Moisture absorption and desorption by a matrix resin, and the resulting deformation, have a critical adverse effect on the shape stability of carbon fiber reinforced plastic space structures. This study evaluates the effect of the moisture content in prepreg sheets on the life-cycle behavior of the prepreg-based carbon fiber reinforced plastic. After evaluating the moisture absorption and desorption characteristics of the prepreg sheets, the cure-induced strain and the moisture absorption and desorption deformation were measured using embedded optical fiber sensors. Furthermore, in order to investigate the relationship between the moisture absorption and desorption behaviors and the chemical structure of the matrix resin, the resin structure was analyzed using Fourier transform infrared spectroscopy. Because absorption and desorption are dependent on the matrix resin, two types of resin were evaluated, an epoxy resin and a low moisture absorption cyanate resin. Finally, recommendations for manufacturing and operation are made with respect to maintaining the long-term shape stability of carbon fiber reinforced plastic space structures.

This study investigates a relationship between carbon fiber arrangement and orientation in CFRP, and the dark-field images captured by X-ray Talbot-Lau interferometer (TLI). The measurement method that can evaluate the carbon fiber arrangement and orientation in a large area is essential for understanding discontinuous carbon fiber reinforced composites because the arrangement and orientation significantly affect their material properties. X-ray TLI can potentially be such a method because X-ray TLI images visualize the phase contrast, which is sensitive to light elements including carbon. The final goal of this study is to develop a method for evaluating carbon fiber arrangement and orientation using X-ray TLI images. In this study, we propose a model that relates carbon fiber arrangement and orientation in CFRP to the dark-field images captured by X-ray TLI. The model is a prerequisite to achieve the final goal. The parameters needed in the model are identified from the TLI measurements of the multi-fiber composite (MFC) specimens. The proposed model was validated by comparing the dark-field images predicted using the model with those measured by X-ray TLI.

The elastic wave propagation in carbon fiber-reinforced plastics (CFRP) with continuous fibers is well known to possess anisotropy. In our previous study, the wave front of an elastic wave in CFRP with curved fiber was confirmed to be distorted due to the fiber curvature effect, while the similarity law held for two-dimensional propagation of bulk waves in CFRP with concentrically curved fibers. In this research, the three-dimensional propagation of bulk waves in CFRP with concentrically curved fibers was studied, and the propagation behavior was formulated. During the investigation, 3D-printed CFRP specimens with three different thicknesses were prepared. A point sound source was assumed on the back surface of each specimen, and the wave propagation on the front surface was visualized. Based on the obtained images, the three-dimensional propagation behavior of the quasi-longitudinal wave emitted from the source position was visualized. Considering these results, the similarity law for CFRP with concentrically curved fibers was expanded to the case of three-dimensional propagation behaviors of the bulk waves mathematically based on the governing equations. By conducting the experimental visualization, it was demonstrated that the shape changes of quasi-longitudinal waves follow the similarity law, which was eventually verified for three-dimensional propagation.

Carbon fiber reinforced plastic (CFRP) composite materials are expected to be the structural members in the construction field because of their high strength and light weight. However, CFRP composite materials must be provided with fire resistance because they deform thermally owing to a decrease in rigidity at high temperatures. Therefore, the fire resistance of the FRP laminate with fire resistance coating was evaluated by a heating test based on ISO834. The results clarified that the composite of the foam insulation layer and the heat absorption layer dramatically improved the fire resistance of the FRP laminate. In addition, it was confirmed that the addition of a fall prevention layer and a heat reflection layer, and that the change of core material could possibly change the fire resistance performance. Depending on the performance, the applicability of the CFRP sandwich panel with fire resistance to the construction field is shown.