Abstract
Fatigue life prediction of a symmetric cross-ply carbon/epoxy laminate subjected to cyclic loading in the 0° fiber direction is attempted on a ply-by-ply basis. First, tension-tension fatigue tests on the cross-ply laminate under constant amplitude cycling at room and high temperatures are performed. The normalized S-N relationship for the cross-ply laminate using the fatigue strength ratio agrees with that for the unidirectional laminate made of the same prepreg tape. This indicates that the fatigue behavior of the cross-ply laminate in the fiber direction is substantially governed by that of the constituent 0° plies in the laminate. Second, under the assumption that the damage and failure of the 90° plies in the laminate occur at an early stage of life and the final failure of the laminate is determined by the failure of the 0° plies, a simple fatigue failure model for the cross-ply laminate is developed on the basis of the classical lamination theory and the ply fatigue model considering the in-situ static strengths. The proposed fatigue model with a consideration of the in-situ strength of ply succeeds in adequately predicting the fatigue strength of the symmetric cross-ply laminate for the fiber direction, in spite of ignoring effects of the stress redistribution in the laminate due to the local damage and failure of the 90° plies during constant amplitude fatigue loading.
