Effects of stacking sequence on static torsional properties of CFRP pipes

Carbon fiber reinforced plastics (CFRP) pipes are expected to substitute for steel drive shafts to improve motorcar's fuel efficiency and driving performance. The static torsional strength of CFRP pipes formed by a modified simultaneous multi ply winding method is 20% higher than that of CFRP pipes formed by a filament winding method owing to few initial flaws. As the results of static torsional tests regarding [90/-45/+45]₆ pipes, it was revealed that the delamination from the prepreg end occurred in the innermost layer and propagated in the interlaminar area of the -45°/+45° plies before the final failure. It is expected to design stacking sequence for preventing the delamination. In this study, effects of stacking sequence on the static torsional properties of the CFRP pipes were investigated. [90₂/-45/+45]₆ and [90/-45/90/+45]₆ pipes were formed to investigate effects of lamination angle difference between adjacent plies. Maximum lamination angle difference of the [90/-45/90/+45]₆ pipe is smaller than that of the [90₂/-45/+45]₆ pipe. In case of the [90/-45/90/+45]₆ pipes with small lamination angle difference, the initiation of the delamination was delayed because the interlaminar stress was reduced. Furthermore, [(90/-45/90/+45)₆/90] pipes were formed to investigate effects of an application of a 90° layer on the innermost layer. The delamination from the prepreg end did not occur before the final failure by the application of a 90° layer on the innermost layer since the applied load on the prereg end was reduced. Finally, the static torsional strength of the [(90/-45/90/+45)₆/90] pipes was 25% higher than that of the [90₂/-45/+45]₆ pipes due to improvement of delamination resistance.