Although though carbon fiber reinforced plastics (CFRPs) have superior specific strength and stiffness, inadequate damping properties limit their usage. The objective of this study is to investigate the influence of the aspect ratio of the added cellulose nanofibers (CNFs) on the damping properties of plane-woven CFRP cloth. To investigate the effect of the fiber aspect ratio on the damping properties of the CFRP plates, four types of CNFs with varying aspect ratios were prepared. The results showed that the loss tangent (tan δ) of the CFRP plates slightly improved when CNFs, having a nominal aspect ratio of 1360, were added to the matrix. In contrast, free damping vibration test with cantilever beam revealed that high loss factor was remarked comparing to that of original specimen when the aspect ratio of CNFs was 1360. Therefore, when their nominal aspect ratio was moderate, the fiber bridges of the added CNFs prevented severe strain concentration in the matrix around the reinforcing carbon fibers. High vibration damping was obtained by preventing strain localization in the matrix, while agglomerations of added CNFs should be prevented.

Ramie fiber surface was physically fibrillated, and a bio based polyamide (PA) resin matrix composite material with a small amount (1 wt%) of the fibrillated fibers was produced via injection molding, and tested for tensile strength. When the results were compared with those of the untreated ramie fiber composite material, it was found that the tensile strength improved with increase in heat-treatment time. The strength was 24–28% higher than that of the neat PA. In contrast, the tensile strength of untreated ramie single fiber was significantly higher than that of the fibrillated fiber. Therefore, it can be concluded that the composite strength did not increase owing to fiber reinforcement. A sample wherein a single fiber was embedded in a PA was prepared, and the state of crystal formation with respect to heat-treatment time was observed. A new crystal that was neither a TCL nor a spherulite was observed around the fibril surface. It was speculated that the formation of this crystal promoted the strengthening effect of the PA resin. By applying this method, the PA resin was efficiently strengthened via crystallization through fibrillation of natural cellulose fibers without using individually produced cellulose nanofibers.

Safety glasses used in machine tools require good impact and solvent resistances and high transparency. These requirements can be satisfied by glass/polycarbonate (G/PC) laminated safety glass incorporating acrylic interlayer (ACIL). Recently, there has been an increasing demand for higher impact resistance and light-weight G/PC laminated safety glasses because of high-speed and precision machining. To improve the impact resistance of G/PC laminated safety glass under the same laminate configuration, enhancement in the energy absorption performance of ACIL is required. For the same, in this study, cellulose nanofibers (CNFs) having a diameter of a few dozen nanometers and high aspect ratio were focused as a filler. Addition of CNFs to ACIL is expected to enhance the energy absorption ability of the G/PC laminated safety glass owing to the internal friction at the interface and microcracking near the CNFs, with retaining the transparency of ACIL. In this study, ACIL with CNFs (CNF/ACIL) was fabricated by using a bead mill and tensile tests were performed on the material. In addition, drop-weight tests were performed on the G/PC laminated safety glass incorporating CNF/ACIL to evaluate its impact resistance. Results from the tests showed that the stress at 300% strain of CNF/ACIL exhibited a maximum value when the CNF concentration was 0.1 wt% and decreased monotonically with further increase in the CNF concentration. Further, the G/PC laminated safety glass incorporating CNF/ACIL showed an enhanced impact resistance when the CNF concentration was not more than 0.5 wt%.

Carbon fiber reinforced plastic (CFRP) is regarded as a suitable material for large, high-precision reflectors (mirrors) used in high-resolution space observatories because of its high specific elasticity and low coefficient of thermal expansion. However, it was made clear that non-negligible out-of-plane thermal deformation is generated in CFRP reflectors because of fiber orientation errors occurring during manufacturing. In this study, first, a method was developed to evaluate the standard deviation of the magnitude of curvature of the CFRP plate because of fiber orientation errors. Then, the standard deviation of curvature was minimized by optimizing the stacking sequence of the laminate using a genetic algorithm. Stacking sequence optimization mitigated the effect of fiber orientation errors, indicating that this is an effective method for suppressing the out-of-plane thermal deformation of CFRP laminates. Moreover, the out-of-plane thermal deformations of CFRP laminates with a quasi-isotropic and the optimum stacking sequence because of representative fiber orientation errors were measured and it was demonstrated that the out-of-plane thermal deformation was suppressed by applying optimum stacking sequence.

The mechanical properties of carbon fiber-reinforced plastic (CFRP) foam core sandwich structures were investigated under cryogenic conditions. The use of CFRP in the manufacture of the cryogenic tanks of launch vehicles has been expected to help achieve weight reduction. The tank structure is required to withstand not only the tension load due to the internal pressure but also the axial external compressive load. Therefore, the CFRP foam core sandwich was considered suitable for use as a cryotank material. In this study, the basic applicability of the sandwich in composite cryotanks was evaluated. Polymethacrylimide foam was utilized to fabricate the sandwich core as it has a closed cell that could eliminate the risks associated with the cryopump. Compression and tension tests were carried out on the foam. Flatwise tension and edgewise compression tests were conducted on the CFRP sandwich. All the tests were conducted under room-temperature and cryogenic conditions. For cryogenic tests, the specimens were immersed in liquid nitrogen. The compressive and tensile strengths of the foam were observed to be lower under cryogenic conditions than those at room temperature. The flatwise tensile strength of the sandwich was lower than that at room temperature and than the tensile strength of the foam. On the other hand, the edgewise compressive strength under cryogenic conditions was higher than that at room temperature; this may be attributed to an increase in the foam-core stiffness under cryogenic conditions.