Prediction of fatigue crack growth retardation using a cyclic cohesive zone model

Cohesive zone modeling of fatigue crack growth retardation in aerospace titanium alloy Ti-6Al-4V subjected to a single overload during constant amplitude is presented in this work. The cyclic softening behavior of the bulk material is simulated according to the Ohno-Wang's cyclic plasticity theory. The fracture process zone is represented by an irreversible cohesive law which governs the material separation of fatigue crack. The material degradation mechanism is described by the gradual reduction of the unloading cohesive stiffness after each loading cycle. The fatigue crack growth behaviors are examined using the proposed cohesive model under both constant and variable amplitude loadings. The computational results are verified according to the experimental data, which confirm that the present model can be applied to predict the transient retardation in fatigue crack growth rate of the Ti-6Al-4V alloy accurately.