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

Abstract

A B S T R A C T 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.Keywords anisotropy; boom-panel model; fatigue damage; life prediction; structural components. N O M E N C L A T U R ED 0 = the initial damage extent D e , D d , D p = the damage extents of edge boom, diagonal boom and panel, respectively E e , E d = the elastic moduli of edge boom and diagonal boom, respectively G p = the shear moduli of panel 2l = edge length of the RVE N = the number of cycles N e , N d = the axial forces of edge boom and diagonal boom, respectively k e , k d , k p = stiffness of edge boom, diagonal boom and panel without damage, respectively R = stress ratio RVE = representative volume element T = the shear force of panel W = the strain energy density Y = the damage driving force α, β, m, Y th , η, γ = fatigue parameters in damage evolution equation Δ e , Δ d = elongations of edge boom and diagonal boom, respectively Δ p = the displacement of panel due to shear deformation ε th = the threshold of strain φ e , φ d , φ p = the continuity of edge boom, diagonal boom and panel, respectively σ th = the threshold of stress

Fatigue life prediction for notched specimen considering modified critical plane method

“…In notched parts, the stress strain is not uniformly distributed within the material. [39][40][41] Due to the inhomogeneity of the notch, the stress and strain spindles will rotate continuously when uniaxial or multiaxial stretching is performed. This will present a multiaxis non-proportional loading characteristic.…”

An anisotropic damage model of elasticity based on a series coupling method

“…In the study of Zhang and Zhao [16], a truss micro-structure model was proposed to describe the anisotropic damage of material in a simple way, but the value of Poisson's ratio ν is a constant of 0.25. Recently, a boom-panel model was proposed to release the restrictions on the Poisson's ratio [17,18], however, the Poisson's ratio is limited to the range of 0~0.25.…”