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Cellulose nanofibers (CNFs) are environmentally friendly materials with a high specific strength. To enhance the impact properties of the carbon fiber reinforced plastics (CFRPs), a method for inse...

Cellulose nanofibers (CNFs) are environmental-friendly nanofiller with high strength and lightweight. To improve the impact properties of carbon fiber reinforced plastics (CFRPs), the application o...

Cellulose nanofibers (CNFs) have high strength. Therefore, many studies have been conducted to improve the mechanical properties of carbon fiber reinforced plastics (CFRP) by dispersing CNF in the matrix. However, since CNFs are hydrophilic, a hydrophobic treatment is required. Previously, authors showed the bending strength of CFRP could be enhanced by CNFs without a hydrophobic treatment. Applying the electro-activated deposition resin molding (ERM) method to fabricate CFRP, CNFs can be applied on the surface since the electro-activated deposition solution is essentially water-based and contains a polymer with epoxy groups. In this study, the CNF sheet was prepared by drying CNF dispersion in advance. Shortly after the ERM, the CNF sheet was applied to the surface of the CFRP. The mechanical properties of the CFRP were enhanced, the maximum elastic modulus and tensile strength were 2.3 times and 1.7 times of the CFRP specimen without the CNF sheet, respectively.

A multi-objective optimization method for the laminated composite fabricated by a tailored fiber placement machine that is an application of embroidering machine is presented. The mechanical properties of composite with curvilinear fibers including stiffness, volume fraction, and density are variable depending on curvatures of fibers. The present study first measures the relation between curvatures and mechanical properties. The measured results indicate that the stiffness of composite decreases linearly as the curvature increases. Then, the obtained relation is applied to the multi-objective optimization where the maximum principal strain and magnitude of curvature are employed as objective functions. Obtained Pareto optimum solutions are widely distributed ranging from the solutions with curvilinear fibers to those with straight fibers, and the curvilinear fiber has still advantages over straight fiber even its weakened stiffness.

Many researches on strengthening the matrix of Carbon Fiber Reinforced Plastic (CFRP) using cellulose nanofibers (CNFs) have been reported. However, hydrophobic treatment to modify the surface of C...

For the efficient manufacturing of carbon fiber reinforced plastics (CFRP), the electro-activated deposition resin molding (ERM) method is developed. The carbon fiber fabric is immersed in an electro-activated deposition solution containing polymer with epoxy groups. By energization , an epoxy resin is precipitated on the surface of the carbon fiber, and impregnation occurred in the solution. In this study, applying the ERM method, CFRP specimen with the hole was manufactured. Furthermore, the reinforcement by arranging the fiber circumferentially around the hole was installed. The carbon fiber fabric was sewn using the tailored fiber placement (TFP) machine. As a results, the effect of the reinforcement was confirmed. The tensile strength of CFRP with the hole and the reinforcement was the same as in the case without the hole. From the finite element analysis , it was confirmed that the reinforcement around the hole reduced the stress concentration.

Cellulose nanofiber (CNF) is high strength and lightweight, additionally, it is produced by sustainable natural resources such as wood. Therefore, it has been reported the mechanical properties of CFRP can be improved by dispersing CNF in the matrix. However, as CNF is hydrophilic, a hydrophobic treatment was applied in many previous studies. For efficient CFRP manufacturing, the authors have developed an electrochemical resin molding method by using aqueous electro-activated deposition which contains the polymer having an epoxy group. In this method, the carbon fiber fabric is immersed in the electro-activated deposition solution and energized, epoxy resin is precipitated around the carbon fiber and impregnated. In this study, shortly after electro-activated deposition, CNF without a hydrophobic treatment was applied to the surface of the resin-impregnated carbon fiber fabric. The mechanical properties of CFRP could be enhanced, and optimum weight fraction of CNF was revealed.

The I-shaped cross-sectional beam of CFRP (CFRP I-beam) is usually manufactured by the continuous protrusion method. Carbon fibers can only be arranged in the longitudinal direction. The CFRP I-bea...

