Multiaxial fatigue life prediction of composite materials

In order to analyze the stress and strain fields in the fibers and the matrix in composite materials, a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced. Assuming matrix cracking as the failure mode of composite materials, an energy-based fatigue damage parameter and a multiaxial fatigue life prediction method are established. This method only needs the material properties of the fibers and the matrix to be known. After the relationship between the fatigue damage parameter and the fatigue life under any arbitrary test condition is established, the multiaxial fatigue life under any other load condition can be predicted. The proposed method has been verified using two different kinds of load forms. One is unidirectional laminates subjected to cyclic off-axis loading, and the other is filament wound composites subjected to cyclic tension-torsion loading. The fatigue lives predicted using the proposed model are in good agreements with the experimental results for both kinds of load forms.