一方向CFRP積層板の高温における非主軸ラチェット挙動とその現象論的モデル化

Abstract

Off-axis ratcheting behavior of a unidirectional carbon/epoxy (CFRP) laminate 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 deformation in unidirectional composites has also been attempted. First, off-axis ratcheting tests are performed on coupon specimens with different fiber orientations under different asymmetric cyclic loading conditions. Off-axis creep tests at constant loads equal in magnitude to the maximum levels of the ratcheting tests are also carried out, and the creep test results are compared with the ratcheting test results. Experimental results show that the off-axis ratcheting strain accumulates more as the stress ratio, i.e. the mean stress level, of cyclic loading becomes larger, regardless of fiber orientation. It is also found that the off-axis ratcheting is transient over the range of testing and similar to the off-axis creep in the unidirectional CFRP laminate in its stress, time and fiber-orientation dependence. Then, a simplified ratcheting model for transversely isotropic media is formulated by means of the classical Bailey-Norton equation and a newly defined effective stress that can account for the effect of the maximum stress as well as the mean stress of cyclic loading. It is shown that the proposed engineering ratcheting model allows predicting the off-axis ratcheting behavior of the unidirectional CFRP laminate for different fiber orientations over a range of stress ratio.