J0301-2-1 Off-Axis Ratcheting Behavior of Unidirectional CFRP Laminate and Its Stress Ratio Dependence

Abstract

Ratcheting behavior of a unidirectional carbon/epoxy (CFRP) laminate under off-axis cyclic loading conditions at high temperature has been examined with a particular emphasis on its load-waveform and fiber-orientation dependence. Development of an engineering model for describing the off-axis ratcheting in unidirectional composites has also been attempted. First, off-axis ratcheting tests are performed on coupon specimens with different fiber orientation angles of 30, 45 and 90°, respectively, under different asymmetric cyclic loading conditions with stress ratios of 0 and 0.5. Experimental results show that the off-axis ratcheting strain accumulates more as the stress ratio of cyclic loading, thus the mean stress level, becomes larger, regardless of the fiber orientation. It is also found that the off-axis ratcheting is similar to the off-axis creeping in the unidirectional CFRP laminate in its stress, time and fiber-orientation dependence. It is demonstrated that the engineering ratcheting model proposed in this study allows adequately predicting the off-axis ratcheting behavior of the unidirectional CFRP laminate for different stress ratios as well as for different fiber orientations.