Next generation 3D mixed mode fracture propagation theory including HCF–LCF interaction

The damage tolerance assessment of complex aerospace structural components requires the capability of effective modeling of 3D cracks and their associated propagation and velocity and path under fatigue loads. A 3D mixed mode crack propagation theory is presented which includes the effect of KI, KII, and KIII, as well as non-proportional loading, elastic and fracture resistance anisotropy, and fracture mode asymmetry (viz. the ability to transition between competing tensile and shear modes of propagation). A modified strain energy release rate criterion including the modeling of crack closure is developed and presented for a representative problem. An elementary, mode I characterization of closure is used, leaving shear mode closure as fertile ground for further study.Use of the model is presented for an example problem with steady–vibratory interaction.

► A method for 3D mixed-mode fatigue crack path/growth-rate prediction is proposed. ► Includes fracture mode asymmetry (transition between dominant growth modes). ► Fracture resistance anisotropy is included and extended to 3D. ► Non-Proportional Loading (NPL) given limited treatment using a closure mechanism. ► NPL 2D test data compares favorably up to shear mode transition.