Effects of stacking sequence on torsional fatigue properties of CFRP pipes

Abstract

Application of carbon fiber reinforced plastics (CFRP) pipes to torque transmission shafts makes it possible to improve automotive driving performance as well as fuel efficiency. A modified simultaneous multi ply winding method was developed as a new forming method for CFRP pipes using prepregs. The CFRP pipes formed by the method have fewer initial flaws, such as voids and fiber waviness. It resulted in 20 % increase in the static torsional strength than conventional CFRP pipes formed by a filament winding method. In this study, effects of stacking sequence on the torsional fatigue properties of the CFRP pipes formed by the modified method were investigated. Torsional fatigue tests were conducted under load control. All tests were conducted at the test frequency f=1 Hz, the maximum applied torque T_max=1.0 kNm and the stress ratio R=0.1. [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. When the CFRP pipes had smaller lamination angle difference, the initiation and growth of the delamination from the prepreg end in the innermost layer were delayed because interlaminar stress was reduced. Moreover, [(90/-45/90/+45)₆/90] pipes were formed to investigate effects of an application of a 90° layer on the innermost layer. As the result, the delamination hardly initiated since the shear stress on the prereg end was reduced. Consequently, the fatigue life of the [(90/-45/90/+45)₆/90] pipes increased seven-fold than that of the [90₂/-45/+45]₆ pipes due to improvement of delamination resistance under cyclic torsional loading.