OS09W0183 Fatigue behavior of CFRP cross-ply laminates under axial cyclic load

Abstract

Laminated composites consisting of unidirectional plies exhibit the complicated characteristics on deformation and strength because ply-cracking damage, delamination and fiber breakage develop from an early stage of deformation. In this paper, the damage and fracture process of CFRP cross-ply laminates under monotonic and cyclic loading has been investigated. Tensile tests in various directions and fatigue tests in the axial direction were carried out on three kinds of CFRP cross-ply laminates. In the tensile tests, the ply-cracking damage develops under 0˚ and 90˚ tension, while the nonlinear deformation due to nonelastic property of the matrix resin is predominant under off-axis tension. On the semi-log S-N curves obtained by the fatigue tests in the 0˚ direction, the fatigue fracture is described by a straight line in the high cycle fatigue region and the fatigue limit is not recognized clearly. In the fatigue tests, the fiber-peeling damage in 0˚ plies develops in addition to the ply-cracking damage in 90˚ plies. Ply-cracking density in 90˚ plies is characterized as a function of number of stress cycles. On the specimen fractured by fatigue, the most of ply-cracking damage develops at the first cycle, and slightly increases during fatigue. This damage behavior is insensitive to the stress level. Therefore, it is concluded that the ply-cracking damage is not a main factor controlling the fatigue fracture. On the other hand, fiber-peeling damage in 0˚ plies initiates from the edges of 0˚ plies and evolves in the whole area of the laminate with an increase in stress cycles. The evolution of the fiber-peeling damage strongly depends on the stress level. The fatigue fracture seems to occur when the 0˚ plies lose their load carrying capacity by the evolution of the fiber-peeling damage. Therefore, it is concluded that the fiber-peeling damage in 0˚ plies is the main factor controlling fatigue fracture.