The reinforcement mechanisms of C (circular) and R (radial) layers, which are novel reinforcement techniques for CFRP (carbon fiber reinforced plastic) bolted joints, were investigated based on finite element results. In the case of the specimens having large edge distance (e/d=3), the longitudinal compressive stress, σLC, at θ≒45º on the 45º layer and at θ≒−45º on the −45º layer was reduced by the R layer, resulting in the improvement of the initial failure strength of the BR (bearing) mode. On the other hand, in the case of the specimen having small edge distance (e/d=1), the in-plane shear stress τLT, in the ranges −90º≦θ≦−45º and 45º≦θ≦90º on the 0º layer was reduced by the C layer, resulting in the transition of the failure mode from SO (shear-out) to the BR mode. Additionally, the longitudinal compressive stress, σLC, at θ≒45º on the 45º layer and at θ≒−45º on the −45º layer was reduced by the R layer, resulting in the improvement of the initial failure strength when the C and R layers were combined.
