecting the natural environment. Accordingly, JRPS is currently developing fiber-reinforced plastic floats for such planes. In this study, we conducted simulations of seaplane behavior during alighting by using the smoothed particle hydrodynamics method, which is one of the functions in the PAM-CRASH solver, and we present the observed trend in the vertical acceleration of the floats as a first step toward deriving the impact force from analytical data.
Dynamic Mechanical Characterization of LLDPE/Clay Nanocomposite
In this study the nanocomposite made of linear low density polyethylene (LLDPE) and organo modified MMT (O-MMT) was processed by melt compounding at different nanoclay loading using a co-rotating twin-screw extruder. The dynamic mechanical properties of pure LLDPE were compared with those of LLDPE/O-MMT nanocomposite using dynamic mechanical thermal analysis (DMTA).The results showed that the addition of nanoclay has improved the storage modulus Eá¿½ and loss modulus Eá¿½á¿½of the linear low density polyethylene (LLDPE)/O-MMT nanocomposites. It was found that at low temperatures (-50 °C), the storage modulus of the nanocomposite increased by 3% and 22% with the addition of 1 and 5 wt % of O-MMT respectively. At high temperature (50°C), the storage modulus Eá¿½ increased by 3.5 % and 56.7 % when 1 and 5 wt% of O-MMT were added, respectively. This remarkable improvement in the thermal-mechanical properties of this nanocomposite material at low and high temperature was caused by the strong interactions between the interface of exfoliated/intercalated nanoclay layers and the polymer matrix.
A Computer Model for Progressive Failure Analysis of Thick Composite Plates
A computing model for the progressive failure analysis of thick composite plates is developed. Since the model is for thick plates, it is based on a higher-order zigzag laminate theory so that the interlaminar continuity conditions of transverse shear stress and the shear free surface conditions are satisfied. The elastic stress analysis is used as an initial failure load. Then, the load is increased step by step, the stresses are evaluated, and the appropriate failure criterion is applied to inspect possible failure. When failure is initiated, the material properties are modified according to the selected failure mode using a non-zero stiffness degradation factor. Thereafter, the modified Newton-Raphson iteration is carried out until convergence is reached. This analysis is repeated for each load increment until the final failure occurs and the ultimate strength is determined. A numerical example of the failure progress of a simply supported plate is investigated. The present method yields a reasonable agreement with three dimensional finite element solutions.
Automated Fiber Placement for Composites
Advanced composites have seen dramatic increase in applications in many important areas, particularly in aerospace. As more and more composites are used, the need for automated composites manufacturing becomes more and more relevant. This is due to many reasons: 1. The need for speed of material deposition. As larger and larger structures are made using composites, it is necessary to have fast deposition of the material such as prepregs. The use of hand-lay-up is too slow. 2. The need to eliminate the variability due to hand work. Hand-lay-up lends itself to possibility in variation from one operator to another, and from day to day even for a single worker. 3. The need to reduce waste. Techniques such as hand-lay-up tend to use fabrics or tapes of relatively large dimensions. Significant amount of waste can and have resulted in large amount of waste of expensive materials. 4. The need to provide uniform tension in the fibers. Properties of the composite laminates depend critically on the tension in the fibers. The use of machine can provide more uniform tension in the fibers as compared to techniques such as hand-lay-up. 5. The need to have seamless transition between manufacturing, analysis and design. Computer files generated from analysis and design can be transferred directly to the machine used for automated manufacturing. As such faster working environment and less error prone process can be developed. Recent advances in automated composite fiber placement can allow the above to be realized. Apart from the above advantages, there are composite structures that can only be made using automated fiber placement technique, since other techniques are not capable to make the structure. This paper addresses the above points and presents an example where automated fiber placement machine can be used to produce unique composite structures with unique capabilities not seen before.
