Kazuhiro Sakata

Fabrication method and compressive properties of CFRP isogrid cylindrical shells

Since isogrid structures are composed of triangular grid stiffeners and a surface skin, they have a high specific strength and stiffness. These structures are now being mainly used for aerospace applications. In order to produce a metal isogrid cylindrical shell, most of the thick metal plates must be cut off while the remaining thin surface skins with the stiffeners and both ends of the skins are welded to each other. This process needs a long lead time and a high cost, and unstable behaviors are observed in the joint parts. On the other hand, carbon fiber reinforced plastics (CFRP) isogrid cylindrical shells can be fabricated with an integral method by using a filament winding apparatus. In this study, a fabrication method of the CFRP isogrid cylindrical shells is proposed and their compressive tests are carried out to investigate the reinforcement effect of the grids on the CFRP isogrid cylindrical shells. Furthermore, the results of the static compressive tests are compared with numerical ones obtained by finite element method (FEM).

Evaluation of new GFRTP and CFRTP using epsilon caprolactam as matrix fabricated with VaRTM

Abstract Thermoplastic resins used as a matrix of fiber reinforced thermoplastics (FRTPs) are composed of high polymers that remain highly viscous even at a higher temperature than their melting points. As a result, they need an even higher temperature, a higher pressure and a longer processing time to allow them to bond with fibers that require large and specialized equipment. In contrast, fiber-reinforced thermoset plastics (FRPs) can be easily molded owing to the use of lower viscosity liquid resin as the matrix using simpler devices. In this paper, a new fabrication method of FRTPs using in situ polymerizable ε caprolactam as the matrix is presented. This method uses vacuum-assisted resin transfer molding without the need for large and specialized equipment. The ε-caprolactam molecules were converted from their monomer form into a polyamide 6 resin, with ring-opening polymerization of ε-caprolactam during the molding process at a lower temperature than its melting temperature. The two kinds of FRTPs obtained using ε-caprolactam as the matrix had neither voids nor unfilled parts because ε-caprolactam had a very low viscosity before the polymerization. These FRTPs not only exhibit superior bending properties but also are suitable for high-speed molding, namely, within a few minutes of process time.

Development of fast fabrication method for cylindrical-shaped grids and mechanical properties of CFRP pressure vessel reinforced with cylindrical-shaped grids

In order to reduce carbon dioxide and air pollution emissions, fuel cell vehicles (FCVs) are being developed, and CFRP pressure vessels have been used as the hydrogen storage systems for the FCVs. Since the FCVs are expected to increase driving distances of at least over 500 km, which is similar to those of conventional gasoline-fueled vehicles, the storage pressure of hydrogen must be raised from 35 to 70 MPa. It is important to decrease the amount of carbon fibers in order to reduce the cost and weight of the CFRP pressure vessels. In this study, a fast fabrication method for the cylindrical-shaped grids (CSG) composed of hoop stiffeners and helical stiffeners was developed with a particular mandrel and a 3-axis filament winding apparatus. Then, the CFRP pressure vessel was inserted into the CSG, and burst tests of the CFRP pressure vessels reinforced with and without the CSG were conducted. Moreover, their experimental results were compared with numerical ones obtained by a FEM analysis, and the mechanical properties and the reinforcement effects of the CFRP pressure vessels reinforced with the CSG were investigated.

Mechanical properties of kenaf composites coated with several nanofibers

This paper describes how to generate nanofibers from four kinds of polymers, such as polylacticacid, polyamide 6, polyethersulfone, and triacetylcellulose by using an electro spinning method. They are used as surface treatments in the green composites composed of kenaf fibers as the reinforcement and biomass-UP as the matrix, respectively. In order to confirm the effects of the nanofibers, the comparisons of tensile tests are performed. The tensile strengths of specimens with the four kinds of nanofibers were from 23% to 36% higher than those of specimens without the nanofibers. Furthermore, the failure strains of two specimens with the PES and TAC nanofibers increased by 5% and 10% compared with the values without the nanofibers.

Optimum structural design of CFRP isogrid cylindrical shell using genetic algorithm

This paper describes an optimum structural design of a CFRP isogrid cylindrical shell using a genetic algorithm (GA). When the CFRP isogrid cylindrical shell receives a prescribed uniaxial compressive load, an objective is to minimize weight of the CFRP isogrid cylindrical shell subjected to the constraint conditions of no buckling and no material failure. The buckling and material failure loads were approximated by a response surface method combined with partitioning of design spaces and these approximated values were used in the process of GA instead of FEM calculations in order to reduce the computational time. Furthermore, the differences from the constraint conditions of the linear or the non-linear (local) buckling loads were also calculated and their results were compared with each other.

Increase of bending strength and maximum deflection of concrete reinforced with CFRP strips

Abstract In 1981, many detached houses collapsed owing to the earthquake which took place at the coast of Miyagi Prefecture in Japan, because ferroconcrete was not used as the base of most of the collapsed houses. Therefore, the earthquake-proof design criterion was revised and it was obliged to use ferroconcrete as the base of detached houses ever since. However, there are still more than 10 million detached houses using aged concrete as the base in Japan. In this paper, a reinforcement method for the aged concrete is demonstrated by using the high performance carbon fiber reinforced plastic (CFRP) strips. Three kinds of concrete beams reinforced with the CFRP strips with different vertical insert positions and different numbers of the CFRP strips were tested by a four point bending test method. In order to clarify the effects of CFRP strips, a concrete beam without reinforcement was also tested. The results of the experiment showed that the maximum deflections of the concrete beams reinforced with the CFRP strip were more than 100 times larger than those of the concrete beams without reinforcement. Although the concrete beams without the CFRP strips collapsed instantly, the concrete beams reinforced with the CFRP strips gradually failed, which were similar to the plastic behavior of metals. This result means that the residents can afford to escape safely from the houses in the event of possible earthquakes. The experimental results were compared with the analytical ones obtained from the composite beam theory and the failure criterion. Both results showed good agreement and the effectiveness of base concrete reinforced with CFRP strips was demonstrated.