A more efficient manufacturing process for CFRP is expected to save energy, time and cost for production. However, it is difficult to impregnate the resin efficiently and uniformly between the carbon fibers, micro void tend to remains and strength decreases. In this study, a novel manufacturing method of CFRP by using the electro-activated deposition resin molding was developed. The non-crimp carbon fiber fabric was immersed in the electro-activated deposition solution, that containing epoxy groups. And, the fabric was energized and heat cured. The electro-activated deposition conditions and tensile properties were investigated for the CFRPs. It was confirmed that resin could be impregnated for multiple plies of the non-crimp carbon fiber fabric without using autoclave and injecting viscous resin like VARTM. Comparing to the traditional manufacturing process, a step of previously mixing an epoxy resin prepolymer and a curing agent was not required. And, a process of vacuum suction could be eliminated, so, wrapping non-crimp carbon fiber fabric with vacuum bag was not necessary.

Recently, theoretical and experimental methods were proposed for organizing carbon fibers in straight and curvilinear arrangements to obtain a uniform stress distribution in the design of three-dimensional (3D) carbon fiber reinforced thermosetting plastic (CFRP). In this study, to establish an efficient CFRP manufacturing method and realize the curvilinear arrangement of carbon fibers, we develop an electrodeposition resin molding technique. That is, immersing a noncrimp fabric in the electrodeposition solution and energizing electricity, the fabric is impregnated by the resin; thus, a CFRP with curvilinear carbon fibers can be efficiently produced without autoclaving and vacuum packing. We then confirm the optimal electrodeposition conditions for maximizing the tensile strength of the CFRP, and obtain the 3D shape of the CFRP by keeping the noncrimp fabric in solution along the mold.

The strength enhancement of the matrix of CFRP has been a major research subject. In particular, strength of the surface resin layer of CFRP is quite important since the bending stress is most effective on the surface but also exposed to foreign object debris (FOD). One of the methods to strengthen resin matrix of CFRP is to disperse cellulose nanofibers (CNF), therefore, many studies have been conducted. However, due to hydrophilicity of CNF, a hydrophobic treatment is indispensable. Although various hydrophobic methods have been proposed, special chemical substances are required and resulted in higher manufacturing costs. In previous study, authors showed that the mechanical properties of CFRP were enhanced by CNF without hydrophobic treatment using the electro-activated deposition resin molding (ERM) method. In the ERM method, a non-crimp carbon fiber fabric (NCF) is immersed in the electro-activated deposition solution which contains polymer with epoxy group. Then, by energization, the resin precipitates around the carbon fiber and is efficiently impregnated to the NCF in the solution. After the ERM, CNF can be applied on the surface of CFRP since the electro-activated deposition solution is water-based. After thermal curing, CNF is embedded on the surface resin layer of CFRP. In this study, the analysis to understand the effect of CNF on the mechanical properties was carried out. As a practical application, the I-shaped cross-sectional beam (I-beam) was selected for the analysis. It was experimentally revealed that the bending strength of I-beam was enhanced by embedding of CNF. With assumed the material constants based on the tensile tests of the CFRP, the bending properties with dispersing CNF on the surface were analyzed by using the finite element method. As a result, the relationship between load and deflection could be well simulated, and the effect of CNF on the bending properties was clarified.

To strengthen carbon fiber reinforced plastics (CFRPs), fiber placement along the principal stress directions have been studied as a promising approach. However, a method to sufficiently impregnate a resin between the curved carbon fibers has not established thus far, although arbitrary arrangement of carbon fibers is feasible using the automated fiber placement (AFP) machine. Previously, the authors had developed an electrodeposition resin molding method based on electrophoresis. In this method, the carbon fiber preforms sewn by the AFP machine is immersed in the electrodeposition solution containing polymers with epoxy groups, and optimal current is applied to impregnate resin between carbon fibers. In this study, we showed that a CFRP specimen could be fabricated with arranging the carbon fibers along the principal stress direction, resulting in approximately 10% higher tensile strength than that of the specimen with unidirectional carbon fibers.

For the thermal management of electric devices, the application of phase change materials (PCMs) such as paraffin has been studied. However, as long as the PCM changes to liquid phase, a sealed structure is required, which is a constraint for weight reduction. Therefore, the authors have focused on trans-1,4-polybutadiene (TPBD), a semi-crystalline polymer that accumulates heat by crystal structure transition at 50~80 °C in the solid phase. However, the strength of TPBD is insufficient and thermal conductivity is not enough to dissipate the heat. In this study, a method to homogeneously apply TPBD to the surface of carbon fiber reinforced plastics (CFRP) was developed using cellulose nanofiber (CNF) and aqueous electrodeposition solution containing a polymer with epoxy group. The heat-storable CFRP was obtained, the maximum exoergic and endoergic heats of 30 J/g were confirmed, and its tensile strength was approximately 61% of CFRP without TPBD/CNF.

