抄録
A novel joining technology for thermoset fiber-reinforced plastics (FRP) has been proposed to achieve a reliable joint structure that can be established in a short time using a welding process. Owing to the formation of a thin layer of thermoplastic resin on the surface of thermoset laminates, composite parts can be joined instantaneously using a heating process. However, the failure of the joints of welded thermoset FRP has not been sufficiently elucidated. Thus, this study conducted a single-lap shear test to investigate the failure behavior of welded thermoset FRP considering the fiber orientation of the substrates. In particular, the fiber angle of the surface ply of the laminates was investigated. The results suggest that the failure mode transition from cohesive failure of the thermoplastic resin layer to substrate failure of the surface ply of the thermoset laminates occurred depending on the fiber angle of the surface ply. Moreover, the lap-shear strength varied according to the failure mode transition and fiber orientation. To analyze the failure mechanisms in detail, a multiscale model was developed to predict the failure of welded thermoset FRP joints. The model was validated by comparing the simulation results with the experimentally evaluated failure mode and stress at failure; they were in good agreement. The simulation results further suggest that failure of the thermoset laminates was induced as the resin matrix adjacent to the carbon fibers was subjected to severe stress when the fiber angle of the near-joint laminae was approximately orthogonal to the loading direction. The developed multiscale model is expected to be utilized in the designing of structure and stacking sequence for future applications of welding technology for thermoset FRP.
