In this study, we propose a low-cost and high-cycle manufacturing process for carbon fiber-reinforced plastic (CFRP) high-pressure hydrogen tanks in hydrogen fuel cell vehicles. The manufacturing process consists of the production of a thermoplastic prepreg using an in situ polymerizing acrylic resin, a preform manufacturing process using the obtained thermoplastic prepreg, and a low-pressure resin transfer molding (RTM) process using the preforms. An acrylic resin was designed using a REDOX radical reaction assisted by UV radical polymerization to achieve high-speed prepreg manufacturing. Rheological measurements of the unreacted in situ polymerizing acrylic resin suggested the attainment of suitable prepreg manufacturing conditions. Strand tests and microdroplet measurements revealed the successful fabrication of prepregs with good interfacial adhesion between the resin and CF.

In this study, a finite element method simulation was performed by designing a porous cement paste and mortar models using glass spheres as fine aggregates to reproduce the splitting tensile test. A tensile simulation of the porous cement paste model was performed using the RVE model, which reflects the pore size distribution in a cement specimen to calculate the strength and elastic modulus with varying porosity. By inversely identifying the ideal elastic modulus and strength with 0％ porosity, they were derived as exponential functions with porosity as the variable. A finite element model of the cylindrical samples was designed to simulate the splitting tensile test. The strength of the mortar model was approximately 14％ lower than that of the cement, which was evaluated through the finite element analysis using the physical properties obtained from the cement specimen, and the experimental results could not be reproduced. However, when the cement was subjected to variations in its physical properties based on the porosity distribution, the strength of the mortar model was comparable to that of the cement, and the experimental results were reproduced.

We conduct a numerical simulation on the joint strength of single-wrap bonded joints in carbon fiber reinforced plastics (CFRP). After bonding two pieces of CFRP, we attempt to improve the joint strength solely through post-processing, such as beveling. Fracture analysis is performed using the finite-element analysis software ABAQUS, assuming that only the adhesive layer fails. Through post-processing, we are able to achieve an increase in joint strength of up to approximately 1.5 times, according to the numerical results. This study provides valuable insights into improving joint strength.

In carbon fiber reinforced plastic adhesive joints, poor adhesion caused by weak bonds may occur because of contamination at the bond line. Weak bonds were reproduced using molecular dynamics simulations to investigate their mechanisms. Furthermore, weak-bond models were created by incorporating water, xylene, and silicone molecules as contaminants into two epoxy models. Tensile and shear analyses were performed to evaluate the mechanical properties of the weak-bond models. The results revealed that the addition of the contaminants reduced the strength of the models. Stress concentration occurred because of the presence of the inserted molecules at the bond line. To consider these results, density and free-volume distributions were evaluated. The molecular size of a contaminant influences its distribution in the epoxy model, thereby affecting the mechanical properties of the model.