The flowability of resins and fibers during the formation of short-fiber-reinforced plastics was evaluated via moving particle semi-implicit (MPS) particle simulation. Extensive design parameters are associated with the injection molding of short-fiber-reinforced plastics. It is time-consuming and expensive to optimize these parameters using experimental procedures. A numerical prediction based on MPS particle simulation was demonstrated in the present study. Here, a novel analysis method for the local flow, accompanied by variations in the time and analysis area, was developed. Using this method, the discrepancies in the velocity distribution between the global injection area and local flow area were addressed. The numerical results indicated that the resin flow during injection molding exhibited similar characteristics for both global injection-molding analysis and the proposed analysis method. The fiber orientation derived via the proposed analysis method was similar to that indicated by the experimental results of a previous study. A model conforming to the experiment of injection molding was constructed, and verification analysis was performed. Thus, the validity of the proposed analysis method was verified. It was concluded that the proposed method facilitated the evaluation of the resin flow and fiber orientation during the injection molding of short-fiber-reinforced plastics.

In thermoset-based carbon-fiber-reinforced plastics, the viscosity of the matrix resin governs their formability. The present study analyzes the relationship between the molecular structure and viscosity of the thermoset resin during curing by employing two types of all-atom molecular dynamics (MD) simulations. One is a crosslinking simulation that considers the reaction dynamics for determining the resultant curing structures. The other is a non-equilibrium MD simulation utilizing the Lees–Edwards boundary condition for viscosity evaluation. The results of this study clarified that the viscosity of the thermoset resin is changed by its composition, and can be described by the Doolittle equation, which presents the relationship with the free volume ratio. Furthermore, the increasing rate of viscosity during curing can be correlated with the increasing weight-averaged molecular weight.

In this study, mode III interlaminar fracture mechanisms were investigated using edge crack torsion (ECT) tests of carbon fiber reinforced plastic (CFRP) laminates. As mode III interlaminar fractures propagate within the closed interlayers, the optimal methods for observing fracture mechanisms are non-destructive. Thus, ultrasonic flaw detection and X-ray phase imaging methods were adopted. In the vicinity of the crack tip in the center region of the CFRP laminate, it was observed that cracks migrated from the initial interlayer to the neighboring one via the transverse cracks that precede delamination. Numerical simulations suggested that these transverse cracks were caused by out-of-plane shear stresses in the center region of the ECT test specimens. From these results, the effects of transverse cracks preceded by the delamination and the migration of crack propagating interlayers are not negligible in the evaluation of Mode III interlaminar fracture toughness using ECT tests.

The use of smart sensors in in-situ monitoring methods for fiber-reinforced plastics (FRPs) has recently attracted significant attention and extensive research is underway. Herein, we focused on a monitoring method that uses a Fresnel-type optical fiber sensor. To realize this, we investigated the measurement accuracy of the Fresnel-type optical fiber sensor to determine the influence of the optical loss on the local bending of the fiber. First, a local bending experiment was conducted on standard and highly flexible optical fibers to characterize their optical losses. Next, the curing degree measurement was performed on locally bent optical fibers, and it was revealed that the amount of optical loss did not affect the accuracy of the degree-of-cure (DOC). Finally, the curing degree measurement of glass fiber-reinforced plastic (GFRP) plates that were molded into a curved shape using vacuum-assisted resin transfer molding (VaRTM), revealed that the optical loss remained unstable for a specific duration. This indicated that it has a significant influence on the accuracy of the DOC. However, fluctuations in the optical loss did not affect the measurement accuracy when the amount of loss was small.