On the Modified Monotonic Loading Concept for the Calculation of the Cyclic J-Integral

This paper investigates an approach for calculating the cyclic J-integral through a new industrial application. A previously proposed method is investigated further with the extension of this technique through a new application of a practical three-dimensional (3D) notched component containing a semi-elliptical surface crack. Current methods of calculating the cyclic J-integral are identified and their limitations discussed. A modified monotonic loading (MML) concept is adapted to calculate the cyclic J-integral of this 3D semi-elliptical surface crack under cyclic loading conditions. Both the finite element method (FEM) and the extended finite element method (XFEM) are discussed as possible methods of calculating the cyclic J-integral in this investigation. Different loading conditions including uniaxial tension and out-of-plane shear are applied, and the relationships between the applied loads and the cyclic J-integral are established. In addition, the variations of the cyclic J-integral along the crack front are investigated. This allows the determination of the critical load that can be applied before crack propagation occurs, as well as the identification of the critical crack direction once propagation does occur. These calculations display the applicability of the method to practical examples and illustrate an accurate method of estimating the cyclic J-integral.