An anisotropic damage model based on microstructure of boom-panel for the fatigue life prediction of structural components

Because of their simplicity, many isotropic damage models have been used to approximately predict the fatigue life of metallic engineering components. However, experimental observations confirm that the anisotropic damage evolves at probable failure sites even for isotropic materials. In this study, a model of microstructure of boom-panel is constructed to simulate a representative volume element (RVE), and the anisotropic damage of the RVE is described by the independent isotropic damage of boom and panel. Firstly, the constitutive equation of the RVE in terms of stiffness of boom-panel is deduced by the principle of deformation and static consistency. Then the expressions of damage-driving force for boom and panel based on the principle of thermodynamics are introduced, and the damage evolution equations are constructed. The parameters of boom and panel are identified from fatigue test data of uniaxial tension and pure torsion, respectively. Finally, the aforementioned method is applied to predict the fatigue life of two structures: one is Pitch-Change-Link, which is a kind of structure in helicopter, and the other is a specimen under tension-torsion. The prediction results all fit well with the experimental data.