SIMULATION OF DELAMINATION UNDER HIGH CYCLE FATIGUE IN COMPOSITE MATERIALS

Mechanical fatigue, especially high-cycle fatigue, is a common cause of failure of aerospace structures. In laminated composite materials, the fatigue process involves several damage mechanisms that result in the degradation of the material. One of the most important fatigue damage mechanisms is interlaminar damage (delamination), especially in the case of laminated structures devoid of reinforcement in the thickness direction. There are two basic approaches for the analysis of delamination under fatigue: Fracture Mechanics, which relates the Fatigue Crack Growth Rate as a function of the Energy Release Rate and Mode Ratio; and Damage Mechanics, in which the concept of a Cohesive Zone Model is used to establish damage evolution as a function of the number of cycles. With Damage Mechanics, delamination under cyclic loading is modeled with a constitutive equation that describes the irreversible material separation in terms of crack surface tractions. In a degradation process involving high cycle-fatigue, damage evolution can be obtained as the sum of the damage caused by static or quasi-static loads and the damage that results from the cyclic loads. The damage evolution produced by cyclic loads is formulated as a function of the number of cycles an