CFRP corrugation structures are used for various purposes, and application to morphing wing has recently been drawing attention. However, an effective manufacturing method for the CFRP corrugation has not established. Vacuum-assisted resin transfer molding (VARTM) method can decrease manufacturing cost, but it cannot be applied for corrugation since vacuum bagging is impossible. Therefore, the conventional method to laminate prepreg and consolidate by using autoclave has been applied. In this study, by using electro-activated deposition resin molding, it was confirmed that CFRP corrugation structures could be easily manufactured. Neither autoclave nor vacuum bagging was necessary. The corrugation and corrugated core sandwiches with different pitches were fabricated and mechanical properties were investigated.

The present paper proposes a multi-objective optimization technique for smart laminated composites to maximize two conflicting objectives. The first objective is the performance of active vibration control of smart composite with piezoelectric (PZT) actuators. The second is the fundamental frequency of smart structures related to the performance of passive vibration control. Both performances of active and passive vibration control are maximized simultaneously. The vibration suppression of smart structures strongly depends on both actuator placements and vibration mode shapes. It is possible to design vibration mode shapes for laminated fibrous composites since their anisotropy for whole thickness is tailorable by arranging fiber orientation angle in each layer. This allows the smart structure with laminated composite to archive higher performance of vibration suppression than those with isotropic materials. However, the optimized structure results in lower natural frequencies than composites with typical fiber orientation angles since an effective input of control force from actuators is realized for the structure with lower stiffness. This reveals that there is a trade-off relation for smart composite structures between the performance of active vibration suppression and natural frequencies. To disclose this relation, the present study applies the effective multi-objective optimization technique, the refined non-dominated genetic algorithm (NSGAII), and obtains Pareto optimal solutions. Calculated results are successfully validated by a comparison with those from the real-time control experiment where a laser excitation technique which is effective to small sized structures is used.

This work presents a method to fabricate the heat-storable CFRP, a multifunctional composite that combines strength, lightweight and heat storability. For mobile electric devices, thermal management system using phase change material (PCM) has been developed. However, as long as the PCM changes to liquid phase, it is difficult to reduce the weight since the sealed container is indispensable. Hence, the authors have focused trans-1,4-polybutadiene (TPBD), which is crystalline polymer that accumulates heat by crystal structure transition in solid phase. In this study, TPBD was incorporated into CFRP. To avoid exposing TPBD to high-temperature and high-pressure processes, the electrodeposition resin molding (ERM) method was applied. That is, a non-crimp carbon fiber fabric (NCF) was immersed in the electrodeposition solution containing epoxy polymers in which the pulverized TPBD was dispersed. Applying a current, resin was deposited and impregnated between carbon fibers. Simultaneously, TPBD was incorporated to obtain heat-storable CFRP.

A multi-objective optimization approach for fibrous composite plates with curvilinear fibers is proposed in the present study. The non-dominated sorting genetic algorithm (NSGA-II) is used to obtain Pareto-optimum solutions, where the presence of a trade-off relation between the mechanical performance and curvatures of reinforcing fibers has been established. The in-plane strength around a circular hole in a finite-width plate with Tsai-Wu failure criteria or the fundamental frequency of the square plate is the mechanical objective function, while the average value of fiber curvatures is used as the conflicting objective function. Numerical results were obtained for angle-ply plates and the effectiveness of the present design approach is demonstrated by widely distributed Pareto-optimum solutions.

The present paper develops a shell element based on the refined zigzag theory (RZT) and applies it to the vibration analysis and optimization problem of the composite sandwich plate composed of CFRP skins and soft-cores. The RZT accepts large differences in layer stiffness, and requires less calculation effort than the layer-wise or three-dimensional theories. Numerical results revealed that the present method predicts vibration characteristics of composite sandwich plates with soft-core accurately. Then, shapes of reinforcing fibers in CFRP composite skins are optimized to maximize fundamental frequencies. As an optimizer, the particle swarm optimization (PSO) approach is employed since curvilinear fiber shapes are defined by continuous design variables. Obtained results showed that the composite sandwich with optimum curvilinear fiber shapes indicates higher fundamental frequencies compared with straight fibers.