Fracture phase-field method based prediction of fatigue crack propagation at a Monopile foundation

A fracture phase-field method based prediction of fatigue crack propagation at a monopile foundation is presented, in which the propagation behavior of surface and embedded cracks at a monopile foundation is investigated. Both surface cracks and embedded cracks are modeled through a diffusive crack representation governed by phase-field variables. Energy-based regularization is employed, where crack evolution is driven by the minimization of total energy, combining elastic strain energy and fracture surface energy. The coupled mechanical-phase field equations are solved to simulate crack initiation and growth without predefined paths, and tensile-compressive energy decomposition is applied to avoid unphysical crack closure. A cycle-jump algorithm is integrated to bypass linear elastic phases and accelerate high-cycle fatigue simulations. Three-dimensional local models are established to analyze crack interactions under stress amplitudes derived from global monopile analysis. Surface cracks, embedded cracks, and their coplanar configurations (with varying thickness- and length-direction spacing) are systematically investigated. Key findings show that surface crack growth rates increase with larger crack depth-to-length ratios, while embedded crack growth is dominated by depth increments. Coplanar crack interactions in the thickness direction accelerate propagation as spacing decreases, whereas increased length-direction separation alters crack paths and delays coalescence.