Multiscale Finite Element Analysis of Delamination Growth in a Double Cantilever Beam Specimen Made of Woven Fabric Composite
Delamination growth in a double cantilever beam (DCB) specimen made of a five harness satin weave fabric composite is simulated by a multiscale finite element model in order to provide a better understanding of toughening mechanism of fabric composites. To accomplish this, a meso-scale model of five harness satin weave fabric composite is placed at the delamination zone in order to model the toughening caused by the fabric structure. R-curves and load-displacement curves from the analyses are compared with those of experiments which agree with the lower bound of experimental results. The numerical results revealed two major types of toughening mechanisms: 1) inter-yarn locking causing stress relaxation at delamination front 2) the creation of sub-surfaces via weft yarn bridging which is observed after the delamination grows. By including and observing these two toughening mechanisms, a more realistic simulation of delamination in fabric composites is achieved.
A Microscopic Experimental Investigation of Failure Mechanisms in a Triaxially Braided Polymer Composite
A microscopic experimental investigation was conducted to track the development of damage leading to failure during tensile static and fatigue loading of a triaxially braided polymeric composite material. Edge replication and scanning electron microscopy were employed to track damage development and to identify existing damage mechanisms, respectively. The results indicate that cracking in the braider yarns is the dominant damage mechanism during static and fatigue loading. The development of damage throughout loading and during the final damage state prior to failure is however markedly different for static and fatigue loaded test specimens. This was confirmed by observation of the fracture surfaces as well as post mortem microscopy. The results provided a better understanding of the damage development, local deformation behaviour and the corresponding failure mechanisms for the braided material during static and fatigue load
Hot Drape Forming of Aerospace Structural Parts
Cost-effective manufacturing of high quality aerospace composite parts can be achieved through new part design and integration as well as through manufacturing process automation. Automated technologies such as tape or fiber placement can be used to make large flat uncured panels to be shaped to the structural parts such as stringers, ribs and other types of stiffeners. Hot drape forming is a process for forming a flat uncured thermoset composite prepreg laminate (or thermoplastic perform) into a straight or curved angle or channel, using heat and pressure (vacuum). During this process in-ply shear deformation (for fabrics) as well as interply slippage must occur. The heat applied during process reduces the resin viscosity and therefore the interply shear. The pressure provides the mechanical action to form the laminate. Part geometry, ply orientation, flange length, temperature, and forming rate are variables that significantly affect hot drape forming process. The major challenges associated with this process are consistently creating components with very high uniformity of fiber content and fiber alignment, while avoiding wrinkling or uncontrolled fiber breakage. Ply wrinkling (buckling of fibers), fiber misalignment, fiber volume fraction variation and thinning at the radii are the common problems. Processing windows has to be defined to achieve a good quality part at the end of forming operation.
Wave Propagation in Laminated Composites
The propagation characteristics of waves depend on the plate thickness, boundary conditions, elastic properties, and density of the material. The analyses of wave propagation provide the information for better interpretation and utilization of composite laminate materials. This paper presents a theoretical approach developed as an extension of Mindlin theory to predict the characterization of wave propagation in antisymmetric angle-ply laminated plates. We formulated the equations of motion by substituting the deformations including three displacement functions and two rotary functions. For any case of laminated plates, more precise wave velocities were calculated. Then, the velocity-frequency curves of waves from the numerical results and the influence of the laminate angle, number of layers, and stacking sequence are investigated systematically.
Electromagnetic Shielding Behavior of CFRP Hybrid Structures
The electromagnetic waves may make our life easier and more comfortable due to its use in the high-speed communication. Recently, polymer composites are extensively employed in EMI shielding for the respected adsorption property of EMI wave. Here, we investigated the EMI property of CFRP with a Cu-mesh in order to obtain a high EMI performance material. The SE and electrical characteristics of the developed composite materials were measured in a flanged coaxial shielding effectiveness test. The behavior of the electromagnetic wave shielding in CFRP /Cu-mesh composites was evaluated and discussed by the measured experimental results, and an optimum hybrid structure for high performance of EMI is designed.
Compressive Properties of a Si-Ti-C-O Fiber-Bonded Ceramic Material
Si-Ti-C-O fiber-bonded ceramics (Tyrannohex®) is a high toughness and heat-resitance material showing approximately 30 times as much fracture energy as a sintered silicon nitride due to existence of a boundary carbon phase. However, Tyrannohex is the laminated structure of eight-harness satin woven fabrics, and shows an anisotropy. To apply widely this material for practical use, further investigation of in-plane and out-of-plane mechanical properties is needed. In this study, the compressive elastic moduli in in-plane and out-of-plane loading of the fiber-bonded ceramic material were first explored. Next, compressive damage mechanism of this material, such as shear failure and kinkband, was discussed.
Multifunctional Sandwich Panels with Jute Fiber-Core and GFRP Skins for Snowfall Regions
This research investigates the processing of sandwich composite structures with overall low density made up of glass fibre-reinforced polymer skins bonded to a jute fiber mat core. Jute fibers have good insulating properties for both of thermal and acoustic energies, totally biodegradable and recyclable materials. Therefore, a needled punched jute mat was used as a thick and lightweight soft core with two thin GFRP laminas as stiff skins for fabricating valuable sandwich composite structures with high performance. This novel sandwich structure exhibited a higher specific total impact energy and specific impact strength than those of composites and neat resin. Larger deformation and non-brittle fracture behavior than those of composites and neat resin were obtained. A multifunctional roof panels fabricated from the above-mentioned sandwich structure was introduced to use in snowfall regions.
Preparation and Characterization of PVA/Halloysite Composite Films
In this study, the characteristics of halloysite subjected to silane coupling treatment as a reinforcing agent are investigated. Halloysite is one of the natural substances that is currently recognized as having a nanotubular structure. Halloysite nanotubes are 50 nm in diameter, 0.5-1 μm in length and 15 nm of inner diameter. Polyvinyl alcohol (PVA) which is a synthetic polymer with characteristics such as biodegradability and solubility in water was used as the matrix. The halloysite/PVA films were characterized by tensile test, scanning electron microscopy (SEM), and optical transmittance. The tensile strength of PVA/untreated halloysite film was decreased, but Young’s modulus was increased compared with neat PVA film. In addition, silane coupling treatment was performed on halloysite to improve the interfacial adhesion between PVA and halloysite. PVA/silane-treated-halloysite film had improved elongation compared with PVA/untreated-halloysite films. SEM images revealed the fracture mode and the distribution of halloysite inside the composites. When the halloysite content was low, a fracture surface formed by dimples originating at the halloysite sites was observed. On the other hand, when the halloysite content was high, brittle fracture occurred. In the case of high halloysite content, agglomeration of nanotubes was observed. The optical transmittances of PVA/silane-treated-halloysite films with 8 wt% halloysite were over 80%.
Novel Optical-Fiber-Based Cure Monitoring Technique for Large-Scale Composite Structures
This study establishes an innovative composite cure-monitoring technique by utilizing a newly developed hybrid Brillouin-Rayleigh optical fiber sensing system. The new system can separately measure strain and temperature distribution with only one optical fiber. This study began by evaluating the measurement accuracy of the hybrid system in a composite application in a step-by-step manner. A single optical fiber was then embedded in a carbon-epoxy specimen, and thermal residual strain development and temperature change were measured during the cooling period of the curing process. The temperature and residual strain obtained by the hybrid Brillouin-Rayleigh system agreed well with the results measured by a conventional sensor set (i.e., fiber Bragg grating (FBG) sensors and thermocouples). Furthermore, the system could identify a non-uniform thermal residual strain field induced by a non-uniform cure temperature. These results clearly demonstrated that the proposed technique is quite useful for cure monitoring of large-scale composite structures. Quality assurance for whole parts of actual products can be effectively accomplished by applying the proposed technique.